An ultrasensitive impedance biosensor for Salmonella detection based on rotating high gradient magnetic separation and cascade reaction signal amplification

Metal and metal oxide nanoparticle-assisted molecular assays for the detection of Salmonella

This paper provides a comprehensive overview of the diverse applications and innovations of nanoparticles in the detection of Salmonella. It encompasses a comprehensive range of novel methods, including efficient enrichment, nucleic acid extraction, immunoassays, nucleic acid tests, biosensors, and emerging strategies with the potential for future applications. The surface modification of specific antibodies or ligands enables nanoparticles to achieve highly selective capture of Salmonella, while optimizing the nucleic acid extraction process and improving detection efficiency. The employment of nanoparticles in immunological and nucleic acid tests markedly enhances the specificity and sensitivity of the reaction, thereby optimizing the determination of detection results. Moreover, the distinctive physicochemical properties of nanoparticles enhance the sensitivity, selectivity, and stability of biosensors, thereby facilitating the rapid advancement of bio-detection technologies. It is particularly noteworthy that there has been significant advancement in the application and innovative research of nanozymes in molecular assays. This progress has not only resulted in enhanced detection efficiency but has also facilitated innovation and improvement in detection technologies. As nanotechnologies continue to advance, the use of metal and metal oxide nanoparticles in Salmonella detection is likely to become a more promising and reliable strategy for ensuring food safety and public health.

Spatially ordered immobilization of cascade enzymes for the construction of a robust colorimetric hydrogel sensor

The development of a suitable mimetic scaffolds for maintaining high activity and stability of co-immobilized multi-enzymes is a key challenge in biotechnology. Herein, we achieved the regular distribution of cascade enzymes through spatially controlled hierarchical loading into protein-inorganic hybrid nanoflowers using a mild biomineralization technique. The comprehensive understanding of sequential regulation in constructing controlled nanoarchitecture enables to combine a continuous reaction and achieve tailoring catalysis for biomimetic application. The ordered-assembled cascade enzymes showed stronger bioactivity in comparison with the disordered format or inappropriate loading format. The stability of the enzyme is incrementally improved by an efficient dual-enhanced mode of immobilizing the free enzyme into hybrid nanoflowers and encapsulating it in a hydrogel system, addressing the inherent fragility of natural enzymes. Benefiting from the structural integration, a protein-inorganic hybrid nanoflowers-embedded hydrogel sensor is constructed for on-site detecting NO2- with a detection limit of 5.08 μM. This work showcases a convenient approach for the efficient design of the ideal cascade biocatalysts, and supports the development of portable devices for practical application.

Biosensing technology for detection and assessment of pathogenic microorganisms

At present, the prevalence of infectious diseases is rising annually, making it an important risk factor for human health that should not be neglected. Consequently, infection control and prevention have become even more important. The key to determining and designing the most effective anti-infectious medication depends upon the immediate and accurate identification of the causative agent. The standard techniques used for routine infection screening and surveillance tests are shifting toward biosensors. Furthermore, biosensors are projected to be employed for microbiological detection to satisfy the higher accuracy required for clinical diagnosis. This is because of their compact size, real-time monitoring and ability to analyze large sample numbers with less sophistication and manpower requirement, which have allowed them to develop quickly with extensive uses. Biosensors have multiple applications in food safety, environmental surveillance, drug sensing and national security because they offer several advantages such as quick response, outstanding sensitivity, remarkable selectivity, high degree of accuracy and precision, ease of use and affordable price. This review highlights the performance aspects of recently developed biosensors for the detection of infectious bacteria and viruses in biological and environmental samples and emphasizes the significance of nanotechnology in signal amplification for enhanced biosensor performance and dependability.

