Peroxidase-encapsulated Zn/Co-zeolite imidazole framework nanosheets on ZnCoO nanowire array for detecting H2O2 derived from mitochondrial superoxide anion.

In this work, we have developed a nanocomposite consisting of horseradish peroxidase (HRP)-encapsulated 2D Zn-Co zeolite imidazole framework (ZIF) nanosheets strung on a ZnCoO nanowire array on a Ti support (denoted as 2D-Zn/Co-ZIF(HRP)|ZnCoO|Ti). This nanocomposite was then applied to constructing an electrochemical biosensor for detecting H2O2 derived from O2∙- released by mitochondria in living cells. This sensing platform shows excellent catalytic performance towards H2O2, attributable to the enzyme/metal-catalytic effect of HRP and Zn/Co-ZIF. The unique nano-string structure alleviates the aggregation of Zn/Co-ZIF nanosheets, readily exposes the catalytic active sites, protects the bioactivity of HRP, and reduces the charge/mass transfer pathway within Zn/Co-ZIF. The 2D-Zn/Co-ZIF(HRP)|ZnCoO|Ti biosensor offers two linear ranges of 0.2-10 µ M and 10-1100 µ M, a limit of detection of 0.082 µ M, a sensitivity of 3.3 mA mM-1 cm-2, good selectivity and stability over 40 days for H2O2 detection. After treating with specific mitochondrial complex inhibitors, the chronoamperometric results at the 2D-Zn/Co-ZIF(HRP)|ZnCoO|Ti confirmed complex I and III within the mitochondria electron transfer chain as the main electron leakage sites. This biosensor may contribute to the development of diagnostic health-care devices that shed light on the precaution and even treatment of oxidative stress diseases.

A High-Performance Hybrid Biofuel Cell with a Honeycomb-Like Ti3 C2 Tx /MWCNT/AuNP Bioanode and a ZnCo2 @NCNT Cathode for Self-Powered Biosensing.

This work focusses on developing a hybrid enzyme biofuel cell-based self-powered biosensor with appreciable stability and durability using murine leukemia fusion gene fragments (tDNA) as a model analyte. The cell consists of a Ti3 C2 Tx /multiwalled carbon nanotube/gold nanoparticle/glucose oxidase bioanode and a Zn/Co-modified carbon nanotube cathode. The bioanode uniquely exhibits strong electron transfer ability and a high surface area for the loading of 1.14 × 10-9  mol cm-2 glucose oxidase to catalyze glucose oxidation. Meanwhile, the abiotic cathode with a high oxygen reduction reaction activity negates the use of conventional bioenzymes as catalysts, which aids in extending the stability and durability of the sensing system. The biosensor offers a 0.1 fm-1 nm linear range and a detection limit of 0.022 fm tDNA. Additionally, the biosensor demonstrates a reproducibility of ≈4.85% and retains ≈87.42% of the initial maximal power density after a 4-week storage at 4 °C, verifying a significantly improved long-term stability.

Fluoride Content of Ready-to-Eat Infant Foods and Drinks in Australia.

The use of fluoride is effective in preventing dental caries. However, an excessive intake of fluoride leads to dental fluorosis, making it necessary to regularly monitor the fluoride intake especially for infants. There is hitherto a lack of information on fluoride content in infant foods from an Australian perspective. Therefore, this study aims to estimate the amount of fluoride content from a range of commercially available ready-to-eat (RTE) infant foods and drinks available in Australia. Based on an external calibration method, potentiometry involving a fluoride ion selective electrode and a silver|silver chloride reference electrode was conducted to analyse the fluoride content of a total of 326 solid food samples and 49 liquid food samples in this work. Our results showed an overall median (range) fluoride content of 0.16 (0.001-2.8) µg F/g of solid food samples, and 0.020 (0.002-1.2) µg F/mL of liquid food samples. In addition, ~77.5% of the liquid samples revealed a fluoride content < 0.05% µg F/mL. The highest variation of fluoride concentration (0.014-0.92 µg F/g) was found in formulas for ≥6 month-old infants. We have attributed the wide fluoride content variations in ready-to-eat infant foods and drinks to the processing steps, different ingredients and their origins, including water. In general, we found the fluoride content in most of the collected samples from Australian markets to be high and may therefore carry a risk of dental fluorosis. These results highlight the need for parents to receive appropriate information on the fluoride content of ready-to-eat infant food and drinks.

