Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.96, #1-3)
Contribution of conformational change of polymer structure to electrochemomechanical deformation based on polyaniline by Keiichi Kaneto; Masamitsu Kaneko (pp. 13-23).
The pH dependencies of electrochemomechanical deformation (ECMD) including the cyclic voltammetry and the expansion ratio in conducting polymers, polyaniline (PANI), and poly(o-methoxyaniline) film were studied to elucidate the mechanisms. It was found that the ECMD is governed by the conformational change of polymer structure as well as the insertion of bulky ions in the manner of comparable magnitude. Expansion ratios >20% in the ECMD were demonstrated for the thickness direction of PANI film. The results suggest that the magnitude of ECMD can be improved by choosing the preparation method of films.
Keywords: Artificial muscles; electrochemomechanical deformation; conducting polymers; polyanilines; pH dependence
Applications of self-assembled monolayers for biomolecular electronics by Kunjukrishna Vijayamohanan; Mohammed Aslam (pp. 25-39).
Preparation and characterization of ordered ultrathin organic films (a few nanometers to several hundred nanometers) has recently attracted considerable attention because of the possibility of controlling order and interactions at the molecular level and has triggered several innovative applications ranging from molecular electronics to tribology. Monomolecular films prepared by self-assembly are attractive for several exciting applications because of the unique possibility of making the selection of different types of terminal functional groups as well as length scales more flexible. The present article discusses various applications of self-assembled monolayers (SAMs) in molecular electronics ranging from biosensors to optoelectronic devices with specific examples. Similarly, SAMs and multilayers of bifunctional molecules on polycrystalline substrates can be effectively used to carry out specific reactions between pendent functionalities and solution or gaseous species to produce new hybrid materials for devices such as molecular diodes. The importance of SAMs in controlling nucleation and growth is also illustrated using biomimetic synthesis of ceramic thin films (biomineralization) of zirconia.
Keywords: Self-assembled monolayers; biomolecular electronics; biosensors; nanocluster superlattices; biomineralization
Pigeonpea (Cajanus cajan L.) urease immobilized on glutaraldehyde-activated chitosan beads and its analytical applications by Arvind M. Kayastha; Punit K. Srivastava (pp. 41-53).
Urease from pigeonpea (Cajanus cajan L.) was covalently linked to crab shell chitosan beads using glutaraldehyde. The optimum immobilization (64% activity) was observed at 4°C, with a protein concentration of 0.24 mg/bead and 3% glutaraldehyde. The immobilized enzyme stored in 0.05 M Trisacetate buffer, pH 7.3, at 4°C had a t 1/2 of 110 d. There was practically no leaching of enzyme (<3%) from the immobilized beads in 30 d. The immobilized urease was used 10 times at an interval of 24 h between each use with 80% residual activity at the end of the period. The chitosan-immobilized urease showed a significantly higher Michaelis constant (8.3 mM) compared to that of the soluble urease (3.0 mM). Its apparent optimum pH also shifted from 7.3 to 8.5. Immobilized urease showed an optimal temperature of 77°C, compared with 47°C for the soluble urease. Time-dependent kinetics of the thermal denaturation of immobilized urease was studied and found to be monophasic in nature compared to biphasic in nature for soluble enzyme. This immobilized urease was used to analyze blood urea of some of the clinical samples from the clinical pathology laboratories. The results compared favorably with those obtained by the various chemical/biochemical methods employed in the clinical pathology laboratories. A column packed with immobilized urease beads was also prepared in a syringe for the regular and continuous monitoring of serum urea concentrations.
Keywords: Urease; pigeonpea; Cajanus cajan ; chitosan; immobilization; urea estimation
Study on photoconductivity of dye-polymer-based solid-state thin film by Sisir K. Dey; N. B. Manik (pp. 55-62).
In this article, we describe a solid-state photoelectrochemical cell for light detection. Safranine-T dye mixed with polyvinyl alcohol (PVA) solution was deposited on a conducting and transparent indium-tin-oxide (ITO)-coated glass that was used as one electrode and another ITO-coated glass as the counterelectrode. A solid polymeric electrolyte consisting of polyethylene oxide-ammonium perchlorate-ethylene carbonate and propylene carbonate with suitable weight ratio was prepared and sandwiched between these two ITO-coated glass electrodes, which were separated by a Teflon spacer about 50 µm thick. The cell was biased with a direct current source to make the dye and PVA-coated ITO as the anode and the other ITO as the cathode. On illumination by a tungsten lamp, from the cathode side, the change of photocurrent was measured. The dark current-voltage characteristics and the growth and decay of the photocurrent for steady and pulsed illumination were studied.
