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Highly selective, sensitive and low potential detection of biological analytes by simple and rapid electrochemical technique using low cost nanocarbons is a demanding research since last decade. Herein, we report a low cost, new, nanocarbon, the carbon black (CL-08) functionalized with syringic acid (SA) modified glassy carbon electrode (GCE) for selective L-cysteine (L-CySH) electrocatalysis at 0.04 V vs Ag/AgCl. The new matrix is competitive in the low potential L-CySH detection compared to the multiwalled carbon nanotube, graphite powder, carbon mesoporous and graphitized mesoporous carbon. The possible in situ generated redox products namely 2,6-dimethoxy benzoquinone and 3,4-dihydroxy-5-methoxy benzoic acid were proposed to form on the GCE/SA@CL-08 with two electron transfer and nernstian behaviours. FTIR and UV–vis analyses collectively revealed the presence of quinone species. The GCE/SA@CL-08 showed L-CySH electrocatalysis with good selectivity, 0.42 nA.μM −1 and 5.4 nA.μM −1 sensitivity in the detection range of 20–100 μM and 100–1000 μM respectively with 639 nM limit of detection, in chronoamperometry. A successful demonstration of L-CySH detection from the simulated blood serum and processed chicken samples with substantial recovery values using the GCE/SA@CL-08 were presented in this study. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical oxidations of phenol and its derivatives (o-cresol and p-cresol) were examined on a carbon nanotube modified glassy carbon electrode (GCE/CNT) in pH 7 phosphate buffer solution. One of the phenol oxidation byproducts, hydroquinone (HQ) has been immobilized selectively on the GCE/CNT (GCE/HQ@CNT) during the electrochemical oxidation process. The GCE/HQ@CNT showed a stable and well-defined surface confined redox peak at 295mV vs. Ag/AgCl in pH 7. Amongst the various CNTs viz., impure-multiwalled carbon nanotube (MWCNT), functionalized-MWCNT, purified (p)-MWCNT and single walled CNT examined, the p-MWCNT modified GCE showed best results for the HQ immobilization. Physico–chemical characterizations of the HQ@p-MWCNT by TEM, XPS and FTIR and an in situ electrochemical quartz crystal microbalance studies reveal the presence of unreacted phenol on outer surface and clusters of HQ and {HQ-biphenol} species inside the walls of the HQ@p-MWCNT hybrid material. The GCE/HQ@p-MWCNT showed highly selective electrocatalytic oxidation of hydrazine through the mediation of the immobilized HQ/quinone redox species, without any interference from cysteine, ascorbic acid, uric acid, dopamine, nitrite, nitrate and hydrogen peroxide. Control experiments with GCE/MWCNT and GCE have failed to show any such electrocatalysis to hydrazine. Most interestingly, twice higher antibacterial activity towards the Escherichia coli bacteria over the native phenol was noticed on the HQ@CNT. These results indicate potential applicability of the HQ@CNT as hydrazine sensor and thin-film based antibacterial agent. [Copyright &y& Elsevier]