Sensitive Detection of Staphylococcus aureus with Vancomycin-Conjugated Magnetic Beads as Enrichment Carriers Combined with Flow Cytometry

Rapid and ultra-sensitive lateral flow assay for pathogens based on multivalent aptamer and magnetic nanozyme

Ultra-sensitive LFA methods for pathogen detection commonly depended on tedious and time-consuming nucleic acid amplification. Here, a high affinity multivalent aptamer (multi-Apt) for S. aureus was obtained through exquisite engineering design. The scaffold and conformation of the multi-Apt were found to be key factors in the detection signal of aptsensors. After optimization, the binding affinity of the multi-Apt to S. aureus was improved by more than 8-fold from 135.9 nM to 16.77 nM. By the joint use of the multi-Apt and a multifunctional nanozyme Fe3O4@MOF@PtPd, a fast and ultra-sensitive LFA for S. aureus was developed (termed MA-MN LFA). In this method, a Fe3O4@MOF@PtPd nanozyme was modified with vancomycin and could efficiently capture and separate S. aureus. Moreover, the multi-Apt worked together with the nanozyme to bind with S. aureus to form a ternary complex at the same time, which simply the fabrication of LFA strip. The developed MA-MN LFA could detect S. aureus as low as 2 CFU/mL within 30 min and a wide linear range of 10-1 × 108 CFU/mL was obtained. The detection is easily operated, fast (can be completed within 30 min) and versatile for Gram-positive pathogens, thus has great potential as a powerful tool in pathogen detection.

Ultrasensitive colorimetric detection of Staphylococcus aureus using wheat germ agglutinin and IgY as a dual-recognition strategy

A novel colorimetric platform was designed for the determination of S. aureus by utilizing a dual-recognition strategy, where wheat germ agglutinin (WGA)-functionalized magnetic beads were served as separation elements to capture and enrich S. aureus efficiently from the matrix. Horseradish peroxidase (HRP) labeled chicken anti-protein A IgY (HRP-IgY) was used to label the captured S. aureus. A chicken IgY was introduced as a signal tracer to bind with staphylococcal protein A (SPA) on the surface of S. aureus, which can circumvent the interference from protein G-producing Streptococcus. Subsequently, the colorimetric signal was achieved by an HRP-catalyzed reaction, which was amplified by HRP-IgY bound by approximately 80,000 SPA molecules on one S. aureus. The entire detection process could be accomplished within 90 min. Under optimal conditions, the linear response of different S. aureus concentrations ranged from 7.8 × 102 to 2.0 × 105 CFU/mL and the limit of detection reached down to 3.9 × 102 CFU/mL. Some common non-target bacteria yielded negative results, indicating the excellent specificity of the method. The developed strategy was successfully applied to the determination of S. aureus in various types of samples with satisfactory recoveries. Therefore, the novel dual-recognition strategy possessed the advantages of high sensitivity, specificity, and low cost and exhibited considerable potential as a promising tool to defend public health.

Electrospun nanofiber-based sensors for the detection of chemical and biological contaminants/hazards in the food industries

Food contamination reveals a major health risk globally and presents a significant challenge for the food industry. It can stem from biological contaminants like pathogens, parasites, and viruses, or chemical contaminants such as heavy metals, pesticides, drugs, and hormones. There is also the possibility of naturally occurring hazardous chemicals. Consequently, the development of sensing platforms has become crucial to accurately and rapidly identify contaminants and hazards in food products. Electrospun nanofibers (NFs) offer a promising solution due to their unique three-dimensional architecture, large specific surface area, and ease of preparation. Moreover, NFs exhibit excellent biocompatibility, degradability, and adaptability, making monitoring more convenient and environmentally friendly. These characteristics also significantly reduce the detection process of contaminants. NF-based sensors have the ability to detect a wide range of biological, chemicals, and physical hazards. Recent research on NFs-based sensors for the detection of various food contaminants/hazards, such as pathogens, pesticide/drugs residues, toxins, allergens, and heavy metals, is presented in this review.

Specific separation and sensitive detection of foodborne pathogens by phage-derived bacterial-binding protein-nano magnetic beads coupled with smartphone-assisted paper sensor

Foodborne pathogen infection poses a significant threat to public health and is considered as one of the most serious hazards in global food safety. Herein, a sensitive and efficient method for on-site monitoring of foodborne pathogens was developed by using a smartphone-assisted paper-sensor combined with phage-derived bacterial-binding proteins-nano magnetic beads (PBPs-MBs). PBPs including tail fiber protein (TFP:gp13), cell-wall binding domain (CBD) of endolysin and tailspike protein (TSP) coated on the surface of MBs were applied for rapid separation and enrichment of targeted bacteria (Escherichia coli O157:H7, Staphylococcus aureus and Salmonella typhimurium, respectively) from food samples in 20 min before detection on paper-based sensors. The paper-based sensor was loaded with the lytic agent (polymyxin B) to induce bacterial lysis and release specific endogenous enzymes. Subsequently, three distinct chromogenic substrates were hydrolyzed by their corresponding enzymes, resulting in characteristic color changes on the paper, respectively. In addition, a smartphone APP for red-green-blue (RGB) color analysis of paper was able to directly detect three foodborne pathogens. As a result, the limit of detection (LOD) values for three foodborne pathogens were found to be 2.44 × 102, 2.68 × 104 and 4.62 × 103 CFU/mL, respectively, which were much lower than other studies (106-108 CFU/mL) based on enzymes. Moreover, the feasibility of this approach was further assessed through the successful detection of targeted bacteria in real samples with satisfactory recovery rates. In conclusion, this smartphone-assisted biosensor offers promising application potential for point-of-care testing (POCT) of foodborne pathogens in resource-scarce areas.

