Electrochemical Detection and Quantification of Lithium Ions in Authentic Human Saliva Using LiMn2O4-Modified Electrodes

We report an electrochemical sensor for the detection of lithium ions (Li+) in authentic human saliva at lithium manganese oxide (LiMn2O4)-modified glassy carbon electrodes (LMO-GCEs) and screen-printed electrodes (LMO-SPEs). The sensing strategy is based on an initial galvanostatic delithiation of LMO followed by linear stripping voltammetry (LSV) to detect the reinsertion of Li+ in the analyte. The process was investigated using powder X-ray diffraction and voltammetry. LSV measurements reveal a measurable lower limit of 50.0 μM in both LiClO4 aqueous solutions and synthetic saliva samples, demonstrating the applicability of the proposed analytical method down to low Li+ concentrations. Four different samples of authentic human saliva were then analyzed with the established sensing strategy using LMO-SPEs, showing good linearity over a concentration range up to 5.0 mM Li+ with high reproducibility (RSD < 7%) and applicability for routine monitoring purposes. The total time needed to analyze a sample is less than 3 min.