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Analytica Chimica Acta (v.766, #)
The enzyme thermistor—A realistic biosensor concept. A critical review by Maria Yakovleva; Sunil Bhand; Bengt Danielsson (pp. 1-12).
.Display Omitted► Major principles and features of enzyme thermistor are described. ► Different types of enzyme thermistors are overviewed and compared. ► Applications of enzyme thermistor for determination of various analytes are presented. ► Advantages and drawbacks of the analytical method are highlighted.This review describes principles and features of thermal biosensors and microbiosensors in flow injection analysis. Examples are given that illustrate the great versatility and excellent operational stability offered by thermal biosensors. The examples are mostly from work with the original type of enzyme thermistor operating with an enzyme column, but there will also be work described involving miniaturised devices including thermal lab-on-chip constructions and other types of sensing materials, such as MIPs (molecularly imprinted polymers) for both affinity and catalytic reactions. Several recently presented thermal biosensor concepts are reviewed including a thermal–electrochemical hybrid sensor for lactose based on immobilised cellobiose dehydrogenase. Another recent method is the determination of fructose using a fructose-6-phosphate kinase column. Operation with complex sample matrices such as blood, plasma and milk and how to avoid non-specific temperature effects are considered.
Keywords: Enzyme thermistor; Thermometric/calorimetric biosensor; Enzyme column; Molecularly imprinted polymers; Apoenzyme; High operational stability
Native fluorescence detection of biomolecular and pharmaceutical compounds in capillary electrophoresis: Detector designs, performance and applications: A review by Bregje J. de Kort; Gerhardus J. de Jong; Govert W. Somsen (pp. 13-33).
Display Omitted► The use of native fluorescence detection in capillary electrophoresis is reviewed. ► Various detector designs are discussed, and their performances are evaluated. ► Specific attention is devoted to fluorescence detection in microfluidic systems. ► Applications of biomolecular and pharmaceutical compound analysis are described.This review treats the coupling of capillary electrophoresis (CE) with fluorescence detection (Flu) for the analysis of natively fluorescent biomolecular and pharmaceutical compounds. CE–Flu combines the excellent separation efficiency of CE with the high selectivity and sensitivity of Flu. In CE–Flu, an appropriate design of the fluorescence detection cell is very important in order to achieve efficient analyte excitation in and emission light collection from the small cylindrically-shaped detection volume. Therefore, due attention is paid to the various optical detection designs used for CE–Flu, including the applied excitation sources and emission light detectors. Special attention is devoted to wavelength-resolved Flu and to sensitivity issues. Furthermore, he specific requirements for fluorescence detection in microfluidic systems ( i.e. chip-based electrophoresis) are discussed. Subsequently, an overview of described applications of CE–Flu for the analysis of natively fluorescent biomolecules and drugs is presented in extensive tables, treating amino acids, peptides, proteins, bioactive compounds, flavins, pharmaceuticals and also single cell analysis. The tables provide information on analyte nature, sample matrix, optical detection aspects, CE mode and limits of detection. A selection of descriptive applications is discussed in detail to illustrate the potential of native fluorescence detection in CE. It is concluded that CE–Flu is a powerful tool for biomolecular and pharmaceutical analysis, and provides good opportunities for use in lab-on-chip devices.
Keywords: Capillary electrophoresis; Microchip electrophoresis; Native fluorescence detection; Instrumentation; Review
Chemometrics assisted resolving of net faradaic current contribution from total current in potential step and staircase cyclic voltammetry by Afsaneh Safavi; Bahram Hemmateenejad; Fatemeh Honarasa (pp. 34-46).
