Plasmonic nanorice antenna on triangle nanoarray for surface-enhanced Raman scattering detection of hepatitis B virus DNA

Advances in rapid point-of-care virus testing

Outbreaks of viral diseases seriously jeopardize people's health and cause huge economic losses. At the same time, virology provides a new perspective for biology, molecular biology and cancer research, and it is important to study the discovered viruses with potential applications. Therefore, the development of immediate and rapid viral detection methods for the prevention and treatment of viral diseases as well as the study of viruses has attracted extensive attention from scientists. With the continuous progress of science and technology, especially in the field of bioanalysis, a series of new detection techniques have been applied to the on-site rapid detection of viruses, which has become a powerful approach for human beings to fight against viruses. In this paper, the latest research progress of rapid point-of-care detection of viral nucleic acids, antigens and antibodies is presented. In addition, the advantages and disadvantages of these technologies are discussed from the perspective of practical application requirements. Finally, the problems and challenges faced by rapid viral detection methods and their development prospects are discussed.

Trace analysis of food by surface-enhanced Raman spectroscopy combined with molecular imprinting technology: Principle, application, challenges, and prospects

Surface-enhanced Raman spectroscopy (SERS) is a rapid detection method with high sensitivity and simple pretreatment, but can be affected by interference from matrix components. By incorporating molecularly imprinted polymers (MIPs) that recognize specific targets, MIP-SERS sensors effectively overcome the interference of complex matrices and offer improved stability and sensitivity. This review provides a comprehensive understanding of the applications of MIP-SERS sensors for the detection of trace toxic substances in food. The underlying mechanism and development of SERS technology and the principle and classification of MIPs technology are discussed. Furthermore, the types of MIP-SERS sensors are introduced, with their advantages and disadvantages systematically illustrated. Recent advances in MIP-SERS technology for the detection of mycotoxins, additives, prohibited dyes, pesticides, veterinary drug residues, and other hazardous substances in food are highlighted. Finally, this review discusses the challenges associated with MIP-SERS technology and proposes future development prospects.

Raman Scattering-Based Optical Sensing Of Chronic Liver Diseases

Chronic liver diseases (CLDs) are a major public health problem. Despite the progress achieved in fighting against viral hepatitis, the emergence of non-alcoholic fatty liver disease might pose a serious challenge to the public's health in the coming decades. Medical management of CLDs represents a substantial burden on the public health infrastructures. The health care cost of these diseases is an additional burden that weighs heavily on the economies of developing countries. Effective management of CLDs requires the adoption of reliable and cost-effective screening and diagnosing methods to ensure early detection and accurate clinical assessment of these diseases. Vibrational spectroscopies have emerged as universal analytical methods with promising applications in various industrial and biomedical fields. These revolutionary analytical techniques rely on analyzing the interaction between a light beam and the test sample to generate a spectral fingerprint. This latter is defined by the analyte's chemical structure and the molecular vibrations of its functional groups. Raman spectroscopy and surface-enhanced Raman spectroscopy have been used in combination with various chemometric tests to diagnose a wide range of malignant, metabolic and infectious diseases. The aim of the current review is to cast light on the use of these optical sensing methods in the diagnosis of CLDs. The vast majority of research works that investigated the potential application of these spectroscopic techniques in screening and detecting CLDs were discussed here. The advantages and limitations of these modern analytical methods, as compared with the routine and gold standard diagnostic approaches, were also reviewed in details.

Diagnostic plasmonic sensors: opportunities and challenges

The medical fraternity is currently burgeoned and stressed with a huge rush of patients who have inflammatory conditions, metabolite diseases, and cardiovascular diseases. In these circumstances, advanced sensing technologies could have a huge impact on the quality of life of patients. Given plasmonic resonance effects significantly improve the ability to rapidly and accurately detect biological markers, plasmonic technology is harnessed to develop a fast and accurate diagnosis that can provide timely intervention with the diseases and can also aid the recovery process by complementing the therapy stage. In this short review, we provide an overlook of how the field of plasmonic sensing has revolutionized the field of medical diagnostics. This article reviews the fundamentals and development of plasmonics. In addition, we highlight the sensitivity of various SPR and LSPR sensors. The chemistry for functionalizing plasmonic sensors is also discussed. This review also outlines some general suggestions for future directions that we feel might be useful to advance our understanding of the universe or speed up the development of plasmonic sensors in the future.

Genosensors as an alternative diagnostic sensing approaches for specific detection of various certain viruses: a review of common techniques and outcomes

Viral infections are responsible for the deaths of millions of people throughout the world. Since outbreak of highly contagious and mutant viruses such as contemporary sars-cov-2 pandemic, has challenged the conventional diagnostic methods, the entity of a thoroughly sensitive, specific, rapid and inexpensive detecting technique with minimum level of false-positivity or -negativity, is desperately needed more than any time in the past decades. Biosensors as minimized devices could detect viruses in simple formats. So far, various nucleic acid, immune- and protein-based biosensors were designed and tested for recognizing the genome, antigen, or protein level of viruses, respectively; however, nucleic acid-based sensing techniques, which is the foundation of constructing genosensors, are preferred not only because of their ultra-sensitivity and applicability in the early stages of infections but also for their ability to differentiate various strains of the same virus. To date, the review articles related to genosensors are just confined to particular pathogenic diseases; In this regard, the present review covers comprehensive information of the research progress of the electrochemical, optical, and surface plasmon resonance (SPR) genosensors that applied for human viruses' diseases detection and also provides a well description of viruses' clinical importance, the conventional diagnosis approaches of viruses and their disadvantages. This review would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

Surface-enhanced Raman spectroscopic analysis of centrifugally filtered HBV serum samples

BACKGROUND

Raman spectroscopy is an effective tool for detecting and discriminating centrifugally filtered hepatitis B virus serum and centrifugally filtered  control serum.

