Electrochemical assay to detect influenza viruses and measure drug susceptibility

A Tetrazine Amplification System for Visual Detection of Trace Analytes via Click-Release Reactions

Achieving visual detection of analytes at ultra-low concentrations in complex mixtures remains a persistent challenge. While sophisticated techniques offer single-molecule sensitivity, practical hurdles remain, necessitating tailored signal amplification systems for direct visual detection. In this study, we develop a strategy for the visualized detection of tetrazine through a "click-release-oxidation-cycle" (CROC) cascade amplification process. We systematically describe the construction and synthesis of this system, the kinetic process of click release, the kinetics of oxidation to tetrazine and its cascade amplification effect in trace amounts of tetrazine. This system is capable of amplifying the signal of tetrazine at a concentration as low as 2 nM by 105-fold, thereby providing a clearly visible purple signal. Finally, as proof of concept, we successfully apply this method to visually detect trace β-galactosidase (β-gal) and Pd2+.

Influenza viruses and SARS-CoV-2 diagnosis via sensitive testing methods in clinical application

The identification of influenza viruses and SARS-CoV-2 has garnered increasing attention due of their longstanding global menace to human life and health. The point-of-care test is a potential approach for identifying influenza viruses and SARS-CoV-2 in clinical settings, leading to timely discovery, documentation, and treatment. The primary difficulties encountered with conventional detection techniques for influenza viruses and SARS-CoV-2 are the limited or inadequate ability to identify the presence of the viruses, the lack of speed, precision, accuracy, sensitivity, and specificity, often resulting in a failure to promptly notify disease control authorities. Recently, point-of-care test methods, along with nucleic acid amplification, optics, electrochemistry, lateral/vertical flow, and minimization, have been demonstrated the characteristics of reliability, sensitivity, specificity, stability, and portability. A point-of-care test offers promising findings in the early detection of influenza viruses and SARS-CoV-2 in both scientific research and practical use. In this review, we will go over the principles, advantages, limitations, and real-world applications of point-of-care diagnostics. The significance of constraints of detection, throughput, sensitivity, and specificity in the analysis of clinical samples in settings with restricted resources is underscored. This discussion concludes with their prospects and challenges.

Extended Review Concerning the Integration of Electrochemical Biosensors into Modern IoT and Wearable Devices

Electrochemical biosensors include a recognition component and an electronic transducer, which detect the body fluids with a high degree of accuracy. More importantly, they generate timely readings of the related physiological parameters, and they are suitable for integration into portable, wearable and implantable devices that are significant relative to point-of-care diagnostics scenarios. As an example, the personal glucose meter fundamentally improves the management of diabetes in the comfort of the patients' homes. This review paper analyzes the principles of electrochemical biosensing and the structural features of electrochemical biosensors relative to the implementation of health monitoring and disease diagnostics strategies. The analysis particularly considers the integration of the biosensors into wearable, portable, and implantable systems. The fundamental aim of this paper is to present and critically evaluate the identified significant developments in the scope of electrochemical biosensing for preventive and customized point-of-care diagnostic devices. The paper also approaches the most important engineering challenges that should be addressed in order to improve the sensing accuracy, and enable multiplexing and one-step processes, which mediate the integration of electrochemical biosensing devices into digital healthcare scenarios.

Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Evaluation of catalytic activity of human and animal origin viral neuraminidase: Current prospect

With the exception of plants, almost all living organisms synthesize neuraminidase/sialidase. It is a one among the crucial proteins that controls how virulent a microorganism is. An essential enzyme in orthomyxoviruses and paramyxoviruses that destroys receptors is neuraminidase. It plays a number of roles throughout the viral life cycle in addition to one that involves the release of progeny virus particles. This protein is an important target for therapeutic interventions and diagnostic assays. Neuraminidase inhibitors effectively prevent the spread of disease and viral infection. Sensitive, quick, and inexpensive high throughput assays are needed to screen for specific neuraminidase inhibitory chemicals. To characterize the neuraminidase catalytic activity, however, the traditional assays are still the most common in laboratories. This review gives a brief overview of these neuraminidase assays and recent, innovative developments, particularly those involving biosensors.

