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Analytica Chimica Acta (v.568, #1-2)
Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices by Dustin K. James; James M. Tour (pp. 2-19).
The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques.
Keywords: Molecular electronics; Single wavelength ellipsometry; Goniometry; Cyclic voltammetry; Infrared spectroscopy; X-ray photoelectron spectroscopy; Scanning tunneling microscopy; Inelastic electron tunneling spectroscopy
Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices by Dustin K. James; James M. Tour (pp. 2-19).
The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques.
Keywords: Molecular electronics; Single wavelength ellipsometry; Goniometry; Cyclic voltammetry; Infrared spectroscopy; X-ray photoelectron spectroscopy; Scanning tunneling microscopy; Inelastic electron tunneling spectroscopy
Metrology for molecular electronics by James G. Kushmerick; Amy Szuchmacher Blum; David P. Long (pp. 20-27).
Building reliable molecular electronic devices requires the ability to accurately and reproducibly measure the electronic response of the system under study. Here we review our work with three distinct molecular electronic test structures which show excellent agreement for measurements on molecular wires and molecular switch molecules. We also discuss how inelastic electron tunneling spectroscopy enables chemical characterization of molecular electronic elements in actual device geometries.
Keywords: Molecular electronics; Charge transport; Conductance switching; Inelastic electron tunneling spectroscopy
Metrology for molecular electronics by James G. Kushmerick; Amy Szuchmacher Blum; David P. Long (pp. 20-27).
Building reliable molecular electronic devices requires the ability to accurately and reproducibly measure the electronic response of the system under study. Here we review our work with three distinct molecular electronic test structures which show excellent agreement for measurements on molecular wires and molecular switch molecules. We also discuss how inelastic electron tunneling spectroscopy enables chemical characterization of molecular electronic elements in actual device geometries.
Keywords: Molecular electronics; Charge transport; Conductance switching; Inelastic electron tunneling spectroscopy
Metal oxide nano-crystals for gas sensing by Elisabetta Comini (pp. 28-40).
This review article is focused on the description of metal oxide single crystalline nanostructures used for gas sensing. Metal oxide nano-wires are crystalline structures with precise chemical composition, surface terminations, and dislocation-defect free. Their nanosized dimension generate properties that can be significantly different from their coarse-grained polycrystalline counterpart. Surface effects appear because of the magnification in the specific surface of nanostructures, leading to an enhancement of the properties related to that, such as catalytic activity or surface adsorption. Properties that are basic phenomenon underlying solid-state gas sensors.Their use as gas-sensing materials should reduce instabilities, suffered from their polycrystalline counterpart, associated with grain coalescence and drift in electrical properties. High degree of crystallinity and atomic sharp terminations make them very promising for better understanding of sensing principles and for development of a new generation of gas sensors. These sensing nano-crystals can be used as resistors, in FET based or optical based gas sensors. The gas experiments presented confirm good sensing properties, the possibility to use dopants and catalyser such in thin film gas sensors and the real integration in low power consumption transducers of single crystalline nanobelts prove the feasibility of large scale manufacturing of well-organized sensor arrays based on different nanostructures. Nevertheless, a greater control in the growth is required for an application in commercial systems, together with a thorough understanding of the growth mechanism that can lead to a control in nano-wires size and size distributions, shape, crystal structure and atomic termination.
Keywords: Nano crystals; Gas sensors; FET; PL; Nanowires
Metal oxide nano-crystals for gas sensing by Elisabetta Comini (pp. 28-40).
This review article is focused on the description of metal oxide single crystalline nanostructures used for gas sensing. Metal oxide nano-wires are crystalline structures with precise chemical composition, surface terminations, and dislocation-defect free. Their nanosized dimension generate properties that can be significantly different from their coarse-grained polycrystalline counterpart. Surface effects appear because of the magnification in the specific surface of nanostructures, leading to an enhancement of the properties related to that, such as catalytic activity or surface adsorption. Properties that are basic phenomenon underlying solid-state gas sensors.Their use as gas-sensing materials should reduce instabilities, suffered from their polycrystalline counterpart, associated with grain coalescence and drift in electrical properties. High degree of crystallinity and atomic sharp terminations make them very promising for better understanding of sensing principles and for development of a new generation of gas sensors. These sensing nano-crystals can be used as resistors, in FET based or optical based gas sensors. The gas experiments presented confirm good sensing properties, the possibility to use dopants and catalyser such in thin film gas sensors and the real integration in low power consumption transducers of single crystalline nanobelts prove the feasibility of large scale manufacturing of well-organized sensor arrays based on different nanostructures. Nevertheless, a greater control in the growth is required for an application in commercial systems, together with a thorough understanding of the growth mechanism that can lead to a control in nano-wires size and size distributions, shape, crystal structure and atomic termination.
Keywords: Nano crystals; Gas sensors; FET; PL; Nanowires
NH3 gas sensing properties of nanocrystalline ZnO based thick films by G. Sarala Devi; V. Bala Subrahmanyam; S.C. Gadkari; S.K. Gupta (pp. 41-46).
Zinc acetate derived precursor used in the present sol–gel synthesis of zinc oxide nanoparticles is described. The reaction product obtained before and after reflux of propanolic zinc acetate solution have been studied by UV–vis, photoluminescence and FT-IR studies which confirm the formation of oligomeric precursor Zn4O(Ac)6 (Ac=CH3COO). The formation of ∼7nm zinc oxide nanoparticles were confirmed by X-ray diffraction (XRD) and Transmission electron microscopic studies (TEM). The gaseous ammonia gas sensing characteristics of the nano-zinc oxide sensor showed high sensitivity compared to sensor fabricated with commercial zinc oxide powder.
Keywords: Sol–gel precursor; UV–vis; Photoluminescence; ZnO nanoparticles; TEM; NH; 3; gas sensor
NH3 gas sensing properties of nanocrystalline ZnO based thick films by G. Sarala Devi; V. Bala Subrahmanyam; S.C. Gadkari; S.K. Gupta (pp. 41-46).
Zinc acetate derived precursor used in the present sol–gel synthesis of zinc oxide nanoparticles is described. The reaction product obtained before and after reflux of propanolic zinc acetate solution have been studied by UV–vis, photoluminescence and FT-IR studies which confirm the formation of oligomeric precursor Zn4O(Ac)6 (Ac=CH3COO). The formation of ∼7nm zinc oxide nanoparticles were confirmed by X-ray diffraction (XRD) and Transmission electron microscopic studies (TEM). The gaseous ammonia gas sensing characteristics of the nano-zinc oxide sensor showed high sensitivity compared to sensor fabricated with commercial zinc oxide powder.
