Analyte-guided precise regulation of gold nanoflower etching mechanism for enhanced dopamine selectivity via bisphenol-triggered Schiff base/Michael addition and intramolecular hydrogen bond synergy

A novel nano-sensing system was developed to enhance the selectivity and sensitivity of dopamine (DA) detection by integrating the strong cleavage effect of β-mercaptoethylamine (MEA) on trypsin-stabilized gold nanoflowers (Trypsin-AuNFs), the Schiff base/Michael addition reactions triggered by the bisphenol structure of DA, and the intramolecular hydrogen bonding within DA. Multiple characterizations including TEM, XPS and FT-IR confirmed that trypsin was anchored on the flower-shaped surface of AuNFs via Au–S bonds, endowing Trypsin-AuNFs with excellent structural stability. In addition, Trypsin-AuNFs can both effectively prevent the interference of biothiols ((cysteine (Cys), homocysteine (Hcy), glutathione (GSH)) in serum and have a strong interaction with MEA, resulting in the rapid cleavage of Trypsin-AuNFs. This is because MEA both induced the cleavage of Trypsin-AuNFs through the formation of Au–S bonds, and directly interacted with trypsin, disrupting its structure and accelerating the decomposition of Trypsin-AuNFs. These dual actions significantly enhanced the selectivity and sensitivity of the sensing system. It is worth noting that a detailed study of the interaction between MEA and trypsin and the optimal binding site through molecular docking was conducted for the first time. A detailed study of the impact of MEA on the spatial structure of trypsin was also conducted for the first time by using molecular dynamics. Moreover, the precise regulation of the Trypsin-AuNFs cleavage mechanism triggered by the DA-bisphenol structure through a Schiff base/Michael addition reaction was thoroughly investigated using UV–vis absorption spectroscopy (including functional group identification, steric hindrance comparison, and bisphenol regulation), ¹H NMR, zeta potential measurements, and TEM. This work provides a novel strategy for probing the interaction between MEA and proteins and offers a new perspective for improving the specificity of DA detection.