Device integration of electrochemical biosensors

Electrochemical biosensors incorporate a recognition element and an electronic transducer for the highly sensitive detection of analytes in body fluids. Importantly, they can provide rapid readouts and they can be integrated into portable, wearable and implantable devices for point-of-care diagnostics; for example, the personal glucose meter enables at-home assessment of blood glucose levels, greatly improving the management of diabetes. In this Review, we discuss the principles of electrochemical biosensing and the design of electrochemical biosensor devices for health monitoring and disease diagnostics, with a particular focus on device integration into wearable, portable and implantable systems. Finally, we outline the key engineering challenges that need to be addressed to improve sensing accuracy, enable multiplexing and one-step processes, and integrate electrochemical biosensing devices in digital health-care pathways.

Peptide Amphiphile Mediated Co-assembly for Nanoplasmonic Sensing

Aromatic interactions are commonly involved in the assembly of naturally occurring building blocks, and these interactions can be replicated in an artificial setting to produce functional materials. Here we describe a colorimetric biosensor using co-assembly experiments with plasmonic gold and surfactant-like peptides (SLPs) spanning a wide range of aromatic residues, polar stretches, and interfacial affinities. The SLPs programmed in DDD-(ZZ)x -FFPC self-assemble into higher-order structures in response to a protease and subsequently modulate the colloidal dispersity of gold leading to a colorimetric readout. Results show the strong aggregation propensity of the FFPC tail without polar DDD head. The SLPs were specific to the target protease, i.e., Mpro , a biomarker for SARS-CoV-2. This system is a simple and visual tool that senses Mpro in phosphate buffer, exhaled breath condensate, and saliva with detection limits of 15.7, 20.8, and 26.1 nM, respectively. These results may have value in designing other protease testing methods.

Peptidic Sulfhydryl for Interfacing Nanocrystals and Subsequent Sensing of SARS-CoV-2 Protease

There is a need for surveillance of COVID-19 to identify individuals infected with SARS-CoV-2 coronavirus. Although specific, nucleic acid testing has limitations in terms of point-of-care testing. One potential alternative is the nonstructural protease (nsp5, also known as Mpro/3CLpro) implicated in SARS-CoV-2 viral replication but not incorporated into virions. Here, we report a divalent substrate with a novel design, (Cys)2-(AA)x-(Asp)3, to interface gold colloids in the specific presence of Mpro leading to a rapid and colorimetric readout. Citrate- and tris(2-carboxyethyl)phosphine (TCEP)-AuNPs were identified as the best reporter out of the 17 ligated nanoparticles. Furthermore, we empirically determined the effects of varying cysteine valence and biological media on the sensor specificity and sensitivity. The divalent peptide was specific to Mpro, that is, there was no response when tested with other proteins or enzymes. Furthermore, the Mpro detection limits in Tris buffer and exhaled breath matrices are 12.2 and 18.9 nM, respectively, which are comparable to other reported methods (i.e., at low nanomolar concentrations) yet with a rapid and visual readout. These results from our work would provide informative rationales to design a practical and noninvasive alternative for COVID-19 diagnostic testing-the presence of viral proteases in biofluids is validated.

Advanced Point-of-Care Testing Technologies for Human Acute Respiratory Virus Detection

The ever-growing global threats to human life caused by the human acute respiratory virus (RV) infections have cost billions of lives, created a significant economic burden, and shaped society for centuries. The timely response to emerging RVs could save human lives and reduce the medical care burden. The development of RV detection technologies is essential for potentially preventing RV pandemic and epidemics. However, commonly used detection technologies lack sensitivity, specificity, and speed, thus often failing to provide the rapid turnaround times. To address this problem, new technologies are devised to address the performance inadequacies of the traditional methods. These emerging technologies offer improvements in convenience, speed, flexibility, and portability of point-of-care test (POCT). Herein, recent developments in POCT are comprehensively reviewed for eight typical acute respiratory viruses. This review discusses the challenges and opportunities of various recognition and detection strategies and discusses these according to their detection principles, including nucleic acid amplification, optical POCT, electrochemistry, lateral flow assays, microfluidics, enzyme-linked immunosorbent assays, and microarrays. The importance of limits of detection, throughput, portability, and specificity when testing clinical samples in resource-limited settings is emphasized. Finally, the evaluation of commercial POCT kits for both essential RV diagnosis and clinical-oriented practices is included.

