Fluorescent labels in biosensors for pathogen detection

Enhancing the understanding of SARS-CoV-2 protein with structure and detection methods: An integrative review

As the rapid and accurate screening of infectious diseases can provide meaningful information for outbreak prevention and control, as well as owing to the existing limitations of the polymerase chain reaction (PCR), it is imperative to have new and validated detection techniques for SARS-CoV-2. Therefore, the rationale for outlining the techniques used to detect SARS-CoV-2 proteins and performing a comprehensive comparison to serve as a practical benchmark for future identification of similar viral proteins is clear. This review highlights the urgent need to strengthen pandemic preparedness by emphasizing the importance of integrated measures. These include improved tools for pathogen characterization, optimized societal precautions, the establishment of early warning systems, and the deployment of highly sensitive diagnostics for effective surveillance, triage, and resource management. Additionally, with an improved understanding of the virus' protein structure, considerable advances in targeted detection, treatment, and prevention strategies are expected to greatly improve our ability to respond to future outbreaks.

AIEgens-enhanced rapid sensitive immunofluorescent assay for SARS-CoV-2 with digital microfluidics

BACKGROUND

Sensitive and rapid antigen detection is critical for the diagnosis and treatment of infectious diseases, but conventional ELISAs including chemiluminescence-based assays are limited in sensitivity and require many operation steps. Fluorescence immunoassays are fast and convenient but often show limited sensitivity and dynamic range.

RESULTS

To address the need, an aggregation-induced emission fluorgens (AIEgens) enhanced immunofluorescent assay with beads-based quantification on the digital microfluidic (DMF) platform was developed. Portable DMF devices and chips with small electrodes were fabricated, capable of manipulating droplets within 100 nL and boosting the reaction efficiency. AIEgen nanoparticles (NPs) with high fluorescence and photostability were synthesized to enhance the test sensitivity and detection range. The integration of AIEgen probes, transparent DMF chip design, and the large magnetic beads (10 μm) as capture agents enabled rapid and direct image-taking and signal calculation of the test result. The performance of this platform was demonstrated by point-of-care quantification of SARS-CoV-2 nucleocapsid (N) protein. Within 25 min, a limit of detection of 5.08 pg mL-1 and a limit of quantification of 8.91 pg mL-1 can be achieved using <1 μL sample. The system showed high reproducibility across the wide dynamic range (10-105 pg mL-1), with the coefficient of variance ranging from 2.6% to 9.8%.

SIGNIFICANCE

This rapid, sensitive AIEgens-enhanced immunofluorescent assay on the DMF platform showed simplified reaction steps and improved performance, providing insight into the small-volume point-of-care testing of different biomarkers in research and clinical applications.

Advances in endotoxin analysis

The outer membrane of gram-negative bacteria is primarily composed of lipopolysaccharide (LPS). In addition to protection, LPS defines the distinct serogroups used to identify bacteria specifically. Furthermore, LPS also act as highly potent stimulators of innate immune cells, a phenomenon essential to understanding pathogen invasion in the body. The complex multi-step process of LPS binding to cells involves several binding partners, including LPS binding protein (LBP), CD14 in both membrane-bound and soluble forms, membrane protein MD-2, and toll-like receptor 4 (TLR4). Once these pathways are activated, pro-inflammatory cytokines are eventually expressed. These binding events are also affected by the presence of monomeric or aggregated LPS. Traditional techniques to detect LPS include the rabbit pyrogen test, the monocyte activation test and Limulus-based tests. Modern approaches are based on protein, antibodies or aptamer binding. Recently, novel techniques including electrochemical methods, HPLC, quartz crystal microbalance (QCM), and molecular imprinting have been developed. These approaches often use nanomaterials such as gold nanoparticles, quantum dots, nanotubes, and magnetic nanoparticles. This chapter reviews current developments in endotoxin detection with a focus on modern novel techniques that use various sensing components, ranging from natural biomolecules to synthetic materials. Highly integrated and miniaturized commercial endotoxin detection devices offer a variety of options as the scientific and technologic revolution proceeds.

Label-Free Electrochemical Methods for Disease Detection

Label-free electrochemical biosensing leverages the advantages of label-free techniques, low cost, and fewer user steps, with the sensitivity and portability of electrochemical analysis. In this review, we identify four label-free electrochemical biosensing mechanisms: (a) blocking the electrode surface, (b) allowing greater access to the electrode surface, (c) changing the intercalation or electrostatic affinity of a redox probe to a biorecognition unit, and (d) modulating ion or electron transport properties due to conformational and surface charge changes. Each mechanism is described, recent advancements are summarized, and relative advantages and disadvantages of the techniques are discussed. Furthermore, two avenues for gaining further diagnostic information from label-free electrochemical biosensors, through multiplex analysis and incorporating machine learning, are examined.

