Lab in a Tube: Point-of-Care Detection of Escherichia coli

Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on self-assembly of MCOF with Au NPs nanozyme coupled AIEgen

Sensitive, accurate, simple and quick monitoring of Salmonella typhimurium (S. typhimurium) in food is significant for preventing food poisoning, but still remains a challenge. Herein, a colorimetry/fluorescence dual-mode sensing strategy was fabricated to detect S. typhimurium by integrating the self-assembly of magnetic covalent organic framework (MCOF) with gold nanoparticles (Au NPs) as the peroxidase-mimicking nanozyme and aggregation-induced emission luminogen (AIEgen). S. typhimurium could competitive bind to aptamer conjugated Au NPs (Au NPs@apt), inhibit the self-assembly of MCOF with Au NPs, and shield the catalytic activity of AuNPs. After adding H2O2 and TPE-4A, the dark green solution changed to light with increasing S. typhimurium concentration, on the contrary, the fluorescent signals were generated. As a result, in colorimetry/fluorescence modes, S. typhimurium could be detected in the linear ranges of 103-108 CFU mL-1 and 101-107 CFU mL-1, with LODs of 1000 and 10 CFU mL-1, respectively. Importantly, different colors consistent with various S. typhimurium concentrations can be accurately classified by smartphone app and linear discriminant analysis (LDA). The smartphone-assisted data interpretation can generate complementary colorimetry and fluorescence signals without any sophisticated equipment and achieve on-site detection. Moreover, the proposed strategy could be explored for S. typhimurium monitoring in milk with satisfactory recoveries (97.6-100.4 %) in colorimetry and fluorescence mode and good classification and prediction performance in smartphone/LDA system, suggesting the feasibility and potential applications of the sensing platform.

Research progress of All-in-One PCR tube biosensors based on functional modification and intelligent fabrication

PCR amplification technology is the cornerstone of molecular biology. All-in-One PCR tube, as an emerging integrated device, is booming in biosensors application. All-in-One PCR tube biosensors are integrated PCR tubes designed for signal recognition, signal amplification or signal output. They enable "one-pot" detection within functionally modified and intelligently fabricated PCR tubes, effectively overcoming the limitations of conventional PCR applications, like complex procedural steps, risk of contamination and so on. Based on this, the review article summarizes the recent advance of All-in-One PCR tube biosensors for the first time as well as systematically categorizes five approaches of functional modification, three types of intelligent fabrication and relevant property characterization techniques. More emphasis is placed on the review of five ways of functional modification, including physical modification, chemical modification, UV photografting surface treatment, plasma surface modification, and layer-by-layer assembly coating. Moreover, All-in-One PCR tube biosensors covering different recognition elements range from small molecules to protein are detailed discussed on principle of sensing, providing a deeper understanding of the design and application of All-in-One-tube biosensor. Last, the future opportunities and challenges in this fascinating field are also deliberated.

Gold Nanoparticle-Based Colorimetric Biosensing for Foodborne Pathogen Detection

Ensuring safe high-quality food is an ongoing priority, yet consumers face heightened risk from foodborne pathogens due to extended supply chains and climate change in the food industry. Nanomaterial-based assays are popular and have recently been developed to ensure food safety and high quality. This review discusses strategies for utilizing gold nanoparticles in colorimetric biosensors. The visible-signal biosensor proves to be a potent sensing technique for directly measuring targets related to foodborne pathogens in the field of food analysis. Among visible-signal biosensors, the localized surface plasmon resonance (LSPR) biosensor has garnered increasing attention and experienced rapid development in recent years. This review succinctly introduces the origin of LSPR theory, providing detailed insights into its fundamental principles. Additionally, this review delves into the application of nanotechnology for the implementation of the LSPR biosensor, exploring methods for utilizing gold nanoparticles and elucidating the factors that influence the generation of visible signals. Several emerging technologies aimed at simple and rapid immunoassays for onsite applications have been introduced in the food industry. In the foreseeable future, field-friendly colorimetric biosensors could be adopted in food monitoring systems. The onsite and real-time detection of possible contaminants and biological substances in food and water is essential to ensure human health and safety.

Functionalized-Graphene Field Effect Transistor-Based Biosensor for Ultrasensitive and Label-Free Detection of β-Galactosidase Produced by Escherichia coli

The detection of β-galactosidase (β-gal) activity produced by Escherichia coli (E. coli) can quickly analyze the pollution degree of seawater bodies in bathing and fishing grounds to avoid large-scale outbreaks of water pollution. Here, a functionalized biosensor based on graphene-based field effect transistor (GFET) modified with heat-denatured casein was developed for the ultrasensitive and label-free detection of the β-gal produced by E. coli in real water samples. The heat-denatured casein coated on the graphene surface, as a probe linker and blocker, plays an important role in fabricating GEFT biosensor. The GFET biosensor response to the β-gal produced by E. coli has a wide concentration dynamic range spanning nine orders of magnitude, in a concentration range of 1 fg·mL-1-100 ng·mL-1, with a limit of detection (LOD) 0.187 fg·mL-1 (1.61 aM). In addition to its attomole sensitivity, the GFET biosensor selectively recognized the β-gal in the water sample and showed good selectivity. Importantly, the detection process of the β-gal produced by E. coli can be completed by a straightforward one-step specific immune recognition reaction. These results demonstrated the usefulness of the approach, meeting environmental monitoring requirements for future use.