Microfluidics for detection of food pathogens: recent trends and opportunities

Safe and healthy food is the fundamental right of every citizen. Problems caused by foodborne pathogens have always raised a threat to food safety and human health. Centers for Disease Control and Prevention (CDC) estimates that around 48 million people are affected by food intoxication, and 3000 people succumb to death. Hence, it is inevitable that an approach that is efficient, reliable, sensitive, and rapid approach that can replace the conventional analytical methods such as microbiological and biochemical methods, high throughput next-generation sequence (NGS), polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA), etc. Even though the accuracy of conventional methods is high, it is tedious; increased consumption of reagents/samples, false positives, and complex operations are the drawbacks of these methods. Microfluidic devices have shown remarkable advances in all branches of science. They serve as an alternative to conventional ways to overcome the abovementioned drawbacks. Furthermore, coupling microfluidics can improve the efficiency and accuracy of conventional methods such as surface plasma resonance, loop-mediated isothermal amplification, ELISA, and PCR. This article reviewed the progress of microfluidic devices in the last ten years in detecting foodborne pathogens. Microfluidic technology has opened the research gateway for developing low-cost, on-site, portable, and rapid assay devices. The article includes the application of microfluidic-based devices to identify critical food pathogens and briefly discusses the necessary research in this area.

Development of a Colorimetric and SERS Dual-Signal Platform via dCas9-Mediated Chain Assembly of Bifunctional Au@Pt Nanozymes for Ultrasensitive and Robust Salmonella Assay

Timely screening for harmful pathogens is a great challenge in emergencies where traditional culture methods suffer from long assay time and alternative methods are limited by poor accuracy and low robustness. Herein, we present a dCas9-mediated colorimetric and surface-enhanced Raman scattering (SERS) dual-signal platform (dCas9-CSD) to address this challenge. Strategically, the platform used dCas9 to accurately recognize the repetitive sequences in amplicons produced by loop-mediated isothermal amplification (LAMP), forming nucleic acid frameworks that assemble numerous bifunctional gold-platinum (Au@Pt) nanozymes into chains on the surface of streptavidin-magnetic beads (SA-MB). The collected Au@Pt converted colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) via its Pt shell and then enhanced the Raman signal of oxTMB by its Au core. Therefore, the presence of Salmonella could be dexterously converted into cross-validated colorimetric and SERS signals, providing more reliable conclusions. Notably, dCas9-mediated secondary recognition of amplicons reduced background signal caused by nontarget amplification, and two-round signal amplification consisting of LAMP reaction and Au@Pt catalysis greatly improved the sensitivity. With this design, Salmonella as low as 1 CFU/mL could be detected within 50 min by colorimetric and SERS modes. The robustness of dCas9-CSD was further confirmed by various real samples such as lake water, cabbage, milk, orange juice, beer, and eggs. This work provides a promising point-of-need tool for pathogen detection.

Mn2+-Mediated Modulation of PfAgo Activity for Biosensing

Argonaute (Ago) as a powerful enzyme has provided new insights into biosensing due to its programmability, high sensitivity, and user-friendly operation. However, current strategies mainly rely on phosphorylated guide DNA to modulate the cleavage activity of Ago, which is limited in versatility and simplicity. Herein, the authors report the Mn2+-enhanced cleavage activity of Ago and employ Mn-ions with variable valence to regulate the activity of Pyrococcus furiosus Ago (PfAgo) for biosensing applications. The conversion of Mn ions with different valence states through MnO2 nanoflowers enables the sensitive detection of ascorbic acid, alkaline phosphatase, and arsenic with limits of detection of 2.5 nmol L-1, 0.009 U L-1, and 0.4 ng mL-1, respectively. A PfAgo-based immunoassay is further developed that allows for the detection of diverse targets, thus providing a promising toolbox to broaden PfAgo-based sensors into versatile bioanalytical and biomedical applications.

