Search

The detection of thiol-containing amino acids, particularly L-cysteine (L-CySH), without any interference from other biochemicals is a challenging research interest in electroanalytical chemistry. Amongst various electrodes, the nanogold modified electrode has been reported to be effective for low potential electrochemical oxidation (∼0 V vs. Ag/AgCl) and sensing of L-CySH. Herein, we report a conductive carbon black (CB, CL-08) modified glassy carbon electrode (GCE/CL-08) with a high surface area (1000 m2 g−1), prepared by a simple drop-casting technique for efficient electrocatalytic oxidation at the lowest oxidation potential, −0.13 V vs. Ag/AgCl, and sensing of L-CySH in a pH 6.65 phosphate buffer solution. The trace metal impurities such as Ni (0.18 wt%) and Fe (0.42 wt%) in CL-08 are found to be key for such unique and unusual electrocatalytic property observed in this study. Compared with the multiwalled carbon nanotube and graphite powder modified electrodes, the GCE/CL-08 showed about 400 mV reduction in the oxidation potential and twenty times enhancement in the current signal for the CySH. A chronoamperometry detection of L-CySH on the GCE/CL-08 at an applied potential = −0.13 V vs. Ag/AgCl yielded a current linearity from 50 to 700 μM with a LOD = 45.87 nM. There are no interferences by common biochemicals such as ascorbic acid, dopamine, uric acid, xanthine, hypoxanthine and homo-cysteine on the L-CySH oxidation potential. Selective chronoamperometric detection of L-CySH in the blood serum demonstrated ∼100% recovery value as a validation for the present protocol.

The present study tested fish embryo toxicity (FET) of o-dianisidine (o-dian) on African catfish (Clarias gariepinus) and its electrochemical treatment through electro-oxidation of real aquatic samples for the first time. The o-dian exposed groups exhibited embryonic malformations, hatching retardation and mortality in a dose- and time-dependent manner compared to the control group even for 5 mg L−1 o-dian, in spite of being under the permissible limit. The LC50 values (with 95% confidence limits) of o-dian for larvae were estimated to be 42.614 (36.851–50.766), 35.327 (29.632–43.819) and 19.442 (15.448–24.539) mg L−1, respectively from 24 to 72 hours post-fertilization (hpf). Subsequently, the electrochemical uptake and treatment of o-dian was successfully demonstrated using a super conductive carbon black (CL-08) modified glassy carbon electrode in pH 2 phosphate buffer solution (PBS). The saturation surface coverage, Γs and adsorption constant, Ka values, evaluated using curve fitting for the Langmuir isotherm model, were 88.354 nmol cm−2 and 48.6 × 103 M−1 respectively. The calculated % yields of o-dian uptake on the electrode surface were 33, 43, 40 and 34. UV-Vis spectra of the electro-oxidized real samples showed 56, 36, 39 and 86% reductions of the o-dian absorbance peak at 363 nm respectively. The electrochemically treated real samples showed an efficient increase in the survival rate of African catfish larvae (p < 0.05).