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In recent years, transition metal dichalcogenides have become increasingly popular in electrochemical sensors due to their excellent redox properties. Herein, a highly efficient electrocatalyst Gd3+ doped molybdenum selenide with carbon nanofibers (Gd-MoSe2/CNF) is synthesized for electrocatalytic sensing of H2S. The synthesis involves a facile and quick hydrothermal treatment. The morphological, elemental, electrochemically active surface area, and impedance properties were investigated to understand its sensing capability. Gd-MoSe2/CNF showed excellent electrocatalytic ability to oxidize H2S. The overpotential for oxidation was minimized to +0.10 V, Ag/AgCl, and the response current increased two-fold compared to control electrodes. High sensitivity, acceptable selectivity, robustness and appreciable reproducibility were observed. The linear range was 12.5 nM–1.2 mM and the detection limit was 1 nM. The method was successful in tracking H2S secreted by HeLa cells. Our reports suggest that Gd-MoSe2/CNF is a useful material in monitoring endogenous H2S.

A three-dimensional hierarchical network of bismuth nanoparticles decorated graphene-carbon nanotubes nanocomposite (Bi NPs@Gr-CNTs) was synthesized and employed for electrocatalytic detection of mercury (Hg (II)). The electrocatalyst was characterized via scanning electron microscopy, transmission electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray diffraction, FT-IR, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrocatalytic activity of Bi NPs@Gr-CNTs modified screen-printed carbon electrode (SPCE) toward Hg (II) was studied using cyclic voltammetry, and differential pulse voltammetry. The Bi NPs@Gr-CNTs/SPCE exhibited excellent electrocatalytic ability to Hg (II) in comparison to control electrodes. Under optimized conditions, Bi NPs@Gr-CNTs/SPCE exhibits excellent Hg (II) sensing attributes in the range of 1.0 nM–217.4 µM with 0.2 nM of detection limit. The electrode was specific for Hg (II) in presence of other metal ions ascribe excellent selectivity. Practicality of the method was demonstrated in tap water, fish oil tablet, human serum, and urine samples (spiked method), which presented acceptable recoveries.

A copper-1,4-naphthalenedicarboxylic acid-based organic framework (Cu-NDCA MOF) with different morphologies was synthesized by solvothermal synthetic route via a simple protonation–deprotonation approach. The synthesized Cu-NDCA MOFs were analyzed by diverse microscopic and spectral techniques. The FE-SEM and TEM image results exhibited the flake-like (FL), partial anisotropic (PAT), and anisotropic (AT)-Cu-NDCA MOFs formation obtained at different pH (3.0, 7.0, and 9.0) of the reaction medium. The AT-Cu-NDCA MOF/GC electrode not only increases the electroactive surface area but also boosts the electron transfer rate reaction compared to other modified electrodes (PAT- and FL-Cu-NDCA MOFs/GCEs). Under the optimized conditions, the modified electrode (AT-Cu-NDCA MOF) exhibited a sharp oxidation peak (+ 0.46 V vs. Ag/AgCl) and higher current response for rutin. The electrode provides a wide linear range from 1 × 10−9 to 50 × 10−6 M, a low detection limit of 1.21 × 10−10 M, LOQ of 0.001 μM, and sensitivity of 0.149 μA μM−1 cm−2. The AT-Cu-NDCA MOF/GC electrode exhibited good stability (RSD = 3.52 ± 0.02% over 8 days of storage), and excellent reproducibility (RSD = 2.62 ± 0.02% (n = 3)). The modified electrode was applied to the determination of rutin in apple, orange, and lemon samples with good recoveries (99.79–99.91, 99.24–99.69, and 99.53–99.83, respectively).

In this study, controlled growth of Ni-MOF was decorated in amino acid-functionalized graphene nanoplatelets (FxGnP) by a solvothermal approach. The synthesized nanocomposite was characterized by various spectral, microscopic, and electrochemical techniques. FE-SEM and TEM image results exhibited the sheet-like structure of FxGnP and spherical-like Ni-MOF with an average size of 5.6 μm. Appreciably, the size of Ni-MOF was reduced to ∼2.3 μm while introducing the FxGnP. The presence of a large number of hydroxyl and epoxy functional groups of FxGnP acts as a nucleation center and restricted the uncontrolled growth of Ni-MOF. The FxGnP-Ni-MOF composite was modified on GCE and then utilized for the oxidation of bisphenol A (BPA). The nanocomposite material showed a sharp peak at +0.38 V vs. Ag/AgCl (saturated NaCl) with a stable response for BPA due to their less particle size with high electroactive surface area and higher electrical conductance, whereas bare GCE failed to the stable determination of BPA. The developed assay for determination of BPA exhibited a wide linear range from 2 × 10−9 M to 10 × 10−6 M, LOD 0.184 × 10−9 M and sensitivity of 247.65 μA mM−1 cm−2. The FxGnP-Ni-MOF/GCE showed good stability and reproducibility against BPA. Finally, the present electrocatalyst was effectively utilized for the quantitative determination of BPA in water samples and obtained results were validated with HPLC method.

In this study, a solution-processing based galvanic deposition approach is described for in-situ deposition of gold nanoparticles (AuNP) on delaminated titanium Ti3C2Tx nanosheets under ultrasonication. The nanocomposite (AuNP@Ti3C2Tx) was placed on a glassy carbon electrode (GCE) and then applied to electrochemically with label-free, and simultaneously sense uric acid (UA), and folic acid (FA) at physiological pH. The modified GCE has attractive figures of merit: (i) The working potentials for UA and AA are well separated (+0.35 V and 0.70 V vs. Ag|AgCl); (ii) wide linear responses (from 0.03–1520 μM for UA and from 0.02–3580 μM for FA; (iii) good electrochemical sensitivities for both UA and FA (0.53 and 0.494 μAμM−1.cm−2, respectively), and (iv) detection limits of 11.5 nM (UA) and 6.20 nM (FA). The electrode exhibited good repeatability (RSD = 4.4%), acceptable reproducibility (RSD = 4.1%), and excellent stability (91.8% over one-month storage). The method was applied to analyze spiked serum samples, and modified GCE is shown appreciable recoveries (97.1–98.8% and 96.8–98.0% for UA, and FA, respectively).

This work was supported by the Ministry of Science and Technology (MOST; 107-2113-M-027-007 – and 108-2221-E-027-063–) Taiwan (ROC) and King Abdullah University of Science and Technology (KAUST), Saudi Arabia.