Keywords: Sol–gel precursor; UV–vis; Photoluminescence; ZnO nanoparticles; TEM; NH; 3; gas sensor
Bacteriorhodopsin—Novel biomolecule for nano devices by P.C. Pandey (pp. 47-56).
The aim of this article is to provide insight on the use of a biological molecule— bacteriorhodopsin (bR) having all the basic properties necessary for the assembly of nanoscale electronic devices. Recent developments made during last decade supported by key references are reviewed in this contribution. Major emphasis on bR-based observations conducted in our laboratory has been elaborated. Important issues concerning structure, widely accepted photocycle of bR has been summarized. The possibility of nano-devices emanating from this biomolecule is briefly presented.
Keywords: Molecular sensors; Photochemistry; Bacteriorhodopsin; Photosensor; Molecular electronics material
Bacteriorhodopsin—Novel biomolecule for nano devices by P.C. Pandey (pp. 47-56).
The aim of this article is to provide insight on the use of a biological molecule— bacteriorhodopsin (bR) having all the basic properties necessary for the assembly of nanoscale electronic devices. Recent developments made during last decade supported by key references are reviewed in this contribution. Major emphasis on bR-based observations conducted in our laboratory has been elaborated. Important issues concerning structure, widely accepted photocycle of bR has been summarized. The possibility of nano-devices emanating from this biomolecule is briefly presented.
Keywords: Molecular sensors; Photochemistry; Bacteriorhodopsin; Photosensor; Molecular electronics material
New nanomaterials for light weight lithium batteries by Enrico Stura; Claudio Nicolini (pp. 57-64).
Technological improvements, allowing to manipulate and investigate the properties of nanomaterials, are nowadays changing the approach to the energy storage and power supply vision. Modern nanoscale techniques led the market in the realization of nanostructured inorganic and organic materials increasing the efficiency of different devices, like lithium batteries, one of the most promising energy storage elements, obtaining everyday higher values of capacity, cyclability and environmental resistance. Each part of the battery, the anode, the cathode and the electrolyte, are here described analyzing the nanomaterials used for their realization.
Keywords: Nanomaterials; Lithium batteries; Energy storage; Nanoscale methods
New nanomaterials for light weight lithium batteries by Enrico Stura; Claudio Nicolini (pp. 57-64).
Technological improvements, allowing to manipulate and investigate the properties of nanomaterials, are nowadays changing the approach to the energy storage and power supply vision. Modern nanoscale techniques led the market in the realization of nanostructured inorganic and organic materials increasing the efficiency of different devices, like lithium batteries, one of the most promising energy storage elements, obtaining everyday higher values of capacity, cyclability and environmental resistance. Each part of the battery, the anode, the cathode and the electrolyte, are here described analyzing the nanomaterials used for their realization.
Keywords: Nanomaterials; Lithium batteries; Energy storage; Nanoscale methods
Interfacial polarization phenomena in organic molecular films by Mitsumasa Iwamoto; Takaaki Manaka (pp. 65-69).
Electrostatic phenomena occurring at the interface between metal/organic and organic/organic materials are discussed from the viewpoint of dielectrics physics. Focusing on two important origins of surface polarization phenomena, orientational ordering of polar molecules and displacement of excess charges at the interface, surface polarization phenomena of organic thin films are discussed. To define the orientational order of polar molecules, orientational order parameters are introduced, and surface polarization due to the alignment of dipoles is expressed.The generation of Maxwell displacement current (MDC) and optical second harmonic generation (SHG) that are specific for surface organic monomolecular films are discussed, and some experimental evidence are shown. As an extension of the concept of surface Fermi level introduced to discuss the electrostatic phenomena due to electron transfer at the interface between metal–organic insulators, the surface Fermi level is extended to the discussion on the electrostatic phenomena of organic semiconductor materials on metals. In this paper, some experimental evidence of surface polarization originating from polar molecules and displacement of excess charges are shown. After that, with consideration of these surface phenomena, single electron tunneling of organic films are briefly discussed in association with surface polarization phenomena.
Keywords: MDC; SHG; Surface potential; Space charge; Single electron tunneling
Interfacial polarization phenomena in organic molecular films by Mitsumasa Iwamoto; Takaaki Manaka (pp. 65-69).
Electrostatic phenomena occurring at the interface between metal/organic and organic/organic materials are discussed from the viewpoint of dielectrics physics. Focusing on two important origins of surface polarization phenomena, orientational ordering of polar molecules and displacement of excess charges at the interface, surface polarization phenomena of organic thin films are discussed. To define the orientational order of polar molecules, orientational order parameters are introduced, and surface polarization due to the alignment of dipoles is expressed.The generation of Maxwell displacement current (MDC) and optical second harmonic generation (SHG) that are specific for surface organic monomolecular films are discussed, and some experimental evidence are shown. As an extension of the concept of surface Fermi level introduced to discuss the electrostatic phenomena due to electron transfer at the interface between metal–organic insulators, the surface Fermi level is extended to the discussion on the electrostatic phenomena of organic semiconductor materials on metals. In this paper, some experimental evidence of surface polarization originating from polar molecules and displacement of excess charges are shown. After that, with consideration of these surface phenomena, single electron tunneling of organic films are briefly discussed in association with surface polarization phenomena.
Keywords: MDC; SHG; Surface potential; Space charge; Single electron tunneling
Electricity and mechanics of biomembrane systems: Flexoelectricity in living membranes by Alexander G. Petrov (pp. 70-83).
Flexoelectricity provides a reciprocal relationship between electricity and mechanics in membranes, i.e., between membrane curvature and polarization. Experimental evidence of biomembrane flexoelectricity (including direct and converse flexoelectric effect) is reviewed. Biological implications of flexoelectricity in membrane transport, membrane contact, mechanosensitivity, electromotility and hearing are underlined. Flexoelectricity enables membrane structures to function like soft micro- and nano-machines, sensors and actuators, thus providing important input to molecular electronics applications.
Keywords: Biomembrane; Curvature; Polarization; Flexoelectricity; Mechanosensitivity; Electromotility; Hearing; Soft membrane machines
Electricity and mechanics of biomembrane systems: Flexoelectricity in living membranes by Alexander G. Petrov (pp. 70-83).
Flexoelectricity provides a reciprocal relationship between electricity and mechanics in membranes, i.e., between membrane curvature and polarization. Experimental evidence of biomembrane flexoelectricity (including direct and converse flexoelectric effect) is reviewed. Biological implications of flexoelectricity in membrane transport, membrane contact, mechanosensitivity, electromotility and hearing are underlined. Flexoelectricity enables membrane structures to function like soft micro- and nano-machines, sensors and actuators, thus providing important input to molecular electronics applications.