Advances in miniaturized nanosensing platforms for analysis of pathogenic bacteria and viruses

Pathogenic bacteria and viruses are the main causes of infectious diseases all over the world. Early diagnosis of such infectious diseases is a critical step in management of their spread and treatment of the infection in its early stages. Therefore, the innovation of smart sensing platforms for point-of-care diagnosis of life-threatening infectious diseases such as COVID-19 is a prerequisite to isolate the patients and provide them with suitable treatment strategies. The developed diagnostic sensors should be highly sensitive, specific, ultrafast, portable, cheap, label-free, and selective. In recent years, different nanosensors have been developed for the detection of bacterial and viral pathogens. We focus here on label-free miniaturized nanosensing platforms that were efficiently applied for pathogenic detection in biological matrices. Such devices include nanopore sensors and nanostructure-integrated lab-on-a-chip sensors that are characterized by portability, simplicity, cost-effectiveness, and ultrafast analysis because they avoid the time-consuming sample preparation steps. Furthermore, nanopore-based sensors could afford single-molecule counting of viruses in biological specimens, yielding high-sensitivity and high-accuracy detection. Moreover, non-invasive nanosensors that are capable of detecting volatile organic compounds emitted from the diseased organ to the skin, urine, or exhaled breath were also reviewed. The merits and applications of all these nanosensors for analysis of pathogenic bacteria and viruses in biological matrices will be discussed in detail, emphasizing the importance of artificial intelligence in advancing specific nanosensors.

Point-of-Care Diagnostic Devices for Detection of Escherichia coli O157:H7 Using Microfluidic Systems: A Focused Review

Bacterial infections represent a serious and global threat in modern medicine; thus, it is very important to rapidly detect pathogenic bacteria, such as Escherichia coli (E. coli) O157:H7. Once treatments are delayed after the commencement of symptoms, the patient's health quickly deteriorates. Hence, real-time detection and monitoring of infectious agents are highly critical in early diagnosis for correct treatment and safeguarding public health. To detect these pathogenic bacteria, many approaches have been applied by the biosensors community, for example, widely-used polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), culture-based method, and adenosine triphosphate (ATP) bioluminescence. However, these approaches have drawbacks, such as time-consumption, expensive equipment, and being labor-intensive, making it critical to develop ultra-sensitive and highly selective detection. The microfluidic platform based on surface plasmon resonance (SPR), electrochemical sensing, and rolling circle amplification (RCA) offers proper alternatives capable of supplementing the technological gap for pathogen detection. Note that the microfluidic biochip allows to develop rapid, sensitive, portable, and point-of-care (POC) diagnostic tools. This review focuses on recent studies regarding accurate and rapid detection of E. coli O157:H7, with an emphasis on POC methods and devices that complement microfluidic systems. We also examine the efficient whole-body detection by employing antimicrobial peptides (AMPs), which has attracted growing attention in many applications.

A point-of-care detection platform for Escherichia coli O157:H7 by integration of smartphone and the structural colour of photonic microsphere

A smartphone-based sensitive, rapid, label-free and high-throughput detection platform for Escherichia coli O157:H7 was established. The specific recognition capability of this platform was dependent of the aptamer modified on the silica photonic microsphere (SPM), whose structural colour was utilized for the quantification of the target bacterium. Gold nanoparticles and silver staining technique were employed to improve the sensitivity of the detection platform. Such smartphone-based detection platform gave a wide linear detection range of 10² ∼ 10⁸ CFU/mL with a low limit of detection (LOD) of 68 CFU/mL and high specificity for Escherichia coli O157:H7. Moreover, the recovery rates of the detection method were measured in the range of 99 ∼ 108% in the milk, pork and purified water samples. Furthermore, the developed detection platform did not require complex sample pretreatment and could be easily manipulated, displaying great application potential in the fields of food safety, environmental monitoring and disease diagnosis.

