Recent developments in rapid multiplexed bioanalytical methods for foodborne pathogenic bacteria detection

NMR Immunosensor Based on a Targeted Gadolinium Nanoprobe for Detecting Salmonella in Milk

Detecting harmful pathogens in food is not only a crucial aspect of food quality management but also an effective way to ensure public health. In this paper, a complete nuclear magnetic resonance biosensor based on a novel gadolinium (Gd)-targeting molecular probe was developed for the detection of Salmonella in milk. First, streptavidin was conjugated to the activated macromolecular polyaspartic acid (PASP) via an amide reaction to generate SA-PASP. Subsequently, the strong chelating and adsorption properties of PASP toward the lanthanide metal gadolinium ions were exploited to generate the magnetic complex (SA-PASP-Gd). Finally, the magnetic complex was linked to biotinylated antibodies to obtain the bioprobe and achieve the capture of Salmonella. Under optimal experimental conditions, the sensor we have constructed can achieve a rapid detection of Salmonella within 1.5 h, with a detection limit of 7.1 × 103 cfu mL-1.

Fast detection of bacterial gut pathogens on miniaturized devices: an overview

INTRODUCTION

Gut microbes pose challenges like colon inflammation, deadly diarrhea, antimicrobial resistance dissemination, and chronic disease onset. Development of early, rapid and specific diagnosis tools is essential for improving infection control. Point-of-care testing (POCT) systems offer rapid, sensitive, low-cost and sample-to-answer methods for microbe detection from various clinical and environmental samples, bringing the advantages of portability, automation, and simple operation.

AREAS COVERED

Rapid detection of gut microbes can be done using a wide array of techniques including biosensors, immunological assays, electrochemical impedance spectroscopy, mass spectrometry and molecular biology. Inclusion of Internet of Things, machine learning, and smartphone-based point-of-care applications is an important aspect of POCT. In this review, the authors discuss various fast diagnostic platforms for gut pathogens and their main challenges.

EXPERT OPINION

Developing effective assays for microbe detection can be complex. Assay design must consider factors like target selection, real-time and multiplex detection, sample type, reagent stability and storage, primer/probe design, and optimizing reaction conditions for accuracy and sensitivity. Mitigating these challenges requires interdisciplinary collaboration among scientists, clinicians, engineers, and industry partners. Future efforts are essential to enhance sensitivity, specificity, and versatility of POCT systems for gut microbe detection and quantification, advancing infectious disease diagnostics and management.

D-tartaric acid doping improves the performance of whole-cell bacteria imprinted polymer for sensing Vibrio parahaemolyticus

Whole-cell bacteria imprinted polymer-based sensors still face challenges in the form of the difficulty of removing the template entirely, low affinity, and poor sensitivity. To further improve their performance, it is pivotal to modulate the morphology and chemical properties of imprintied polymer by taking advantage of doping engineering. Here we introduced D-tartaric acid (D-TA) as a dopant and employed pyrrole as a functional monomer to construct D-TA/polypyrrole (PPy)-based bacteria imprinted polymer (DPBIP) sensor for Vibrio parahaemolyticus (VP) detection. It is demonstrated that D-TA doping can synergistically accelerate the removal of template bacteria from imprinted polymers (1.5 h), improve bacteria affinity of imprinted sites (the recognition time of 30 min), and enhance the sensitivity of DPBIP sensor (a detection limit of 19 CFU mL-1). The DPBIP sensor had a linear range of 102∼106 CFU mL-1 and exhibited high selectivity and good repeatability. Moreover, a recovery of 94.8%-105.3% was achieved in drinking water and oyster samples. Therefore, small functional molecules doping opens a new avenue to engineering BIP-based sensors with high performance, holding potential applications in securing food safety.

Multi-Probe Nano-Genomic Biosensor to Detect S. aureus from Magnetically-Extracted Food Samples

One of the most prevalent causes of foodborne illnesses worldwide is staphylococcal food poisoning. This study aimed to provide a robust method to extract the bacteria Staphylococcus aureus from food samples using glycan-coated magnetic nanoparticles (MNPs). Then, a cost-effective multi-probe genomic biosensor was designed to detect the nuc gene of S. aureus rapidly in different food matrices. This biosensor utilized gold nanoparticles and two DNA oligonucleotide probes combined to produce a plasmonic/colorimetric response to inform users if the sample was positive for S. aureus. In addition, the specificity and sensitivity of the biosensor were determined. For the specificity trials, the S. aureus biosensor was compared with the extracted DNA of Escherichia coli, Salmonella enterica serovar Enteritidis (SE), and Bacillus cereus. The sensitivity tests showed that the biosensor could detect as low as 2.5 ng/µL of the target DNA with a linear range of up to 20 ng/µL of DNA. With further research, this simple and cost-effective biosensor can rapidly identify foodborne pathogens from large-volume samples.

Antimicrobial peptides: Promising alternatives over conventional capture ligands for biosensor-based detection of pathogenic bacteria

The detection of pathogenic bacteria using biosensing techniques could be a potential alternative to traditional culture based methods. However, the low specificity and sensitivity of conventional biosensors, critically related to the choice of bio-recognition elements, limit their practical applicability. Mammalian antibodies have been widely investigated as biorecognition ligands due to high specificity and technological advancement in antibody production. However, antibody-based biosensors are not considered as an efficient approach due to the batch-to-batch inconsistencies as well as low stability. In recent years, antimicrobial peptides (AMPs) have been increasingly investigated as ligands as they have demonstrated high stability and possessed multiple sites for capturing bacteria. The conjugation of chemo-selective groups with AMPs has allowed effective immobilization of peptides on biosensor surface. However, the specificity of AMPs is a major concern for consideration as an efficient ligand. In this article, we have reviewed the advances and concerns, particularly the selectivity of AMPs for specific detection of pathogenic bacteria. This review also focuses the state-of-the-art mechanisms, challenges and prospects for designing potential AMP conjugated biosensors. The application of AMP in different biosensing transducers such as electrochemical, optical and piezoelectric varieties has been widely discussed. We argue that this review would provide insights to design and construct AMP conjugated biosensors for the pathogenic bacteria detection.

