Semi-quantitative Lateral Flow Assay Using a Handheld Device with a Transmissive Readout

Lateral flow assays (LFAs) are widely used for rapid and cost-effective diagnostic testing. The assays are often qualitative relying on a binary interpretation of the results on test strips. In many applications, however, quantitative or semi-quantitative readout is needed to define the analyte molecule concentration in a sample matrix, such as, saliva or urine. This study focuses on developing a semi-quantitative LFA test concept with a customized test strip cartridge and transmissive optical detection. LFA was developed to detect Covid-19 proteins and the coloration of the test line was induced by the concentration of plasmonic nanoparticles. Spectroscopic characterization of the test strips showed that the signal strength was enhanced by 82% on average when the conventional reflection-based detection was substituted by a transmission detection. When a set of LFA tests were read with the developed handheld optoelectronic device, the observed standard deviation was found to be below 3% meeting the requirements for semi-quantitative analyses.