Display Omitted► A new method for treating of charging current in voltammetry has been proposed. ► Chemometrics analysis of voltammetric data revealed the presence of faradaic, step charging and induced charging currents. ► MCR-ALS analyses could separate the contribution of each current type in the total signal. ► The results were in agreement with previous theoretical models.Total current in the electroanalytical data is assumed to be consisting of three main constituents: faradaic current, step charging current and induced charging current. Both charging currents can cause an interfering effect on precise determination of faradaic currents, and hence insert direct effects on sensitivity and detection limit of the electroanalytical techniques. Despite the widespread techniques introduced until now, the extraction of the net faradaic current from total current still remains a challenge. In this work, by using multivariate curve resolution-alternating least square (MCR-ALS) as a powerful curve resolution-based chemometrics method, a straightforward method has been introduced for resolving faradaic current from the two types of charging currents (step charging current and induced charging current) in single potential step and staircase cyclic voltammetric methods. By simultaneous analyses of the current data matrices for different electrochemical systems, the three sources of current were successfully identified and their contributions in the total signal were easily calculated. Also, in this manner, the cell time constant can be obtained easily. Contrary to the previously reported methods, the present method does not need any pre-determined mathematical method; particularly there is no need to know the cell time constant.
Keywords: Faradaic current; Charging current; Voltammetry; Chemometrics; MCR-ALS
A derivative photoelectrochemical sensing platform for 4-nitrophenolate contained organophosphates pesticide based on carboxylated perylene sensitized nano-TiO2 by Hongbo Li; Jing Li; Qin Xu; Zhanjun Yang; Xiaoya Hu (pp. 47-52).
Display Omitted► A novel enzymeless photoelectrochemical sensor for 4-nitrophenolate contained OPs. ► Sensors have performances of rapid response, good sensitivity and selectivity. ► PTCA as sensitizer can form ultrastable thin film and is economic as well. ► The strategy extends the application of PTCA for photoelectrochemical sensor.A novel visible light sensitized photoelectrochemical sensing platform was constructed based on the perylene-3,4,9,10-tetracarboxylic acid/titanium dioxide (PTCA/TiO2) heterojunction as the photoelectric beacon. PTCA was synthesized via facile steps of hydrolysis and neutralization reaction, and then the PTCA/TiO2 heterojunction was easily prepared by coating PTCA on nano-TiO2 surface. The resulting photoelectric beacon was characterized by transmission electron microscope, scanning electron microscopy, X-ray diffractometry, FTIR spectroscopy, and ultraviolet and visible spectrophotometer. Using parathion-methyl as a model, after a simple hydrolyzation process, p-nitrophenol as the hydrolysate of parathion-methyl could be obtained, the fabricated derivative photoelectrochemical sensor showed good performances with a rapid response, instrument simple and portable, low detection limit (0.08nmolL−1) at a signal-to-noise ratio of 3, and good selectivity against other pesticides and possible interferences. It had been successfully applied to the detection of parathion-methyl in green vegetables and the results agreed well with that by GC–MS. This strategy not only extends the application of PTCA, but also presents a simple, economic and novel methodology for photoelectrochemical sensing.
Keywords: Photoelectrochemistry; Sensor; Heterojunction; Nano-titania; Carboxylated perylene
Characterisation of iron binding ligands in seawater by reverse titration by Jeffrey A. Hawkes; Martha Gledhill; Douglas P. Connelly; Eric P. Achterberg (pp. 53-60).
Display Omitted► We have applied the reverse titration technique for analysis of Fe(III) speciation. ► The technique can be used in waters with high Fe(III). ► We examine the technique with dFOB, coastal seawater and hydrothermal plume water.Here we demonstrate the use of reverse titration - competitive ligand exchange–adsorptive cathodic stripping voltammetry (RT-CLE–ACSV) for the analysis of iron (Fe) binding ligands in seawater. In contrast to the forward titration, which examines excess ligands in solution, RT-CLE–ACSV examines the existing Fe-ligand complexes by increasing the concentration of added (electroactive) ligand (1-nitroso-2-naphthol) and analysis of the proportion of Fe bound to the added ligand. The data manipulation allows the accurate characterisation of ligands at equal or lower concentrations than Fe in seawater, and disregards electrochemically inert dissolved Fe such as some colloidal phases. The method is thus superior to the forward titration in environments with high Fe and low ligand concentrations or high concentrations of inert Fe.We validated the technique using the siderophore ligand ferrioxamine B, and observed a stability constantK′Fe3+FoB of 0.74–4.37×1021mol−1, in agreement with previous results. We also successfully analysed samples from coastal waters and a deep ocean hydrothermal plume. Samples from these environments could not be analysed with confidence using the forward titration, highlighting the effectiveness of the RT-CLE–ACSV technique in waters with high concentrations of inert Fe.