Preparation of an AgNPs@Polydimethylsiloxane (PDMS) multi-hole filter membrane chip for the rapid identification of food-borne pathogens by surface-enhanced Raman spectroscopy

The consumption of food infected with food-borne pathogens has become a global public health problem. Therefore, it is monitor food-borne infections to avoid health and financial consequences. The rapid detection and differentiation of bacteria for biomedical and food safety applications continues to be a significant challenge. Herein, we present a label-free surface-enhanced Raman scattering approach for separating harmful bacteria from food. The method relies on the ascorbic acid reduction method to synthesize silver nanoparticles (AgNPs) and a polydimethylsiloxane (PDMS) multi-hole filter membrane chip (AgNPs@PDMS multi-hole filter membrane chip). Surface-enhanced Raman spectroscopy (SERS) was used, followed by multivariate statistical analysis to differentiate five important food-borne pathogens, including Staphylococcus aureus, Salmonella typhimurium, Listeria monocytogenes, Clostridium difficiles and Clostridium perfringens. The results demonstrated that compared to normal Raman signals, the intensity of the SERS signal was greatly enhanced with an analytical enhancement factor of 5.2 × 10³. The spectral ranges of 400-1800 cm^-1 were analyzed using principal component analysis (PCA) and stepwise linear discriminant analysis (SWLDA) were used to determine the optimal parameters for the discrimination of food-borne pathogens. The first three principal components (PC1, PC2, and PC3) accounted for 87.3% of the total variance in the spectra. The established SWLDA model had 100% accuracy and cross-validation accuracy, which accurately distinguished the SERS spectra of the five species. In conclusion, the SERS technology based on the AgNPs@PDMS multi-hole filter membrane chip was useful for the rapid identification of food-borne pathogens and can be employed for food quality management.

Recent Progress of the Practical Applications of the Platinum Nanoparticle-Based Electrochemistry Biosensors

The detection of biomolecules using various biosensors with excellent sensitivity, selectivity, stability, and reproducibility, is of great significance in the analytical and biomedical fields toward achieving their practical applications. Noble metal nanoparticles are favorable candidates due to their unique optical, surface electrical effect, and catalytic properties. Among these noble metal nanoparticles, platinum nanoparticles (Pt NPs) have been widely employed for the detection of bioactive substances such as glucose, glutamic acid, and hormones. However, there is still a long way to go before the potential challenges in the practical applications of biomolecules are fully overcome. Bearing this in mind, combined with our research experience, we summarized the recent progress of the Pt NP-based biosensors and highlighted the current problems that exist in their practical applications. The current review would provide fundamental guidance for future applications using the Pt NP-based biosensors in food, agricultural, and medical fields.

Application of Multiplexed Aptasensors in Food Contaminants Detection

The existence of contaminants in food poses a serious threat to human health. In recent years, aptamer sensors (aptasensors) have been developed rapidly for the detection of food contaminants because of their high specificity, design flexibility, and high efficiency. However, the development of high-throughput, highly sensitive, on-site, and cost-effective methods for simultaneous detection of food contaminants is still restricted due to multiple signal overlap or mutual interference and cross-reaction between different analytes with similar molecular structures. To overcome these problems, this Review summarizes some effective strategies from the articles published in recent years about multiplexed aptasensors for the simultaneous detection of food contaminants. This work focuses on the application of multiplexed aptasensors to simultaneously detect antibiotics, pathogens, and mycotoxins in food. These aptasensors mainly contain fluorescent aptasensors, electrochemical aptasensors, surface-enhanced Raman scattering-based aptasensors, microfluidic chip aptasensors, and paper-based multiplexed aptasensors. In addition, this Review also covers the application of nucleic acid cycle amplification and nanomaterial amplification strategies to improve the detection sensitivity. Finally, the limitations and challenges in the design of multiplexed aptasensor are also taken into account.

A Reusable Column Method Using Glycopolymer-Functionalized Resins for Capture-Detection of Proteins and Escherichia coli

The use of glycopolymer-functionalized resins (Resin-Glc), as a solid support, in column mode for bacterial/protein capture and quantification is explored. The Resin-Glc is synthesized from commercially available chloromethylated polystyrene resin and glycopolymer, and is characterized by fourier transform infrared spectroscopy, thermogravimetry, and elemental analysis. The percentage of glycopolymer functionalized on Resin-Glc is accounted to be 5 wt%. The ability of Resin-Glc to selectively capture lectin, Concanavalin A, over Peanut Agglutinin, reversibly, is demonstrated for six cycles of experiments. The bacterial sequestration study using SYBR (Synergy Brands, Inc.) Green I tagged Escherichia coli/Staphylococcus aureus reveals the ability of Resin-Glc to selectively capture E. coli over S. aureus. The quantification of captured cells in the column is carried out by enzymatic colorimetric assay using methylumbelliferyl glucuronide as the substrate. The E. coli capture studies reveal a consistent capture efficiency of 10⁵  CFU (Colony Forming Units) g^-1 over six cycles. Studies with spiked tap water samples show satisfactory results for E. coli cell densities ranging from 10² to 10⁷  CFU mL^-1 . The method portrayed can serve as a basis for the development of a reusable solid support in capture and detection of proteins and bacteria.

