citrate capped silver nanoparticles as naked-eye colorimetric sensor for sensitive and rapid detection of cysteine in biological and environmental samples

Ysteine (cys) is an essential intracellular biothiol, which performs very important role in various biological process [1-3]. once the content of cys is out of the normal range, it will lead to a variety of diseases. increased levels of cys has been associated with vascular disease and neurotoxicity. conversely, cys deficiency can also lead to diverse diseases such as hematopoiesis decline, leukopenia, psoriasis, liver damage, weakness, slow growth rate, skin lesion, hair depigmentation, lethargy, edema, and neurological disorders [4]. therefore, it is highly important to detect and quantify this biothiol with high sensitivity and selectivity. in this work, we have proposed a simple, very fast, easy synthesis and cost effective colorimetric sensor for sensitive detection of cysteine using citrate capped agnps (cit/ag nps). the colorimetric recognition strategy was based on the significant change in the surface plasmon resonance (spr) band of cit/ag nps from 403 to 550 nm with cysteine. by adding cysteine to the cit/ag nps solution, the color of solution rapidly changed from yellow to red. this is attributed to the aggregation of citrate-capped ag nps induced by cysteine due to formation of the strong covalent ag-s bond and electrostatic binding. the proposed method was successfully applied for detection of cysteine in biological (human serum and urine) and environmental (tap and lake water) samples with significant recovery rates in the range of 95.5-105.1% and the relative standard deviation (rsd) lower than 5.5%. the interaction process between cys and cit/ag nps is very fast, so that the whole test can be completed within 1 minutes. moreover, the colorimetric detection operation is very simple and cost-effective without any further modification process. therefore, the cit/ag nps as a chemical sensor in colorimetry assay is simple, very fast, easy synthesis, highly selective and sensitive, a single-step process and mainly cost-effective, providing a possibility to develop an analysis in real-time and an effective rapid detection way for monitoring and visualizing cys.