Optical Biosensors for Virus Detection: Prospects for SARS-CoV-2/COVID-19

Advances and opportunities in process analytical technologies for viral vector manufacturing

Viral vectors are an emerging, exciting class of biologics whose application in vaccines, oncology, and gene therapy has grown exponentially in recent years. Following first regulatory approval, this class of therapeutics has been vigorously pursued to treat monogenic disorders including orphan diseases, entering hundreds of new products into pipelines. Viral vector manufacturing supporting clinical efforts has spurred the introduction of a broad swath of analytical techniques dedicated to assessing the diverse and evolving panel of Critical Quality Attributes (CQAs) of these products. Herein, we provide an overview of the current state of analytics enabling measurement of CQAs such as capsid and vector identities, product titer, transduction efficiency, impurity clearance etc. We highlight orthogonal methods and discuss the advantages and limitations of these techniques while evaluating their adaptation as process analytical technologies. Finally, we identify gaps and propose opportunities in enabling existing technologies for real-time monitoring from hardware, software, and data analysis viewpoints for technology development within viral vector biomanufacturing.

Recent advances in the development of multiplexed nanophotonic biosensors

The field of nanophotonics has advanced and can be utilized as a method to detect different infectious diseases. The introduction of multiplex nanophotonic diagnostics has enabled the speedy and simultaneous detection of viral infections and specific biomarkers. The quick reaction times, high sensitivity, and specificity of multiplex nanophotonic diagnostics enable real-time identification of viruses without the need for nucleic acid amplification. This review presents an overview of nanophotonic tools used to identify diseases and particular biomarkers. The paper also examines possible research areas for the development of unique, cutting-edge multiplex nanophotonic diagnostics capable of concurrently detecting various diseases or biomarkers/biomolecules. Furthermore, it discusses barriers to further advancement and offers insight into anticipated trends.

Advanced protein nanobiosensors to in-situ detect hazardous material in the environment

Determining hazardous substances in the environment is vital to maintaining the safety and health of all components of society, including the ecosystem and humans. Recently, protein-based nanobiosensors have emerged as effective tools for monitoring potentially hazardous substances in situ. Nanobiosensor detection mode is a combination of particular plasmonic nanomaterials (e.g., nanoparticles, nanotubes, quantum dots, etc.), and specific bioreceptors (e.g., aptamers, antibodies, DNA, etc.), which has the benefits of high selectivity, sensitivity, and compatibility with biological systems. The role of these nanobiosensors in identifying dangerous substances (e.g., heavy metals, organic pollutants, pathogens, toxins, etc.) is discussed along with different detection mechanisms and various transduction methods (e.g., electrical, optical, mechanical, electrochemical, etc.). In addition, topics discussed include the design and construction of these sensors, the selection of proteins, the integration of nanoparticles, and their development processes. A discussion of the challenges and prospects of this technology is also included. As a result, protein nanobiosensors are introduced as a powerful tool for monitoring and improving environmental quality and community safety.

A Label-free Optical Biosensor-Based Point-of-Care Test for the Rapid Detection of Monkeypox Virus

Diagnostic approaches that combine the high sensitivity and specificity of laboratory-based digital detection with the ease of use and affordability of point-of-care (POC) technologies could revolutionize disease diagnostics. This is especially true in infectious disease diagnostics, where rapid and accurate pathogen detection is critical to curbing the spread of disease. We have pioneered an innovative label-free digital detection platform that utilizes Interferometric Reflectance Imaging Sensor (IRIS) technology. IRIS leverages light interference from an optically transparent thin film, eliminating the need for complex optical resonances to enhance the signal by harnessing light interference and the power of signal averaging in shot-noise-limited operation to achieve virtually unlimited sensitivity. In our latest work, we have further improved our previous 'Single-Particle' IRIS (SP-IRIS) technology by allowing the construction of the optical signature of target nanoparticles (whole virus) from a single image. This new platform, 'Pixel-Diversity' IRIS (PD-IRIS), eliminated the need for z-scan acquisition, required in SP-IRIS, a time-consuming and expensive process, and made our technology more applicable to POC settings. Using PD-IRIS, we quantitatively detected the Monkeypox virus (MPXV), the etiological agent for Monkeypox (Mpox) infection. MPXV was captured by anti-A29 monoclonal antibody (mAb 69-126-3) on Protein G spots on the sensor chips and were detected at a limit-of-detection (LOD) - of 200 PFU/ml (~3.3 attomolar). PD-IRIS was superior to the laboratory-based ELISA (LOD - 1800 PFU/mL) used as a comparator. The specificity of PD-IRIS in MPXV detection was demonstrated using Herpes simplex virus, type 1 (HSV-1), and Cowpox virus (CPXV). This work establishes the effectiveness of PD-IRIS and opens possibilities for its advancement in clinical diagnostics of Mpox at POC. Moreover, PD-IRIS is a modular technology that can be adapted for the multiplex detection of pathogens for which high-affinity ligands are available that can bind their surface antigens to capture them on the sensor surface.

Recent advances towards point-of-care devices for fungal detection: Emphasizing the role of plasmonic nanomaterials in current and future technologies

Fungal infections are a significant global health problem, particularly affecting individuals with weakened immune systems. Moreover, as uncontrolled antibiotic and immunosuppressant use increases continuously, fungal infections have seen a dramatic increase, with some strains developing antibiotic resistance. Traditional approaches to identifying fungal strains often rely on morphological characteristics, thus owning limitations, such as struggles in identifying several strains or distinguishing between fungal strains with similar morphologies. This review explores the multifaceted impact of fungi infections on individuals, healthcare providers, and society, highlighting the often-underestimated economic burden and healthcare implications of these infections. In light of the serious constraints of traditional fungal identification methods, this review discusses the potential of plasmonic nanoparticle-based biosensors for fungal infection identification. These biosensors can enable rapid and precise fungal pathogen detection by exploiting several readout approaches, including various spectroscopic techniques, colorimetric and electrochemical assays, as well as lateral-flow immunoassay methods. Moreover, we report the remarkable impact of plasmonic Lab on a Chip technology and microfluidic devices, as they recently emerged as a class of advanced biosensors. Finally, we provide an overview of smartphone-based Point-of-Care devices and the associated technologies developed for detecting and identifying fungal pathogens.

Research progress on the mechanism of exosome-mediated virus infection

Exosomes are extracelluar vesicles that facilitate intercellular communication and are pivotal in post-transcriptional regulation within cellular gene regulatory networks, impacting pathogen dynamics. These vesicles serve as crucial regulators of immune responses, mediating cellular interactions and enabling the introduction of viral pathogenic regions into host cells. Exosomes released from virus-infected cells harbor diverse microRNAs (miRNAs), which can be transferred to recipient cells, thereby modulating virus infection. This transfer is a critical element in the molecular interplay mediated by exosomes. Additionally, the endosomal sorting complex required for transport (ESCRT) within exosomes plays a vital role in virus infection, with ESCRT components binding to viral proteins to facilitate virus budding. This review elucidates the roles of exosomes and their constituents in the invasion of host cells by viruses, aiming to shed new light on the regulation of viral transmission via exosomes.