Development of an Approach of High Sensitive Chemiluminescent Assay for Cystatin C Using a Nanoparticle Carrier

Cystatin C is an important cysteine protease inhibitor in the human body and is proposed as a new indicator of glomerular filtration rate for the detection of kidney damage. In this article, we report an ultra-sensitive, simple, and rapid chemiluminescence immunoassay method for cystatin C detection using functionalized mesoporous silica nanoparticles. After a three step hydrolysis, the amino-functionalized MSN encapsulating dye resulted in a hydrophobic environment for fixing the dye and amino groups for biological modification. The NaIO₄ immobilization method maintained the activity of the antibody notably well. The sandwich immunoassay using two monoclonal antibodies was chosen for its selectivity. The analysis demonstrated that the detection upper was 0.0029 ng/mL and linear relationship within the range of 0.0035-0.5 ng/mL (R ² = 0.9936). The relative standard deviation (RSD) for 11 parallel measurements of 0.25 ng/mL CysC was 4.7%. The automated chemiluminescence analyzer could detect 96 wells continuously. The results demonstrated that this method is ultra-sensitive, simple, and rapid for detecting cystatin C.

A novel and facile immunosensor based on a barometer: Application for rapid analysis of Escherichia coli in waters

A facile immunosensor was constructed based on a barometer indicator using a double-antibody- sandwich method for rapid and sensitive detection of Escherichia coli (E. coli) from water samples. At the present study, Anti- E. coli DH-5 polyclonal antibody was modified through enriching carboxylated magnetic beads and catalase functionalized gold nanoparticles (AuNPs)- loaded nanospheres. The functionalized AuNPs-loaded nanospheres exhibited an excellent catalysis towards decomposition of hydrogen peroxide (H₂O₂), generating a large volume of oxygen (O₂) into waters, increasing the pressure inside the glass vial, which in turn raised the water level in barometer. Under the optimized experimental conditions, the proposed method showed wide linear ranges (10²- 10⁷ cfu mL^-1), good accuracy and precision (recoveries, 86.7- 107%; CV, 3.2- 8.1%) with a limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N = 10) were 80 cfu mL^-1and 267 cfu mL^-1, respectively. Furthermore, the fabricated portable immunosensor device showed some distinct features in low cost and visibility, suggesting great potential for rapid and on-site analysis of this bacteria from waters in less developed areas of developing countries.

G-quadruplex-based assay combined with aptamer and gold nanoparticles for Escherichia coli K88 determination

A colorimetric method was developed using G-quadruplex and gold nanoparticles (AuNPs) for determination of Escherichia coli K88 (ETEC K88). It was composed of two modules: (1) an aptamer as biorecognizing element and (2) a capturing DNA (modified with AuNPs at 5') as a transducer. In the absence of target bacteria, the aptamer can form stable double strands with capturing DNA, preventing the binding of capturing DNA to the G-quadruplex. However, the double strands of capturing DNA and aptamer are untied due to the stronger binding of aptamers to bacteria in the presence of target bacteria. As a result, the G-quadruplex binds to capture DNA and leads to the aggregation and color change of AuNPs, which can be monitored by a spectrophotometer or visualization. The quantitative determination was achieved by monitoring the optical density change of AuNPs solution at 524 nm after target addition. Under optimal conditions, the method has a low detection limit (1.35 × 10² CFU mL^-1) and a linear response in the range 10² to 10⁶ CFU mL^-1. Graphical abstract The manuscripts describe a colorimetric method for the detection of ETEC K88 by using intermolecular G-quadruplex to induce the agglomeration of gold nanoparticles, which can be directly used to determine the presence of bacteria with our naked eyes.

Integrated Microfluidic Preconcentration and Nucleic Amplification System for Detection of Influenza A Virus H1N1 in Saliva

Influenza A viruses are often present in environmental and clinical samples at concentrations below the limit of detection (LOD) of molecular diagnostics. Here we report an integrated microfluidic preconcentration and nucleic amplification system (μFPNAS) which enables both preconcentration of influenza A virus H1N1 (H1N1) and amplification of its viral RNA, thereby lowering LOD for H1N1. H1N1 virus particles were first magnetically preconcentrated using magnetic nanoparticles conjugated with an antibody specific for the virus. Their isolated RNA was amplified to cDNA through thermocycling in a trapezoidal chamber of the μFPNAS. A detection limit as low as 100 TCID50 (50% tissue culture infective dose) in saliva can be obtained within 2 hours. These results suggest that the LOD of molecular diagnostics for virus can be lowered by systematically combining immunomagnetic separation and reverse transcriptase-polymerase chain reaction (RT-PCR) in one microfluidic device.

Identifying non-O157 Shiga toxin-producing Escherichia coli (STEC) using deep learning methods with hyperspectral microscope images

Non-O157 Shiga toxin-producing Escherichia coli (STEC) serogroups such as O26, O45, O103, O111, O121 and O145 often cause illness to people in the United States and the conventional identification of these "Big-Six" are complex. The label-free hyperspectral microscope imaging (HMI) method, which provides spectral "fingerprints" information of bacterial cells, was employed to classify serogroups at the cellular level. In spectral analysis, principal component analysis (PCA) method and stacked auto-encoder (SAE) method were conducted to extract principal spectral features for classification task. Based on these features, multiple classifiers including linear discriminant analysis (LDA), support vector machine (SVM) and soft-max regression (SR) methods were evaluated. Different sizes of datasets were also tested in search for the suitable classification models. Among the results, SAE-based classification models performed better than PCA-based models, achieving classification accuracy of SAE-LDA (93.5%), SAE-SVM (94.9%) and SAE-SR (94.6%), respectively. In contrast, classification results of PCA-based methods such as PCA-LDA, PCA-SVM and PCA-SR were only 75.5%, 85.7% and 77.1%, respectively. The results also suggested the increasing number of training samples have positive effects on classification models. Taking advantage of increasing dataset, the SAE-SR classification model finally performed better than others with average accuracy of 94.9% in classifying STEC serogroups. Specifically, O103 serogroup was classified with the highest accuracy of 97.4%, followed by O111 (96.5%), O26 (95.3%), O121 (95%), O145 (92.9%) and O45 (92.4%), respectively. Thus, the HMI technology coupled with SAE-SR classification model has the potential for "Big-Six" identification.

