In recent years, nanoplasmonic sensors have become widely used for the label-free detection of biomolecules across medical, biotechnology, and environmental science applications. To date, many nanoplasmonic sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level. One of the most promising directions has been surface-based nanoplasmonic sensors, and the potential of such technologies is still emerging. Going beyond detection, surface-based nanoplasmonic sensors open the door to enhanced, quantitative measurement capabilities across the biointerfacial sciences by taking advantage of high surface sensitivity that pairs well with the size of medically important biomacromolecules and biological particulates such as viruses and exosomes. The goal of this review is to introduce the latest advances in nanoplasmonic sensors for the biointerfacial sciences, including ongoing development of nanoparticle and nanohole arrays for exploring different classes of biomacromolecules interacting at solid–liquid interfaces. The measurement principles for nanoplasmonic sensors based on utilizing the localized surface plasmon resonance (LSPR) and extraordinary optical transmission (EOT) phenomena are first introduced. The following sections are then categorized around different themes within the biointerfacial sciences, specifically protein binding and conformational changes, lipid membrane fabrication, membrane–protein interactions, exosome and virus detection and analysis, and probing nucleic acid conformations and binding interactions. Across these themes, we discuss the growing trend to utilize nanoplasmonic sensors for advanced measurement capabilities, including positional sensing, biomacromolecular conformation analysis, and real-time kinetic monitoring of complex biological interactions. Altogether, these advances highlight the rich potential of nanoplasmonic sensors and the future growth prospects of the community as a whole. With ongoing development of commercial nanoplasmonic sensors and analytical models to interpret corresponding measurement data in the context of biologically relevant interactions, there is significant opportunity to utilize nanoplasmonic sensing strategies for not only fundamental biointerfacial science, but also translational science applications related to clinical medicine and pharmaceutical drug development among countless possibilities.

Nanoplasmonic sensors for biointerfacial science

We present a U-bent fiber optic SPR sensor based on the graphene/AgNPs, combined the virtues of graphene, AgNPs and U-bent fiber. By changing the laser-induced time, we achieved the optimal time for the deposition of AgNPs. With the proposed graphene/AgNPs U-bent fiber optic sensor, we discussed and investigated the SPR behaviors. The shifts up to 32 and 16 nm are observed respectively for the detection of 90% aqueous ethanol and 20% aqueous glucose, corresponding refractive index (RI) 1.3657 and 1.3557. The sensitivity of this proposed is calculated as 1198 nm/RIU and the response and recovery time of this U-bent fiber optic sensor are respectively 3 s and 80 s. These experimental results indicate that our proposed graphene/AgNPs U-bent fiber optic sensor will be expected to open new avenue for the detection in the field of medicine, biotechnology and food safety.

U-bent fiber optic SPR sensor based on graphene/AgNPs

Functionalized etched tilted fiber Bragg grating aptasensor for label-free protein detection.

Rapid and low-cost diagnosis of COVID-19 is essential to identify the infected subjects, particularly the asymptomatic cases, primarily to arrest the spread of the disease through local transmission Antibody-based chromatographic serological tests, as an alternative to RT-PCR, offer only limited help due to high false positives We propose to exploit our field-deployable/portable plasmonic fiber-optic absorbance biosensor (P-FAB) platform for one-step, wash-free detection of SARS-CoV-2 virus particles directly in saliva sample with minimal sample pre-processing

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P-FAB: A Fiber-Optic Biosensor Device for Rapid Detection of COVID-19

Early diagnosis and ultrahigh sample throughput screening are the need of the hour to control the geological spread of the COVID-19 pandemic. Traditional laboratory tests such as enzyme-linked immunosorbent assay (ELISA), reverse transcription polymerase chain reaction (RT-PCR) and computed tomography are implemented for the detection of COVID-19. However, they are limited by the laborious sample collection and processing procedures, longer wait time for test results and skilled technicians to operate sophisticated facilities. In this context, the point of care (PoC) diagnostic platform has proven to be the prospective approach in addressing the abovementioned challenges. This review emphasizes the mechanism of viral infection spread detailing the host-virus interaction, pathophysiology, and the recent advances in the development of affordable PoC diagnostic platforms for rapid and accurate diagnosis of COVID-19. First, the well-established optical and electrochemical biosensors are discussed. Subsequently, the recent advances in the development of PoC biosensors, including lateral flow immunoassays and other emerging techniques, are highlighted. Finally, a focus on integrating nanotechnology with wearables and smartphones to develop smart nanobiosensors is outlined, which could promote COVID-19 diagnosis accessible to both individuals and the mass population at patient care.

Recent Advances in Nanomaterials based Biosensors for Point of Care (PoC) Diagnosis of Covid-19 - A Minireview.

