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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.)

A colorimetric immunosensor was developed for the determination of Salmonella Typhimurium using rotating magnetic separation, gold nanorod (GNR) indication, and click chemistry amplification. The target bacteria were first separated from large-volume sample using a rotating magnetic field and a small amount (50 μg) of immunomagnetic nanoparticles (MNPs), resulting in the forming of magnetic bacteria. Then, the magnetic bacteria were conjugated with catalase (CAT)-labeled antibodies, which were synthesized using trans-cyclooctene/1,2,4,5-tetrazine click chemistry reaction, resulting in the forming of enzymatic bacteria. Then the CATs on the enzymatic bacteria were used to decompose an excessive amount of hydrogen peroxide (H 2 O 2 ), the remaining H 2 O 2 was mixed with horseradish peroxidase to etch the GNRs, resulting in color change and absorbance peak shift of the GNRs. Finally, the peak shift was measured and analyzed for the quantitative determination of target bacteria. This immunosensor was able to detect Salmonella Typhimurium with a linear range of 10 1 -10 5  CFU mL -1 in 3 h with a low detection limit of 35 CFU mL -1 . The mean recovery for Salmonella Typhimurium in spiked chicken samples was 109%. Graphical abstractSchematic representation of a colorimetric immunosensor for the determination of Salmonella Typhimurium as low as 35 CFU mL -1 using rotating magnetic separation of Salmonella from a large-volume sample, click chemistry reaction of catalase with antibodies for signal amplification, and HRP-mediated gold nanorod etching for result indication.

Nanochannels hold great prospects in intelligent systems; however, current research focuses on the inner space of the nanochannel while the outer surface is rarely explored. Here, we report on a cooperation mode of the outer surface and inner space of the nanochannel using an integrated nanochannel-electrode (INCE) and its application as a separation-detection system for rapid and facile detection of foodborne bacteria. Unlike conventional nanochannel systems, the INCE integrates two electrodes as a sensitive electrochemical interface and the nanochannel itself as nanofilter, generating a novel separation-detection system. The system is examined in a biosensing strategy based on magnetic nanoparticles (MNPs). Salmonella typhimurium ( St ) is taken as the target due to its severe threat to human health and food safety. By electrochemically probing the MNPs- St complex themselves on the surface of INCE, this method eliminates the requirement on additional signal labels. The biosensor presents a linear detection range from 10 2 to 10 7 CFU mL -1 and a limit of detection of 50 CFU mL -1 , being comparable or even better than those of analogues with complicated signal amplification designs. Moreover, the biosensor exhibits good specificity against four types of interfering bacteria. This concept may bring new insight into the development of nanochannel research and contribute a new way to the fields of separation and detection.

A disposable visual microfluidic immunosensor is described for the determination of foodborne pathogens using immunomagnetic separation, enzymatic catalysis and distance indication. Specifically, a sensor was designed to detect Salmonella typhimurium as a model pathogen. Magnetic nanoparticles (MNPs) were modified with the anti-Salmonella monoclonal antibodies and then used to enrich S. typhimurium from the sample. This is followed by conjugation to polystyrene microspheres modified with anti-Salmonella polyclonal antibodies and catalase to form the MNP-bacteria-polystyrene-catalase sandwich. The catalase on the complexes catalyzes the decomposition of hydrogen peroxide to produce oxygen after passing a micromixer. The generated oxygen gas increases the pressure in the chip and pushes the indicating red dye solution to travel along the channel towards the unsealed outlet. The travel distance of the red dye can be visually read and related to the amount of S. typhimurium using the calibration scale. The sensor can detect as low as 150 CFU·mL -1 within 2 h. Graphical abstractSchematic representation of the distance-based microfluidic immunosensor for visual detection of foodborne bacteria using immunomagnetic nanoparticles for bacteria separation, catalase for decomposition of hydrogen peroxide to form oxygen which causes a pressure increase, and red dyed particles movement for distance indication.