Smartphone-assisted lab-in-a-tube device using gold nanocluster-based aptasensor for detection of MUC1-overexpressed tumor cells

Developing smartphone technology for point-of-care diagnosis is one of the current favorable trends in the field of biosensors. In fact, using smartphones can provide better accessibility and facility for rapid diagnosis of diseases. On the other hand, the detection of circulating tumor cells (CTCs) is one of the recent methods for the early diagnosis of cancer. Here, a new smartphone-assisted lab-in-a-tube device is introduced for the detection of Mucin 1 (MUC1) overexpressed tumor-derived cell lines using gold nanoclusters (GNCs)-based aptasensor. Accordingly, commercial polyurethane (PU) foam was first coated with graphene oxide (GO) to increase its surface area (8.45-fold), and improve its wettability. The surface of the resulting three-dimensional PU-GO (3DPU-GO) platform was then modified by MUC1 aptamer-GNCs to provide the required sensitivity and specificity through a turn "on/off" detection system. The proposed biosensor was first optimized with a spectrophotometer method. Afterward, findings were evaluated based on the red color intensity of the lab-in-a-tube system; and indicated the high ability of the biosensor for detection of MUC1-overexpressed tumor cell lines in the range of 250-20,000 cells mL^-1 with a limit of detection of 221 cells mL^-1. In addition, the developed biosensor showed a decent selectivity against positive-control cell lines (MCF-7, and HT-29) in comparison to negative-control cell lines (HEK293, and L929). Notably, the results represented good accordance with reference methods including spectroscopy devices. Ultimately, the results of this work bring a new perspective to the field of point-of-care detection and can be considered in future biosensors.

Ultrasensitive visual detection of the food-borne pathogen via MOF encapsulated enzyme

Various methods have been made to achieve sensitive detection (10 CFU/mL) of Escherichia coli O157:H7 (E. coli) in real samples, however, they are complex, time-consuming, or instrument-dependent. Enzyme-catalyzed reactions are one of the most efficient methods to amplify signals for sensitive detection. ZIF-8 owning stability, porosity, and high specific area are suitable for embedding enzymes which can effectively protect enzyme activity and thus improve detection sensitivity. Herein, a simple visual assay of E. coli with the limits of detection of 1 CFU/mL was developed based on this stable enzyme-catalyzed amplified system. A microbial safety test of milk, orange juice, seawater, cosmetic, and hydrolyzed yeast protein, was successfully performed with the limits of detection of 10 CFU/mL by the naked eye. And this bioassay possessed high selectivity and stability making the developed detection method practically promising.

Microfluidic biosensor for one-step detection of multiplex foodborne bacteria ssDNA simultaneously by smartphone

As a major threat to food safety due to their pathogenicity, foodborne bacteria have received much attention. In this paper, we present a one-step and wash-free microfluidic biosensor platform by smartphone for simultaneous multiple foodborne bacteria target single-stranded DNA (ssDNA) detection. This technology is based on the fluorescence resonance energy transfer (FRET) between the graphene oxide (GO) and fluorescence molecules modified capture ssDNA of the target bacteria ssDNA (ctDNA) which were coated on the microfluidic chips. The fluorescence recovery was recorded by a smartphone fluorescent detector. With an optimal analytical performance, the platform realized the detection of four kinds of bacteria ssDNA simultaneously within 5 min, with the limits of detection (LODs) of 0.17, 0.18, 0.27, and 0.17 nM, respectively. And the throughput analysis of trace amounts of foodborne bacteria ssDNA in milk and water samples were successfully detected. This one-step and wash-free microfluidic biosensor can be used as a tool for food safety analysis.

Encapsulating gold nanoclusters into metal-organic frameworks to boost luminescence for sensitive detection of copper ions and organophosphorus pesticides

Gold nanoclusters (Au NCs) with luminescence property are emerging as promising candidates in fluorescent methods for monitoring contaminants, but low luminescence efficiency hampers their extensive applications. Herein, GSH-Au NCs@ZIF-8 was designed by encapsulating GSH-Au NCs with AIE effect into metal-organic frameworks, achieving high luminescence efficiency and good stability through the confinement effect of ZIF-8. Accordingly, a fluorescent sensing platform was constructed for the sensitive detection of copper ions (Cu²⁺) and organophosphorus pesticides (OPs). Firstly, the as-prepared GSH-Au NCs@ZIF-8 could strongly accumulate Cu²⁺ due to the adsorption property of MOFs, accompanied by a significant fluorescence quenching effect with a low detection limit of 0.016 μM for Cu²⁺. Besides, thiocholine (Tch), the hydrolysis product of acetylthiocholine (ATch) by acetylcholinesterase (AchE), could coordinate with Cu²⁺ by sulfhydryl groups (-SH), leading to a significant fluorescence recovery, which was further used for the quantification of OPs owing to its inhibition to AChE activity. Furthermore, a hydrogel sensor was explored to accomplish equipment-free, visual, and quantitative monitoring of Cu²⁺ and OPs by a smartphone sensing platform. Overall, this work provides an effective and universal strategy for enhancing the luminescence efficiency and stability of Au NCs, which would greatly promote their applications in contaminants monitoring.