Specific PCR method for detection of species origin in biochemical drugs via primers for the ATPase 8 gene by electrophoresis

A PCR method is described to identify the species origin of various animal and human tissue-derived biochemical drugs. Four commercialized drugs, including spermary tablets, compound embryonic bovine liver extract tablets, spleen aminopeptide solution, and placenta polypeptide injection, were used as a proof-of-principle in this study. Primers were designed to amplify conservative regions of mitochondrial cytochrome b and ATPase 8 genes from beef, pork, lamb and human DNA, respectively. The specificity of primers for ATPase 8 gene is found to be higher than those for cytochrome b under the given experimental conditions. The amplicon sizes of ATPase 8 were 212, 271, 293 and 405 bp for pork, beef, lamb and human tissue, respectively. The minimum detectable concentration of DNA sample for species identification is 0.05-0.5 pg·μL^-1. The species origin can be distinguished by this method in extremely low concentrations of template DNAs extracted. Conceivably, this PCR method for meat authentication may be extended to quality control of other biochemical drugs and raw materials. Graphical abstract A specific PCR method was developed for the detection of species origin in biochemical drugs via species-specific primers targeting mitochondrial ATPase 8 genes. The PCR products were separated by gel electrophoresis and species origins were indicated by comparison to references.

Porous Silicon-Based Aptasensors: The Next Generation of Label-Free Devices for Health Monitoring

Aptamers are artificial nucleic acid ligands identified and obtained from combinatorial libraries of synthetic nucleic acids through the in vitro process SELEX (systematic evolution of ligands by exponential enrichment). Aptamers are able to bind an ample range of non-nucleic acid targets with great specificity and affinity. Devices based on aptamers as bio-recognition elements open up a new generation of biosensors called aptasensors. This review focuses on some recent achievements in the design of advanced label-free optical aptasensors using porous silicon (PSi) as a transducer surface for the detection of pathogenic microorganisms and diagnostic molecules with high sensitivity, reliability and low limit of detection (LoD).

Click-conjugated photon-upconversion nanoparticles in an immunoassay for honeybee pathogen Melissococcus plutonius

European foulbrood (EFB) is an infectious disease affecting honeybee larvae caused by the bacterium Melissococcus plutonius. The enzyme-linked immunosorbent assay (ELISA) is the gold standard for antibody-based bacteria detection, however, its sensitivity is not high enough to reveal early-stage EFB infection. Photon-upconversion nanoparticles (UCNPs) are lanthanide-doped nanomaterials that emit light of shorter wavelength under near-infrared (NIR) excitation and thus avoid optical background interference. After conjugation with specific biorecognition molecules, UCNPs can be used as ultrasensitive labels in immunoassays. Here, we introduce a method for conjugation of UCNPs with streptavidin based on copper-free click chemistry, which involves surface modification of UCNPs with alkyne-modified bovine serum albumin (BSA) that prevents the non-specific binding and provides reactive groups for conjugation with streptavidin-azide. To develop a sandwich upconversion-linked immunosorbent assay (ULISA) for M. plutonius detection, we have prepared a rabbit polyclonal anti-Melissococcus antibody. The specific capture of the bacteria was followed by binding of biotinylated antibody and UCNP-BSA-streptavidin conjugate for a highly sensitive upconversion readout. The assay yielded an LOD of 340 CFU mL-1 with a wide working range up to 109 CFU mL-1, which is 400 times better than the LOD of the conventional ELISA. The practical applicability of the ULISA was successfully demonstrated by detecting M. plutonius in spiked real samples of bees, larvae and bottom hive debris. These results show a great potential of the assay for early diagnosis of EFB, which can prevent uncontrolled spreading of the infection and losses of honeybee colonies.

Rapid and Simple Detection of Viable Foodborne Pathogen Staphylococcus aureus

Staphylococcus aureus (S. aureus) contamination in food safety has become a worldwide health problem. In this work, we utilized RNA one-step detection of denaturation bubble-mediated Strand Exchange Amplification (SEA) method to realize the detection of viable foodborne pathogen S. aureus. A pair of S. aureus specific primers were designed for the SEA reaction by targeting hypervariable V2 region of 16S rDNA and the amplification reaction was finished about 1 h. The results of amplification reaction could be observed by the naked eyes with a significant color change from light yellow to red to realize the colorimetric detection of S. aureus. Therefore, there only required an isothermal water bath, which was very popular for areas with limited resources. In real sample testing, although the SEA detection was so time-saving compared with the traditional plating method, the SEA method showed great consistency with the traditional plating method. In view of the above-described advantages, we provided a simple, rapid and equipment-free detection method, which had a great potential on ponit-of-care testing (POCT) application. Our method reported here will also provide a POCT detection platform for other food-borne pathogens in food, even pathogenic bacteria from other fields.

Sensitive assay of Escherichia coli in food samples by microchip capillary electrophoresis based on specific aptamer binding strategy

The rapid and cost-effective detection of bacteria is of great importance to ensuring food safety, preventing food poisoning. Herein, we developed a sensitive detection of Escherichia coli (E. coli) using bacteria-specific aptamer in conjunction with microchip capillary electrophoresis-coupled laser-induced fluorescence (MCE-LIF). Based on the differences between charge to mass ratios of free aptamer and bacteria-aptamer complex, which influence their electrophoretic mobilities, the separation of free aptamers and complex peaks by MCE could be achieved. Under optimal conditions, the sensitive detection of E. coli was achieved with a detection limit of 3.7 × 10² CFU mL^-1, at a fast response of 135 s and a short detection length of 2.3 cm. The spiked recovery experiment showed that E. coli could be recovered from spiked drinking water and milk samples with recovery rates of 94.7% and 92.8%, respectively. This work demonstrates that the established detection strategy can be a useful tool for the detection and/or monitoring of E. coli in food and environment.