OBJECTIVES

The purpose of current study is to separate high molecular weight fractions from low molecular weight fractions present hepatitis B serum to increase the disease diagnostic ability of surface enhanced Raman spectroscopy (SERS).

METHODS

Clinically diagnosed centrifugally filtered serum samples of hepatitis B patients are subjected for surface enhanced Raman spectroscopy (SERS) in comparison with centrifugally filtered serum samples of healthy individuals by using silver nanoparticles (Ag-NPs) as SERS substrates. Some SERS spectral features are solely observed in centrifugally filtered serum samples of hepatitis B and some SERS spectral are solely observed in centrifugally filtered serum samples of healthy individuals. The diagnostic ability of SERS is further enhanced with different statistical techniques like principal component analysis (PCA), partial least square discriminant analysis (PLS-DA) and partial least square regression analysis (PLSR) have applied.

RESULTS

The disease biomarkers of hepatitis B are more pronounced after their centrifugation as compared with uncentrifuged form. Statistical tools like principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA) clearly differentiated centrifugally filtered serum samples of hepatitis B from centrifugally filtered serum samples of healthy individuals. Furthermore, partial least square regression analysis (PLSR) has been applied for predicting unknown viral load of centrifugally filtered serum sample of hepatitis B.

CONCLUSION

SERS technique along with chemometric tools have successfully differentiated centrifugally filtered serum samples of hepatitis B from centrifugally filtered serum samples of healthy individuals. The centrifugal filtration process has increased the differentiation accuracy of PLS-DA in terms of percentage 98% and regression accuracy of PLSR regression analysis in terms of RMSEP (0.30 IU/mL) of this diagnostic method as compared with that of uncentrifuged method.

Layered filter paper-silver nanoparticle-ZIF-8 composite for efficient multi-mode enrichment and sensitive SERS detection of thiram

A SERS substrate FP/Ag/ZIF-8 composed of filter paper (FP), silver nanoparticles (AgNPs) and zeolitic imidazolate framework (ZIF-8) film arranged in a layered structure was developed for sensitive detection of pesticide thiram in various samples. Roles of these components in analyte adsorption and Raman signal enhancement were studied using a pesticide intermediate 4-Aminothiophenol (4-ATP) as the probe. The substrate showed high adsorption and optimized SERS response with thick metal organic framework (MOF) coating (125 nm), which is different from previous reported plasmonic particle-MOF composite substrate, where thinnest MOF coating produced the strongest SERS signal. Detection limit for 4-ATP improved 1000-fold on FP/Ag/ZIF-8 (3 pM) compared with that on FP/Ag (3 nM). Importantly, the FP/Ag/ZIF-8 with porous and flexible property can efficiently capture pesticide thiram in different real samples using soaking, filtration or swabbing operation. The subsequent SERS detection of thiram showed advantages of low detection limit (soaking, LOD: 0.04 nM in lake water), fast detection (filtration, within 1 min in peach juice) and suitable for curve surface analysis (swabbing, LOD: 0.1 ng/cm² on apple peel), respectively. The substrate also displayed good reproducibility, high stability and size-selective response for thiram detection. Such a layered plasmonic particle/MOF hybrid may hold great promise for toxicant analysis in environment and food.

Rapid Detection of Virus Nucleic Acid via Isothermal Amplification on Plasmonic Enhanced Digitizing Biosensor

Rapid detection for infectious diseases is highly demanded in diagnosis and infection prevention. In this work, we introduced a plasmonic enhanced digitizing biosensor for the rapid detection of nucleic acids. The sensor successfully achieved the detection of loop-mediated isothermal amplification for the hepatitis virus in this work. The sensor comprised a nanodisc array and Bst polymerases conjugated on the rough surface of a nanodisc. The rough surface of the nanodisc provided plasmonic hot spots to enhance the fluorescence signal. The virus DNA was detected by conducting a modified loop-mediated isothermal amplification with fluorescence resonance energy transfer reporter conjugated primers on the sensor. The modified isothermal amplification improved the signal contrast and detection time compared to the original assay. By integrating the modified amplification assay and plasmonic enhancement sensor, we achieved rapid detection of the hepatitis virus. Nucleic acid with a concentration of 10⁻³ to 10⁻⁴ mg/mL was detected within a few minutes by our design. Our digitizing plasmonic nanoarray biosensor also showed 20–30 min earlier detection compared to conventional loop-mediated isothermal amplification sensors.

