Diagnosis of SARS-CoV-2 infection allows for disease intervention, control, and management for COVID-19. The realtime reverse transcriptase-polymerase chain reaction (RT-PCR) is considered the gold standard used to detect the virus. Due to the high testing volumes, the process has a long turnaround time, i.e., 2-3 days. It also requires expensive equipment and involves highly trained staff. Other fast diagnostic methods, such as lateral flow assay based on antibody detection, have limitations such as lower specificity and sensitivity. Thus, there is a critical need for a rapid and low-cost point-ofcare (POC) diagnostic method to accurately diagnose SARS-CoV-2 infections in patients. In this study, three rapid, portable, and cost-effective methods to detect SARS-CoV-2 in human nasopharyngeal swab specimens are developed using surface enhanced Raman spectroscopy (SERS) and deep learning: RNA hybridization, ACE-2 capture, and direct detection. Combining the SERS spectra with a deep learning algorithm, all methods can achieve > 99% accuracy to classify the positive and negative specimens and the test-to-answer time is within 30 min. The RNA hybridization method can achieve a limit of detection of 1000 copies/ml, and the ACE-2 method is capable of differentiating between different variants of SARS-CoV-2 viruses. The direct detection method can additionally quantitatively predict the cycle threshold (Ct) value of RT-PCR tests for positive specimens, demonstrating a diagnostic accuracy of 99.04% in blind tests of 104 specimens. These results indicate that SERS combined with deep learning could be a potential rapid POC COVID-19 diagnostic platform.
Chiral nanohole arrays (NAs) are of significant research interest for their label-free enantiodiscrimination of biomolecules and drug compounds, even at the picogram level. This study systematically explored the impact of various parameters on chiral optical responses of NAs, enhancing our understanding of underlying mechanisms and optimization strategies. We designed dual-layer nanohole arrays with 3600 elements each, alternating Ag and Au layers. We manipulated incident angles (Δθ, θ1) and azimuthal angles (Δφ, φ1) using shadow sphere lithography (SSL) and introduced SiO2 between the Au and Ag layers to enhance the response. MATLAB generated the NAs, subsequently simulated using the finite-difference time-domain (FDTD) program. Findings revealed central symmetry in circular dichroism (CD) value changes concerning Δθ and Δφ, with a more pronounced effect than variations in θ1 and φ1. The inclusion of SiO2 led to a notable 118% increase in the maximum |CD|max value, reaching 6.50° for the 100 nm sandwiched NA (SNA150) with a radius of r = 150 nm. The maximum |g-factor| of the Ag-Au SNA150 increased with the r. An efficient model categorized NAs with similar CD responses, reducing simulations to 498 based on mirror, symmetry and a 60° differential rotation property. This research provides a valuable resource for future machine learning analyses and predictions across diverse structural configurations, significantly advancing applications such as the detection of weak chiral optical molecules or proteins, compact polarization converters, and label-free chiral sensors, fostering innovation in nanohole array technology, particularly in biomedicine and optoelectronics.
Hydrogen has become as a significant energy source. Nonetheless, its threat of explosion poses a challenge to the production and use of hydrogen. This study employs electron beam evaporation technology to produce the Ag-Pd multilayer composite plasmonic hydrogen sensors (PHS), which fulfills the requirement for hydrogen safety detection. The sensing characteristics of monolayer, double-layer and multilayer metal film arrays are systematically compared. The excited local surface plasmon resonance (LSPR) on the multilayer composite films enhance the signal intensity effectively. At the same time, the hot spots area excited by the electric field provide energy for hydrogen adsorption, which synergically promotes the fast response of hydrogen. The PHS based on the Ag-Pd multilayer composite films array has the advantages of fast response, high sensitivity and low detection limit. The multilayer composite plasmonic hydrogen sensing platform developed provides an important theoretical basis and technical support for the development of high-performance hydrogen sensors.
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