Ultra-sensitive fluorescent biosensor for multiple bacteria detection based on CDs/QDs@ZIF-8 and microfluidic fluidized bed

An ultra-sensitive fluorescent biosensor based on CDs/QDs@ZIF-8 and microfluidic fluidized bed was developed for rapid and ultra-sensitive detection of multiple target bacteria. The zeolitic imidazolate frameworks (ZIF-8) act as the carrier to encapsulate three kinds of fluorescence signal molecules from the CDs/QDs@ZIF-8 signal amplification system. Besides, three kinds of target pathogenic bacteria were automatically, continuously, and circularly captured by the magnetic nanoparticles (MNPs) in the microfluidic fluidized bed. The neutral Na2EDTA solution was the first time reported to not only dissolve the ZIF-8 frameworks from the MNPs-bacteria-CDs/QDs@ZIF-8 sandwich complexes, but also release the CDs/QDs from sandwich complexes with no loss of fluorescence signal. Due to the advantages of signal amplification and automated sample pretreatment, the proposed fluorescent biosensor can simultaneously detect Escherichia coli O157:H7, Salmonella paratyphi A, and Salmonella paratyphi B as low as 101 CFU/mL within 1.5 h, respectively. The mean recovery in spiked milk samples can reach 99.18%, verifying the applicability of this biosensor in detecting multiple bacteria in real samples.

Advances in signal amplification strategies applied in pathogenic bacteria apta-sensing analysis-A review

Pathogenic bacteria are primarily kinds of food hazards that provoke serious harm to human health via contaminated or spoiled food. Given that pathogenic bacteria continue to reproduce and expand once they contaminate food, pathogenic bacteria of high concentration triggers more serious losses and detriments. Hence, it is essential to detect low-dose pollution at an early stage with high sensitivity. Aptamers, also known as "chemical antibodies", are oligonucleotide sequences that have attracted much attention owing to their merits of non-toxicity, small size, variable structure as well as easy modification of functional group. Aptamer-based bioanalysis has occupied a critical position in the field of rapid detection of pathogenic bacteria. This is attributed to the unique advantage of using aptamers as recognition elements in signal amplification strategies. The signal amplification strategy is an effective means to improve the detection sensitivity. Some diverse signal amplification strategies emphasize the synthesis and assembly of nanomaterials with signal amplification capabilities, while others introduce various nucleic acid amplification techniques into the detection system. This review focuses on a variety of signal amplification strategies employed in aptamer-based detection approaches to pathogenic bacteria. Meanwhile, we provided a detailed introduction to the design principles and characteristics of signal amplification strategies, as well as the improvement of sensor sensitivity. Ultimately, the existing issues and development trends of applying signal amplification strategies in apta-sensing analysis of pathogenic bacteria are critically proposed and prospected. Overall, this review discusses from a new perspective and is expected to contribute to the further development of this field.

Recent Advances in Metallic Nanostructures-assisted Biosensors for Medical Diagnosis and Therapy

The field of nanotechnology has witnessed remarkable progress in recent years, particularly in its application to medical diagnosis and therapy. Metallic nanostructures-assisted biosensors have emerged as a powerful and versatile platform, offering unprecedented opportunities for sensitive, specific, and minimally invasive diagnostic techniques, as well as innovative therapeutic interventions. These biosensors exploit the molecular interactions occurring between biomolecules, such as antibodies, enzymes, aptamers, or nucleic acids, and metallic surfaces to induce observable alterations in multiple physical attributes, encompassing electrical, optical, colorimetric, and electrochemical signals. These interactions yield measurable data concerning the existence and concentration of particular biomolecules. The inherent characteristics of metal nanostructures, such as conductivity, plasmon resonance, and catalytic activity, serve to amplify both sensitivity and specificity in these biosensors. This review provides an in-depth exploration of the latest advancements in metallic nanostructures-assisted biosensors, highlighting their transformative impact on medical science and envisioning their potential in shaping the future of personalized healthcare.

Research progress in the detection of common foodborne hazardous substances based on functional nucleic acids biosensors

