Dextran-coated gold nanoprobes for the concentration and detection of protein biomarkers.

The lateral-flow immunoassay (LFA) is a well-established point-of-care detection assay that is rapid, inexpensive, easy to use, and portable. However, its sensitivity is lower than that of traditional lab-based assays. Previously, we improved the sensitivity of LFA by concentrating the target biomolecules using aqueous two-phase systems (ATPSs) prior to their detection. In this study, we report the first-ever utilization of dextran-coated gold nanoprobes (DGNPs) as the colorimetric indicator for LFA. In addition, the DGNPs are the key component in our pre-concentration process, where they remain stable and functional in the high salt environment of our ATPS solution, capture the target protein with conjugated antibodies, and allow the rapid concentration of the target protein in our ATPS for use in the subsequent LFA detection step. By combining this pre-concentration step with LFA, the detection limit of LFA for a model protein was improved by 10-fold. We further improved our ATPS from previous studies by enabling phase separation at room temperature in 30 min. By using DGNPs for the concentration and detection of protein biomarkers in the sequential combination of the ATPS and LFA steps, we move closer to developing an effective protein detection assay which uses no power or lab-based equipment.