Receptor-based detection of microplastics and nanoplastics: Current and future

Plastic pollution is an emerging environmental concern, gaining significant attention worldwide. They are classified into microplastics (MP; defined from 1 μm to 5 mm) and smaller nanoplastics (NP; <1 μm). NPs may pose higher ecological risks than MPs. Various microscopic and spectroscopic techniques have been used to detect MPs, and the same methods have occasionally been used for NPs. However, they are not based on receptors, which provide high specificity in most biosensing applications. Receptor-based micro/nanoplastics (MNP) detection can provide high specificity, distinguishing MNPs from the environmental samples and, more importantly, identifying the plastic types. It can also offer a low limit of detection (LOD) required for environmental screening. Such receptors are expected to detect NPs specifically at the molecular level. This review categorizes the receptors into cells, proteins, peptides, fluorescent dyes, polymers, and micro/nanostructures. Detection techniques used with these receptors are also summarized and categorized. There is plenty of room for future research to test for broader classes of environmental samples and many plastic types, to lower the LOD, and to apply the current techniques for NPs. Portable and handheld MNP detection should also be demonstrated for field use since the current demonstrations primarily utilized laboratory instruments. Detection on microfluidic platforms will also be crucial in miniaturizing and automating the assay and, eventually, collecting an extensive database to support machine learning-based classification of MNP types.

Conventional and advanced detection techniques of foodborne pathogens: A comprehensive review

Foodborne pathogens are a major public health concern and have a significant economic impact globally. From harvesting to consumption stages, food is generally contaminated by viruses, parasites, and bacteria, which causes foodborne diseases such as hemorrhagic colitis, hemolytic uremic syndrome (HUS), typhoid, acute, gastroenteritis, diarrhea, and thrombotic thrombocytopenic purpura (TTP). Hence, early detection of foodborne pathogenic microbes is essential to ensure a safe food supply and to prevent foodborne diseases. The identification of foodborne pathogens is associated with conventional (e.g., culture-based, biochemical test-based, immunological-based, and nucleic acid-based methods) and advances (e.g., hybridization-based, array-based, spectroscopy-based, and biosensor-based process) techniques. For industrial food applications, detection methods could meet parameters such as accuracy level, efficiency, quickness, specificity, sensitivity, and non-labor intensive. This review provides an overview of conventional and advanced techniques used to detect foodborne pathogens over the years. Therefore, the scientific community, policymakers, and food and agriculture industries can choose an appropriate method for better results.

An indolizine squaraine-based water-soluble NIR dye for fluorescence imaging of multidrug-resistant bacteria and antibacterial/antibiofilm activity using the photothermal effect

The majority of nosocomial infections are caused by bacteria with antimicrobial resistance and the formation of biofilms, such as implant-related bacterial infections and sepsis. There is an urgent need to develop new strategies for early-stage screening, destruction of multidrug-resistant bacteria, and efficient inhibition of biofilms. Organic dyes that absorb and emit in the near-infrared (NIR) region are potentially non-invasive, high-resolution, and rapid biological imaging materials. In this study, a non-toxic and biocompatible indolizine squaraine dye with water-solubilizing sulfonate groups (SO₃SQ) is studied for bacterial imaging and photothermal therapy (PTT). PTT is efficient in eliminating microorganisms through local hyperthermia without the risk of developing drug-resistant bacteria. The optical properties of SO₃SQ are studied extensively in phosphate-buffered saline (PBS). UV-Vis-NIR absorption spectra analysis shows a strong absorption between 650 nm - 1000 nm. SO₃SQ allows for the wash-free fluorescence imaging of drug-resistant bacteria via NIR fluorescence imaging due to a "turn-on" fluorescence property of the dye when interacting with bacteria. Although SO₃SQ exhibits no toxicity against both Gram-positive bacteria and Gram-negative bacteria, the PTT property of SO₃SQ is efficient in killing bacteria as well as inhibiting and eradicating biofilms. PTT experiments demonstrate that SO₃SQ reduces 90% of cell viability in bacterial strains under NIR radiation with a minimum inhibition concentration (MIC₉₀) of >450 μg/mL. The PTT property of SO₃SQ can also inhibit biofilms (BIC₉₀ = 1000-2000 μg/mL) and eradicate both preformed young and mature biofilms (MBEC₉₀ = 1500-2000 μg/mL) as observed by crystal violet assays.

Progress in Fluorescence Biosensing and Food Safety towards Point-of-Detection (PoD) System

The detection of pathogens in food substances is of crucial concern for public health and for the safety of the natural environment. Nanomaterials, with their high sensitivity and selectivity have an edge over conventional organic dyes in fluorescent-based detection methods. Advances in microfluidic technology in biosensors have taken place to meet the user criteria of sensitive, inexpensive, user-friendly, and quick detection. In this review, we have summarized the use of fluorescence-based nanomaterials and the latest research approaches towards integrated biosensors, including microsystems containing fluorescence-based detection, various model systems with nano materials, DNA probes, and antibodies. Paper-based lateral-flow test strips and microchips as well as the most-used trapping components are also reviewed, and the possibility of their performance in portable devices evaluated. We also present a current market-available portable system which was developed for food screening and highlight the future direction for the development of fluorescence-based systems for on-site detection and stratification of common foodborne pathogens.