Silicon Microring Resonator Biosensor for Detection of Nucleocapsid Protein of SARS-CoV-2

A high-sensitivity silicon microring (Si MRR) optical biosensor for detecting the nucleocapsid protein of SARS-CoV-2 is proposed and demonstrated. In the proposed biosensor, the surface of a Si MRR waveguide is modified with antibodies, and the target protein is detected by measuring a resonant wavelength shift of the MRR caused by the selective adsorption of the protein to the surface of the waveguide. A Si MRR is fabricated on a silicon-on-insulator substrate using a CMOS-compatible fabrication process. The quality factor of the MRR is approximately 20,000. The resonant wavelength shift of the MRR and the detection limit for the environmental refractive index change are evaluated to be 89 nm/refractive index unit (RIU) and 10-4 RIU, respectively. The sensing characteristics are examined using a polydimethylsiloxane flow channel after the surface of the Si MRR waveguide is modified with the IgG antibodies through the Si-tagged protein. First, the selective detection of the protein by the MRR sensor is experimentally demonstrated by the detection of bovine serum albumin and human serum albumin. Next, various concentrations of nucleocapsid protein solutions are measured by the MRR, in which the waveguide surface is modified with the IgG antibodies through the Si-tagged protein. Although the experimental results are very preliminary, they show that the proposed sensor has a potential nucleocapsid sensitivity in the order of 10 pg/mL, which is comparable to the sensitivity of current antigen tests. The detection time is less than 10 min, which is much shorter than those of other antigen tests.

Optical biosensors for diagnosis of COVID-19: nanomaterial-enabled particle strategies for post pandemic era

The COVID-19 pandemic underlines the need for effective strategies for controlling virus spread and ensuring sensitive detection of SARS-CoV-2. This review presents the potential of nanomaterial-enabled optical biosensors for rapid and low-cost detection of SARS-CoV-2 biomarkers, demonstrating a comprehensive analysis including colorimetric, fluorescence, surface-enhanced Raman scattering, and surface plasmon resonance detection methods. Nanomaterials including metal-based nanomaterials, metal-organic frame-based nanoparticles, nanorods, nanoporous materials, nanoshell materials, and magnetic nanoparticles employed in the production of optical biosensors are presented in detail. This review also discusses the detection principles, fabrication methods, nanomaterial synthesis, and their applications for the detection of SARS-CoV-2 in four categories: antibody-based, antigen-based, nucleic acid-based, and aptamer-based biosensors. This critical review includes reports published in the literature between the years 2021 and 2024. In addition, the review offers critical insights into optical nanobiosensors for the diagnosis of COVID-19. The integration of artificial intelligence and machine learning technologies with optical nanomaterial-enabled biosensors is proposed to improve the efficiency of optical diagnostic systems for future pandemic scenarios.

Electrochemical and optical (bio)sensors for analysis of antibiotic residuals

Antibiotic residuals in foods may lead to crucial health and safety issues in the human body. Rapid and in-time analysis of antibiotics using simple and sensitive techniques is in high demand. Among the most commonly applicable modalities, chromatography-based techniques like HPLC and LC-MS, along with immunological approaches, particularly ELISA have been exampled in the analysis of antibiotics. Despite being highly sensitive, these methods are considerably time-consuming, thus the presence of skilled personnel and costly equipment is essential. Nanomaterial-based (bio)sensors, however, are de novo analytical equipment with some beneficial characteristics, such as simplicity, low price, on-site, high accuracy, and sensitivity for the detection of analytes. This review aimed to collect the latest developments in NM-based sensors and biosensors for the observation of highly used antibiotics like Vancomycin (Van), Linezolid (Lin), and Clindamycin (Clin). The current challenges and developmental perspectives are also debated in detail for future research directions.

On-The-Spot Sampling and Detection of Viral Particles on Solid Surfaces Using a Sponge Virus Sensor Incorporated with Finger-Press Fluid Release

This paper presents a sponge-based electrochemical sensor for rapid, on-site collection and analysis of infectious viruses on solid surfaces. The device utilizes a conducting porous sponge modified with graphene, graphene oxide, and specific antibodies. The sponge serves as a hydrophilic porous electrode capable of liquid collection and electrochemical measurements. The device operation involves spraying an aqueous solution on a target surface, swiping the misted surface using the sponge, discharging an electrolyte solution with a simple finger press, and performing in situ incubation and electrochemical measurements. By leveraging the water-absorbing ability of the biofunctionalized conducting sponge, the sensor can effectively collect and quantify virus particles from the surface. The portability of the device is enhanced by introducing a push-release feature that dispenses the liquid electrolyte from a miniature reservoir onto the sensor surface. This reservoir has sharp edges to rupture a liquid sealing film with a finger press. The ability of the device to sample and quantify viral particles is demonstrated by using influenza A virus as the model. The sensor provided a calculated limit of detection of 0.4 TCID50/mL for H1N1 virus, along with a practical concentration range from 1-106 TCID50/mL. Additionally, it achieves a 15% collection efficiency from single-run swiping on a tabletop surface. This versatile device allows for convenient on-site virus detection within minutes, eliminating the need for sample pretreatment and simplifying the entire sample collecting and measuring process. This device presents significant potential for rapid virus detection on solid surfaces.

Engineered two-dimensional nanomaterials based diagnostics integrated with internet of medical things (IoMT) for COVID-19

More than four years have passed since an inimitable coronavirus disease (COVID-19) pandemic hit the globe in 2019 after an uncontrolled transmission of the severe acute respiratory syndrome (SARS-CoV-2) infection. The occurrence of this highly contagious respiratory infectious disease led to chaos and mortality all over the world. The peak paradigm shift of the researchers was inclined towards the accurate and rapid detection of diseases. Since 2019, there has been a boost in the diagnostics of COVID-19 via numerous conventional diagnostic tools like RT-PCR, ELISA, etc., and advanced biosensing kits like LFIA, etc. For the same reason, the use of nanotechnology and two-dimensional nanomaterials (2DNMs) has aided in the fabrication of efficient diagnostic tools to combat COVID-19. This article discusses the engineering techniques utilized for fabricating chemically active E2DNMs that are exceptionally thin and irregular. The techniques encompass the introduction of heteroatoms, intercalation of ions, and the design of strain and defects. E2DNMs possess unique characteristics, including a substantial surface area and controllable electrical, optical, and bioactive properties. These characteristics enable the development of sophisticated diagnostic platforms for real-time biosensors with exceptional sensitivity in detecting SARS-CoV-2. Integrating the Internet of Medical Things (IoMT) with these E2DNMs-based advanced diagnostics has led to the development of portable, real-time, scalable, more accurate, and cost-effective SARS-CoV-2 diagnostic platforms. These diagnostic platforms have the potential to revolutionize SARS-CoV-2 diagnosis by making it faster, easier, and more accessible to people worldwide, thus making them ideal for resource-limited settings. These advanced IoMT diagnostic platforms may help with combating SARS-CoV-2 as well as tracking and predicting the spread of future pandemics, ultimately saving lives and mitigating their impact on global health systems.