Attomolar Sensitive Magnetic Microparticles and a Surface-Enhanced Raman Scattering-Based Assay for Detecting SARS-CoV-2 Nucleic Acid Targets

Highly sensitive, reliable assays with strong multiplexing capability for detecting nucleic acid targets are significantly important for diagnosing various diseases, particularly severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The nanomaterial-based assay platforms suffer from several critical issues such as non-specific binding and highly false-positive results. In this paper, to overcome such limitations, we reported sensitive and remarkably reproducible magnetic microparticles (MMPs) and a surface-enhanced Raman scattering (SERS)-based assay using stable silver nanoparticle clusters for detecting viral nucleic acids. The MMP-SERS-based assay exhibited a sensitivity of 1.0 fM, which is superior to the MMP-fluorescence-based assay. In addition, in the presence of anisotropic Ag nanostructures (nanostars and triangular nanoplates), the assay exhibited greatly enhanced sensitivity (10 aM) and excellent signal reproducibility. This assay platform intrinsically eliminated the non-specific binding that occurs in the target detection step, and the controlled formation of stable silver nanoparticle clusters in solution enabled the remarkable reproducibility of the results. These findings indicate that this assay can be employed for future practical bioanalytical applications.

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

Amplification-free smartphone-based attomolar HBV detection

Classical gold standard HBV detection relies on expensive devices and complicated procedures, thus is always restricted in large-scale hospitals and centers for disease control and prevention. To extend HBV detection to primary clinics especially in underdeveloped areas, we design amplification-free smartphone-based attomolar HBV detecting technique based on single molecule sensing. Verified by synthesized HBV target DNA, this technique reaches a detection limit at attomolar concentration (100 aM); and verified by 110 clinical samples, it also reaches a rather high sensitivity of 10⁴ copy/mL (≈2000 IU/mL) with a high accuracy of 93.64% certificated by gold standard HBV detecting devices. Besides, this technique can quantify HBV viral load in 70 min only using portable and inexpensive devices as well as simple operations. Because of its cost-effective, field-portable and operable design, highly sensitive and selective detecting capability and wireless data connectivity, this technique can be potentially used in mobile HBV diagnoses and share HBV epidemic information especially in resource limited situations.

Strand Displacement Amplification Assisted CRISPR-Cas12a Strategy for Colorimetric Analysis of Viral Nucleic Acid

The development of a sensitive, facile, and cost-effective colorimetric method is of great significance for the point-of-care testing of viral nucleic acid. Herein, we reported a strand displacement amplification assisted CRISPR-Cas12a (SDACC) method for the colorimetric analysis of viral nucleic acid. The hepatitis B virus (HBV) DNA was chosen as the target to trigger strand displacement amplification (SDA) and generate abundant single-strand DNA (ssDNA) products. The ssDNA amplicon hybridized with template DNA to activate the trans-cleavage activity of CRISPR-Cas12a, leading to the nonspecific cleavage of ssDNA on GOx-ssDNA-modified magnetic beads and the release of GOx. The released GOx was capable of catalyzing the substrate solution to generate a color change, which could be directly observed by naked eyes. The SDACC strategy could identify a single-base mismatch located in the DNA sequence and achieve a sensitive detection for HBV DNA with the limit of detection as low as 41.8 fM. Notably, the sophisticated primer design for target amplification and complicated detection process could be circumvented. The current approach realizes a simple, low-cost, and sensitive colorimetric detection for viral nucleic acid and holds great promise for the practical application of virus infection diagnosis.

Amplification-Free Identification and Determination of Nucleic Acids by Surface Plasmon Resonance and Surface-Enhanced Raman Spectroscopy

This review discusses contemporary approaches to designing sensory systems for the identification and determination of nucleic acids (NAs) without amplifying target molecules. Here we summarize the data about methods based on surface plasmon resonance and surface-enhanced Raman spectroscopy, as well as their possibilities, limitations, and prospects for further development.

Applications of laboratory findings in the prevention, diagnosis, treatment, and monitoring of COVID-19

The worldwide pandemic of coronavirus disease 2019 (COVID-19) presents us with a serious public health crisis. To combat the virus and slow its spread, wider testing is essential. There is a need for more sensitive, specific, and convenient detection methods of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Advanced detection can greatly improve the ability and accuracy of the clinical diagnosis of COVID-19, which is conducive to the early suitable treatment and supports precise prophylaxis. In this article, we combine and present the latest laboratory diagnostic technologies and methods for SARS-CoV-2 to identify the technical characteristics, considerations, biosafety requirements, common problems with testing and interpretation of results, and coping strategies of commonly used testing methods. We highlight the gaps in current diagnostic capacity and propose potential solutions to provide cutting-edge technical support to achieve a more precise diagnosis, treatment, and prevention of COVID-19 and to overcome the difficulties with the normalization of epidemic prevention and control.

Role of plasmonics in detection of deadliest viruses: a review

Viruses have threatened animal and human lives since a long time ago all over the world. Some of these tiny particles have caused disastrous pandemics that killed a large number of people with subsequent economic downturns. In addition, the quarantine situation itself encounters the challenges like the deficiency in the online educational system, psychiatric problems and poor international relations. Although viruses have a rather simple protein structure, they have structural heterogeneity with a high tendency to mutation that impedes their study. On top of the breadth of such worldwide worrying issues, there are profound scientific gaps, and several unanswered questions, like lack of vaccines or antivirals to combat these pathogens. Various detection techniques like the nucleic acid test, immunoassay, and microscopy have been developed; however, there is a tradeoff between their advantages and disadvantages like safety in sample collecting, invasiveness, sensitivity, response time, etc. One of the highly resolved techniques that can provide early-stage detection with fast experiment duration is plasmonics. This optical technique has the capability to detect viral proteins and genomes at the early stage via highly sensitive interaction between the biological target and the plasmonic chip. The efficiency of this technique could be proved using commercialized techniques like reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) techniques. In this study, we aim to review the role of plasmonic technique in the detection of 11 deadliest viruses besides 2 common genital viruses for the human being. This is a rapidly moving topic of research, and a review article that encompasses the current findings may be useful for guiding strategies to deal with the pandemics. By investigating the potential aspects of this technique, we hope that this study could open new avenues toward the application of point-of-care techniques for virus detection at early stage that may inhibit the progressively hygienic threats.

