Human saliva can be treated as a pool of biological markers able to reflect on the state of personal health. Recent years have witnessed an increase in the use of optical devices for the analysis of body fluids. Several groups have carried out studies investigating the potential of saliva as a non-invasive and reliable clinical specimen for use in medical diagnostics. This brief review aims to highlight the optical technologies, mainly surface plasmon resonance (SPR), Raman, and Fourier transform infrared (FTIR) spectroscopy, which are being used for the probing of saliva for diverse biomedical applications. Advances in bio photonics offer the promise of unambiguous, objective and fast detection of abnormal health conditions and viral infections (such as COVID-19) from the analysis of saliva.

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The use of normal saline for washing red blood cells and treating critically ill patients is a regular medical practice in hospital settings. An optical tweezer in combination with Raman spectroscopy is an analytical tool employed for the investigation of single cell dynamics, thus providing molecular fingerprint of the cell by optically trapping the cell at a laser focus. In this study, the impact of normal saline on individual human red blood cell was compared with that of blood plasma using Raman tweezers spectroscopy.Major spectral variations in the marker frequencies at 1209 cm À1 , 1222 cm À1 , 1544 cm À1 , and 1561 cm À1 of the Raman spectrum of the treated cells imply that the transition of hemoglobin to the deoxygenated state occurs when 0.9% normal saline is used. This may result in serious implications in blood transfusion. The results obtained from the principal component analysis also displayed clear differentiation among the red blood cells diluted in normal saline and those diluted in plasma. In future studies, efforts will be made to correlate the deoxygenation status of red blood cells with various human disorders. Fig. 3 Average Raman spectra of RBCs diluted in normal saline and plasma where spectral variations are dominant (a), (b) the spin marker region, (c) the methine deformation region, (d) the FeO 2 stretch, and (e) the porphyrin breathing mode.This journal is

Extracellular tonicity has a significant influence on human red blood cell deformation capability. Advancements in the area of laser physics and optical trapping have opened up a plethora of applications for understanding cell structure and dynamics. Here, Raman Tweezers technique was employed to investigate the impact of extracellular tonicity by exposing human red blood cells to both hypertonic and hypotonic intravenous fluids. Heme aggregation was observed in hypertonic saline solution, accompanied with damage in membrane protein. Loss of intracellular hemoglobin in hypotonic solution was evident from the decrease in porphyrin breathing mode present at 752 cm −1 . Oxygen binding to the central iron in the red blood cell heme was also affected under both hyper/hypo tonicity conditions. Morphological deviation of discocytes to echinocytes/spherocytes were also evident from quantitative phase imaging. Principal component analysis have showed clear differentiation of samples in order to classify the control erythrocytes and the tonicity stressed erythrocytes. Present study has also demonstrated the application of Raman Tweezers spectroscopy as a potential tool for probing red blood cell under different stress conditions.

Raman spectroscopy offers the potential for fingerprinting biological molecules at ultra-low concentration and therefore has potential for the detection of viruses. Here we review various Raman techniques employed for the investigation of viruses. Different Raman techniques are discussed including conventional Raman spectroscopy, surface-enhanced Raman spectroscopy, Raman tweezer, tip-enhanced Raman Spectroscopy, and coherent anti-Stokes Raman scattering. Surface-enhanced Raman scattering can play an essential role in viral detection by multiplexing nanotechnology, microfluidics, and machine learning for ensuring spectral reproducibility and efficient workflow in sample processing and detection. The application of these techniques to diagnose the SARS-CoV-2 virus is also reviewed. Graphical abstract