All-fiber label-free optical fiber biosensors: from modern technologies to current applications [Invited]

Biosensors are established as promising analytical tools for detecting various analytes important in biomedicine and environmental monitoring. Using fiber optic technology as a sensing element in biosensors offers low cost, high sensitivity, chemical inertness, and immunity to electromagnetic interference. Optical fiber sensors can be used in in vivo applications and multiplexed to detect several targets simultaneously. Certain configurations of optical fiber technology allow the detection of analytes in a label-free manner. This review aims to discuss recent advances in label-free optical fiber biosensors from a technological and application standpoint. First, modern technologies used to build label-free optical fiber-based sensors will be discussed. Then, current applications where these technologies are applied are elucidated. Namely, examples of detecting soluble cancer biomarkers, hormones, viruses, bacteria, and cells are presented.

Sensing of Quercetin With Cobalt-Doped Manganese Nanosystems by Electrochemical Method

BACKGROUND

The pressing need for precise, quick, and affordable detection of diverse biomolecules has led to notable developments in the realm of biosensors. Quercetin, a biomolecule rich in flavonoids predominantly found in our diet, is sensed by the electrochemical method. The electrochemical properties show remarkable improvement when Mn2O3 (MO) is doped with cobalt (Co).  Aim: This study aimed to investigate the biomolecule sensing of quercetin using Co-doped MO by electrochemical method.  Materials and methods: Co-doped MO nanospheres were prepared by hydrothermal method. The crystal structure of the synthesized material was evaluated by using X-ray diffraction analysis. The sample morphology was assessed by using field emission scanning electron microscopy (FE-SEM) techniques. The cyclic voltammetry technique was used for the detection of quercetin biomolecules.  Results: The synthesized Co-doped MO appeared to be spherical in morphology in FE-SEM. Energy-dispersive X-ray spectroscopy showed the only presence of Co, Mn, and O, which confirmed the purity of the sample. The modified electrode sensed the biomolecule with a higher current of 7.35 µA than the bare glassy carbon electrode of 6.1 µA.

CONCLUSION

The Co-doped MO exhibited enhanced conductivity, reactivity, and electrochemical performance. This tailored approach will help in the optimization of material properties toward specific biomolecule sensing applications.

Low-Cost Biosensor Technologies for Rapid Detection of COVID-19 and Future Pandemics

Many systems have been designed for the detection of SARS-CoV-2, which is the virus that causes COVID-19. SARS-CoV-2 is readily transmitted, resulting in the rapid spread of disease in human populations. Frequent testing at the point of care (POC) is a key aspect for controlling outbreaks caused by SARS-CoV-2 and other emerging pathogens, as the early identification of infected individuals can then be followed by appropriate measures of isolation or treatment, maximizing the chances of recovery and preventing infectious spread. Diagnostic tools used for high-frequency testing should be inexpensive, provide a rapid diagnostic response without sophisticated equipment, and be amenable to manufacturing on a large scale. The application of these devices should enable large-scale data collection, help control viral transmission, and prevent disease propagation. Here we review functional nanomaterial-based optical and electrochemical biosensors for accessible POC testing for COVID-19. These biosensors incorporate nanomaterials coupled with paper-based analytical devices and other inexpensive substrates, traditional lateral flow technology (antigen and antibody immunoassays), and innovative biosensing methods. We critically discuss the advantages and disadvantages of nanobiosensor-based approaches compared to widely used technologies such as PCR, ELISA, and LAMP. Moreover, we delineate the main technological, (bio)chemical, translational, and regulatory challenges associated with developing functional and reliable biosensors, which have prevented their translation into the clinic. Finally, we highlight how nanobiosensors, given their unique advantages over existing diagnostic tests, may help in future pandemics.

On-chip screening of SARS-CoV-2 cDNA by LAMP-integrated rotational diffusometry

The unprecedented pandemic has raised the demand for prompt, precise, and large-scale virus detection techniques to control the transmission of contagious illnesses. In this study, a loop-mediated isothermal amplification (LAMP) based on-chip platform was developed to address this challenge using rotational diffusometry and functionalized Janus particles. A recombinant plasmid containing a cDNA sequence of the SARS-CoV-2 non-structural protein 2 (nsp2) gene was employed here as a proof-of-concept for COVID-19 detection. Specifically, designed primers and the functionalized Janus particles were simultaneously loaded on a microfluidic chip to perform the LAMP reaction on a hot plate. The optimal Janus particle concentrations for diffusometric analysis were thoroughly validated, and the performance of the on-chip LAMP reaction was assessed using thermal image analysis. Utilization of the highly sensitive rotational diffusometry achieved a limit of detection of 1 pg/μL in just 10 min with a sample volume of 20 μL. Our method delivered a tenfold higher sensitivity than the conventional method by utilizing only half of its usual required time. Overall, this study proposes a potential nucleic acid (NA) amplification device to aid the rapid diagnosis of various diseases by modifying the primers for different target genes.

Advances in nanobiosensors during the COVID-19 pandemic and future perspectives for the post-COVID era

The unprecedented threat of the highly contagious virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes exponentially increased infections of coronavirus disease 2019 (COVID-19), highlights the weak spots of the current diagnostic toolbox. In the midst of catastrophe, nanobiosensors offer a new opportunity as an alternative tool to fill a gap among molecular tests, rapid antigen tests, and serological tests. Nanobiosensors surpass the potential of antigen tests because of their enhanced sensitivity, thus enabling us to see antigens as stable and easy-to-access targets. During the first three years of the COVID-19 pandemic, a substantial number of studies have reported nanobiosensors for the detection of SARS-CoV-2 antigens. The number of articles on nanobiosensors and SARS-CoV-2 exceeds the amount of nanobiosensor research on detecting previous infectious diseases, from influenza to SARS-CoV and MERS-CoV. This unprecedented publishing pace also implies the significance of SARS-CoV-2 and the present pandemic. In this review, 158 studies reporting nanobiosensors for detecting SARS-CoV-2 antigens are collected to discuss the current challenges of nanobiosensors using the criteria of point-of-care (POC) diagnostics along with COVID-specific issues. These advances and lessons during the pandemic pave the way for preparing for the post-COVID era and potential upcoming infectious diseases.

Gold single atom-based aptananozyme as an ultrasensitive and selective colorimetric probe for detection of thrombin and C-reactive protein

An ultra-efficient biocatalytic peroxidase-like Au-based single-atom nanozyme (Au-SAzymes) has been synthesized from isolated Au atoms on black nitrogen doped carbon (Au-N-C) using a simple complexation-adsorption-pyrolysis method. The atomic structure of AuN4 centers in black carbon was revealed by combined high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy. The Au-SAzymes showed a remarkable peroxidase activity with 1.7 nM as Michaelis-Menten constant, higher than most previously reported SAzyme activity. Density functional theory and Monte Carlo calculations revealed the adsorption of H2O2 on AuN4 with formation of OH* and O*. Molecular recognition was greatly enhanced via label-free integration of thiol-terminal aptamers on the surface of single Au atoms (Aptamer/Au-SAzyme) to design off-on ultrasensitive aptananozyme-based sensor for detecting thrombin and CRP with 550 pM and 500 pg mL-1 limits of detection, respectively. The Aptamer/Au-SAzyme showed satisfactory accuracy and precision when applied to the serum and plasma of COVID-19 patients. Due to the maximum Au atom utilization, approximately 3636 samples can be run per 1 mg of gold, highlighting the commercialization potential of the developed Aptamer/Au-SAzyme approach.