This study presents design and development of evanescent wave absorbance based U-bent plastic optical fiber (POF) probe with high sensitivity and its applications to refractive index (RI) sensing. The probes were fabricated by a controlled decladding procedure to remove the fluorinated polymer without damaging the poly methyl methacrylate (PMMA) core and a simple and scalable fabrication technique to obtain POF U-bent probes of desired geometry. U-bent probes of fiber diameter from 250 to 1000 μm were fabricated and optimum bend diameter for each fiber diameter was investigated. The sensitivity was found to be maximum when the bend diameter of the probe varies from 2 to 3 times the fiber diameter. Probes with 500 μm core and 1.25 mm bend diameter showed highest sensitivity (5.57Δ A 560 nm /ΔRIU) in the visible region to RI changes from 1.33 to 1.47 with a resolution better than 1 milli RI units. Furthermore, U-bent probes were amine functionalized and coated with gold nanoparticles to obtain a localized surface plasmon resonance (LSPR) based RI sensor that has an 8-fold improvement in RI sensitivity, hence extending their applicability to plasmonic biosensing.

Development of LSPR based U-bent plastic optical fiber sensors

This study describes the development of a refractive index (RI) based fiber optic chemical sensor using a U-bent plastic optical fiber (BPOF) probe made of 0.5 mm polymethylmethacrylate (PMMA) core and optimum bend diameter of 1.4 mm coated with graphene oxide (GO) film. GO film on BPOF sensor surface significantly enhance the RI sensitivity of the sensor as well as its chemical resistance due to improved refractive index contrast and (PMMA) surface passivation by GO respectively. GO was chemisorbed to hexamethylenediamine (HMDA) functionalized BPOF probe surface by identifying the optimum GO concentration (100 μg/ml) and incubation time (24 h). An enhanced RI sensitivity of 9.42 ± 0.37 (ΔA845nm/ΔRIU) was achieved using GO coating of thickness 3.3 μm, which is 3.6 times higher than that of the bare BPOF probe. The RI sensitivities in presence of organic solvents including methanol, ethanol and isopropyl alcohol are found to be 12.75 ± 1.19, 9.97 ± 0.66 and 13.93 ± 0.92 (ΔA845nm/ΔRIU) respectively. GO film over BPOF was stable even after incubation of the probes in the alcohols over 12 h. In addition, GO-BPOF probes were able to tolerate acetone environment for a prolonged duration of 30 min as opposed to 10 min in case of the bare probes due to improved chemical resistance. Hence, the GO-BPOF could potentially be utilized as a sensitive RI sensor not only for aqueous solutions but also for reactive organic solvents such as alcohols and acetone which are known to damage the PMMA surface.

Graphene oxide coated U-bent plastic optical fiber based chemical sensor for organic solvents

Agriculture and global warming are correlated with each other, particularly, it may affect nutrient cycles, microbial activities, and physiological activities of the crops. Agricultural development plays a crucial role in the growth of the economy of developing countries. The agriculture sector is a major source of employment in most of the developing countries. Over the year, there were changes and productivity loss due to the abiotic stresses and imbalance of nutrients of the plants. A continuous increase in temperature may affect the yields of crops up to 17%. Each plant has different characteristics in growth and some plants are susceptible to high temperature, some are quite the opposite. A Brassica Juncea L. belongs to a mustard family Brassicaceae or Cruciferae that are susceptible to high temperature. So, in this work, an attempt has been made for Brassica Juncea L. to grow and yield under temperature stress by controlling the temperature with the use of the Internet of Things (IoT). The experiment has been conducted where Brassica Juncea neither production nor consumption. IoT sensors are used to monitor the temperature and humidity in two different scenarios. This paper analyses the factors that affect the growth of Brassica Juncea and provide a solution to increase productivity.

Acclimatization of the Growth of Brassica Juncea to Temperature Stress: Future of IoT Technology in Sustainable Agriculture

Silica and polymeric (GOF and POF) based U-bent fiber optic sensor probes are an excellent candidate for low-cost refractive index (RI) based sensors. GOF is expensive and fragile but stable, while POF is contradictory. To evaluate the relative advantages and limitations of the GOF and POF sensor probes with respect to RI measurements, a detailed study is carried out. Measurement reproducibility and temperature stability of the RI sensor probes were investigated using a compact, hand-held fiber-optic refractometer for real-time monitoring, developed in-house. POF probes show a wider measurement range with higher deviation and poorer temperature stability with respect to GOF.

A. Gowri

Papers

Development of LSPR based U-bent plastic optical fiber sensors

Graphene oxide coated U-bent plastic optical fiber based chemical sensor for organic solvents

Acclimatization of the Growth of Brassica Juncea to Temperature Stress: Future of IoT Technology in Sustainable Agriculture

Silica and polymeric fiber optic refractometric sensor probes: Performance evaluation