Keywords: Iron; Fe; Reverse titration; CLE–ACSV; Speciation
Natural deep eutectic solvents as new potential media for green technology by Yuntao Dai; Jaap van Spronsen; Geert-Jan Witkamp; Robert Verpoorte; Young Hae Choi (pp. 61-68).
Display Omitted► Natural products were used as a source for deep eutectic solvents and ionic liquids. ► We define own chemical and physical properties of natural deep eutectic solvents. ► Interaction between natural deep eutectic solvents and solutes was confirmed by NMR. ► The developed natural deep eutectic solvents were applied as green media.Developing new green solvents is one of the key subjects in Green Chemistry. Ionic liquids (ILs) and deep eutectic solvents, thus, have been paid great attention to replace current harsh organic solvents and have been applied to many chemical processing such as extraction and synthesis. However, current ionic liquids and deep eutectic solvents have still limitations to be applied to a real chemical industry due to toxicity against human and environment and high cost of ILs and solid state of most deep eutectic solvents at room temperature. Recently we discovered that many plant abundant primary metabolites changed their state from solid to liquid when they were mixed in proper ratio. This finding made us hypothesize that natural deep eutectic solvents (NADES) play a role as alternative media to water in living organisms and tested a wide range of natural products, which resulted in discovery of over 100 NADES from nature. In order to prove deep eutectic feature the interaction between the molecules was investigated by nuclear magnetic resonance spectroscopy. All the tested NADES show clear hydrogen bonding between components. As next step physical properties of NADES such as water activity, density, viscosity, polarity and thermal properties were measured as well as the effect of water on the physical properties. In the last stage the novel NADES were applied to the solubilization of wide range of biomolecules such as non-water soluble bioactive natural products, gluten, starch, and DNA. In most cases the solubility of the biomolecules evaluated in this study was greatly higher than water. Based on the results the novel NADES may be expected as potential green solvents at room temperature in diverse fields of chemistry.
Keywords: Natural deep eutectic solvents; Ionic liquids; Physicochemical properties; Green technology; Solubility
Ultrasound-assisted hydrolysis and chemical derivatization combined to lab-on-valve solid-phase extraction for the determination of sialic acids in human biofluids by μ-liquid chromatography-laser induced fluorescence by M.I. Orozco-Solano; F. Priego-Capote; M.D. Luque de Castro (pp. 69-76).
Display Omitted► Semiautomated approach for determination of sialic acids in different biofluids. ► Ultrasound-enhanced hydrolysis and derivatization to shorten the analysis time. ► Lab-on-valve approach for automated solid-phase extraction with high concentration and cleanup efficiency. ► Validation of the method by application to biological samples with different characteristics.The determination of sialic acids (SIAs) has recently gained interest because of their potential role as markers of inflammatory disorders or chronic diseases. Hydrolysis of conjugated derivatives, solid-phase extraction (SPE) and derivatization steps constitute sample preparation prior to insertion of the analytical sample into a μ-liquid chromatograph-laser induced fluorescence (μ-LC-LIF) detector in the present method for the determination of two representative SIAs of human metabolism. Ultrasound-accelerated hydrolysis released free SIAs, which were efficiently concentrated in a dynamic manner using a lab-on-valve (LOV) module that allows automation of SPE for preconcentration and cleanup. This step was on-line connected with DMB-labeling of SIAs (derivatization), which was shortened from 180min required with the conventional heating method to 20min with ultrasound assistance. Individual separation of the target analytes was achieved within 20min by μ-LC, while LIF detection endowed the overall method with high sensitivity. The LODs and LOQs provided by the method ranged 0.1–0.8ngmL−1 and 0.4–1.0ngmL−1 (between 0.1–0.8pg and 0.4–1.0pg expressed as on-column amount), respectively. High efficiency for interferents removal by SPE enabled the application of the method to four different biofluids—serum, urine, saliva and breast milk—for the determination of the target metabolites.