Amplified detection signal at a photoelectrochemical aptasensor with a poly(diphenylbutadiene)-BiOBr heterojunction and Au-modified CeO2 octahedrons.

A major aspect of this work is the synergistic application of a poly(diphenylbutadiene)-BiOBr composite and a gold nanoparticle-linked CeO2 octahedron to develop a photoelectrochemical aptasensor with an easily measurable detection signal change. Specifically, poly(diphenylbutadiene) nanofiber-immobilised BiOBr flower-like microspheres were developed as a hybrid material with a heterojunction that facilitates high visible light absorption and efficient photo-generated charge separation, which are essential features for sensitive photoelectrochemical sensors. The model analyte acetamiprid was attached via its specific aptamer on the aptasensor. Separately, a gold nanoparticle-linked CeO2 octahedron was strategically used to significantly diminish the photocurrent by impeding electron transfer at the aptasensor surface. After acetamiprid binding, the CeO2 octahedrons were displaced from the aptasensor. This caused a weakened quenching effect and restored the photocurrent to accomplish an "on-off-on" detection mechanism. This photoelectrochemical aptasensor exhibited a detection limit of 0.05 pM over a linear range of 0.1 pM-10 µM acetamiprid. The use of an aptamer has provided good specificity to acetamiprid and anti-interference. In addition, an ∼5.8% relative standard deviation was estimated as the reproducibility of the photoelectrochemical aptasensor. Furthermore, nearly 90% of the initial photocurrent was still measurable after storing these aptasensors at room temperature for 4 weeks, demonstrating their stability.

Detection signal amplification strategies at nanomaterial-based photoelectrochemical biosensors.

This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical (PEC) biosensors with utmost sensitivity and selectivity. These successes have partly been achieved by applying photoactive materials that significantly circumvent major limitations including poor absorption of visible light, severe aggregation of nanostructures, easy charge recombination and low conductivity. In addition, several signal enhancement techniques were also demonstrated to have effectively improved the detection performance of PEC biosensors. Accordingly, we have begun this review with a systematic introduction of the concept, working principle, and characteristics of PEC biosensors. This was followed by a discussion of a range of material modification techniques, including quantum dot modification, metal/non-metal ion doping, the formation of heterojunctions and Z-scheme composites, used in the construction of PEC biosensors. Various signal amplification strategies including quantum dot sensitisation, the application of electron donors, energy transfer effect, steric hindrances of biomolecules, and the exfoliation of biomolecules from sensing surfaces are also presented in this review. Wherever possible, we have referred to relevant examples to explain and illustrate the corresponding working mechanism and effectiveness of the nanomaterials. Therefore, this review is aimed at providing an overall view on the current trend in material modification and signal amplification strategies for the development of PEC biosensors, which will aid in stimulating ideas for future progress in this field.

Amplified oxygen reduction signal at a Pt-Sn-modified TiO2 nanocomposite on an electrochemical aptasensor.