Fucoidan-based antibody-free magnetic nanoparticle for on-site detection of waterborne SARS-CoV-2

The portable and sensitive point-of-care-test (POCT) method is in urgent need to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for ensuring public health and safety. However, detection of trace number of pathogens in real water sample from the environment still faces challenges, because complex environment disruptors can rapidly degrade targets. Herein, magnetic beads coated with fucoidan and polydopamine (Fuc-PDA-MBs) were introduced as the capture carrier for pretreatment of samples. Fucoidan, a sulfated polysaccharide, can recognize the SARS-CoV-2 spike (S1) protein receptor-binding domain (S1 RBD) and was chosen for replacement of antibody in enrichment. Environmental water seeded with SARS-CoV-2 spike pseudovirus was applied to test performance of Fuc-PDA-MBs method. Under optimal conditions, the use of Fuc-PDA-MBs showed average 76 % capture efficiency at SARS-CoV-2 spike pseudovirus concentration ranging from 107.62 to 104.34 gene copies (gc)/L. Compared with Electronegative filtration (ENF), Fuc-PDA-MBs showed better virion sorption effectiveness. Fuc-PDA-MBs also validated by raw contaminated urban wastewater and showed high recovery results for SARS-CoV-2 variants. To rapidly detect virus in POCT, nucleic acid extraction-free Loop-Mediated Isothermal Amplification (LAMP) was used for simplifying experimental process. The Fuc-PDA-MBs-LAMP assay showed the quantitation limit of sample (LOQ) was 105.49 gc/L. The whole procedure could be completed within 90 min, including 30 min for virus pre-enrichment, 10 min nucleic acid release and 45 min LAMP analysis. Compared with regular antibody-based immunodetection, this integrated system provides broad-spectrum, economic way to detect SARS-CoV-2 mutants in complex environments and also adaptable for high throughput test, which might be used for on-site early warning of SARS-CoV-2 outbreaks in developing area.

New application of bimetallic Ag/Pt nanoplates in a colorimetric biosensor for specific detection of E. coli in water

A fast and sensitive aptasensor was developed using nanoplates with peroxidase activity as a novel approach. E. coli detection is described using a silver/platinum nanoplate (Ag/Pt NPL) that interacts with an oligonucleotide aptamer as a bioreceptor. The size of the Ag/Pt NPLs was about 42 nm according to the FE-SEM images. The EDS result indicates that a thin layer of Pt ions was coated on the surface of the Ag NPLs. This nanobiosensor has the ability to specifically bind to E. coli, increasing the peroxidase activity of the apt-Ag/Pt NPL. Finally, the blue color of the solution in the contaminated water samples was increased in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate and H2O2. The assay can be completed in 30 min and the presence of E. coli levels can be distinguished with the naked eye. The absorbance at 652 nm is proportional to pathogen concentration from 10 to 108 CFU·mL-1, with a detection limit of 10 CFU·mL-1. The percent recovery for the water samples spiked with E. coli is 95%. The developed assay should serve as a general platform for detecting other pathogenic bacteria which affect water and food quality. The proposed E. coli detection strategy has appealing characteristics such as high sensitivity, simple operation, short testing time, and low cost.

A paper-based photoelectrochemical aptsensor using near-infrared light-responsive AgBiS2 nanoflowers as probes for the detection of Staphylococcus aureus in pork

Staphylococcus aureus is a gram-positive bacterium that can easily cause outbreaks of food-borne diseases. In this work, a signal-enhanced three-dimensional paper-based photoelectrochemical (PEC) aptsensor for the rapid and sensitive determination of S. aureus was developed. Specifically, gold nanoparticles (AuNPs) were electrodeposited on a paper-based working electrode to provide binding sites for a sulfhydryl-functionalized aptamer. Subsequently, S. aureus was captured with high specificity by a carboxyl-functionalized aptamer modified with amino-functionalized AgBiS2 nanoflowers (NH2-AgBiS2 NFs), which functionalized as PEC probes that generated strong photocurrent under irradiation with 980-nm light. By exploiting the "aptamer-target-aptamer" PEC sensing platform, the rapid and ultrasensitive detection of S. aureus was achieved. The sensor had a wide linear range of 20 to 2 × 107 CFU/mL and low limit of detection of 4 CFU/mL. Further, the applicability of the as-prepared aptsensor was successfully certified for the analysis of pork samples artificially contaminated with S. aureus.

Quantitative real-time PCR and magnetic separation strategy for specific detection of group B streptococcus in perinatal Women's urine

Introduction

Group B streptococcus(GBS)often causes adverse outcomes such as urinary system infection, intrauterine infection, premature birth, and stillbirth in perinatal women. Perinatal screening of GBS is conducive to guiding clinical scientific intervention and improving delivery outcomes.This study quantitative real-time PCR (RT-qPCR) combined with magnetic separation was used for GBS detection.

Materials and methods

Sample pre-treatment in this study involved the utilization of magnetic separation (MS) technology, aiming to expedite the detection process and enhance detection sensitivity, and the cfb gene of group B streptococcus was used as the target gene to establish quantitative real-time PCR (RT-qPCR) to detect group B streptococcus.

Results

It was found that penicillin-functionalized magnetic beads had a good ability to enrich and capture group B Streptococcus.The findings revealed an exceptional detection sensitivity, with the ability to detect B streptococcus in urine samples at levels as low as 102 CFU/mL.

Conclusions

The utilization of MS technology in conjunction with the RT-qPCR (MS-RT-qPCR) assay, as demonstrated in this study, offers a viable approach for prenatal screening of group B streptococcus among perinatal women.

Combining hybrid nanoflowers with hybridization chain reaction for highly sensitive detection of SARS-CoV-2 nucleocapsid protein

BACKGROUND

COVID-19 (coronavirus disease 2019) pandemic has had enormous social and economic impacts so far. The nucleocapsid protein (N protein) is highly conserved and is a key antigenic marker for the diagnosis of early SARS-CoV-2 infection.

