Porous GaN electrode for anodic stripping voltammetry of silver(I)

Rapid microwave-assisted green synthesis of guanine-derived carbon dots for highly selective detection of Ag+ in aqueous solution

In this work, a simple and green synthetic approach of novel guanine decorated carbon dots (G-CDs) using guanosine 5'-monophosphate and ethylenediamine through a domestic microwave oven was established for the first time. The as-prepared fluorescent G-CDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and fluorescence spectroscopy. The obtained fluorescent G-CDs with a uniform morphology had desirable functional groups and excellent optical performances. Furthermore, the fluorescence intensity of G-CDs was remarkably quenched by Ag⁺ than that of other nucleotides-derived CDs. The density functional theory calculations were performed to confirm that the strong interaction of guanine-Ag⁺ was responsible for the remarkable fluorescence response of G-CDs towards Ag⁺. In addition, as a label-free fluorescence probe, the G-CDs displayed a good linear detection for highly selective Ag⁺ sensing over the range of 0-80 μM with the low detection limit of 90 nM. Therefore, the proposed G-CDs had the capacity for Ag⁺ detection in the real samples.

Direct Growth of Polycrystalline GaN Porous Layer with Rich Nitrogen Vacancies: Application to Catalyst-Free Electrochemical Detection

It has been demonstrated that defect engineering is an effective strategy to enhance the activity of materials. Herein, a polycrystalline GaN porous layer (PGP) with high catalytic activity was grown by self-assembly on GaN-coated sapphire substrate by using low-temperature (LT) MOCVD growth. Without doping, LT growth can significantly improve the activity and electrical conductivity of PGP, owing to the presence of rich N-vacancies (∼10²⁰ cm^-3). Identification of rich N-vacancies in the PGP material was realized by using atomically resolved STEM (AR-STEM) characterization. The optimized PGP was applied to catalyst-free electrochemical detection of H₂O₂ with a limit of detection (LOD) of 50 nM, a fast response speed of 3 s, a wide linear detection range (50 nM to 12 mM), and a high stability. The LOD is exceeding 40 fold lower than that of reported metal-catalyst decorated GaN. Moreover, a quantitative relationship between the sensing performances and N-vacancy of PGP was established. To our knowledge, it is the first time that intrinsic GaN materials can exhibit high catalytic activity.

Simultaneous detection of trace Ag(I) and Cu(II) ions using homoepitaxially grown GaN micropillar electrode

Driven by the motivation to quantitively control and monitor trace metal ions in water, the development of environmental-friendly electrodes with superior detection sensitivity is extremely important. In this work, we report the design of a stable, ultrasensitive and biocompatible electrode for the detection of trace Ag⁺ and Cu²⁺ ions by growing n-type GaN micropillars on conductive p-type GaN substrate. The electrochemical measurement based on cyclic voltammetry indicates that the GaN micropillars exhibit quasi-reversible and mass-controlled reaction in redox probe solution. In the application of trace Ag⁺ and Cu²⁺ determination, the GaN micropillars show superior sensitivity and excellent conductivity by presenting a detection limit of 3.3 ppb for Ag⁺ and 3.3 ppb for Cu²⁺. Comparative studies on the electrochemical response of GaN micropillars and GaN film in the simultaneous Ag⁺ and Cu²⁺ detection reveal that GaN micropillars show three orders of magnitude higher stripping peak current than GaN film. It is assumed that the microarray morphology with large active area and the hydrophilia nature of GaN micropillars are responsible for the excellent sensitivity. This work will open up some opportunities for GaN nanostructure electrodes in the application of trace metal ions detection.

Ultrasensitive electrochemiluminescence determination of trace Ag ions based on the signal amplification caused by its catalytic effect on Mn(II) oxidation using graphite catheter as electrode

In this work, an ultrasensitive electrochemiluminescence (ECL) method was established for the detection of trace amount of Ag ions (Ag⁺). In sulfuric acid medium, Ag(II), the electro-oxidized product of Ag(I), oxidizes manganese ions (Mn²⁺) to produce permanganate (MnO₄^-) by using a pair of graphite catheters as electrodes. While permanganate and luminol can produce strong chemiluminescence, based on the catalytic effect of Ag(II) on Mn²⁺ oxidation, there is a good linear relationship between the concentration of Ag⁺ and luminescence intensity. Under optimized conditions, the linear range of this method for Ag⁺ is from 0.2 to 150 nM with a detection limit of 0.06 nM. The method was applied for determination of Ag⁺ in various water samples with satisfactory results.