Paper-Based Multiplex Surface-Enhanced Raman Scattering Detection Using Polymerase Chain Reaction Probe Codification

We construct a multiplex surface-enhanced Raman scattering (SERS) platform based on a plasmonic paper substrate and a double-labeled probe for the detection of multiple fluorescent dyes at high sensitivity in a single-wavelength light source system. Plasmonic paper, made of silver nanodots on three-dimensional cellulose fibers, enables highly sensitive SERS biosensing based on localized surface plasmon resonance (LSPR). The proposed method enables the identification and quantification of a range of fluorescent dyes ranging from picomolar to millimolar concentrations. The use of 5' fluorescent dyes and 3' biotin-modified probes as SERS-coded probes renders possible the separation of fluorescent dyes with streptavidin-coated magnetic beads (SMBs) and the sensitive detection of multiple dyes after the reverse transcription polymerase chain reaction (RT-PCR). This experimental study reveals the multiplex detection capability of PCR-based SERS under existing PCR conditions without modifying primer and probe sequences. The combination of magnetic bead-based separation and paper SERS platform is efficient, economical, and can be used for the simultaneous detection of two or more pathogens.

Plasmonic nano-antimicrobials: properties, mechanisms and applications in microbe inactivation and sensing

Bacterial, viral and fungal infections pose serious threats to human health and well-being. The continuous emergence of acute infectious diseases caused by pathogenic microbes and the rapid development of resistances against conventional antimicrobial drugs necessitates the development of new and effective strategies for the safe elimination of microbes in water, food or on surfaces, as well as for the inactivation of pathogenic microbes in human hosts. The need for new antimicrobials has triggered the development of plasmonic nano-antimicrobials that facilitate both light-dependent and -independent microbe inactivation mechanisms. This review introduces the relevant photophysical mechanisms underlying these plasmonic nano-antimicrobials, and provides an overview of how the photoresponses and materials properties of plasmonic nanostructures can be applied in microbial pathogen inactivation and sensing applications. Through a systematic analysis of the inactivation efficacies of different plasmonic nanostructures, this review outlines the current state-of-the-art in plasmonic nano-antimicrobials and defines the application space for different microbial inactivation strategies. The advantageous optical properties of plasmonic nano-antimicrobials also enhance microbial detection and sensing modalities and thus help to avoid exposure to microbial pathogens. Sensitive and fast plasmonic microbial sensing modalities and their theranostic and targeted therapeutic applications are discussed.

Monitoring hepatitis B by using point-of-care testing: biomarkers, current technologies, and perspectives

Introduction: Liver diseases caused by hepatitis B virus (HBV) are pandemic infectious diseases that seriously endanger human health, conventional diagnosis methods can not meet the requirements in resource-limited areas. The point of acre detection methods can easily resolve those problems. Herein, we review the most recent advances in POC-based hepatitis B detection methods and present some recommendations for future development. It aims to provide ideas for future research.Areas covered: Epidemiological data on Hepatitis B, conventional diagnostic methods for hepatitis B detection, some latest point of care detection methods for hepatitis B detection and list out the recommendations for future development.Expert opinion: This manuscript summarized traditional biomarkers of different hepatitis B stages and recent-developed POCT platforms (including microfluidic platforms and lateral-flow strips) and discuss the challenges associated with their use. Some emerging biomarkers that can be used in hepatitis B diagnosis are also listed. This manuscript has certain guiding significance to the development of hepatitis B detection.

Stimuli-responsive microgels for controlled deposition of gold nanoparticles on surfaces

A variety of gold nanoparticle (AuNP) core/poly(N-isopropylacrylamide) (pNIPAm) shell microgels (Au@pNIPAm) were generated using seed-mediated polymerization. The shell thickness and AuNP core diameter were easily tunable at the time of synthesis. The resultant Au@pNIPAm microgels were characterized via photon-correlation spectroscopy, transmission electron microscopy and ultraviolet-visible spectroscopy. AuNP arrays were generated by "painting" the microgels on a surface, using the shell thickness to define the distance between the AuNPs, followed by shell removal via plasma etching. We found that when the pNIPAm shell thickness decreased (via its tuning at the time of synthesis or deposition at elevated temperature at which the shell is collapsed) the AuNPs were closer to one another. We also showed that via sequential deposition Au@pNIPAm microgels with different AuNP core sizes could be deposited on a single surface. The presented "painting protocol" offers a facile way to coat large area surfaces quickly which is not easily achievable using other approaches. We envision that this approach is extremely versatile, allowing a number of different nanomaterials embedded in pNIPAm shells to be deposited/patterned on surfaces. With the control over the deposition on the surface that we show here, we hope that the Au@pNIPAm microgels will find use in lithography/surface patterning applications.