In this work, a metallic composite with strong electrocatalytic property was designed by uniformly decorating Pt and Sn nanoparticles on the surface of TiO2 nanorods (Pt-Sn@TiO2). A detection scheme was then developed based on a dual signal amplification strategy involving the Pt-Sn@TiO2 composite and exonuclease assisted target recycling. The Pt-Sn@TiO2 composite exhibited an enhanced oxygen reduction current owing to the synergistic effect between Pt and Sn, as well as high exposure of Pt (111) crystal face. Initially, a Pt-Sn@TiO2 modified glassy carbon electrode produced an amplified electrochemical signal for the reduction of dissolved oxygen in the analyte solution. Next, a DNA with a complementary sequence to a streptomycin aptamer (cDNA) was immobilised on the Pt-Sn@TiO2 modified electrode, followed by the streptomycin aptamer that hybridised with cDNA. The corresponding oxygen reduction current was diminished by 51% attributable to the hindrance from the biomolecules. After a mixture of streptomycin and RecJf exonuclease was introduced, both the streptomycin-aptamer complex and the cDNA were cleaved from the electrode, making the Pt-Sn and Pt (111) surface available for oxygen reduction. RecJf would also release streptomycin from the streptomycin-aptamer complex, allowing it to complex again with aptamers on the electrode. This has then promoted a cyclic amplification of the oxygen reduction current by 85%, which is quantitatively related to streptomycin. Under optimal conditions, the aptasensor exhibited a linear range of 0.05-1500 nM and a limit of detection of 0.02±0.0045 nM streptomycin. The sensor was then used in the real-life sample detection of streptomycin to demonstrate its potential applications to bioanalysis.

A photoelectrochemical aptasensor based on a 3D flower-like TiO2-MoS2-gold nanoparticle heterostructure for detection of kanamycin.

In this work, a sensitive photoelectrochemical aptasensor was developed for kanamycin detection using an enhanced photocurrent response strategy, which is based on the surface plasmon resonance effect of gold nanoparticles deposited on a 3D TiO2-MoS2 flower-like heterostructure. A significant aspect of this development lies in the photoelectrochemical and morphological features of the unique ternary composite, which have contributed to the excellent performance of the sensor. To develop an aptasensor, mercapto-group modified aptamers were immobilised on the photoactive composite as a recognition unit for kanamycin. The TiO2-MoS2-AuNP composite was demonstrated to accelerate the electron transfer, increase the loading of aptamers and improve the visible light excitation of the sensor. Under optimal conditions, the aptasensor exhibited a dynamic range from 0.2 nM to 450 nM of kanamycin with a detection limit of 0.05 nM. Overall, we have successfully synergised both the electrical and the optical merits from individual components to form a ternary composite, which was then demonstrated as an effective scaffold for the development of PEC biosensors.

A TiO2 nanosheet-g-C3N4 composite photoelectrochemical enzyme biosensor excitable by visible irradiation.

In this work, g-C3N4 and TiO2 nanosheets were synergistically employed as a novel composite for developing a scaffold of a photoelectrochemical enzyme biosensor. In this way, we have improved the poor visible light excitation of TiO2 and retarded the photo-generated charge recombination on g-C3N4 to achieve an enhanced response at the photoelectrochemical biosensor, compared to that generated by the corresponding biosensors consisting of each individual component. Using glucose oxidase as a model enzyme, the biosensor was demonstrated to show strong visible light activity towards the enzyme mediated glucose oxidation. We have also observed a 350% enhanced photocurrent compared to that at a g-C3N4 based ITO electrode. In addition, the high specific surface area and excellent biocompatibility of TiO2 nanosheets have also positively contributed to the performance of the photoelectrochemical enzyme biosensor with a 0.05-16 mM linear range and a 0.01 mM glucose detection limit.

An intimately bonded titanate nanotube-polyaniline-gold nanoparticle ternary composite as a scaffold for electrochemical enzyme biosensors.

In this work, titanate nanotubes (TNTs), polyaniline (PANI) and gold nanoparticles (GNPs) were assembled to form a ternary composite, which was then applied on an electrode as a scaffold of an electrochemical enzyme biosensor. The scaffold was constructed by oxidatively polymerising aniline to produce an emeraldine salt of PANI on TNTs, followed by gold nanoparticle deposition. A novel aspect of this scaffold lies in the use of the emeraldine salt of PANI as a molecular wire between TNTs and GNPs. Using horseradish peroxidase (HRP) as a model enzyme, voltammetric results demonstrated that direct electron transfer of HRP was achieved at both TNT-PANI and TNT-PANI-GNP-modified electrodes. More significantly, the catalytic reduction current of H2O2 by HRP was ∼75% enhanced at the TNT-PANI-GNP-modified electrode, compared to that at the TNT-PANI-modified electrode. The heterogeneous electron transfer rate constant of HRP was found to be ∼3 times larger at the TNT-PANI-GNP-modified electrode than that at the TNT-PANI-modified electrode. Based on chronoamperometric detection of H2O2, a linear range from 1 to 1200 µM, a sensitivity of 22.7 µA mM(-1) and a detection limit of 0.13 µM were obtained at the TNT-PANI-GNP-modified electrode. The performance of the biosensor can be ascribed to the superior synergistic properties of the ternary composite.