RESULTS

In this study, the N protein was first captured by an aptamer (Aptamer 58) coupled to magnetic beads (MBs), which in turn were bound to another DNA sequence containing the aptamer (Aptamer 48-Initiator). After adding 5'-biotinylated hairpin DNA Amplifier 1 and Amplifier 2 with cohesive ends for complementary hybridization, the Initiator in the Aptamer 48-Initiator began to trigger the hybridization chain reaction (HCR), generating multiple biotin-labeled DNA concatamers. When incubated with synthetic streptavidin-invertase-Ca3(PO4)2 hybrid nanoflower (SICa), DNA concatamers could specifically bind to SICa through biotin-streptavidin interaction with high affinity. After adding sucrose, invertase in SICa hydrolyzed sucrose to glucose, whose concentration could be directly read with a portable glucometer, and its concentration was positively correlated with the amount of captured N protein. The method is highly sensitive with a detection limit as low as 1 pg/mL.

SIGNIFICANCE

We believe this study provided a practical solution for the early detection of SARS-CoV-2 infection, and offered a new method for detecting other viruses through different target proteins.

Dual-Modal Biosensor for Staphylococcus aureus Detection Based on a Porphyrin-Based Porous Organic Polymer FePor-TPA with Excellent Peroxidase-like, Catalase-like, and Photoelectrochemical Properties

Bacterial infections seriously harm human health and cause many severe diseases, which triggered urgent demands to exploit specific and sensitive biosensor strategies for Staphylococcus aureus detection. Here, a colorimetric and photoelectrochemical dual-mode biosensor for S. aureus assay based on FePor-TPA was constructed. 2D FePor-TPA thin film and its bulk powder (FePor-TPA) were synthesized by in situ growth on ITO and a solvothermal condition, respectively, both of which exhibited excellent peroxidase-like and catalase-like activity, originating from their metalloporphyrin linkers. Benefiting from the in situ growth on ITO electrodes, the 2D FePor-TPA thin film also possessed a more ordered stacking mode and in turn exhibited good electrical conductivity, stable initial photocurrent, and high sensitivity to O2. As for bulk FePor-TPA, its porous structure and high specific surface area make it a possible scaffold to load an amount of AuNPs, the rabbit anti-Staphylococcus aureus Rosenbach tropina antibody (Ab2), and GOx for constructing the signal probe (GOx/Ab2@Au@FePor-TPA) and realizing catalytic amplification. With these satisfactory features in mind, the 2D FePor-TPA thin film and its bulk powder (FePor-TPA) were utilized to construct a dual and signal-on bioplatform for sensitively and selectively detecting S. aureus, which, as far as we know, has not been reported.

MXene@Au based electrochemical biosensor with pretreatment by magnetic nanoparticles for determination of MRSA from clinical samples

Pathogenic bacteria are associated with high morbidity rates and present significant diagnostic challenges in terms of rapid detection. This study introduces a magnetic separation-based electrochemical biosensor for the detection of Methicillin-resistant Staphylococcus aureus (MRSA). Vancomycin (Van) was used to modify on the surface of polyethyleneimine (PEI) mediated MBs (MBs-PEI-Van) for separation and enrichment of MRSA. The MBs-PEI-Van shown a satisfactory stability and applicability with capture effective (CE) > 85% in both PBS and cerebrospinal fluid (CSF) samples. MXene@Au with controllable size of AuNPs was synthesized by a self-reduction method and employed to modify the glassy carbon electrode (GCE). Immunoglobulin G (IgG) was loaded onto the modified electrode to immobilize MRSA, and ferroceneboronic acid (Fc-BA) was used as a probe for quantitative determination. The differential pulse voltammetry (DPV) current was plotted against the concentration of MRSA from 3.8 × 101 to 3.8 × 107 CFU/mL with a limit of detection (LOD) of 3.8 × 101 CFU/mL. In addition, MRSA was successfully detected in spiked CSF samples with satisfactory recoveries (94.35-107.81 %) and validation results (RSD < 11 %). Overall, this study presents a promising method for the detection of MRSA, with the potential to be further developed into a universal pathogen detection method.

Rapid separation and detection of Listeria monocytogenes with the combination of phage tail fiber protein and vancomycin-magnetic nanozyme

In this work, a lateral flow assay for Listeria monocytogenes was developed based on phage tail fiber protein (TFP) and triple-functional nanozyme probes with capture-separation-catalytic activity. Inspired by interaction between phage and bacteria, TFP of L. monocytogenes phage was immobilized on test line as capture molecule, which replaced traditional antibody and aptamer. After Gram-positive bacteria was captured and separated from samples by nanozyme probes modified with vancomycin (Van), TFP specifically recognized L. monocytogenes and overcame non-specific binding of Van. Special color reaction between Coomassie Brilliant Blue and bovine serum albumin which was an amplification carrier on probe was simply utilized as control zone to replace traditional control line. Relying on enzyme-like catalytic activity of nanozyme, this biosensor realized improved sensitivity and colorimetric quantitative detection with a detection limit of 10 CFU mL^-1. Analytic performance results suggested this TFP-based biosensor provided a portable, sensitive and specific strategy to detect pathogen.

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 10⁵, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 10⁵ CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

Evaluation of volume-based flow cytometry as a potential primary method for quantification of bacterial reference material

Bacterial reference materials (RMs) play a crucial role in many analytical processes of microbiological detection. Currently, bacteria are typically counted using the traditional plate-based approach, which results in a higher uncertainty of bacterial RMs unfortunately. Therefore, novel methods are urgently required for the value assignment of RMs in the field of microbiology to derive measurement traceability and accuracy. A potential primary method for microbiological quantification based on flow cytometry (FCM) is described in this study using Escherichia coli O157 (E. coli O157) as an example. The proposed method was applied to determine the number of viable E. coli O157 cells in the RMs with a result of (5.48 ± 0.27) × 10⁸ cells mL^-1, which was in good agreement with the result obtained using the plate-based method (E_n = 0.47). Additionally, this method could be entirely described and understood by equations, and provides formal traceability to the SI for counts of viable bacterial cells, while the associated relative expanded uncertainty (4.93%, k = 2) was significantly lower in comparison to the plate-based method. Therefore, the FCM-based method might be a potential primary method for characterizing bacterial RMs. To our knowledge, this is the first description of FCM as a potential primary method for accurate and traceable quantification of viable bacterial cells with a comprehensive uncertainty statement in microbiological metrology.