With the further improvement of food safety requirements, the development of fast, highly sensitive, and portable methods for the determination of foodborne hazardous substances has become a new trend in the food industry. In recent years, biosensors and platforms based on functional nucleic acids, along with a range of signal amplification devices and methods, have been established to enable rapid and sensitive determination of specific substances in samples, opening up a new avenue of analysis and detection. In this paper, functional nucleic acid types including aptamers, deoxyribozymes, and G-quadruplexes which are commonly used in the detection of food source pollutants are introduced. Signal amplification elements include quantum dots, noble metal nanoparticles, magnetic nanoparticles, DNA walkers, and DNA logic gates. Signal amplification technologies including nucleic acid isothermal amplification, hybridization chain reaction, catalytic hairpin assembly, biological barcodes, and microfluidic system are combined with functional nucleic acids sensors and applied to the detection of many foodborne hazardous substances, such as foodborne pathogens, mycotoxins, residual antibiotics, residual pesticides, industrial pollutants, heavy metals, and allergens. Finally, the potential opportunities and broad prospects of functional nucleic acids biosensors in the field of food analysis are discussed.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Recent Advances in Electrochemical Biosensors for Food Control

The rapid and sensitive detection of food contaminants is becoming increasingly important for timely prevention and treatment of foodborne disease. In this review, we discuss recent developments of electrochemical biosensors as facile, rapid, sensitive, and user-friendly analytical devices and their applications in food safety analysis, owing to the analytical characteristics of electrochemical detection and to advances in the design and production of bioreceptors (antibodies, DNA, aptamers, peptides, molecular imprinted polymers, enzymes, bacteriophages, etc.). They can offer a low limit of detection required for food contaminants such as allergens, pesticides, antibiotic traces, toxins, bacteria, etc. We provide an overview of a broad range of electrochemical biosensing designs and consider future opportunities for this technology in food control.

Quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe for sensitive and specific detection of Salmonella in food matrices

As a commonly pathogenic bacterium, the rapid detection of Salmonella outbreaks and assurance of food safety require a highly efficient detection method. Herein, a novel approach to Salmonella detection using quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe is reported. RBP 55, a novel phage receptor binding protein (RBP), was identified and characterized from phage STP55. RBP 55 was functionalized onto quantum dots (QDs) to form fluorescent nanoprobes. The assay was based on the combination of immunomagnetic separation and RBP 55-QDs, which formed a sandwich composite structure. The results showed a good linear correlation between the fluorescence values and the concentration of Salmonella (10¹-10⁷ CFU/mL) with a low detection limit of 2 CFU/mL within 2 h. The method was used to successfully detect Salmonella in spiked food samples. This approach can be used for the simultaneous detection of multiple pathogens by labeling different phage-encoded RBPs using polychromatic QDs in the future.

Translating conventional wisdom on chicken comb color into automated monitoring of disease-infected chicken using chromaticity-based machine learning models

Bacteria- or virus-infected chicken is conventionally detected by manual observation and confirmed by a laboratory test, which may lead to late detection, significant economic loss, and threaten human health. This paper reports on the development of an innovative technique to detect bacteria- or virus-infected chickens based on the optical chromaticity of the chicken comb. The chromaticity of the infected and healthy chicken comb was extracted and analyzed with International Commission on Illumination (CIE) XYZ color space. Logistic Regression, Support Vector Machines (SVMs), K-Nearest Neighbors (KNN), and Decision Trees have been developed to detect infected chickens using the chromaticity data. Based on the X and Z chromaticity data from the chromaticity analysis, the color of the infected chicken's comb converged from red to green and yellow to blue. The development of the algorithms shows that Logistic Regression, SVM with Linear and Polynomial kernels performed the best with 95% accuracy, followed by SVM-RBF kernel, and KNN with 93% accuracy, Decision Tree with 90% accuracy, and lastly, SVM-Sigmoidal kernel with 83% accuracy. The iteration of the probability threshold parameter for Logistic Regression models has shown that the model can detect all infected chickens with 100% sensitivity and 95% accuracy at the probability threshold of 0.54. These works have shown that, despite using only the optical chromaticity of the chicken comb as the input data, the developed models (95% accuracy) have performed exceptionally well, compared to other reported results (99.469% accuracy) which utilize more sophisticated input data such as morphological and mobility features. This work has demonstrated a new feature for bacteria- or virus-infected chicken detection and contributes to the development of modern technology in agriculture applications.

