Highly sensitive and selective colorimetric sensing of histidine by NAC functionalized AuNPs in aqueous medium with real sample application

An extremely sensitive and highly selective sensing assay for histidine (His) in biological sample is demonstrated through the N-acetyl-cysteine (NAC) functionalized gold nanoparticles (AuNPs). To improve the detection efficiency, the external conditions of temperature and pH value are optimized. We assume that three main forces of hydrogen bond, electrostatic attraction, and hydrophobic force between His and NAC cause the formation of close crosslinking, resulting in the aggregation of AuNPs accompanied by an obvious color change. Thus, the assay is highly sensitive for His with a fast readout within 10 s and the detection limit of 176 pM which is the lowest one from what's been reported in the colorimetric detection. Furthermore, due to the special imidazole ring in His structure, the assay exhibits the high selectivity of His sensing among 18 common amino acids. Besides, the system has been successfully used for His detection in spiked urine and serum samples. This novel colorimetric sensor significantly improves the analytical merit of His sensing and applies in the biological sample detection.