Highly-selective detection of EGFR mutation gene in lung cancer based on surface enhanced Raman spectroscopy and asymmetric PCR

The evaluation of EGFR mutation genes in circulating tumor DNA (ctDNA) in blood sample is key for patients with lung cancer. Surface-enhanced Raman scattering (SERS) has potential for trace detection of DNA or RNA. The detection rate offered by current methods can not meet clinical demand. By combining asymmetric polymerase chain reaction (PCR) and SERS, a highly-selective detection for EGFR mutation genes in lung cancer was developed. Sea-urchin like Au nanoclusters (AuNCs) were synthesized via Ag seed-mediated growth. AuNCs with a diameter of 120 nm were covered with 79 nanopricks (20 nm). Then, EGFR mutation specific molecular beacons (MBs) labeled with Cy3 were coated on the surface of AuNCs. The loading amount of MBs was calculated as 5720 ± 740 on one AuNCs. These AuNCs probes had good efficiency (equilibrium time: 20 minutes) with high sensitivity (detection limit: 5.8 nM), high specificity (capable of single-base mismatch recognition) and good stability against nucleases. Following this, asymmetric PCR was performed to obtain large numbers of single-stranded DNA (ssDNA, E746-A750del). The ssDNA was incubated with the AuNCs probes and tested quantitatively based on the SERS signals of the AuNCs probes. This combined asymmetric PCR-SERS method had a very high detection threshold (4.24 fM). The asymmetric PCR-SERS method was shown to have an overall sensitivity of 75% and specificity of 100% in a further 15 clinical blood samples. This method is proved to be promising for non-invasive and sensitive detection of EGFR mutations in ctDNA.

Current progress on COVID-19 related to biosensing technologies: New opportunity for detection and monitoring of viruses

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COVID-19 infection poses a serious risk to human life by causing acute lung damage.

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Various techniques used to identify and quantify COVID-19 infection.

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Major challenges for containing the spread of COVID-19 is the ability to identify asymptomatic cases.

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Currently available diagnostic methods, biosensing technology developed during COVID-19 infection.

The technologies used for coronavirus testing consist of a pre-existing device developed to examine different pathologies, such as bacterial infections, or cancer biomarkers. However, for the 2019 pandemic, researchers knew that their technology could be modified to detect a low viral load at an early stage. Today, countries around the world are working to control the new coronavirus disease (n-SARS-CoV-2). From this perspective, laboratories, universities, and companies around the world have embarked on a race to develop and produce much-needed test kits. This review has been developed to provide an overview of current trends and strategies in n-SARS-CoV-2 diagnostics based on traditional and new emerging assessment technologies, to continuous innovation. It focuses on recent trends in biosensors to build a fast, reliable, more sensitive, accessible, user-friendly system and easily adaptable technology n-SARS-CoV-2 detection and monitoring. On the whole, we have addressed and identified research evidence supporting the use of biosensors on the premise that screening people for n-SARS-CoV-2 is the best way to contain its spread.

Scalable COVID-19 Detection Enabled by Lab-on-Chip Biosensors

Introduction

The emergence of a novel coronavirus, SARS-CoV-2, has highlighted the need for rapid, accurate, and point-of-care diagnostic testing. As of now, there is not enough testing capacity in the world to meet the stated testing targets, which are expected to skyrocket globally for broader testing during reopening

Aim

This review focuses on the development of lab-on-chip biosensing platforms for diagnosis of COVID-19 infection.

Results

We discuss advantages of utilizing lab-on-chip technologies in response to the current global pandemic, including their potential for low-cost, rapid sample-to-answer processing times, and ease of integration into a range of healthcare settings. We then highlight the development of magnetic, colorimetric, plasmonic, electrical, and lateral flow-based lab-on-chip technologies for the detection of SARS-CoV-2, in addition to other viruses. We focus on rapid, point-of-care technologies that can be deployed at scale, as such devices could be promising alternatives to the current gold standard of reverse transcription-polymerase chain reaction (RT-PCR) diagnostic testing.

Conclusion

This review is intended to provide an overview of the current state-of-the-field and serve as a resource for innovative development of new lab-on-chip assays for COVID-19 detection.

Point-of-Use Rapid Detection of SARS-CoV-2: Nanotechnology-Enabled Solutions for the COVID-19 Pandemic

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the COVID-19 pandemic that has been spreading around the world since December 2019. More than 10 million affected cases and more than half a million deaths have been reported so far, while no vaccine is yet available as a treatment. Considering the global healthcare urgency, several techniques, including whole genome sequencing and computed tomography imaging have been employed for diagnosing infected people. Considerable efforts are also directed at detecting and preventing different modes of community transmission. Among them is the rapid detection of virus presence on different surfaces with which people may come in contact. Detection based on non-contact optical techniques is very helpful in managing the spread of the virus, and to aid in the disinfection of surfaces. Nanomaterial-based methods are proven suitable for rapid detection. Given the immense need for science led innovative solutions, this manuscript critically reviews recent literature to specifically illustrate nano-engineered effective and rapid solutions. In addition, all the different techniques are critically analyzed, compared, and contrasted to identify the most promising methods. Moreover, promising research ideas for high accuracy of detection in trace concentrations, via color change and light-sensitive nanostructures, to assist fingerprint techniques (to identify the virus at the contact surface of the gas and solid phase) are also presented.