Keywords: Sialic acids; N; -Acetylneuraminic acid; N; -Glycolylneuraminic acid; Lab-on-valve; μ-LC-laser induced fluorescence; Solid-phase extraction; Ultrasound-assisted hydrolysis and derivatization
Coffee-ring effects in laser desorption/ionization mass spectrometry by Jie-Bi Hu; Yu-Chie Chen; Pawel L. Urban (pp. 77-82).
Display Omitted► Coffee rings occur during sample preparation for MALDI-MS and LDI-MS. ► They partly contribute to chemical heterogeneity of sample deposits. ► Coffee rings may be hidden within sample spots. ► Occurrence of coffee rings permits partial separation of sample components. ► In some cases, formation of coffee rings can be suppressed during sample preparation.This report focuses on the heterogeneous distribution of small molecules ( e.g. metabolites) within dry deposits of suspensions and solutions of inorganic and organic compounds with implications for chemical analysis of small molecules by laser desorption/ionization (LDI) mass spectrometry (MS). Taking advantage of the imaging capabilities of a modern mass spectrometer, we have investigated the occurrence of “coffee rings” in matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) sample spots. It is seen that the “coffee-ring effect” in MALDI/SALDI samples can be both beneficial and disadvantageous. For example, formation of the coffee rings gives rise to heterogeneous distribution of analytes and matrices, thus compromising analytical performance and reproducibility of the mass spectrometric analysis. On the other hand, the coffee-ring effect can also be advantageous because it enables partial separation of analytes from some of the interfering molecules present in the sample. We report a “hidden coffee-ring effect” where under certain conditions the sample/matrix deposit appears relatively homogeneous when inspected by optical microscopy. Even in such cases, hidden coffee rings can still be found by implementing the MALDI-MS imaging technique. We have also found that to some extent, the coffee-ring effect can be suppressed during SALDI sample preparation.
Keywords: Coffee-ring effect; Matrix-assisted laser desorption/ionization; Mass spectrometry; Surface-assisted laser desorption/ionization; sample preparation; laser desorption/ionization
Lectin sensitized anisotropic silver nanoparticles for detection of some bacteria by Vardan K. Gasparyan; Inga L. Bazukyan (pp. 83-87).
A novel approach for quantitative detection of bacteria in biological fluids was developed. Lectin sensitized anisotropic silver nanoparticles are able to bind Gram positive as well as Gram negative bacterial species. In this case the spectra of nanoparticles undergo serious changes.Display Omitted► A novel approach for quantitative detection of bacteria in biological fluids was developed. ► Lectin sensitized anisotropic silver nanoparticles are able to bind as Gram positive as well Gram negative bacterial species. ► In this case the optical spectra of nanoparticles undergo a serious changes.A method of bacteria detection by sensitized anisotropic silver nanoparticles is presented. Anisotropic silver nanoparticles with two bands of surface plasmon resonance (SPR) are prepared and sensitized with potato lectin. These nanoparticles are able to detect three bacterial species: Escherichia coli, Bacillus subtilis and Staphylococcus aureus. The interaction of these bacteria with such nanoparticles induces drastic changes in optical spectra of nanoparticles that are correlated with bacteria titer. The maximal sensitivity is observed for S. aureus (up to 1.5×104mL−1).
Keywords: Anisotropic silver nanoparticles; Lectins; Bacteria detection
Colorimetric assay for T4 polynucleotide kinase activity based on the horseradish peroxidase-mimicking DNAzyme combined with λ exonuclease cleavage by Cheng Jiang; Chunyan Yan; Jianhui Jiang; Ruqin Yu (pp. 88-93).
