Fluorophore-encapsulated nanobeads for on-site, rapid, and sensitive lateral flow assay.

Since December 2019, the rapid and sensitive detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a priority for public health. Although the lateral flow assay (LFA) sensor has emerged as a rapid and on-site SARS-CoV-2 detection technique, the conventional approach of using gold nanoparticles for the signaling probe had limitations in increasing the sensitivity of the sensor. Herein, our newly suggested methodology to improve the performance of the LFA system could amplify the sensor signal with a facile fabrication method by concentrating fluorescent organic molecules. A large Stokes shift fluorophore (single benzene) was encapsulated into polystyrene nanobeads to enhance the fluorescence intensity of the probe for LFA sensor, which was detected on the test line with a longpass filter under ultraviolet light irradiation. This approach provides comparatively high sensitivity with the limit of detection of 1 ng mL-1 for the SARS-CoV-2 spike protein and a fast detection process, which takes less than 20 min. Furthermore, our sensor showed higher performance than gold nanoparticle-based commercial rapid diagnostics test kits in clinical tests, proving that this approach is more suitable and reliable for the sensitive and rapid detection of viruses, bacteria, and other hazardous materials.

Plasmonic digital PCR for discriminative detection of SARS-CoV-2 variants.

We developed a novel strategy for discriminative detection of SARS-CoV-2 variants based on the plasmonic photothermal effect of gold nanofilms and digital polymerase chain reaction (dPCR) technology. This method consists of the gold nanofilm-based dPCR chip fabrication for ultrafast heating and cooling cycles by the plasmonic photothermal effect, the LED quencher immobilization through the interfacing compound on the surface of the gold nanofilm to prevent photoquenching of PCR signaling dye, and the discriminative detection of the variant viruses from the COVID-19 clinical samples by photothermal cycles with fabricated dPCR chips and a portable plasmonic PCR device. Compared to conventional sequencing or RT-qPCR-based variant detection methods, this technology can be effectively applied to point-of-care testing by enabling ultrafast quantitative analysis with a small device. With this method, we successfully detected the delta variant and the omicron variant with a high sensitivity of 10 copies from COVID-19 patients' clinical samples within 25 min, including reverse transcription. This method can be applied universally to rapid and accurate point-of-care testing for various pandemic viruses as well as the coronavirus.

Recombinant protein embedded liposome on gold nanoparticle based on LSPR method to detect Corona virus.

Antibody sensor to detect viruses has been widely used but has problems such as the difficulty of right direction control of the receptor site on solid substrate, and long time and high cost for design and production of antibodies to new emerging viruses. The virus detection sensor with a recombinant protein embedded liposome (R/Li) was newly developed to solve the above problems, in which R/Li was assembled on AuNPs (Au@R/Li) to increase the sensitivity using localized surface plasmon resonance (LSPR) method. Recombinant angiotensin-converting enzyme-2 (ACE2) was used as host receptors of SARS-CoV and SARS-CoV-2, and the direction of enzyme active site for virus attachment could be controlled by the integration with liposome. The recombinant protein embedded liposomes were assembled on AuNPs, and LSPR method was used for detection. With the sensor platform S1 protein of both viruses was detected with detection limit of 10 pg/ml and SARS-CoV-2 in clinical samples was detected with 10 ~ 35 Ct values. In the selectivity test, MERS-CoV did not show a signal due to no binding with Au@R/Li. The proposed sensor platform can be used as promising detection method with high sensitivity and selectivity for the early and simple diagnosis of new emerging viruses.