SERS-Based Biosensors for Virus Determination with Oligonucleotides as Recognition Elements

Viral infections are among the main causes of morbidity and mortality of humans; sensitive and specific diagnostic methods for the rapid identification of viral pathogens are required. Surface-enhanced Raman spectroscopy (SERS) is one of the most promising techniques for routine analysis due to its excellent sensitivity, simple and low-cost instrumentation and minimal required sample preparation. The outstanding sensitivity of SERS is achieved due to tiny nanostructures which must be assembled before or during the analysis. As for specificity, it may be provided using recognition elements. Antibodies, complimentary nucleic acids and aptamers are the most usable recognition elements for virus identification. Here, SERS-based biosensors for virus identification with oligonucleotides as recognition elements are reviewed, and the potential of these biosensors is discussed.

Surface Enhanced Raman Spectroscopy for DNA Biosensors-How Far Are We?

A sensitive and accurate identification of specific DNA fragments (usually containing a mutation) can influence clinical decisions. Standard methods routinely used for this type of detection are PCR (Polymerase Chain Reaction, and its modifications), and, less commonly, NGS (Next Generation Sequencing). However, these methods are quite complicated, requiring time-consuming, multi-stage sample preparation, and specially trained staff. Usually, it takes weeks for patients to obtain their results. Therefore, different DNA sensors are being intensively developed by many groups. One technique often used to obtain an analytical signal from DNA sensors is Raman spectroscopy. Its modification, surface-enhanced Raman spectroscopy (SERS), is especially useful for practical analytical applications due to its extra low limit of detection. SERS takes advantage of the strong increase in the efficiency of Raman signal generation caused by a local electric field enhancement near plasmonic (typically gold and silver) nanostructures. In this condensed review, we describe the most important types of SERS-based nanosensors for genetic studies and comment on their potential for becoming diagnostic tools.

Plasmonic-based platforms for diagnosis of infectious diseases at the point-of-care

Infectious diseases such as HIV-1/AIDS, tuberculosis (TB), hepatitis B (HBV), and malaria still exert a tremendous health burden on the developing world, requiring rapid, simple and inexpensive diagnostics for on-site diagnosis and treatment monitoring. However, traditional diagnostic methods such as nucleic acid tests (NATs) and enzyme linked immunosorbent assays (ELISA) cannot be readily implemented in point-of-care (POC) settings. Recently, plasmonic-based biosensors have emerged, offering an attractive solution to manage infectious diseases in the developing world since they can achieve rapid, real-time and label-free detection of various pathogenic biomarkers. Via the principle of plasmonic-based optical detection, a variety of biosensing technologies such as surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR), colorimetric plasmonic assays, and surface enhanced Raman spectroscopy (SERS) have emerged for early diagnosis of HIV-1, TB, HBV and malaria. Similarly, plasmonic-based colorimetric assays have also been developed with the capability of multiplexing and cellphone integration, which is well suited for POC testing in the developing world. Herein, we present a comprehensive review on recent advances in surface chemistry, substrate fabrication, and microfluidic integration for the development of plasmonic-based biosensors, aiming at rapid management of infectious diseases at the POC, and thus improving global health.

Photodegradable CuS SERS Probes for Intraoperative Residual Tumor Detection, Ablation, and Self-Clearance

Surface-enhanced Raman scattering (SERS) probes have exhibited great potential in biomedical applications. However, currently reported SERS probes are mainly fabricated by nondegradable Au or Ag nanostructures, which are not favorably cleared from the imaged tissues. This bottleneck hinders their in vivo applications. We herein explore a degradable SERS probe consisting of hollow CuS nanoparticles (NPs) to circumvent the current limitation. We identify, for the first time, the Raman enhancement effects of hollow CuS NPs as a SERS probe for Raman imaging of residual tumor lesions. Uniquely, CuS SERS probes are degradable, which stems from laser-induced photothermal effects of CuS NPs, leading to their disintegration from shell structures into individual crystals, thus facilitating their self-clearance from imaged tissues. This novel CuS SERS probe with photodegradation characteristics opens avenues for applying Raman imaging toward a myriad of biomedical applications.

Plasmonic Gold Nanohole Array for Surface-Enhanced Raman Scattering Detection of DNA Methylation

Surface-enhanced Raman spectroscopy (SERS), which utilizes nanogaps between noble-metal nanostructures as hot spots to yield ultrasensitive SERS signals, is an outstanding label-free and straightforward tool for DNA methylation analysis. Herein, a plasmonic gold nanohole array (PGNA) with well-controlled hot spots and an open surface was designed as a SERS substrate for DNA methylation detection. A finite-difference time-domain (FDTD) simulation was first employed to investigate the electric field distributions of the PGNA as a function of the geometric parameters. The plasmonic response was tuned to 785 cm^-1 to match the ring breathing vibrational band of cytosine, the intensity change of which was revealed to be a marker of DNA methylation. Then, guided by the FDTD simulation results, the PGNA was fabricated via the electron beam lithography (EBL) technique. The fabricated PGNA had an open and easily accessible surface topology, a SERS enhancement factor of ∼10⁶, and a relative standard deviation (RSD) of 7.1% for 500 repetitions over an area of 20 × 20 μm² using 1 μM Rhodamine 6G as the Raman reporter. The fabricated PGNA was further used as a platform for determining DNA methylation. The proposed method exhibited a sensitivity for detecting 1% of methylation changes. Moreover, insight into the dynamic information on methylation events was obtained by combining principal component analysis (PCA) with 2D correlation spectroscopy analysis. Finally, clear discrimination of the different methylation sites, such as 5-methylcytosine and N6-methyladenine, was demonstrated.

