Detection of a Neurotoxin Quinolinic Acid at Ultra‐Trace Amount: SERS and DFT Study

ABSTRACT The presence of quinolinic acid (QA) below 100 nM is a normal condition while its increased amount may cause variety of neurodegenerative diseases. The precise detection of QA in trace amounts (nanomolar) is crucial to control its toxic effects. In the present study, the SERS‐based detection of QA and its interaction at varying concentrations in human serum is carried out using silver nanoparticle substrates. The analysis of conformational dynamics of QA across different concentrations ranging from 10 −3 to 10 −9 M has been done. The adsorption mechanism between QA and silver nanoparticles has been studied using DFT, and the detection of QA up to nanomolar concentration is achieved. A significant shift in the SERS spectra of QA is observed between 10 −4 and 10 −5 M concentration, attributed to changes in adsorption geometry with varying pH and conformational change from zwitterionic QA → neutral QA. These findings are supported by UV–visible spectra, pH measurements, and DFT calculations.