A novel optical γ-aminobutyric acid (GABA)-based sensor was developed on interacting thiol compounds and o-phthalaldehyde (OPA) to form thiacetal compounds. Then, the thiacetal interacts with the GABA molecule to form an isoindole compound. The effects of four thiol compounds on the stability of the resulting isoindole compound were assessed. The 2-mercaptoethanol, "one of the most used derivatizing agents," is unexpectedly the least stable; while, 16-mercaptohexadecanoic acid resulted in the most durable isoindole compound. The developed sensor showed the capability for detecting GABA within a wide concentration range spanning from 500 nmol L-1 to 100 µmol L-1. The detection limit was about 330 nmol L-1, which indicated the high sensitivity of the developed sensor compared with those previously reported. The findings illustrated the ability to detect GABA at the physiological pH (pH = 7.4) without adjusting the pH value, opening the door for real applications. Furthermore, the sensor could detect various GABA concentrations in human serum with good recovery percentages (98% to 101.4%). In addition, this assay was applied to monitor GABA release from the SH-SY5Y cell line to convert glutamate into GABA. This result indicates the capability of the proposed assay for visually monitoring the release of GABA neurotransmitters.
Keywords: 4-aminobutyric acid; O-Phthalaldehyde; Optical GABA sensor; SH-SY5Y cells; Thiol compounds.
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