Keywords: Organic photodetector; solid-state photoelectrochemical cell; photoconductivity
Copper(II) ion-selective microelectrochemical transistor by Vibha Saxena; Vinay Shirodkar; Rajiv Prakash (pp. 63-69).
A device has been developed for the measurement of copper(II) ions (Cu++) in aqueous medium. The device reported here is an electrochemical transistor that consists of two platinum electrodes separated by 100-µm spacing and bridged with an anodically grown polycarbazole film. The undoped polycarbazole film is observed to be highly selective for the Cu(II) ions. In a completed device, the conductivity of the polycarbazole film changes on addition of Cu (II)ions. This change in conductivity is attributed to the conformational changes in the polymer phase on occupation of the Cu(II) ions, without affecting electron/proton transfer. The device turns on by adding 2.5×10−6 M Cu(II) ions and reaches a saturation region above a concentration of 10−4 M Cu(II) ions. In this concentration range, the plot of I D vs log[Cu(II)] is linear. The selectivity of the device for other metal ions such as Cu(I), Co(II), Fe(II), Fe(III), Zn(II), and Pb(II) is also studied.
Keywords: Conducting polymers; electrochemical transistor; sensor
Semi-solid-state fermentation of Eicchornia crassipes biomass as lignocellulosic biopolymer for cellulase and β-glucosidase production by cocultivation of Aspergillus niger RK3 and Trichoderma reesei MTCC164 by Raj Kumar; R. P. Singh (pp. 71-82).
An aquatic weed biomass, Eicchornia crassipes, present in abundance and leading to a threatening level of water pollution was used as substrate for cellulase and β-glucosidase production using wild-type strain Aspergillus niger RK3 that was isolated from decomposing substrate. Alkali treatment of the biomass (10%) resulted in a 60–66% increase in endoglucanase, exoglucanase, and β-glucosidase production by the A. niger RK3 strain in semi-solid-state fermentation. Similarly, the alkali-treated biomass led to a 45–54% increase in endo- and exoglucanase and a higher (98%) increase in β-glucosidase production by Trichoderma reesei MTCC164 under similar conditions. However, the cocultivation of A. niger RK3 and T. reesei MTCC164 at a ratio of 3:1 showed a 20–24% increase in endo- and exoglucanase activities and about a 13% increase in the β-glucosidase activity over the maximum enzymatic activities observed under single culture conditions. Multistep physical (ultraviolet) and chemical (N-methyl-N′-nitrosoguanidine, sodium azide, colchicine) mutagenesis of the A. niger RK3 strain resulted in a highly cellulolytic mutant, UNSC-442, having an increase of 136, 138, and 96% in endoglucanase, exoglucanase, and β-glucosidase, activity, respectively. The cocultivation of mutant UNSC-442 along with T. reesei MTCC164 (at a ratio of 3:1) showed a further 10–11% increase in endo- and exoglucanase activities and a 29% increase in β-glucosidase activity in semi-solid-state fermentation.
Keywords: Cellulase; β-glucosidase; Eicchornia crassipes ; cocultivation; mutagenesis
Electrochemically synthesized polymer of the plant substance embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) by R. Renuka; S. Rajasekaran; Ganga Radhakrishnan (pp. 83-92).
Among the possible new materials for microelectronics, quinones have a number of significant advantages. Similarly, polymers with quinone functionality possess biodegradability. Because natural polymers are promising candidates for functional materials for the future, we have initiated studies on the polymers of natural products. In the present study, a natural quinone (a plant substance) extracted from Embelier libes distributed in the Kerala state of India was electrochemically polymerized and its properties were investigated. The redox activity, electrical conductivity, and biodegradability are discussed.
Keywords: Embelin; polymerization of embelin; biodegradable polymers; quinone polymer; conducting polymer
Free-energy analysis of enzyme-inhibitor binding by Parul Kalra; Achintya Das; B. Jayaram (pp. 93-108).