Construction of Optimal SERS Hotspots Based on Capturing the Spike Receptor-Binding Domain (RBD) of SARS-CoV-2 for Highly Sensitive and Specific Detection by a Fish Model

It is highly challenging to construct the best SERS hotspots for the detection of proteins by surface-enhanced Raman spectroscopy (SERS). Using its own characteristics to construct hotspots can achieve the effect of sensitivity and specificity. In this study, we built a fishing mode device to detect the receptor-binding domain (RBD) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at low concentrations in different detection environments and obtained a sensitive SERS signal response. Based on the spatial resolution of proteins and their protein-specific recognition functions, SERS hotspots were constructed using aptamers and small molecules that can specifically bind to RBD and cooperate with Au nanoparticles (NPs) to detect RBD in the environment using SERS signals of beacon molecules. Therefore, two kinds of AuNPs modified with aptamers and small molecules were used in the fishing mode device, which can specifically recognize and bind RBD to form a stable hotspot to achieve high sensitivity and specificity for RBD detection. The fishing mode device can detect the presence of RBD at concentrations as low as 0.625 ng/mL and can produce a good SERS signal response within 15 min. Meanwhile, we can detect an RBD of 0.625 ng/mL in the mixed solution with various proteins, and the concentration of RBD in the complex environment of urine and blood can be as low as 1.25 ng/mL. This provides a research basis for SERS in practical applications for protein detection work.

Printed Nanochain-Based Colorimetric Assay for Quantitative Virus Detection

Fast and ultrasensitive detection of pathogens is very important for efficient monitoring and prevention of viral infections. Here, we demonstrate a label-free optical detection approach that uses a printed nanochain assay for colorimetric quantitative testing of viruses. The antibody-modified nanochains have high activity and specificity which can rapidly identify target viruses directly from biofluids in 15 min, as well as differentiate their subtypes. Arising from the resonance induced near-field enhancement, the color of nanochains changes with the binding of viruses that are easily observed by a smartphone. We achieve the detection limit of 1 PFU μL^-1 through optimizing the optical response of nanochains in visible region. Besides, it allows for real-time response to virus concentrations ranging from 0 to 1.0×10⁵  PFU mL^-1 . This low-cost and portable platform is also applicable to rapid detection of other biomarkers, making it attractive for many clinical applications.

The enhanced photoelectrochemical platform constructed by N-doped ZnO nanopolyhedrons and porphyrin for ultrasensitive detection of brain natriuretic peptide

Nowadays, brain natriuretic peptide (BNP-32) is fundamental to early cardiovascular clinical diagnosis, whose accurate assay is of significance by photoelectrochemistry (PEC) for the low background and high precision. Herein, a novel enhanced PEC platform was built by successive deposition of N-doped ZnO nanopolyhedra (N-ZnO NP) and protoporphyrin IX (PPIX). Specifically, the N-ZnO NP with a narrow bandgap of 2.60 eV was synthesized by direct calcination of zeolitic imidazole framework-8 (ZIF-8), and performed as the substrate to enhance the photocurrents of PPIX (as photosensitizer) whose photoelectron transfer pathway and enhanced PEC mechanism were studied in detail. Under such foundation, a label-free PEC aptasensor was developed by deposition of DNA aptamer onto the PEC platform and then ultrasensitive assay of BNP-32 based on a "signal off" model. The biosensor showed a wide linear range (1 pg mL^-1- 0.1 μg mL^-1) with a limit of detection (LOD) as low as 0.14 pg mL^-1. This doping technique of ZnO nanomaterials provides some valuable guidelines for synthesis of advanced PEC probes in bioanalysis.