Magnetic Bead Manipulation in Microfluidic Chips for Biological Application

Magnetic beads manipulation in microfluidic chips is a promising research field for biological application, especially in the detection of biological targets. In this review, we intend to present a thorough and in-depth overview of recent magnetic beads manipulation in microfluidic chips and its biological application. First, we introduce the mechanism of magnetic manipulation in microfluidic chip, including force analysis, particle properties, and surface modification. Then, we compare some existing methods of magnetic manipulation in microfluidic chip and list their biological application. Besides, the suggestions and outlook for future developments in the magnetic manipulation system are also discussed and summarized.

Semi-circle magnetophoretic separation under rotated magnetic field for colorimetric biosensing of Salmonella

Magnetic separation was often applied to isolate and concentrate foodborne bacteria using immunomagnetic nanobeads before downstream bacterial detection. However, nanobead-bacteria conjugates (magnetic bacteria) were coexisting with excessive unbound nanobeads, limiting these nanobeads on magnetic bacteria to further act as signal probes for bacterial detection. Here, a new microfluidic magnetophoretic biosensor was elaboratively developed using a rotated high gradient magnetic field and platinum modified immunomagnetic nanobeads for continuous-flow isolation of magnetic bacteria from free nanobeads, and combined with nanozyme signal amplification for colorimetric biosensing of Salmonella. First, the platinum modified immunomagnetic nanobeads were mixed with the bacterial sample to form the magnetic bacteria, and magnetically separated to eliminate non-magnetic background. Then, the mixture of free immunomagnetic nanobeads and magnetic bacteria was injected with sheath flow (PBS) at higher flowrate into the semi-circle magnetophoretic separation channel under rotated magnetic field, which was generated by two repulsive cylindric magnets and their in-between ring iron gear, leading to continuous-flow isolation of magnetic bacteria from free immunomagnetic nanobeads because they suffered from different magnetic forces and thus had different deviating positions at the outlet. Finally, the separated magnetic bacteria and unbound magnetic nanobeads were respectively collected and used to catalyze coreless substrate into blue product, which was further analyzed using the microplate reader to obtain bacterial amount. This biosensor could determinate Salmonella as low as 41 CFU/mL in 40 min.

Coronavirus: a comparative analysis of detection technologies in the wake of emerging variants

An outbreak of the coronavirus disease caused by a novel pathogen created havoc and continues to affect the entire world. As the pandemic progressed, the scientific community was faced by the limitations of existing diagnostic methods. In this review, we have compared the existing diagnostic techniques such as reverse transcription polymerase chain reaction (RT-PCR), antigen and antibody detection, computed tomography scan, etc. and techniques in the research phase like microarray, artificial intelligence, and detection using novel materials; on the prospect of sample preparation, detection procedure (qualitative/quantitative), detection time, screening efficiency, cost-effectiveness, and ability to detect different variants. A detailed comparison of different techniques showed that RT-PCR is still the most widely used and accepted coronavirus detection method despite certain limitations (single gene targeting- in context to mutations). New methods with similar efficiency that could overcome the limitations of RT-PCR may increase the speed, simplicity, and affordability of diagnosis. In addition to existing devices, we have also discussed diagnostic devices in the research phase showing high potential for clinical use. Our approach would be of enormous benefit in selecting a diagnostic device under a given scenario, which would ultimately help in controlling the current pandemic caused by the coronavirus, which is still far from over with new variants emerging.

Recent Progress and Challenges on the Microfluidic Assay of Pathogenic Bacteria Using Biosensor Technology

Microfluidic technology is one of the new technologies that has been able to take advantage of the specific properties of micro and nanoliters, and by reducing the costs and duration of tests, it has been widely used in research and treatment in biology and medicine. Different materials are often processed into miniaturized chips containing channels and chambers within the microscale range. This review (containing 117 references) demonstrates the significance and application of nanofluidic biosensing of various pathogenic bacteria. The microfluidic application devices integrated with bioreceptors and advanced nanomaterials, including hyperbranched nano-polymers, carbon-based nanomaterials, hydrogels, and noble metal, was also investigated. In the present review, microfluid methods for the sensitive and selective recognition of photogenic bacteria in various biological matrices are surveyed. Further, the advantages and limitations of recognition methods on the performance and efficiency of microfluidic-based biosensing of photogenic bacteria are critically investigated. Finally, the future perspectives, research opportunities, potential, and prospects on the diagnosis of disease related to pathogenic bacteria based on microfluidic analysis of photogenic bacteria are provided.

