Biosensors for rapid detection of Salmonella in food: A review

Endoprotein-activating DNAzyme assay for nucleic acid extraction- and amplification-free detection of viable pathogenic bacteria

Pathogenic bacteria in food or environment, can pose threats to public health, highlighting the requirement of tools for rapid and accurate detection of viable pathogenic bacteria. Herein, we report a sequential endoprotein RNase H2-activating DNAzyme assay (termed epDNAzyme) that enables nucleic acid extraction- and amplification-free detection of viable Salmonella enterica (S. enterica). The direct detection allows for a rapid detection of viable S. enterica within 25 min. Besides, the assay, based on sequential reporting strategy, circumvents internal modifications in the DNAzyme's active domain and improve its catalytic activity. The multiple-turnover DNAzyme cutting and the enhanced catalytic activity of DNAzyme render the epDNAzyme assay to be highly sensitive, and enables the detection of 190 CFU/mL and 0.1% viable S. enterica. The assay has been utilized to detect S. enterica contamination in food and clinical samples, indicating its potential as a promising tool for monitoring pathogen-associated biosafety.

A multimetallic nanozyme enhanced colorimetric biosensor for Salmonella detection on finger-actuated microfluidic chip

Salmonella screening is essential to avoid food poisoning. A simple, fast and sensitive colorimetric biosensor was elaborately developed for Salmonella detection on a microfluidic chip through limiting air chambers for precise air control, switching rotary valves for accurate fluid selection, a convergence-and-divergence passive micromixer and an extrusion-and-suction active micromixer for efficient fluid mixing, and immune gold@platinum palladium nanocatalysts for effective signal amplification. The mixture of bacteria, immune magnetic nanobeads and nanocatalysts was first rapidly mixed to form nanobead-bacteria-nanocatalyst conjugates and magnetically separated for enrichment. After washing with water, the conjugates were used to catalyze colorless substrate and blue product was finally analyzed using ImageJ for quantifying bacterial concentration. The finger-actuated microfluidic chip enabled designated control of designated fluids in designated places towards designated directions by simple press-release operations on designated air chambers without any external power. Under optimal conditions, this sensor could detect Salmonella at 45 CFU/mL in 25 min.

Active Quantum Biomaterials-Enhanced Microrobots for Food Safety

Timely disruptive tools for the detection of pathogens in foods are needed to face global health and economic challenges. Herein, the utilization of quantum biomaterials-enhanced microrobots (QBEMRs) as autonomous mobile sensors designed for the precise detection of endotoxins originating from Salmonella enterica (S. enterica) as an indicator species for food-borne contamination globally is presented. A fluorescent molecule-labeled affinity peptide functions as a specific probe, is quenched upon binding to the surface of QBEMRs. Owing to its selective affinity for endotoxin, in the presence of S. enterica the fluorescence is restored and easy to observe and quantifies optical color change to indicate the presence of Salmonella. The devised approach is designed to achieve highly sensitive detection of the S. enterica serovar Typhimurium endotoxin with exquisite selectivity through the utilization of QBEMRs. Notably, no fluorescence signal is observed in the presence of endotoxins bearing similar structural characteristics, highlighting the selectivity of the approach during food sample analysis. Technically, the strategy is implemented in microplate readers to extend microrobots-based approaches to the routine laboratory. This new platform can provide fast and anticipated results in food safety.

A dual-mode composite nanozyme-based cascade colorimetric-fluorescence aptasensor for Salmonella Typhimurium detection

BACKGROUND

Salmonella Typhimurium poses a serious threat to human health worldwide, necessitating the development of a rapid, sensitive, and convenient method for S. Typhimurium detection. Nanozymes are considered ideal signal report elements, which are extensively used for developing colorimetric methods. However, single-component nanozymes display low catalytic activity, and colorimetric methods are susceptible to environmental interference, reducing the sensitivity and accuracy of detection results. To address these drawbacks, this study constructed a dual-mode composite nanozyme-based cascade colorimetric-fluorescence aptasensor for S. Typhimurium detection in food.

RESULTS

In this study, the composite Fe3O4@MIL-100(Fe) nanozymes were successful synthesized and demonstrated substantial peroxide-like activity, with 4.76-fold higher specificity activity (SA) than that of Fe3O4 nanozymes. Then, a glucose oxidase (GOx)-Fe3O4@MIL-100(Fe) cascade reaction was developed for colorimetric detection via an aptamer to facilitate the formation of Fe3O4@MIL-100(Fe)/S. Typhimurium/carboxylated g-C3N4 (CCN)-GOx sandwich complexes. Meanwhile, the fluorescence mode was achieved by measuring the fluorescence intensity of the sandwich complexes. In optimum conditions, the dual-mode detection limits (LOD) were 1.8 CFU/mL (colorimetric mode) and 1.2 CFU/mL (fluorescence mode), respectively, with the S. Typhimurium concentration ranging from 10 CFU/mL to 107 CFU/mL. Finally, the feasibility of the dual-mode colorimetric-fluorescence method was validated via three actual samples, yielding recovery rates of 77.32 % to91.17 % and 82.17 % to 103.7 %, respectively.

SIGNIFICANCE AND NOVELTY

This study successfully develops a composite nanozyme-based cascade colorimetric and fluorescence dual-mode aptasensor for S. Typhimurium detection. It presents several distinct benefits, such as a broader linear range (10-107 CFU/mL), a lower LOD value (1.2 CFU/mL), and more accurate results. More importantly, the proposed dual-mode method displays a low LOD in colorimetric mode, demonstrating considerable potential for S. Typhimurium on-site detection in food.

CRISPR/Cas12a-Triggered Visible-Light-Driven Photoelectrochemical Assay with Single-Nucleotide Resolution for Drug-Resistant Foodborne Salmonella Detection

The prevalence of foodborne pathogenic bacteria, especially drug-resistant strains, such as Salmonella enterica, poses serious threats to public health, highlighting the requirement for the development of rapid and precise detection methods. Herein, a CRISPR/Cas12a-triggered visible-light-driven photoelectrochemical (PEC) assay (CasPEC) was developed using a SiO2-quenched BiVO4/MoS2 p/n-type heterojunction as the photoactive material. The CRISPR/Cas12a recognition endowed the CasPEC assay with high specificity capable of resolving single-nucleotide polymorphisms (SNPs) and identifying SNP-involved drug-resistant bacteria. SiO2 was linked to the surface of the BiVO4/MoS2 heterojunction by single-stranded DNA (ssDNA), which would be cleaved by target-activated CRISPR/Cas12a. This cleavage of ssDNA resulted in the detachment of SiO2, thereby achieving a "signal-on" PEC output. Leveraging the multiple-turnover CRISPR cleavage and the outstanding photoactive performance of PEC signaling, the CasPEC assay for S. enterica showed a detection limit of 103 colony-forming units (CFU)/mL and the ability to detect as few as 0.01% drug-resistant strains. The CasPEC assay can accurately sense the S. enterica contamination in complex food matrices, including beef and milk. These findings demonstrated the great potential of the CasPEC assay for detecting pathogenic bacterial contamination in food, particularly concerning food safety related to SNP-involved drug-resistant bacteria.

