Label-free colorimetric detection of serum cysteine using Ag-NP probes in the presence of Be2+ ions†
Amino acids play a crucial role in a variety of significant metabolic processes and their homeostasis is essential for cell growth and survival. Cysteine (Cys) furnishes imperative information about peculiar physiological functions and disease diagnosis. Cys detection in a biological solution has certain challenges. In this study, we present an appropriate and cost-effective colorimetric technique for the quantitative detection of Cys using label-free silver nanoparticles (Ag-NPs) as color indicators and Be2+ ions as cross-linking agents. The determination process needed to be based on the interaction of Ag-NPs with Cys molecules in the presence of beryllium ions, which induced a rapid pale yellow to red color conversion. The results indicate that this is a rapid and simple technique for quantitative analysis of Cys. In the linear range of 0.1–1000 μM, a detection limit of 50 nM was obtained. In addition, the technique was profitably applied to the detection of cysteine in human serum samples spiked with 250–5 μM and recoveries were in an acceptable range of 95.0–120.0%. This study might promote the implementation of label-free biomolecule detection in medical diagnostics and biochemistry.