COVID-19 Diagnostics: Past, Present, and Future

Label-free integrated microfluidic plasmonic biosensor from vertical-cavity surface-emitting lasers for SARS-CoV-2 receptor binding domain protein detection

The nanoplasmonic sensor of the nanograting array has a remarkable ability in label-free and rapid biological detection. The integration of the nanograting array with the standard vertical-cavity surface-emitting lasers (VCSEL) platform can achieve a compact and powerful solution to provide on-chip light sources for biosensing applications. Here, a high sensitivity and label-free integrated VCSELs sensor was developed as a suitable analysis technique for COVID-19 specific receptor binding domain (RBD) protein. The gold nanograting array is integrated on VCSELs to realize the integrated microfluidic plasmonic biosensor of on-chip biosensing. The 850 nm VCSELs are used as a light source to excite the localized surface plasmon resonance (LSPR) effect of the gold nanograting array to detect the concentration of attachments. The refractive index sensitivity of the sensor is 2.99 × 10⁶ nW/RIU. The aptamer of RBD was modified on the surface of the gold nanograting to detect the RBD protein successfully. The biosensor has high sensitivity and a wide detection range of 0.50 ng/mL - 50 µg/mL. This VCSELs biosensor provides an integrated, portable, and miniaturized idea for biomarker detection.

Conventional and Novel Diagnostic Tools for the Diagnosis of Emerging SARS-CoV-2 Variants

Accurate identification at an early stage of infection is critical for effective care of any infectious disease. The "coronavirus disease 2019 (COVID-19)" outbreak, caused by the virus "Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)", corresponds to the current and global pandemic, characterized by several developing variants, many of which are classified as variants of concern (VOCs) by the "World Health Organization (WHO, Geneva, Switzerland)". The primary diagnosis of infection is made using either the molecular technique of RT-PCR, which detects parts of the viral genome's RNA, or immunodiagnostic procedures, which identify viral proteins or antibodies generated by the host. As the demand for the RT-PCR test grew fast, several inexperienced producers joined the market with innovative kits, and an increasing number of laboratories joined the diagnostic field, rendering the test results increasingly prone to mistakes. It is difficult to determine how the outcomes of one unnoticed result could influence decisions about patient quarantine and social isolation, particularly when the patients themselves are health care providers. The development of point-of-care testing helps in the rapid in-field diagnosis of the disease, and such testing can also be used as a bedside monitor for mapping the progression of the disease in critical patients. In this review, we have provided the readers with available molecular diagnostic techniques and their pitfalls in detecting emerging VOCs of SARS-CoV-2, and lastly, we have discussed AI-ML- and nanotechnology-based smart diagnostic techniques for SARS-CoV-2 detection.

Specific intracellular signature of SARS-CoV-2 infection using confocal Raman microscopy

SARS-CoV-2 infection remains spread worldwide and requires a better understanding of virus-host interactions. Here, we analyzed biochemical modifications due to SARS-CoV-2 infection in cells by confocal Raman microscopy. Obtained results were compared with the infection with another RNA virus, the measles virus. Our results have demonstrated a virus-specific Raman molecular signature, reflecting intracellular modification during each infection. Advanced data analysis has been used to distinguish non-infected versus infected cells for two RNA viruses. Further, classification between non-infected and SARS-CoV-2 and measles virus-infected cells yielded an accuracy of 98.9 and 97.2 respectively, with a significant increase of the essential amino-acid tryptophan in SARS-CoV-2-infected cells. These results present proof of concept for the application of Raman spectroscopy to study virus-host interaction and to identify factors that contribute to the efficient SARS-CoV-2 infection and may thus provide novel insights on viral pathogenesis, targets of therapeutic intervention and development of new COVID-19 biomarkers.

Phototherapy and optical waveguides for the treatment of infection

With rapid emergence of multi-drug resistant microbes, it is imperative to seek alternative means for infection control. Optical waveguides are an auspicious delivery method for precise administration of phototherapy. Studies have shown that phototherapy is promising in fighting against a myriad of infectious pathogens (i.e. viruses, bacteria, fungi, and protozoa) including biofilm-forming species and drug-resistant strains while evading treatment resistance. When administered via optical waveguides, phototherapy can treat both superficial and deep-tissue infections while minimizing off-site effects that afflict conventional phototherapy and pharmacotherapy. Despite great therapeutic potential, exact mechanisms, materials, and fabrication designs to optimize this promising treatment option are underexplored. This review outlines principles and applications of phototherapy and optical waveguides for infection control. Research advances, challenges, and outlook regarding this delivery system are rigorously discussed in a hope to inspire future developments of optical waveguide-mediated phototherapy for the management of infection and beyond.