Recent Advances of Representative Optical Biosensors for Rapid and Sensitive Diagnostics of SARS-CoV-2

The outbreak of Corona Virus Disease 2019 (COVID-19) has again emphasized the significance of developing rapid and highly sensitive testing tools for quickly identifying infected patients. Although the current reverse transcription polymerase chain reaction (RT-PCR) diagnostic techniques can satisfy the required sensitivity and specificity, the inherent disadvantages with time-consuming, sophisticated equipment and professional operators limit its application scopes. Compared with traditional detection techniques, optical biosensors based on nanomaterials/nanostructures have received much interest in the detection of SARS-CoV-2 due to the high sensitivity, high accuracy, and fast response. In this review, the research progress on optical biosensors in SARS-CoV-2 diagnosis, including fluorescence biosensors, colorimetric biosensors, Surface Enhancement Raman Scattering (SERS) biosensors, and Surface Plasmon Resonance (SPR) biosensors, was comprehensively summarized. Further, promising strategies to improve optical biosensors are also explained. Optical biosensors can not only realize the rapid detection of SARS-CoV-2 but also be applied to judge the infectiousness of the virus and guide the choice of SARS-CoV-2 vaccines, showing enormous potential to become point-of-care detection tools for the timely control of the pandemic.

The role of Nucleic Acid Mimics (NAMs) on FISH-based techniques and applications for microbial detection

Fluorescent in situ hybridization (FISH) is a powerful tool that for more than 30 years has allowed to detect and quantify microorganisms as well as to study their spatial distribution in three-dimensional structured environments such as biofilms. Throughout these years, FISH has been improved in order to face some of its earlier limitations and to adapt to new research objectives. One of these improvements is related to the emergence of Nucleic Acid Mimics (NAMs), which are now employed as alternatives to the DNA and RNA probes that have been classically used in FISH. NAMs such as peptide and locked nucleic acids (PNA and LNA) have provided enhanced sensitivity and specificity to the FISH technique, as well as higher flexibility in terms of applications. In this review, we aim to cover the state-of-the-art of the different NAMs and explore their possible applications in FISH, providing a general overview of the technique advancement in the last decades.

Continuous monitoring of molecular biomarkers in microfluidic devices

The ability to monitor molecular targets is crucial in fields ranging from healthcare to industrial processing to environmental protection. Devices employing biomolecules to achieve this goal are called biosensors. Over the last half century researchers have developed dozens of different biosensor approaches. In this chapter we analyze recent advances in the biosensing field aiming at adapting these to the problem of continuous molecular monitoring in complex sample streams, and how the merging of these sensors with lab-on-a-chip technologies would be beneficial to both. To do so we discuss (1) the components that comprise a biosensor, (2) the challenges associated with continuous molecular monitoring in complex sample streams, (3) how different sensing strategies deal with (or fail to deal with) these challenges, and (4) the implementation of these technologies into lab-on-a-chip architectures.

Optical bio-sensing of DNA methylation analysis: an overview of recent progress and future prospects

DNA methylation as one of the most important epigenetic modifications has a critical role in regulating gene expression and drug resistance in treating diseases such as cancer. Therefore, the detection of DNA methylation in the early stages of cancer plays an essential role in disease diagnosis. The majority of routine methods to detect DNA methylation are very tedious and costly. Therefore, designing easy and sensitive methods to detect DNA methylation directly and without the need for molecular methods is a hot topic issue in bioscience. Here we provide an overview on the optical biosensors (including fluorescence, FRET, SERs, colorimetric) that have been applied to detect the DNA methylation. In addition, various types of labeled and label-free reactions along with the application of molecular methods and optical biosensors have been surveyed. Also, the effect of nanomaterials on the sensitivity of detection methods is discussed. Furthermore, a comprehensive overview of the advantages and disadvantages of each method are provided. Finally, the use of microfluidic devices in the evaluation of DNA methylation and DNA damage analysis based on smartphone detection has been discussed.

Here, we provide an overview on the optical biosensors (including fluorescence, FRET, SERs, colorimetric) that have been applied to detect the DNA methylation.