Keywords: Biomembrane; Curvature; Polarization; Flexoelectricity; Mechanosensitivity; Electromotility; Hearing; Soft membrane machines
Self assembled monolayers on silicon for molecular electronics by D.K. Aswal; S. Lenfant; D. Guerin; J.V. Yakhmi; D. Vuillaume (pp. 84-108).
We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler–Nordheim), thermionic emission, Poole–Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains (σ- molecule) and conjugated molecules (π-molecule) have been presented.
Keywords: Self-assembled monolayers; Molecular electronics; Electronic transport
Self assembled monolayers on silicon for molecular electronics by D.K. Aswal; S. Lenfant; D. Guerin; J.V. Yakhmi; D. Vuillaume (pp. 84-108).
We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler–Nordheim), thermionic emission, Poole–Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains (σ- molecule) and conjugated molecules (π-molecule) have been presented.
Keywords: Self-assembled monolayers; Molecular electronics; Electronic transport
Langmuir–Blodgett films of octadecanethiol – properties and potential applications by Raj Kumar Gupta; K.A. Suresh; Rui Guo; Satyendra Kumar (pp. 109-118).
Octadecanethiol (ODT) is known to form self-assembled monolayer on noble metal surfaces which has potential technological applications. Langmuir–Blodgett (LB) technique is another useful method of obtaining highly ordered assembly of molecules. It is of interest to find whether ODT molecules can also form a stable Langmuir monolayer which facilitates the preparation of LB films. In literature, it has been reported that ODT molecules form an unstable Langmuir monolayer. We have studied the stability of the monolayer of the ODT molecules at air–water interface using surface manometry and microscopy techniques. We find the monolayer to be stable on ultrapure water of resistivity greater than 18MΩcm. However, the behavior changes in the presence of even small amount of additives like NaOH or CdCl2 in the subphase. Our AFM studies on the LB films of ODT deposited from ion-free ultrapure water showed streak-like bilayer domains. The LB films of ODT deposited from CdCl2 containing aqueous subphase yield dendritic domains of the complexed unit grown over ODT monolayer. These nanostructures on surfaces may have potential applications in molecular electronics.
Keywords: Langmuir–Blodgett films; Octadecanethiol; Monolayer stability; Atomic force microscopy
Langmuir–Blodgett films of octadecanethiol – properties and potential applications by Raj Kumar Gupta; K.A. Suresh; Rui Guo; Satyendra Kumar (pp. 109-118).
Octadecanethiol (ODT) is known to form self-assembled monolayer on noble metal surfaces which has potential technological applications. Langmuir–Blodgett (LB) technique is another useful method of obtaining highly ordered assembly of molecules. It is of interest to find whether ODT molecules can also form a stable Langmuir monolayer which facilitates the preparation of LB films. In literature, it has been reported that ODT molecules form an unstable Langmuir monolayer. We have studied the stability of the monolayer of the ODT molecules at air–water interface using surface manometry and microscopy techniques. We find the monolayer to be stable on ultrapure water of resistivity greater than 18MΩcm. However, the behavior changes in the presence of even small amount of additives like NaOH or CdCl2 in the subphase. Our AFM studies on the LB films of ODT deposited from ion-free ultrapure water showed streak-like bilayer domains. The LB films of ODT deposited from CdCl2 containing aqueous subphase yield dendritic domains of the complexed unit grown over ODT monolayer. These nanostructures on surfaces may have potential applications in molecular electronics.
Keywords: Langmuir–Blodgett films; Octadecanethiol; Monolayer stability; Atomic force microscopy
Biosensing and drug delivery by polypyrrole by S. Geetha; Chepuri R.K. Rao; M. Vijayan; D.C. Trivedi (pp. 119-125).
Conducting polypyrrole is a biological compatible polymer matrix wherein number of drugs and enzymes can be incorporated by way of doping. The polypyrrole, which is obtained as freestanding film by electrochemical polymerization, has gained tremendous recognition as sophisticated electronic measuring device in the field of sensors and drug delivery. In drug delivery the reversing of the potential 100% of the drug can be released and is highly efficient as a biosensor in presence of an enzyme. In this review we discuss the applications of conducting polypyrrole as biosensor for some biomolecules and drug delivery systems.
Keywords: Polypyrrole; Biosensor; Drug delivery; Immobilization
Biosensing and drug delivery by polypyrrole by S. Geetha; Chepuri R.K. Rao; M. Vijayan; D.C. Trivedi (pp. 119-125).
Conducting polypyrrole is a biological compatible polymer matrix wherein number of drugs and enzymes can be incorporated by way of doping. The polypyrrole, which is obtained as freestanding film by electrochemical polymerization, has gained tremendous recognition as sophisticated electronic measuring device in the field of sensors and drug delivery. In drug delivery the reversing of the potential 100% of the drug can be released and is highly efficient as a biosensor in presence of an enzyme. In this review we discuss the applications of conducting polypyrrole as biosensor for some biomolecules and drug delivery systems.
Keywords: Polypyrrole; Biosensor; Drug delivery; Immobilization
Covalent immobilization of cholesterol esterase and cholesterol oxidase on polyaniline films for application to cholesterol biosensor by Suman Singh; Pratima R. Solanki; M.K. Pandey; B.D. Malhotra (pp. 126-132).
Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) have been covalently immobilized on electrochemically prepared polyaniline (PANI) films. These PANI/ChEt/ChOx enzyme films have been characterized using UV–visible, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Electrochemical behavior of these films has been studied using cyclic voltammetry (CV) and amperometric techniques, respectively. The PANI/ChEt/ChOx enzyme films show broad oxidation peak from 0.2 to 0.5V. These PANI/ChEt/ChOx biosensing electrodes have a response time of about 40s, linearity from 50 to 500mg/dl of cholesterol oleate concentration. These PANI/ChEt/ChOx films are thermally stable up to 46°C. This polyaniline based cholesterol biosensor has optimum pH in the range of 6.5–7.5, sensitivity as 7.5×10−4nA/mgdl and a lifetime of about 6 weeks.
Keywords: Polyaniline; Cholesterol esterase; Cholesterol oxidase; Covalent immobilization
Covalent immobilization of cholesterol esterase and cholesterol oxidase on polyaniline films for application to cholesterol biosensor by Suman Singh; Pratima R. Solanki; M.K. Pandey; B.D. Malhotra (pp. 126-132).
Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) have been covalently immobilized on electrochemically prepared polyaniline (PANI) films. These PANI/ChEt/ChOx enzyme films have been characterized using UV–visible, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Electrochemical behavior of these films has been studied using cyclic voltammetry (CV) and amperometric techniques, respectively. The PANI/ChEt/ChOx enzyme films show broad oxidation peak from 0.2 to 0.5V. These PANI/ChEt/ChOx biosensing electrodes have a response time of about 40s, linearity from 50 to 500mg/dl of cholesterol oleate concentration. These PANI/ChEt/ChOx films are thermally stable up to 46°C. This polyaniline based cholesterol biosensor has optimum pH in the range of 6.5–7.5, sensitivity as 7.5×10−4nA/mgdl and a lifetime of about 6 weeks.
Keywords: Polyaniline; Cholesterol esterase; Cholesterol oxidase; Covalent immobilization
Tubular linear actuators using conducting polymer, polypyrrole by Kentaro Yamato; Keiichi Kaneto (pp. 133-137).
Conducting polymers show an electrochemomechanical deformation (ECMD), which is able to be utilized as soft actuators. A tubular linear actuator of polypyrrole film is fabricated and the characteristics are examined. The film was electrochemically prepared on an acryl resin rod in an aqueous electrolyte solution of pyrrole and dodecylbenzensulfonic acid (DBS), followed by removing the rod. The actuations of tubular polypyrrole film due to ECMD in various conditions have been examined to clarify the mechanism. It has been found that the tubular actuator elongates upon reduction with the strain of 7%, which is more than twice of that observed in a rectangular film. The facts indicate that cations play the role of dopants instead of large DBS anion and the tubular structure gives the better performance for large strain.
Keywords: Conducting polymer; Polypyrrole; Electrochemomechanical deformation; Soft actuator; Artificial muscle; Linear actuators; Strain
Tubular linear actuators using conducting polymer, polypyrrole by Kentaro Yamato; Keiichi Kaneto (pp. 133-137).
Conducting polymers show an electrochemomechanical deformation (ECMD), which is able to be utilized as soft actuators. A tubular linear actuator of polypyrrole film is fabricated and the characteristics are examined. The film was electrochemically prepared on an acryl resin rod in an aqueous electrolyte solution of pyrrole and dodecylbenzensulfonic acid (DBS), followed by removing the rod. The actuations of tubular polypyrrole film due to ECMD in various conditions have been examined to clarify the mechanism. It has been found that the tubular actuator elongates upon reduction with the strain of 7%, which is more than twice of that observed in a rectangular film. The facts indicate that cations play the role of dopants instead of large DBS anion and the tubular structure gives the better performance for large strain.
Keywords: Conducting polymer; Polypyrrole; Electrochemomechanical deformation; Soft actuator; Artificial muscle; Linear actuators; Strain
DNA and microfluidics: Building molecular electronics systems by Yun Ye; Lu Chen; Xuezhu Liu; Ulrich J. Krull (pp. 138-145).
The development of molecular electronics using DNA molecules as the building blocks and using microfluidics to build nanowire arrays is reviewed. Applications of DNA conductivity to build sensors and nanowire arrays, and DNA conjugation with other nanostructures, offers an exciting opportunity to build extremely small analytical devices that are suitable for single-molecule detection and also target screening.
Keywords: Molecular electronics; DNA; Conductivity; Microfluidics
DNA and microfluidics: Building molecular electronics systems by Yun Ye; Lu Chen; Xuezhu Liu; Ulrich J. Krull (pp. 138-145).
The development of molecular electronics using DNA molecules as the building blocks and using microfluidics to build nanowire arrays is reviewed. Applications of DNA conductivity to build sensors and nanowire arrays, and DNA conjugation with other nanostructures, offers an exciting opportunity to build extremely small analytical devices that are suitable for single-molecule detection and also target screening.
Keywords: Molecular electronics; DNA; Conductivity; Microfluidics
Unimolecular rectifiers: Methods and challenges by Robert M. Metzger (pp. 146-155).
Six unimolecular rectifiers have been studied at the University of Alabama: Langmuir–Blodgett (LB) or Langmuir–Schaefer (LS), or self-assembled monolayers of these molecules show asymmetric electrical conductivity between Au or Al electrodes. These molecules are γ-hexadecylquinolinium tricyanoquinodimethanide (,2), 2,6-di[dibutylamino-phenylvinyl]-l-butylpyridinium iodide,3, dimethylanilino-aza[C60]-fullerene,4, fullerene-bis-[4-diphenylamino-4″-( N-ethyl-N-2?-ethyl)-amino-1,4-diphenyl-1,3 -butadiene] malonate,5, N-(10-nonadecyl)- N-(2-ferrocenyl-ethyl)-pyrenyl-methyl)pery-lene-3,4,9,10-bis(dicarboxyimide),6, and 4,5-dipentyl-5′-methyltetrathiaful-valen-4′-methyl-oxy-2,4,5-trinitro-9-dicyanomethylenefluorene-7-(3-sulfonylpropionate),7. Many ancillary experiments must be performed before unimolecular rectification can be fully understood. This review will focus on the fabrication techniques and the analytical tools that can help understand the asymmetric current–voltage ( IV) curves. These tools include molecular orbital calculations, cyclic voltammetry, ultraviolet photoelectron spectroscopy, scanning tunneling microscopy, contact angle goniometry, ultraviolet–visible-near-infrared spectroscopy, grazing-angle Fourier transform infrared spectroscopy, surface plasmon resonance, spectroscopic ellipsometry, grazing-incidence X-ray reflectometry, core-level and valence-band X-ray photoelectron spectroscopy.
Keywords: Unimolecular electronics; Rectifiers; Molecular devices; Aviram–Ratner model; Organic computers
Unimolecular rectifiers: Methods and challenges by Robert M. Metzger (pp. 146-155).