Expeditious in silico determinations of the free energies of binding of a series of inhibitors to an enzyme are of immense practical value in structure-based drug design efforts. Some recent advances in the field of computational chemistry have rendered a rigorous thermodynamic treatment of biologic molecules feasible, starting from a molecular description of the biomolecule, solvent, and salt. Pursuing the goal of developing and making available a software for assessing binding affinities, we present here a computationally rapid, albeit elaborate, methodology to estimate and analyze the molecular thermodynamics of enzyme-inhibitor binding with crystal structures as the point of departure. The complexes of aspartic proteinases with seven inhibitors have been adopted for this study. The standard free energy of complexation is considered in terms of a thermodynamic cycle of six distinct steps decomposed into a total of 18 well-defined components. The model we employed involves explicit all-atom accounts of the energetics of electrostatic interactions, solvent screening effects, van der Waals components, and cavitation effects of solvation combined with a Debye-Huckel treatment of salt effects. The magnitudes and signs of the various components are estimated using the AMBER parm94 force field, generalized Born theory, and solvent accessibility measures. Estimates of translational and rotational entropy losses on complexation as well as corresponding changes in the vibrational and configurational entropy are also included. The calculated standard free energies of binding at this stage are within an order of magnitude of the observed inhibition constants and necessitate further improvements in the computational protocols to enable quantitative predictions. Some areas such as inclusion of structural adaptation effects, incorporation of site-dependent amino acid pK a shifts, consideration of the dynamics of the active site for fine-tuning the methodology are easily envisioned. The present series of studies, nonetheless, creates potentially useful qualitative information for design purposes on what factors favor protein-drug binding. The net binding free energies are a result of several competing contributions with 6 of the 18 terms favoring complexation. The nonelectrostatic contributions (i.e., the net van der Waals interactions) and the differential cavitation effects favor binding. Electrostatic contributions show considerable diversity and turn out to be favorable in a consensus view for the seven aspartic proteinase-inhibitor complexes examined here. Implications of these observations to drug design are discussed.
Keywords: Protein-ligand interactions; binding free energy; computer modeling
Effect of synthesis temperature and doping level on conductivity and structure of poly(3-methyl thiophene) by Amarjeet K. Narula; Ramadhar Singh; K. L. Yadav; K. B. Ravat; Subhas Chandra (pp. 109-117).
Poly(3-methyl thiophene) was synthesized by oxidative chemical polymerization technique using ferric chloride as the dopant in an inert atmosphere. Samples of different doping levels were prepared and analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and direct current (dc) conductivity measurement at room temperature (300 K). Synthesis of the polymer was confirmed by FTIR studies. FTIR spectra showed a shift in the heterocyclic bands in the region of 700–1200 cm−1 with a decrease in synthesis temperature. It was evident from the scanning electron micrographs that the surface structure of the polymer became denser with an increase in doping level. The measured dc conductivity increased initially up to the doping level of 0.8 M and then this increase tended to slow down. Samples having a doping level of 0.4 M were synthesized at 300, 280, and 270 K while maintaining the other synthesis parameters. The conductivity and yield were found to increase as the temperature of the polymerization decreased.
Keywords: Oxidative chemical polymerization; poly(3-methyl thiophene); surface structure; direct current conductivity
Direct current conductivity studies on poly(3-methyl thiophene) by Kanhaiya L. Yadav; Amarjeet K. Narula; Ramadhar Singh; Subhas Chandra (pp. 119-124).
The direct current (dc) conductivity of poly(3-methyl thiophene) was measured in the temperature range of 77–300 K. The observed dc conductivity data were analyzed in the light of Mott’s variable range hopping model. Different Mott’s parameters such as characteristic temperature (T 0), average hopping distance (R), average hopping energy (W), and density of states at the Fermi level (N [E F ]) were evaluated. By taking the inverse of the coefficient of exponential decay of the localized states involved in the hopping process as 0.5 nm, a realistic value of density of states at the Fermi level (N [E F ]) was obtained that agrees well with the values reported earlier for other conjugated polymers.