Optical Biosensors for Diagnostics of Infectious Viral Disease: A Recent Update

The design and development of biosensors, analytical devices used to detect various analytes in different matrices, has emerged. Biosensors indicate a biorecognition element with a physicochemical analyzer or detector, i.e., a transducer. In the present scenario, various types of biosensors have been deployed in healthcare and clinical research, for instance, biosensors for blood glucose monitoring. Pathogenic microbes are contributing mediators of numerous infectious diseases that are becoming extremely serious worldwide. The recent outbreak of COVID-19 is one of the most recent examples of such communal and deadly diseases. In efforts to work towards the efficacious treatment of pathogenic viral contagions, a fast and precise detection method is of the utmost importance in biomedical and healthcare sectors for early diagnostics and timely countermeasures. Among various available sensor systems, optical biosensors offer easy-to-use, fast, portable, handy, multiplexed, direct, real-time, and inexpensive diagnosis with the added advantages of specificity and sensitivity. Many progressive concepts and extremely multidisciplinary approaches, including microelectronics, microelectromechanical systems (MEMSs), nanotechnologies, molecular biology, and biotechnology with chemistry, are used to operate optical biosensors. A portable and handheld optical biosensing device would provide fast and reliable results for the identification and quantitation of pathogenic virus particles in each sample. In the modern day, the integration of intelligent nanomaterials in the developed devices provides much more sensitive and highly advanced sensors that may produce the results in no time and eventually help clinicians and doctors enormously. This review accentuates the existing challenges engaged in converting laboratory research to real-world device applications and optical diagnostics methods for virus infections. The review's background and progress are expected to be insightful to the researchers in the sensor field and facilitate the design and fabrication of optical sensors for life-threatening viruses with broader applicability to any desired pathogens.

Fast label-free identification of bacteria by synchronous fluorescence of amino acids

Fast identification of pathogenic bacteria is an essential need for patient's diagnostic in hospitals and environmental monitoring of water and air quality. Bacterial cells consist of a very high amount of biological molecules whose content changes in response to different environmental conditions. The similarity between the molecular compositions of different bacterial cells limits the possibility to find unique markers to enable differentiation among species. Although many biological molecules in the cells absorb at the UV-Vis region, only a few of them can be detected in whole cells by their intrinsic fluorescence. Among these molecules are the amino acids phenylalanine, tyrosine, and tryptophan. In this work, we develop a rapid method for bacterial identification by synchronous fluorescence. We show that we can quantify the concentration for the 3 amino acids without any significant interference from other fluorophores in the cells and that we can differentiate among 6 pathogenic bacterial species by using the concentrations of their amino acids as a bacterial fingerprint. Fluorescent amino acids exist in all living cells. Therefore, this method has the potential to be applicative for the rapid identification of cells from all kinds of organisms.

Prevent or Cure-The Unprecedented Need for Self-Reporting Materials

Self-reporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than self-healing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of self-reporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring self-reporting research concepts from the laboratory to the real world. Especially in the space of diagnostic self-reporting systems, the recent SARS-CoV-2 (COVID-19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a self-reporting fashion.

Biosensor Technologies for Early Detection and Quantification of Plant Pathogens

Plant pathogens are a major reason of reduced crop productivity and may lead to a shortage of food for both human and animal consumption. Although chemical control remains the main method to reduce foliar fungal disease incidence, frequent use can lead to loss of susceptibility in the fungal population. Furthermore, over-spraying can cause environmental contamination and poses a heavy financial burden on growers. To prevent or control disease epidemics, it is important for growers to be able to detect causal pathogen accurately, sensitively, and rapidly, so that the best practice disease management strategies can be chosen and enacted. To reach this goal, many culture-dependent, biochemical, and molecular methods have been developed for plant pathogen detection. However, these methods lack accuracy, specificity, reliability, and rapidity, and they are generally not suitable for in-situ analysis. Accordingly, there is strong interest in developing biosensing systems for early and accurate pathogen detection. There is also great scope to translate innovative nanoparticle-based biosensor approaches developed initially for human disease diagnostics for early detection of plant disease-causing pathogens. In this review, we compare conventional methods used in plant disease diagnostics with new sensing technologies in particular with deeper focus on electrochemical and optical biosensors that may be applied for plant pathogen detection and management. In addition, we discuss challenges facing biosensors and new capability the technology provides to informing disease management strategies.

Recent progress in fluorescent probes for bacteria

Food fermentation, antibiotics, and pollutant degradation are closely related to bacteria. Bacteria play an irreplaceable role in life. However, some bacteria seriously threaten human health and cause large-scale infectious diseases. Therefore, there is a pressing need to develop strategies to accurately monitor bacteria. Technology based on molecular probes and fluorescence imaging is noninvasive, results in little damage, and has high specificity and sensitivity, so it has been widely applied in the detection of bacteria. In this review, we summarize the recent progress in bacterial detection using fluorescence. In particular, we generalize the mechanisms commonly used to design organic fluorescent probes for detecting and imaging bacteria. Moreover, a perspective regarding fluorescent probes for bacterial detection is discussed.

Imaging, Identification and Inhibition of Microorganisms Using AIEgens

Microorganisms, including bacteria, viruses and fungi, are ubiquitous in nature. Some are extremely beneficial to life on Earth, whereas some cause diseases and disrupt normal human physiology. Pathogenic microorganisms can also undergo mutations and develop resistance to antimicrobial agents, which complicates diagnostic and therapeutic regimens. This calls for continuing efforts to develop new strategies and tools that can provide fast, sensitive and accurate diagnosis, as well as effective treatment of ever-evolving infectious diseases. Aggregation-induced emission luminogens (AIEgens) have shown promise in imaging, identification and inhibition of various microbial species. Compared to conventional organic fluorophores, AIEgens can offer improved photostability, and have found utilities in imaging microorganisms. AIEgens have been shown to detect microbial viability and differentiate among different microbial strains. Theranostic AIEgens that integrate imaging and killing of microbes have also been developed. This review highlights examples in the literature where AIEgens have been employed as molecular probes in the imaging, discrimination and killing of bacteria, viruses and fungi.