Six unimolecular rectifiers have been studied at the University of Alabama: Langmuir–Blodgett (LB) or Langmuir–Schaefer (LS), or self-assembled monolayers of these molecules show asymmetric electrical conductivity between Au or Al electrodes. These molecules are γ-hexadecylquinolinium tricyanoquinodimethanide (,2), 2,6-di[dibutylamino-phenylvinyl]-l-butylpyridinium iodide,3, dimethylanilino-aza[C60]-fullerene,4, fullerene-bis-[4-diphenylamino-4″-( N-ethyl-N-2⁗-ethyl)-amino-1,4-diphenyl-1,3 -butadiene] malonate,5, N-(10-nonadecyl)- N-(2-ferrocenyl-ethyl)-pyrenyl-methyl)pery-lene-3,4,9,10-bis(dicarboxyimide),6, and 4,5-dipentyl-5′-methyltetrathiaful-valen-4′-methyl-oxy-2,4,5-trinitro-9-dicyanomethylenefluorene-7-(3-sulfonylpropionate),7. Many ancillary experiments must be performed before unimolecular rectification can be fully understood. This review will focus on the fabrication techniques and the analytical tools that can help understand the asymmetric current–voltage ( IV) curves. These tools include molecular orbital calculations, cyclic voltammetry, ultraviolet photoelectron spectroscopy, scanning tunneling microscopy, contact angle goniometry, ultraviolet–visible-near-infrared spectroscopy, grazing-angle Fourier transform infrared spectroscopy, surface plasmon resonance, spectroscopic ellipsometry, grazing-incidence X-ray reflectometry, core-level and valence-band X-ray photoelectron spectroscopy.
Keywords: Unimolecular electronics; Rectifiers; Molecular devices; Aviram–Ratner model; Organic computers
Consolidating molecular AND logic with two chemical inputs by David C. Magri; Gregory D. Coen; Robert L. Boyd; A. Prasanna de Silva (pp. 156-160).
A novel molecular AND logic gate1 is demonstrated based on the competition between fluorescence and photoinduced electron transfer (PET). It is constructed according to a ‘receptor2-spacer-fluorophore-spacer-receptor1-spacer-fluorophore-spacer-receptor2’ format where receptor1 is a tertiary amine, receptor2 is a benzo-15-crown-5 ether and the fluorophore is an anthracene moiety, which are separated from each other by methylene spacers. The fluorescence response in methanol is significantly enhanced only when both H+ and Na+ are the inputs at high enough concentrations in accordance with AND logic. Cs+ behaves similarly to Na+, but with a lower fluorescence enhancement, whereas the other alkali metal cations are not effective. Electrospray ionization mass spectrometry provides evidence for formation of 1:1 and 1:2 (1:metal) complexes with alkali cations, and formation of a 1:2:1 (1:metal:proton) complex in the additional presence of acid.
Keywords: Photoinduced electron transfer; Fluorescence; Molecular logic; Benzocrown ether; Sensors
Consolidating molecular AND logic with two chemical inputs by David C. Magri; Gregory D. Coen; Robert L. Boyd; A. Prasanna de Silva (pp. 156-160).
A novel molecular AND logic gate1 is demonstrated based on the competition between fluorescence and photoinduced electron transfer (PET). It is constructed according to a ‘receptor2-spacer-fluorophore-spacer-receptor1-spacer-fluorophore-spacer-receptor2’ format where receptor1 is a tertiary amine, receptor2 is a benzo-15-crown-5 ether and the fluorophore is an anthracene moiety, which are separated from each other by methylene spacers. The fluorescence response in methanol is significantly enhanced only when both H+ and Na+ are the inputs at high enough concentrations in accordance with AND logic. Cs+ behaves similarly to Na+, but with a lower fluorescence enhancement, whereas the other alkali metal cations are not effective. Electrospray ionization mass spectrometry provides evidence for formation of 1:1 and 1:2 (1:metal) complexes with alkali cations, and formation of a 1:2:1 (1:metal:proton) complex in the additional presence of acid.
Keywords: Photoinduced electron transfer; Fluorescence; Molecular logic; Benzocrown ether; Sensors
Optical properties and photonic devices of doped carbon nanotubes by Jijun Zhao; Xiaoshuang Chen; John R.H. Xie (pp. 161-170).
Chemical doping of carbon nanotubes provides a variety of opportunities for tailoring the physical properties of carbon nanotubes. In this review, we discussed the optical properties of doped carbon nanotubes and the related applications as nanoscale photonic devices. The fundamental optical properties of carbon nanotubes with various chemical doping have been summarized. Novel optoelectronic and photonic devices based on doped carbon nanotubes, such as optical nonlinear materials, optical limiting devices, photovoltaic devices, etc., have been discussed.
Keywords: Carbon nanotube; Photonic devices; Doping; Functionalization; Optical absorption; Nonlinear optical property; Photoconductivity
Optical properties and photonic devices of doped carbon nanotubes by Jijun Zhao; Xiaoshuang Chen; John R.H. Xie (pp. 161-170).
Chemical doping of carbon nanotubes provides a variety of opportunities for tailoring the physical properties of carbon nanotubes. In this review, we discussed the optical properties of doped carbon nanotubes and the related applications as nanoscale photonic devices. The fundamental optical properties of carbon nanotubes with various chemical doping have been summarized. Novel optoelectronic and photonic devices based on doped carbon nanotubes, such as optical nonlinear materials, optical limiting devices, photovoltaic devices, etc., have been discussed.
Keywords: Carbon nanotube; Photonic devices; Doping; Functionalization; Optical absorption; Nonlinear optical property; Photoconductivity
Analytical potential of the quadruplex DNA-based FRET probes by Bernard Juskowiak (pp. 171-180).
DNA exhibits structural flexibility and may adopt also tetraplex structures known as guanine-quadruplexes or G-quadruplexes. These G-quadruplexes have recently received great attention because G-rich sequences are often found in genome and because of their potential links to mechanisms that relate to cancer, HIV, and other diseases. The unique structure of quadruplexes has also stimulated development of new analytical and bioanalytical assays based on fluorescence resonance energy transfer (FRET). Intramolecular folding of a flexible single-stranded DNA molecule into a compact G-quadruplex is a structural transition leading to closer proximity of its 5′- and 3′-ends. Thus, labeling both ends of a DNA strand with donor and acceptor fluorophores enables monitoring the quadruplex formation process by means of the FRET signal.This review shows how FRET technique contributes to G-quadruplex research and focuses mainly on analytical applications of FRET-labeled quadruplexes. Applications include studies of structural transitions of quadruplexes, FRET-based selection of ligands that bind to quadruplexes, design of molecular probes for protein recognition and development of sensors for detection of potassium ions in aqueous solution.
Keywords: Fluorescence; FRET; G-quadruplex; Potassium ion; Proteins; Quadruplex-binding ligands; Telomeric DNA; Tetraplex DNA; Thrombin aptamer
Analytical potential of the quadruplex DNA-based FRET probes by Bernard Juskowiak (pp. 171-180).
