4-Amino nicotinic acid mediated synthesis of gold nanoparticles for visual detection of arginine, histidine, methionine and tryptophan

In this paper, we have described a simple, sensitive and reliable colorimetric method for assay of arginine, histidine, methionine and tryptophan in biological samples using 4-amino nicotinic acid assembled gold nanoparticles (ANA-Au NPs) as a colorimetric reader. 4-Amino nicotinic acid acts as a multifunctional agent to reduce Au3+ and to functionalize the synthesized Au NPs surfaces with an average size 13.1 nm. The surface plasmon resonance band of ANA-Au NPs was located at 534 nm and shifted to longer wavelengths at 676, 695, 701 and 647 nm for Arg, His, Met and Trp, respectively, indicating the aggregation of ANA-Au NPs induced by the above amino acids via electrostatic interactions and hydrogen bonding between ANA-Au NPs and amino acids, which results a colour change from dark pink to blue. Under optimum conditions, good linear relationships existed between the absorption ratios (at A676/A534, A695 /A534, A(701) /A(534) and As47/As34) and the concentrations of Arg, His, Met and Trp in the range of 0.001-100 mu M (R-2=0.995, 0.991, 0.996 and 0.996), with detection limits of 7.2, 4.2, 5.1 and 6.5 nM for Arg, His, Met and Trp, respectively. This probe was successfully applied to detect His in biological samples (urine and plasma), and recoveries ranges from 98.7% to 105.5%. (C) 2015 Elsevier B.V. All rights reserved.