Kinetic model and thermodynamic study of Acid Red 1 entrapment at electropolymerised polypyrrole films.

This work is focussed on the determination of a kinetic model and the thermodynamic study of the electrochemical entrapment of the model azo dye, Acid Red 1, at conducting polypyrrole films, which is proposed as a potential green technology for treatment of azo dyes in industrial effluents. The entrapment kinetic data were found to follow a pseudosecond order model involving an intra-particle diffusion. However, the equilibrium data obtained for Acid Red 1 entrapment at polypyrrole did not obey any common surface adsorption models such as the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. Accordingly, the entrapment process may lead to an enhanced quantity of dye embedded in a polypyrrole film, making it a more effective and efficient technology than those involving only adsorption. Similarly, dye leakage from polypyrrole film surface to a sample matrix will be easily prevented. For this treatment process, a negative ΔG° range between -1.46±0.78 and -2.94±0.24 kJ mol(-1) at the corresponding temperature range of 298-318 K, and a ΔH° of 20.5±2.5 kJ mol(-1) indicate a spontaneous and endothermic entrapment process. Also, a positive ΔS° (73.6±8.2 J mol(-1) K(-1)) reveals increased randomness of the interface and an affinity of Acid Red 1 towards polypyrrole films. A low activation energy (7.67±0.80 kJ mol(-1)) confirms a physical process for Acid Red 1 entrapment at polypyrrole films.

Conducting polypyrrole films as a potential tool for electrochemical treatment of azo dyes in textile wastewaters.

In this paper, we demonstrate conducting polypyrrole films as a potential green technology for electrochemical treatment of azo dyes in wastewaters using Acid Red 1 as a model analyte. These films were synthesised by anodically polymerising pyrrole in the presence of Acid Red 1 as a supporting electrolyte. In this way, the anionic Acid Red 1 is electrostatically attracted to the cationic polypyrrole backbone formed to maintain electroneutrality, and is thus entrapped in the film. These Acid Red 1-entrapped polypyrrole films were characterised by electrochemical, microscopic and spectroscopic techniques. Based on a two-level factorial design, the solution pH, Acid Red 1 concentration and polymerisation duration were identified as significant parameters affecting the entrapment efficiency. The entrapment process will potentially aid in decolourising Acid Red 1-containing wastewaters. Similarly, in a cathodic process, electrons are supplied to neutralise the polypyrrole backbone, liberating Acid Red 1 into a solution. In this work, following an entrapment duration of 480 min in 2000 mg L(-1) Acid Red 1, we estimated 21% of the dye was liberated after a reduction period of 240 min. This allows the recovery of Acid Red 1 for recycling purposes. A distinctive advantage of this electrochemical Acid Red 1 treatment, compared to many other techniques, is that no known toxic by-products are generated in the treatment. Therefore, conducting polypyrrole films can potentially be applied as an environmentally friendly treatment method for textile effluents.

Evaluation of a carbon nanotube-titanate nanotube nanocomposite as an electrochemical biosensor scaffold.