DNA exhibits structural flexibility and may adopt also tetraplex structures known as guanine-quadruplexes or G-quadruplexes. These G-quadruplexes have recently received great attention because G-rich sequences are often found in genome and because of their potential links to mechanisms that relate to cancer, HIV, and other diseases. The unique structure of quadruplexes has also stimulated development of new analytical and bioanalytical assays based on fluorescence resonance energy transfer (FRET). Intramolecular folding of a flexible single-stranded DNA molecule into a compact G-quadruplex is a structural transition leading to closer proximity of its 5′- and 3′-ends. Thus, labeling both ends of a DNA strand with donor and acceptor fluorophores enables monitoring the quadruplex formation process by means of the FRET signal.This review shows how FRET technique contributes to G-quadruplex research and focuses mainly on analytical applications of FRET-labeled quadruplexes. Applications include studies of structural transitions of quadruplexes, FRET-based selection of ligands that bind to quadruplexes, design of molecular probes for protein recognition and development of sensors for detection of potassium ions in aqueous solution.
Keywords: Fluorescence; FRET; G-quadruplex; Potassium ion; Proteins; Quadruplex-binding ligands; Telomeric DNA; Tetraplex DNA; Thrombin aptamer
Fluorescence resonance energy transfer (FRET) for DNA biosensors: FRET pairs and Förster distances for various dye–DNA conjugates by Melissa Massey; W. Russ Algar; Ulrich J. Krull (pp. 181-189).
Fluorescence resonance energy transfer (FRET) between the extrinsic dye labels Cyanine 3 (Cy3), Cyanine 5 (Cy5), Carboxytetramethyl Rhodamine (TAMRA), Iowa Black Fluorescence Quencher (IabFQ), and Iowa Black RQ (IabRQ) has been studied. The Förster distances for these FRET-pairs in single- and double-stranded DNA conjugates have been determined. In particular, it should be noted that the quantum yield of the donors Cy3 and TAMRA varies between single- and double-stranded DNA. While this alters the Förster distance for a donor–acceptor pair, this also allows for detection of thermal denaturation events with a single non-intercalating fluorophore. The utility of FRET in the development of nucleic acid biosensor technology is illustrated by using TAMRA and IabRQ as a FRET pair in selectivity experiments. The differential quenching of TAMRA fluorescence by IabRQ in solution has been used to discriminate between 0 and 3 base pair mismatches at 60°C for a 19 base sequence. At room temperature, the quenching of TAMRA fluorescence was not an effective indicator of the degree of base pair mismatch. There appears to be a threshold of duplex stability at room temperature which occurs beyond two base pair mismatches and reverses the observed trend in TAMRA fluorescence prior to that degree of mismatch. When this experimental system is transferred to a glass surface through covalent coupling and organosilane chemistry, the observed trend in TAMRA fluorescence at room temperature is similar to that obtained in bulk solution, but without a threshold of duplex stability. In addition to quenching of fluorescence by FRET, it is believed that several other quenching mechanisms are occurring at the surface.
Keywords: Fluorescence resonance energy transfer; DNA; Förster distance; Hybridization; Biosensor
Fluorescence resonance energy transfer (FRET) for DNA biosensors: FRET pairs and Förster distances for various dye–DNA conjugates by Melissa Massey; W. Russ Algar; Ulrich J. Krull (pp. 181-189).
Fluorescence resonance energy transfer (FRET) between the extrinsic dye labels Cyanine 3 (Cy3), Cyanine 5 (Cy5), Carboxytetramethyl Rhodamine (TAMRA), Iowa Black Fluorescence Quencher (IabFQ), and Iowa Black RQ (IabRQ) has been studied. The Förster distances for these FRET-pairs in single- and double-stranded DNA conjugates have been determined. In particular, it should be noted that the quantum yield of the donors Cy3 and TAMRA varies between single- and double-stranded DNA. While this alters the Förster distance for a donor–acceptor pair, this also allows for detection of thermal denaturation events with a single non-intercalating fluorophore. The utility of FRET in the development of nucleic acid biosensor technology is illustrated by using TAMRA and IabRQ as a FRET pair in selectivity experiments. The differential quenching of TAMRA fluorescence by IabRQ in solution has been used to discriminate between 0 and 3 base pair mismatches at 60°C for a 19 base sequence. At room temperature, the quenching of TAMRA fluorescence was not an effective indicator of the degree of base pair mismatch. There appears to be a threshold of duplex stability at room temperature which occurs beyond two base pair mismatches and reverses the observed trend in TAMRA fluorescence prior to that degree of mismatch. When this experimental system is transferred to a glass surface through covalent coupling and organosilane chemistry, the observed trend in TAMRA fluorescence at room temperature is similar to that obtained in bulk solution, but without a threshold of duplex stability. In addition to quenching of fluorescence by FRET, it is believed that several other quenching mechanisms are occurring at the surface.
Keywords: Fluorescence resonance energy transfer; DNA; Förster distance; Hybridization; Biosensor
Structurally integrated organic light emitting device-based sensors for gas phase and dissolved oxygen by Ruth Shinar; Zhaoqun Zhou; Bhaskar Choudhury; Joseph Shinar (pp. 190-199).
A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol–gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4′-bis(2,2′-diphenylviny1)-1,1′-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime τ of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of τ in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, Sg≡ τ(0% O2)/ τ(100% O2), at 23°C, were ∼35 to ∼50 for the [Alq3 OLED[/[PtOEP dye] pair; Sg exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, SDO (defined as the ratio of τ in de-oxygenated and oxygen-saturated solutions) was ∼9.5 and ∼11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.
Keywords: Oxygen gas sensors; Dissolved oxygen sensors; Organic light emitting devices; OLEDs; Structurally integrated oxygen sensors
Structurally integrated organic light emitting device-based sensors for gas phase and dissolved oxygen by Ruth Shinar; Zhaoqun Zhou; Bhaskar Choudhury; Joseph Shinar (pp. 190-199).
A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol–gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4′-bis(2,2′-diphenylviny1)-1,1′-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime τ of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of τ in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, Sg≡ τ(0% O2)/ τ(100% O2), at 23°C, were ∼35 to ∼50 for the [Alq3 OLED[/[PtOEP dye] pair; Sg exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, SDO (defined as the ratio of τ in de-oxygenated and oxygen-saturated solutions) was ∼9.5 and ∼11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.
Keywords: Oxygen gas sensors; Dissolved oxygen sensors; Organic light emitting devices; OLEDs; Structurally integrated oxygen sensors
Microbial biosensors by Yu Lei; Wilfred Chen; Ashok Mulchandani (pp. 200-210).
