Simultaneous chemosensing of tryptophan and the bacterial signal molecule indole by boron doped diamond electrode

S-S bridged Schiff bases as versatile ionophores: Synthesis and application for electrochemical sensing of Copper(II) and Mercury(II)

Schiff base derivates (3, 4 and 5) comprising pseudo cavity with different heteroatoms (O, N and S) were designed, synthesized and explored for their detection behaviour towards diverse metal ions. In UV and fluorescence studies, all three receptors exhibited sensitive response towards Cu2+ while 5 showed sensitivity for Hg2+ also. To explore the synthesized receptors for electrochemical behaviour, voltammetric studies were conducted where 3, 4 and 5 exhibited sensitive response towards Cu2+ with detection limits of 9.8 × 10-7 M, 9.0 × 10-7 M and 1.41 × 10-7 M, respectively. The receptor 5 also showed response towards Hg2+ with detection limit of 5.61 × 10-8 M. The formation of complexes, 3/4+Cu2+ and 5+Cu2+/Hg2+ was supported by large values of binding constant and associated negative free energy change. The binding mechanism of 3, 4 and 5 towards respective metal ions was confirmed using 1H-NMR and HR-MS studies. Further, to utilize the proposed sensors for on-site monitoring of analyte metal ions, carbon paste electrodes (CPEs) were constructed by incorporating 3, 4 and 5. All CPEs showed Nernstian response with lower detection limits and excellent selectivity and successfully utilized for the determination of Cu2+ and Hg2+ in groundwater samples.

A sensitive electrochemical method for indole based on the signal amplification strategy by gold/iron-oxide composite nanoparticles

Indole is a major metabolite of tryptophan, which plays an important role in the intestinal microecological balance and human physiological activities. The determination of indole becomes important for its researches. So, it is urgent to establish a sensitive and cost-effective method for indole detection. Herein, a sensitive electrochemical method was constructed to determine the concentration of indole using screen-printed carbon electrode (SPCE) with the signal amplification strategy by gold/iron-oxide composite nanoparticles (Au/Fe₃O₄). Au/Fe₃O₄ nanoparticles were successfully synthesized under the irradiation by high-energy electron beams. 4-aminothiophenol (4-ATP) was connected to Au/Fe₃O₄ via Au-S bond. And then NaNO₂ reacted with 4-ATP to form the azo bond, which could form the final product of Au/Fe₃O₄@ATP-azo-indole by the coupling reaction. Thus, the concentration of indole was detected by the electrochemical signal produced by Au/Fe₃O₄@ATP-azo-indole indirectly. The detection sensitivity was greatly improved by the large specific surface area provided by Au/Fe₃O₄ after the modification. The linear range of indole was from 0.50 to 120.00 μg L^-1 and the limit of detection (LOD) was as low as 0.10 μg L^-1 (S/N = 3). Furthermore, the developed method exhibited acceptable intra-day and inter-day precisions with the coefficient of variations (CV) less than 4.9% and 8.2%, respectively. And the recoveries were from 97.2% to 105.4%. An innovative, sensitive, cost-effective method was established for indole determination in human plasma matrix in this manuscript, which provides a promising way for indole detection in conventional laboratories.