Smart phone assisted rapid, simplistic, straightforward sensitive biosensing of cysteine over essential amino acids by β-cyclodextrin functionalized gold nanoparticles as a colorimetric probe
In this paper, -cyclodextrin (-CD) functionalized gold nanoparticles (-CD AuNPs) based simple, rapid, on-site and naked eye colorimetric sensor for the sensitive detection of cysteine (Cys) were reported. -CD AuNPs nanoprobe was completely characterized with respect to morphology, optical properties and stability. Surface plasmon resonance (SPR) band and colorimetric nature of -CD AuNPs sensitively reacts with Cys, whereas, decreasing SPR band with red shift and resulting in a distinctive colour evolution from wine red to purple were observed. This colour change is easily visualized by naked eye or absorption spectrophotometry. The observed spectral and colour changes is due to Cys have the thiol group which has high binding affinity towards the -CD AuNPs surface via Au-thiol bond formation, which lead to the aggregation (SPR band and colorimetric changes). Further, the lowest limit of detection of Cys is calculated as 25.47 × 10-9 mol dm-3 and this method exhibits linear detection range of Cys 2.50 to 45.00 × 10-7 mol dm-3. -CD AuNPs based colorimetric sensor demonstrates that high selectivity towards the Cys over other essential amino acids. Moreover, the present naked eye visual tactic is further applied for the quantification of Cys in clinical samples, like human urine and blood serum. In addition, the present method was further extended to smart phone device and makes easy changes in these devices into a quantitative Cys detector.