A microbial biosensor is an analytical device that couples microorganisms with a transducer to enable rapid, accurate and sensitive detection of target analytes in fields as diverse as medicine, environmental monitoring, defense, food processing and safety. The earlier microbial biosensors used the respiratory and metabolic functions of the microorganisms to detect a substance that is either a substrate or an inhibitor of these processes. Recently, genetically engineered microorganisms based on fusing of the lux, gfp or lacZ gene reporters to an inducible gene promoter have been widely applied to assay toxicity and bioavailability. This paper reviews the recent trends in the development and application of microbial biosensors. Current advances and prospective future direction in developing microbial biosensor have also been discussed.
Keywords: Microbial biosensors; Amperometric; Potentiometric; Optical; Luminescence; Fluorescence
Microbial biosensors by Yu Lei; Wilfred Chen; Ashok Mulchandani (pp. 200-210).
A microbial biosensor is an analytical device that couples microorganisms with a transducer to enable rapid, accurate and sensitive detection of target analytes in fields as diverse as medicine, environmental monitoring, defense, food processing and safety. The earlier microbial biosensors used the respiratory and metabolic functions of the microorganisms to detect a substance that is either a substrate or an inhibitor of these processes. Recently, genetically engineered microorganisms based on fusing of the lux, gfp or lacZ gene reporters to an inducible gene promoter have been widely applied to assay toxicity and bioavailability. This paper reviews the recent trends in the development and application of microbial biosensors. Current advances and prospective future direction in developing microbial biosensor have also been discussed.
Keywords: Microbial biosensors; Amperometric; Potentiometric; Optical; Luminescence; Fluorescence
Cellular biosensing: Chemical and genetic approaches by Tetsuya Haruyama / (pp. 211-216).
Biosensors have been developed to determine the concentration of specific compounds in situ. They are already widely employed as a practical technology in the clinical and healthcare fields. Recently, another concept of biosensing has been receiving attention: biosensing for the evaluation of molecular potency. The development of this novel concept has been supported by the development of related technologies, as such as molecular design, molecular biology (genetic engineering) and cellular/tissular engineering. This review is addresses this new concept of biosensing and its application to the evaluation of the potency of chemicals in biological systems, in the field of cellular/tissular engineering. Cellular biosensing may provide information on both pharmaceutical and chemical safety, and on drug efficacy in vitro as a screening tool.
Keywords: Biosensor; Cellular biosensing; Cellular response; Artificial enzyme; Synapse model cell; Reporter gene; BLET; Bioassay; High through-put; Drug screening; Chemical safety
Cellular biosensing: Chemical and genetic approaches by Tetsuya Haruyama / (pp. 211-216).
Biosensors have been developed to determine the concentration of specific compounds in situ. They are already widely employed as a practical technology in the clinical and healthcare fields. Recently, another concept of biosensing has been receiving attention: biosensing for the evaluation of molecular potency. The development of this novel concept has been supported by the development of related technologies, as such as molecular design, molecular biology (genetic engineering) and cellular/tissular engineering. This review is addresses this new concept of biosensing and its application to the evaluation of the potency of chemicals in biological systems, in the field of cellular/tissular engineering. Cellular biosensing may provide information on both pharmaceutical and chemical safety, and on drug efficacy in vitro as a screening tool.
Keywords: Biosensor; Cellular biosensing; Cellular response; Artificial enzyme; Synapse model cell; Reporter gene; BLET; Bioassay; High through-put; Drug screening; Chemical safety
Microbial biosensor for direct determination of nitrophenyl-substituted organophosphate nerve agents using genetically engineered Moraxella sp. by Priti Mulchandani; Wilfred Chen; Ashok Mulchandani (pp. 217-221).
A microbial biosensor consisting of a dissolved oxygen electrode modified with the genetically engineered PNP-degrader Moraxella sp. displaying organophosphorus hydrolase (OPH) on the cell surface for sensitive, selective, rapid and direct determination of p-nitrophenyl (PNP)-substituted organophosphates (OPs) is reported. Surface-expressed OPH works in tandem with the PNP oxidation machinery of the Moraxella sp. to degrade PNP-substituted OPs and PNP simultaneously while consuming oxygen, that is proportional to the analyte concentration. The optimum performance was obtained by electrodes constructed using 0.35mg dry weight of cell and operating at pH 7.5. Operating at optimum conditions the biosensor was able to measure as low as 0.1μM (27.5ppb) of paraoxon and had excellent selectivity against triazines, carbamates and OPs without PNP substitutent. The biosensor was stable for a week when stored at 4°C. The applicability of the biosensor to measure OPs in lake water was demonstrated.
Keywords: Nerve agents; Pesticides; Organophosphorus hydrolase; Microbial biosensor; Moraxella; sp.
Microbial biosensor for direct determination of nitrophenyl-substituted organophosphate nerve agents using genetically engineered Moraxella sp. by Priti Mulchandani; Wilfred Chen; Ashok Mulchandani (pp. 217-221).
A microbial biosensor consisting of a dissolved oxygen electrode modified with the genetically engineered PNP-degrader Moraxella sp. displaying organophosphorus hydrolase (OPH) on the cell surface for sensitive, selective, rapid and direct determination of p-nitrophenyl (PNP)-substituted organophosphates (OPs) is reported. Surface-expressed OPH works in tandem with the PNP oxidation machinery of the Moraxella sp. to degrade PNP-substituted OPs and PNP simultaneously while consuming oxygen, that is proportional to the analyte concentration. The optimum performance was obtained by electrodes constructed using 0.35mg dry weight of cell and operating at pH 7.5. Operating at optimum conditions the biosensor was able to measure as low as 0.1μM (27.5ppb) of paraoxon and had excellent selectivity against triazines, carbamates and OPs without PNP substitutent. The biosensor was stable for a week when stored at 4°C. The applicability of the biosensor to measure OPs in lake water was demonstrated.
Keywords: Nerve agents; Pesticides; Organophosphorus hydrolase; Microbial biosensor; Moraxella; sp.
Recent advances in biosensor techniques for environmental monitoring by K.R. Rogers (pp. 222-231).
Biosensors for environmental applications continue to show advances and improvements in areas such as sensitivity, selectivity and simplicity. In addition to detecting and measuring specific compounds or compound classes such as pesticides, hazardous industrial chemicals, toxic metals, and pathogenic bacteria, biosensors and bioanalytical assays have been designed to measure biological effects such as cytotoxicity, genotoxicity, biological oxygen demand, pathogenic bacteria, and endocrine disruption effects. This article is intended to discuss recent advances in the area of biosensors for environmental applications.
Keywords: Biosensors; Bioassays; Environmental monitoring
Recent advances in biosensor techniques for environmental monitoring by K.R. Rogers (pp. 222-231).
