VIBRANT-BIO explores enhanced light-matter interactions to develop high performance biosensors with new functionalities, well beyond the state-of the art. The project exploits novel nanophotonic phenomena enabled with (I) plasmonics and (II) dielectric metasurfaces operating at Mid-IR.
I) Using plasmonic metasurfaces, we have introduced label-free mid-infrared biosensors, which are able to detect minute quantities of biomolecules, resolve protein secondary structure and distinguish multiple analytes simultaneously from heterogeneous biological samples in real-time and at high sensitivity. One of our work (10.1038/s41467-018-04594-x) is based on dual-resonant plasmonic metasurfaces engineered to extract distinct chemical fingerprint information of bioanalytes from a mixture. We showed that it can spectroscopically resolve the interaction of biomimetic lipid membranes with peptides as well as the dynamics of vesicular cargo release. These are biologically important mass-preserving processes that are inaccessible to standard label-free techniques, regardless of their sensitivity. In a follow up work (10.1002/adma.202006054) we implemented deep learning algorithm with SEIRA to achieve better spectral selectivity and showed dynamic analysis of a bioassay featuring interactions of analytes from all four major biomolecular classes: proteins, lipids, carbohydrates, and nucleic acids. In another work (10.1021/acsphotonics.8b01050) we studied engineering of multi-resonant metasurfaces to simultaneously support four resonances over a wide spectrum covering from 1.5um to 10 um for expending into additional molecular absorption bands.
We have been also opening up new frontiers for label-free spectroscopic identification of secondary structure conformation of nanometric thin protein layers in aqueous solution. In one of our work (10.1038/lsa.2017.29) we demonstrated the first use of plasmonic SEIRA to study α-synuclein (aSyn) protein which is associated with Parkinson’s disease pathology. We performed structure analysis of aSyn in purified monomeric or fibrillated forms by resolving the spectroscopic content of SEIRA enhanced amide I signatures. In a follow up work, we extended this capability to monitor in real-time externally induced secondary structure changes in the aSyn monolayer immobilized on the sensor surface (10.1021/acssensors.8b00115).
We have been contributing to the fundamental understanding of SEIRA and determining its limitations. Since SEIRA is a new field, the general notion on sensitivity parameters is still not well developed. In one of our work (10.1021/acsphotonics.8b00847) we addressed this need by introducing methodologies in order to quantify the limit of detection which can provide a valuable reference points for determining biosensor performance metrics. Related to the fundamentals, in a collaborative work (10.1021/acsphotonics.8b00425) we reported the excitation of molecular vibrations through interactions of a nanotip with an infrared resonant nanowire that supports tunable bright and nonradiative dark modes. We demonstrated electromagnetically induced scattering through phase controlled near-field interactions, which presents a new regime of IR spectroscopy using vibrational coherence.
II) Using dielectric metasurfaces, we have investigated the use of high-Q resonances for SEIRA sensing. In one of our work (DOI: 10.1126/science.aas9768) we introduced a new method that have the potentials to identify molecular absorption characteristics without using conventional bulky and expensive spectrometry instruments. The method uses an engineered surface covered with ~hundreds of individual sensing elements called metapixels where they are tuned to resonate at distinct frequencies. The design provides one-to-one correspondence between spectral and spatial positions. When the metasurface is covered with a molecule layer, the method creates a pixelated map of light absorption that can be translated into what we call “molecular barcode”. By using different molecules on the sensor surface such as proteins, polymers and pesticides we showed distinct molecular barcodes. A follow-up work expanded dielectric metasurfaces to detect molecular absorption fingerprints over a broad spectrum (DOI: 10.1126/sciadv.aaw2871) by using polarization and angle dependence of the designed metasurfaces.
Low-cost manufacturing of Mid-IR metasurfaces is essential to transfer their application. In a collaborative effort (10.1021/acs.nanolett.7b05295) we studied a wafer-scale array of plasmonic resonators consisting of coaxial nanoapertures with sub-10 nm gaps as a new platform for SEIRA. In another work (10.1002/adma.202102232) we introduced a wafer-scale low-cost nanofabrication method based on CMOS-compatible processes in which large-area mid-IR metasurfaces are fabricated on silicon wafers having optically transparent free-standing oxide membranes. We used the new method to fabricate Aluminum-based CMOS compatible SEIRA substrates and integrated them with microfluidics to show their compatibility for in-flow IR sensing.