Detection of foodborne pathogens in contaminated food using nanomaterial-based electrochemical biosensors

Foodborne pathogens are a grave concern for the for food, medical, environmental, and economic sectors. Their ease of transmission and resistance to treatments, such as antimicrobial agents, make them an important challenge. Food tainted with these pathogens is swiftly rejected, and if ingested, can result in severe illnesses and even fatalities. This review provides and overview of the current status of various pathogens and their metabolites transmitted through food. Despite a plethora of studies on treatments to eradicate and inhibit these pathogens, their indiscriminate use can compromise the sensory properties of food and lead to contamination. Therefore, the study of detection methods such as electrochemical biosensors has been proposed, which are devices with advantages such as simplicity, fast response, and sensitivity. However, these biosensors may also present some limitations. In this regard, it has been reported that nanomaterials with high conductivity, surface-to-volume ratio, and robustness have been observed to improve the detection of foodborne pathogens or their metabolites. Therefore, in this work, we analyze the detection of pathogens transmitted through food and their metabolites using electrochemical biosensors based on nanomaterials.

Food nanotechnology: opportunities and challenges

Food nanotechnology, which applies nanotechnology to food systems ranging from food production to food processing, packaging, and transportation, provides tremendous opportunities for conventional food science and industry innovation and improvement. Although great progress and rapid growth have been achieved in food nanotechnology research owing to the unique food features rendered by nanotechnology, at a fundamental level, food nanotechnology is still in its initial stages and the potential adverse effects of nanomaterials are still a controversial problem that attract public attention. Food-derived nanomaterials, compared to some inorganic nanoparticles and synthetic organic macromolecules, can be digested rapidly and produce similar digestion products to those produced normally, which become the mainstream and trend for food nanotechnology in practical applications, and are expected to be a vital tool for addressing the security problem and easing public concerns. These food-derived materials enable the favourable characteristics of nanostructures to be combined with the safety, biocompatibility, and bioactivity of natural food. Very recently, diverse food-derived nanomaterials have been explored and widely applied in multiple fields. Herein, we thoroughly summarize the fabrication and development of nanomaterials for use in food technology, as well as the recent advances in the improvement of food quality, revolutionizing food supply, and boosting food industries based on foodborne nanomaterials. The current challenges in food nanotechnology are also discussed. We hope this review can provide a detailed reference for experts and food manufacturers and inspire researchers to participate in the development of food nanotechnology for highly efficient food industry growth.

Biotemplated Janus Magnetic Microrobots Based on Diatomite for Highly Efficient Detection of Salmonella

Foodborne illnesses caused by Salmonella bacteria pose a significant threat to public health. It is still challenging to detect them effectively. Herein, biotemplated Janus disk-shaped magnetic microrobots (BJDMs) based on diatomite are developed for the highly efficient detection of Salmonella in milk. The BJDMs were loaded with aptamer, which can be magnetically actuated in the swarm to capture Salmonella in a linear range of 5.8 × 102 to 5.8 × 105 CFU/mL in 30 min, with a detection limit as low as 58 CFU/mL. In addition, the silica surface of BJDMs exhibited a large specific surface area to adsorb DNA from captured Salmonella, and the specificity was also confirmed via tests of a mixture of diverse foodborne bacteria. These diatomite-based microrobots hold the advantages of mass production and low cost and could also be extended toward the detection of other types of bacterial toxins via loading different probes. Therefore, this work offers a reliable strategy to construct robust platforms for rapid biological detection in practical applications of food safety.

An emerging assay for rapid diagnosis of live Salmonella Typhimurium by exploiting aqueous/liquid crystal interface

The rapid and accurate identification of live pathogens with high proliferative ability is in great demand to mitigate foodborne infection outbreaks. Herein, we have developed an ultrasensitive image-based aptasensing array to directly detect live Salmonella typhimurium (S.T) cells. This method relies on the long-range orientation of surfactant-decorated liquid crystals (LCs) and the superiority of aptamers (aptST). The self-assembling of hydrophobic surfactant tails leads to a perpendicular/vertical ordered film at the aqueous/LC interface and signal-off response. The addition of aptST perturbed LCs' ordering into a planar/tilted state at the aqueous phase due to electrostatic interactions between the surfactant with the aptST, and a signal-on response. Following the conformational switch of aptST in the presence of live S. typhimurium, a relative reversing signal-off response was observed upon the target concentration. This aptasensor could promptly confirm the presence of S. typhimurium without intricate DNA-extraction or pre-enrichment stats over a linear range of 1-1.1 × 106 CFU/mL and a detection limit of 1.2 CFU/mL within ∼30 min. These results were successfully validated using molecular and culture-based methods in spiked-milk samples, with a 92.61-104.61 % recovery value. Meanwhile, the flexibility of this portable sensing platform allows for its development and adoption for the precise detection of various pathogens in food and the environment.

CRISPR/Cas12a and Hybridization Chain Reaction-Coregulated Magnetic Relaxation Switching Biosensor for Sensitive Detection of Viable Salmonella in Animal-Derived Foods

We combined a CRISPR/Cas12a system with a hybridization chain reaction (HCR) to develop an ultrasensitive magnetic relaxation switching (MRS) biosensor for detecting viable Salmonella typhimurium (S. typhimurium). Magnetic nanoparticles of two sizes (30 and 1000 nm: MNP30 and MNP1000, respectively) were coupled through HCR. The S. typhimurium gene-activated CRISPR/Cas12a system released MNP30 from the MNP1000-HCR-MNP30 complex through a trans-cleavage reaction. After magnetic separation, released MNP30 was collected from the supernatant and served as a transverse relaxation time (T2) signal probe. Quantitative detection of S. typhimurium is achieved by establishing a linear relationship between the change in T2 and the target gene. The biosensor's limit of detection was 77 CFU/mL (LOD = 3S/M, S = 22.30, M = 0.87), and the linear range was 102-108 CFU/mL. The accuracy for detecting S. typhimurium in real samples is comparable to that of qPCR. Thus, this is a promising method for the rapid and effective detection of foodborne pathogens.

Ultra-sensitive electrochemical immunosensor based on 2D vanadium diselenide (VSe2) for efficient detection of pathogens: Salmonella Typhimurium

Layered transition metal dichalcogenides (TMDs), with an extensive surface area, intriguing tunable electrical and optical features, and a distinctive Van der Waals layered structure, yield outstanding sensing properties. Essentially, most TMDs originally existed in the crystallographic phase of a 2H trigonal prismatic structure, which is semiconducting in nature with poor electrocatalytic activity. In contrast, vanadium diselenide (VSe2) with its metastable metallic 1 T octahedral crystal structure has been proven to be an outstanding electrode material, embracing exceptional electrocatalytic behavior for various electrochemical (EC) applications. However, practically, VSe2 has hardly ever been explored in the field of biosensing technology. This study presents a novel EC biosensor based on the antibody of Salmonella Typhimurium (Anti-ST) immobilized on VSe2-supported Indium tin oxide (Anti-ST/VSe2/ITO) for quantitative and efficient Salmonella Typhimurium (ST) detection. The Anti-ST/VSe2/ITO bioelectrode displayed a linear relationship with ST concentration (1.3 × 10-107 CFU/ml) with a limit of detection (LOD) (0.096 CFU/ml) that is lower than previously reported ST biosensors and impressively high sensitivity (0.001996 μA.mL/CFU). Furthermore, the proposed electrode's electroanalytical activity was evaluated in spiked sugarcane juice, demonstrating distinguished applicability for specific ST detection in real samples.

Universal CRISPR-Cas12a and Toehold RNA Cascade Reaction on Paper Substrate for Visual Salmonella Genome Detection

Salmonella, the most prevalent food-borne pathogen, poses significant medical and economic threats. Swift and accurate on-site identification and serotyping of Salmonella is crucial to curb its spread and contamination. Here, a synthetic biology cascade reaction is presented on a paper substrate using CRISPR-Cas12a and recombinase polymerase amplification (RPA), enabling the programming of a standard toehold RNA switch for a genome of choice. This approach employs just one toehold RNA switch design to differentiate between two different Salmonella serotypes, i.e., S. Typhimurium and S. Enteritidis, without the need for reengineering the toehold RNA switch. The sensor exhibits high sensitivity, capable of visually detecting as few as 100 copies of the whole genome from a model Salmonella pathogen on a paper substrate. Furthermore, this robust assay is successfully applied to detect whole genomes in contaminated milk and lettuce samples, demonstrating its potential in real sample analysis. Due to its versatility and practical features, genomes from different organisms can be detected by merely changing a single RNA element in this universal cell-free cascade reaction.

