(484f) Quantification of Biomarkers at Point of Need Using Metal Enhanced Fluorescence and Surface Acoustic Waves

Point of need (PON) quantification of cancer biomarkers such as those used in monitoring disease progression requires sensing at low (pg/ml) limits of detection from body fluids such as blood. For example, proteins such as CEA and CA19-9 are monitored by clinicians for progression of pancreatic cancer, and CA125 is monitored for ovarian cancer progression. Proteins such as PSA are used for initial screening for prostate cancer. All such tests are currently performed in clinical laboratories, off site. The capability to provide such monitoring at the clinician’s office or hospital is challenging, as these proteins need quantification at low, pg/ml to ng/ml levels from a body fluid such as blood, which contains interfering proteins at orders of magnitude higher concentrations. We present concepts and results for such detection using plasmonic (metal) enhancement of fluorescence for lowering detection limits, and Rayleigh surface acoustic waves (SAWs) for reducing interference from non-specific binding (NSB) of other proteins in an immunofluorescence format. These same Rayleigh SAWs are utilized in our platform to reduce incubation time, by inducing sample mixing.

In metal enhanced fluorescence (MEF), fluorescence intensity is increased by metallic nanostructures in the proximity of the fluorophore, leading to lower limits of detection. Recent methods for creating metallic nanostructures, such as e-beam nanolithography, colloidal lithography, and colloidal self-assembling, require complicated processes and have various drawbacks. In this work, we have developed a simple nanostructure fabrication process combining thermal annealing and oxide deposition. A thin silver film is treated with rapid thermal annealing to generate the nanostructures on a SAW device surface. These nanostructures are then coated with a thin silica film to protect them and also to control the distance between the metallic structures and fluorophores. This process provides a solution to achieving silver nanostructures over a large area with simple processing techniques. Immunofluorescence experiments conducted using these surfaces show significant enhancement of fluorescence intensity. The effect of initial silver film, and oxide coating thicknesses on fluorescence enhancement was studied in detail. All fabricated nanostructures showed enhancement, with the silica layer producing an additional enhancement. The optimized structure produced a significant intensity enhancement of ~19X, leading to the construction of an immuno-sensor with a limit of detection of a few 10’s of pg/ml. Finite difference time domain (FDTD) simulations for the enhancement factor allowed for understanding the role of the silica coating, and optimization of the immuno-sensor.

Acoustic streaming from Rayleigh SAWs is utilized to remove NSB proteins to improve sensor signal in our PON sensor platform. We show that NSB proteins which interfere with sensor signal are removed effectively, and incubation times are reduced significantly utilizing these SAWs. The sensor electronics and optics for this proposed sensor platform can be easily reduced to a small, hand-held package, which we present, with further reduction in size possible. The platform is demonstrated with quantification of a typical biomarker, CEA, from blood samples.