Biomimetic Nanopillar-Based Biosensor for Label-Free Detection of Influenza A Virus

Since the first emergence of influenza viruses, they have caused the flu seasonally worldwide. Precise detection of influenza viruses is required to prevent the spreading of the disease. Herein, we developed an optical biosensor using peptide-immobilized nanopillar structures for the label-free detection of influenza viruses. The spin-on-glass nanopillar structures were fabricated by nanoimprint lithography. A sialic acid-mimic peptide, which can specifically bind to hemagglutinin on the surface of the influenza virus, was immobilized onto the nanopillars via polymerized dopamine. The constructed nanopillar sensor enabled us to detect influenza A viruses in the range of 10³-10⁵ plaque-forming units through simple measurements of reflectance. Our findings suggest that biomimetic modification of nanopillar structures can be an alternative method for the immunodiagnosis of influenza viruses.

SERS imaging-based aptasensor for ultrasensitive and reproducible detection of influenza virus A

Surface-enhanced Raman scattering (SERS)-based aptasensors display high sensitivity for influenza A/H1N1 virus detection but improved signal reproducibility is required. Therefore, in this study, we fabricated a three-dimensional (3D) nano-popcorn plasmonic substrate using the surface energy difference between a perfluorodecanethiol (PFDT) spacer and the Au layer. This energy difference led to Au nanoparticle self-assembly; neighboring nanoparticles then created multiple hotspots on the substrate. The localized surface plasmon effects at the hot spots dramatically enhanced the incident field. Quantitative evaluation of A/H1N1 virus was achieved using the decrease of Raman peak intensity resulting from the release of Cy3-labeled aptamer DNAs from nano-popcorn substrate surfaces via the interaction between the aptamer DNA and A/H1N1 virus. The use of a Raman imaging technique involving the fast mapping of all pixel points enabled the reproducible quantification of A/H1N1 virus on nano-popcorn substrates. Average ensemble effects obtained by averaging all randomly distributed hot spots mapped on the substrate made it possible to reliably quantify target viruses. The SERS-based imaging aptasensor platform proposed in this work overcomes the issues inherent in conventional approaches (the time-consuming and labor-intensiveness of RT-PCR and low sensitivity and quantitative analysis limits of lateral flow assay kits). Our SERS-based assay for detecting A/H1N1 virus had an estimated limit of detection of 97 PFU mL-1 (approximately three orders of magnitude more sensitive than that determined by the enzyme-linked immunosorbent assay) and the approximate assay time was estimated to be 20 min. Thus, this approach provides an ultrasensitive, reliable platform for detecting viral pathogens.

Avian Influenza Virus Detection by Optimized Peptide Termination on a Boron-Doped Diamond Electrode

The development of a simple detection method with high sensitivity is essential for the diagnosis and surveillance of infectious diseases. Previously, we constructed a sensitive biosensor for the detection of pathological human influenza viruses using a boron-doped diamond electrode terminated with a sialyloligosaccharide receptor-mimic peptide that could bind to hemagglutinins involved in viral infection. Circulation of influenza induced by the avian virus in humans has become a major public health concern, and methods for the detection of avian viruses are urgently needed. Here, peptide density and dendrimer generation terminated on the electrode altered the efficiency of viral binding to the electrode surface, thus significantly enhancing charge-transfer resistance measured by electrochemical impedance spectroscopy. The peptide-terminated electrodes exhibited an excellent detection limit of less than one plaque-forming unit of seasonal H1N1 and H3N2 viruses. Furthermore, the improved electrode was detectable for avian viruses isolated from H5N3, H7N1, and H9N2, showing the potential for the detection of all subtypes of influenza A virus, including new subtypes. The peptide-based electrochemical architecture provided a promising approach to biosensors for ultrasensitive detection of pathogenic microorganisms.

