Integrating Metal-Enhanced Fluorescence and Surface Acoustic Waves for Sensitive and Rapid Quantification of Cancer Biomarkers from Real Matrices.

Metal-enhanced fluorescence (MEF) is utilized to lower the detection limit of carcinoembryonic antigen (CEA), a prognostic biomarker for colorectal cancer among others, in immunofluorescence assays. In addition, Rayleigh surface acoustic waves (SAWs) were utilized to remove nonspecifically bound proteins, improve mixing, and reduce incubation times. Fluorescence intensity was plasmonically enhanced by incubating silver nanocubes (AgNCs) of 50 nm edge-length on a SAW device. This increased sensor sensitivity by a factor of 6 and lowered the limit of detection to below 1 ng/mL in fluorescence detection of the antigen. Surface density of the AgNCs was optimized to produce the largest MEF, which increased the signal intensity by an order of magnitude. Acoustic streaming induced by Rayleigh SAWs was found to decrease antibody/antigen incubation times to 1/6th of the values without such micromixing, and to increase the fluorescence signal strength. Overall, the demonstrated results allow for construction of a sensor capable of detecting CEA rapidly in clinically relevant concentrations. Variables relevant for optimizing this sensor performance were identified, which will enable even better performance in immunofluorescence assays.