Recent Advances in Electrochemical Biosensors for the Detection of Salmonellosis: Current Prospective and Challenges

Salmonellosis is a major cause of foodborne infections, caused by Salmonella, posing a major health risk. It possesses the ability to infiltrate the food supply chain at any point throughout the manufacturing, distribution, processing or quality control process. Salmonella infection has increased severely and requires effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction and culture plate, consume a lot of time and are labor-intensive. Therefore, new quick detection methods for on-field applications are urgently needed. Biosensors provide consumer-friendly approaches for quick on-field diagnoses. In the last few years, there has been a surge in research into the creation of reliable and advanced electrochemical sensors for the detection of Salmonella strains in food samples. Electrochemical sensors provide extensive accuracy and reproducible results. Herein, we present a comprehensive overview of electrochemical sensors for the detection of Salmonella by focusing on various mechanisms of electrochemical transducer. Further, we explain new-generation biosensors (microfluidics, CRISPR- and IOT-based) for point-of care applications. This review also highlights the limitations of developing biosensors in Salmonella detection and future possibilities.

An ultra-fast, one-step RNA amplification method for the detection of Salmonella in seafood

Salmonella is one of the most common pathogens associated with food-borne illness resulting from seafood consumption. Herein, an accelerated strand exchange amplification (ASEA) requiring only a pair of primers and one polymerase was first reported for ultra-fast, one-step RNA amplification detection of Salmonella in seafood. The ASEA method could detect Salmonella typhimurium DNA in dilutions as low as 10 copies per reaction and displayed good specificity for Salmonella under the interference of a variety of food-borne pathogens. In particular, ASEA could detect RNA in one step without additional reverse transcription. The detection limit for Salmonella in artificially contaminated oyster was 1 CFU mL^-1 following 12 h of enrichment. Moreover, excellent performance of this assay was observed with 99.02% consistency relative to real-time PCR through actual sample detection. Combined with the rapid nucleic acid extraction method, the entire detection process could be completed within 20 min. Therefore, this assay opens up new prospects for the detection of food-borne pathogens in seafood with its rapidity, which would be very beneficial for food safety supervision and pathogen detection of high-throughput samples.

Single-tube analysis for ultra-fast and visual detection of Salmonella

Herein, we developed an ultra-fast and visual single-tube nucleic acid detection approach, which combined the advantages of self-settling characteristics of chitosan-functionalized diatomaceous earth (CDE) and accelerated PCR (AC-PCR). DNA was rapidly extracted by CDE within 3 min for the next nucleic acid amplification based on the nucleic acid attached on the chitosan in pH = 5.0. Under the action of gravity, the DNA-enriched CDE self-sediments to the bottom of the tube could be directly used for AC-PCR to achieve single-tube extraction and amplification. Our method detected Salmonella culture fluids with a detection limit of 1 CFU/mL, which was 100-fold more sensitive than conventional method that have not undergone nucleic acid enrichment. Furthermore, it also displayed high specificity and sensitivity for a variety of spiked samples. The entire process could be completed within 17 min in a single tube, and in particular, the result was visualized by the naked eyes. Overall, it is an all-in-one detection strategy without the requirement of redundant procedure, which greatly improved the detection efficiency, and saved the time and the cost. With these advantages, the approach will supply a promising tool in the field of point-of-care testing for Salmonella and other foodborne pathogens.