An automated bacterial concentration and recovery system for pre-enrichment required in rapid Escherichia coli detection

One of the biggest challenges in rapid low concentration bacterial detection is the pre-concentration or pre-enrichment, which aims to increase bacteria concentration and reduce sample volume for easy bacterial detection. In practical bacterial detection, large-volume water samples with a pathogenic bacterial concentration of less than 1 CFU/mL have to be tested rapidly. The reported biosensors either have insufficient detection limit or have limited capability of handling a sufficiently large water sample. Therefore, a high-performance automated pre-enrichment process is strongly demanded in rapid practical bacterial detection. In this paper, a practical high performance automated bacterial concentration and recovery system (ABCRS) based on the combination of a ceramic membrane and tangential flow filtration technique was presented with short processing time (less than one hour), low pre-enrichment limit (≤0.005 CFU/mL), high concentration ratio (≥ 500), high recovery efficiency (~ 90%), and small final retentate volume (≤ 5 mL).

Surface-Enhanced Raman Scattering (SERS) With Silver Nano Substrates Synthesized by Microwave for Rapid Detection of Foodborne Pathogens

Rapid and sensitive methods have been developed to detect foodborne pathogens, a development that is important for food safety. The aim of this study is to explore Surface-enhanced Raman scattering (SERS) with silver nano substrates to detect and identify the following three foodborne pathogens: Escherichia coli O157: H7, Staphylococcus aureus and Salmonella. All the cells were resuspended with 10 mL silver colloidal nanoparticles, making a concentration of 107 CFU/mL, and were then exposed to 785 nm laser excitation. In this study, the results showed that all the bacteria can be sensitively and reproducibly detected directly by SERS. The distinctive differences can be observed in the SERS spectral data of the three food-borne pathogens, and the silver colloidal nanoparticles can be used as highly sensitive SERS-active substrates. In addition, the assay time required only a few minutes, which indicated that SERS coupled with the silver colloidal nanoparticles is a promising method for the detection and characterization of food-borne pathogens. At the same time, principle component analysis (PCA) and hierarchical cluster analysis (HCA) made the different bacterial strains clearly differentiated based on the barcode spectral data reduction. Therefore, the SERS methods hold great promise for the detection and identification of food-borne pathogens and even for applications in food safety.

Advances of magnetic nanoparticles in environmental application: environmental remediation and (bio)sensors as case studies

Nanotechnology is an emerging technique drawing increasing attentions in biomedical, electronic, environmental, and industrial application. Nanoparticles (NPs) possess unique optical, electrical, catalytic, and thermal properties, among which magnetic NPs (MNPs) are one of the most important groups with excellent superparamagnetism property, large surface area, and biocompatibility. In this review, methods for synthesizing and functionalizing MNPs are summarized and linked to their applications in environmental science as either adsorbents or catalysts for removing contaminants from environmental matrices, illustrating stronger reactivity, higher removal capacity, and fast kinetics. Additionally, we also comprehensively discuss the application of MNPs as (bio)sensors to selectively and sensitively detect the presence of environmental contaminants or pathogenic bacteria. This work summarizes the recent progresses of using MNPs as powerful tools in environmental science and engineering, raising their state-of-art application from environmental perspectives and benefiting researchers interested in NPs and environmental studies.

Electrochemical sandwich immunoassay for Escherichia coli O157:H7 based on the use of magnetic nanoparticles and graphene functionalized with electrocatalytically active Au@Pt core/shell nanoparticles

A highly sensitive electrochemical sandwich immunoassay is described for determination of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated magnetite nanoparticles (Fe₃O₄) were modified with primary antibody to capture E. coli O157:H7. Gold-platinum core/shell nanoparticles (Au@Pt NPs) with different Pt shell thicknesses were prepared via changing the molar ratio of H₂PtCl₆ to HAuCl₄ in the precursor solution. The optimized Au@Pt NPs exhibit enhanced activity in the electrocatalytic reduction of hydrogen peroxide (H₂O₂). The Au@Pt NPs were modified with graphene that was functionalized with Neutral Red, and then used as an electrochemical label for secondary antibodies and horseradish peroxidase (HRP). The sandwich immunocomplexes were magnetically absorbed on a 4-channel screen printed carbon electrode. Due to the catalysis of the Au@Pt NPs and HRP, the signal is strongly amplified in the presence of H₂O₂ when using thionine as the electron mediator. Under optimal conditions, the immunoassay has a linear response in the 4.0 × 10² to 4.0 × 10⁸ CFU·mL^-1 concentration range, with a limit of detection of 91 CFU·mL^-1 (at an S/N ratio of 3). Graphical abstract Preparation of Au@Pt core/shell nanoparticles with different Pt shell thickness (A), rGO-NR (B), rGO-NR-Au@Pt-Ab₂-HRP (C) and the preparation and the detection process of the immunoassay (D). rGO: reduced graphene oxide, GO: graphene oxide, NR: Neutral Red, HRP: horseradish peroxidase, AuNPs: gold nanoparticles, Fe₃O₄@SiO₂: Silica coated magnetite nanoparticles, 4-SPCE: 4-channel screen printed carbon electrode.