A significant aspect of this work is the development of a multi-wall carbon nanotube (MWCNT)-titanate nanotube (TNT) nanocomposite to serve as a biocompatible scaffold with high conductivity on a biosensor surface. Unlike other scaffolds consisting of MWCNTs alone or TNTs alone, the MWCNT-TNT nanocomposite synergistically provides excellent biocompatibility, good electrical conductivity, low electrochemical interferences and a high signal-to-noise ratio. For comparison, after characterising a scaffold consisting of MWCNTs alone, TNTs alone and a MWCNT-TNT nanocomposite using several spectroscopic techniques, the analytical performance of a horseradish peroxidase (HRP) electrochemical biosensor was evaluated using cyclic voltammetry and differential pulse voltammetry. The scaffold consisting of MWCNTs alone displayed a high background charging current, a low signal-to-noise ratio and distinct electrochemical interference from its surface functional groups. In contrast, the direct electrochemistry and the catalytic capability of HRP at MWCNT-TNT modified biosensors towards H2O2 was demonstrated to be ~51% and ~144% enhanced, respectively, compared to those at TNT modified biosensors. Meanwhile, MWCNT-TNT nanocomposite modified HRP biosensors also exhibited higher sensitivity (4.42µAmM(-1)) than TNT modified HRP biosensors (1.48µAmM(-1)). The above superior performance was attributed to the improved properties of MWCNT-TNT nanocomposite as biosensor scaffold compared to its two individual components by complementing each component and synergistically sustaining the characteristic features of each component.

Minimizing fouling at hydrogenated conical-tip carbon electrodes during dopamine detection in vivo.

In this paper, physically small conical-tip carbon electrodes (∼2-5 µm diameter and ∼4 µm axial length) were hydrogenated to develop a probe capable of withstanding fouling during dopamine detection in vivo. Upon hydrogenation, the resultant hydrophobic sp(3) carbon surface deters adsorption of amphiphilic lipids, proteins, and peptides present in extracellular fluid and hence minimizes electrode fouling. These hydrogenated carbon electrodes showed a 35% decrease in sensitivity but little change in the limit of detection for dopamine over a 7-day incubation in a synthetic laboratory solution containing 1.0% (v/v) caproic acid (a lipid), 0.1% (w/v) bovine serum albumin and 0.01% (w/v) cytochrome C (both are proteins), and 0.002% (w/v) human fibrinopeptide B (a peptide). Subsequently, during dopamine detection in vivo, over 70% of the dopamine oxidation current remained after the first 30 min of a 60-min experiment, and at least 50% remained over the next half-period at the hydrogenated carbon electrodes. On the basis of these results, an initial average electrode surface fouling rate of 1.2% min(-1) was estimated, which gradually declined to 0.7% min(-1). These results support minimal fouling at hydrogenated carbon electrodes applied to dopamine detection in vivo.

Application of an ELISA-type screen printed electrode-based potentiometric assay to the detection of Cryptosporidium parvum oocysts.

We report a novel electrochemical method for the rapid detection of the parasitic protozoan, Cryptosporidium parvum. An antibody-based capture format was transferred onto screen-printed electrodes and the presence of horseradish peroxidase-labelled antibodies binding to the oocysts was potentiometrically detected. This method allowed the detection of 5 × 10(2)Cryptosporidium oocysts per mL in 60 min.

Gold nanoparticle encapsulated-tubular TIO2 nanocluster as a scaffold for development of thiolated enzyme biosensors.

In this work, a highly sensitive and stable sensing scaffold consisting of gold nanoparticle-encapsulated TiO2 nanotubes, the hydrophilic ionic liquid, 1-decyl-3-methylimidazolium bromide, and Nafion was developed for the fabrication of electrochemical enzyme biosensors. A significant aspect of our work is the application of 12-phosphotungstic acid as both a highly localized photoactive reducing agent to deposit well-dispersed gold nanoparticles on TiO2 nanotubes and an electron mediator to accelerate the electron transfer between an enzyme and the electrode. After characterizing the nanocomposite component of the scaffold by Fourier transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy, thiolated horseradish peroxidase (as a model enzyme) was immobilized on the scaffold and the biosensor was applied to the detection of H2O2. The direct electron transfer between the enzyme and the electrode was promoted by the excellent biocompatibility and conductivity of the scaffold. In addition, a thiolated enzyme has significantly improved the stability and direct electron transfer of horseradish peroxidase on the biosensor, which could be ascribed to the strong affinity between the sulfhydryl group on the enzyme and gold nanoparticles on the biosensor surface. Cyclic voltammetry, chronoamperometry, and square wave voltammetry were used to study the electrochemistry and analytical performance of the biosensor. A dynamic range from 65 to 1600 µM, a limit of detection of 5 µM, and a sensitivity of (18.1 ± 0.43) × 10(-3) µA µM(-1) H2O2 were obtained. The sensing scaffold based on the nanocomposite was demonstrated to be effective and promising in developing enzyme biosensors.