Recent advances in the biosensors application for the detection of bacteria and viruses in wastewater

The presence of disease-causing pathogens in wastewater can provide an excellent diagnostic tool for infectious diseases. Biosensors are far superior to conventional methods used for regular infection screening and surveillance testing. They are rapid, sensitive, inexpensive portable and carry no risk of exposure in their detection schemes. In this context, this review summarizes the most recently developed biosensors for the detection of bacteria and viruses in wastewater. The review also provides information on the new detection methods aimed at screening for SARS-CoV-2, which has now caused more than 4 million deaths. In addition, the review highlights the potential behind on-line and real-time detection of pathogens in wastewater pipelines. Most of the biosensors reported were not targeted to wastewater samples due to the complexity of the matrix. However, this review highlights on the performance factors of recently developed biosensors and discusses the importance of nanotechnology in amplifying the output signals, which in turn increases the accuracy and reliability of biosensors. Current research on the applicability of biosensors in wastewater promises a dramatic change to the conventional approach in the field of medical screening.

Biomimetic-mineralized bifunctional nanoflowers for enzyme-free and colorimetric immunological detection of protein biomarker

Detection of protein biomarkers relies largely on the development of modern immunological methods. Herein, a new enzyme-free immunological method is proposed to detect protein biomarkers. Employment of antibody-Cu₃(PO₄)₂ hybrid nanoflowers, which are prepared through a facile and mild biomimetic-mineralizing process, is the core concept of the method. These nanoflowers can perform functions: one is to bind to target protein biomarkers with high specificity; the other is to release large amounts of Cu²⁺ upon acid treatment, which can interact with creatinine and exert peroxidase-mimicking enzyme activity, therefore producing a distinctly amplified signal. Using osteocalcin, a well-known circulating protein biomarker for bone formation, as a model, the method affords a linear range from 0.1 to 50 ng/mL with a detection limit of 0.042 ng/mL, which is superior to reported methods. Moreover, the method shows considerable specificity, desirable performance in serum samples and eliminates the use of enzymes, so a great potential for this method is expected to meet the need of the clinical diagnosis.

A novel electrochemical immunosensor based on Fe3O4@graphene nanocomposite modified glassy carbon electrode for rapid detection of Salmonella in milk

Foods contaminated by foodborne pathogens have always been a great threat to human life. Herein, we constructed an electrochemical immunosensor for Salmonella detection by using a Fe₃O₄@graphene modified electrode. Because of the excellent electrical conductivity and mechanical stability of graphene and the large specific surface area of Fe₃O₄, the Fe₃O₄@graphene nanocomposite exhibits an excellent electrical signal, which greatly increased the sensitivity of the immunosensor. Gold nanoparticles were deposited on Fe₃O₄@graphene nanocomposite by electrochemical technology for the immobilization of the antibody. Cyclic voltammetry was selected to electrochemically characterize the construction process of immunosensors. The microstructure and morphology of related nanocomposites were analyzed by scanning electron microscopy. Under optimized experimental conditions, a good linear relationship was achieved in the Salmonella concentration range of 2.4 × 10² to 2.4 × 10⁷ cfu/mL, and the limit of detection of the immunosensor was 2.4 × 10² cfu/mL. Additionally, the constructed immunosensor exhibited acceptable selectivity, reproducibility, and stability and provides a new reference for detecting pathogenic bacteria in milk.

A lab-on-a-tube biosensor for automatic detection of foodborne bacteria using rotated Halbach magnetic separation and Raspberry Pi imaging

A lab-on-a-tube biosensor was established to rapidly, sensitively and automatically detect foodborne bacteria through a rotatable Halbach magnet to form and rotate magnetic nanobead (MNB) chains for specific isolation of target bacteria, gold@platinum nanocatalysts (Au@PtNCs) to label target bacteria for efficient amplification of detection signal and Raspberry Pi App to collect and analyze the image of catalysate. First, the glass tube was successively preloaded with the mixture of MNBs, sample and Au@PtNCs, the washing buffer (skim milk) and the substrate (hydrogen peroxide-3,30,5,50-tetramethylbenzidine), and they were separated by air gaps. After the tube was placed on the biosensor, the MNB chains were stably formed and continuously rotated using the Halbach magnet and the mixture was moved back and forth using a programmable peristaltic pump, thus making the formation of MNB-bacteria-Au@PtNCs complexes. After the washing buffer was moved to wash the complexes, the substrate was then moved to resuspend the complexes, resulting in the catalytic reaction that changed the color of the substrate. Finally, the catalysate was moved to the designated area, the image of which was analyzed by the Raspberry Pi App to quantitatively determine the concentration of bacteria in the samples. This biosensor was able to detect Salmonella in spiked chicken samples in 1 h with lower detection limit of 8 CFU/50 μL and a recovery from 88.96% to 99.74%. This biosensor based on a single tube is very promising to automatically detect foodborne bacteria due to its low cost, high integration and simple operation.