Recent Advances in Colorimetric Sensors Based on Gold Nanoparticles for Pathogen Detection

Infectious pathogens cause severe threats to public health due to their frightening infectivity and lethal capacity. Rapid and accurate detection of pathogens is of great significance for preventing their infection. Gold nanoparticles have drawn considerable attention in colorimetric biosensing during the past decades due to their unique physicochemical properties. Colorimetric diagnosis platforms based on functionalized AuNPs are emerging as a promising pathogen-analysis technique with the merits of high sensitivity, low-cost, and easy operation. This review summarizes the recent development in this field. We first introduce the significance of detecting pathogens and the characteristics of gold nanoparticles. Four types of colorimetric strategies, including the application of indirect target-mediated aggregation, chromogenic substrate-mediated catalytic activity, point-of-care testing (POCT) devices, and machine learning-assisted colorimetric sensor arrays, are systematically introduced. In particular, three biomolecule-functionalized AuNP-based colorimetric sensors are described in detail. Finally, we conclude by presenting our subjective views on the present challenges and some appropriate suggestions for future research directions of colorimetric sensors.

"Lighting-up" methylene blue-embedded zirconium based organic framework triggered by Al3+ for advancing the sensitivity of E. coli O157:H7 analysis in dual-signal lateral flow immunochromatographic assay

The sensitive detection of foodborne pathogens is of great significance for ensuring food safety and quality. Herein, on the basis of methylene blue-embedded zirconium based organic framework (UIO@MB) as the remarkable capture carrier and signal indicator, with the Al³⁺-assisted the fluorescent signal response, we developed a label-free and dual-signal lateral flow immunochromatographic assay (LDLFIA) for sensitive detection of Escherichia coli (E. coli) O157:H7. The UIO@MB sensing carrier without monoclonal antibodies (mAbs) was manufactured, which adhered to bacteria to form the UIO@MB-E. coli O157:H7 conjugate, resulting in visible blue band. Then the fluorescent response of the OH-rich UIO@MB was excited by introducing Al³⁺, arising from capturing of Al³⁺ by -OH through coordination and electrostatic affinity, thus generating a green fluorescent band. Impressively, a smartphone-based portable reading system was developed that can reflect the test results of UIO@MB-LDLFIA immediately. Under optimum conditions, UIO@MB-LDLFIA can complete colorimetric and fluorescent mode detection within 90 min, with a detection sensitivity of 10³ CFU/mL, which were 100 times lower than traditional gold nanoparticles-based LFIA and polymerase chain reaction (PCR). Moreover, the feasibility of the method was further evaluated by the determination of E. coli O157: H7 in drinking water and cabbage with average recoveries of 85.1-123.0%.

Biosensors and Point-of-Care Devices for Bacterial Detection: Rapid Diagnostics Informing Antibiotic Therapy

With an exponential rise in antimicrobial resistance and stagnant antibiotic development pipeline, there is, more than ever, a crucial need to optimize current infection therapy approaches. One of the most important stages in this process requires rapid and effective identification of pathogenic bacteria responsible for diseases. Current gold standard techniques of bacterial detection include culture methods, polymerase chain reactions, and immunoassays. However, their use is fraught with downsides with high turnaround time and low accuracy being the most prominent. This imposes great limitations on their eventual application as point-of-care devices. Over time, innovative detection techniques have been proposed and developed to curb these drawbacks. In this review, a systematic summary of a range of biosensing platforms is provided with a strong focus on technologies conferring high detection sensitivity and specificity. A thorough analysis is performed and the benefits and drawbacks of each type of biosensor are highlighted, the factors influencing their potential as point-of-care devices are discussed, and the authors' insights for their translation from proof-of-concept systems into commercial medical devices are provided.

Development of a Screening Method for Sulfamethoxazole in Environmental Water by Digital Colorimetry Using a Mobile Device

Antibiotic resistance is a major health concern of the 21st century. The misuse of antibiotics over the years has led to their increasing presence in the environment, particularly in water resources, which can exacerbate the transmission of resistance genes and facilitate the emergence of resistant microorganisms. The objective of the present work is to develop a chemosensor for screening of sulfonamides in environmental waters, targeting sulfamethoxazole as the model analyte. The methodology was based on the retention of sulfamethoxazole in disks containing polystyrene divinylbenzene sulfonated sorbent particles and reaction with p-dimethylaminocinnamaldehyde, followed by colorimetric detection using a computer-vision algorithm. Several color spaces (RGB, HSV and CIELAB) were evaluated, with the coordinate a_star, from the CIELAB color space, providing the highest sensitivity. Moreover, in order to avoid possible errors due to variations in illumination, a color palette is included in the picture of the analytical disk, and a correction using the a_star value from one of the color patches is proposed. The methodology presented recoveries of 82–101% at 0.1 µg and 0.5 µg of sulfamethoxazole (25 mL), providing a detection limit of 0.08 µg and a quantification limit of 0.26 µg. As a proof of concept, application to in-field analysis was successfully implemented.