Point-of-care diagnostics for infectious diseases: From methods to devices

The current widespread of COVID-19 all over the world, which is caused by SARS-CoV-2 virus, has again emphasized the importance of development of point-of-care (POC) diagnostics for timely prevention and control of the pandemic. Compared with labor- and time-consuming traditional diagnostic methods, POC diagnostics exhibit several advantages such as faster diagnostic speed, better sensitivity and specificity, lower cost, higher efficiency and ability of on-site detection. To achieve POC diagnostics, developing POC detection methods and correlated POC devices is the key and should be given top priority. The fast development of microfluidics, micro electro-mechanical systems (MEMS) technology, nanotechnology and materials science, have benefited the production of a series of portable, miniaturized, low cost and highly integrated POC devices for POC diagnostics of various infectious diseases. In this review, various POC detection methods for the diagnosis of infectious diseases, including electrochemical biosensors, fluorescence biosensors, surface-enhanced Raman scattering (SERS)-based biosensors, colorimetric biosensors, chemiluminiscence biosensors, surface plasmon resonance (SPR)-based biosensors, and magnetic biosensors, were first summarized. Then, recent progresses in the development of POC devices including lab-on-a-chip (LOC) devices, lab-on-a-disc (LOAD) devices, microfluidic paper-based analytical devices (μPADs), lateral flow devices, miniaturized PCR devices, and isothermal nucleic acid amplification (INAA) devices, were systematically discussed. Finally, the challenges and future perspectives for the design and development of POC detection methods and correlated devices were presented. The ultimate goal of this review is to provide new insights and directions for the future development of POC diagnostics for the management of infectious diseases and contribute to the prevention and control of infectious pandemics like COVID-19.

Nanobiosensors for the Detection of Novel Coronavirus 2019-nCoV and Other Pandemic/Epidemic Respiratory Viruses: A Review

The coronavirus disease 2019 (COVID-19) pandemic is considered a public health emergency of international concern. The 2019 novel coronavirus (2019-nCoV) or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused this pandemic has spread rapidly to over 200 countries, and has drastically affected public health and the economies of states at unprecedented levels. In this context, efforts around the world are focusing on solving this problem in several directions of research, by: (i) exploring the origin and evolution of the phylogeny of the SARS-CoV-2 viral genome; (ii) developing nanobiosensors that could be highly effective in detecting the new coronavirus; (iii) finding effective treatments for COVID-19; and (iv) working on vaccine development. In this paper, an overview of the progress made in the development of nanobiosensors for the detection of human coronaviruses (SARS-CoV, SARS-CoV-2, and Middle East respiratory syndrome coronavirus (MERS-CoV) is presented, along with specific techniques for modifying the surface of nanobiosensors. The newest detection methods of the influenza virus responsible for acute respiratory syndrome were compared with conventional methods, highlighting the newest trends in diagnostics, applications, and challenges of SARS-CoV-2 (COVID-19 causative virus) nanobiosensors.

Fractal Silver Dendrites as 3D SERS Platform for Highly Sensitive Detection of Biomolecules in Hydration Conditions

In this paper, we report on the realization of a highly sensitive and low cost 3D surface-enhanced Raman scattering (SERS) platform. The structural features of the Ag dendrite network that characterize the SERS material were exploited, attesting a remarked self-similarity and scale invariance over a broad range of length scales that are typical of fractal systems. Additional structural and optical investigations confirmed the purity of the metal network, which was characterized by low oxygen contamination and by broad optical resonances introduced by the fractal behavior. The SERS performances of the 3D fractal Ag dendrites were tested for the detection of lysozyme as probe molecule, attesting an enhancement factor of ~2.4 × 10⁶. Experimental results assessed the dendrite material as a suitable SERS detection platform for biomolecules investigations in hydration conditions.

Recent advances in thread-based microfluidics for diagnostic applications

Over the past decades, researchers have been seeking attractive substrate materials to keep microfluidics improving to outbalance the drawbacks and issues. Cellulose substrates, including thread, paper and hydrogels are alternatives due to their distinct structural and mechanical properties for a number of applications. Thread have gained considerable attention and become promising powerful tool due to its advantages over paper-based systems thus finds numerous applications in the development of diagnostic systems, smart bandages and tissue engineering. To the best of our knowledge, no comprehensive review articles on the topic of thread-based microfluidics have been published and it is of significance for many scientific communities working on Microfluidics, Biosensors and Lab-on-Chip. This review gives an overview of the advances of thread-based microfluidic diagnostic devices in a variety of applications. It begins with an overall introduction of the fabrication followed by an in-depth review on the detection techniques in such devices and various applications with respect to effort and performance to date. A few perspective directions of thread-based microfluidics in its development are also discussed. Thread-based microfluidics are still at an early development stage and further improvements in terms of fabrication, analytical strategies, and function to become low-cost, low-volume and easy-to-use point-of-care (POC) diagnostic devices that can be adapted or commercialized for real world applications.