Antibiotic-enzyme-inorganic nanoflowers based immunoassay for the ultrasensitive detection of Staphylococcus aureus

In this work, we constructed a moderate and convenient approach for the determination of staphylococcus aureus (S. aureus) by using organic-inorganic flower-like hybrid nanoflowers and Pig IgG together in an enzyme-linked immunosorbent assay (ELISA) system. To ensure efficient capture, the hybrid nanoflowers were prepared by encapsulating horseradish peroxidase (HRP) and vancomycin (VAN) in the inorganic nanocrystal composites (calcium ion solution), just like the mimic biomineralization process. Owing to the self-assembly technique, the synthesized VAN-HRP-CaHPO₄ nanoflowers (NFs) can not only retain the ability to particularly capture the gram-positive bacteria but also enhance the stability and enzymatic activity to achieve the signal output amplification. Then, taking advantage of the integration of signal amplification elements (HRP) and biorecognition unit (VAN), the VAN-HRP-CaHPO₄ NFs were utilized as a new kind of capture & signal regent in the procedure of S. aureus detection. Based on this ELISA system, S. aureus could be clearly detected within the concentration ranging from 1.0 × 10² to 1.0 × 10⁷ CFU mL^-1. The detection limit was defined as 4.3 CFU mL^-1, which performance is superior to some commercial ELISA kits. Additionally, this system detected the S. aureus in food samples and showed an acceptable recovery. As a cost-effective and sensitive platform, this proposed assay was enable to fulfill the requirement of a quick and effective detection of S. aureus.

Simultaneous detection of foodborne pathogenic bacteria in milk by fluorescence immunoassay

Rapid, sensitive and simultaneous detection of multiple bacteria in foodborne is still a major challenge in public health field. Here, a fluorescence immunoassay that can achieve high-throughput detection of three Gram-positive foodborne pathogenic bacteria simultaneously was proposed. Vancomycin and bovine serum albumin conjugate (Van-BSA) was immobilized on a polycarbonate chip to capture three Gram-positive foodborne pathogenic bacteria, Staphylococcus aureus (S. aureus), Bacillus cereus (B. cereus) and Listeria monocytogenes (L. monocytogenes). CdSe/ZnS quantum dot modified antibodies (Ab-QD) were prepared by carbodiimide coupling chemistry. Due to the affinity reaction between antibodies and proteins on the bacterial surface, the simultaneous detection of multiple Gram-positive bacteria was achieved by monitoring the fluorescence signal of quantum dot by a portable microfluidic chip analyzer. Under optimal conditions, low detection limits was 18 CFU/well, 3 CFU/well and 36 CFU/well for S. aureus, B. cereus and L. monocytogenes, respectively. With satisfactory accuracy and precision, the proposed fluorescence immunoassay holds good prospects to detect pathogens in real food samples.

Portable sensor based on magnetic separation and enzyme-mediated immune nanomaterials for point-of-care testing of Listeria monocytogenes in food

Listeria monocytogenes (L. monocytogenes), a typical foodborne pathogen, poses a serious threat to public health safety. This stimulates to develop a point-of-care testing (POCT) method to achieve rapid, sensitive detection of L. monocytogenes. In this study, polyethylene glycol (PEG) mediated ampicillin functionalized magnetic beads (Amp-PEG-MBs) was prepared successfully and it achieved high efficiency (>90%) and rapid (5 min) capture for L. monocytogenes at room temperature. The innovative combination of antibody (Ab), glucose oxidase (GOD) and graphene oxide (GO) prepared Ab@GO@GOD for the specific recognition of L. monocytogenes. Finally, Amp-PEG-MBs and Ab@GO@GOD were successfully assembled into Amp-PEG-MBs@L. monocytogenes-Ab@GO@GOD sandwich structure which could catalyze the glucose, and the final detection results were recorded by a blood glucose meter (BGM). Magnetic separation (MS) combined with enzyme-catalyzed sensor (MS-Ab@GO@GOD-BGM) was successfully established to achieve the detection of L. monocytogenes in artificially contaminated juice within 66 min with the limit of detection was 10¹ CFU/mL. This sensor has potential for other pathogens detection by modifying specific antibodies.

Flow cytometry-based rapid detection of Staphylococcus aureus and Pseudomonas aeruginosa using fluorescent antibodies

Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) are major pathogens frequently detected in food and beverage poisoning, and persistent infections. Therefore, the development of a rapid method that can detect these pathogens before serious multiplication is required. In this study, we established a flow cytometry (FCM)-based detection method that allows rapid acquisition of cell populations in fluid samples by using a fluorescent antibody against S. aureus or P. aeruginosa. Using this method, we detected these pathogens with a 10³ to 10⁵ CFU order of limit of detection value within 1 hour. The FCM-based method for the detection of S. aureus and P. aeruginosa offers the possibility of high-throughput analysis of pathogens in food, environmental, and clinical sources.