Display Omitted► The strategy was based on the coupled reaction triggered by polynucleotide kinase. ► The strategy was a colorimetric assay visible to the naked eye. ► The strategy had obvious advantages in controlling cost and simplifying operations. ► The strategy exhibited an improved signal to noise ratio and a wide linear range. ► The strategy could be extended to high-throughput phosphorylation investigations.T4 polynucleotide kinase (PNK) plays a critical role in various cellular events. Here, we describe a novel colorimetric strategy for estimating the activity of PNK and screening its inhibitors taking advantage of the efficient cleavage of λ exonuclease and the horseradish peroxidase-mimicking DNAzyme (HRPzyme) signal amplification. A label-free hairpin DNA with the sequence of HRPzyme was utilized in the assay. The 5′-hydroxyl terminal of the hairpin DNA was firstly phosphorylated in the presence of PNK and then digested by λ exonuclease. As a result, the blocked ‘HRPzyme’ sequence of the hairpin DNA was released due to the removal of its completely complementary sequence. Using this strategy, the assay for PNK activity was successfully translated into the detection of HRPzyme. Because of the completely blocking and efficiently releasing of HRPzyme, the colorimetric method exhibited an excellent performance in PNK analysis with a low detection limit of 0.06UmL−1 and a wide detection range from 0.06 to 100UmL−1. Additionally, the effects of different inhibitors on PNK activity were also evaluated. The proposed strategy holds great potential in the development of high-throughput phosphorylation investigation as well as in the screening of the related drugs.
Keywords: Polynucleotide kinase; λ exonuclease; The horseradish peroxidase-mimicking DNAzyme; Colorimetric assay
A rapid and highly sensitive portable chemiluminescent immunosensor of carcinoembryonic antigen based on immunomagnetic separation in human serum by Shuxue Qu; Juntao Liu; Jinping Luo; Yiqing Huang; Wentao Shi; Bin Wang; Xinxia Cai (pp. 94-99).
Display Omitted► The anti-CEA antibody can bound to the bead with a conjugation rate of 73%. ► IMBs could be stored for 2 months without reduction of biological activity. ► The limit of detection (LOD) of this method was as low as 5.0pgmL−1 ( S/N=3). ► The novel immunosensor was highly sensitive with an assay time of <35min. ► There was a good agreement between our method and ELISA kit. ► A home-made luminometer was used to detect the optical signal.To detect a biomarker for lung cancer, carcinoembryonic antigen (CEA), a highly sensitive, selective, rapid and portable immunosensor based on immunomagnetic separation and chemiluminescence immunoassay was introduced. A sandwich scheme assay has been utilized with horseradish peroxidase (HRP) labeled anti-CEA antibody and immunomagnetic beads (IMBs). The presence of target protein CEA caused the formation of the sandwich structures (IMBs-CEA-HRP labeled antibody). IMBs were applied to capture CEA and immobilize CEA through the external magnetic field. The HRP at the surface of the antibody catalytically oxidized the luminescence substrate to generate optical signals which were detected by a portable home-made luminometer and which were directly proportional to the concentration of CEA in the samples. The signals were dependent on CEA concentrations in a linear range from 0 to 50ngmL−1. The limit of detection (LOD) of this method was as low as 5.0pgmL−1 ( S/N=3). The novel immunosensor was highly sensitive with an assay time of <35min. The intra- and inter-assay coefficients of variation were <10%. The anti-CEA antibody can be bound to the bead efficiently with a conjugation rate of 73%. IMBs could be stored in 4°C protecting from light for 2 months without obvious reduction of biological activity. Human reference sera mixed with various concentrations of CEA were tested with the proposed method and commercial enzyme-linked immunosorbent assay (ELISA) kit, and a good linear relationship was obtained. This proposed technique demonstrated an excellent performance for quantifying CEA and was expected to be used for clinical testing.
Keywords: Carcinoembryonic antigen; Immunomagnetic beads; Chemiluminescence immunoassay; Luminometer; Superparamagnetism