Diagnosis of Tamiflu-Resistant Influenza Virus in Human Nasal Fluid and Saliva Using Surface-Enhanced Raman Scattering

Influenza viruses cause respiratory infection, spread through respiratory secretions, and are shed into the nasal secretion and saliva specimens. Therefore, nasal fluid and saliva are effective clinical samples for the diagnosis of influenza virus-infected patients. Although several methods have been developed to detect various types of influenza viruses, approaches for detecting mutant influenza viruses in clinical samples are rarely reported. Herein, we report for the first time a surface-enhanced Raman scattering (SERS)-based sensing platform for oseltamivir-resistant pandemic H1N1 (pH1N1) virus detection in human nasal fluid and saliva. By combining SERS-active urchin Au nanoparticles and oseltamivir hexylthiol, an excellent receptor for the pH1N1/H275Y mutant virus, we detected the pH1N1/H275Y virus specifically and sensitively in human saliva and nasal fluid samples. Considering that the current influenza virus infection testing methods do not provide information on the antiviral drug resistance of the virus, the proposed SERS-based diagnostic test for the oseltamivir-resistant virus will inform clinical decisions about the treatment of influenza virus infections, avoiding the unnecessary prescription of ineffective drugs and greatly improving therapy.

Magnetic SERS Strip for Sensitive and Simultaneous Detection of Respiratory Viruses

Rapid and early diagnosis of respiratory viruses is key to preventing infections from spreading and guiding treatments. Here, we developed a sensitive and quantitative surface-enhanced Raman scattering-based lateral flow immunoassay (SERS-based LFIA) strip for simultaneous detection of influenza A H1N1 virus and human adenovirus (HAdV) by using Fe₃O₄@Ag nanoparticles as magnetic SERS nanotags. The new type of Fe₃O₄@Ag magnetic tags, which were conjugated with dual-layer Raman dye molecules and target virus-capture antibodies, performs the following functions: specific recognition and magnetic enrichment of target viruses in the solution and SERS detection of the viruses on the strip. Based on this strategy, the magnetic SERS strip can directly be used for real biological samples without any sample pretreatment steps. The limits of detection for H1N1 and HAdV were 50 and 10 pfu/mL, respectively, which were 2000 times more sensitive than those from the standard colloidal gold strip method. Moreover, the proposed strip is easy to operate, rapid, stable, and can achieve high throughput and is thus a potential tool for early detection of virus infection.

Detection Methods of Human and Animal Influenza Virus-Current Trends

The basic affairs connected to the influenza virus were reviewed in the article, highlighting the newest trends in its diagnostic methods. Awareness of the threat of influenza arises from its ability to spread and cause a pandemic. The undiagnosed and untreated viral infection can have a fatal effect on humans. Thus, the early detection seems pivotal for an accurate treatment, when vaccines and other contemporary prevention methods are not faultless. Public health is being attacked with influenza containing new genes from a genetic assortment between animals and humankind. Unfortunately, the population does not have immunity for mutant genes and is attacked in every viral outbreak season. For these reasons, fast and accurate devices are in high demand. As currently used methods like Rapid Influenza Diagnostic Tests lack specificity, time and cost-savings, new methods are being developed. In the article, various novel detection methods, such as electrical and optical were compared. Different viral elements used as detection targets and analysis parameters, such as sensitivity and specificity, were presented and discussed.

Thiophene-Conjugated Ligand Probe for Nonenzymatic Turn-On Electrochemical Protein Detection

A new type of turn-on electrochemical protein detection is developed using an electropolymerizable molecular probe. To detect trypsin, a benzamidine ligand is conjugated with a thiophene moiety. Encapsulation of the probe in the trypsin pocket prevents electropolymerization, leading to efficient electron transfer from the electrolyte to the electrode. In contrast, unbound probes can become electropolymerized, yielding a polythiophene layer on the electrode. The polythiophene formed this way suppressed electron transfer. The detection limit of trypsin using this electrochemical strategy is 50 nM. The method is shown to be useful for nonenzymatic turn-on electrochemical detection.

Synthesis of biotinylated bivalent zanamivir analogs as probes for influenza viruses

The synthesis of a biotinylated bivalent zanamivir analog as a probe for influenza viruses is reported. The compound was used in a ‘glycan’ based sandwich assay; where glycans were immobilized on glass slides to capture strains of influenza A H1N1, A/Brisbane/59/2007 virus; the biotinylated bivalent zanamivir analog-labeled streptavidin complex was used as reporter. This research strongly suggests that glycans can be used for capturing and reporting influenza viruses and the biotinylated compounds can be used as probes for capturing and isolating influenza viruses from complex mixtures.