Cascade signal enhancement by integrating DNA walking and RCA reaction-assisted "silver-link" crossing electrode for ultrasensitive electrochemical detection of Staphylococcus aureus

The key factor to control the incidence rate of diseases caused by bacteria is rapid detection and early diagnosis. Herein, we proposed a new electrochemical bacterial sensor by coupling DNA walking and rolling circle amplification (RCA) reaction-assisted "silver-link" crossing electrode. Staphylococcus aureus (S. aureus) was detected using this proof-of concept strategy. Aptamer/DNA walker and auxiliary sequence (AS)/RCA reaction probe (RP) duplexes were modified on the electrode surface. The binding of S. aureus with its aptamer caused the disintegration of aptamer/DNA walker and released DNA walker. With the help of Exo III, DNA walker moved along the electrode surface and AS in AS/RP duplex was continuously digested to release RP. By introducing phi29 DNA polymerase, RCA reaction was performed using RP as the reaction primer to form long single-strand RCA extension products between the electrodes. The "silver-link" crossing electrode was formed by metallization of "gene-link", significant conductivity was thus acquired for bacteria detection. The limit of detection (LOD) was 10 CFU/mL and detection time was 2 h. The proposed sensor has high efficiency, good stability and low background signal, human serum and milk samples were successfully detected, which emerged a promising potential in the food monitoring and clinical diagnosis.

Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application

Foodborne pathogens contamination is one of the main sources of food safety problems. Although the existing detection methods have been developed for a long time, the complexity of food samples is still the main factor affecting the detection time and sensitivity, and the rapid separation and enrichment of pathogens is still an objective to be studied. Magnetic separation strategy based on magnetic nanoparticles (MNPs) is considered to be an effective tool for rapid separation and enrichment of foodborne pathogens in food. Therefore, this study comprehensively reviews the development of MNPs in the separation of foodborne pathogens over the past decade. First, various biorecognition reagents for identification of foodborne pathogens and their modifications on the surface of MNPs are introduced. Then, the factors affecting the separation of foodborne pathogens, including the size of MNPs, modification methods, separation strategies and separation forms are discussed. Finally, the application of MNPs in integrated detection methods is reviewed. Moreover, current challenges and prospects of MNPs for the analysis of foodborne pathogens are discussed. Further research should focus on the design of multifunctional MNPs, the processing of large-scale samples, the simultaneous analysis of multiple targets, and the development of all-in-one small analytical device with separation and detection.

Rapid-Response Magnetic Enrichment Strategy for Significantly Improving Sensitivity of Multiplex PCR Analysis of Pathogenic Listeria Species

Listeria monocytogenes and Listeria ivanovii are important pathogenic Listeria spp. that cause infections in humans and animals. Establishing a rapid and sensitive method for the simultaneous screening of pathogenic Listeria spp. is of great significance for ensuring food safety. Multiplex polymerase chain reaction (mPCR) has been extensively reported to simultaneously detect several pathogens in food with high sensitivity, but a time-consuming pre-enrichment process is necessary. In this study, we report the usage of surface-modified polyethyleneimine-coated positively charged magnetic nanoparticles (PEI-MNPs) for rapid enrichment of pathogenic Listeria spp. through electrostatic interactions. The enrichment process takes only 10 min with high capture efficiency (more than 70%) at a wide pH range and ionic strength. Combined with mPCR analysis, the PEI-MNPs-mPCR strategy can simultaneously, rapidly, and sensitively detect pathogenic Listeria spp. without a time-consuming pre-concentration process. Under the optimal conditions, the detection limits of L. monocytogenes and L. ivanovii in lettuce were both as low as 101 CFU/mL, which was a hundred times lower than that without magnetic enrichment. In conclusion, the magnetic enrichment strategy based on charge interaction combined with mPCR analysis has great application potential in shortening the pre-concentration time of foodborne pathogens and improving the detection sensitivity.

Rapid and Multiplexed Detection of Single Cells of Salmonella, Escherichia coli O157, and Shigella flexneri in Ground Beef by Flow Cytometry

Salmonella, Escherichia coli O157, and Shigella flexneri are typical foodborne pathogens in ground beef, which can cause severe infection even when present as a single cell. Flow cytometry (FCM) methods are widely applied in the rapid detection of pathogens in food products. In this study, we report an FCM-based method for detecting single cells of Salmonella, E. coli O157, and S. flexneri in 25 g ground beef samples. We fluorescently labeled specific antibodies that could effectively identify bacterial cells, prepared single-cell samples by serial dilution, and optimized the pre-enrichment time. The results showed that 7 h of pre-enrichment is appropriate for sensitive single-cell detection by FCM. Finally, we evaluated this method in artificially contaminated and retail beef samples. This study outlines a novel highly sensitive FCM-based method to detect Salmonella, E. coli O157, and S. flexneri in beef samples within 8 h that can be applied to the rapid and multiplexed detection of foodborne pathogens.

Vancomycin recognition and induced-aggregation of the Au nanoparticles through freeze-thaw for foodborne pathogen Staphylococcus aureus detection

Infectious diseases caused by foodborne pathogens have become a serious public health problem. It is urgent to develop simple, rapid, and visual methods for pathogen detection. Herein, gold nanoparticles (AuNPs), aptamer and vancomycin (Van) based dual-recognition molecules and magnetic enrichment were combined to realize visual detection of Staphylococcus aureus (S. aureus). Initially, S. aureus was bounded to aptamer coupled Fe₃O₄ with high affinity and selectivity, which can achieve the separation and enrichment of S. aureus in complex sample matrix. Subsequently, the second recognition molecule, Van, was conjugated to S. aureus -Apt - Fe₃O₄. Finally, the unbound Van supernatant was dropped in AuNPs solution that induced the aggregation of the AuNPs through freeze-thaw. Firstly, it was found that AuNPs were stable in the presence of Van after a freeze-thaw cycle. A facile visual colorimetric detection of S. aureus was constructed with the linear range from 10¹ to 10⁴ CFU/mL and the limit of detection (LOD) of 0.2 CFU/mL. By altering the aptamer, this method can be extended to the other Gram-positive bacteria. The proposed method has great potential applications in monitoring food contamination and infectious diseases.