An Aggregation-Induced Emission-Based Indirect Competitive Immunoassay for Fluorescence "Turn-On" Detection of Drug Residues in Foodstuffs

A new fluorescent "turn-on" probe-based immunosensor for detecting drug residues in foodstuffs was established by combining the mechanism of aggregation-induced emission (AIE) and an indirect competitive enzyme-linked immunosorbent assay (ELISA). In this study, a luminogen, with negligible fluorescence emission (TPE-HPro), aggregated in the presence of H2O2, and exhibited astrong yellow emission based on its AIE characteristics. This AIE process was further configured into an immunoassay for analyzing drug residues in foodstuffs. In this approach, glucose oxidase (GOx) was used as an enzyme label for the immunoassay and triggered GOx/glucose-mediated H2O2 generation, which caused oxidation of TPE-HPro and a "turn-on" fluorescence response at 540 nm. To quantitatively analyze the drug residues in foodstuffs, we used amantadine (AMD) as an assay model. By combining the AIE-active "turn-on" fluorescent signal generation mechanism with conventional ELISAs, quantifying AMD concentrations in chicken muscle samples was realized with an IC50 (50% inhibitory concentration) value of 0.38 ng/mL in buffer and a limited detection of 0.06 μg/kg in chicken samples. Overall, the conceptual integration of AIE with ELISA represents a potent and sensitive strategy that broadens the applicability of the AIE-based fluorometric assays.

Optimizing channel selection for excitation-scanning hyperspectral imaging

A major benefit of fluorescence microscopy is the now plentiful selection of fluorescent markers. These labels can be chosen to serve complementary functions, such as tracking labeled subcellular molecules near demarcated organelles. However, with the standard 3 or 4 emission channels, multiple label detection is restricted to segregated regions of the electromagnetic spectrum, as in RGB coloring. Hyperspectral imaging allows the user to discern many fluorescence labels by their unique spectral properties, provided there is significant differentiation of their emission spectra. The cost of this technique is often an increase in gain or exposure time to accommodate the signal reduction from separating the signal into many discrete excitation or emission channels. Recent advances in hyperspectral imaging have allowed the acquisition of more signal in a shorter time period by scanning the excitation spectra of fluorophores. Here, we explore the selection of optimal channels for both significant signal separation and sufficient signal detection using excitation-scanning hyperspectral imaging. Excitation spectra were obtained using a custom inverted microscope (TE-2000, Nikon Instruments) with a Xe arc lamp and thin film tunable filter array (VersaChrome, Semrock, Inc.) Tunable filters had bandwidths between 13 and 17 nm. Scans utilized excitation wavelengths between 340 nm and 550 nm. Hyperspectral image stacks were generated and analyzed using ENVI and custom MATLAB scripts. Among channel consideration criteria were: number of channels, spectral range of scan, spacing of center wavelengths, and acquisition time.

Aptasensors for pesticide detection

Pesticide contamination has become one of the most serious problems of public health in the world, due to their wide application in agriculture industry to guarantee the crop yield and quality. The detection of pesticide residues plays an important role in food safety management and environment protection. However, the conventional detection methodologies cannot realize highly sensitive, selective and on-site detection, which limits their applications. Aptamers are short single-stranded oligonucleotides (RNA or DNA) selected by SELEX method, which can selectively bind to their targets with high affinity. Compared with the commonly used antibodies or enzymes in designing biosensors, aptamers exhibit better stability, low molecular weight, easy modification and low cost, and were regarded as excellent candidates for developing aptasensors for pesticide detection. In this review, application of aptamers for pesticide detection was reviewed. Firstly, aptamers specifically bind to various pesticides were first summarized. Secondly, the progresses and highlights of developing aptasensors for highly-sensitive and selective detection of pesticide residues were systematically provided. Finally, the present challenges and future perspectives for developing novel highly-effective aptasensor for the detection of pesticide residues were discussed.

Recent Advances in AIV Biosensors Composed of Nanobio Hybrid Material

Since the beginning of the 2000s, globalization has accelerated because of the development of transportation systems that allow for human and material exchanges throughout the world. However, this globalization has brought with it the rise of various pathogenic viral agents, such as Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), Zika virus, and Dengue virus. In particular, avian influenza virus (AIV) is highly infectious and causes economic, health, ethnical, and social problems to human beings, which has necessitated the development of an ultrasensitive and selective rapid-detection system of AIV. To prevent the damage associated with the spread of AIV, early detection and adequate treatment of AIV is key. There are traditional techniques that have been used to detect AIV in chickens, ducks, humans, and other living organisms. However, the development of a technique that allows for the more rapid diagnosis of AIV is still necessary. To achieve this goal, the present article reviews the use of an AIV biosensor employing nanobio hybrid materials to enhance the sensitivity and selectivity of the technique while also reducing the detection time and high-throughput process time. This review mainly focused on four techniques: the electrochemical detection system, electrical detection method, optical detection methods based on localized surface plasmon resonance, and fluorescence.

