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Nucleic acid amplification is crucial for disease diagnosis, especially lethal infectious diseases such as COVID-19. Compared with PCR, isothermal amplification methods are advantageous for point-of-care testing (POCT). However, complicated primer design limits their application in detecting some short targets or sequences with abnormal GC content. Herein, we developed a novel linear displacement isothermal amplification (LDIA) method using two pairs of conventional primers and Bacillus stearothermophilus (Bst) DNA polymerase, and reactions could be accelerated by adding an extra primer. Pseudorabies virus gE (high GC content) and Salmonella fimW (low GC content) genes were used to evaluate the LDIA assay. Using strand displacement (SD) probes, a LDIA-SD method was developed to realize probe-based specific detection. Additionally, we incorporated a nucleic acid-free extraction step and a pocket-sized device to realize POCT applications of the LDIA-SD method. The LDIA-SD method has advantages including facile primer design, high sensitivity and specificity, and applicability for POCT, especially for amplification of complex sequences and detection of infectious diseases., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 Published by Elsevier B.V.)

Early finding of pathogens is significant to avoid foodborne diseases. Here, a novel lab-in-centrifugal-tube colorimetric biosensor was reported for Salmonella typhimurium detection using immune nickel nanowires (NNWs) to form capture nets for specific bacterial separation, gold@platinum nanozymes (GPNs) to mark target bacteria for effective signal amplification, and a smartphone App to analyze color change for quantitative bacterial determination. A 3D-printed cylindrical magnetic separator with air pressure self-regulating structure and NNW capture nets was elaboratively constructed and assembled inside the disposable centrifuge tube to simply perform the bacterial separation, label, wash, coloration and detection. Under optimal conditions, Salmonella typhimurium could be quantitatively detected in 2 h with a low detection limit of 21 CFU/mL. The recovery of target bacteria in spiked pork samples ranged from 87.0% to 97.6% with the averaged recovery of 93.9%. This biosensor was Affordable, Sensitive, Specific, User-friendly, Rapid and robust, Equipment-free and Deliverable to end-users (ASSURED), and had shown the potential for point-of-care testing of foodborne pathogens to ensure food safety., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

A novel colorimetric biosensor was explored for fast, sensitive, and on-site detection of Salmonella on a microfluidic chip employing immune gold@platinum nanoparticles (Au@Pt NPs) for specific bacterial labeling, a finger-driven mixer with two serial air chambers for efficient immunoreaction and a nuclear track membrane as specific-size microfilter for effective bacterial isolation from excessive immune Au@Pt NPs. First, the bacterial sample and immune Au@Pt NPs were pipetted into the mixing chamber and mixed sufficiently through repeated press-release actions on the small air chamber which could precisely control the air volume, leading to the formation of bacteria-immune Au@Pt NP conjugates. Then, the small and large air chambers were pressed simultaneously to push all the solution in the mixing chamber to flow through the microfilter for trap of the formed larger-size conjugates on the membrane and removal of the unbound smaller-size immune Au@Pt NPs. After the H 2 O 2 -TMB substrate was pipetted into the microfilter and catalyzed by the conjugates, ImageJ was used to analyze the color change for bacterial determination. This simple biosensor enabled Salmonella detection as low as 168 CFU/mL in 25 min., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In-field screening of pathogenic bacteria is important for preventing food poisoning. Here, a portable pipette-adapted biosensor using magnetic grid separation and nanocatalyst signal amplification was elaboratively developed for rapid detection of Salmonella typhimurium. A common pipette was innovatively adapted with multiple functions to complete the whole bacterial detection procedure, including mixing, separation, catalysis, washing, detection, analysis and display. The target bacteria were effectively captured by the immune magnetic nanobeads and labeled with immune gold@platinum nanocatalysts through pipette-blowing mixing to form the nanobeads-bacteria-nanocatalyst complexes, which were separated against the magnetic grid separation tip under the magnetic field. The pressure change resulting from oxygen production due to mimicking catalysis of hydrogen peroxide by these nanocatalysts on the complexes was quantified through measuring the moving duration of the conductive liquid in the pipette for bacteria determination. Under optimal conditions, this biosensor could detect target bacteria in 90 min with low detection limit of 180 CFU/mL. This pipette-adapted biosensor is affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to end-users (ASSURED), and has the potential for in-field testing of foodborne pathogens to ensure food safety, especially in resource-constrained areas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

