Enabling Direct Protein Detection in a Drop of Whole Blood with an “On-Strip” Plasma Separation Unit in a Paper-Based Lateral Flow Strip

Conventional paper lateral flow assays have low sensitivity and suffer from severe interference from complex human fluid sample matrices, which prevents their practical application in the testing of whole blood samples in the point-of-care settings. To solve this problem, gold nanostar@Raman reporter@silica-sandwiched nanoparticles have been developed as the surface-enhanced Raman scattering (SERS) probes for sensing transduction; and a functionalized filter membrane assembly has been designed and constructed in the paper-based lateral flow strip (PLFS) as a built-in plasma separation unit. In this "on-strip" plasma separation unit, three layers of filter membranes are stacked and surface-modified to maximize the separation efficiency and the plasma yield. As a result, the integrated PLFS has been successfully used for the detection of carcinoembryonic antigen (CEA) in 30 μL of whole blood with the assistance of a portable Raman reader, achieving a limit of detection of 1.0 ng mL^-1. In short, this report presents an inexpensive, disposable, portable, and field-deployable paper-based device as a general point-of-care testing tool for protein biomarker detection in a drop of whole blood.