As physical sensors get to be micro- and nano-scale, their detection thresholds require much fewer target molecules or cells to accumulate on their surface. Indeed, nano-scale transducers with single molecular detection capabilities have already been demonstrated. However, the overall sensitivity of a bio-assay is currently limited by diffusion-based mass transport towards the sensor surface, and is typically orders of magnitude worse than the capabilities of the transducer itself. As such, none of the state-of-the-art, solution- based biosensing schemes can quote actual sensitivity numbers much below 1 femtoMolar (fM) for biomolecules or below 103 cells/ml in cellular detection schemes. The purpose of this proposal is to demonstrate, characterize and adapt a truly universal, versatile, cost-effective and label-free mass-transport and cellular manipulation scheme that overcomes the diffusion barrier in bio-assays, while enabling the choice of virtually any transducer as the detection mechanism. This scheme is based on ferrofluid dynamics within microfluidic devices in the presence of traveling magnetic fields. The PI's group has recently discovered and demonstrated continuous ferrohydrodynamic pumping both at the macro- and micro-scales via a traveling magnetic field excitation that requires no mechanically moving parts. The same phenomenon leads to strong and localized vortices within the ferrofluid under appropriate conditions. What is more, the PI's research has shown that non-magnetic particles suspended in a ferrofluid can be manipulated rapidly using traveling wave excitations from integrated electrodes. These preliminary results present a reliable and scalable method to significantly increase analyte or cellular transport towards a sensor surface, thereby overcoming the diffusion barrier. The proposed program depends critically on developing bio-compatible, water-based ferrofluids; as such, it focuses on engineering bio-compatible ferrofluids through the use of genetically engineered peptides for inorganics (GEPI's). The research work will also involve the demonstration and characterization of both molecular and cellular mass-transport schemes based on ferrohydrodynamics. One of the goals of this research effort will be to demonstrate below 1 fM detection capability in a standard enzyme-linked immunosorbent assay (ELISA) for Her2 (a cancer marker) utilizing ferrofluid-mediated mass transport to achieve over two orders of magnitude increase in sensitivity. In addition, biomolecular manipulation will be quantified through conformation studies of surface bound oligonucleotides using spectral self-interference microscopy. Micron-sized particle and cell manipulation in ferrofluids will also be investigated, with the goal of demonstrating an extremely rapid, wash-free assay to quantify binding forces of any ligand-receptor pair. Statement Anticipated Impact: If the methods proposed here are successful, they will demonstrate orders of magnitude faster mixing and mass-transport in biosensors compared to what is achievable through static or flow-based assays. As a result, rapid bio-assays with overall sensitivities much below 1 femtoMolar will be made possible, enabling much earlier and accurate diagnoses of certain types of cancer, as well as neurodegenerative and infectious diseases. In addition, ferrofluid-based assays offer the possibility to eliminate the need for manually- intensive handling and wash cycles, which will further increase analysis throughput and enable quicker diagnoses of disease. ? ? ?