An hourglass-mimicking biosensor was developed to detect target bacteria in 15 mL centrifugal tube using immune magnetic nanobeads to isolate the target from large-volume sample, gold@platinum nanozymes to label the target for amplification of biological signals, and a microplate reader/colorimetric card for determination of the target. First, a centrifugal tube with an iron ball framework was first coaxially assembled in the center of a Halbach ring magnet. After immune magnetic nanobeads, gold@platinum nanozymes and bacterial sample were mixed by repeated bottom-up of the tube using a stepper motor, nanobead-bacteria-nanozyme complexes were formed. Then, colorless H 2 O 2 -TMB was catalyzed by the nanozymes to produce blue TMBox. The color change was finally analyzed using the microplate reader or colorimetric card to determine bacterial concentration. This hourglass-mimicking biosensor could separate ∼95% targets from 10 mL bacteria sample and detect targets from 1.6 × 10 1 to 1.6 × 10 6  CFU/mL in 1.0 h with low detection limit of 16 CFU/mL., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Tumor necrosis factor-alpha (TNF-α) neutralization has become increasingly important in the treatment of inflammatory bowel diseases (IBD). A series of monoclonal antibodies were approved in the clinic for anti-TNF-α therapy. However, a comprehensive assessment of TNF-α levels throughout the colon, which facilitates the diagnosis of IBD and predicts anti-TNF-α efficacy, remains challenging. Here, we radiolabeled infliximab with long-lived radionuclides 89 Zr for immuno-positron emission tomography (PET) imaging of TNF-α in vivo . The increased TNF-α level was detected in the inflammatory colon of the dextran sodium sulfate-induced colitis mice. The immuno-PET imaging of 89 Zr-desferrioxamine-infliximab reveals a high uptake (7.1 ± 0.3%ID/g) in the inflammatory colon, which is significantly higher than in the healthy control and blocked groups. The colon-to-muscle ratio reached more than 10 and was maintained at a high level for 10 h after injection. The ex vivo biodistribution study also verified the superior uptake in the inflammatory colon. This study provides an in vivo immune-PET approach to molecular imaging of the pro-inflammatory cytokine TNF-α. It is promising in diagnosing and predicting efficacy in both IBD and other autoimmune diseases.

In this study, a power-free biosensor was presented to detect Salmonella typhimurium on a microfluidic chip using a slide multivalve for channel selection and a disposable syringe for fluidic transfer. First, bacterial sample with immunomagnetic nanoparticles (IMNPs) and glucose oxidase (GOx) modified immune polystyrene nanoparticles (IPNPs), washing buffer, glucose, and peroxide test strip (PTS) were preloaded in their respective chambers at the periphery of chip. After the slide multivalve was selected to connect sample chamber with common separation chamber, which was connected with a syringe, the mixture of Salmonella, IMNPs and IPNPs was back and forth moved through 3D Tesla-structure micromixer using the syringe, resulting in the formation of IMNP-Salmonella-IPNP complexes, which were captured in the separation chamber using a magnet. Then, two washing chambers were selectively connected respectively to remove sample background and excessive IPNPs, and glucose chamber was connected, allowing the GOx to catalyze glucose to produce hydrogen peroxide in the separation chamber. Finally, PTS chamber was connected and the catalysate was transferred from the separation chamber to the PTS chamber, leading to the color change of PTS, followed by using smartphone App to collect and analyze the image of PTS for bacterial determination. The simple biosensor enabled simple detection of Salmonella as few as 130 CFU/mL within 60 min and is promising for practical applications in the resource-limited regions due to its low cost, simple operation, and small size., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Foodborne probiotics substantially impact human health. Thus, there is an urgent need for real-time and in situ detection of targeted probiotics. In this paper, a novel nanopopcorn fluorescent probe based on DNA-mediated Au@Ag@silica was designed and shown to display plasma resonance characteristics