Combining Thermo-plasmonics with Microfluidics for Biological Applications

In this project we, for the first time, integrated microfluidics with thermo-plasmonics. While microfluidics is a popular platform allowing experiments with small volumes of fluid, thermo-plasmonics can be used for powerful particle manipulation including capturing, mixing, filtering and projection. Combined, these two techniques give us an opportunity to work with numerous complex fluids containing particles, cells, and micro-beads. Here we designed, developed and tested several devices demonstrating various aspects of this exciting hybrid technology. This required use of soft lithography, metal deposition, 3D printing, oxygen plasma treatment and several other surface modification techniques. Additional challenges were in the fabrication of a multi-layer chip with several types of surfaces binding at several interfaces. The detailed design optimization was conducted, and many characteristics of the microfluidic channel were varied. After that, optimal flow patterns were determined using high-quality syringe pumps. An experiment with the simultaneous flow of two colored solutions through the same microfluidic chip demonstrated controlled laminar flow with minimal mixing. Next, thermo-plasmonic experiments were conducted in optimized micro-fluidic channels. Efficient capturing of microbeads were demonstrated using low power green laser with a wavelength 532 nm. In future, these experiments have many important applications including separation of bacteria from blood on a microfluidic chip. This might help with treatment of sepsis, analysis of blood pathogens and better prescription of antibiotics

Nanophotonics and Nanomaterials for Microbial Inactivation

The study of light-matter interaction at nanoscale, also termed as nanophotonics, has gained vast attention due to its multidisciplinary application in the field of chemical engineering for the synthesis of nanomaterials, in the field of physics to study non-linear optical processes and optical phenomena in nanocavities and in the field of biology, biomedicine to study and develop novel optical nanoprobes for diagnostics, nanobiosensing and near-field imaging. We studied UV-irradiation-based inactivation of SARS-CoV-2 and other respiratory viruses. In this work, we fabricated a device comprising a pulsed nanosecond 266 nm UV laser coupled to an integrating cavity (LIC), composed of a UV-reflective material, polytetrafluoroethylene (PTFE). This device overcomes the limitations of state-of-the art UV inactivation strategies via UV lamps by providing higher efficiency, low power and dose requirement and shorter irradiation times. Our results show that LIC device inactivated SARS-CoV-2 at ~ 1 millisecond effective irradiation time, with \u3e 2 orders of magnitude higher efficiency compared to UV lamps. This LIC device due to its exceptional virus inactivation efficiency has a huge potential for development of real-time UV air and water purification systems. Next, we used two-dimensional transition metal dichalcogenides (2D-TMDs), and their exceptional mechanical and optoelectronic properties provide flexible platform for nanophotonic engineering. Using strain engineering, continuous band gap tunability has been achieved in 2D TMDs. In our work, we presented a new method of nanobubble fabrication on monolayer 2D-lateral heterostructure (MoS2-WS2) using high temperature superacid treatment. We used tip enhanced photoluminescence (TEPL) spectroscopy to perform near-field imaging with nanoscale resolution on the fabricated nanobubbles. TEPL nanoimaging revealed the coupling between MoS2 and WS2 nanobubbles with a large synergistic photoluminescence (PL) enhancement due to the plasmonic tip, hot electrons and exciton funneling. This work opens new avenue in exploration of novel nanophotonic coupling schemes. In addition, we used TEPL to analyze the optical properties of heterojunction, which are atomically thin p-n junction, formed by lattice mismatch of monolayer 2D TMDs. We performed picoscale control of quantum plasmonic PL at 2D heterojunctions and observed more than three-orders magnitude of PL enhancement than the pure material, due to the classical near-field mechanism and charge transfer across the junction. The controllable photoresponse of these lateral heterojunctions can be used to develop novel nanodevices for chemical and biosensing. Finally, we utilized strong optical properties of 2D TMDs for detection of untreated and antibiotic-treated bacteria. We introduced two bacteria-2D TMD interaction models, mechanical and electrical. Using mechanical model we determined the intensity of the exciton funnels created by both untreated and antibiotic-treated bacteria. Our hypothesis states that an antibiotic treated bacteria forms weaker funnels because of the inhibitory effect of the antibiotic on the bacterial adhesion proteins. On the other hand, the electrical model involves two mechanisms, firstly tunneling from the plasmonic tip to the bacteria and to the 2D TMD and secondly, the charge transfer mechanism between the 2D TMD and bacteria. A correlated study using AFM, KPFM and TEPL measurements show that tunneling was more prominent in the case of the untreated bacteria at the bacterial adhesion sites (poles). Lastly, we show the application of heterojunction, by dropcasting bacteria on top of it. We observed tunneling was stronger at the junction than the pure materials, providing with new avenues for biosensing using heterojunctions

Quantum Leap from Gold and Silver to Aluminum Nanoplasmonics for Enhanced Biomedical Applications

Nanotechnology has been used in many biosensing and medical applications, in the form of noble metal (gold and silver) nanoparticles and nanostructured substrates. However, the translational clinical and industrial applications still need improvements of the efficiency, selectivity, cost, toxicity, reproducibility, and morphological control at the nanoscale level. In this review, we highlight the recent progress that has been made in the replacement of expensive gold and silver metals with the less expensive aluminum. In addition to low cost, other advantages of the aluminum plasmonic nanostructures include a broad spectral range from deep UV to near IR, providing additional signal enhancement and treatment mechanisms. New synergistic treatments of bacterial infections, cancer, and coronaviruses are envisioned. Coupling with gain media and quantum optical effects improve the performance of the aluminum nanostructures beyond gold and silver