Enzyme-free fluorescence microarray for determination of hepatitis B virus DNA based on silver nanoparticle aggregates-assisted signal amplification

In this study, we designed a fluorescence enhancement strategy based on silver nanoparticle (AgNP) aggregates for the detection of hepatitis B virus DNA sequences. AgNPs were functioned with recognition probes (Cy3-probe) and hybrid probes (Oligomer-A and Oligomer-B). The presence of target DNA mediated the formation of sandwich complexes between the immobilized capture probes and the functionalized AgNPs, which was followed by hybridization-induced formation of AgNP aggregates. The fluorescent intensity could be extremely amplified by both the increasing number of fluorophores and metal enhanced fluorescence (MEF) effect. Under optimal conditions, this method achieved a detection limit of 50 fM which was 1560-fold lower than that of un-enhanced fluorescent assays. It was illustrated that the HBV DNA concentrations ranging from 100 fM to 10 nM had a good log-linear correlation with the corresponding fluorescent intensity (R = 0.991). Moreover, this method had high specificity both for distinguishing single-base mismatches and identifying target DNA under the interference of genomic DNA. This fluorescent microarray had high-throughput analytical potential and could apply to many other disease diagnoses.

Novel Surface-Enhanced Raman Spectroscopy Techniques for DNA, Protein and Drug Detection

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopic technique in which the Raman scattering signal strength of molecules, absorbed by rough metals or the surface of nanoparticles, experiences an exponential growth (10³-10⁶ times and even 10¹⁴-10¹⁵ times) because of electromagnetic or chemical enhancements. Nowadays, SERS has attracted tremendous attention in the field of analytical chemistry due to its specific advantages, including high selectivity, rich informative spectral properties, nondestructive testing, and the prominent multiplexing capabilities of Raman spectroscopy. In this review, we present the applications of state-of-the-art SERS for the detection of DNA, proteins and drugs. Moreover, we focus on highlighting the merits and mechanisms of achieving enhanced SERS signals for food safety and clinical treatment. The machine learning techniques, combined with SERS detection, are also indicated herein. This review concludes with recommendations for future studies on the development of SERS.

Combining magnetic nanoparticle capture and poly-enzyme nanobead amplification for ultrasensitive detection and discrimination of DNA single nucleotide polymorphisms

The development of ultrasensitive methods for detecting specific genes and discriminating single nucleotide polymorphisms (SNPs) is important for biomedical research and clinical disease diagnosis. Herein, we report an ultrasensitive approach for label-free detection and discrimination of a full-match target-DNA from its cancer related SNPs by combining magnetic nanoparticle (MNP) capture and poly-enzyme nanobead signal amplification. It uses a MNP linked capture-DNA and a biotinylated signal-DNA to sandwich the target followed by ligation to offer high SNP discrimination: only the perfect-match target-DNA yields a covalently linked biotinylated signal-DNA on the MNP surface for subsequent binding to a neutravidin-horseradish peroxidase conjugate (NAV-HRP) for signal amplification. The use of polymer nanobeads each tagged with thousands of copies of HRPs greatly improves the signal amplification power, allowing for direct, amplification-free quantification of low aM target-DNA over 6 orders of magnitude (0.001-1000 fM). Moreover, this sensor also offers excellent discrimination between the perfect-match gene and its cancer-related SNPs and can positively detect 1 fM perfect-match target-DNA in the presence of 100 fold excess of co-existing single-base mismatch targets. Furthermore, it works robustly in clinically relevant media (e.g. 10% human serum) and gives even higher SNP discrimination than that in clean buffers. This ultrasensitive DNA sensor appears to have excellent potential for rapid detection and diagnosis of genetic diseases.

Surface-enhanced Raman spectroscopy (SERS) nanoprobes for ratiometric detection of cancer cells

A surface-enhanced Raman spectroscopic strategy is developed for ratiometric detection of cancer cells by quantifying the expression ratio of extracellular biomarkers.

Label free hepatitis B detection based on serum derivative surface enhanced Raman spectroscopy combined with multivariate analysis

Surface-enhanced Raman spectroscopy (SERS) was developed here for the non-invasive detection of the hepatitis B virus (HBV). Chronic hepatitis B virus (HBV) infection is a primary health problem in the world and may further develop into cirrhosis and hepatocellular carcinoma (HCC). SERS measurement was applied to two groups of serum samples. One group included 93 HBV patients and the other group included 94 healthy volunteers as control subjects. Tentative assignments of the Raman bands in the measured SERS spectra have shown the difference of the serum SERS spectra between HBV patients and healthy volunteers. The differences indicated an increase in the relative amounts of L-arginine, Saccharide band (overlaps with acyl band), phenylalanine and tyrosine, together with a decrease in the percentage of nucleic acid, valine and hypoxanthine in the serum of HBV patients compared with those of healthy volunteers. For better analysis of the spectral data, the first-order derivation was applied to the SERS data. Furthermore, principal components analysis (PCA), combined with linear discriminant analysis (LDA), were employed to distinguish HBV patients from healthy volunteers and to realize the diagnostic sensitivity of 78.5% and 91.4%, and specificity of 75% and 83% for SERS and the first order derivative SERS spectrum, respectively. These results suggest that derivative analysis could be an effective method to improve the classification of SERS spectra belonging to different groups. This exploratory work demonstrated that first-order derivative serum SERS spectrum combined with PCA-LDA has great potential for improving the detection of HBV.