Mycobacterium tuberculosis piezoelectric sensor based on AuNPs-mediated enzyme assisted signal amplification

Rapid diagnosis of tuberculosis disease (TB) still remained a pressing need for TB control efforts all over the world. However, the existing detection approaches cannot satisfy demand of rapid detection of clinical Mycobacterium tuberculosis (M. tuberculosis) because of the long detection time and high cost. Herein, we proposed a new M. tuberculosis piezoelectric sensor based on AuNPs-mediated enzyme assisted signal amplification. A hairpin-shaped DNA duplex with a protrusion of the 3' end was designed. In the presence of specific 16 S rDNA fragment of M. tuberculosis, the hairpin probe was opened, which triggered the selective cleavage of hairpin probe by Exonuclease III (Exo III), resulting in the release of uncut DNA probe and target DNA. The released target DNA hybridized with another hairpin-shaped DNA duplex, and a new digestion cycle was started, thus generating large amounts of uncut DNA probes. The uncut DNA was pulled to the electrode surface by the hybridization with capture probe modified on the electrode. Subsequently detection probe labeled AuNPs was hybridized with uncut DNA and entered between the two electrodes. The AuNPs linked to hybridized detection probe were grown in the HAuCl₄ and Nicotinamide adenine dinucleotide (NADH) solution and offered the conductive connection between the gaps of electrode. The changes were monitored by the piezoelectric sensor. The piezoelectric biosensor could achieve a detection of M. tuberculosis (10²-10⁸ CFU mL^-1) within 3 h, the detection limit (LOD) was 30 CFU mL^-1. The methodology could be transformed into different microbial targets, which is suitable for further development of small portable equipment and multifunctional detection.

Reusable and universal impedimetric sensing platform for the rapid and sensitive detection of pathogenic bacteria based on bacteria-imprinted polythiophene film

A bacteria-imprinted polythiophene film (BIF)-based impedimetric sensor was proposed for the rapid and sensitive detection of S. aureus. A significant improvement is the reduced time for both BIF fabrication (15 min) and bacterial capturing (10 min).

Sandwich method-based sensitivity enhancement of Ω-shaped fiber optic LSPR for time-flexible bacterial detection

The development of rapid and sensitive detection methods for pathogenic bacteria is crucial for the therapy and prevention of related diseases. However, the rapid and ultrasensitive assays are difficult to be realized simultaneously. To solve the problem, a sandwich method based on Ω-shaped fiber optic localized surface resonance (Ω-FOLSPR) was constructed, where poly adenine-tailed aptamer (PolyA-apt) and SH modified gold nanoparticles tags (AuNPs tags) were chosen as the capturing aptamer and amplifying tags, respectively. The small AuNPs were modified on the surface of fiber-optic (FO) rapidly, which saved the preparation time. Then, the PolyA-apt was modified on the AuNPs surface to capture the bacteria effectively due to its ability to adjust the density and conformation of aptamer on the AuNPs surface. Finally, the large AuNPs tags were used to generate intense signal enhancement. It is found that the sandwich method enables the unique characteristic of a time-dependent sensitivity enhancement. Specifically, the LOD of 108.0 CFU/mL and 7.4 CFU/mL was achieved with the analysis time of 10 min and 100 min, respectively. Besides, the Ω-FOLSPR sensor exhibits excellent selectivity against the other bacteria and good performance for detecting the spiked and natural samples. This sandwich method provides a time-flexible strategy due to the combination of effective signal amplification and real-time analysis for bacterial detection, displaying great potential for practical bacterial detection.

Enhanced electrochemiluminescence bioassay triggered by intracellular leakage for detection of Escherichia coli

An intracellular leakage-trigged signal-on solid-state electrochemiluminescent (ECL) assay is developed for the detection of Escherichia coli (E. coli). A self-assembled multilayer ensemble of N, S co-doped carbon dots -poly dimethyl diallylammonium chloride grafted carbon nanospheres is used as ECL luminophores with peroxydisulfate (PS) ions as coreactants. The incorporation of molecularly imprinted electrospun nanofibers with the multilayer ensemble enables a robust, highly selective solid-state ECL probe without using any expensive and fragile biological receptor. Upon the imprinted E. coli exposed to the assay, under bactericidal effects of PS ions by destroying the integrity of E. coli cell membrane, intracellular leakage K⁺-triggered ECL enhancement is first disclosed via prompting the involved ¹O₂-mediated ECL process. Benefiting from the ECL enhancement upon increasing the concentration of E. coli, a unique intracellular leakage-trigged signal-on ECL system is created for sensing E. coli. Such a assay is proved to be highly specific and sensitive for sensing E. coli in the concentration range from 5 to 10⁷ cfu mL^-1, achieving a detection limit of 1 cfu mL^-1 (S/N = 3). This label-free, simple and facile assay provides a promising point-of-care diagnostic tool for pathogen detection.

