pH-Dependent discriminative detection of catecholamine neurotransmitters using 4-boronobenzoic acid functionalized plasmonic silver nanoparticles as a colorimetric probe

Catecholamines constitute an important class of biogenic amines functioning both as hormones and as neurotransmitters. Dopamine (DA), norepinephrine (NE), and epinephrine (EP) are the main types. Elevated levels of these neurotransmitters in biological fluids are associated with hypertension, headache, palpitations, spontaneous sweating, anxiety, and even panic attacks. Conversely, their significant depletion may lead to conditions such as Parkinson's disease and dementia. Hence, rapid and accurate detection of these catecholamines is essential for both diagnostic and therapeutic purposes. This work describes the first-ever use of a silver nanoparticle-based selective and sensitive protocol for the simultaneous detection of dopamine (DA), norepinephrine (NE), and epinephrine (EP) in real time. This study explores the behaviour of DA, NE, and EP across a wide pH range (1-14) in the presence and absence of the as-synthesized AgNPs. At the same time, a pH of 9.0 was identified as the optimal pH for their simultaneous detection through three distinct visual color changes supported by UV-Vis measurements. The corresponding limits of detection (LODs) were found to be 92 nM, 93 nM, and 97 nM for DA, NE, and EP, respectively. This approach was further validated by quantifying DA, NE, and EP in their respective injection ampoules as well as spiked blood serum, and the recoveries were found to exceed 90% in all the cases. AgNPs used as the nanosensor were synthesized through a wet chemical approach using 4-formylphenylboronic acid as a stabilizing and reducing agent via Tollen's method at pH 11. The synthesized AgNPs were characterized using spectroscopic and microscopic techniques, viz. FTIR, UV-Vis, XPS, HRMS, SEM, TEM, DLS, EDAX, etc.