Two-Dimensional (2D) materials in the detection of SARS-CoV-2

The SARS-CoV-2 pandemic has resulted in a devastating effect on human health in the last three years. While tremendous effort has been devoted to the development of effective treatment and vaccines against SARS-CoV-2 and controlling the spread of it, collective health challenges have been encountered along with the concurrent serious economic impacts. Since the beginning of the pandemic, various detection methods like PCR-based methods, isothermal nucleic acid amplification-based (INAA) methods, serological methods or antibody tests, and evaluation of X-ray chest results have been exploited to diagnose SARS-CoV-2. PCR-based detection methods in these are considered gold standards in the current stage despite their drawbacks, including being high-cost and time-consuming procedures. Furthermore, the results obtained from the PCR tests are susceptible to sample collection methods and time. When the sample is not collected properly, obtaining a false result may be likely. The use of specialized lab equipment and the need for trained people for the experiments pose additional challenges in PCR-based testing methods. Also, similar problems are observed in other molecular and serological methods. Therefore, biosensor technologies are becoming advantageous with their quick response, high specificity and precision, and low-cost characteristics for SARS-CoV-2 detection. In this paper, we critically review the advances in the development of sensors for the detection of SARS-CoV-2 using two-dimensional (2D) materials. Since 2D materials including graphene and graphene-related materials, transition metal carbides, carbonitrides, and nitrides (MXenes), and transition metal dichalcogenides (TMDs) play key roles in the development of novel and high-performance electrochemical (bio)sensors, this review pushes the sensor technologies against SARS-CoV-2 detection forward and highlights the current trends. First, the basics of SARS-CoV-2 detection are described. Then the structure and the physicochemical properties of the 2D materials are explained, which is followed by the development of SARS-CoV-2 sensors by exploiting the exceptional properties of the 2D materials. This critical review covers most of the published papers in detail from the beginning of the outbreak.

Recent Advances in DNA Nanotechnology-Enabled Biosensors for Virus Detection

Virus-related infectious diseases are serious threats to humans, which makes virus detection of great importance. Traditional virus-detection methods usually suffer from low sensitivity and specificity, are time-consuming, have a high cost, etc. Recently, DNA biosensors based on DNA nanotechnology have shown great potential in virus detection. DNA nanotechnology, specifically DNA tiles and DNA aptamers, has achieved atomic precision in nanostructure construction. Exploiting the programmable nature of DNA nanostructures, researchers have developed DNA nanobiosensors that outperform traditional virus-detection methods. This paper reviews the history of DNA tiles and DNA aptamers, and it briefly describes the Baltimore classification of virology. Moreover, the advance of virus detection by using DNA nanobiosensors is discussed in detail and compared with traditional virus-detection methods. Finally, challenges faced by DNA nanobiosensors in virus detection are summarized, and a perspective on the future development of DNA nanobiosensors in virus detection is also provided.

Optical Biosensors for the Diagnosis of COVID-19 and Other Viruses-A Review

The sudden outbreak of the COVID-19 pandemic led to a huge concern globally because of the astounding increase in mortality rates worldwide. The medical imaging computed tomography technique, whole-genome sequencing, and electron microscopy are the methods generally used for the screening and identification of the SARS-CoV-2 virus. The main aim of this review is to emphasize the capabilities of various optical techniques to facilitate not only the timely and effective diagnosis of the virus but also to apply its potential toward therapy in the field of virology. This review paper categorizes the potential optical biosensors into the three main categories, spectroscopic-, nanomaterial-, and interferometry-based approaches, used for detecting various types of viruses, including SARS-CoV-2. Various classifications of spectroscopic techniques such as Raman spectroscopy, near-infrared spectroscopy, and fluorescence spectroscopy are discussed in the first part. The second aspect highlights advances related to nanomaterial-based optical biosensors, while the third part describes various optical interferometric biosensors used for the detection of viruses. The tremendous progress made by lab-on-a-chip technology in conjunction with smartphones for improving the point-of-care and portability features of the optical biosensors is also discussed. Finally, the review discusses the emergence of artificial intelligence and its applications in the field of bio-photonics and medical imaging for the diagnosis of COVID-19. The review concludes by providing insights into the future perspectives of optical techniques in the effective diagnosis of viruses.

Medical viruses: diagnostic techniques

The recent epidemics and pandemics caused by different viruses such as SARS-CoV-2, monkey pox, H1N1, ebola virus etc. have been a cause of mass destruction in the human race, the biggest decline slope in the global economy and mental trauma. A number of viruses have been discovered that may cause serious problems and to overcome this problem, early diagnosis of the viruses and understanding their infection pattern is a must. Early detection of viruses inside the host provides timely management in a strategic manner. Scientists have developed some effective and efficient methods to detect the viruses. In this review, we have explained a few types of diagnostic techniques: Biosensor based, immunological-based, and molecular-based diagnostic techniques that are prominent methodologies to identify and detect the course of infection related to the medical viruses. In biosensor-based diagnostic technique, an analytical device consisting of biological elements and physicochemical component gives a signal upon detection of viral antigen. In immunological-based diagnostic techniques, enzyme-linked antibodies are utilized to find the particular antiviral antibody or viral antigen in human specimens, and nucleic acid-based diagnostic techniques are based on the principle of amplification of the viral genome.

Insight of smart biosensors for COVID-19: A review

The review discusses the diagnostic application of biosensors as point-of-care devices in the COVID-19 pandemic. Biosensors are important analytical tools that can be used for the robust and effective detection of infectious diseases in real-time. In this current scenario, the utilization of smart, efficient biosensors for COVID-19 detection is increasing and we have included a few smart biosensors such as smart and intelligent based biosensors, plasmonic biosensors, field effect transistor (FET) biosensors, smart optical biosensors, surface enhanced Raman scattering (SERS) biosensor, screen printed electrode (SPE)-based biosensor, molecular imprinted polymer (MIP)-based biosensor, MXene-based biosensor and metal-organic frame smart sensor. Their significance as well as the benefits and drawbacks of each kind of smart sensor are mentioned in depth. Furthermore, we have compiled a list of various biosensors which have been developed across the globe for COVID-19 and have shown promise as commercial detection devices. Significant challenges in the development of effective diagnostic methods are discussed and recommendations have been made for better diagnostic outcomes to manage the ongoing pandemic effectively.

Polarimetric imaging for the detection of synthetic models of SARS-CoV-2: A proof of concept

OBJECTIVE

To conduct a proof-of-concept study of the detection of two synthetic models of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using polarimetric imaging.

APPROACH

Two SARS-CoV-2 models were prepared as engineered lentiviruses pseudotyped with the G protein of the vesicular stomatitis virus, and with the characteristic Spike protein of SARS-CoV-2. Samples were prepared in two biofluids (saline solution and artificial saliva), in four concentrations, and deposited as 5-µL droplets on a supporting plate. The angles of maximal degree of linear polarization (DLP) of light diffusely scattered from dry residues were determined using Mueller polarimetry from87 samples at 405 nm and 514 nm. A polarimetric camera was used for imaging several samples under 380-420 nm illumination at angles similar to those of maximal DLP. Per-pixel image analysis included quantification and combination of polarization feature descriptors in 475 samples.