Rapid Detection of Single Viable Escherichia coli O157 Cells in Fresh Lettuce and Strawberry by Immunomagnetic Flow Cytometry in Combination with Pre-Enrichment

Enterohemorrhagic Escherichia coli are an important pathogen causing food poisoning. The rapid detection of viable E. coli O157 in vegetables and fruits at single-cell level is critical because of the low infective dose of this pathogen. In this study, an immunomagnetic flow cytometry (IMFC)-based method was developed to detect E. coli O157 in lettuce and strawberries inoculated with 1 CFU/25 g. This method developed immunomagnetic (IM)-beads to capture E. coli O157 cells. The pre-enrichment of E. coli O157 and IM-bead separation rapidly increased the concentration of cells to a detectable range for flow cytometry. Compared with the plate-based method, the diagnostic sensitivity and specificity of the IMFC-based method were 100% in 166 samples, including 100 artificially contaminated samples, 60 retail samples, and six O157-positive samples for proficiency testing. The developed IMFC-based method was found to be effective in detecting E. coli O157 at single-cell level in 25 g of lettuce or strawberry with relatively shorter associated time to results of 5.7 h. Therefore, the IMFC-based method could improve detection efficiency and also make early warnings in a short time.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

Highly efficient enrichment and identification of pathogens using a herringbone microfluidic chip and by MALDI-TOF mass spectrometry

Bacterial infections cause considerable morbidity and expensive healthcare costs. The prescription of broad-spectrum antimicrobial drugs results in failure of treatment or overtreatment and exacerbates the spread of multidrug-resistant pathogens. There is an emergent demand for rapid and accurate methods to identify pathogens and conduct personalized therapy. Here, we develop a herringbone microfluidic chip integrated with vancomycin modified magnetic beads (herringbone-VMB microchip) to enrich pathogens. The enriched pathogens are identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The herringbone-VMB microchip applies passive mixing of bacterial samples by generating microvortices, which significantly enhances the interaction between bacteria and vancomycin modified magnetic beads and leads to more efficient enrichment compared to in-tube extraction. Four common pathogens in urinary tract infections are utilized to validate the method, and the capture efficiency of the bacteria from urine is up to 90%. The whole procedure takes 1.5 hours from enrichment to identification. This method shows potential in shortening the turnaround time in the clinical diagnosis of bacterial infections.

Ultrasensitive Detection of Bacteria Using a 2D MOF Nanozyme-Amplified Electrochemical Detector

Bacterial infection is one of the major causes of human death worldwide. To prevent bacterial infectious diseases from spreading, it is of critical importance to develop convenient, ultrasensitive, and cost-efficient methods for bacteria detection. Here, an electrochemical detector of a functional two-dimensional (2D) metal-organic framework (MOF) nanozyme was developed for the sensitive detection of pathogenic Staphylococcus aureus. A dual recognition strategy consisting of vancomycin and anti-S. aureus antibody was proposed to specifically anchor S. aureus. The 2D MOFs with excellent peroxidase-like activity can efficiently catalyze o-phenylenediamine to 2,2-diaminoazobenzene, which is an ideal electrochemical signal readout for monitoring the bacteria concentration. Under optimal conditions, the present bioassay provides a wide detection range of 10-7.5 × 10⁷ colony-forming units CFU/mL with a detection limit of 6 CFU/mL, which is better than most of the previous reports. In addition, the established electrochemical sensor can selectively and accurately identify S. aureus in the presence of other bacteria. The present work provides a new pathway for sensitive and selective detection of S. aureus and presents a promising potential in the realm of clinical diagnosis.

Sensitive detection of S. Aureus using aptamer- and vancomycin -copper nanoclusters as dual recognition strategy

The proposed aptamer- and antibiotic-based dual detection sensor, combines copper nanoclusters (CuNCs) as an effective approach for the recognition and quantification of Staphylococcus aureus (S. aureus) as a pathogenic bacteria. A facile method for CuNCs based on vancomycin as the template using a fluorescence platform was proposed for the recognition of the S. aureus whole cells via antibiotic and aptamer. Using dual receptor functionalized CuNCs linked to vancomycin and a specific aptamer and during aggregation induce emission process enhanced fluorescence signal linearly with S. aureus concentrations between 10²-10⁸ CFU/mL, and the detection limit was 80 CFU/mL after 45 min as the optimum incubation time. Non-target bacteria generated negative results, proving the high specificity of the presented sensor. This strategy showed recoveries ranging 86%-98% in milk as real sample and can be used for the development of universal detection platforms for efficient and specific S. aureus detection with great potential applications for monitoring pathogenic bacteria.

Rapid identification of bacteria directly from blood cultures by Co-magnetic bead enrichment and MALDI-TOF MS profiling

Direct identification of bacteria in blood cultures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is interfered with by a variety of non-bacterial proteins derived from blood cells and culture media. Thus, appropriate pre-treatments are needed for successful identification. Here, the bacteria in blood culture bottles were enriched using co-magnetic beads and processed for MALDI-TOF MS profiling. In this strategy, the Fc-containing mannose-binding lectin-coated Fe₃O₄ (Fc-MBL@Fe₃O₄) is incorporated with human IgG-coated Fe₃O₄ (IgG@Fe₃O₄) to form co-magnetic beads, which can recognize both Gram-positive and Gram-negative bacteria. Compared to single magnetic beads Fc-MBL@Fe₃O₄ or IgG@Fe₃O₄, co-magnetic beads resulted in better bacterial capture efficiency and, therefore, could decrease the false-negative results. Our proposed strategy is much more suitable for enrichment of clinically unknown bacteria from blood culture bottles for MALDI-TOF MS database identification.

