Fluorescence and UV-vis spectrophotometry: a dual-mode competitive approach for selective sensing of dopamine†

The quantification of dopamine (DA) is essential due its vital role as a neurotransmitter. Here, we used a sensing strategy, which is based on competition between the DA–resorcinol (RA) reaction and resorcinol-stabilized silver nanoparticle (AgNP) formation in slightly alkaline medium. The AgNP and DA–RA reaction product formation were well characterized, specifically by transmission electron microscopy (TEM) and mass spectrometry, respectively, and also by other well-known techniques. The beauty of this sensing strategy is that the quantification of dopamine using both UV-visible and fluorescence spectrophotometry employing simple chemistry, where the RA molecule itself acts as a reducing agent and stabilizing agent for the formation of AgNPs and also selectively reacts with DA to produce fluorescent entities under alkaline conditions. A dual approach with naked-eye recognition of dopamine with an ambient light source was developed using the well-known chemistry between DA–RA and RA–AgNPs. The interference study was performed using both methods, and almost no interference observed in the fluorescence method. The strategy exhibits high selectivity and sensitivity toward DA with a wide linear range of 0.25 μM to 30 μM and a limit of quantification (LOQ) of 0.25 μM. Additionally, the assay was performed using a human urine sample. The initial assessment of dopamine by the fast colorimetric method, followed by the confirmation with a fluorescence technique, makes this strategy highly promising and thereby attracting much attention for applications.