Attomolar analyte sensing techniques (AttoSens): a review on a decade of progress on chemical and biosensing nanoplatforms

Detecting the ultra-low abundance of analytes in real-life samples, such as biological fluids, water, soil, and food, requires the design and development of high-performance biosensing modalities. The breakthrough efforts from the scientific community have led to the realization of sensing technologies that measure the analyte's ultra-trace level, with relevant sensitivity, selectivity, response time, and sampling efficiency, referred to as Attomolar Analyte Sensing Techniques (AttoSens) in this review. In an AttoSens platform, 1 aM detection corresponds to the quantification of 60 target analyte molecules in 100 μL of sample volume. Herein, we review the approaches listed for various sensor probe design, and their sensing strategies that paved the way for the detection of attomolar (aM: 10^-18 M) concentration of analytes. A summary of the technological advances made by the diverse AttoSens trends from the past decade is presented.

Flexible electrospun nanofibrous film integrated with fluorescent carbon dots for smartphone-based detection and cellular imaging application

The dose of administered chemotherapy drugs is crucial to determine due to the potential for efficient or adverse outcomes for cancer patients. To date, no user-friendly and low-cost method of doxorubicin (DOX) detection using nontoxic and biodegradable materials has been reported. For this reason, in this work, we have developed for the first time a nanofiber-based sensing platform for sensitive and on-site DOX assay in just 10 min. This is obtained thanks to printable, porosity and embeddability features of electrospun nanofibrous films (ENFFs) combined with nitrogen and sulfur co-doped carbon dots (NS-CDs) as sensing probes. The assay was done by just pipetting analyte on the hydrophilic spots of the fabricated photoluminescence water-stable ENFFs where the color intensity was being darkened. DOX quenched NS-CDs fluorescence onto ENFFs through inner filter effect. The developed sensor was either coupled with smartphone technology to provide miniaturized, portable and easy-to-use device or an ordinary spectrofluorimeter for solid-state sensing applications (detection limit of 5.4 nM). Moreover, applicability of the designed sensor was evaluated in human serum with satisfactory recoveries. It is more interesting that the fabricated NS-CDs/ENF scaffolds have a high potential to detect the intracellular DOX to enhance cell proliferation leading to be considered as a multimodal tool in biomedical research and clinical diagnostics.

Dual-site recognition of Pseudomonas aeruginosa using polymyxin B and bacteriophage tail fiber protein

As one of the top three opportunistic pathogens, Pseudomonas aeruginosa (P. aeruginosa) has long accounted for hospital-acquired infections with high risk of death. In this work, a fluorescent method based on a dual-site recognition mode was developed for rapid assay of P. aeruginosa. Employing its strong binding capability towards lipid A on the outer membrane of Gram-negative bacteria, polymyxin B acted as one recognition element for P. aeruginosa. To overcome the poor binding specificity of polymyxin B, a recombinant bacteriophage tail fiber protein was expressed and employed as a species-specific recognition element for the target pathogen. Thus a dual-site recognition mode was developed for specific assay of P. aeruginosa species by using fluorescein isothiocyanate as a fluorescent probe. The target pathogen can be assayed within a broad dynamic range from 2.0 × 10³ CFU mL^-1 to 2.0 × 10⁷ CFU mL^-1. Due to the ideal specificity of tail fiber protein, the method is capable of excluding the interference from other Gram-negative bacteria and all Gram-positive bacteria. It has been employed for assaying P. aeruginosa in various types of sample matrixes inclusive of lake water, physiological saline injection, human urine and milk. The acceptable assay results demonstrate its promising prospect for practical application in various areas such as environmental hygiene, medical diagnosis, as well as drug and food safety.

Minute-scale detection of SARS-CoV-2 using a low-cost biosensor composed of pencil graphite electrodes

COVID-19 has led to over 3.47 million deaths worldwide and continues to devastate primarily middle- and low-income countries. High-frequency testing has been proposed as a potential solution to prevent outbreaks. However, current tests are not sufficiently low-cost, rapid, or scalable to enable broad COVID-19 testing. Here, we describe LEAD (Low-cost Electrochemical Advanced Diagnostic), a diagnostic test that detects severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) within 6.5 min and costs $1.50 per unit to produce using easily accessible and commercially available materials. LEAD is highly sensitive toward SARS-CoV-2 spike protein (limit of detection = 229 fg⋅mL-1) and displays an excellent performance profile using clinical saliva (100.0% sensitivity, 100.0% specificity, and 100.0% accuracy) and nasopharyngeal/oropharyngeal (88.7% sensitivity, 86.0% specificity, and 87.4% accuracy) samples. No cross-reactivity was detected with other coronavirus or influenza strains. Importantly, LEAD also successfully diagnosed the highly contagious SARS-CoV-2 B.1.1.7 UK variant. The device presents high reproducibility under all conditions tested and preserves its original sensitivity for 5 d when stored at 4 °C in phosphate-buffered saline. Our low-cost and do-it-yourself technology opens new avenues to facilitate high-frequency testing and access to much-needed diagnostic tests in resource-limited settings and low-income communities.