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.

A novel biosensing strategy on the dynamic and on-site detection of Vibrio coralliilyticus eDNA for coral health warnings

Heat stress and coral diseases are the predominant factors causing the degradation of coral reef ecosystems. Over recent years, Vibrio coralliilyticus was identified as a temperature-dependent pathogen causing tissue lysis in Pocillopora damicornis and one of the primary pathogens causing bleaching and mortality in other corals. Yet current detection techniques for V. coralliilyticus rely primarily on qPCR and ddPCR, which cannot meet the requirements for non-invasive and real-time detection. Herein, we developed an effective electrochemical biosensor modified by an Au-MoS2/rGO (AMG) nanocomposites and a specific capture probe to dynamically detect V. coralliilyticus environment DNA (eDNA) in aquarium experiments, with a lower limit of detection (0.28 fM) for synthetic DNA and a lower limit of quantification (9.8 fg/µL, ∼0.86 copies/µL) for genomic DNA. Its reliability and accuracy were verified by comparison with the ddPCR method (P > 0.05). Notably, coral tissue started to lyse at only 29 °C when the concentration of V. coralliilyticus increased abruptly to 880 copies/µL, indicating the biosensor could reflect the types of pathogen and health risks of corals under heat stress. Overall, the novel and reliable electrochemical biosensing technology provides an efficient strategy for the on-site monitoring and early warning of coral health in the context of global warming.

Multi-functional nanozyme-based colorimetric, fluorescence dual-mode assay for Salmonella typhimurium detection in milk

Rapid and high-sensitive Salmonella detection in milk is important for preventing foodborne disease eruption. To overcome the influence of the complex ingredients in milk on the sensitive detection of Salmonella, a dual-signal reporter red fluorescence nanosphere (RNs)-Pt was designed by combining RNs and Pt nanoparticles. After being equipped with antibodies, the immune RNs-Pt (IRNs-Pt) provide an ultra-strong fluorescence signal when excited by UV light. With the assistance of the H2O2/TMB system, a visible color change appeared that was attributed to the strong peroxidase-like catalytic activity derived from Pt nanoparticles. The IRNs-Pt in conjunction with immune magnetic beads can realize that Salmonella typhimurium (S. typhi) was captured, labeled, and separated effectively from untreated reduced-fat pure milk samples. Under the optimal experimental conditions, with the assay, as low as 50 CFU S. typhi can be converted to detectable fluorescence and absorbance signals within 2 h, suggesting the feasibility of practical application of the assay. Meanwhile, dual-signal modes of quantitative detection were realized. For fluorescence signal detection (emission at 615 nm), the linear correlation between signal intensity and the concentration of S. typhi was Y = 83C-3321 (R2 = 0.9941), ranging from 103 to 105 CFU/mL, while for colorimetric detection (absorbamce at 450 nm), the relationship between signal intensity and the concentration of S. typhi was Y = 2.9logC-10.2 (R2 = 0.9875), ranging from 5 × 103 to 105 CFU/mL. For suspect food contamination by foodborne pathogens, this dual-mode signal readout assay is promising for achieving the aim of convenient preliminary screening and accurate quantification simultaneously.

Cu(II)-induced magnetic resonance tuning and enhanced magnetic relaxation switching immunosensor for sensitive detection of chlorpyrifos and Salmonella

Magnetic relaxation switching (MRS) biosensors have been recognized as useful analytical tools for a range of targets; however, traditional MRS biosensors are limited by the "prozone effect", resulting in a narrow linear range and low sensitivity. Herein, we proposed a paramagnetic Cu2+-induced magnetic resonance tuning (MRET) strategy, based on which Cu2+ ions and magnetic nanoparticles (MNPs) were adopted to construct a Cu-MNP-mediated MRS (Cu-M-MRS) immunosensor with Cu2+ ions acting as a quencher and MNPs as an enhancer. An Fe3O4@polydopamine-secondary antibody conjugate was prepared and used to correlate the amount of Cu2+ ions to the target concentration through an immunoassay. Based on the immunoreaction, the Cu-M-MRS immunosensor enabled the sensitive detection of chlorpyrifos (0.05 ng/mL, a 77-fold enhancement in sensitivity compared with the traditional MRS immunosensor) and Salmonella (50 CFU/mL). The proposed MRET strategy effectively improved the sensitivity and accuracy of the MRS immunosensor, offering a promising and versatile platform for food safety detection.

A biphasic accelerated strand exchange amplification strategy for culture-independent and rapid detection of Salmonella enterica in food samples

Salmonella enterica is a common foodborne pathogen that can cause food poisoning in humans. The organism also infects and causes disease in animals. Rapid and sensitive detection of S. enterica is essential to prevent the spread of this pathogen. Traditional technologies for the extraction and detection of this pathogen from complex food matrices are cumbersome and time-consuming. In this study, we introduced a novel strategy of biphasic assay integrated with an accelerated strand exchange amplification (ASEA) method for efficient detection of S. enterica without culture or other extraction procedures. Food samples are rapidly dried, resulting in a physical fluidic network inside the dried food matrix, which allows polymerases and primers to access the target DNA and initiate ASEA. The dried food matrix is defined as the solid phase, while amplification products are enriched in the supernatant (liquid phase) and generate fluorescence signals. The analytical performances demonstrated that this strategy was able to specifically identify S. enterica and did not show any cross-reaction with other common foodborne pathogens. For artificially spiked food samples, the strategy can detect 5.0 × 101 CFU mL-1S. enterica in milk, 1.0 × 102 CFU g-1 in duck, scallop or lettuce, and 1.0 × 103 CFU g-1 in either oyster or cucumber samples without pre-enrichment of the target pathogen. We further validated the strategy using 82 real food samples, and this strategy showed 92% sensitivity. The entire detection process can be finished, sample-to-answer, within 50 min, dramatically decreasing the detection time. Therefore, we believe that the proposed method enables rapid and sensitive detection of S. enterica and holds great promise for the food safety industry.

Self-assembled bifunctional nanoflower-enabled CRISPR/Cas biosensing platform for dual-readout detection of Salmonella enterica

Sensitive detection and point-of-care test of bacterial pathogens is of great significance in safeguarding the public health worldwide. Inspired by the characteristics of horseradish peroxidase (HRP), we synthesized a hybrid nanoflower with peroxidase-like activity via a three-component self-assembled strategy. Interestingly, the prepared nanozyme not only could act as an alternative to HRP for colorimetric biosensing, but also function as a unique signal probe that could be recognized by a pregnancy test strip. By combining the bifunctional properties of hybrid nanoflower, isothermal amplification of LAMP, and the specific recognition and non-specific cleavage properties of CRISPR/Cas12a system, the dual-readout CRISPR/Cas12a biosensor was developed for sensitive and rapid detection of Salmonella enterica. Moreover, this platform in the detection of Salmonella enterica had limits of detection of 1 cfu/mL (colorimetric assay) in the linear range of 101-108 cfu/mL and 102 cfu/mL (lateral flow assay) in the linear range of 102-108 cfu/mL, respectively. Furthermore, the developed biosensor exhibited good recoveries in the spiked samples (lake water and milk) with varying concentrations of Salmonella enterica. This work provides new insights for the design of multifunctional nanozyme and the development of innovative dual-readout CRISPR/Cas system-based biosensing platform for the detection of pathogens.