A non-enzymatic electrochemical immunoassay for quantitative detection of Escherichia coli O157:H7 using Au@Pt and graphene

Herein, a non-enzymatic sandwich-type electrochemical immunoassay was fabricated for quantitative monitoring of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated Fe₃O₄ magnetic nanoparticles (Fe₃O₄@SiO₂) were modified with mouse anti-E. coli O157:H7 monoclonal antibody (Ab₁) to act as capture probes to reduce detection time and increase the sensitivity of the immunoassay. The Au@Pt nanoparticles were loaded on neutral red (NR) functionalized graphene to form composite complex rGO-NR-Au@Pt. rGO-NR-Au@Pt has high specific surface area and good biocompatibility. rGO-NR-Au@Pt was used as the carriers of detection antibodies (Ab₂). Au@Pt catalyzed the reduction of hydrogen peroxide (H₂O₂) to detection of E. coli O157:H7 with the thionine (TH) as electron mediator to effectually amply the current signal. Under the optimized conditions, a linear relationship between the reduction peak current change (ΔI_pc) and the logarithm of the E. coli O157:H7 concentration is obtained in the range from 4.0 × 10³ to 4.0 × 10⁸ CFU mL^-1 and the limit of detection (LOD) is 4.5 × 10² CFU mL^-1 at a signal-to-noise ratio of 3. The immunoassay exhibits acceptable specificity, reproducibility and stability on the detection of E. coli O157:H7. Furthermore, the immunoassay showed good performance in pork and milk samples. The results suggest that this immunoassay will be promising in the food safety area.

Magnetism-Resolved Separation and Fluorescence Quantification for Near-Simultaneous Detection of Multiple Pathogens

In the modern era of molecular evidence-based medicine and advanced biomedical technologies, the rapid, sensitive and specific assay of multiple pathogens is critical to, but largely absent from, clinical practice. Therefore, to improve the current ordinary separation and collection method, we report herein a strategy of magnetism-resolved separation and fluorescence quantification for near-simultaneous detection of multiple pathogens, followed by the direct antimicrobial susceptibility testing (AST). To accomplish this strategy, we utilized aptamer-modified fluorescent-magnetic multifunctional nanoprobes (apt-FMNPs). FMNPs with intriguing different magnetic responses and excellent fluorescence quality were first self-assembled based on metal coordination interaction using (3-mercaptopropyl) trimethoxysilane, magnetic γ-Fe₂O₃, and fluorescent quantum dots as matrix components. Then, aptamers, which specific to target pathogens of Escherichia coli O157:H7 ( E. coli) and Salmonella typhimurium ( S. typ), were conjugated with FMNPs to yield apt-FMNPs nanoprobes for multiple pathogens assay. Based on the discrepant magnetic response of pathogen@nanoprobes complex under the identical external magnetic field, the model bacteria were fished out by magnetic adsorption at different time points and subjected to fluorescence quantification with good linear ranges and detection limits within 1h. Multiple pathogens spiked in real samples were also effectively detected by the apt-FMNPs and sequentially fished out for AST assay, which showed similar results to that for pure pathogens. The apt-FMNPs-based strategy of near-simultaneous detection of multiple pathogens shows promise for the potential application in the diagnosis and treatment of pathogen-related infectious diseases.

Circular exponential amplification of photoinduced electron transfer using hairpin probes, G-quadruplex DNAzyme and silver nanocluster-labeled DNA for ultrasensitive fluorometric determination of pathogenic bacteria

The authors describe a fluorometric strategy for the detection of pathogenic bacteria with ultrasensitivity and high specificity. This strategy relies on the combination of target-modulated photoinduced electron transfer (PET) between G-quadruplex DNAzyme and DNA (labeled with silver nanoclusters) along with hairpin probe-based circular exponential amplification. The reaction system involves three hairpin probes (H1, H2 and H3). Probe H1 contains an aptamer against S. Typhimurium and the recognition sequence for nicking endonuclease. It is used to recognize S. Typhimurium and participates in polymerase-catalyzed target recycle amplification and secondary-target recycle amplification. Probe H2 contains an aptamer against hemin and is used to form the G-quadruplex DNAzyme in the presence of hemin and potassium ion. It acts as the electron acceptor and quenches the fluorescence of the labeled DNA. Fluorescence is best measured at excitation/emission wavelengths of 567/650 nm. Probe H3 contains the template sequence for the synthesis of AgNCs and the H2-annealing sequence. Both H2 and H3 are utilized to perform a strand displacement reaction and to achieve PET between G-quadruplex DNAzyme and DNA/AgNCs. To the best of our knowledge, this is the first example of a PET between G-quadruplex DNAzyme and DNA/AgNCs coupled with circular exponential amplification. The assay has an ultra-low detection limit 8 cfu·mL^-1 of S. Typhimurium. The assay is rapid, accurate, inexpensive and simple. Hence, the strategy may represent a useful platform for ultrasensitive and highly specific detection of pathogenic bacteria as encountered in food analysis and clinical diagnosis. Graphical abstract The reaction system includes three hairpin probes (H1, H2 and H3), primer probe (P), Phi 29 DNA ploymerase (Phi 29) and nicking endonuclease Nt.AlwI (Nt.AlwI). Phi 29 and Nt.AlwI -assisted signal amplification leads to the recycling of target and produces numerous single stranded-DNAs (S). Strand displacement amplification leads to photoinduced electron transfer (PET) between G-quadruplex DNAzyme and DNA/AgNCs. HAP-based circular exponential amplification of PET results in an ultrasensitive fluorometric assay.