MAIN RESULTS

The angles (from sample surface) of maximal DLP were 3° for 405 nm and 6° for 514 nm. Similar viral particles that differed only in the characteristic spike protein of the SARS-CoV-2, their corresponding negative controls, fluids, and the sample holder were discerned at 10-degree and 15-degree configurations.

SIGNIFICANCE

Polarimetric imaging in the visible spectrum may help improve fast, non-contact detection and identification of viral particles, and/or other microbes such as tuberculosis, in multiple dry fluid samples simultaneously, particularly when combined with other imaging modalities. Further analysis including realistic concentrations of real SARS-CoV-2 viral particles in relevant human fluids is required. Polarimetric imaging under visible light may contribute to a fast, cost-effective screening of SARS-CoV-2 and other pathogens when combined with other imaging modalities.

Solid-Phase Optical Sensing Techniques for Sensitive Virus Detection

Viral infections can pose a major threat to public health by causing serious illness, leading to pandemics, and burdening healthcare systems. The global spread of such infections causes disruptions to every aspect of life including business, education, and social life. Fast and accurate diagnosis of viral infections has significant implications for saving lives, preventing the spread of the diseases, and minimizing social and economic damages. Polymerase chain reaction (PCR)-based techniques are commonly used to detect viruses in the clinic. However, PCR has several drawbacks, as highlighted during the recent COVID-19 pandemic, such as long processing times and the requirement for sophisticated laboratory instruments. Therefore, there is an urgent need for fast and accurate techniques for virus detection. For this purpose, a variety of biosensor systems are being developed to provide rapid, sensitive, and high-throughput viral diagnostic platforms, enabling quick diagnosis and efficient control of the virus's spread. Optical devices, in particular, are of great interest due to their advantages such as high sensitivity and direct readout. The current review discusses solid-phase optical sensing techniques for virus detection, including fluorescence-based sensors, surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS), optical resonators, and interferometry-based platforms. Then, we focus on an interferometric biosensor developed by our group, the single-particle interferometric reflectance imaging sensor (SP-IRIS), which has the capability to visualize single nanoparticles, to demonstrate its application for digital virus detection.

Rational design of multivalent biosensor surfaces to enhance viral particle capture

Viral particles bind to receptors through multivalent protein interactions. Such high avidity interactions on sensor surfaces are less studied. In this work, three polyelectrolytes that can form biosensing surfaces with different interfacial characteristics in probe density and spatial arrangement were designed. Quartz crystal microbalance, interferometry and atomic force microscopy were used to study their surface density and binding behaviors with proteins and virus particles. A multivalent adsorption kinetic model was developed to estimate the number of bonds from the viral particles bound to the polyelectrolyte surfaces. Experimental results show that the heterogeneous 3D surface with jagged forest-like structure enhances the virus capture ability by maximizing the multivalent interactions. As a proof of concept, specific coronavirus detection was achieved in spiked swab samples. These results indicate the importance of both probe density and their spatial arrangement on the sensing performance, which could be used as a guideline for rational biosensing surface design.

Bifunctional Au@Pt/Au nanoparticles as electrochemiluminescence signaling probes for SARS-CoV-2 detection

A novel immunosensor based on electrochemiluminescence resonance energy transfer (ECL-RET) for the sensitive determination of N protein of the SARS-CoV-2 coronavirus is described. For this purpose, bifunctional core@shell nanoparticles composed of a Pt-coated Au core and finally decorated with small Au inlays (Au@Pt/Au NPs) have been synthesized to act as ECL acceptor, using [Ru (bpy)₃]²⁺ as ECL donor. These nanoparticles are efficient signaling probes in the immunosensor developed. The proposed ECL-RET immunosensor has a wide linear response to the concentration of N protein of the SARS-CoV-2 coronavirus with a detection limit of 1.27 pg/mL. Moreover, it has a high stability and shows no response to other proteins related to different virus. The immunosensor has achieved the quantification of N protein of the SARS-CoV-2 coronavirus in saliva samples. Results are consistent with those provided by a commercial colorimetric ELISA kit. Therefore, the developed immunosensor provides a feasible and reliable tool for early and effective detection of the virus to protect the population.

Emerging trends in point-of-care biosensing strategies for molecular architectures and antibodies of SARS-CoV-2

COVID-19, a highly contagious viral infection caused by the occurrence of severe acute respiratory syndrome coronavirus (SARS-CoV-2), has turned out to be a viral pandemic then ravaged many countries worldwide. In the recent years, point-of-care (POC) biosensors combined with state-of-the-art bioreceptors, and transducing systems enabled the development of novel diagnostic tools for rapid and reliable detection of biomarkers associated with SARS-CoV-2. The present review thoroughly summarises and discusses various biosensing strategies developed for probing SARS-CoV-2 molecular architectures (viral genome, S Protein, M protein, E protein, N protein and non-structural proteins) and antibodies as a potential diagnostic tool for COVID-19. This review discusses the various structural components of SARS-CoV-2, their binding regions and the bioreceptors used for recognizing the structural components. The various types of clinical specimens investigated for rapid and POC detection of SARS-CoV-2 is also highlighted. The importance of nanotechnology and artificial intelligence (AI) approaches in improving the biosensor performance for real-time and reagent-free monitoring the biomarkers of SARS-CoV-2 is also summarized. This review also encompasses existing practical challenges and prospects for developing new POC biosensors for clinical monitoring of COVID-19.

CoVSense: Ultrasensitive Nucleocapsid Antigen Immunosensor for Rapid Clinical Detection of Wildtype and Variant SARS-CoV-2

The widespread accessibility of commercial/clinically-viable electrochemical diagnostic systems for rapid quantification of viral proteins demands translational/preclinical investigations. Here, Covid-Sense (CoVSense) antigen testing platform; an all-in-one electrochemical nano-immunosensor for sample-to-result, self-validated, and accurate quantification of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid (N)-proteins in clinical examinations is developed. The platform's sensing strips benefit from a highly-sensitive, nanostructured surface, created through the incorporation of carboxyl-functionalized graphene nanosheets, and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conductive polymers, enhancing the overall conductivity of the system. The nanoengineered surface chemistry allows for compatible direct assembly of bioreceptor molecules. CoVSense offers an inexpensive (<$2 kit) and fast/digital response (<10 min), measured using a customized hand-held reader (<$25), enabling data-driven outbreak management. The sensor shows 95% clinical sensitivity and 100% specificity (Ct<25), and overall sensitivity of 91% for combined symptomatic/asymptomatic cohort with wildtype SARS-CoV-2 or B.1.1.7 variant (N = 105, nasal/throat samples). The sensor correlates the N-protein levels to viral load, detecting high Ct values of ≈35, with no sample preparation steps, while outperforming the commercial rapid antigen tests. The current translational technology fills the gap in the workflow of rapid, point-of-care, and accurate diagnosis of COVID-19.

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.