Characterization and resistance mechanism of phage-resistant strains of Salmonella enteritidis

In the face of the increasingly severe problem of antibiotic resistance, phage therapy is regarded as a highly potential alternative. Compared with traditional antimicrobial agents, a key research area of phage therapy is the study of phage-resistant mutant bacteria. To effectively monitor and prevent this resistance, it is crucial to conduct in-depth exploration of the mechanism behind phage resistance. In this study, a strain of Salmonella enteritidis (sm140) and the corresponding phage (Psm140) were isolated from chicken liver and sewage, respectively. Using the double-layer plate method, successfully screened out phage-resistant mutant strains. Whole-genome resequencing of 3 resistant strains found that the wbaP gene of all 3 strains had mutations at a specific position (1,118), with the base changing from G to A. This mutation causes the gene-encoded glycine to be replaced by aspartic acid. Subsequent studies found that the frequency of this gene mutation is extremely high, reaching 84%, and all mutations occur at the same position. To further explore the relationship between the wbaP gene and phage resistance, knockout strains and complement strains of the wbaP gene were constructed. The experimental results confirmed the association between the wbaP gene and phage resistance. At the same time, biological characteristics and virulence were evaluated for wild strains, resistant strains, knockout strains, and complement strains. It was found that mutations or deletions of the wbaP gene lead to a decrease in bacterial environmental adaptability and virulence. Through systematic research on the mechanism and biological characteristics of phage resistance, this study provides important references and guidance for the development of new phage therapies, promoting progress in the field of antimicrobial treatment. At the same time, the emergence of phage resistance due to wbaP gene mutations is reported for the first time in salmonella, providing a new perspective and ideas for further studying phage resistance mechanisms.

Research progress of microfluidics-based food safety detection

High demands for food safety detection and analysis have been advocated with people's increasing living standards. Even though numerous analytical testing techniques have been proposed, their widespread adoption is still constrained by the high limit of detection, narrow detection ranges, and high implementation costs. Due to their advantages, such as reduced sample and reagent consumption, high sensitivity, automation, low cost, and portability, using microfluidic devices for food safety monitoring has generated significant interest. This review provides a comprehensive overview of the latest microfluidic detection platforms (published in recent 4 years) and their applications in food safety, aiming to provide references for developing efficient research strategies for food contaminant detection and facilitating the transition of these platforms from laboratory research to practical field use.

Gold Nanoparticle-Based Plasmonic Detection of Escherichia coli, Salmonella enterica, Campylobacter jejuni, and Listeria monocytogenes from Bovine Fecal Samples

Current diagnostic methods for detecting foodborne pathogens are time-consuming, require sophisticated equipment, and have a low specificity and sensitivity. Magnetic nanoparticles (MNPs) and plasmonic/colorimetric biosensors like gold nanoparticles (GNPs) are cost-effective, high-throughput, precise, and rapid. This study aimed to validate the use of MNPs and GNPs for the early detection of Escherichia coli O157:H7, Salmonella enterica spp., Campylobacter jejuni, and Listeria monocytogenes in bovine fecal samples. The capture efficiency (CE) of the MNPs was determined by using Salmonella Typhimurium (ATCC_13311) adjusted at an original concentration of 1.5 × 108 CFU/mL. One (1) mL of this bacterial suspension was spiked into bovine fecal suspension (1 g of fecal sample in 9 mL PBS) and serially diluted ten-fold. DNA was extracted from Salmonella Typhimurium to determine the analytical specificity and sensitivity/LOD of the GNPs. The results showed that the CE of the MNPs ranged from 99% to 100% and could capture as little as 1 CFU/mL. The LOD of the GNPs biosensor was 2.9 µg/µL. The GNPs biosensor was also tested on DNA from 38 naturally obtained bovine fecal samples. Out of the 38 fecal samples tested, 81.6% (31/38) were positive for Salmonella enterica spp., 65.8% (25/38) for C. jejuni, 55.3% (21/38) for L. monocytogenes, and 50% (19/38) for E. coli O157:H7. We have demonstrated that MNP and GNP biosensors can detect pathogens or their DNA at low concentrations. Ensuring food safety throughout the supply chain is paramount, given that these pathogens may be present in cattle feces and contaminate beef during slaughter.

Functionalized sampling swabs array-based portable ATP bioluminescence sensor with on-site enrichment and high specificity for live Salmonella detection

Live food-borne pathogens, featured with rapid proliferative capacity and high pathogenicity, pose an emerging food safety and public health crisis. The high-sensitivity detection of pathogens is particularly imperative yet remains challenging. This work developed a functionalized nylon swab array with enhanced affinity for Salmonella typhimurium (S.T.) for high-specificity ATP bioluminescence-based S.T. detection. In brief, the nylon swabs (NyS) were turned to N-methylation nylon (NyS-OH) by reacting with formaldehyde, and NyS-OH were further converted to NyS-CA by reacting with carboxylic groups of citric acid (CA) and EDC/NHS solution, for altering the NyS surface energy to favor biomodification. The antibody-immobilized nylon swab (MNyS-Ab) was ready for S.T.-specific adsorption. Three prepared MNyS-Ab were installed on a stirrer to form an MNyS-Ab array, allowing for on-site enrichment of S.T. through absorptive extraction. The enriched S.T. was quantified by measuring the bioluminescence of ATP released from cell lysis utilizing a portable ATP bioluminescence sensor. The bioassay demonstrated a detectable range of 102-107 CFU mL-1 with a detection limit (LOD) of 8 CFU/mL within 35 min. The signal of single MNyS-Ab swabs was 500 times stronger than the direct detection of 106 CFU/mL S.T. The MNyS-Ab array exhibited a 100-fold increase in extraction level compared to a single MNyS. This combination of a portable bioluminescent sensor and modified nylon swab array offers a novel strategy for point-of-care testing of live S.T. strains. It holds promise for high-sensitivity measurements of other pathogens and viruses.

Review of Detection Limits for Various Techniques for Bacterial Detection in Food Samples

Foodborne illnesses can be infectious and dangerous, and most of them are caused by bacteria. Some common food-related bacteria species exist widely in nature and pose a serious threat to both humans and animals; they can cause poisoning, diseases, disabilities and even death. Rapid, reliable and cost-effective methods for bacterial detection are of paramount importance in food safety and environmental monitoring. Polymerase chain reaction (PCR), lateral flow immunochromatographic assay (LFIA) and electrochemical methods have been widely used in food safety and environmental monitoring. In this paper, the recent developments (2013-2023) covering PCR, LFIA and electrochemical methods for various bacterial species (Salmonella, Listeria, Campylobacter, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)), considering different food sample types, analytical performances and the reported limit of detection (LOD), are discussed. It was found that the bacteria species and food sample type contributed significantly to the analytical performance and LOD. Detection via LFIA has a higher average LOD (24 CFU/mL) than detection via electrochemical methods (12 CFU/mL) and PCR (6 CFU/mL). Salmonella and E. coli in the Pseudomonadota domain usually have low LODs. LODs are usually lower for detection in fish and eggs. Gold and iron nanoparticles were the most studied in the reported articles for LFIA, and average LODs were 26 CFU/mL and 12 CFU/mL, respectively. The electrochemical method revealed that the average LOD was highest for cyclic voltammetry (CV) at 18 CFU/mL, followed by electrochemical impedance spectroscopy (EIS) at 12 CFU/mL and differential pulse voltammetry (DPV) at 8 CFU/mL. LOD usually decreases when the sample number increases until it remains unchanged. Exponential relations (R2 > 0.95) between LODs of Listeria in milk via LFIA and via the electrochemical method with sample numbers have been obtained. Finally, the review discusses challenges and future perspectives (including the role of nanomaterials/advanced materials) to improve analytical performance for bacterial detection.