that generated more hot spots. This led to >18-fold greater fluorescence of indocyanine green dye with strong emission in the near-infrared (NIR-I and NIR-II) regions. Moreover, the new fluorescent probe exhibited high stability and low biotoxicity, having a strong linear relationship (R 2  = 0.9615) with Lactobacillus Plantarum concentration over the range of 10 5 -10 9  cfu/mL; it enabled in vivo tracing of exogenous probiotics. Compared with the traditional inductively coupled mass spectrometry (ICP-MS), the results are consistent (Correlation coefficient = 0.994), but the analysis time is much reduced by 89.6%. It is remarkable that the probe enabled real-time and in situ monitoring of target probiotic behavior in a simple, robust, and effective manner., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Rapid and sensitive screening of pathogens is a key to prevent the outbreak of foodborne illnesses. Herein, a new colorimetric immunoassay was proposed based on the release of Ag + ions from AgNPs and the inhibition of PtNPs, and its supporting microfluidic platform was developed to automatically perform the whole bacterial detection procedure using Raspberry Pi and smartphone App. First, the immune AgNPs and magnetic nanobeads (MNBs) were used to conjugate with Salmonella typhimurium. Then, H 2 O 2 was used to etch the AgNPs for release Ag +  ions. Finally, the colorimetric signal was greatly diminished because of the specific and efficient inhibition of Ag + toward the peroxidase-like activity of the PtNPs. This colorimetric immunoassay showed a good specificity and an ultralow detection limit of 16.8 CFU/mL, which was about 3 orders of magnitude improvement compared with conventional ELISA, and the averaged recovery for the spiked chicken samples was 95.6%. The combination of this immunoassay with this microfluidic platform might be promising for rapid and sensitive screening of foodborne pathogens to ensure food safety., (Copyright © 2022 Elsevier B.V. All rights reserved.)

A lab-on-a-tube biosensor was established to rapidly, sensitively and automatically detect foodborne bacteria through a rotatable Halbach magnet to form and rotate magnetic nanobead (MNB) chains for specific isolation of target bacteria, gold@platinum nanocatalysts (Au@PtNCs) to label target bacteria for efficient amplification of detection signal and Raspberry Pi App to collect and analyze the image of catalysate. First, the glass tube was successively preloaded with the mixture of MNBs, sample and Au@PtNCs, the washing buffer (skim milk) and the substrate (hydrogen peroxide-3,30,5,50-tetramethylbenzidine), and they were separated by air gaps. After the tube was placed on the biosensor, the MNB chains were stably formed and continuously rotated using the Halbach magnet and the mixture was moved back and forth using a programmable peristaltic pump, thus making the formation of MNB-bacteria-Au@PtNCs complexes. After the washing buffer was moved to wash the complexes, the substrate was then moved to resuspend the complexes, resulting in the catalytic reaction that changed the color of the substrate. Finally, the catalysate was moved to the designated area, the image of which was analyzed by the Raspberry Pi App to quantitatively determine the concentration of bacteria in the samples. This biosensor was able to detect Salmonella in spiked chicken samples in 1 h with lower detection limit of 8 CFU/50 μL and a recovery from 88.96% to 99.74%. This biosensor based on a single tube is very promising to automatically detect foodborne bacteria due to its low cost, high integration and simple operation., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Rapid screening of foodborne pathogens is key to preventing food poisoning. In this study, a slidable centrifugal disc was developed for automatic and multi-channel detection of Salmonella typhimurium using Flinders Technology Associates (FTA) cards for nucleic acid extraction and recombinase aided amplification (RAA) for nucleic acid detection. The slidable FTA switching and centrifugal fluidic control were elaborately combined to achieve fully automatic operations, including centrifugation of the bacterial sample to obtain the concentrated bacteria, heating and drying of the FTA card to extract the nucleic acids, washing of the FTA card to remove the impurities, and RAA detection of the extracted DNA to determine the concentration. Under the optimal conditions, this slidable centrifugal disc was able to detect 10 CFU mL -1 in a spiked chicken meat supernatant in 1 h with an average recovery of 101.8% and an average standard deviation of 6.5%. This disc has been demonstrated as an alternative for sample-in-result-out detection of Salmonella and has shown potential for simultaneous detection of multiple bacteria.

