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The electrochemical oxidation of Ferulic acid (FA) was assiduously scrutinized by cyclic voltammetry and more sensitive amperometry technique using silver decorated multi-walled carbon nano-tubes modified carbon paste electrode. The modified electrode showed superior catalytic activity at physiological pH. The synergistic outcome of multiwalled carbon nano-tubes and silver nano-particles resulted in superior electro-catalytic activity and a significant three time increase of anodic peak current sensitivity and a remarkable lower energetics by 120 mV shift in potential thereby decreasing over-potential for electro-oxidation of FA in comparison to bare carbon paste electrode. Under optimized conditions, a linear dynamic range of 4.0 × 10− 8 to 1.0 × 10− 3 M, with a lower detection limit of 3.0 × 10− 8 M (S/N = 3) was obtained. The surface morphology of the sensor was studied using field emission scanning electron microscopy and atomic force microscopy. EDX was used determine the elemental composition of the electrode. The electrochemical impedance study revealed the least charge transfer resistance for the modified electrode. The effect of variation of scan rate, pH and concentration towards the electro-catalytic oxidation of FA was also investigated. Absence of peak for interfering molecules like Ascorbic acid, Uric acid and Glucose makes this sensor unique with significant analytical advantage. The fabricated sensor revealed adequate reproducibility, long term stability and enhanced selectivity in presence of commonly existing interfering molecules. The sensor was employed for the validation of spiked human urine and the wine which gave recoveries ranging from 97.5 to 99.4%, making it a potential alternative tool for the quantitative detection of FA in the biomedical field.

Iron nanoparticles decorated multi-wall carbon nanotubes modified carbon paste electrode (Fe-MWCNTs/MCPE) was prepared by bulk-modification method. The electrochemical impedance spectroscopy (EIS) suggests least charge transfer resistance at the modified electrode. The electrochemical behavior of UA was studied in 0.1M phosphate buffer solution (PBS) of pH3.0 using cyclic voltammetry (CV) while differential pulse voltammetry (DPV) was used for quantification. The spectroelectrochemial study of oxidation of UA at Fe-MWCNTs/MCPE showed a decrease in the absorbance of two peaks with time, which are ascribed to π to π(⁎) and n to π(⁎) transitions. Under optimum condition, the DPV response offered two linear dynamic ranges for UA in the concentration range 7.0×10(-8)M-1.0×10(-6)M and 2.0×10(-6)M-1.0×10(-5)M with detection limit (4.80±0.35)×10(-8)M (S/N=3). The practical analytical application of this sensor was successfully evaluated by determination of spiked UA in clinical samples, such as human blood serum and urine with good percentage recovery. The proposed electrochemical sensor offers a simple, reliable, rapid, reproducible and cost effective analysis of a quaternary mixture of biomolecules containing AA, DA, UA and Tyr which was free from mutual interferences.

An electrochemical sensor for the amperometric determination of l -tryptophan (Trp) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using drop cast method. 4.0 μL of the dispersion containing 2.0 mg of MWCNTs in 1.0 mL of ethanol was drop cast onto the electrode surface and dried in hot air oven to form a stable layer of MWCNTs. The electro-catalytic activity of the modified electrode towards the oxidation of Trp was thoroughly investigated. The modification with MWCNTs has greatly improved the current sensitivity of CPE for the oxidation of Trp. A very minimal amount of the modifier was required to achieve such a high sensitivity. The field emission scanning electron microscopy (FESEM) images revealed a uniform coverage of the surface of CPE by MWCNTs. Nyquist plots revealed the least charge transfer resistance for the modified electrode. The analytical performance of the modified electrode was examined using amperometry under hydro-dynamic conditions. The two linear dynamic ranges observed for Trp were 0.6–9.0 μM and 10.0–100.0 μM. The amperometric determination of Trp did not suffer any interference from other biomolecules. The detection limit of Trp at modified electrode was (3.30 ± 0.37) × 10 −8 M ( S / N = 3). The analytical applications of the modified electrode were demonstrated by estimating Trp in the spiked milk and biological fluid such as blood serum. The modified electrode showed good reproducibility, long-term stability and anti-fouling effects.