A Food Poisoning Caused by Salmonella Enterica (S. Enteritidis) ST11 Carrying Multi-Antimicrobial Resistance Genes in 2019, China

Purpose

This study was to identify and analyze the pathogen responsible for food poisoning in a tourist group traveling from Macao to Zhuhai.

Patients and Methods

Samples were obtained from 27 patients of 96 cases, as well as samples of contaminated food in Macau. The collected samples were subjected to serological identification, drug sensitivity analysis, drug resistance gene identification, virulence factor analysis, and tracing.

Results

Twenty-six isolates and the salad isolate were S. enteritidis ST11. Isolates from patients were exhibited significant resistance to Penicillin AMP (Ampicillin) and quinolones NAL (Nalidixic acid). Among these isolates, 21 strains were resistant to two or more antibiotics, indicating the multi-drug resistance (MDR). Genomic characteristics and phylogenetic analysis were performed on 9 of the isolates using whole genome sequencing (WGS). The analysis revealed that the resistance to AMP and NAL was primarily caused by a gryA mutation D87Y (9/9, 100%), and the presence of beta-lactam resistance genes blaOXA-1 (1/9, 11.11%), blaTEM-141 (1/9, 11.11%), and blaTEM-1B (8/9, 88.89%). It was also found a strains isolated from patients had two resistance genes to quinolones or beta-lactam drugs (1/8, 12.5%), respectively. The strains were found to possess 165 virulence genes, one adherence class virulence factor, one invasion class virulence factor and various pathogenicity islands, including SPI-1, SPI-2, SPI-3, SPI-4, SPI-5, SPI-9, SPI-10, SPI-13, SPI-14, SPI-15, SGI 1, CS54_island, and C63PI-1. Additionally, the virulence plasmids were detected, including IncFIB(s)-IncFII(s)-IncX1 (55.56%), IncFIB(s)-IncFII(s) (33.33%), and IncFIB(s)-IncFII(s)-IncHI2-IncHI2A (11.11%). PFGE (Pulsed Field Gel Electrophoresis) and phylogenetic tree analysis revealed a high degree of similarity between Salmonella isolates from patients and food samples from Macao.

Conclusion

This study identified Salmonella enterica ST11 as the cause of the food poisoning outbreak. The findings highlight the importance of phenotypic characterization and next-generation sequencing (NGS) tools in epidemiological studies and emphasize the potential risk of a new emerging multi-antibiotic ST11 clone for S. enteritidis.

Establishment of a Simple, Sensitive, and Specific Salmonella Detection Method Based on Recombinase-Aided Amplification Combined with dsDNA-Specific Nucleases

Salmonella is a common foodborne pathogen that can cause food poisoning, posing a serious threat to human health. Therefore, quickly, sensitively, and accurately detecting Salmonella is crucial to ensuring food safety. For the Salmonella hilA gene, we designed Recombinase-aided amplification (RAA) primers and dsDNA-specific nuclease (DNase) probes. The ideal primer and probe combination was found when conditions were optimized. Under UV light, a visual Salmonella detection technique (RAA-dsDNase) was developed. Additionally, the RAA-dsDNase was modified to further reduce pollution hazards and simplify operations. One-pot RAA-dsDNase-UV or one-pot RAA-dsDNase-LFD was developed as a Salmonella detection method, using UV or a lateral flow dipstick (LFD) for result observation. Among them, one-pot RAA-dsDNase and one-pot RAA-dsDNase-LFD had detection times of 50 min and 60 min, respectively, for detecting Salmonella genomic DNA. One-pot RAA-dsDNase-UV had a detection limit of 101 copies/μL and 101 CFU/mL, while one-pot RAA-dsDNase-LFD had a sensitivity of 102 copies/μL and 102 CFU/mL. One-pot RAA-dsDNase-UV and one-pot RAA-dsDNase-LFD assays may identify 17 specific Salmonella serovars witho ut causing a cross-reaction with the remaining 8 bacteria, which include E. coli. Furthermore, Salmonella in tissue and milk samples has been reliably detected using both approaches. Overall, the detection method developed in this study can quickly, sensitively, and accurately detect Salmonella, and it is expected to become an important detection tool for the prevention and control of Salmonella in the future.

Ultra-sensitive and rapid detection of Salmonella enterica and Staphylococcus aureus to single-cell level by aptamer-functionalized carbon nanotube field-effect transistor biosensors

Foodborne diseases caused by Salmonella enterica (S. enterica) and Staphylococcus aureus (S. aureus) significantly impact public health, underscoring the imperative for highly sensitive, rapid, and accurate detection technologies to ensure food safety and prevent human diseases. Nanomaterials hold great promise in the development of high-sensitivity transistor biosensors. In this work, field-effect transistor (FET) comprising high-purity carbon nanotubes (CNTs) were fabricated and modified with corresponding nucleic acid aptamers for the high-affinity and selective capture of S. enterica and S. aureus. The aptamer-functionalized CNT-FET biosensor demonstrated ultra-sensitive and rapid detection of these foodborne pathogens. Experimental results indicated that the biosensor could detect S. enterica at a limit of detection (LOD) as low as 1 CFU in PBS buffer, and S. aureus at an LOD of 1.2 CFUs, achieving single-cell level detection accuracy with exceptional specificity. The biosensor exhibited a rapid response time, completing single detections within 200 s. Even in the presence of interference from six complex food matrices, the biosensor maintained its ultra-sensitive (3.1 CFUs) and rapid response (within 200 s) characteristics for both pathogens. The developed aptamer-functionalized CNT-FET biosensor demonstrates a capability for low-cost, ultra-sensitive, label-free, and rapid detection of low-abundance S. enterica and S. aureus in both buffer solutions and complex environments. This innovation holds significant potential for applying this detection technology to on-site rapid testing scenarios, offering a promising solution to the pressing need for efficient and reliable pathogen monitoring in various settings.

Rapid detection of Salmonella in milk by labeling-free electrochemical immunosensor based on an Fe3O4-ionic liquid-modified electrode

Electrochemical sensors show distinct advantages over other types of sensors in the rapid detection of microorganisms. Here, we attempted to construct a label-free electrochemical immunosensor based on an Fe3O4-ionic liquid (IL)-modified electrode to rapidly detect Salmonella in milk. The excellent ionic conductivity of the IL facilitated sensor construction, and the large surface area of nano-Fe3O4 provided numerous sites for subsequent experiments. An antibody was fixed on the Fe3O4-IL complex with polyglutamic acid modification by a simple infusion method. The microstructure of the Fe3O4-IL composites was investigated by scanning electron microscopy, and the elements and structures of the composites were analyzed by energy dispersive X-ray and Fourier transform infrared spectroscopy. Under optimized experimental conditions, the detection range of the constructed sensor was 3.65 × 102-3.65 × 108 CFU mL-1, and the LOD was 1.12 × 102 CFU mL-1 (S/N = 3). In addition, the prepared electrochemical immunosensor is convenient for detecting foodborne pathogens because of its outstanding stability, good selectivity, and repeatability.