Recent progress in the optical detection of pathogenic bacteria based on noble metal nanoparticles

Pathogenic bacteria have become a huge threat to social health and economy for their frighteningly infectious and lethal capacity. It is quite important to make a diagnosis in advance to prevent infection or allow a rapid treatment after infection. Noble metal nanoparticles, due to their unique physicochemical properties, especially optical properties, have drawn a great attention during the past decades and have been widely applied into all kinds of fields related to human health. By utilizing these noble metal nanoparticles, optical diagnosis platforms towards pathogenic bacteria have emerged continually, providing highly sensitive, selective, and particularly facile detection tools for clinic or point-of-care diagnosis. This review summarizes the recent development in this field. It begins with a brief introduction of pathogenic bacteria and noble metal nanoparticles. And then, optical detection methods are systematically discussed in three distinct aspects. In addition to these proof-of-concept methods, corresponding algorithms and point-of-care detection devices are also described. Finally, the review ends up with subjective views on present limitations and some appropriate advice for future research directions.

Addressing the Theoretical and Experimental Aspects of Low-Dimensional-Materials-Based FET Immunosensors: A Review

Electrochemical immunosensors (EI) have been widely investigated in the last several years. Among them, immunosensors based on low-dimensional materials (LDM) stand out, as they could provide a substantial gain in fabricating point-of-care devices, paving the way for fast, precise, and sensitive diagnosis of numerous severe illnesses. The high surface area available in LDMs makes it possible to immobilize a high density of bioreceptors, improving the sensitivity in biorecognition events between antibodies and antigens. If on the one hand, many works present promising results in using LDMs as a sensing material in EIs, on the other hand, very few of them discuss the fundamental interactions involved at the interfaces. Understanding the fundamental Chemistry and Physics of the interactions between the surface of LDMs and the bioreceptors, and how the operating conditions and biorecognition events affect those interactions, is vital when proposing new devices. Here, we present a review of recent works on EIs, focusing on devices that use LDMs (1D and 2D) as the sensing substrate. To do so, we highlight both experimental and theoretical aspects, bringing to light the fundamental aspects of the main interactions occurring at the interfaces and the operating mechanisms in which the detections are based.

A novel smartphone-based colorimetric aptasensor for on-site detection of Escherichia coli O157:H7 in milk

Effective testing tools for Escherichia coli O157:H7 can prevent outbreaks of foodborne illness. In this paper, a smartphone-based colorimetric aptasensor was developed using functionalized gold nanoparticles (GNP) and multi-walled carbon nanotubes (MWCNT) for monitoring E. coli O157:H7 in milk. The maximum absorption peak of GNP bonded with aptamer (Apt) generated evident transformation from 518 to 524 nm. The excess GNP-Apt was removed by functionalized MWCNT magnetized with carbonyl iron powder (CIP) and hybridized with a DNA probe, whereas the GNP-Apt immobilized on E. coli O157:H7 remained in the system. In the presence of a high-salt solution, the GNP-Apt that captured E. coli O157:H7 remained red, but the free GNP-Apt aggregated and appeared blue. The chromogenic results were analyzed by a smartphone-based colorimetric device that was fabricated using acrylic plates, a light-emitting diode, and a mobile power pack. To our knowledge, this was the first attempt to use a smartphone-based colorimetric aptasensor employing the capture of GNP-Apt coupled with separation of MWCNT@CIP probe to detect E. coli O157:H7. The aptasensor exhibited good reproducibility and no cross-reaction for other bacteria. A concentration of 8.43 × 10³ cfu/mL of E. coli O157:H7 could be tested in pure culture, and 5.24 × 10² cfu/mL of E. coli O157:H7 could be detected in artificially contaminated milk after 1 h of incubation. Therefore, the smartphone-based colorimetric aptasensor was an efficient tool for the detection of E. coli O157:H7 in milk.

Lateral flow assay of methicillin-resistant Staphylococcus aureus using bacteriophage cellular wall-binding domain as recognition agent

As one of the most common and noticeable superbugs, methicillin-resistant Staphylococcus aureus (MRSA) has long been a major threat to public health. To meet the demand for effective diagnosis of MRSA-induced infection, it is urgent to establish rapid assay method for this type of pathogen. In this study, an aqueous soluble cellular wall-binding domain (CWBD) protein from bacteriophage P108 was obtained with a recombinant expression technique. It can act as a wide-spectrum binding agent for all MRSA strains and exclude the interference from methicillin-susceptible strains of Staphylococcus aureus and other species of bacteria. To establish a lateral flow assay (LFA) method for MRSA, CWBD-coupled time-resolved fluorescent microspheres (FMs) were used as signal probes for tracing MRSA, and a nitrocellulose membrane immobilized with porcine IgG was used to capture MRSA. With the LFA based on sandwich format, MRSA can be assayed within 10 min with a broad linear range of 6.6 × 10²-6.6 × 10⁷ CFU/mL. Its application potential has been demonstrated by assaying different types of bacteria-contaminated real samples. The results suggest that the LFA strip using recombinant CWBD as the recognition agent provides a rapid, portable, cost-effective approach for point-of-care testing of MRSA.

