Plasmonic Nanoparticles Enabled Rapid and Ultrasensitive Infectious Disease Diagnostics

In vitro diagnosis of respiratory infectious diseases is of paramount importance as evidenced by the current COVID-19 pandemic. Standard diagnostic methods, such as polymerase chain reaction (PCR) and enzyme-linked immunoassay (ELISA), provide specific and sensitive detection yet cause delayed sample-to-answer time. In contrast, rapid methods such as lateral flow assays (LFAs), have compromised sensitivity and specificity. To address these issues, herein, we have developed new plasmonic nanoparticle-based techniques for rapid and ultrasensitive diagnostics of infectious diseases, including respiratory syncytial virus (RSV) and severe acute respiratory syndrome (SARS)-associated coronavirus 2 (SARS-CoV-2). First, we studied gold nanourchins for colorimetric detection of RSV with a one-step sample-to- answer homogeneous immunoassay. We found that nanourchins have improved plasmonic coupling and virus targeting properties. We further integrated this rapid detection method onto a smartphone-based spectrometer and realized a sensitive diagnosis of the intact virus at room temperature within 30 minutes. Second, we developed plasmonic sensing of loop-mediated isothermal amplification (termed as Plasmonic LAMP). We engineered gold and silver (Au-Ag) alloy nanoshells with strong extinction in the visible wavelengths for SARS-CoV-2 detection. It also provides an additional sequence identification enabled by the plasmonic recognition of the LAMP products, thus improving detection specificity and sensitivity over the conventional LAMP. Third, we utilize the unique photothermal effects of plasmonic gold nanoparticles to substantially lower the detection limit of conventional plasmonic coupling assay by innovative DIgitAl plasMONic nanobubble Detection (DIAMOND). Taking RSV as a model target, we endeavor to build a pump-probe two laser system to generate and detect plasmonic nanobubbles (PNB) synchronically. Upon digital counting of PNB signals, we achieved rapid and ultrasensitive diagnostics of intact viruses at the single molecular level, representing viral infections in the early phase. Last, we built a simplified digital photoacoustic (dPA) detection module based on the DIAMOND platform. The plasmonic nanoparticles generate acoustic waves at much lower pulse energy with a single pulse laser stimulation than the vapor nanobubble phenomenon. Also, the dPA detection approach only requires a low-cost ultrasound transducer in the setup, which significantly reduces the complexity of the device and is practical for both laboratory and POC testing. We integrated dPA detection technique in a benchtop device and realize RSV detection at high performance (i.e., a single copy equivalent detection) and high specificity. Collectively, our work provides new capabilities for rapid, sensitive, and specific detection of infectious and other diseases.