In-field screening of foodborne pathogens plays an important role in ensuring food safety. Thus, a microfluidic biosensor was developed for rapid and sensitive detection of Salmonella using manganese dioxide nanoflowers (MnO 2 NFs) for amplifying the biological signal, a microfluidic chip with a convergence-divergence spiral micromixer for performing automatic operations, and a smartphone app with a saturation calculation algorithm for processing the image. First, immune magnetic nanoparticles (MNPs), the sample, and immune MnO 2 NFs were fully mixed and sufficiently incubated in the spiral micromixer to form MNP-bacteria-MnO 2 sandwich complexes, which were magnetically captured in a separation chamber in the microfluidic chip. Then, a 3,3',5,5'-tetramethylbenzidine (TMB) substrate was injected and catalyzed by a MnO 2 NF nanomimetic enzyme on the complexes, resulting in the production of yellow catalysate. Finally, the catalysate was transferred into a detection chamber and its image was measured and processed using the smartphone app to determine the number of bacteria. This biosensor was able to detect Salmonella from 4.4 × 10 1 to 4.4 × 10 6 CFU/mL in 45 min with a detection limit of 44 CFU/mL, and has the potential to provide a promising platform for on-site detection of foodborne bacteria.

Microbial stability and evolution are a critical aspect for biosensors, especially in detecting dynamic and emerging anaerobic biohythane production. In this study, two upflow air-cathode chamber microbial fuel cells (UMFCs) were developed for in situ monitoring of the biohydrogen and biomethane reactors under a COD range of 1000-6000 mg/L and 150-1000 mg/L, respectively. Illumina MiSeq sequencing evidenced the dramatic shift of dominant microbial communities in UMFCs from hydrolytic and acidification bacteria (Clostridiaceae_1, Ruminococcaceae, Peptostreptococcaceae) to acetate-oxidizing bacteria (Synergistaceae, Dysgonomonadaceae, Spirochaetaceae). In addition, exoelectroactive bacteria evaluated from Enterobacteriaceae and Burkholderiaceae to Desulfovibrionaceae and Propionibacteriaceae. Especially, Hydrogenotrophic methanogens (Methanobacteriaceae) were abundant at 93.41% in UMFC (for monitoring hydrogen reactor), which was speculated to be a major metabolic pathway for methane production. Principal component analysis revealed a similarity in microbial structure between UMFCs and methane bioreactors. Microbial network analysis suggested a more stable community structure of UMFCs with 205 days' operation., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this study, we firstly propose a novel smartphone-assisted visualization SNP genotyping method termed competitive activation cross amplification (CACA). The mutation detection strategy depends on the ingenious design of both a start primer and a verification probe with ribonucleotide insertion through competitive combination and perfect matching with the target DNA, Meanwhile, the RNase H2 enzyme was utilized to specifically cleave ribonucleotide insertion and achieve extremely specific dual verification. Simultaneously, the results allow both colorimetric and fluorescence product dual-mode visualization by using self-designed 3D-printed dual function cassette. We validated this novel CACA by analyzing the Salmonella Pullorum rfbS gene at the 237th site, successfully solve the current bottleneck of specific identification and visual detection of this pathogen. The concentration detection limits of the plasmid and genomic DNA were 1500 copies/μL and 3.98 pg/μL, respectively, and as low as the presence of 0.1% mutant-type can be distinguished from 99.9% wild-type. Combined with a powerful hand-warmer, which can provide heating more than 60 °C for 20 h to realize power-free, dual function cassette and smartphone quantitation, our novel CACA platform firstly realizes user-friendly, cost-effective, portable, rapid, and accurate POC detection of SNP., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Rapid screening of pathogenic bacteria contaminated foods is crucial to prevent food poisoning. However, available methods for bacterial detection are still not ready for in-field screening because culture is time-consuming; PCR requires complex DNA extraction and ELISA lacks sensitivity. In this study, a microfluidic biosensor was developed for rapid, sensitive and automatic detection of Salmonella using metal-organic framework (MOF) NH 2 -MIL-101(Fe) with mimic peroxidase activity to amplify biological signal and Raspberry Pi with self-developed App to analyze color image. First, the target bacteria were separated and concentrated with the immune magnetic nanobeads (MNBs), and labeled with the immune MOFs to form MNB-Salmonella-MOF complexes. Then, the complexes were used to catalyze colorless o-phenylenediamine and H 2 O 2 to produce yellow 2,3-diaminophenazine (DAP). Finally, the image of the catalysate was collected under the narrow-band blue light and analyzed using the Raspberry Pi App to determine the bacterial concentration. The experimental results showed that this biosensor was able to detect Salmonella Typhimurium from 1.5 × 10 1 to 1.5 × 10 7  CFU/mL in 1 h with the lower detection limit of 14 CFU/mL. The mean recovery for Salmonella in spiked chicken meats was ~112%. This biosensor integrating mixing, separation, labelling and detection onto a single microfluidic chip has demonstrated the merits of automatic operation, fast reaction, less reagent and small size, and is promising for in-field detection of foodborne bacteria., (Copyright © 2021 Elsevier B.V. All rights reserved.)