Nanotechnology-based analytical techniques for the detection of contaminants in aquatic products

Food safety of aquatic products has attracted considerable attention worldwide. Although a series of conventional bioassays and instrumental methods have been developed for the detection of pathogenic bacteria, heavy metal residues, marine toxins, and biogenic amines during the production and storage of fish, shrimp, crabs et al., the nanotechnology-based analyses still have their advantages and are promising since they are cost-efficient, highly sensitive and selective, easy to conduct, facial design, often require no sophisticated instruments but with excellent detection performance. This review aims to summarize the advances of various biosensing strategies for bacteria, metal ions, and small molecule contaminants in aquatic products during the last five years, The review highlights the development in nanotechnologies applied for biorecognition process, signal transduction and amplification methods in each novel approach, the nuclease-mediated DNA amplification, nanomaterials (noble metal nanoparticle, metal-organic frameworks, carbon dots), lateral flow-based biosensor, surface-enhanced Raman scattering, microfluidic chip, and molecular imprinting technologies were especially emphasized. Moreover, this study provides a view of current accomplishments, challenges, and future development directions of nanotechnology in aquatic product safety evaluation.

Microfluidic systems for infectious disease diagnostics

Microorganisms, encompassing both uni- and multicellular entities, exhibit remarkable diversity as omnipresent life forms in nature. They play a pivotal role by supplying essential components for sustaining biological processes across diverse ecosystems, including higher host organisms. The complex interactions within the human gut microbiota are crucial for metabolic functions, immune responses, and biochemical signalling, particularly through the gut-brain axis. Viruses also play important roles in biological processes, for example by increasing genetic diversity through horizontal gene transfer when replicating inside living cells. On the other hand, infection of the human body by microbiological agents may lead to severe physiological disorders and diseases. Infectious diseases pose a significant burden on global healthcare systems, characterized by substantial variations in the epidemiological landscape. Fast spreading antibiotic resistance or uncontrolled outbreaks of communicable diseases are major challenges at present. Furthermore, delivering field-proven point-of-care diagnostic tools to the most severely affected populations in low-resource settings is particularly important and challenging. New paradigms and technological approaches enabling rapid and informed disease management need to be implemented. In this respect, infectious disease diagnostics taking advantage of microfluidic systems combined with integrated biosensor-based pathogen detection offers a host of innovative and promising solutions. In this review, we aim to outline recent activities and progress in the development of microfluidic diagnostic tools. Our literature research mainly covers the last 5 years. We will follow a classification scheme based on the human body systems primarily involved at the clinical level or on specific pathogen transmission modes. Important diseases, such as tuberculosis and malaria, will be addressed more extensively.

Key steps for improving bacterial SERS signals in complex samples: Separation, recognition, detection, and analysis

Rapid and reliable detection of pathogenic bacteria is absolutely essential for research in environmental science, food quality, and medical diagnostics. Surface-enhanced Raman spectroscopy (SERS), as an emerging spectroscopic technique, has the advantages of high sensitivity, good selectivity, rapid detection speed, and portable operation, which has been broadly used in the detection of pathogenic bacteria in different kinds of complex samples. However, the SERS detection method is also challenging in dealing with the detection difficulties of bacterial samples in complex matrices, such as interference from complex matrices, confusion of similar bacteria, and complexity of data processing. Therefore, researchers have developed some technologies to assist in SERS detection of bacteria, including both the front-end process of obtaining bacterial sample data and the back-end data processing process. The review summarizes the key steps for improving bacterial SERS signals in complex samples: separation, recognition, detection, and analysis, highlighting the principles of each step and the key roles for SERS pathogenic bacteria analysis, and the interconnectivity between each step. In addition, the current challenges in the practical application of SERS technology and the development trends are discussed. The purpose of this review is to deepen researchers' understanding of the various stages of using SERS technology to detect bacteria in complex sample matrices, and help them find new breakthroughs in different stages to facilitate the detection and control of bacteria in complex samples.

Dual-mode colorimetric and fluorescence biosensors for the detection of foodborne bacteria

Due to the growing demand for detection technologies, there has been significant interest in the development of integrated dual-modal sensing technologies, which involve combining two signal transduction channels into a single technique, particularly in the context of food safety. The integration of two detection signals not only improves diagnostic performance by reducing assumptions, but also enhances diagnostic functions with increased application flexibility, improved accuracy, and a wider detection linear range. The top two output signals for emerging dual-modal probes are fluorescent and colorimetric, due to their exceptional advantages for real-time sensitive sensing and point-of-care applications. With the rapid progress of nanotechnology and material chemistry, the integrated colorimetric/fluorimetric dual-mode systems show immense potential in sensing foodborne pathogenic bacteria. In this comprehensive review, we present a detailed summary of various colorimetric and fluorimetric dual-modal sensing methods, with a focus on their application in detecting foodborne bacteria. We thoroughly examine the sensing methodologies and the underlying principles of the signal transduction systems, and also discuss the challenges and future prospects for advancing research in this field.

Recent Developments in Lateral Flow Assays for Salmonella Detection in Food Products: A Review

Salmonellosis is a disease transmitted by contaminated food and is one of the leading causes of infections worldwide, making the early detection of Salmonella of crucial importance for public health. However, current detection methods are laborious and time-consuming, thus impacting the entire food supply chain and leading to production losses and economic sanctions. To mitigate these issues, a number of different biosensors have been developed, including lateral flow assays (LFAs), which have emerged as valuable tools in pathogen detection due to their portability, ease of use, time efficiency, and cost effectiveness. The performance of LFAs has been considerably enhanced by the development of new nanomaterials over the years. In this review, we address the principles and formats of the assay and discuss future prospects and challenges with an emphasis on LFAs developed for the detection of different Salmonella serovars in food.

DNA Extraction- and Amplification-Free Nucleic Acid Biosensor for the Detection of Foodborne Pathogens Based on CRISPR/Cas12a and Argonaute Protein-Mediated Cascade Signal Amplification

A novel method for detecting low levels of viable foodborne pathogens, specifically Salmonella typhimurium (S. typhimurium), has been developed. Traditional nucleic acid assay, such as polymerase chain reaction (PCR), often requires complex DNA extraction and amplification, making it challenging to differentiate between viable and nonviable pathogens. This assay employed a phage as the recognition element to precisely identify and lyse viable S. typhimurium that can undergo DNA extraction. It combined the efficient trans-cleavage activities of CRISPR/Cas12a with the specific cleavage advantages of Argonaute proteins, enabling ultrasensitive detection. This double-enzyme-mediated nucleic acid test can accurately distinguish viable and nonviable S. typhimurium with a detection limit of 23 CFU/mL without DNA amplification. The method was successfully applied to common food samples, producing results consistent with quantitative PCR tests. This work provides a promising platform for easily detecting viable foodborne pathogens with high sensitivity without the need for DNA extraction and amplification.

Magnetic nanobead chain-assisted real-time impedance monitoring using PCB interdigitated electrode for Salmonella detection

Pathogen testing is effective to prevent food poisoning. Here, an electrochemical biosensor was explored for Salmonella detection by combining magnetic grid based bacterial separation with enzymatic catalysis based signal amplification on a PCB interdigitated electrode in a microfluidic chip. First, immune magnetic nanobeads, target bacteria, and immune polystyrene microspheres decorated with glucose oxidase were sufficiently mixed to form nanobead-bacteria-microsphere sandwich conjugates. Then, these conjugates were injected into the chip to form conjugate chains right over the electrode under an iron grid enhanced magnetic field. After non-conductive glucose was injected and catalyzed by glucose oxidase on the conjugate chains, conductive glucose acid and non-conductive hydrogen peroxide were continuously produced and rapidly diffused from the conjugate chains to the electrode. Finally, the impedance change was real-timely monitored and used to determine the bacterial amount. This sensor enabled detection of 50 CFU/mL Salmonella typhimurium in 1 h.

