Gold-nanoparticle-based colorimetric array for detection of dopamine in urine and serum

A highly selective method is presented for the colorimetric determination of dopamine (DA) using gold nanoparticles (AuNPs). DA caps on the surface of AuNPs (DA-AuNPs) induces the aggregation of AuNPs in alkaline solution. The DA-AuNPs are modified by the hydrolysate of thioglycolic acid (TGA 2 − ) through Au–S bonds. The aggregation of AuNPs is accelerated by TGA 2− , due to the strong hydrogen-bonds (NH⋯OC and OH⋯OC) formed between TGA 2 − and DA. Upon the addition of DA, the solution shows a color change from red to purple (or yellow), which is also monitored to detect DA in human urine and fetal bovine serum samples. Here, the limits of colorimetric detection are as low as 10 −7 M observed in Milli-Q water, urine and serum. Based on UV–vis absorption spectra, the limits of detection have been calculated to be 3.3×10 −8 M, 1.0×10 −7 M and 9.4×10 −8 M in Milli-Q water, urine, and serum, respectively. All the limits of detection are lower than the lowest abnormal concentrations of DA in urine (5.7×10 −7 M) and blood (1.6×10 −5 M). The good linear ranges from 0 to 10 −6 M are used for the quantitative assay of DA in urine and serum samples. The applicability of our detection system is also verified by analysis of DA in urine and serum samples. The developed approach is without using complex financial instruments.