Keywords: Poly(3-methyl thiophene); direct current conductivity; average hopping distance; average hopping energy; density of states; localized states
Strategies for molecular designing of novel low-band-gap electrically conducting polymers by A. K. Bakhshi; Sangeeta Kaul (pp. 125-133).
Molecular designing of low-band-gap electrically conducting polymers continues to be a major challenge of the field of electrically conducting polymers. Such polymers are expected to show not only good intrinsic conductivity but also possibly a good transparency in the visible spectrum for their use as infrared sensors/detectors. Low-band-gap polymers can also be of great interest as new polymeric materials for nonlinear optics. Various routes presently followed to achieve this designing with special reference to the donor-acceptor polymers and important results obtained with this route are briefly reviewed.
Keywords: Electronic structure; conduction properties; designing; band gap; copolymers; conducting polymers
Theoretical study of electronic structures and conduction properties of copolymers based on poly(cyclopentadienylene) by A. K. Bakhshi; Pooja Rattan (pp. 135-143).
Various quasi-one-dimensional superlattices (copolymers) (A m B n ) x of two novel donor-acceptor polymers PPDCF ([A] x ) and PPDCN ([B] x ) based on poly(cyclopentadienylene) (PPD) and belonging to the class of type II staggered superlattices were investigated using a negative factor counting method in the tight-binding approximation. Both PPDCF and PPDCN consist of a bicyclopentadienylene unit bridged by an electron-accepting group >C=CF2 in PPDCF and >C=C(CN)2 in PPDCN. The trends in the electronic structures and conduction properties of the copolymers (A m B n ) x as a function of the block sizes m and n, arrangement of the units (periodic or random) in the copolymer chain, and length of the copolymer chain are discussed.
Keywords: Conducting polymers; electronic structure; conduction properties; superlattice; designing of polymers; band gap
The role of molecular recognition in charge transport properties of doped polyaniline by A. K. Mukherjee; Reghu Menon (pp. 145-153).
Molecular recognition plays a significant role in the counterion-induced processibility, morphological features, and physical properties of doped polyaniline (PANI). The interaction of the counterion and solvent controls the chain conformation and, as a result, the formation of extended and localized electronic states; hence, it holds the key for tuning a wide range of electrical and optical properties of doped PANI. The combined effects of counterion, solvent, and processing conditions tune the metal-insulator transition, temperature dependence of conductivity, magnetoresistance, and so forth in doped PANI. The typical examples are shown in the case of PANI doped by camphor sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, and dodecylbenzoyl sulfonic acid.
Keywords: Molecular recognition; polyaniline; electrical conductivity; magnetoresistance
Synthesis and characterization of fluoro-substituted polyaniline by Amit L. Sharma; Manju Gerard; Rahul Singhal; B. D. Malhotra; S. Annapoorni (pp. 155-165).
Poly(2-fluoroaniline) was prepared by both chemical and electrochemical polymerization in acidic medium. Characterization of poly(2-fluoroaniline) was accomplished experimentally using ultraviolet-visible, Fourier transform infrared, differential scanning calorimetry, thermal gravimetric analysis, and X-ray diffraction techniques, respectively. Scanning electron microscopy studies revealed globular morphology of chemically synthesized poly(2-fluoroaniline). The cyclic voltammetric studies revealed diffusion-controlled phenomenon in electrochemically synthesized poly(2-fluoroaniline).
Keywords: Poly(2-fluoroaniline); cyclic voltammetry; scanning electron microscopy; X-ray diffraction
Biochemical evaluation of sulfur and nitrogen assimilation potential of mustard (Brassica juncea L. Czern. & Coss.) under application of slow-release sulfur fertilizer by Altaf Ahmad; Gerard Abraham; M. Z. Abdin (pp. 167-172).
Pot experiments were conducted to study the efficacy of a slow sulfur-releasing fertilizer, sulfur glass fritz (SGF 1), on growth, photosynthesis, and sulfur, and nitrogen assimilation potentials of brown mustard (Brassica juncea L. Czern. & Coss. cv. Pusa Jaikisan). Growth as indicated by biomass accumulation slowed down in response to the application of sulfur glass fritz. A similar trend was observed in the case of photosynthesis rate. The activity of two marker enzymes, ATP-sulfurylase and nitrate reductase, showed very low levels of activity, indicating poor assimilation of sulfur and nitrogen by the plant under sulfur glass fritz. It is therefore concluded that the release of sulfur by sulfur glass fritz is too slow and that the initial nonavailability of sulfur to the plants could lead to suboptimization of both sulfur- and nitrogen-assimilating enzymes. These factors may contribute to low rates of photosynthesis and poor growth.