A performance comparison of heterostructure surface plasmon resonance biosensor for the diagnosis of novel coronavirus SARS-CoV-2

This paper presents a performance comparison of heterostructure surface plasmon resonance (SPR) biosensors for the application of Novel Coronavirus SARS-CoV-2 diagnosis. The comparison is performed and compared with the existing literature based on the performance parameters in terms of several prisms such as BaF₂, BK₇, CaF₂, CsF, SF₆, and SiO₂, several adhesion layers such as TiO₂, Chromium, plasmonic metals such as Ag, Au, and two-dimensional (2D) transition metal dichalcogenides materials such as BP, Graphene, PtSe₂ MoS₂, MoSe₂, WS₂, WSe₂. To study the performance of the heterostructure SPR sensor, the transfer matrix method is applied, and to analyses, the electric field intensity near the graphene-sensing layer contact, the finite-difference time-domain approach is utilized. Numerical results show that the heterostructure comprised of CaF₂/TiO₂/Ag/BP/Graphene/Sensing-layer has the best sensitivity and detection accuracy. The proposed sensor has an angle shift sensitivity of 390°/refractive index unit (RIU). Furthermore, the sensor achieved a detection accuracy of 0.464, a quality factor of 92.86/RIU, a figure of merit of 87.95, and a combined sensitive factor of 85.28. Furthermore, varied concentrations (0-1000 nM) of biomolecule binding interactions between ligands and analytes have been observed for the prospects of diagnosis of the SARS-CoV-2 virus. Results demonstrate that the proposed sensor is well suited for real-time and label-free detection particularly SARS-CoV-2 virus detection.

Nanotechnology-Assisted Biosensors for the Detection of Viral Nucleic Acids: An Overview

The accurate and rapid diagnosis of viral diseases has garnered increasing attention in the field of biosensors. The development of highly sensitive, selective, and accessible biosensors is crucial for early disease detection and preventing mortality. However, developing biosensors optimized for viral disease diagnosis has several limitations, including the accurate detection of mutations. For decades, nanotechnology has been applied in numerous biological fields such as biosensors, bioelectronics, and regenerative medicine. Nanotechnology offers a promising strategy to address the current limitations of conventional viral nucleic acid-based biosensors. The implementation of nanotechnologies, such as functional nanomaterials, nanoplatform-fabrication techniques, and surface nanoengineering, to biosensors has not only improved the performance of biosensors but has also expanded the range of sensing targets. Therefore, a deep understanding of the combination of nanotechnologies and biosensors is required to prepare for sanitary emergencies such as the recent COVID-19 pandemic. In this review, we provide interdisciplinary information on nanotechnology-assisted biosensors. First, representative nanotechnologies for biosensors are discussed, after which this review summarizes various nanotechnology-assisted viral nucleic acid biosensors. Therefore, we expect that this review will provide a valuable basis for the development of novel viral nucleic acid biosensors.

Recent Progress on Optical Biosensors Developed for Nucleic Acid Detection Related to Infectious Viral Diseases

Optical biosensors have many advantages over traditional analytical methods. They enable the identification of several biological and chemical compounds directly, instantly, and without the need of labels. Their benefits include excellent specificity, sensitivity, compact size, and low cost. In this review, the main focus is placed on the nucleic acid-based optical biosensor technologies, including colorimetric, fluorescence, surface plasmon resonance (SPR), Evanescent-Wave Optical, Fiber optic and bioluminescent optical fibre. The fundamentals of each type of biosensor are briefly explained, and particular emphasis has been placed on the achievements which have been gained in the last decade on the field of diagnosis of infectious viral diseases. Concluding remarks concerning the perspectives of further developments are discussed.

Aptamer-based rapid diagnosis for point-of-care application

Aptasensors have attracted considerable interest and widespread application in point-of-care testing worldwide. One of the biggest challenges of a point-of-care (POC) is the reduction of treatment time compared to central facilities that diagnose and monitor the applications. Over the past decades, biosensors have been introduced that offer more reliable, cost-effective, and accurate detection methods. Aptamer-based biosensors have unprecedented advantages over biosensors that use natural receptors such as antibodies and enzymes. In the current epidemic, point-of-care testing (POCT) is advantageous because it is easy to use, more accessible, faster to detect, and has high accuracy and sensitivity, reducing the burden of testing on healthcare systems. POCT is beneficial for daily epidemic control as well as early detection and treatment. This review provides detailed information on the various design strategies and virus detection methods using aptamer-based sensors. In addition, we discussed the importance of different aptamers and their detection principles. Aptasensors with higher sensitivity, specificity, and flexibility are critically discussed to establish simple, cost-effective, and rapid detection methods. POC-based aptasensors' diagnostic applications are classified and summarised based on infectious and infectious diseases. Finally, the design factors to be considered are outlined to meet the future of rapid POC-based sensors.

Single-chirality of single-walled carbon nanotubes (SWCNTs) through chromatography and its potential biological applications

Gel chromatography is used to separate single-chirality and selective-diameter SWCNTs. We also explore the use of photothermal therapy and biosensor applications based on single-chirality, selected-diameter, and unique geometric shape.

Application of nanomaterials against SARS-CoV-2: An emphasis on their usefulness against emerging variants of concern

Researchers are now looking to nanomaterials to fight serious infectious diseases that cause outbreaks and even pandemics. SARS-CoV-2 brought chaos to almost every walk of life in the past 2 years and has challenged every available treatment method. Although vaccines were developed in no time against it, the most pressing issue was the emergence of variants of concern arising because of the rapidly evolving viral strains. The higher pathogenicity and, in turn, the higher mortality rate of infections caused by these variants renders the existing vaccines less effective and the effort to produce further vaccines a costly endeavor. While several techniques, such as immunotherapy and repurposed pharmaceutical research, are being studied to minimize viral infection, the fundamentals of nanotechnology must also be considered to enhance the anti-SARS-CoV-2 efforts. For instance, silver nanoparticles (AgNPs) have been applied against SARS-CoV-2 effectively. Similarly, nanomaterials have been tested in masks, gloves, and disinfectants to aid in controlling SARS-CoV-2. Nanotechnology has also contributed to diagnoses such as rapid and accurate detection and treatment such as the delivery of mRNA vaccines and other antiviral agents into the body. The development of polymeric nanoparticles has been dubbed a strategy of choice over traditional drugs because of their tunable release kinetics, specificity, and multimodal drug composition. Our article explores the potential of nanomaterials in managing the variants of concern. This will be achieved by highlighting the inherent ability of nanomaterials to act against the virus on fronts such as inhibition of SARS-CoV-2 entry, inhibition of RNA replication in SARS-CoV-2, and finally, inhibition of their release. In this review, a detailed discussion on the potential of nanomaterials in these areas will be tallied with their potential against the current and emerging future variants of concern.

