Surface-Enhanced Raman Scattering Spectroscopy for the Detection of Glutamate and $\gamma$-Aminobutyric Acid in Serum by Partial Least Squares Analysis

Glutamate (GLU) and γ-aminobutyric acid (GABA) are important amino acid neurotransmitters that, respectively, mediate rapid excitatory and inhibitory neurotransmission in the brain. Serum GLU and GABA levels could play a significant role in pathogenesis of the encephalopathic state, early detection of autism, and the neurobiology of depression. The optimal concentration ratio of GLU and GABA is vital for neuroendocrine control, and deviations in their synthesis are linked to epilepsy. Additionally, circulating GLU affects GABA levels in striatal extracellular fluid. The present work explores the feasibility of employing surface-enhanced Raman scattering spectroscopy, in conjunction with partial least squares (PLS) , for simultaneous measurement of physiological concentrations of GLU and GABA in their aqueous solution and blood serum. A PLS calibration model showed a high coefficient of determination (R
²
>0.98) between the spectral data of GLU and GABA and their respective concentrations. The low root mean square error of prediction (RMSEP) value was ~2.7 μM, and it established the accuracy of the calibration model. The present methodology enabled the detection of GLU and GABA as low as 8 μM. This provides a cost-effective alternative to existing techniques for quantification of neurotransmitters.