(244f) Plasmonic ELISA Biosensor with Tunable Sensitivity and Selectivity

In today’s connected world, rapid, cost-effective, transformational, operator-friendly biosensors are the need of the hour to prevent sudden outbreaks, disease spread or for preventive intervention. This has lead to extensive research in biosensors, firmly divided into two important subclasses, namely, the point-of-screening devices and point-of-care devices. Here we describe a tunable device that uses current well-established device architecture like ELISA, plate readers and translates it into a faster, cheaper, more selective and more sensitive biosensor. The tunability of our Biosensor allows it to be used as both, point-of-screening or as a point-of-care device. Our biosensor architecture is composed of two 500 μm X 100 μm thick channels separated by a gold coated polycarbonate membrane. Interdigitated electrodes with a width of 10 μm and separated by a pitch of 10 μm enclose the channels. The porous gold membrane allows for multiple activities. Namely, the binding of the antibody to the gold membrane, the passage of the solution and the unique repetitive structure of the membrane allows for plasmonic enhancement of any optical signal. A DNA with a hairpin structure is used for fluorescent characterization of our gold coated membrane-based biosensor to quantify the plasmonic enhancement. The previous literature states that proximity to metal surface leads to quenching while plasmonic enhancement decreases with increasing distance. The distance between the fluorescent dye and the membrane surface is altered using a molecular separator (ssDNA and thiol linkers). This allows us to optimize the plasmonic enhancement curve with distance. The enhancement results are further verified using finite difference time domain simulation using commercial software. Glancing angle deposition (GLAD) of metals on a regular well-ordered nanometer-sized architecture lead to nano-ordered hierarchical structures. These hierarchical structures can result in local surface plasmon resonance (LSPR) which can cause tremendous enhancement of the electric field. Using our membrane as the nanometer-sized architecture, we deposited gold at multiple different GLAD angles from 0° to 75°. Each GLAD angle deposition leads to unique nano-ordered hierarchical structures that were analyzed using AFM and SEM. The fluorescent enhancement from each structure was quantified and the results matched to theoretical simulations. We performed the well-established sandwich ELISA to compare the performance of our biosensor against those found in the literature. We concluded that our biosensor was more selective and more sensitive than those in literature. Finally, the AC electric field between the interdigitated electrodes and the gold coated membrane will be modulated to observe the effect of the AC frequency on the binding chemistry and the orientation of the antibody linked to the gold membrane. As has been illustrated elsewhere, the electric field can be used to orient the antibody leading to significant increase in the sensitivity and selectivity of the antibody. By changing the orientation of the antibody in the fluidic field with respect to the pores of the membrane, the selectivity of the antibody can be altered. Interestingly, the orientation of the antibody also allows to either diminish the fluorescence from the molecule (quenching from the gold coated membrane) or increase the fluorescence enhancement (minimal quenching and maximal plasmonic). This allows us to modulate the sensitivity and selectivity of the biosensor in real-time and hence the tunability of our Biosensor.