Rapid Conductometric Detection of SARS-CoV-2 Proteins and Its Variants Using Molecularly Imprinted Polymer Nanoparticles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) biosensors have captured more attention than the conventional methodologies for SARS-CoV-2 detection due to having cost-effective platforms and fast detection. However, these reported SARS-CoV-2 biosensors suffer from drawbacks including issues in detection sensitivity, degradation of biomaterials on the sensor's surface, and incapability to reuse the biosensors. To overcome these shortcomings, molecularly imprinted polymer nanoparticles (nanoMIPs) incorporated conductometric biosensor for highly accurate, rapid, and selective detection of two model SARS-CoV-2 proteins: (i) receptor binding domain (RBD) of the spike (S) glycoprotein and (ii) full length trimeric spike protein are introduced. In addition, these biosensors successfully responded to several other SARS-CoV-2 RBD spike protein variants including Alpha, Beta, Gamma, and Delta. Our conductometric biosensor selectively detects the two model proteins and SARS-CoV-2 RBD spike protein variant samples in real-time with sensitivity to a detection limit of 7 pg mL-1 within 10 min of sample incubation. A battery-free, wireless near-field communication (NFC) interface is incorporated with the biosensor for fast and contactless detection of SARS-CoV-2 variants. The smartphone enabled real-time detection and on-screen rapid result for SARS-CoV-2 variants can curve the outbreak due to its ability to alert the user to infection in real time.

Surface Plasmon Resonance Sensitivity Enhancement Based on Protonated Polyaniline Films Doped by Aluminum Nitrate

Complex composite films based on polyaniline (PANI) doped hydrochloric acid (HCl) incorporated with aluminum nitrate (Al(NO₃)₃) on Au-layer were designed and synthesized as a surface plasmon resonance (SPR) sensing device. The physicochemical properties of (PANI-HCl)/Al(NO₃)₃ complex composite films were studied for various Al(NO₃)₃ concentrations (0, 2, 4, 8, 16, and 32 wt.%). The refractive index of the (PANI-HCl)/Al(NO₃)₃ complex composite films increased continuously as Al(NO₃)₃ concentrations increased. The electrical conductivity values increased from 5.10 µS/cm to 10.00 µS/cm as Al(NO₃)₃ concentration increased to 32 wt.%. The sensitivity of the SPR sensing device was investigated using a theoretical approach and experimental measurements. The theoretical system of SPR measurement confirmed that increasing Al(NO₃)₃ in (PANI-HCl)/Al(NO₃)₃ complex composite films enhanced the sensitivity from about 114.5 [Deg/RIU] for Au-layer to 159.0 [Deg/RIU] for Au-((PANI-HCl)/Al(NO₃)₃ (32 wt.%)). In addition, the signal-to-noise ratio for Au-layer was 3.95, which increased after coating by (PANI-HCl)/Al(NO₃)₃ (32 wt.%) complex composite layer to 8.82. Finally, we conclude that coating Au-layer by (PANI-HCl)/Al(NO₃)₃ complex composite films enhances the sensitivity of the SPR sensing device.

Recent Development in Plasmonic Nanobiosensors for Viral DNA/RNA Biomarkers

Recently, due to the coronavirus pandemic, the need for early diagnosis of infectious diseases, including viruses, is emerging. Though early diagnosis is essential to prevent infection and progression to severe illness, there are few technologies that accurately measure low concentrations of biomarkers. Plasmonic nanomaterials are attracting materials that can effectively amplify various signals, including fluorescence, Raman, and other optical and electromagnetic output. In this review, we introduce recently developed plasmonic nanobiosensors for measuring viral DNA/RNA as potential biomarkers of viral diseases. In addition, we discuss the future perspective of plasmonic nanobiosensors for DNA/RNA detection. This review is expected to help the early diagnosis and pathological interpretation of viruses and other diseases.

Aptamer-based biosensors for virus protein detection

Virus threatens life health seriously. The accurate early diagnosis of the virus is vital for clinical control and treatment of virus infection. Aptamers are small single-stranded oligonucleotides (DNAs or RNAs). In this review, we summarized aptasensors for virus detection in recent years according to the classification of the viral target protein, and illustrated common detection mechanisms in the aptasensors (colorimetry, fluorescence assay, surface plasmon resonance (SPR), surface-enhanced raman spectroscopy (SERS), electrochemical detection, and field-effect transistor (FET)). Furthermore, aptamers against different target proteins of viruses were summarized. The relationships between the different biomarkers of the viruses and the detection methods, and their performances were revealed. In addition, the challenges and future directions of aptasensors were discussed. This review will provide valuable references for constructing on-site aptasensors for detecting viruses, especially the SARS-CoV-2.

Recent trends and advancements in electrochemiluminescence biosensors for human virus detection

Researchers are constantly looking to find new techniques of virus detection that are sensitive, cost-effective, and accurate. Additionally, they can be used as a point-of-care (POC) tool due to the fact that the populace is growing at a quick tempo, and epidemics are materializing greater often than ever. Electrochemiluminescence-based (ECL) biosensors for the detection of viruses have become one of the most quickly developing sensors in this field. Thus, we here focus on recent trends and developments of these sensors with regard to virus detection. Also, quantitative analysis of various viruses (e.g., Influenza virus, SARS-CoV-2, HIV, HPV, Hepatitis virus, and Zika virus) with a specific interest in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was introduced from the perspective of the biomarker and the biological receptor immobilized on the ECL-based sensors, such as nucleic acids-based, immunosensors, and other affinity ECL biosensors.

A Short Review Comparing Carbon-Based Electrochemical Platforms With Other Materials For Biosensing SARS-Cov-2

Due to the 2019 SARS-CoV-2 outbreak, low-cost, fast, and user-friendly diagnostic kits for biosensing SARS-CoV-2 in real samples employing multiple working electrodes are in high demand. Choosing SARS-CoV-2 detecting electrodes is difficult because each has advantages and limitations. Carbon-based electrochemical sensing applications have attracted attention from the electrochemical sensing community because carbon and carbon-based materials have been a godsend for testing utilizing an electrochemical platform. Carbon working electrode electrochemical platforms are cost-effective and fast. Covid-sensors use carbon-based materials because they can be easily changed (with inorganic and organic functionalities), have quick response kinetics, and are chemically resistant. Covid-19 sensing materials include graphene and graphite. This review explains how carbon materials have been employed in N and S protein electrochemical detection. Here, we discussed a carbon-based technology for SARS-CoV-2 biosensing. We've compared carbon-based electrochemical sensing to different electrodes.

A systematic review of the advancement on colorimetric nanobiosensors for SARS-CoV-2 detection

The current pandemic of the acute severe respiratory syndrome coronavirus 2 (SARS-CoV-2) killed about 6.4 million and infected more than 600 million individuals by august of 2022, and researchers worldwide are searching for fast and selective approaches for this virus detection. Colorimetric biosensors are an excellent alternative because they are sensitive, simple, fast, and low-cost for rapid detection of SARS-CoV-2 compared to standard Enzyme-linked immunosorbent assay (ELISA) and Polymerase Chain Reaction (PCR) techniques. This study systematically searched and reviewed literature data related to colorimetric biosensors in detecting SARS-CoV-2 viruses, recovered from the Scopus (n = 16), Web of Science (n = 19), PubMed (n = 19), and Science Direct (n = 17) databases totalizing n = 71 articles. Data were analyzed for the type of nanomaterial, biorecognition material at the detection limit (LOD), and devices designed for diagnostics. The most applied nanomaterial were gold nanoparticles, in their original form and hybrid in quantum dots and core-shell. In addition, we show high specificity in point-of-care (POC) diagnostic devices as a faster and cheaper alternative for clinical diagnosis. Finally, the highlights of the colorimetric biosensor developed for diagnostic devices applied in swabs, surgical masks, and lateral flow immunoassays were presented.

