Laser Induced Gold Nanoparticle Heating: Thermal Contrast in Lateral Flow Immunoassays

Abstract

Nanomaterial research has grown exponentially for biomedical applications in imaging, diagnostics and therapeutics. Within these areas laser nanoparticle heating uniquely enables important applications including molecular delivery or destruction, endosomal release of genes or siRNA, and selective cell or tumor destruction, with nano to macro-scale spatiotemporal control and precision. While our studies were initially motivated to support in vitro and in vivo biomedical applications, further study of laser nanoparticle heat transfer at a fundamental level, suggested a further opportunity for use in point-of-care diagnostics, in particular for gold nanoparticle (GNP) based lateral flow assays. The lateral flow immunoassay (LFA) is a point-of-care diagnostic test that has found broad applications in medicine, agriculture, and over-the-counter personal use such as for pregnancy testing. Within the LFA, antibody-coated GNPs are used as reporters due to accumulation (i.e. antigen-antibody recognition) on a test line that leads to a visually detectable signal due to a deep red color indicative of GNP accumulation. However, one universally recognized limitation of LFA is the low sensitivity of this visual readout. In this work, we developed a low cost solution to this sensitivity using laser GNP heating. Specifically, metallic nanoparticles generate heat upon optical (i.e. laser) stimulation. This in turn can be used to enhance detection of GNPs, creating a thermal contrast amplification (TCA). We have shown that TCA improves the analytical sensitivity on several existing, commercial LFAs. For instance, our results show a 32-fold improvement in analytical sensitivity using an FDA-approved cryptococcal antigen LFA. My dissertation then describes the development of TCA devices and components that will ultimately allow clinical, laboratory and eventually lay people alike to use and benefit from the technology. In particular, a benchtop TCA prototype device is described and engineering efforts continue to place TCA in a number of clinical laboratories and eventually create a product for infectious disease detection. The absorption and heat generation from nanoparticles eventually determine the magnitude of TCA. Thus, the use of higher heat generating nanoparticles can further improve the LFA sensitivity. Literature suggests that nanoparticle morphology plays an important role in the optical absorption, and nanorods absorb more light energy than nanospheres with the same amount of gold per particle based on previous calculations. Our study suggests that the optical absorption and extinction of gold nanorods are significantly reduced (more than 70%) by polydispersity (i.e. distribution of size and shape) while relatively unaffected for gold nanospheres (less than 10% change). This indicates that the expected enhancement due to absorption of gold nanorods over nanospheres may be greatly diminished by the presence of polydispersity in real nanoparticle samples. Further work incorporating higher heating gold nanoparticles (i.e. larger gold spheres and well characterized gold nanorods) to improve existing lateral flow assays such as to one day rival the sensitivity of more costly, time and labor intesive laboratory testing is underway. In summary, this dissertation describes the foundation of a new technology entitled: Thermal Contrast Amplication (TCA). TCA has been patented and licensed by a start up that is pursuing commercialization and broader societal impact of the technology. Future work including the development of a handheld TCA device for point-of-care diagnostics, and a next generation LFA optimized for TCA are underway. TCA and LFA together represent a potential disruptive platform technology that can improve early diagnosis of infectious diseases and general biomolecular screening in areas of medicine, agriculture, and biodefense where a quick and sensitive detection is needed.