Self-Assembly of Antigen Proteins into Nanowires Greatly Enhances the Binding Affinity for High-Efficiency Target Capture

High-efficiency target capture is an essential prerequisite for sensitive immunoassays. However, the current available immunoassay approaches are subject to deficient binding affinities between predator-prey molecules that greatly restrict the target capture efficiency and immunoassay sensitivity. Herein, we present a new strategy through the self-assembly of antigen proteins into nanowires to enhance the binding affinity between an antigen and antibody. Through the genetic fusion of antigen proteins (e.g., HIV p24) with the yeast amyloid protein Sup35 self-assembly domain, specific antigen nanowires (Ag nanowires) were constructed and demonstrated a remarkable enhancement in binding affinity compared with that of the monomeric antigen molecule. The Ag nanowires were further combined with magnetic beads to form a 3D magnetic probe based on a seed-induced self-assembly strategy. Taking advantage of both the strong binding affinity and the rapid magnetic separation and enrichment capacity, the specific 3D magnetic probe achieved a 100-fold improvement in detection sensitivity within a significantly shorter period of 20 min over that of the conventional enzyme-linked immunosorbent assay method.

Towards DNA methylation detection using biosensors

DNA methylation, a stable and heritable covalent modification which mostly occurs in the context of a CpG dinucleotide, has great potential as a biomarker to detect disease, provide prognoses and predict therapeutic responses. It can be detected in a quantitative manner by many different approaches both genome-wide and at specific gene loci, in various biological fluids such as urine, plasma, and serum, which can be obtained without invasive procedures. The current, classical methods are effective in studying DNA methylation patterns, however, for the most part; they have major drawbacks such as expensive instruments, complicated and time consuming protocols as well as relatively low sensitivity, and high false positive rates. To overcome these obstacles, great efforts have been made toward the development of reliable sensor devices to solve these limitations, providing sensitive, fast and cost-effective measurements. The use of biosensors for DNA methylation biomarkers has increased in recent years, because they are portable, simple, rapid, and inexpensive which offers a straightforward way to detect methylated biomarkers. In this review, we give an overview of the conventional techniques for the detection of DNA methylation and then will focus on recent advances in biosensor based methylation detection that eliminate bisulfite conversion and PCR amplification.

Encapsulation-Stabilized, Europium Containing Nanoparticle as a Probe for Time-Resolved luminescence Detection of Cardiac Troponin I

The use of a robust optical signaling probe with a high signal-to-noise ratio is important in the development of immunoassays. Lanthanide chelates are a promising material for this purpose, which provide time-resolved luminescence (TRL) due to their large Stokes shift and long luminescence lifetime. From this, they have attracted considerable interest in the in vitro diagnostics field. However, the direct use of lanthanide chelates is limited because their luminescent signal can be easily affected by various quenchers. To overcome this drawback, strategies that rely on the entrapment of lanthanide chelates inside nanoparticles, thereby enabling the protection of the lanthanide chelate from water, have been reported. However, the poor stability of the lanthanide-entrapped nanoparticles results in a significant fluctuation in TRL signal intensity, and this still remains a challenging issue. To address this, we have developed a Lanthanide chelate-Encapsulated Silica Nano Particle (LESNP) as a new immunosensing probe. In this approach, the lanthanide chelate is covalently crosslinked within the silane monomer during the silica nanoparticle formation. The resulting LESNP is physically stable and retains TRL properties of the parent lanthanide chelate. Using the probe, a highly sensitive, sandwich-based TRL immunoassay for the cardiac troponin I was conducted, exhibiting a limit of detection of 48 pg/mL. On the basis of the features of the LESNP such as TRL signaling capability, stability, and the ease of biofunctionalization, we expect that the LESNP can be widely applied in the development of TRL-based immunosensing.

Multifunctional Nanotechnology-Enabled Sensors for Rapid Capture and Detection of Pathogens

Nanomaterial-based sensing approaches that incorporate different types of nanoparticles (NPs) and nanostructures in conjunction with natural or synthetic receptors as molecular recognition elements provide opportunities for the design of sensitive and selective assays for rapid detection of contaminants. This review summarizes recent advancements over the past ten years in the development of nanotechnology-enabled sensors and systems for capture and detection of pathogens. The most common types of nanostructures and NPs, their modification with receptor molecules and integration to produce viable sensing systems with biorecognition, amplification and signal readout are discussed. Examples of all-in-one systems that combine multifunctional properties for capture, separation, inactivation and detection are also provided. Current trends in the development of low-cost instrumentation for rapid assessment of food contamination are discussed as well as challenges for practical implementation and directions for future research.