Early screening of foodborne pathogens is a key to ensure food safety. In this study, we developed a microfluidic biosensor for online and sensitive detection of Salmonella based on immunomagnetic separation, fluorescence labeling and smartphone video processing. First, the immune magnetic nanoparticles were used to specifically separate and efficiently concentrate the target bacteria and the magnetic bacteria were formed. Then, the magnetic bacteria were labeled with the immune fluorescent microspheres and the fluorescent bacteria were formed. Finally, the fluorescent bacteria were continuously injected into the microfluidic chip on the smartphone-based fluorescent microscopic system, and the fluorescent spots were online counted using the smartphone App based on inter-frame difference algorithm to obtain the amount of the target bacteria. Under the optimal conditions, this proposed biosensor was able to quantitatively detect Salmonella typhimurium ranging from 1.4 × 10 2 to 1.4 × 10 6  CFU/mL, and its lower detection limit was 58 CFU/mL. This biosensor could be extended for detection of multiple foodborne pathogens using different fluorescent materials., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this study, an enzyme-free biosensor was developed for sensitive and specific detection of Salmonella typhimurium (S. typhimurium) using curcumin (CUR) as signal reporter and 1,2,4,5-tetrazine (Tz)-trans-cyclooctene (TCO) click chemistry for signal amplification., Methods: Nanoparticles composed of CUR and bovine serum albumin (BSA) were formulated and reacted with Tz and TCO to form Tz-TCO-CUR conjugates through Tz-TCO click chemistry. Then, the Tz-TCO-CUR conjugates were functionalized with polyclonal antibodies (pAbs) against S. typhimurium to form CUR-TCO-Tz-pAb conjugates. Magnetic nanoparticles (MNPs) conjugated with monoclonal antibodies (mAbs) against S. typhimurium through streptavidin-biotin binding were used to specifically and efficiently separate S. typhimurium from the background by magnetic separation. CUR-TCO-Tz-pAb conjugates were reacted with the magnetic bacteria to form CUR-Tz-TCO bacteria. Finally, CUR was released quickly from the CUR-Tz-TCO bacteria in the presence of NaOH, and the color change was measured at the characteristic wavelength of 468 nm for bacteria quantification., Results: A linear relationship between absorbance at 468 nm and concentration of S. typhimurium from 102 to 106 CFU/mL was found. The lower detection limit was calculated to be as low as 50 CFU/mL and the mean recovery was 107.47% for S. typhimurium in spiked chicken samples., Conclusion: This biosensor has the potential for practical applications in the detection of foodborne pathogens., Competing Interests: Competing Interests: The authors have declared that no competing interest exists.

Aptamers are single-stranded oligonucleotide ligands that can bind to targets with high affinity and specificity. They have been widely studied in the field of diagnostics as alternatives to antibodies due to their favorable features such as easy labeling, temperature tolerance, lower cost and recognition of a wide variety of targets. In this study, an aptamer-based PCR method coupled with magnetic immunoseparation was developed to detect S. Typhimurium from ground turkey. Firstly, biotinylated polyclonal anti-S. Typhimurium antibody was immobilized on streptavidin-coated magnetic nanobeads to capture S. Typhimurium. Secondly, the aptamers were added and bound to the surface of S. Typhimurium after blocking the magnetic nanobeads with short ssDNA. Finally, the aptamers were released by heating and amplified by PCR. After optimization, this assay was able to detect 10 2  CFU/mL of S. Typhimurium in pure culture, and 10 3  CFU/mL of S. Typhimurium in ground turkey. This study demonstrated the feasibility and application of an aptamer-based PCR method coupled with magnetic immunoseparation for sensitive detection of S. Typhimurium in ground turkey., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Salmonella Typhimurium 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., Competing Interests: The authors declare no conflicts of interest.