Prussian Blue Nanoparticles as a Catalytic Label in a Sandwich Nanozyme-Linked Immunosorbent Assay

Enzyme immunoassays are widely used for detection of analytes within various samples. However, enzymes as labels suffer several disadvantages such as high production cost and limited stability. Catalytic nanoparticles (nanozymes) can be used as an alternative label in immunoassays overcoming the inherent disadvantages of enzymes. Prussian blue nanoparticles (PBNPs) are nanozymes composed of the Fe₄[Fe(CN)₆]₃-based coordination polymer. They reveal peroxidase-like activity and are capable of catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine in the presence of H₂O₂ to form intensely blue product. Here, we introduce the method for conjugation of PBNPs with antibodies and their application in nanozyme-linked immunosorbent assay (NLISA). Sandwich NLISA for detection of human serum albumin in urine was developed with limit of detection (LOD) of 1.2 ng·mL^-1 and working range up to 1 μg·mL^-1. Furthermore, the microbial contamination of Salmonella Typhimurium in powdered milk was detected with LOD of 6 × 10³ colony-forming units (cfu)·mL^-1 and working range up to 10⁶ cfu·mL^-1. In both cases, a critical comparison with the same immunoassay but using native peroxidase as label was realized. The achieved results confirmed the suitability of PBNPs for universal and robust replacement of enzyme labels.

An integrated microfluidic PCR system with immunomagnetic nanoparticles for the detection of bacterial pathogens

There is growing interest in rapid microbial pre-concentration methods to lower the detection limit of bacterial pathogens of low abundance in samples. Here, we report an integrated microfluidic PCR system that enables bacterial cells of interest in samples to be concentrated prior to PCR. It consists of two major compartments: a preconcentration chamber for the immunomagnetic separation of bacterial cells, and a PCR chamber for the DNA amplification of the concentrated cells. We demonstrate the feasibility of the system for the detection of microbial pathogens by preconcentrating the human pathogen Escherichia coli O157:H7, and also amplifying its DNA. The detection limit of E. coli O157:H7 in the PCR system is 1 × 10³ CFU (colony forming unit)/mL. On-chip processing steps, including preconcentration and PCR steps, take less than two hours. Our system can serve as a rapid, specific, and quantitative platform for the detection of microbial pathogens in samples of large volume.

A Portable Impedance Immunosensing System for Rapid Detection of Salmonella Typhimurium

SalmonellaTyphimurium is one of the most dangerous foodborne pathogens and poses a significant threat to human health. The objective of this study was to develop a portable impedance immunosensing system for rapid and sensitive detection of S. Typhimurium in poultry. The developed portable impedance immunosensing system consisted of a gold interdigitated array microelectrode (IDAM), a signal acquisitive interface and a laptop computer with LabVIEW software. The IDAM was first functionalized with 16-Mercaptohexadecanoic acid, and streptavidin was immobilized onto the electrode surface through covalent bonding. Then, biotin-labelled S. Typhimurium-antibody was immobilized onto the IDAM surface. Samples were dropped on the surface of the IDAM and the S. Typhimurium cells in the samples were captured by the antibody on the IDAM. This resulted in impedance changes that were measured and displayed with the LabVIEW software. An equivalent circuit of the immunosensor demonstrated that the largest change in impedance was due to the electron-transfer resistance. The equivalent circuit showed an increase of 35% for the electron-transfer resistance value compared to the negative control. The calibration result indicated that the portable impedance immunosensing system could be used to measure the standard impedance elements, and it had a maximum error of measurement of approximately 13%. For pure culture detection, the system had a linear relationship between the impedance change and the logarithmic value of S. Typhimurium cells ranging from 76 to 7.6 × 10⁶ CFU (colony-forming unit) (50 μL)⁻¹. The immunosensor also had a correlation coefficient of 0.98, and a high specificity for detection of S. Typhimurium cells with a limit of detection (LOD) of 10² CFU (50 μL)⁻¹. The detection time from the moment a sample was introduced to the display of the results was 1 h. To conclude, the portable impedance immunosensing system for detection of S. Typhimurium achieved an LOD that is comparable with commercial electrochemical impedance instruments. The developed impedance immunosensor has advantages in portability, low cost, rapid detection and label-free features showing a great potential for in-field detection of foodborne pathogens.

Efficacy of a titanium dioxide nanoparticles - based indoor anti-odor product as assessed by electronic nose and gaschromatography-mass spectrometry

Indoor air pollutants and odorants may have psychological and physical impact on exposed individuals and the unpleasant room air is considered as one of the factors associated with sick building syndrome comprising general symptoms such as headache and lethargy. Approaches for improving the quality of indoor air are thus important as support for human health and well-being. Photo-oxidation catalyzed by titanium dioxide (TiO₂), is one of the methods used for elimination of volatile organic compounds, which are the cause of odor nuisance in indoor and outdoor air. In the present investigation, the efficacy of an experimental anti-odor air freshener based on TiO₂ nanoparticles was estimated by testing its ability in removing from a small air chamber (200mL) the odor of triethylamine solutions (50μL at concentrations between 0.700 to 700mM), used as a model volatile molecule for simulating fish-like unpleasant indoor environment. The evaluation was performed by electronic nose which provided a holistic and objective data on the efficacy of the product, demonstrating that the effects of triethylamine even at the highest tested concentrations can be completely removed by application of 3.0g of the product at 25% TiO₂ nanoparticles concentration. The obtained results were confirmed by gaschromatography-mass spectrometry (GC-MS) analysis addressed to the quantitative determination of residual triethylamine in the environment after treatment by the anti-odor product.

3D-printed microfluidic magnetic preconcentrator for the detection of bacterial pathogen using an ATP luminometer and antibody-conjugated magnetic nanoparticles

Various types of microfluidic systems have been developed to detect bacterial pathogens. However, most of these require enrichment steps that take at least several hours when detecting bacteria that are present with a low number of cells and, in addition, fabrication requires complicated assembly steps. In this study, we report the development of 3D microfluidic magnetic preconcentrator (3DμFMP) made of plastic via 3D printing without the need for any assembly. 3DμFMP could selectively preconcentrate enterohemorrhagic Escherichia coli O157:H7 in 100mL by a factor of 700 within 1h using antibody-conjugated magnetic nanoparticles (Ab-MNPs). With the combined use of an ATP luminometer, as low as 10 E. coli O157:H7 CFU (colony forming unit)/mL could be detected in blood. These results demonstrate the feasibility of 3DμFMP as a preconcentrator to improve the detection limit of existing bacterial detection systems.

