Sagnik Basuray, Ph.D.
Department of Chemical Engineering
The metal/dielectric/bio Interface -- Rich physiological phenomenon
In the first part of my talk, I will be talking about Microfluidics, which has become the instrument of choice and Dielectrophoresis the methodology for the development of rapid and portable detection devices for point-of-care application. Conventional laboratory based microarray technology is relatively slow, employs multistep protocols, and uses bulky and expensive fluorescent microscopy operated by trained staff restricting the usage of such systems to laboratory settings. I will show you an electrochemical DNA detection platform with Pico-molar sensitivity and a 20 minute detection time using equipment that is being turned into a hand held, portable device operated by workers with minimal instruction. The system utilizes dielctrophoretic trapping of carbon nanotube in a continuous microfluidic lab-on-a-chip platform with inter-digitated electrodes for DNA detection. It utilizes electrochemical impedance spectroscopy (EIS) to sense hybridization events between target sequences and short oligonucleotide probes with shear discrimination. We qualify and quantify the open flow microfluidic chip to account for the rich physical phenomenon’s that takes place. The EIS signature resulting from the docking of a multitude of biomolecules to CNTs shows the promise of the platform for a host of point of care diagnostic devices.
In the second part of the talk, I will concentrate on the need to develop a single biophysical instrument with sufficient spatial and temporal resolution to detect complex biological kinetics over broad spatiotemporal scales at the single molecule (SM) level. Here, I will show you a cost effective soft lithography technique to make plasmonic structures that can lead to the development of multi spatial/temporal techniques from a single platform. The structures are made using a simple PDMS stamping of grating structure from commercially produced HD-DVDs with a thermally deposited metallic cap. Modifying the metallic capping process by using oblique (non-normal) angle thermal deposition, significant enhancements (tuning to optimized coupling parameters) is obtained with respect to quartz and a nano-patterned substrate with three major surface morphological features is observed at definite deposition angles for a fixed deposition thickness. The surface consists of a shallow nano-gap region, a conical grating peak with a plateau region between the two aforementioned regions that leads to a concentration of the electric field due to antenna (nano-gap) and lightning rod (grating peak) effects. However, SEM, AFM images show distinct secondary peaks on the grating peak, that gives rise to an extreme concentration of the electric field, leading to localized surface plasmon resonance, called “hot-spots”. This causes any fluorophore at “hot-spot” to fluoresce with intensities that are extra-ordinarily enhanced in comparison to gratings. We found that these nano-gaps on the gratings are ideally suited to study SM phenomenon like Single Molecule Förster resonance energy transfer (smFRET), due to increased signal to noise ratio and high enhancement factors using a simple epi-fluorescence microscope. In addition, dye close to the hotspot region shows an increase in the FRET distance as a result of the localized SPR. The same plasmonic substrates are used for Surface Enhanced Raman Spectroscopy (SERS).