One-step colorimetric detection of Staphylococcus aureus based on target-induced shielding against the peroxidase mimicking activity of aptamer-functionalized gold-coated iron oxide nanocomposites

Staphylococcus aureus (S. aureus) is one of the most threatened food-borne pathogens. Thus, it is necessary to establish fast, portable and reliable tools to realize the identification of S. aureus. Herein, the authors describe an effective colorimetric-based biosensor for the detection of S. aureus in multiple types of samples. Initially, a nanozyme composed of gold and iron oxide nanoparticles was synthesized and further modified with S. aureus-specific aptamer via Au-S bond. By utilizing the intrinsic peroxidase-like activity of the above magnetic conjugates, 3,3',5,5'-tetramethylbenzidine (TMB) can be transferred to oxTMB by oxidation of hydrogen peroxide (H₂O₂), resulting in a visible blue color. However, the introduction of S. aureus can turn off the UV-vis absorbance signals of TMB-H₂O₂ system, due to the identification property of the nanozyme probe. Consequently, the optical density of the mixed solution measured at 652 nm decreased linearly as the concentration of S. aureus increased from 10 to 10⁶ CFU mL^-1, with the visible limit of detection as low as 10 CFU mL^-1. The as-prepared sensor can detect S. aureus in spiked water, milk and urine samples quantitatively during 12 min without any pre-enrichment, separation or washing steps. In our perception, the one-step colorimetric assay show promise in practical on-site detection of S. aureus.

Tryptamine-functionalized magnetic nanoparticles for highly sensitive detection of Salmonella typhimurium

There is significant demand for the development of rapid, sensitive, and specific methods for detecting bacterial pathogens in order to identify the causes of food poisoning. Nucleic acid amplification tests (NAATs) allow for the culture-free detection of bacterial pathogens and are not as labor intensive and time consuming as culture-based detection methods. However, suitable sample preparation methods must be developed for the realization of simple, rapid, and sensitive NAATs. To resolve this problem, we developed a new sample preparation method that integrates bacterial pathogen enrichment and DNA extraction. We engineered magnetic nanoparticles (MNPs) with a physicochemical probe (tryptamine) for single-tube sample preparation with minimal sample loss. The tryptamine-functionalized MNPs (Indole@MNPs) showed inherent hydrophobicity owing to the indole side chain and a change in their zeta potential with a decrease in the pH. Because of their physicochemical characteristics, the Indole@MNPs could adsorb bacterial pathogens, thus allowing sample enrichment and DNA binding and release through weak electrostatic interactions via pH control. We successfully detected Salmonella enterica serovar Typhimurium, a common cause of bacterial food poisoning, at a concentration of 10 CFU/10 mL in milk samples using quantitative PCR. Thus, the proposed method allows for the simple and sensitive detection of Salmonella typhimurium and can be used for nontyphoidal salmonella detection to ensure food safety.

Vancomycin-dendrimer based multivalent magnetic separation nanoplatforms combined with multiplex quantitative PCR assay for detecting pathogenic bacteria in human blood

Sepsis caused by bacteria has high morbidity and mortality, and it is neccerssay to establish a fast, convenient, and facility assays for detection of bacteria. In this study, we have developed established a simple, rapid, and ultrasensitive vancomycin (Van) and dendrimer nanoparticles-based method to isolate and detect bacteria in human blood using a multivalent binding strategy. The proposed Bio-den-Van multivalent capture nanoplatform combined with m-qPCR for simultaneous detection of two kinds of bacteria was demonstrated with rapid 2 min bacteria isolation with a linear range at 3.2 × 10¹-3.2 × 10⁶ CFU·mL^-1 for L. monocytogenes and 4.1 × 10¹-4.1 × 10⁶ CFU·mL^-1 for S. aureus, respectively. The limit of detection (LOD) for simultaneous detection of L. monocytogenes and S. aureus were 32 and 41 CFU·mL^-1 in spiked human blood samples, respectively. Other bacteria had an insignificant interference with the test results. This Bio-den-Van multivalent capture nanoplatform combined with m-qPCR detection exhibited rapid, high sensitivity and specificity in simultaneous detection of various bacteria. To our knowledge, this is the first time that Bio-den-Van multivalent capture nanoplatform was used with Van as a recognition molecule for the simultaneous capture and subsequent detection of two bacteria from spiked human blood sample. This method holds great potential for future clinical applications.

Bioinspired Electro-Responsive Multispectral Controllable Dye-Doped Liquid Crystal Yolk-Shell Microcapsules for Advanced Textiles

Liquid crystal microcapsules have attracted increasing attention due to their sophisticated structures and adjustable multifunctional features. However, the synthesis of a microscale substrate with wide electromagnetic waveband modulation characteristics and good photoelectric stabilization is still limited and challenging. Herein, a new breed of microcapsules containing dye-doped liquid crystals in a yolk-shell configuration with VTES (vinyl-trim-ethyl-silane)-modified Fe₃O₄@SiO₂ is created. It exhibits an unexpected color enhancement effect, reversible electrochromic performance, and excellent magnetically controllable characteristics. Additionally, a multispectral (visible light, near-infrared light, and high-frequency electromagnetic wave) electro-responsive fabric based on the proposed microcapsules was developed to explore its application in wearable sensors. The present work opens an avenue toward the fabrication of microscale microencapsulated soft materials with a continuous and stable yolk-shell structure. Moreover, it will expand the application regimes of liquid crystal materials in smart windows and advanced textiles.

Faster Detection of Staphylococcus aureus in Milk and Milk Powder by Flow Cytometry

A flow cytometry (FCM)-based method was developed for the faster detection of Staphylococcus aureus in milk and milk powder. Viable S. aureus cells were recognized by highly selective, fluorescently labeled antibodies and Propidium Iodide, and then analyzed by FCM. Using a 5-h pre-enrichment period, the method could detect low numbers of S. aureus cells in 6 h, with a limit of detection of 7.50 cells/mL in milk and 8.30 cells/g in milk powder. The established method was compared with the plate-based method using 75 ultra-high-temperature-treated milk samples, 25 pasteurized milk samples, 66 raw milk samples, and 123 milk powder samples. The two methods yielded similar results for the detection of the pathogen in all sample types. The FCM-based method allows effective and faster monitoring of S. aureus contamination and can be applied to the rapid detection of microorganisms in milk and dairy products.

