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Highly infectious viral diseases are a serious threat to mankind as they can spread rapidly among the community, possibly even leading to the loss of many lives. Early diagnosis of a viral disease not only increases the chance of quick recovery, but also helps prevent the spread of infections. There is thus an urgent need for accurate, ultrasensitive, rapid, and affordable diagnostic techniques to test large volumes of the population to track and thereby control the spread of viral diseases, as evidenced during the COVID-19 and other viral pandemics. This review paper critically and comprehensively reviews various emerging nanophotonic biosensor mechanisms and biosensor technologies for virus detection, with a particular focus on detection of the SARS-CoV-2 (COVID-19) virus. The photonic biosensing mechanisms and technologies that we have focused on include: (a) plasmonic field enhancement via localized surface plasmon resonances, (b) surface enhanced Raman scattering, (c) nano-Fourier transform infrared (nano-FTIR) near-field spectroscopy, (d) fiber Bragg gratings, and (e) microresonators (whispering gallery modes), with a particular emphasis on the emerging impact of nanomaterials and two-dimensional materials in these photonic sensing technologies. This review also discusses several quantitative issues related to optical sensing with these biosensing and transduction techniques, notably quantitative factors that affect the limit of detection (LoD), sensitivity, specificity, and response times of the above optical biosensing diagnostic technologies for virus detection. We also review and analyze future prospects of cost-effective, lab-on-a-chip virus sensing solutions that promise ultrahigh sensitivities, rapid detection speeds, and mass manufacturability.

Etched fiber Bragg grating (eFBG) sensors have shown to be highly sensitive with the capability of giving accurate real‐time response to a variety of measurands such as pressure, gas, biomolecules, to name a few. These sensors have not shown their mettle as competitive products mainly due to nonreproducibility in results and inefficiency in upscaling for large‐scale production; the main reason being nonuniform and complicated coating procedures. Herein, the enhancement in refractive index (RI) sensitivity (≈4 times) obtained with electrospinning of polyvinyl alcohol–reduced graphene oxide (PVA–rGO) nanofibers onto eFBG sensor using a customized target and a unique sandwich arrangement is demonstrated. The enhancement in RI sensitivity has led to a lower detection limit and increased sensitivity and linear range for a case study using myoglobin (Mb), an early‐stage cardiac biomarker with high reproducible results (standard error ≤±2.3%). rGO embedded PVA nanofiber electrospun onto an eFBG sensor (PVA–rGO sensor) is the first of its kind and has significant importance in developing cost‐effective, label‐free, multianalyte, portable, real‐time, point‐of‐care (POC) kits at ambient conditions. Reduced graphene oxide (rGO) embedded polyvinyl alcohol nanofibers are electrospun coated on etched fiber Bragg grating sensor with increase in refractive index sensitivity (≈4×) effecting an increase in Mb sensitivity (24×) and linear range (10 000×) for myoglobin, a cardiac biomarker, with highly reproducible result (standard error ≤±2.3%) in comparison with a standard method (rGO dip coat).

The present study reports an in vivo, novel methodology for the dynamic measurement of the bite force generated by individual tooth using a Fiber Bragg Grating Bite Force Recorder (FBGBFR). Bite force is considered as one of the major indicators of the functional state of the masticatory system, which is dependent on the craniomandibular structure comprising functional components such as muscles of mastication, joints and teeth. The proposed FBGBFR is an intra-oral device, developed for the transduction of the bite force exerted at the occlusal surface, into strain variations on a base plate, which in turn is sensed by the FBG sensor bonded over it. The FBGBFR is calibrated against a Micro Universal Testing Machine (UTM) for 0–900N range and the resolution of the developed FBGBFR is found to be 0.54N. 36 volunteers (20 males and 16 females) performed the bite force measurement test at molar, premolar and incisor tooth on either side of the dental arch and the obtained results show clinically relevant bite forces varying from 176N to 635N. The bite forces obtained from the current study for a substantial sample size, show that the bite forces increases along the dental arch from the incisors towards the molars and are found to be higher in male than in female. The FBG sensor element utilized in FBGBFR is electrically passive, which makes it a safe in vivo intra-oral device. Hence the FBGBFR is viable to be employed in clinical studies on biomechanics of oral function.

In this paper, two novel methods are discussed, wherein Fiber Bragg Gratings are used as sensors to discriminate strain and temperature, simultaneously. These methods provide a good linear response and involve simple fabrication & implementation of the sensors.

The reversible photostriction (photomechanical strain) in Ge 35 S 65 chalcogenide thin film deposited by a solvent casting method has been monitored using a fiber Bragg grating (FBG) sensor. The shift in Bragg wavelength is used as a probing parameter to quantitatively measure the photoinduced strain arising because of structural modifications in these films under illumination. Exposure to band gap light (405 nm) and above band gap light (302 and 254 nm) leads to a reversible photostriction effect of the order of 100 µε. The present study shows that FBG sensors can be used to effectively measure the optomechanical actuation in chalcogenide films caused by the reversible photostriction effect in the visible and ultraviolet wavelength region.

In this paper, two novel methods are discussed, wherein Fiber Bragg Gratings are used as sensors to discriminate strain and temperature, simultaneously. These methods provide a good linear response and involve simple fabrication & implementation of the sensors.

In this work, we observe the rigidity percolation phenomena in a fast ion conducting, conditional glass forming system (AgI)75-x-(Ag2O)25-(MoO3)x. To find out where, why and how the rigidity percolation phenomenon occurs within the range of 20 < x < 37.5, calorimetry and photoelectron spectroscopy experiments are performed. The temperature dependence of heat capacity (normalized) at glass transition temperature (Tg), exhibits fluctuations for samples with higher AgI concentration. This specific quality attributes to fragile glass. The wide range of composition accommodates both the fragile and strong glasses, and therefore a fragility threshold. The heat capacity (absolute) values, at Tg when plotted over the whole range of compositions, exhibits an abrupt sign shift, from negative to positive, revealing the fragility threshold. The appearance of negative heat capacity has been corroborated with the thermodynamic behavior of nanoclusters. This technique has been identified as a novel method to recognize the existence of nanoclusters in this type of glasses. The photoelectron spectroscopy study shows the formation of essential covalent structural units, [- Mo - O - Ag - O -] and complex molybdenum oxides in the positive heat capacity region. Finally, the non-reversing enthalpy profile has been studied over the whole composition range. The global, square well minima sandwiched between floppy and stress rigid region has been identified to be the intermediate phase, within the range 32.25 < x < 35.