Keywords: Mustard; gypsum; sulfur glass fritz; biomass; photosynthesis; ATP-sulfurylase; nitrate reductase; slow release sulfur fertilizer
Study of vibrational spectra of polyaniline doped with sulfuric acid and phosphoric acid by Manju Arora; Vandna Luthra; Ramadhar Singh; S. K. Gupta (pp. 173-181).
Vibrational spectra of insulator emeraldine base (EB) form of polyaniline and electrical conductive sulfuric acid-and phosphoric acid-doped emeraldine salts (ES) were studied in the region of 4000-400 cm−1 at ambient temperature by Fourier transform infrared spectroscopy. Infrared transmittance spectra of EB and ES were investigated to understand the bonding behavior of different organic and inorganic groups present in the polymeric chains and their structural variations on protonation by sulfate or phosphate ion inclusion in the polymer salt network. These studies revealed the para-coupling of deformed disubstituted benzenoid (B) and quinoid (Q) rings with ends capped predominantly by (B4Q1) units. The deformation of B and Q rings was confirmed by the appearance of many weak bands, very weak bands, and satellite structures in strong transmittance peaks of polymeric chain-constituting groups. Protonation takes place at the nitrogen sites of Q rings and forms semiquinone radical ions in ES. The vibrational bands pertaining to B rings, Q rings, B4Q1 units, semiquinone segment, sulfate ions, and phosphate ions were observed and assigned from these measurements. The shift in peak position of some bands with gain or loss in intensity and appearance of some new bands were observed in sulfuric acid-and phosphoric acid-doped ES spectra. These variations are attributed to the formation of new structural groups in ES on protonation and a change in crystalline field by sulfate and phosphate ion doping for crosslinking the polymeric chains.
Keywords: Vibrational spectra; polyaniline; sulfuric acid; phosphoric acid
Oncologic applications of biophotonics by Nabo K. Chaudhury; Sushil Chandra; Thalakkothur L. Mathew (pp. 183-204).
The understanding of various intrinsic photobiophysical processes has prompted researchers to develop different types of biodevices for health care. In the recent past, because of extensive contributions from various groups in the field of biophotonics, several important biomedical applications are emerging in the fields of both diagnostics and therapy. In this brief review, we discuss a few specific applications related to early detection and characterization of premalignant and malignant lesions using optical spectroscopic techniques, namely, fluorescence and Raman, and in management of cancer, the emerging scene of photodynamic therapy.
Keywords: Fluorescence spectroscopy; Raman spectroscopy; tissue characterization; cancer detection; photodynamic therapy
An optical tweezers-based immunosensor for detection of femtomoles-per-liter concentrations of antigens by Kristian Helmerson; Rani Kishore; William D. Phillips; Howard H. Weetall (pp. 205-213).
We used optical tweezers—optical trapping with focused laser beams—to pull microspheres coated with antigens off of an antibody-coated surface. Using this technique, we could quantify the force required to separate antigen to antibody bonds. At very low surface density of antigen, we were able to detect the single antigen to antibody binding. The force required to break the antigen-antibody bonds and pull the microsphere off the surface was shown to increase monotonically with increasing surface density of antigens. Using the force determination as a transducer, we were able to detect concentrations of free antigens in solution as small as 10−15 mol/L in a competitive binding assay.
Keywords: Optical tweezers; laser trap; immunosensor; assay; antigen; antibody; BSA
Soluble substituted poly-p-phenylenes—A new material for application in light-emitting diodes by Amita Verma; Kanchan Saxena; Chanderkant; S. K. Dhawan; R. K. Sharma; C. P. Sharma; M. N. Kamalasanan; S. Chandra (pp. 215-223).