Signal Amplification Strategy Design in Nanozyme-Based Biosensors for Highly Sensitive Detection of Trace Biomarkers

Nanozymes show great promise in enhancing disease biomarker sensing by leveraging their physicochemical properties and enzymatic activities. These qualities facilitate signal amplification and matrix effects reduction, thus boosting biomarker sensing performance. In this review, recent studies from the last five years, concentrating on disease biomarker detection improvement through nanozyme-based biosensing are examined. This enhancement primarily involves the modulations of the size, morphology, doping, modification, electromagnetic mechanisms, electron conduction efficiency, and surface plasmon resonance effects of nanozymes for increased sensitivity. In addition, a comprehensive description of the synthesis and tuning strategies employed for nanozymes has been provided. This includes a detailed elucidation of their catalytic mechanisms in alignment with the fundamental principles of enhanced sensing technology, accompanied by the presentation of quantitatively analyzed results. Moreover, the diverse applications of nanozymes in strip sensing, colorimetric sensing, electrochemical sensing, and surface-enhanced Raman scattering have been outlined. Additionally, the limitations, challenges, and corresponding recommendations concerning the application of nanozymes in biosensing have been summarized. Furthermore, insights have been offered into the future development and outlook of nanozymes for biosensing. This review aims to serve not only as a reference for enhancing the sensitivity of nanozyme-based biosensors but also as a catalyst for exploring nanozyme properties and their broader applications in biosensing.

Multiple electromagnet synergistic control enabled fast and automatic biosensing of Salmonella in a sealed microfluidic chip

Point-of-care testing of pathogens is vital for prevention of food poisoning. Herein, a colorimetric biosensor was elaborately developed to rapidly and automatically detect Salmonella in a sealed microfluidic chip with one central chamber for housing immunomagnetic nanoparticles (IMNPs), bacterial sample and immune manganese dioxide nanoclusters (IMONCs), four functional chambers for housing absorbent pad, deionized water and H2O2-TMB substrate, and four symmetric peripheral chambers for achieving fluidic control. Four electromagnets were placed under peripheral chambers and synergistically controlled to manipulate their respective iron cylinders at the top of these chambers for deforming these chambers, resulting in precise fluidic control with designated flowrate, volume, direction and time. First, the electromagnets were automatically controlled to mix IMNPs, target bacteria and IMONCs, resulting in the formation of IMNP-bacteria-IMONC conjugates. Then, these conjugates were magnetically separated by a central electromagnet and the supernatant was directionally transferred to the absorbent pad. After these conjugates were washed by deionized water, the H2O2-TMB substrate was directionally transferred to resuspend the conjugates and catalyzed by the IMONCs with peroxidase-mimic activity. Finally, the catalysate was directionally transferred back to its initial chamber, and its color was analyzed by the smartphone APP to determinate bacterial concentration. This biosensor could detect Salmonella quantitatively and automatically in 30 min with a low detection limit of 101 CFU/mL. More importantly, the whole bacterial detection procedure from bacterial separation to result analysis was achieved on a sealed microfluidic chip through multiple electromagnet synergistic control, and this biosensor has great potential for point-of-care testing of pathogens without cross contaminations.

Surface plasmon resonance-based oligonucleotide biosensor for Salmonella Typhi detection

Due to high mortality rates, typhoid fever still is one of the major health problems in the world, particularly in developing countries. The lack of highly specific and sensitive diagnostic tests and the great resemblance of typhoid fever symptoms to other diseases made the false-negative diagnosis a major challenge in typhoid fever management. Hence, we decided to design a Surface Plasmon Resonance (SPR) based biosensor for specific detection of Salmonella typhi through DNA hybridization. The results showed that the 10 nM of the synthetic target sequence, as well as 1 nM of PCR product, were the lowest feasible detected concentrations by the designed biosensor. This genosensor was also found to significantly distinguish the complementary sequence with the accuracy of one base mismatch sequence. The surface of the chip can be regenerated with NaOH solution and used for consecutive diagnosis. Therefore, the function of the designed biosensor indicates its high potential for Salmonella typhi detection practice.

Gold nanoparticle-decorated covalent organic frameworks as amplified light-scattering probes for highly sensitive immunodetection of Salmonella in milk

Traditional immunoassays exhibit insufficient screening sensitivity for foodborne pathogens due to their low colorimetric signal intensities. Herein, we propose an ultrasensitive dynamic light scattering (DLS) immunosensor for Salmonella based on a "cargo release-seed growth" strategy enabled by a probe, namely gold nanoparticle-decorated covalent organic frameworks (COF@AuNP). Large amounts of AuNPs in COF@AuNP can be released by acid treatment-induced decomposition of the imine-linked COF, and then they are enlarged via gold growth to generate a dramatically enhanced light-scattering signal, leading to a vast improvement in detection sensitivity. Based on an immunomagnetic microbead carrier, the proposed DLS immunosensor is capable of detecting trace Salmonella in milk in the range of 2.0 × 102-2.0 × 105 CFU mL-1, with a limit of detection of 60 CFU mL-1. The immunosensor also demonstrated excellent selectivity, good accuracy and precision, and high reliability for detecting Salmonella in milk.

Enzymatic Catalysis in Size and Volume Dual-Confined Space of Integrated Nanochannel-Electrodes Chip for Enhanced Impedance Detection of Salmonella

Nanochannel-based confinement effect is a fascinating signal transduction strategy for high-performance sensing, but only size confinement is focused on while other confinement effects are unexplored. Here, a highly integrated nanochannel-electrodes chip (INEC) is created and a size/volume-dual-confinement enzyme catalysis model for rapid and sensitive bacteria detection is developed. The INEC, by directly sandwiching a nanochannel chip (60 µm in thickness) in nanoporous gold layers, creates a micro-droplet-based confinement electrochemical cell (CEC). The size confinement of nanochannel promotes the urease catalysis efficiency to generate more ions, while the volume confinement of CEC significantly enriches ions by restricting diffusion. As a result, the INEC-based dual-confinement effects benefit a synergetic enhancement of the catalytic signal. A 11-times ion-strength-based impedance response is obtained within just 1 min when compared to the relevant open system. Combining this novel nanoconfinement effects with nanofiltration of INEC, a separation/signal amplification-integrated sensing strategy is further developed for Salmonella typhimurium detection. The biosensor realizes facile, rapid (<20 min), and specific signal readout with a detection limit of 9 CFU mL-1 in culturing solution, superior to most reports. This work may create a new paradigm for studying nanoconfined processes and contribute a new signal transduction technique for trace analysis application.

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.

Dual targets-induced specific hemin/G-quadruplex assemblies for label-free electrochemical detection capable of distinguishing Salmonella and its common serotype in food samples

Efficient detection of pathogenic bacteria is paramount for ensuring food safety and safeguarding public health. Herein, we developed a label-free and signal-on dual-target recognition electrochemical DNA sensing platform based on the conformational formation of split G-quadruplex. This platform focused on achieving sensitive and low-cost detection of Salmonella and its most human-infecting S. typhimurium serotype. In simple terms, the dual-target recognition probe (DTR-6P) was ingeniously designed for the loop sequence on the loop-mediated isothermal amplification (LAMP) amplicons. It could recognize two different genes and release their corresponding G-rich sequences. The exfoliated G-rich sequences could be captured by the capture probes on the electrode, and then the bimolecular G-quadruplex or the tetramolecular G-quadruplex would be formed to capture hemin, thereby enabling dual-signal reporting. The minimum detection amount of target genes can be as low as 2 copies/μL. Encouragingly, the real food samples contaminated by Salmonella and the S. typhimurium serotype can be readily identified. The sensing platform with ingenious design paves a new way for label-free, multi-target simultaneous detection, whose advantage of rapidity, sensitivity, cost-effectiveness, and specificity also lay a solid foundation for practical applications.

