An electrochemical sensor for L-cysteine (Cys) based on nanocomposite of Prussian blue (PB) was developed. The nanocomposite of PB was made using: (1) 3-glycidoxypropyltrimethoxysilane mediated in situ generated gold nanoparticles (AuNP) sol, and (2) nanostructured palladium powder (Pd) obtained by the calcinations of palladium-linked 3-glycidoxypropyltrimethoxysilane at 1000 degrees C. Chemically synthesized PB, AuNP sol and nanostructured palladium powder were used to fabricate; PB, PB-AuNP, and PB-AuNP-Pd; modified electrodes. These modified electrodes were characterized by cyclic voltammetry. The electrochemical sensing of Cys over these modified electrodes were examined based on amperometric measurements under optimized conditions. The results on Cys sensing revealed the following findings: (i) PB alone was least sensitive to Cys, (ii) PB-AuNP resulted into increased sensitivity, (iii) PB-AuNP-Pd significantly increased the sensitivity of Cys analysis as compared to that of PB-AuNP and PB, justifying synergetic effect of coupled catalytic behavior of AuNP and nanostructured Pd, (iv) PB-AuNP-Pd system showed lowest detection limit of 0.18 mu M having linear range between 0.3 and 400 mu M, (v) Cys analysis in dietary supplement provided selective and reliable data for practical applications, (vi) the sensing data were selective to Cys and showed negligible sensitivity to interfering analytes. (C) 2012 Elsevier Ltd. All rights reserved.