There is an urgent need to development reliable and accurate methods of detection and identification of low concentrations of circulating tumor cells (CTCs). Especially attractive would be detection of CTCs in whole blood samples that can be implemented at the point of service. Very small abundances of CTCs in blood pose a tremendous technological challenge, preventing direct detection and necessitating CTC isolation/enrichment prior to any sensing/diagnostic measurement. Recent advances in nanotechnology enable combining the isolation/enrichment and sensing/diagnostic functions in a single entity. The overall goal of our program is to develop a simple but accurate detection platform for CTCs from whole blood samples that will combine selective capturing of CTCs with their unique spectroscopic fingerprinting. Our approach is based on surface-enhanced infrared absorption spectroscopy (SEIRAS) of tumor cell membranes using a new metamaterial-based plasmonic platform: Fano-resonant Asymmetric Metamaterials (FRAMMs). Different FRAMM-based infrared "pixels" will be tuned to different infrared frequencies, thereby enabling spatial localization of the target cells attached to the sensor. To improve the specificity and robustness of target cell's attachment to the sensor, all FRAMM pixels will be functionalized by a range of antibodies. Cell's binding to the substrate will be interrogated using difference-reflectivity FTIR spectroscopy that will not only detect binding events, but will also yield highly specific cell fingerprints. Spectroscopic data sets will be analyzed using principal component analysis to differentiate between different target cells and to detect their spatial location. FRAMMs will provide field penetration of 50-100nm into the cell, ensuring that the entire cellular membrane is spectrally interrogated. By combining electrically connected FRAMMs into an AC electrode, we will use cell-specific dielectrophoresis (DEP) to greatly enrich the population of tumor cells on the sensor surface with respect to blood cells that are much more abundant in whole blood samples. Cell-specific DEP will be accomplished by labeling CTCs with molecular-specific silica-coated plasmonic nanorods, thereby greatly increasing the AC polarizability of CTCs with respect to blood cells. Captured tumor cells will be further distinguished from blood cells through their native distinct IR fingerprint, as well as through the vibrational fingerprints of the nanoro labels. The nanorods will serve as both infrared contrast agents and as delivery vehicles for cell-specific dielectrophoresis. The proposed approach combines the advantages of (a) highly-sensitive label-free identification of tumor cells using FRAMM-SEIRAS, and (b) robust enrichment/isolation mechanism for rare tumor cells in a single device.
The overall goal of our program is to develop a nanoparticle-based platform for separating circulating tumor cells from small whole blood samples and determining their numerical count. Accurate tumor cell counting can be used for detecting cancer metastasis and monitoring therapeutic outcomes. Our approach a multi-functional platform that enables capturing and spectroscopic characterization of rare tumor cells that does not require complex fluorescent labels and can be deployed at a point-of-care.