Autonomous Internal Reflux of Magnetic Nanoparticle Chains in a Flow Channel for Efficient Detection of Waterborne Bacteria

Herein, we developed a novel method for the efficient capture of waterborne bacteria by creating an autonomous internal reflux of the magnetic nanoparticle chains (MNCs) inside a flow channel. A glass tube containing positively charged polyethyleneimine-coated MNCs (PEI-MNCs) was placed at the center of a Halbach ring, generating a strong and uniform magnetic field inside the ring. When a bacteria-spiked solution was injected into the tube, the target bacteria bound to the PEI-MNCs via an electrostatic interaction remained in the tube, whereas the unbound bacteria left the tube. Some PEI-MNC-bacteria complexes left the glass tube at high flow rates because of the drag force, which reduced the capture efficiency of the device. The loss of the PEI-MNC-bacteria complexes at high flow rates was suppressed by placing a k₀ ring behind the Halbach ring. The k₀ ring was used to apply a magnetic force in the opposite direction of the solution flow and create an autonomous reflux of the PEI-MNCs inside the glass tube, reducing their loss and increasing their capture efficiency. The capture efficiency of Escherichia coli O157 was determined based on the cell count to be greater than 90% at a flow rate of 15 mL/min. E. coli O157 was detected using quantitative polymerase chain reaction, and the limits of detection were 2 and 3 cfu/mL in deionized water and river water, respectively.

Electrochemical Biosensors in Food Safety: Challenges and Perspectives

Safety and quality are key issues for the food industry. Consequently, there is growing demand to preserve the food chain and products against substances toxic, harmful to human health, such as contaminants, allergens, toxins, or pathogens. For this reason, it is mandatory to develop highly sensitive, reliable, rapid, and cost-effective sensing systems/devices, such as electrochemical sensors/biosensors. Generally, conventional techniques are limited by long analyses, expensive and complex procedures, and skilled personnel. Therefore, developing performant electrochemical biosensors can significantly support the screening of food chains and products. Here, we report some of the recent developments in this area and analyze the contributions produced by electrochemical biosensors in food screening and their challenges.

Organic-Inorganic Hybrid Nanoflower Production and Analytical Utilization: Fundamental to Cutting-Edge Technologies

Over the past decade, science has experienced a growing rise in nanotechnology with ground-breaking contributions. Through various laborious technologies, nanomaterials with different architectures from 0 D to 3 D have been synthesized. However, the 3 D flower-like organic-inorganic hybrid nanomaterial with the most direct one-pot green synthesis method has attracted widespread attention and instantly become research hotspot since its first allusion in 2012. Mild synthesis procedure, high surface-to-volume ratio, enhanced enzymatic activity and stability are the main factor for its rapid development. However, its lower mechanical strength, difficulties in recovery from the reaction system, lower loading capacity, poor reusability and accessibility of enzymes are fatal, which hinders its wide application in industry. This review first discusses the selection of non-enzymatic biomolecules for the synthesis of hybrid nanoflowers followed by the innovative advancements made in organic-inorganic hybrid nanoflowers to overcome aforementioned issues and to enhance their extensive downstream applications in transduction technologies. Besides, the role of hybrid nanoflower has been successfully utilized in many fields including, water remediation, biocatalyst, pollutant adsorption and decolourization, nanoreactor, biosensing, cellular uptake and others, accompanied with several quantification technologies, such as ELISA, electrochemical, surface plasmon resonance (SPR), colorimetric, and fluorescence were comprehensively reviewed.