Detection of estradiol at an electrochemical immunosensor with a Cu UPD|DTBP-Protein G scaffold.

A copper monolayer was formed on a gold electrode surface via underpotential deposition (UPD) method to construct a Cu UPD|DTBP-Protein G immunosensor for the sensitive detection of 17ß-estradiol. Copper UPD monolayer can minimize the non-specific adsorption of biological molecules on the immunosensor surface and enhance the binding efficiency between immunosensor surface and thiolated Protein G. The crosslinker DTBP (Dimethyl 3,3'-dithiobispropionimidate · 2HCl) has strong ability to immobilize Protein G molecules on the electrode surface and the immobilized Protein G provides an orientation-controlled binding of antibodies. A monolayer of propanethiol was firstly self-assembled on the gold electrode surface, and a copper monolayer was deposited via UPD on the propanethiol modified electrode. Propanethiol monolayer helps to stabilize the copper monolayer by pushing the formation and stripping potentials of the copper UPD monolayer outside the potential range in which copper monolayer can be damaged easily by oxygen in air. A droplet DTBP-Protein G was then applied on the modified electrode surface followed by the immobilization of estradiol antibody. Finally, a competitive immunoassay was conducted between estradiol-BSA (bovine serum albumin) conjugate and free estradiol for the limited binding sites of estradiol antibody. Square wave voltammetry (SWV) was employed to monitor the electrochemical reduction current of ferrocenemethanol and the SWV current decreased with the increase of estradiol-BSA conjugate concentration at the immunosensor surface. Calibration of immunosensors in waste water samples spiked with 17ß-estradiol yielded a linear response up to ≈ 2200 pg mL(-1), a sensitivity of 3.20 µA/pg mL(-1) and a detection limit of 12 pg mL(-1). The favorable characteristics of the immunosensors such as high selectivity, sensitivity and low detection limit can be attributed to the Cu UPD|DTBP-Protein G scaffold.

A label-free electrochemical DNA biosensor based on a Zr(IV)-coordinated DNA duplex immobilised on a carbon nanofibre|chitosan layer.

A label-free electrochemical biosensor for detecting DNA hybridisation was developed by monitoring the change in the voltammetric activity of ferrocenecarboxylic acid at the biosensor­solution interface. The biosensor was constructed by initially immobilising on a glassy carbon electrode an anchoring layer consisting of chitosan, carboxyl group functionalised carbon nanofibres and glutaraldehye. Chitosan acted as an adhering agent and carbon nanofibres were strategically used to provide a large surface area with binding points for DNA immobilisation, while glutaraldehye was a linker for DNA probes on the electrode surface. Based on a two-factorial design, cyclic voltammetry of [Fe(CN)(6)](3-/4-) was performed to optimise the composition of the anchoring layer.Next, a 17-base pair DNA probe was attached to the anchoring layer, followed by its complementary target. Zr(IV) ion, known to exhibit affinity for oxygen-containing electroactive markers, for example, ferrocenecarboxylic acid, was then coordinated in the DNA duplex. In this way, ferrocenecarboxylic acid was attracted towards the biosensor for oxidation. A change in the voltammetric oxidation current of ferrocenecarboxylic acid pre- and post-hybridisation was used to provide an indication of hybridisation. A linear dynamic range between 0.5 and 40 nM and a detection limit of 88 pM of DNA target were then achieved. In addition, the biosensor exhibited good selectivity, repeatability and stability for the determination of DNA sequences.

