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We report on the hydrothermal synthesis of boron-doped carbon dots (B-CDs) starting from glucose and boric acid. Doping of the CDs with boron was confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy. The B-CDs have an average diameter of about 4 nm and display blue fluorescence which is dynamically quenched by Fe(III) ions. This finding was exploited to design a method for the determination of Fe(III) in water. The relative fluorescence intensity at 359 nm in the presence and of absence ions is inversely proportional to the concentration of Fe(III) ions, and a Stern-Volmer calibration plot is linear in the concentration range of 0-16 μM, with a 242 nM detection limit. The assay is sensitive, robust and selective. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The influence of polymerization conditions on the morphology of thin films of poly-(N-methylaniline) (PNMA) was studied. The films were prepared by electropolymerization on gold and platinum electrodes and studied by optical and electron microscopy. It was demonstrated that the film morphology does not depend on the polymerization rate or on the electrode metal. However, it is sensitive to the kind of counter ion of PNMA. The polymers containing acetate or chloride do not form stable films. Polymer films containing phosphate or sulfate display inhomogeneous structures. A formation of sprouts and “nanotubes” was observed for PNMA sulfate. The films formed by PNMA perchlorate are smooth and transparent (glass-like structure). A sublayer of 4-aminothiophenol increases the adhesion of polymers to the gold surface. [ABSTRACT FROM AUTHOR]

A sandwich "signal-off" type photoelectrochemical (PEC) immunosensor was fabricated based on a composite heterojunction of tungsten oxide/titanium oxide microspheres (WO3/TiO2) acting as signal amplification platform and carbon microspheres loaded by gold nanoparticles (Cs@Au NPs) utilized as the label for detecting antibody. WO3/TiO2 had excellent photoelectric performance, and the results of Mott-Schottky plots, open-circuit voltage, and electron spin resonance spectroscopy indicated that it belonged to the Z-scheme heterojunction transfer mechanism of photogenerated carriers. To achieve the sensitization of PEC immunosensor, Cs@Au NP–labeled immunocomplex can effectively reduce the photocurrent signal. The PEC immunosensors were fabricated under the optimal conditions of 1:1 WO3/TiO2 (molar ratio), 2.0 mg mL−1 WO3/TiO2, and 1.5 mg mL−1 Cs@Au NPs. Through comparison of the detection results of label-free and sandwich-type PEC immunosensors for nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we found that the sensitivity of the sandwich type was 2.53 times the label-free type, and the limit of detection was 0.006 ng mL−1, i.e., 3.17 times lower than the label-free type. This demonstrates that the developed sandwich-type PEC immunosensor will have a brighter application prospect. [ABSTRACT FROM AUTHOR]

The authors describe a nonenzymatic glucose sensor that was obtained by electrochemical deposition and oxidization of metallic nickel on the surface of nitrogen-doped reduced graphene oxide (N-RGO) placed on a glassy carbon electrode (GCE). An analysis of the morphology and chemical structure indicated the composite to possess a well-defined vermicular Ni(OH) nanorods combined with N-RGO. The electrochemical performance of the modified GCE with respect to the detection of glucose in 0.1 M NaOH was investigated by cyclic voltammetry and amperometry. The wrinkle and protuberance of N-RGO for loading of nanostructured Ni(OH) are found to increase electrical conductivity, surface area, electrocatalytical activity and stability. The modified GCE displays a high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution. The lower detection limit is 0.12 μM at an applied potential of +0.45 V (vs Ag/AgCl) (S/N=3), and the sensitivity is 3214 μA mM cm. The modified GCE possesses long-term stability, good reproducibility and high selectivity over fructose, sucrose and lactose. [ABSTRACT FROM AUTHOR]

This review (with 79 references) summarizes the recent work on the development of chemical sensors and biosensors based on the use of composites made from conducting polymers (CPs) and graphene. Owing to the unique electrical, mechanical, optical, chemical and structural properties of CP and graphene, these kinds of composites have generated increasing interest in senor field. In this review, we first discuss methods for preparation of CP/GE composites by chemical, electrochemical, or physical methods including electrostatic interactions. We then cover aspects of the fabrication of modified electrodes and the performance of respective sensors with electrochemical, electronic or optical signal transduction. We then discuss sensors for the determination of inorganic and organic species, gases and vapors. We also review the state of the art in respective biosensors for hydrogen peroxide and glucose, for oligomers (DNA, RNA, and aptamers), for biogenic amines, NAD^+/NADH, cytochromes and the like, and in immunosensors. Finally, the perspective and current challenges of CP/GE composites for use in (bio)sensors are outlooked. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]