Quantitative detection of C-reactive protein in human saliva using an electrochemical lateral flow device

Abstract

Lateral flow devices (LFDs) allow for low-cost decentralized testing with a short time to result and are therefore an indispensable tool for point-of-care diagnostics. Here, we report on a novel LFD with electrochemical readout for the quantitative detection of C-reactive protein (CRP), a known biomarker for inflammation, in filtered human saliva and demonstrate the possibility of simultaneous multichannel measurements. The detection of CRP is enabled by a sandwich assay with target specific capture antibodies immobilized in a nitrocellulose membrane and target specific detection antibodies conjugated to an enzyme label. The subsequent enzymatic reaction leads to a product, which can be oxidized by an electrochemical sensor placed on top of the LFD strip and produce a concentration dependent and analyte specific electrical current. To optimize the system, single channel sensors were used to investigate different conjugate compositions and loads for their effect on assay performance. That way, limits of detection (LOD) of 3 and 25 ng/mL were achieved in buffer and filtered saliva, respectively. Then, a single sensor with four distinct channels was introduced for the testing of simultaneous multichannel measurements. There, the CRP dedicated channel showed a typical concentration dependency (with LODs of 13 and 55 ng/mL in buffer and filtered saliva, respectively), while the control channel expectedly produced elevated signals across all CRP concentrations. The signals corresponding to the other two channels (zeros) remained low with no indication of crosstalk, showing the ability to measure multiple locations on the LFD simultaneously and thus, paving the way for multiplexing.