Dual enzyme induced colorimetric sensor for simultaneous identifying multiple pathogens

Rapid and accurate identification of foodborne pathogens improves public health. Currently employed methods are time-consuming, sensitive to environmental factors, and complex. This study develops a colorimetric sensor for detecting multiple bacteria with one probe using double-enzyme-induced colorimetry. Based on alkaline phosphatase (ALP) in bacteria decomposes L-ascorbic acid 2-magnesium phosphate salt hydrate into ascorbic acid (AA). Manganese dioxide flowers (MnO₂ NFs) can oxidize TMB to etch gold nanorods (Au NRs), which can be inhibited by AA reduction to produce rich colors. Bacteria with varying ALP levels can be identified based on color changes and plasmon resonance wavelength signals produced from Au NRs. Furthermore, the conversion of RGB signals to digital signals and the use of linear discriminant analysis (LDA) allowed 99.57% accuracy in identifying multiple bacteria. It can simultaneously identify five foodborne pathogens across diverse environments (shrimp, meat, milk, etc.). This method may be useful for the rapid and simple identification of foodborne illnesses.

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.

Sensitive detection of viable salmonella bacteria based on tertiary cascade signal amplification via splintR ligase ligation-PCR amplification-CRISPR/Cas12a cleavage

Several viable Salmonella bacteria are capable of causing severe human diseases and huge economic losses. In this regard, viable Salmonella bacteria detection techniques that can identify small numbers of microbial cells are highly valuable. Here, we present a detection method (referred to as SPC) based on the amplification of tertiary signals using splintR ligase ligation, PCR amplification and CRISPR/Cas12a cleavage. The detection limit of the SPC assay was 6 copies (HilA RNA) and 10 CFU (cell). Based on Intracellular HilA RNA detection, this assay can be used to distinguish between viable and dead Salmonella. In addition, it is able to detect multiple serotypes of Salmonella and has been successfully used to detect Salmonella in milk or isolated from farms. Overall, this assay is a promising test for viable pathogens detection and biosafety control.

An Overview of the Public Health Challenges in Diagnosing and Controlling Human Foodborne Pathogens

Pathogens found in food are believed to be the leading cause of foodborne illnesses; and they are considered a serious problem with global ramifications. During the last few decades, a lot of attention has been paid to determining the microorganisms that cause foodborne illnesses and developing new methods to identify them. Foodborne pathogen identification technologies have evolved rapidly over the last few decades, with the newer technologies focusing on immunoassays, genome-wide approaches, biosensors, and mass spectrometry as the primary methods of identification. Bacteriophages (phages), probiotics and prebiotics were known to have the ability to combat bacterial diseases since the turn of the 20th century. A primary focus of phage use was the development of medical therapies; however, its use quickly expanded to other applications in biotechnology and industry. A similar argument can be made with regards to the food safety industry, as diseases directly endanger the health of customers. Recently, a lot of attention has been paid to bacteriophages, probiotics and prebiotics most likely due to the exhaustion of traditional antibiotics. Reviewing a variety of current quick identification techniques is the purpose of this study. Using these techniques, we are able to quickly identify foodborne pathogenic bacteria, which forms the basis for future research advances. A review of recent studies on the use of phages, probiotics and prebiotics as a means of combating significant foodborne diseases is also presented. Furthermore, we discussed the advantages of using phages as well as the challenges they face, especially given their prevalent application in food safety.

Self-Assembly of Multivalent Aptamer-Tethered DNA Monolayers Dedicated to a Fluorescence Polarization-Responsive Circular Isothermal Strand Displacement Amplification for Salmonella Assay

Pathogenic bacteria are pathogens widely spread that are capable of causing mild to life-threatening diseases in human beings or other organisms. Rationally organizing the simple helical motif of double-stranded DNA (dsDNA) tiles into designed ensemble structures with architecturally defined collective properties could lead to promising biosensing applications for pathogen detection. In this work, we facilely engineered multivalent hairpin aptamer probe-tethered DNA monolayers (MHAP-DNA monolayers) and applied them to build a fluorescence polarization-responsive circular isothermal strand displacement amplification (FP-CSDA) for Salmonella assay. In this system, the MHAP-DNA monolayers were constructed based on a dsDNA tile-directed self-assembly. A FAM-labeled reporting probe (RP^FAM) with an inherent low FP signal serves as the signaling unit. The presence of target Salmonella leads to the trapping of F RP^FAM into the super DNA monolayers via a target-triggered CSDA to peel off the tethered hairpin-structured aptamer probes (HAPs) responsible for the binding of RP^FAM. As a result, the FP signal of the FAM fluorophore can be remarkably amplified due to the recycling of target Salmonella and the capacity of structural DNA materials to strongly restrict the free rotation of the FAM fluorophore but without a fluorescence quenching effect. Experimental results demonstrate that the FP assay is able to detect Salmonella with a low limit of detection (LOD) of 7.2 × 10⁰ CFU/mL and high specificity. As a proof-of-concept study, we envision our study using DNA nanoarchitecture as the foundation to modulate CSDA-based FP assays, promising to open up a new avenue for disease diagnosis, food safety detection, and biochemical studies.

Piezocatalytic Medicine: An Emerging Frontier using Piezoelectric Materials for Biomedical Applications

Emerging piezocatalysts have demonstrated their remarkable application potential in diverse medical fields. In addition to their ultrahigh catalytic activities, their inherent and unique charge-carrier-releasing properties can be used to initiate various redox catalytic reactions, displaying bright prospects for future medical applications. Triggered by mechanical energy, piezocatalytic materials can release electrons/holes, catalyze redox reactions of substrates, or intervene in biological processes to promote the production of effector molecules for medical purposes, such as decontamination, sterilization, and therapy. Such a medical application of piezocatalysis is termed as piezocatalytic medicine (PCM) herein. To pioneer novel medical technologies, especially therapeutic modalities, this review provides an overview of the state-of-the-art research progress in piezocatalytic medicine. First, the principle of piezocatalysis and the preparation methodologies of piezoelectric materials are introduced. Then, a comprehensive summary of the medical applications of piezocatalytic materials in tumor treatment, antisepsis, organic degradation, tissue repair and regeneration, and biosensing is provided. Finally, the main challenges and future perspectives in piezocatalytic medicine are discussed and proposed, expecting to fuel the development of this emerging scientific discipline.

Molecular Detection of Virulence Factors in Salmonella serovars Isolated from Poultry and Human Samples

Salmonellosis is a common infectious disease in humans caused by Salmonella spp., which in recent years has shown an increase in its incidence, with products of avian origin being a common source of transmission. To present a successful infective cycle, there are molecular mechanisms such as virulence factors that provide characteristics that facilitate survival, colonization, and damage to the host. According to this, the study aims to characterize the virulence factors of Salmonella spp. strains isolated from broilers (n = 39) and humans (n = 10). The presence of 24 virulence genes was evaluated using end-point PCR. All the strains of Salmonella spp. isolated from broiler chickens revealed presence of 7/24 (29, 16%) virulence genes (lpfA, csgA, sitC, sipB, sopB, sopE, and sivH). Regarding the strains isolated from cases of gastroenteritis in humans, all strains contained (14/24, 58, 33%) virulence genes (lpfA, csgA, pagC, msgA, spiA, sitC, iroN, sipB, orgA, hilA, sopB, sifA, avrA, and sivH). In summary, the presence of virulence genes in different strains of Salmonella isolated from broilers and humans could be described as bacteria with potential pathogenicity due to the type and number of virulence genes detected. These findings are beneficial for the pathogenic monitoring of Salmonella in Colombia.