Porous Silicon-Based Biosensors: Towards Real-Time Optical Detection of Target Bacteria in the Food Industry

Rapid detection of target bacteria is crucial to provide a safe food supply and to prevent foodborne diseases. Herein, we present an optical biosensor for identification and quantification of Escherichia coli (E. coli, used as a model indicator bacteria species) in complex food industry process water. The biosensor is based on a nanostructured, oxidized porous silicon (PSi) thin film which is functionalized with specific antibodies against E. coli. The biosensors were exposed to water samples collected directly from process lines of fresh-cut produce and their reflectivity spectra were collected in real time. Process water were characterized by complex natural micro-flora (microbial load of >10⁷ cell/mL), in addition to soil particles and plant cell debris. We show that process water spiked with culture-grown E. coli, induces robust and predictable changes in the thin-film optical interference spectrum of the biosensor. The latter is ascribed to highly specific capture of the target cells onto the biosensor surface, as confirmed by real-time polymerase chain reaction (PCR). The biosensors were capable of selectively identifying and quantifying the target cells, while the target cell concentration is orders of magnitude lower than that of other bacterial species, without any pre-enrichment or prior processing steps.

A new analytical platform based on field-flow fractionation and olfactory sensor to improve the detection of viable and non-viable bacteria in food

An integrated sensing system is presented for the first time, where a metal oxide semiconductor sensor-based electronic olfactory system (MOS array), employed for pathogen bacteria identification based on their volatile organic compound (VOC) characterisation, is assisted by a preliminary separative technique based on gravitational field-flow fractionation (GrFFF). In the integrated system, a preliminary step using GrFFF fractionation of a complex sample provided bacteria-enriched fractions readily available for subsequent MOS array analysis. The MOS array signals were then analysed employing a chemometric approach using principal components analysis (PCA) for a first-data exploration, followed by linear discriminant analysis (LDA) as a classification tool, using the PCA scores as input variables. The ability of the GrFFF-MOS system to distinguish between viable and non-viable cells of the same strain was demonstrated for the first time, yielding 100 % ability of correct prediction. The integrated system was also applied as a proof of concept for multianalyte purposes, for the detection of two bacterial strains (Escherichia coli O157:H7 and Yersinia enterocolitica) simultaneously present in artificially contaminated milk samples, obtaining a 100 % ability of correct prediction. Acquired results show that GrFFF band slicing before MOS array analysis can significantly increase reliability and reproducibility of pathogen bacteria identification based on their VOC production, simplifying the analytical procedure and largely eliminating sample matrix effects. The developed GrFFF-MOS integrated system can be considered a simple straightforward approach for pathogen bacteria identification directly from their food matrix. Graphical abstract An integrated sensing system is presented for pathogen bacteria identification in food, in which field-flow fractionation is exploited to prepare enriched cell fractions prior to their analysis by electronic olfactory system analysis.

Optical biosensors for bacteria detection by a peptidomimetic antimicrobial compound

In this work we present a label-free optical biosensor for rapid bacteria detection using a novel peptide-mimetic compound, as the recognition element. The biosensor design is based on an oxidized porous silicon (PSiO2) nanostructure used as the optical transducer, functionalized with the sequence K-[C12K]7 (referred to as K-7α12), which is a synthetic antimicrobial peptide. This compound is a member of a family of oligomers of acylated lysines (OAKs), mimicking the hydrophobicity and charge of natural antimicrobial peptides. The OAK is tethered to the PSiO2 film and the changes in the reflectivity spectrum are monitored upon exposure to Escherichia coli (E. coli) bacterial suspensions and their lysates. We show that capture of bacterial cell fragments induces predictable changes in the reflectivity spectrum, proportional to E. coli concentrations, thereby enabling rapid, sensitive and reproducible detection of E. coli at concentrations as low as 10(3) cells per mL. While for intact bacterial cells, the K-7α12-tethered PSiO2 shows a poor capturing ability, resulting in an insignificant optical response. The biosensor performance is also studied upon exposure to model Gram positive and negative bacterial lysates, suggesting preferential capture of E. coli cell fragments in the presented scheme. These OAK-based biosensors offer significant advantages in comparison with conventional antibody-based assays, in terms of their simple and cost-effective production, while providing numerous possible sequence combinations for designing new detection schemes.

Rapid multiplex detection of 10 foodborne pathogens with an up-converting phosphor technology-based 10-channel lateral flow assay

The rapid high-throughput detection of foodborne pathogens is essential in controlling food safety. In this study, a 10-channel up-converting phosphor technology-based lateral flow (TC-UPT-LF) assay was established for the rapid and simultaneous detection of 10 epidemic foodborne pathogens. Ten different single-target UPT-LF strips were developed and integrated into one TC-UPT-LF disc with optimization. Without enrichment the TC-UPT-LF assay had a detection sensitivity of 10(4) CFU mL(-1) or 10(5) CFU mL(-1) for each pathogen, and after sample enrichment it was 10 CFU/0.6 mg. The assay also showed good linearity, allowing quantitative detection, with a linear fitting coefficient of determination (R(2)) of 0.916-0.998. The 10 detection channels did not cross-react, so multiple targets could be specifically detected. When 279 real food samples were tested, the assay was highly consistent (100%) with culture-based methods. The results for 110 food samples artificially contaminated with single or multiple targets showed a high detection rate (≥ 80%) for most target bacteria. Overall, the TC-UPT-LF assay allows the rapid, quantitative, and simultaneous detection of 10 kinds of foodborne pathogens within 20 min, and is especially suitable for the rapid detection and surveillance of foodborne pathogens in food and water.