Biosensors for environmental applications continue to show advances and improvements in areas such as sensitivity, selectivity and simplicity. In addition to detecting and measuring specific compounds or compound classes such as pesticides, hazardous industrial chemicals, toxic metals, and pathogenic bacteria, biosensors and bioanalytical assays have been designed to measure biological effects such as cytotoxicity, genotoxicity, biological oxygen demand, pathogenic bacteria, and endocrine disruption effects. This article is intended to discuss recent advances in the area of biosensors for environmental applications.
Keywords: Biosensors; Bioassays; Environmental monitoring
Protein-sensing assay formats and devices by Ursula Bilitewski (pp. 232-247).
Proteins are used as biocatalysts, therapeutic or diagnostic agents, and as such they are biotechnological products. Moreover, they are biomarkers for health states, diseases or toxic or other adverse effects, and the intracellular protein network is essential for the adaptation of an organism to its environment. Thus, there is a strong need for analytical methods for protein determination, which allow not only to indicate the presence of a protein, but also its concentration, covalent modification and activity, and corresponding developments of new methods experienced strong support. Among those methods only those were considered here, which are based on affinity reactions between an immobilized capture agent, such as an antibody or a receptor, and the target protein.Immobilization methods range from adsorption on hydrophobic materials, in membranes or gels to covalent binding and bioaffinity reactions, such as the oriented immobilization of antibodies on protein A/G layers. The applicability of the various methods is dependent on physical and chemical properties of the immobilization substrate and of the capture agent, i.e. the presence of surface charges, hydrophobic areas or functional groups for chemical coupling. The choice of the immobilization substrate is influenced by the combination of the assay and detection principle, which meets best the practical requirements. Assay formats range from direct, label-free one-step detection of the affinity reaction between the capture agent and the target protein to multi-step procedures, such as an enzyme-tracer-based sandwich assays. Each approach has its particular advantages and disadvantages with respect to the complexity of the assay, i.e. number of required reagents and of incubation steps, the possible degree of automation, assay time, availability of suitable reagents, required sample volume, sensitivity and specificity, including the possibility to determine several proteins simultaneously. No general recommendation for the “best choice? was given in this contribution, but examples were chosen, which illustrate the potential of the different systems.
Keywords: Protein chips; Arrays; Phosphorylation; Protein activity; Immobilization
Protein-sensing assay formats and devices by Ursula Bilitewski (pp. 232-247).
Proteins are used as biocatalysts, therapeutic or diagnostic agents, and as such they are biotechnological products. Moreover, they are biomarkers for health states, diseases or toxic or other adverse effects, and the intracellular protein network is essential for the adaptation of an organism to its environment. Thus, there is a strong need for analytical methods for protein determination, which allow not only to indicate the presence of a protein, but also its concentration, covalent modification and activity, and corresponding developments of new methods experienced strong support. Among those methods only those were considered here, which are based on affinity reactions between an immobilized capture agent, such as an antibody or a receptor, and the target protein.Immobilization methods range from adsorption on hydrophobic materials, in membranes or gels to covalent binding and bioaffinity reactions, such as the oriented immobilization of antibodies on protein A/G layers. The applicability of the various methods is dependent on physical and chemical properties of the immobilization substrate and of the capture agent, i.e. the presence of surface charges, hydrophobic areas or functional groups for chemical coupling. The choice of the immobilization substrate is influenced by the combination of the assay and detection principle, which meets best the practical requirements. Assay formats range from direct, label-free one-step detection of the affinity reaction between the capture agent and the target protein to multi-step procedures, such as an enzyme-tracer-based sandwich assays. Each approach has its particular advantages and disadvantages with respect to the complexity of the assay, i.e. number of required reagents and of incubation steps, the possible degree of automation, assay time, availability of suitable reagents, required sample volume, sensitivity and specificity, including the possibility to determine several proteins simultaneously. No general recommendation for the “best choice” was given in this contribution, but examples were chosen, which illustrate the potential of the different systems.
Keywords: Protein chips; Arrays; Phosphorylation; Protein activity; Immobilization
Enzyme biosensors based on ion-selective field-effect transistors by Sergei V. Dzyadevych; Alexey P. Soldatkin; Anna V. El'skaya; Claude Martelet; Nicole Jaffrezic-Renault (pp. 248-258).
The key theoretical principles of the work on ion-selective field-effect transistor connected with their application in bioanalytical practice, some specifics of modern microtechnologies for their creation, and measurement schemes with set-ups are discussed. The achievements in the creation of enzyme biosensors based on ion-selective field-effect transistors and prospects for their application are described in detail.
Keywords: Biosensor; Field-effect transistor; pH-electrode; Enzyme; Microtechnology
Enzyme biosensors based on ion-selective field-effect transistors by Sergei V. Dzyadevych; Alexey P. Soldatkin; Anna V. El'skaya; Claude Martelet; Nicole Jaffrezic-Renault (pp. 248-258).
The key theoretical principles of the work on ion-selective field-effect transistor connected with their application in bioanalytical practice, some specifics of modern microtechnologies for their creation, and measurement schemes with set-ups are discussed. The achievements in the creation of enzyme biosensors based on ion-selective field-effect transistors and prospects for their application are described in detail.
Keywords: Biosensor; Field-effect transistor; pH-electrode; Enzyme; Microtechnology
Recent developments in bio-molecular electronics techniques for food pathogens by Kavita Arora; Subhash Chand; B.D. Malhotra (pp. 259-274).
Food borne illnesses contribute to the majority of infections caused by pathogenic microorganisms. Detection of these pathogens originating from different sources has led to increased interest of researchers. New bio-molecular techniques for food pathogen detection are being developed to improve the sensor characteristics such as sensitivity, reusability, simplicity and economic viability. Present article deals with the various methods of food pathogen detection with special emphasis on bio-molecular electronics techniques such as biosensors, microarrays, electronic nose, and nano-materials based methods.
Keywords: Food pathogens; Bio-molecular electronics; Biosensors; Microarrays; Nano-devices; Electronic nose
Recent developments in bio-molecular electronics techniques for food pathogens by Kavita Arora; Subhash Chand; B.D. Malhotra (pp. 259-274).
Food borne illnesses contribute to the majority of infections caused by pathogenic microorganisms. Detection of these pathogens originating from different sources has led to increased interest of researchers. New bio-molecular techniques for food pathogen detection are being developed to improve the sensor characteristics such as sensitivity, reusability, simplicity and economic viability. Present article deals with the various methods of food pathogen detection with special emphasis on bio-molecular electronics techniques such as biosensors, microarrays, electronic nose, and nano-materials based methods.
Keywords: Food pathogens; Bio-molecular electronics; Biosensors; Microarrays; Nano-devices; Electronic nose