An impedance biosensor using rotary magnetic separation and cascade reaction was developed for rapid and ultrasensitive detection of Salmonella typhimurium. First, magnetic nanoparticles (MNPs) modified with anti-Salmonella monoclonal antibodies were injected into a capillary at the presence of a rotary high gradient magnetic field, which was rotated by a stepper motor. Then, a bacterial sample was injected into the capillary and the target bacteria were continuous-flow captured onto the MNPs. After organic-inorganic hybrid nanoflowers were prepared using manganese dioxide (MnO 2 ), glucose oxidase (GOx) and anti-Salmonella polyclonal antibodies (pAbs), they were injected to label the bacteria, resulting in the formation of MNP-bacteria-nanoflower sandwich complexes. Finally, glucose (low conductivity) was injected and oxidized by GOx on the complexes to produce H 2 O 2 (low conductivity) and gluconic acid (high conductivity), leading to impedance decrease. Besides, the produced H 2 O 2 triggered a cascade reduction of MnO 2 into Mn 2+ , leading to further impedance decrease. The impedance changes were measured using an interdigitated microelectrode and used to determine the concentration of target bacteria. This biosensor was able to detect Salmonella ranging from 10 1 to 10 6  CFU/mL in 2 h with a low detection limit of 10 1  CFU/mL and a mean recovery of 100.1% for the spiked chicken samples., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Screening of pathogenic bacteria in foods is an effective way to prevent foodborne diseases. In this study, an impedance biosensor was developed for rapid and sensitive detection of Salmonella typhimurium using multiple magnetic nanobead (MNB) nets in a ring channel for continuous-flow separation of target bacteria from 10 mL of sample, manganese dioxide nanoflowers (MnO 2 NFs) for efficient amplification of biological signal, and an interdigitated microelectrode for sensitive measurement of impedance change. First, the MNBs modified with capture antibodies were vortically injected from outer periphery of this ring channel to form multiple ring MNB nets at specific locations with high gradient magnetic fields. Then, the bacterial sample was continuous-flow injected, resulting in specific capture of target bacteria onto the nets, and the MnO 2 NFs modified with detection antibodies were injected to form MNB-bacteria-MnO 2 NF complexes. After the complexes were washed with deionized water to remove excessive nanoflowers and residual ions, H 2 O 2 with poor conductivity was injected to reduce MnO 2 NFs to conductive Mn 2+ at neutral medium, leading to impedance decrease. Finally, impedance change was measured using the microelectrode for quantitative determination of Salmonella. This biosensor was able to separate ~60% of Salmonella from 10 mL of bacterial sample and detect Salmonella with a linear range of 3.0 × 10 1 to 3.0 × 10 6  CFU/mL in 1.5 h with lower detection limit of 19 CFU/mL. This biosensor might be further improved with higher sensitivity using a larger volume (100 mL or more) for routine screening of foodborne bacteria without bacterial pre-culture., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this study, a sensitive immunoassay using immunomagnetic nanobeads (MNBs), manganese dioxide nanoflowers (MnO 2 NFs) and quantum dots (QDs) was developed for simultaneous detection of E. coli O157: H7 and Salmonella typhimurium. MnO 2 NFs were synthesized, functionalized and incubated with QDs to obtain QDs@MnO 2 nanocomposites, followed by modification with antibodies (pAbs) to obtain pAb-QDs@MnO 2 nanocomposites (QM NCs). Target bacteria were first conjugated with MNBs and QM NCs to form MNB-bacteria-QM complexes. Then, QDs were quickly released from the complexes using glutathione to reduce MnO 2 to Mn 2+ . Finally, fluorescent intensity at characteristic wavelength was measured by optical detector to determine target bacteria. This immunoassay could simultaneously and quantitatively detect E. coli from 1.5 × 10 1 to 1.5 × 10 6  CFU/mL with detection limit of 15 CFU/mL and Salmonella from 4.0 × 10 1 to 4.0 × 10 6  CFU/mL with detection limit