Highly specific and rapid glycan based amperometric detection of influenza viruses

Rapid and precise detection of influenza viruses in a point of care setting is critical for applying appropriate countermeasures. Current methods such as nucleic acid or antibody based techniques are expensive or suffer from low sensitivity, respectively. We have developed an assay that uses glucose test strips and a handheld potentiostat to detect the influenza virus with high specificity. Influenza surface glycoprotein neuraminidase (NA), but not bacterial NA, cleaved galactose bearing substrates, 4,7di-OMe N-acetylneuraminic acid attached to the 3 or 6 position of galactose, to release galactose. In contrast, viral and bacterial NA cleaved the natural substrate, N-acetylneuraminic acid attached to the 3 or 6 position of galactose. The released galactose was detected amperometrically using a handheld potentiostat and dehydrogenase bearing glucose test strips. The specificity for influenza was confirmed using influenza strains and different respiratory pathogens that include Streptococcus pneumoniae and Haemophilus influenzae; bacteria do not cleave these molecules. The assay was also used to detect co-infections caused by influenza and bacterial NA. Viral drug susceptibility and testing with human clinical samples was successful in 15 minutes, indicating that this assay could be used to rapidly detect influenza viruses at primary care or resource poor settings using ubiquitous glucose meters.

Fluorescent Neuraminidase Assay Based on Supramolecular Dye Capture After Enzymatic Cleavage

A conceptually new type of enzymatic cleavage assay is reported that utilizes in situ supramolecular capture of the fluorescent product. A squaraine-derived substrate with large blocking groups at each end of its structure cannot be threaded by a tetralactam macrocycle until the blocking groups are removed by enzyme cleavage. A prototype design responds to viral neuraminidase, an indicator of influenza infection, and also measures susceptibility of the sample to neuraminidase inhibitor drugs. The substrate structure incorporates three key features: (a) a bis(4-amino-3-hydroxyphenyl)squaraine core with bright deep-red fluorescence and excellent photostability, (b) an N-methyl group at each end of the squaraine core that ensures fast macrocycle threading kinetics, and (c) sialic acid blocking groups that prevent macrocycle threading until they are removed by viral neuraminidase. The enzyme assay can be conducted in aqueous solution where dramatic colorimetric and fluorescence changes are easily observed by the naked eye. Alternatively, affinity capture beads coated with macrocycle can be used to immobilize the liberated squaraine and enable a range of heterogeneous analysis options. With further optimization, this new type of neuraminidase assay may be useful in a point of care clinic to rapidly diagnose influenza infection and also determine which of the approved antiviral inhibitor drugs is likely to be the most effective treatment for an individual patient. The assay design is generalizable and can be readily modified to monitor virtually any type of enzyme-catalyzed cleavage reaction.

Label-free Detection of Influenza Viruses using a Reduced Graphene Oxide-based Electrochemical Immunosensor Integrated with a Microfluidic Platform

Reduced graphene oxide (RGO) has recently gained considerable attention for use in electrochemical biosensing applications due to its outstanding conducting properties and large surface area. This report presents a novel microfluidic chip integrated with an RGO-based electrochemical immunosensor for label-free detection of an influenza virus, H1N1. Three microelectrodes were fabricated on a glass substrate using the photolithographic technique, and the working electrode was functionalized using RGO and monoclonal antibodies specific to the virus. These chips were integrated with polydimethylsiloxane microchannels. Structural and morphological characterizations were performed using X-ray photoelectron spectroscopy and scanning electron microscopy. Electrochemical studies revealed good selectivity and an enhanced detection limit of 0.5 PFU mL-1, where the chronoamperometric current increased linearly with H1N1 virus concentration within the range of 1 to 104 PFU mL-1 (R2 = 0.99). This microfluidic immunosensor can provide a promising platform for effective detection of biomolecules using minute samples.