Recent Advances of Optical Sensors for Copper Ion Detection

A trace element copper (Cu²⁺) ion is the third most plentiful metal ion that necessary for all living organisms and playing a critical role in several processes. Nonetheless, according to cellular needs, deficient or excess Cu²⁺ ion cause various diseases. For all these reasons, optical sensors have been focused rapid Cu²⁺ ion detection in real-time with high selectivity and sensitivity. Optical sensors can measure fluorescence in the refractive index-adsorption from the relationships between light and matter. They have gained great attention in recent years due to the excellent advantages of simple and naked eye recognition, real-time detection, low cost, high specificity against analytes, a quick response, and the need for less complex equipment in analysis. This review aims to show the significance of Cu²⁺ ion detection and electively current trends in optical sensors. The integration of optical sensors with different systems, such as microfluidic systems, is mentioned, and their latest studies in medical and environmental applications also are depicted. Conclusions and future perspectives on these advances is added at the end of the review.

The Pivotal Role of Quantum Dots-Based Biomarkers Integrated with Ultra-Sensitive Probes for Multiplex Detection of Human Viral Infections

The spread of viral diseases has caused global concern in recent years. Detecting viral infections has become challenging in medical research due to their high infectivity and mutation. A rapid and accurate detection method in biomedical and healthcare segments is essential for the effective treatment of pathogenic viruses and early detection of these viruses. Biosensors are used worldwide to detect viral infections associated with the molecular detection of biomarkers. Thus, detecting viruses based on quantum dots biomarkers is inexpensive and has great potential. To detect the ultrasensitive biomarkers of viral infections, QDs appear to be a promising option as biological probes, while physiological components have been used directly to detect multiple biomarkers simultaneously. The simultaneous measurement of numerous clinical parameters of the same sample volume is possible through multiplex detection of human viral infections, which reduces the time and cost required to record any data point. The purpose of this paper is to review recent studies on the effectiveness of the quantum dot as a detection tool for human pandemic viruses. In this review study, different types of quantum dots and their valuable properties in the structure of biomarkers were investigated. Finally, a vision for recent advances in quantum dot-based biomarkers was presented, whereby they can be integrated into super-sensitive probes for the multiplex detection of human viral infections.

Bioactive hybrid metal-organic framework (MOF)-based nanosensors for optical detection of recombinant SARS-CoV-2 spike antigen

Fast, efficient, and accurate detection of SARS-CoV-2 spike antigen is pivotal to control the spread and reduce the mortality of COVID-19. Nevertheless, the sensitivity of available nanobiosensors to detect recombinant SARS-CoV-2 spike antigen seems insufficient. As a proof-of-concept, MOF-5/CoNi₂S₄ is developed as a low-cost, safe, and bioactive hybrid nanostructure via the one-pot high-gravity protocol. Then, the porphyrin, H₂TMP, was attached to the surface of the synthesized nanomaterial to increase the porosity for efficient detection of recombinant SARS-CoV-2 spike antigen. AFM results approved roughness in different ranges, including 0.54 to 0.74 μm and 0.78 to ≈0.80 μm, showing good physical interactions with the recombinant SARS-CoV-2 spike antigen. MTT assay was performed and compared to the conventional synthesis methods, including hydrothermal, solvothermal, and microwave-assisted methods. The synthesized nanodevices demonstrated above 88% relative cell viability after 24 h and even 48 h of treatment. Besides, the ability of the synthesized nanomaterials to detect the recombinant SARS-CoV-2 spike antigen was investigated, with a detection limit of 5 nM. The in-situ synthesized nanoplatforms exhibited low cytotoxicity, high biocompatibility, and appropriate tunability. The fabricated nanosystems seem promising for future surveys as potential platforms to be integrated into biosensors.

Photonic Quasi-Crystal Fiber-Based Plasmonic Biosensor: a Platform for Detection of Coronavirus

Since the coronavirus pandemic began, research groups worldwide developed diagnostic tests. One of the promising platforms for testing is an optical and plasmonic biosensor. Localized surface plasmon resonances owing to their highly concentrated field intensity provide highly sensitive devices. A beneficial approach to excite localized surface plasmon modes for field-based applications is using photonic crystal fibers while photonic quasi-crystals demonstrate a higher order of symmetry, the more isotropic Brillouin zone, and the easier achievement of photonic bandgap as compared with conventional photonic crystals. In this work, by exploiting a photonic quasi-crystal fiber, we are designing a surface plasmon resonance biosensor for the on-chip and real-time detection of coronaviruses. In our miniaturized design, a thin gold layer is employed on the outer layer of an air hole of a photonic quasi-crystal fiber with a 12-fold symmetry where the leakage of the fiber core mode can excite the surface plasmon resonance mode on the gold. According to three-dimensional finite-difference time-domain simulations, the proposed biosensor shows the sensitivity of 1172 nm/RIU in the detection of coronaviruses within the saliva. Moreover, the smallest detection limit obtained in the simulation is about 12 nm. These promising results altogether indicate that this reconfigurable and lab-on-a-chip platform can potentially be used in the detection of all kinds of coronaviruses.

Plasmonic Micro-Channel Assisted Photonic Crystal Fiber Based Highly Sensitive Sensor for Multi-Analyte Detection

A dual-channel propagation controlled photonic crystal fiber (PCF)-based plasmonic sensor was presented to detect multiple analytes simultaneously. Plasmonic micro-channels were placed on the outer surface of the PCF, which facilitates an easy sensing mechanism. The sensor was numerically investigated by the finite element method (FEM) with the perfectly matched layer (PML) boundary conditions. The proposed sensor performances were analyzed based on optimized sensor parameters, such as confinement loss, resonance coupling, resolution, sensitivity, and figure of merit (FOM). The proposed sensor showed a maximum wavelength sensitivity (WS) of 25,000 nm/refractive index unit (RIU) with a maximum sensor resolution (SR) of 4.0 × 10⁻⁶ RIU for channel 2 (Ch-2), and WS of 3000 nm/RIU with SR of 3.33 × 10⁻⁵ RIU for channel 1 (Ch-1). To the best of our knowledge, the proposed sensor exhibits the highest WS compared with the previously reported multi-analyte based PCF surface plasmon resonance (SPR) sensors. The proposed sensor could detect the unknown analytes within the refractive index (RI) range of 1.32 to 1.39 in the visible to near infrared region (550 to 1300 nm). In addition, the proposed sensor offers the maximum Figure of Merit (FOM) of 150 and 500 RIU⁻¹ with the limit of detection (LOD) of 1.11 × 10⁻⁸ RIU²/nm and 1.6 × 10⁻¹⁰ RIU²/nm for Ch-1 and Ch-2, respectively. Due to its highly sensitive nature, the proposed multi-analyte PCF SPR sensor could be a prominent candidate in the field of biosensing to detect biomolecule interactions and chemical sensing.