Aptamer-based detection of serotonin based on the rapid in situ synthesis of colorimetric gold nanoparticles

Serotonin, a neurotransmitter that affects brain function, is associated with cancer progression, thus making it a potential biomarker. Despite the increasing efforts and ideas for gold nanoparticle (AuNP)-based colorimetric detection over the years, preparing AuNPs and sensing targets are separate processes, and this incurs more time to operate and produces excess waste. Herein, we report a simple, sensitive, and rapid colorimetric detection method for serotonin based on the in situ formation of AuNP. When only the aptamer is present, it can prevent chloride-induced aggregation of AuNPs because it easily binds to the freshly synthesized AuNPs through its exposed bases to increase the positive charge of the AuNP surfaces. When a complex of serotonin and its aptamer is formed, this complex disturbs the adsorption between aptamers and AuNPs, resulting in reduced stability of AuNPs and easy aggregation of nanoparticles. Therefore, serotonin was measured by color change, consistent with the change in peak intensity in the UV-vis absorption spectrum. The sensor demonstrated good sensitivity with a detection limit of 1 ng/mL (5.7 nM) for serotonin, which is comparable to or better than that of other aptamer-based colorimetric detection methods, further exhibiting the requisite selectivity against possible interferents. These results serve as a basis for developing other biosensors using aptamer-mediated in situ growth of AuNPs.