A Simple Electrochemical Swab Assay for the Rapid Quantification of Clonazepam in Unprocessed Saliva Enabled by Lubricin Antifouling Coatings

The electrochemical sensing of clonazepam in samples of unprocessed saliva is reported, using commercially available reduced graphene oxide (rGO) screen printed electrodes (SPEs). The rGO electrodes were modified with self-assembled lubricin (LUB) antiadhesive coatings that function as a size-selective molecular sieve that partitions small molecule analytes from large fouling molecules at the electrode-fluid interface. By mitigating the adverse effects of protein fouling, these LUB coatings enable direct, reliable, and quantitative electrochemical measurements of clonazepam concentrations in untreated saliva, which was not possible with uncoated rGO electrodes in identical tests. The proposed assay design, which is suitable for disposable point-of-care diagnostics requires no sample pre-treatment and shows a linear detection response over a concentration range of 25–250 nM with a correlation coefficient of R2=0.987 and a limit of detection (LoD) of 16.67 nM. The swab-based sample acquisition method paired with the antifouling properties of the LUB coatings provide a cost effective and practical biosensing platform for assessing electroactive drug concentrations in saliva in a point-of-care setting.