Poly-p-phenylenes have attracted a great deal of attention with respect to their applications in displays, light-emitting devices, and batteries. However, the polymer poly-p-phenylene obtained by the Kovacic method is insoluble and intractable. The present study reports the preparation of soluble poly(p-phenylenes) by polymerization of derivatives of benzene in the presence of a specific aromatic nuclei. The resultant copolymer so obtained is soluble in common organic solvents such as chloroform and toluene. Preliminary studies have indicated that the polymer shows orange photoluminescence and electroluminescence when a potential of 7–10 V is applied to the device.
Keywords: Poly-p-phenylene; toluene-naphthalene copolymer; lightemitting diode; photoluminescence; electroluminescence
Immobilization and stabilization of biomaterials for biosensor applications by S. F. D’Souza (pp. 225-238).
Biosensors are finding applications in a variety of analytical fields. A biosensor basically consists of a transducer in conjunction with a biologically active molecule that converts a biochemical signal into a quantifiable electric response. The specificity of the biosensor depends on the selection of the biomaterial. Enzymes, antibodies, DNA, receptors, organelles, microorganisms as well as animal and plant cells or tissues have been used as biologic sensing materials. Advances in biochemistry, molecularbiology, and immunochemistry are expected to lead to a rapid expansion in the range of biologic recognition elements to be used in the field of biosensors. Biomaterials that are stable and function even in highly acidic, alkaline, hydrophobic, or oxidizing environments as well as stable to high temperature and immune to toxic substrates in the processing stream will play an important role. Techniques for immobilization of the biomaterials have played a significant role in the biosensor field. Immobilization not only brings about the intimate contact of the biologic catalysts with the transducer, but also helps in the stabilization of the biologic system, thus enhancing its operational and storage stability. A number of techniques have been developed in our laboratory for the immobilization of enzymes, multienzyme systems, cells, and enzymecell conjugates. Some of these aspects that are of significance in biosensor applications have been highlighted.
Keywords: Biosensors; immobilization; stabilization; permeabilized cells; microbial sensors
Signal amplification by substrate recycling on polyaniline/lactate oxidase/lactate dehydrogenase bienzyme electrodes by Asha Chaubey; Krishan K. Pande; Manoj K. Pandey; Vijai S. Singh (pp. 239-248).
The bienzyme electrodes were fabricated by coimmobilization of lactate oxidase (LOD) and lactate dehydrogenase (LDH) onto electrochemically prepared polyaniline (PANI) films. These PANI/LOD/LDH bienzyme electrodes were shown to provide signal amplification by substrate recycling, making it possible to detect l-lactate at lower concentrations (0.1-1 mM). The PANI/LOD/LDH bienzyme electrodes were found to be stable for about 21 d at 4–10°C.
Keywords: Lactate oxidase; lactate dehydrogenase; substrate recycling; coimmobilization; bienzyme electrode
Coimmobilization of urease and glutamate dehydrogenase in electrochemically prepared polypyrrole-polyvinyl sulfonate films by Anamika Gambhir; Manju Gerard; A. K. Mulchandani; B. D. Malhotra (pp. 249-257).
Immobilization of urease and glutamate dehydrogenase enzymes in electrochemically prepared polypyrrole-polyvinyl sulfonate films (PPY-PVS) was carried out using physical adsorption and electrochemical entrapment techniques. Detailed studies on optimum pH, Fourier transform infrared spectroscopy, cyclic voltammetry, and scanning electron microscopy of the enzymes in the immobilized state were conducted. The value of the apparent Michaelis-Menten constant was experimentally determined to be 2.5 and 2.7 for physically adsorbed and electrochemically entrapped urease in PPY-PVS films, respectively.
Keywords: Coimmobilization; urease; glutamate dehydrogenase; urea; biosensor
Preparation and characterization of poly-N-vinyl carbazole langmuir-blodgett films by Rahul Singhal; Anamika Gambhir; S. Annapoorni (pp. 259-267).
Langmuir monolayers of poly-N-vinyl carbazole (PNVK) were obtained by dispensing PNVK dissolved in tetrahydrofuran onto an air-water interface. Surface pressure-area isotherms of mixed monolayer of the PNVK were studied under different subphase conditions such as temperature and pH of the subphase. It was demonstrated that the monolayer of PNVK remained stable over a temperature range of 10–40°C. The area per molecule of the solid phase was found to be 31Å2. These monolayers were transferred onto indium-tin-oxide-coated glass plates and characterized by spectroscopic and electrochemical techniques.
