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We report a novel micro-potentiometric hemoglobin (Hb) immunosensor based on electrochemically synthesized polypyrrole (PPy)-gold nanoparticles (AuNPs) composite. PPy-AuNPs film with AuNPs uniformly distributed in it was deposited on gold electrode surface by a simple and direct procedure, without the addition of any nanoparticles or reducing agent. And this generic method makes it possible to deposite different polymers on miniaturized electrodes. With the existence of AuNPs, the antibody immobilization onto the electrode surface was facilitated. Morphology study by field emission scanning electron microscope (FE-SEM) confirms the presence of AuNPs in PPy. Based on an ion-sensitive field-effect transistors (ISFETs) integrated chip, a micro-potentiometric immunosensor for Hb and hemoglobin-A1c (HbA1c) has been constructed. The sensor response was linear over the concentration range 60-180 microg/ml Hb and 4-18 microg/ml HbA1c. The Hb concentration in whole blood samples has also been analysed, with a linear dose-response behavior between 125 and 197 microg/ml and a sensitivity of 0.20 mV microg(-1)ml. The measuring ranges of the developed Hb and HbA1c immunosensors meet the clinical demand for measuring the HbA1c/Hb ratio of 5-20%. This sensor results in simple and rapid differential measurement of Hb and HbA1c, and has great potential to become an inexpensive and portable device for monitoring of diabetes.

A highly sensitive and accurate dual-signal strategy is developed for trace Cu2+ detection based on the inner filter effect (IFE) between Tween 20-gold nanoparticles (AuNPs) and CdSe/ZnS quantum dots (QDs). Tween 20-AuNPs are utilized as colorimetric probes and excellent fluorescent absorbers. The fluorescence of CdSe/ZnS QDs can be quenched efficiently by Tween 20-AuNPs via IFE. In the presence of D-penicillamine, D-penicillamine induces the aggregation of Tween 20-AuNPs and the fluorescent recovery of CdSe/ZnS QDs at high ionic strength. Upon addition of Cu2+, D-penicillamine tends to selectively chelate with Cu2+ and then forms the mixed-valence complexes, which consequently inhibits the aggregation of Tween 20-AuNPs and the fluorescent recovery. The dual-signal method is used to quantitatively detect trace Cu2+, with low detection limits of 0.57 μg/L and 0.36 μg/L for colorimetry and fluorescence, respectively. In addition, the proposed method using a portable spectrometer is applied to the detection of Cu2+ in water. This sensitive, accurate and miniature sensing system has potential in environmental evaluations. [ABSTRACT FROM AUTHOR]

Biomass-derived carbon materials have received a surge of scientific attention to develop lightweight and broadband microwave absorbers. Herein, rodlike porous carbon materials derived from cotton have been fabricated with uniformly dispersed CoFe2O4 nanoparticles via facile and scalable process. The combination of magnetic particles and carbonaceous material is advantageous to realize the magnetic-dielectric synergistic effect which could effectively promote the dissipation of incident waves, giving rise to an optimal reflection loss value of â€"48.2 dB over a qualified bandwidth (4.8 GHz) at 2.5 mm. The cotton-derived carbon rods with conductive network not only act as a supporter to carry the CoFe2O4 nanoparticles, but also provide massive heterointerfaces to facilitate the interfacial polarization. In consideration of the renewable and abundant resource of cotton, the as-prepared CoFe2O4/C composites would meet the increasing demand of lightweight and highly efficient microwave absorbers. [ABSTRACT FROM AUTHOR]

The authors describe a microsensor for the determination of biochemical oxygen demand. Different from established BOD detection schemes that incorporate a film of immobilized microbes, the sensitive element of this BOD microsensor consists of magnetite-functionalized Bacillus subtilis that can be immobilized and regenerated on an ultramicroelectrode array (UMEA). Modification and regeneration are magnetically controlled. The oxygen consumed is amperometrically quantified by using an UMEA modified with palladium nanoparticles and reduced carboxy graphene. The assay can be performed within 5 min owing to the fast mass transfer of the magnetite-functionalized microbes on the surface of the UMEA. The calibration plot, best acquired at a voltage of -0.4 V vs. Ag/AgCl, is linear in the 2 to 15 mg⋅L BOD concentration range. A critical comparison with other BOD sensor shows the sensitivity of this sensor to be largely improved. It was successful applied to the determination of BOD in spiked water samples. [ABSTRACT FROM AUTHOR]