Hydrogen peroxide detection at a horseradish peroxidase biosensor with a Au nanoparticle-dotted titanate nanotube|hydrophobic ionic liquid scaffold.

In this work, a novel sensing scaffold, consisting Au nanoparticle (GNP)-dotted TiO(2) nanotubes (TNTs) as the rigid material and the hydrophobic ionic liquid (HIL), 1-decyl-3-methylimidazolium tetrafluoroborate, as the entrapping agent, was applied to facilitate the electron transfer of horseradish peroxidase (HRP) on a glassy carbon electrode. GNPs were immobilised on the TNTs in our work using a one-step reduction of HAuCl(4)·3H(2)O by sodium borohydride in the presence of sodium citrate as a stabilising reagent. The morphology and composition of the as-synthesised composite materials were characterised by transmission electron microscopy, scanning electron microscopy, X-ray diffraction and Fourier-transform infrared spectroscopy. Cyclic voltammetry of HRP at the modified electrode presented a pair of reproducible, quasi-reversible redox peaks with a peak-to-peak separation of 69 mV, indicating electron transfer between HRP and composite electrode. The GNP-TNT|HIL|HRP electrode was then applied to the detection of H(2)O(2) in a pH 7.0 phosphate buffer using chronoamperometry. The biosensor exhibited a linear response in the 15-750 µM range, and a limit of detection of 2.2 µM. The biosensor also exhibited stability with 90% of the detection signal retained over a two-week duration.

Detection of cortisol at a gold nanoparticle|Protein G-DTBP-scaffold modified electrochemical immunosensor.

An ultrasensitive electrochemical immmunosensor was demonstrated to be capable of detecting the hormone cortisol down to concentrations as low as 16 pg mL(-1). In addition, the immunosensor displayed a sensitivity of 1.6 µA pg(-1) mL(-1) and a linear range up to ∼2500 pg mL(-1) of cortisol. This immunosensor was constructed based on a Au nanoparticle|dimethyl 3,3'-dithiobispropionimidate·2HCl (DTBP)-Protein G scaffold-modified Au electrode. In this work, the Au nanoparticles were used to increase the electrochemically active surface area by 28% (with a standard deviation of 3%) to enhance the quantity of the Protein G scaffold on the electrode. Thiolation of Protein G by DTBP aided in avoiding the confirmation change of Protein G, while this Protein G-DTBP component offered an orientation-controlled immobilisation of the capture antibody on the Au electrode. In this immunosensor, a monoclonal anti-cortisol capture antibody was optimally aligned by the scaffold before a competitive immunoassay between sample cortisol and a horseradish peroxidase-labelled cortisol conjugate was conducted. For quantitative analysis, square wave voltammetry was used to monitor the reduction current of benzoquinone produced from a horseradish peroxidase catalysed reaction. The improved analytical performance of our immunosensor was attributed to the synergetic effect of Au nanoparticles and the Protein G-DTBP scaffold.

Electrocatalytic detection of phenolic estrogenic compounds at NiTPPS|carbon nanotube composite electrodes.

A Ni(II)tetrakis(4-sulfonatophenyl) porphyrin (NiTPPS)|carbon nanotube composite electrode that shows strong catalytic and antifouling capability was developed to detect a series of phenolic endocrine compounds including bisphenol A, nonylphenol and ethynylestradiol. This electrode was fabricated by electropolymerizing NiTPPS complexes on a carbon nanotube-modified glassy carbon electrode. Optimized experimental parameters including a hydrodynamic potential of 0.7 V for flow injection analysis (FIA) and a NiTPPS surface coverage of 2.2 nmol cm(-2) (standard deviation 0.2 nmol cm(-2); n=6) were obtained for detection of the endocrine disrupting compounds. The sensor responded well to all the tested compounds with limits of detection ranging from 15 nmol L(-1) to 260 nmol L(-1) (based on three times S/N ratio) under FIA conditions. Both carbon nanotubes and NiTPPS account for the excellent performance of the composite modified electrode.