New and developing diagnostic technologies for urinary tract infections

Timely and accurate identification and determination of the antimicrobial susceptibility of uropathogens is central to the management of UTIs. Urine dipsticks are fast and amenable to point-of-care testing, but do not have adequate diagnostic accuracy or provide microbiological diagnosis. Urine culture with antimicrobial susceptibility testing takes 2-3 days and requires a clinical laboratory. The common use of empirical antibiotics has contributed to the rise of multidrug-resistant organisms, reducing treatment options and increasing costs. In addition to improved antimicrobial stewardship and the development of new antimicrobials, novel diagnostics are needed for timely microbial identification and determination of antimicrobial susceptibilities. New diagnostic platforms, including nucleic acid tests and mass spectrometry, have been approved for clinical use and have improved the speed and accuracy of pathogen identification from primary cultures. Optimization for direct urine testing would reduce the time to diagnosis, yet these technologies do not provide comprehensive information on antimicrobial susceptibility. Emerging technologies including biosensors, microfluidics, and other integrated platforms could improve UTI diagnosis via direct pathogen detection from urine samples, rapid antimicrobial susceptibility testing, and point-of-care testing. Successful development and implementation of these technologies has the potential to usher in an era of precision medicine to improve patient care and public health.

Monoclonal Antibodies and Immunoassay for Medical Plant-Derived Natural Products: A Review

Owing to the widespread application value, monoclonal antibodies (MAbs) have become a tool of increasing importance in modern bioscience research since their emergence. Recently, some researchers have focused on the production of MAbs against medical plant-derived natural products (MPNP), the secondary metabolites of medical plants. At the same time, various immunoassay methods were established on the basis of these MPNP MAbs, and then rapidly developed into a novel technique for medical plant and phytomedicine research in the area of quality control, pharmacological analysis, drug discovery, and so on. Dependent on the research works carried out in recent years, this paper aims to provide a comprehensive review of MAbs against MPNP and the application of various immunoassay methods established on the basis of these MAbs, and conclude with a short section on future prospects and research trends in this area.

Fluorescent Protein Nanowire-Mediated Protein Microarrays for Multiplexed and Highly Sensitive Pathogen Detection

Protein microarrays are powerful tools for high-throughput and simultaneous detection of different target molecules in complex biological samples. However, the sensitivity of conventional fluorescence-labeling protein detection methods is limited by the availability of signal molecules for binding to the target molecule. Here, we built a multifunctional fluorescent protein nanowire (FNw) by harnessing self-assembly of yeast amyloid protein. The FNw integrated a large number of fluorescent molecules, thereby enhancing the fluorescent signal output in target detection. The FNw was then combined with protein microarray technology to detect proteins derived from two pathogens, including influenza virus (hemagglutinin 1, HA1) and human immunodeficiency virus (p24 and gp120). The resulting detection sensitivity achieved a 100-fold improvement over a commercially available detection reagent.

Fabricating Upconversion Fluorescent Probes for Rapidly Sensing Foodborne Pathogens

Rare earth-doped upconversion nanoparticles (UCNPs) have promising potential in the field of food safety because of their unique frequency upconverting capability and high detection sensitivity. Here, we report a rapid and sensitive UCNP-based bacterium-sensing strategy using Escherichia coli. Highly fluorescent and water-soluble UCNPs were fabricated and conjugated with antibodies against E. coli for use as fluorescent probes. The E. coli were successively captured by the fluorescent probes. After the captured cell samples were pelleted, the differences in the fluorescence intensities between sample supernatants and the control were observed to increase linearly with E. coli concentration from 42 to 42 × 10(6) colony-forming units (cfu)/mL (R(2) = 0.9802), resulting in a relatively low limit of detection of 10 cfu/mL. Furthermore, the ability of the bioassay to detect E. coli was also confirmed in adulterated meat and milk samples.

Advances and challenges in biosensor-based diagnosis of infectious diseases

Rapid diagnosis of infectious diseases and timely initiation of appropriate treatment are critical determinants that promote optimal clinical outcomes and general public health. Conventional in vitro diagnostics for infectious diseases are time-consuming and require centralized laboratories, experienced personnel and bulky equipment. Recent advances in biosensor technologies have potential to deliver point-of-care diagnostics that match or surpass conventional standards in regards to time, accuracy and cost. Broadly classified as either label-free or labeled, modern biosensors exploit micro- and nanofabrication technologies and diverse sensing strategies including optical, electrical and mechanical transducers. Despite clinical need, translation of biosensors from research laboratories to clinical applications has remained limited to a few notable examples, such as the glucose sensor. Challenges to be overcome include sample preparation, matrix effects and system integration. We review the advances of biosensors for infectious disease diagnostics and discuss the critical challenges that need to be overcome in order to implement integrated diagnostic biosensors in real world settings.