Hydrangea-like mesoporous WO3 nanoflowers with crystalline framework for 3-hydroxy-2-butanone sensing

In this study, a simple and efficient strategy for the construction of hydrangea-like mesoporous WO₃ nanoflowers templated using diblock copolymer PS₁₁₉-PtBA₁₂₉ was developed. The nanoflower shows good gas sensing properties, especially for 3-hydroxy-2-butanone (3H-2B), which is the signature metabolite of Listeria monocytogenes (L. monocytogenes). Therefore, the gas sensing of 3H-2B by hydrangea-like mesoporous WO₃ nanoflowers can be used to detect L. monocytogenes. In the case of 25 ppm 3H-2B as target gas, the response (R_a/R_g) of the hydrangea-like mesoporous WO₃ nanoflowers at 205 °C is 152, where R_a and R_g are the resistances of the sensing device in air and target gas, respectively, and the response and recovery times at 25 ppm are 25 s and 146 s, respectively. Schematic illustration of the formation of hydrangea-like mesoporous WO₃ nanoflowers and its gas sensing implication.

Ultra-fast and universal detection of Gram-negative bacteria in complex samples based on colistin derivatives

Gram-negative bacteria are a significant cause of infections acquired in both hospital and community settings, resulting in a high mortality rate worldwide. Currently, a Gram-negative infection is diagnosed by symptom evaluation and is treated with empiric antibiotics which target both Gram-negative and Gram-positive bacteria. A rapid and simple diagnostic method would enable immediate and targeted treatment, while dramatically reducing antibiotic overuse. Herein, we introduce a method utilizing a fluorescent derivative of colistin (COL-FL), that can directly label the Gram-negative cell wall of live bacteria and universally detect the targets within 10 min. By using the COL-FL assay, we achieved the differential labeling of various Gram-negative pathogens related to hospital-acquired infections, which could be subsequently detected via spectrofluorometry and microscopy. Further, we determined that our method can be used for complex samples, such as combinations of multiple bacterial types; bacteria in the presence of mammalian cells; and bacteria with serum components. This assay can be integrated into a simple diagnostic platform for rapid screening tests and the stratification of Gram-negative bacterial infections in the clinic.

Advances in Portable Visual Detection of Pathogenic Bacteria

Food safety and regulation of consumer welfare are of great concern, so it is necessary to be able to detect pathogenic bacteria quickly and effectively. Although traditional methods of pathogen detection are reliable and widely used, the detection and analysis processes are cumbersome and time-consuming, which is not conducive to fast assays in the field. New detection strategies have emerged in recent years, especially point-of-care testing (POCT) methods, which do not rely on the laboratory and have become an important development direction for pathogen detection. Many visual detection schemes have been developed that integrate portable glucose meters (PGMs), test strips, smartphones, and other portable devices. Importantly, portable and ultrasensitive biosensors have vast promise in detecting pathogens, as they can be suitable tools for clinical diagnosis and the regulation of food safety. This Review focuses on the latest advances in portable device-based methods for visual detection of pathogens, evaluating their advantages and disadvantages.

A single-tube sample preparation method based on a dual-electrostatic interaction strategy for molecular diagnosis of gram-negative bacteria

A single-tube method based on a dual-electrostatic interaction (EI) strategy for bacteria capture and DNA extraction was designed to enable the highly sensitive detection of nucleic acids. Specially designed magnetic nanoparticles were developed to meet the opposing requirements of a single-tube method, which exist between the strong EI required for efficient bacteria capture and the weak EI required for DNA extraction with minimal DNA adsorption. A dual-EI strategy for the single-tube (DESIGN) method was thus developed to integrate bacteria enrichment, bacteria cell lysis, and DNA recovery in a single tube, thereby minimizing precious sample loss and reducing handling time. Subsequently, we evaluated the performance with a variety of concentrations from 5 to 100 colony-forming units (CFU)/10 mL human urine and milk samples. The DESIGN method achieved the simple and sensitive detection of Salmonella enterica serovar Typhimurium in 10 mL of human urine and milk samples up to 5 CFU by quantitative PCR. Furthermore, the DESIGN method detected Brucella ovis and Escherichia coli from 10 mL of human urine with a detection limit up to 5 CFU/10 mL. Graphical abstract.

The potential risks of paclobutrazol residue on yogurt fermentation from the level of chiral enantiomers

In recent years, pesticide residues in food have increasingly become the focus of public attention. However, the standard system of pesticide maximum residue limits in fermented food is imperfect, which can lead to potential safety risks to consumers. In this context, the aim of the study was to assess the potential effects of paclobutrazol residue on the yogurt fermentation process. We examined the stereoselective behaviors of the 2 paclobutrazol enantiomers from the perspective of chirality during the yogurt fermentation process. The results indicated that no significant degradation occurred for either of the 2 enantiomers (2R, 3R-paclobutrazol, 2S, 3S-paclobutrazol), and no visible enantiomer conversion behavior was observed. In addition, the reason paclobutrazol did not significantly degrade was explained from the perspective of the microbial function. Results from 16S rRNA sequencing indicated that paclobutrazol significantly affected the microbial composition and inhibited metabolic function of microorganisms to exogenous substances, which impeded the degradation of residual pesticide in yogurt. Furthermore, the stable residue of exogenous substance may cause potential food safety problems. Microbial α-diversity analysis indicated that fermentation time played a more important role on diversity than did paclobutrazol concentration. Moreover, Staphylococcus was found in yogurt after treatment with paclobutrazol; Staphylococcus aureus causes dangerous infectious diseases in humans. We devised a method to investigate the presence of pesticide residues during food fermentation and provided a theoretical basis for food safety assessment.