para-Aminothiophenol Radical Reaction-Functionalized Gold Nanoprobe for One-to-All Detection of Five Reactive Oxygen Species In Vivo

Five major reactive oxygen species (ROS) are generated in diseases including H₂O₂, ^•OH, O₂^•-, ROO^•, and ¹O₂. Simultaneous detection of the five ROS with a single probe is crucial for a comprehensive understanding of the development and progression of many diseases, such as cancer and inflammatory diseases. However, currently reported detection systems are limited by targeting one ROS with one probe. This one-to-one detection mode may fail to sufficiently unveil the diseased state. In this study, we achieved simultaneous detection of all the five ROS with one probe (i.e., one-to-all detection), by designing a novel para-aminothiophenol (PATP) and hemin-decorated gold (Au/PATP/Hemin) nanoprobe. The design is principled by our discovery that PATP can react with ^•OH, O₂^•-, ROO^•, and ¹O₂ by a radical oxidative coupling mechanism to form 4,4'-dimercaptoazobenzene (DMAB). The DMAB then elicited strong characteristic surface-enhanced Raman scattering (SERS) peaks at 1142, 1386, and 1432 cm^-1; which in turn enables direct detection of ^•OH, O₂^•-, ROO^•, and ¹O₂ and indirect detection of H₂O₂ by hemin-catalyzed fenton reaction to convert H₂O₂ into ^•OH. In two representative ROS-elevated mice models of tumors and allergic dermatitis, the Au/PATP/Hemin nanoprobe demonstrated its robust performance of monitoring tumor development and inflammation progression in a highly sensitive and quantitative manner.

Direct Detection of Unamplified Pathogen RNA in Blood Lysate using an Integrated Lab-in-a-Stick Device and Ultrabright SERS Nanorattles

Direct detection of genetic biomarkers in body fluid lysate without target amplification will revolutionize nucleic acid-based diagnostics. However, the low concentration of target sequences makes this goal challenging. We report a method for direct detection of pathogen RNA in blood lysate using a bioassay using surface-enhanced Raman spectroscopy (SERS)-based detection integrated in a "lab-in-a-stick" portable device. Two levels of signal enhancement were employed to achieve the sensitivity required for direct detection. Each target sequence was tagged with an ultrabright SERS-encoded nanorattle with ultrahigh SERS signals, and these tagged target sequences were concentrated into a focused spot for detection using hybridization sandwiches with magnetic microbeads. Furthermore, the washing process was automated by integration into a "lab-in-a-stick" portable device. We could directly detect synthetic target with a limit of detection of 200 fM. More importantly, we detected plasmodium falciparum malaria parasite RNA directly in infected red blood cells lysate. To our knowledge, this is the first report of SERS-based direct detection of pathogen nucleic acid in blood lysate without nucleic acid extraction or target amplification. The results show the potential of our integrated bioassay for field use and point-of-care diagnostics.

Nanomaterial-based biosensors for detection of pathogenic virus

Viruses are real menace to human safety that cause devastating viral disease. The high prevalence of these diseases is due to improper detecting tools. Therefore, there is a remarkable demand to identify viruses in a fast, selective and accurate way. Several biosensors have been designed and commercialized for detection of pathogenic viruses. However, they present many challenges. Nanotechnology overcomes these challenges and performs direct detection of molecular targets in real time. In this overview, studies concerning nanotechnology-based biosensors for pathogenic virus detection have been summarized, paying special attention to biosensors based on graphene oxide, silica, carbon nanotubes, gold, silver, zinc oxide and magnetic nanoparticles, which could pave the way to detect viral diseases and provide healthy life for infected patients.

Dependence of plasmon coupling on curved interfaces

The optical properties of coupled plasmon systems can be tuned by individual material and geometry, gap distance, and surrounding dielectric. This paper reports a dramatic effect of a curved interface in the nanoparticles dimer on the optical responses. Compared with gold nanorod (AuNR) monomer, AuNR dimers with different assembly types (such as end-to-end and side-by-side) can manipulate the longitudinal surface plasmon resonance (SPR_L) to red/blueshift. The electromagnetic field of the dimer is further enhanced in the interactive region. Under the incident polarization along the gap, a new resonance mode will be excited when AuNR dimers touch each other, and the SPR mode turns to blueshift from redshift due to the formation of the conductive coupling. It can be assumed that when one of the interactive surfaces is curved, an additional plasmon resonance can be stimulated under the polarization of incident light along the gap. The particular phenomenon can be explained by the plasmon hybridization theory. Silver nanocubes dimers (with sharp or smooth corners and edges) also possess the same property. Supported by finite-difference time-domain solutions, the coupled plasmon resonance mode represents high sensitivity to structural geometry.