Derivatization-assisted dual-mode colorimetric and fluorometric detection of dopamine using 4-hexyl resorcinol

The quantification of dopamine (DA) is of great significance because abnormal DA levels are closely linked to several neurological and psychiatric disorders, such as Parkinson's disease, schizophrenia, and depression. In addition, DA analysis plays an important role in clinical diagnosis, pharmaceutical quality assessment, and the investigation of biochemical events in complex biological systems. In this work, a derivatization-based dual-mode sensing strategy was developed for DA determination based on its induced oxidative coupling reaction with 4-hexyl resorcinol (4-HRS) under alkaline conditions. This reaction produces azamonardine, a highly emissive compound that exhibits a strong absorption band at 445 nm and intense fluorescence emission at 490 nm under excitation at 450 nm. The proposed method provided linear responses over the ranges of 0.05-520 µM for colorimetric detection and 10-600 nM for fluorescence detection, with detection limits of 0.018 µM and 3.0 nM, respectively. In addition, the method showed strong sensitivity, acceptable selectivity, mild experimental conditions, and reduced analytical expense. When applied to injection and human serum samples, it produced results consistent with those obtained by LC-MS. Recovery values ranged from 95.0% to 107.2%, and all relative standard deviation (RSD) values were below 3.89%, confirming the method's good accuracy and repeatability.