From Diagnosis to Treatment: Recent Advances in Patient-Friendly Biosensors and Implantable Devices

Patient-friendly medical diagnostics and treatments have been receiving a great deal of interest due to their rapid and cost-effective health care applications with minimized risk of infection, which has the potential to replace conventional hospital-based medical procedures. In particular, the integration of recently developed materials into health care devices allows the rapid development of point-of-care (POC) sensing platforms and implantable devices with special functionalities. In this review, the recent advances in biosensors for patient-friendly diagnosis and implantable devices for patient-friendly treatment are discussed. Comprehensive analysis of portable and wearable biosensing platforms for patient-friendly health monitoring and disease diagnosis is provided, including topics such as materials selection, device structure and integration, and biomarker detection strategies. Moreover, specific challenges related to each biological fluid for wearable biosensor-based POC applications are presented. Also, advances in implantable devices, including recent materials development and wireless communication strategies, are discussed. Furthermore, various patient-friendly surgical and treatment approaches are reviewed, such as minimally invasive insertion and mounting, in vivo electrical and optical modulations, and post-operation health monitoring. Finally, the challenges and future perspectives toward the development of the patient-friendly diagnosis and treatment are provided.

Emerging point-of-care biosensors for rapid diagnosis of COVID-19: current progress, challenges, and future prospects

Coronavirus disease 2019 (COVID-19) pandemic is currently a serious global health threat. While conventional laboratory tests such as quantitative real-time polymerase chain reaction (qPCR), serology tests, and chest computerized tomography (CT) scan allow diagnosis of COVID-19, these tests are time-consuming and laborious, and are limited in resource-limited settings or developing countries. Point-of-care (POC) biosensors such as chip-based and paper-based biosensors are typically rapid, portable, cost-effective, and user-friendly, which can be used for COVID-19 in remote settings. The escalating demand for rapid diagnosis of COVID-19 presents a strong need for a timely and comprehensive review on the POC biosensors for COVID-19 that meet ASSURED criteria: Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end users. In the present review, we discuss the importance of rapid and early diagnosis of COVID-19 and pathogenesis of COVID-19 along with the key diagnostic biomarkers. We critically review the most recent advances in POC biosensors which show great promise for the detection of COVID-19 based on three main categories: chip-based biosensors, paper-based biosensors, and other biosensors. We subsequently discuss the key benefits of these biosensors and their use for the detection of antigen, antibody, and viral nucleic acids. The commercial POC biosensors for COVID-19 are critically compared. Finally, we discuss the key challenges and future perspectives of developing emerging POC biosensors for COVID-19. This review would be very useful for guiding strategies for developing and commercializing rapid POC tests to manage the spread of infections.Graphical abstract.

An innovative prussian blue nanocubes decomposition-assisted signal amplification strategy suitable for competitive lateral flow immunoassay to sensitively detect aflatoxin B1

A prussian blue nanocubes decomposition-assisted signal amplification strategy for competitive lateral flow immunoassay (PBNCD-SALFIA) was innovatively proposed to analyze aflatoxin B₁ (AFB₁) in foodstuffs. The signal was amplified on account of the PBNCs can degrade and fade under alkaline condition, which could weak the color of the test- and control-lines, thereby improving the sensitivity of the sensor. The strategy was technically-simple, just using NaOH as an amplifier can realize signal amplification in the competition assay. Under optimized conditions, the enhanced strip exhibited excellent specificity and sensitivity in AFB₁ monitoring with a detection limit of 23 pg/mL, which was approximately 4- and 8-folds lower than those of PBNCs-LFIA (90 pg/mL) and conventional gold nanoparticles-LFIA (175 pg/mL), respectively. Taking the advantage of the color-fading, this platform revealing the lowest detectable concentration of 0.184, 0.368 and 0.184 μg/kg for AFB₁ in corn, peanut and pumpkin seed within 58 min, separately, showing reliable results.

Application of smartphone-based spectroscopy to biosample analysis: A review

The emergence of the smartphones has brought extensive changes to our lifestyles, from communicating with one another, to shopping and enjoyment of entertainment, and from studying to functioning at the workplace (and in the field). At the same time, this portable device has also provided new possibilities in scientific research and applications. Based on the growing awareness of good health management, researchers have coupled health monitoring to smartphone sensing technologies. Along the way, there have been developed a variety of smartphone-based optical detection platforms for analyzing biological samples, including standalone smartphone units and integrated smartphone sensing systems. In this review, we outline the applications of smartphone-based optical sensors for biosamples. These applications focus mainly on three aspects: Microscopic imaging sensing, colorimetric sensing and luminescence sensing. We also discuss briefly some limitations of the current state of smartphone-based spectroscopy and present prospects of the future applicability of smartphone sensors.