of 40 CFU/mL in 2 h. The mean recovery for both bacteria in spiked chicken samples was ∼96%., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Screening of foodborne pathogens is an effective way to prevent microbial food poisoning. A microfluidic biosensor was developed for rapid and sensitive detection of Salmonella Typhimurium using quantum dots (QDs) as fluorescent probes for sensor readout and manganese dioxide nanoflowers (MnO 2 NFs) and as QDs nanocarriers for signal amplification. Prior to testing, amino-modified MnO 2 nanoflowers (MnO 2 -NH 2 NFs) were conjugated with carboxyl-modified QDs through EDC/NHSS method to form MnO 2 -QD NFs, and MnO 2 -QD NFs were functionalized with polyclonal antibodies (pAbs) to form MnO 2 -QD-pAb NFs. First, the mixture of target Salmonella Typhimurium cells and magnetic nanoparticles (MNPs) modified with monoclonal antibodies (mAbs) was injected with MnO 2 -QD-pAb NFs into a microfluidic chip to form MNP-bacteria-QD-MnO 2 complexes. Then, glutathione (GSH) was injected to dissolve MnO 2 on the complexes into Mn 2+ , resulting in the release of QDs. Finally, fluorescent intensity of the released QDs was measured using the fluorescent detector to determine the amount of Salmonella . A linear relationship between fluorescent intensity and bacterial concentration from 1.0 × 10 2 to 1.0 × 10 7 CFU/mL was found with a low detection limit of 43 CFU/mL and mean recovery of 99.7% for Salmonella in spiked chicken meats, indicating the feasibility of this biosensor for practical applications., Competing Interests: The authors declare no conflict of interest.

Screening of pathogenic bacteria is a key to avoid food poisoning. The major drawbacks of existing assays for foodborne bacteria detection include long time for culture, complex DNA extraction for the polymerase chain reaction (PCR), and low sensitivity for enzyme-linked immunosorbent assay (ELISA), greatly limiting their practical applications. Here, we developed a sensitive optical biosensor based on porous gold@platinum nanocatalysts (Au@PtNCs) and a passive three-dimensional (3D) micromixer for fast detection of Salmonella typhimurium . The target Salmonella cells were first separated using immunomagnetic nanoparticles and the passive 3D micromixer. Then, immune Au@PtNCs were labeled onto the target cells as signal output to catalyze hydrogen peroxide-3,3',5,5'-tetramethylbenzidine. Finally, the absorbance was measured at 652 nm to calculate the bacterial amount. This optical biosensor could detect Salmonella at concentrations from 1.8 × 10 1 to 1.8 × 10 7 CFU/mL in 1 h. Its detection limit was calculated to be 17 CFU/mL. Besides, this passive 3D micromixer could magnetically separate 99% of target bacteria from the sample in 10 min. This biosensor has the potential to be extended to detect other bacteria by changing the antibodies.

Separation and concentration of target bacteria has become essential to sensitive and accurate detection of foodborne bacteria to ensure food safety. In this study, we developed a bacterial separation system for continuous-flow separation and efficient concentration of foodborne bacteria from large volume using a nickel nanowire (NiNW) bridge in the microfluidic chip. The synthesized NiNWs were first modified with the antibodies against the target bacteria and injected into the microfluidic channel to form the NiNW bridge in the presence of the external arc magnetic field. Then, the large volume of bacterial sample was continuous-flow injected to the channel, resulting in specific capture of the target bacteria by the antibodies on the NiNW bridge to form the NiNW-bacteria complexes. Finally, these complexes were flushed out of the channel and concentrated in a lower volume of buffer solution, after the magnetic field was removed. This bacterial separation system was able to separate up to 74% of target bacteria from 10 mL of bacterial sample at low concentrations of ≤10 2 CFU/mL in 3 h, and has the potential to separate other pathogenic bacteria from large volumes of food samples by changing the antibodies., Competing Interests: The authors declare no conflict of interest.