Keywords: LB films; conducting polymers; PNVK, cyclic voltammetry; FTIR
Biomolecular electronics in the twenty-first century by Ratna S. Phadke (pp. 279-286).
A relentless decrease in the size of silicon-based microelectronics devices is posing problems. The most important among these are limitations imposed by quantum-size effects and instabilities introduced by the effects of thermal fluctuations. These inherent envisaged problems of present-day systems have prompted scientists to look for alternative options. Advancement in the understanding of natural systems such as photosynthetic apparatuses and genetic engineering has enabled attention to be focused on the use of biomolecules. Biomolecules have the advantages of functionality and specificity. The invention of scanning tunneling microscopy and atomic force microscopy has opened up the possibility of addressing and manipulating individual atoms and molecules. Realization of the power of self-assembly principles has opened a novel approach for designing and assembling molecular structures with desired intricate architecture. The utility of molecules such as DNA as a three-dimensional, high-density memory element and its capability for molecular computing have been fully recognized but not yet realized. More time and effort are necessary before devices that can transcend existing ones will become easily available. An overview of the current trends that are envisaged to give rich dividends in the next millen-nium are discussed.
Keywords: Biomolecular electronics; molecular electronics
Biomaterials for molecular electronics development of optical biosensor for retinol by Kumaran Ramanathan; Juraj Svitel; Anatoli Dzgoev; P. V. Sundaram; Bengt Danielsson (pp. 287-301).
Molecular electronics involves expertise from several branches of science. Various biomaterials and electronics are involved in the fabrication of such devices. While passive biomaterials are involved in anchoring the active biomolecules, the latter are involved in switching and/or signal transduction. In the present investigation we have used a glass-capillary-based approach to design a biosensor for retinol. The sensing element is retinol-binding protein (RBP). The affinity of retinoic-acid-horseradish peroxidase (conjugate) to RBP is tested using a surface plasmon resonance technique. A simple photomultiplier-tube-based system is exploited to monitor the chemiluminescent signal generated upon reaction of hydrogen peroxide and luminol with the conjugate bound to RBP. The photomultiplier tube is directly coupled to a computer for data logging.
Keywords: Retinol; retinol-binding protein; molecular electronics; biosensor; chemiluminescence; capillary
Immobilization of lactate dehydrogenase on tetraethylorthosilicate-derived sol-gel films for application to lactate biosensor by Asha Chaubey; Manju Gerard; V. S. Singh; B. D. Malhotra (pp. 303-311).
Tetraethylorthosilicate (TEOS)-derived sol-gel films were utilized for the immobilization of lactate dehydrogenase (LDH) by physical adsorption and sol-gel/LDH/sol-gel sandwich configuration. An attempt was made to ascertain the optimum pH and temperature for the immobilized LDH. It was shown that TEOS-derived sol-gel films containing physically adsorbed LDH exhibited linearity from 0.5 to 4 mM, whereas those containing LDH in sandwich configuration showed linearity from 0.5 to 3 mM l-lactate. These sol-gel films, immobilized with LDH, were found to be stable for about 4 weeks at 4–10°C.
Keywords: Immobilization; lactate dehydrogenase; tetraethylorthosilicate (TEOS); sol-gel; lactate; biosensor; physical adsorption; sandwich configuration
Characterization of DNA immobilized on electrochemically prepared conducting polypyrrole-polyvinyl sulfonate films by Anamika Gambhir; Manju Gerard; Shailesh K. Jain; B. D. Malhotra (pp. 313-319).
The article describes the adsorption characteristics of DNA onto electrochemically generated polypyrrole-polyvinyl sulfonate (PPY-PVS) films obtained as a function of pH. Adsorption on PPY doped with an anion proceeds by anion exchange, and since DNA possesses a fixed negative charge owing to PO 4 − , it favors a very strong binding displacing PVS with favorable energetic interactions. Characterization of adsorbed DNA onto the PPY-PVS films was carried out by ultraviolet-visible, Fourier transform infrared spectroscopy, and cyclic voltammetric studies.
Keywords: DNA biosensor; immobilization; conducting polymers; polypyrrole/polyvinyl sulfonate