In this paper, reduced carboxylic graphene/palladium nanoparticles (rGN-COOH/PdNPs) modified ultramicroelectrode array (UMEA) was investigated and applied in electrochemical determination of biochemical oxygen demand (BOD). The UMEAs were fabricated by micro electro-mechanical system technique. The sensitive film of rGN-COOH/PdNPs was prepared by self-assembling of carboxylic graphene (GN-COOH), electroreducing the GN-COOH and electrodepositing the palladium nanoparticles on UMEA. This modification method is suitable to UMEA, which can immobilize the sensitive film on the designed sites and maintain the unique characteristics of UMEA. Compared with the sensitive film of GN-COOH, rGN-COOH and PdNPs, the sensitive film of rGN-COOH/PdNPs showed satisfied electroreduction performance to dissolved oxygen (DO). A BOD microsensor was fabricated based on the rGN-COOH/PdNPs modified UMEA. A good linear range from 1 to 30 mg/L for BOD determination was displayed. [ABSTRACT FROM AUTHOR]

This work mainly describes an electrochemical microsensor based on the reduction of molybdophosphate complex for total phosphorus (TP) determinations in water. The microelectrode was fabricated using microelectromechanical systems (MEMS) techniques and porous, branching gold nanoparticles (AuNPs) were electrodeposited on the microelectrode to improve its sensitivity. Calibration of the microsensor was performed with standard phosphate solutions prepared with KH2 PO4 with pH adjusted to 1.0. The experimental results showed that both sensitivity and current response are improved effectively using this modified microelectrodes: The limit of detection of the microsensor is 1.2 × 10−7 mol/l and linear range is 3 × 10−7 to 3 × 10−4 mol/l. The sensitivity of unmodified electrode is −0.27 nA/μmol·l−1 (R2 = 0.994), whereas the sensitivity of AuNPs modified electrode is −0.89 nA/μmol l−1 (R2 = 0.98). The current response of modified electrode is 6 times larger than that of unmodified electrode in average. Detection of TP was also carried out with digested TP standard solutions for both modified and unmodified electrodes, and results were consistent with the nominal value of phosphorus concentration. This microsensor provides the probability of combining TP detection device with micro‐digesting device to form a TP detection system, which can realise the automotive and on‐line monitoring of TP in surface water. [ABSTRACT FROM AUTHOR]

This paper presents a microsensor chip integrated with a gold nanoparticles-modified ultramicroelectrode array (UMEA) as the working electrode for the detection of copper ions in water. The microsensor chip was fabricated with Micro-Electromechanical System technique. Gold nanoparticles were electrodeposited onto the surface of UMEA at a constant potential of −0.3 V. The ratio d/ Rb of interelectrode spacing ( d) over the individual electrode's radius ( Rb) was investigated to improve the electrochemical performance. The UMEA with a d/ Rb of 20 showed the best hemispherical diffusion mode, resulted in fast response time and high current response. The gold nanoparticles increased the active surface area of UMEA by not changing the geometries of UMEA, and the current response was increased further. Incorporating the optimized characteristic of UMEA and gold nanoparticles, the microsensor showed a good linear range from 0.5 to 200 µg L−1 of copper ions in the acetate buffer solutions with the method of square wave stripping voltammetry. Compared with the gold nanoparticles-modified disk electrode, the gold nanoparticles-modified UMEA showed higher sensitivity (0.024 µA mm−2 µg−1 L) and lower limit of detection (0.2 µg L−1). Water samples from river water and tap water were analyzed by the microsensor chip with recovery ranging from 100.7 % to 107.8 %. [ABSTRACT FROM AUTHOR]

Abstract: A novel amperometric immunosensor for the detection of α-fetoprotein (AFP) based on the integration of microelectronic technology, mixed self-assembled monolayers (mixed SAMs), gold nanoparticles (nanogold) and enzyme amplification has been developed. Using microelectronic technology, an immunosensor was fabricated which has an “Au, Pt, Pt” three-microelectrode system and two microwells constructed by SU-8 photoresist on silicon wafer. Using mixed SAMs and nanogold, a mixed monolayer comprising cysteamine and 1,6-hexanedithiol was formed on the working electrode surface to assemble nanogold and further to immobilize AFP antibody for detecting AFP in human serum samples. The stepwise mixed SAMs and nanogold based immobilization procedure was characterized by means of cyclic voltammetry. The factors influencing the performance of the resulting immunosensor were studied in detail. After the addition of H2O2 and KI to the immunosensor incubated with AFP and further with horseradish peroxidase-labeled AFP antibody, the cathodic current varied linearly in concentration range of AFP from 15 to 350ng/ml with a detection limit of 5ng/ml. Moreover, the studied immunosensor has attractive advantages, such as miniaturization, compatibility with the complementary metal oxide semiconductor (CMOS) techniques, high specificity, good reproducibility and long-term stability, which make it potentially attractive for clinical immunoassays. [Copyright &y& Elsevier]