Simple, rapid detection of influenza A (H1N1) viruses using a highly sensitive peptide-based molecular beacon

A peptide-based molecular beacon (PEP-MB) was prepared for the simple, rapid, and specific detection of H1N1 viruses using a fluorescence resonance energy transfer (FRET) system. The PEP-MB exhibited minimal fluorescence in its "closed" hairpin structure. However, in the presence of H1N1 viruses, the specific recognition of the hemagglutinin (HA) protein of H1 strains by the PEP-MB causes the beacon to assume an "open" structure that emits strong fluorescence. The PEP-MB could detect H1N1 viruses within 15 min or even 5 min and can exhibit strong fluorescence even at low viral concentrations, with a detection limit of 4 copies.

A promising magnetic SERS immunosensor for sensitive detection of avian influenza virus

Avian influenza viruses infect a great number of global populations every year and can lead to severe epidemics with high morbidity and mortality. Facile, rapid and sensitive detection of viruses is very crucial to control the viral spread at its early stage. In this work, we developed a novel magnetic immunosensor based on surface enhanced Raman scattering (SERS) spectroscopy to detect intact but inactivated influenza virus H3N2 (A/Shanghai/4084T/2012) by constructing a sandwich complex consisting of SERS tags, target influenza viruses and highly SERS-active magnetic supporting substrates. The procedure of sample pretreatment could be significantly simplified since the magnetic supporting substrates allowed the enrichment and separation of viruses from a complex matrix. With a portable Raman spectrometer, the immunosensor could detect H3N2 down to 10²TCID₅₀/mL (TCID₅₀ refers to tissue culture infection dose at 50% end point), with a good linear relationship from 10² to 5×10³ TCID₅₀/mL. Considering its time efficiency, portability and sensitivity, the proposed SERS-based magnetic immunoassay is very promising for a point-of-care (POC) test in clinical and diagnostic praxis.

Colorimetric detection of influenza A (H1N1) virus by a peptide-functionalized polydiacetylene (PEP-PDA) nanosensor

​We developed a peptide-functionalized polydiacetylene nanosensor for pH1N1 virus detection with the naked eye.

Dose-Dependent Response of Personal Glucose Meters to Nicotinamide Coenzymes: Applications to Point-of-Care Diagnostics of Many Non-Glucose Targets in a Single Step

We report a discovery that personal glucose meters (PGMs) can give a dose-dependent response to nicotinamide coenzymes, such as the reduced form of nicotinamide adenine dinucleotide (NADH). We have developed methods that take advantage of this discovery to perform one-step homogeneous assays of many non-glucose targets that are difficult to recognize by DNAzymes, aptamers, or antibodies, and without the need for conjugation and multiple steps of sample dilution, separation, or fluid manipulation. The methods are based on the target-induced consumption or production of NADH through cascade enzymatic reactions. Simultaneous monitoring of the glucose and L-lactate levels in human plasma from patients with diabetes is demonstrated and the results are comparable to those from current standard test methods. Since a large number of commercially available enzymatic assay kits utilize NADH in their detection, this discovery will allow the transformation of almost all of these clinical lab tests into POC tests that use a PGM.

Transmutation of Personal Glucose Meters into Portable and Highly Sensitive Microbial Pathogen Detection Platform

Herein, for the first time, we presented a simple and general approach by using personal glucose meters (PGM) for portable and ultrasensitive detection of microbial pathogens. Upon addition of pathogenic bacteria, glucoamylase-quaternized magnetic nanoparticles (GA-QMNPS) conjugates were disrupted by the competitive multivalent interactions between bacteria and QMNPS, resulting in the release of GA. After magnetic separation, the free GA could catalyze the hydrolysis of amylose into glucose for quantitative readout by PGM. In such way, PGM was transmuted into a bacterial detection device and extremely low detection limits down to 20 cells mL(-1) was achieved. More importantly, QMNPS could inhibit the growth of the bacteria and destroy its cellular structure, which enabled bacteria detection and inhibition simultaneously. The simplicity, portability, sensitivity and low cost of presented work make it attractive for clinical applications.