Highly selective colorimetric cysteine sensor based on the formation of cysteine layer on copper nanoparticles

CuNPs selectively recognize the amino acid, cysteine through inducing color change. [Display omitted] •Stable CuNPs were prepared using fatty acid amide, N-lauryltyramine.•CuNPs has the ability to sense selectively amino acid, cysteine in blood plasma.•CuNPs detects cysteine with limit of detection of 0.10μM.•Electrochemical and FTIR study showed that Cys self-assemble on the CuNPs. Herein, we report a facile method to synthesis copper nanoparticles (CuNPs) using fatty acid amide, N-lauryltyramine (NLTA) and hydrazine as capping and reducing agent, respectively. As prepared CuNPs aqueous solution appears brown in color and shows intense surface plasmon resonance (SPR) band at 580nm. In presence of amino acid, cysteine (Cys), the brown CuNPs solution turned to olive green with concomitant change in SPR maximum, while other amino acids show negligible change in the color and UV–vis spectra of CuNPs. The spectrophotometry detection limit of the proposed sensor is 0.10μM, whereas naked eye limit of detection was estimated to 20μM. FTIR studies revealed that Cys forms layer on the surface of the CuNPs, which was further supported by electrochemical studies. The proposed method has been successfully validated by detecting Cys in blood plasma and tap water samples.