In this study, quartz crystal microbalance (QCM) was used to select aptamers against Salmonella typhimurium. To increase the success rate of Systematic Evolution of Ligands Exponential Enrichment (SELEX), the affinity of DNA pool in each round was simultaneously tracked using QCM in order to avoid the loss of high-quality aptamers. When the frequency change reached a maximum value after several rounds of selection and counter-selection, the candidate pool was cloned and sequenced. Out of three aptamer candidates, aptamer B5 showed high specificity and binding affinity with dissociation constant (K d value) of 58.5nM, and was chosen for further studies. Subsequently, a QCM-based aptasensor was developed to detect S. typhimurium. This aptasensor was able to detect 10 3 CFU/mL of S. typhimurium with less than 1h. This study demonstrated QCM-based selection could be more effective selection of aptamers and QCM-based aptasensor could be more sensitive in detecting S. typhimurium., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Foodborne pathogens have continuously been a serious food safety issue and there is a growing demand for a rapid and sensitive method to screen the pathogens for on-line or in-field applications. Therefore, an impedimetric immunosensor based on the use of magnetic beads (MBs) for separation and a screen-printed interdigitated microelectrode (SP-IDME) for measurement was studied for the rapid detection of Escherichia coli O157:H7 and Salmonella Typhimurium in foods. Streptavidin coated MBs were functionalized with corresponding biotinylated antibodies (Ab) to capture the target bacteria. The glucose oxidase (GOx)-Ab conjugates were employed to label the MBs-Ab-cell complexes. The yielded MBs-Ab-cell-Ab-GOx biomass was mixed with the glucose solution to trigger an enzymatic reaction which produced gluconic acid. This increased the ion strength of the solution, thus decreasing the impedance of the solution measured on the SP-IDME. Our results showed that the immunosensor was capable of specifically detecting E. coli O157:H7 and S. Typhimurium within the range of 10(2)-10(6) cfu ml(-1) in the pure culture samples. E. coli O157:H7 in ground beef and S. Typhimurium in chicken rinse water were also examined. The limits of detection (LODs) for the two bacteria in foods were 2.05×10(3) cfu g(-1) and 1.04×10(3) cfu ml(-1), respectively. This immunosensor required only a bare electrode to measure the impedance changes, and no surficial modification on the electrode was needed. It was low-cost, reproducible, easy-to-operate, and easy-to-preserve. All these merits demonstrated this immunosensor has great potential for the rapid and on-site detection of pathogenic bacteria in foods., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Losses caused by foodborne diseases are enormous in terms of human life, illness, medical costs, and food product recalls. Rapid detection of multiple bacterial pathogens in foods is extremely important to ensure food safety. The objective of this research was to develop a multiplex immunoassay by integrating magnetic nanobeads (MNBs) for immunoseparation with quantum dots (QDs) as fluorescent labels for rapid, sensitive, and simultaneous detection of three major pathogenic bacteria, Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes, in food products. In this research, both streptavidin-conjugated MNBs (30- and 150-nm diameter) and QDs (530-, 580-, and 620-nm emission wavelength) were separately coated with biotinylated anti-Salmonella, anti-E. coli, and anti-Listeria antibodies. The immuno-MNBs were mixed with a food sample to capture the three target bacteria. After being magnetically separated from the sample, the MNB-cell conjugates were mixed with the immuno-QDs to form the MNB-cell-QD complexes, and unattached QDs were removed. The fluorescence intensity of the MNB-cell-QD complexes was measured at wavelengths of 530, 580, and 620 nm to determine the populations of Salmonella Typhimurium, E. coli O157:H7, and L. monocytogenes, respectively. This multiplex immunoassay simultaneously detected Salmonella Typhimurium, E. coli O157:H7, and L. monocytogenes at levels as low as 20 to 50 CFU/ml in food samples in less than 2 h without enrichment. The change in fluorescence intensity was linearly correlated (R(2) > 0.96) with the logarithmic value of bacterial level in the range of 10 to 10(3) CFU/ml. More than 85% of the three target pathogens could be simultaneously separated from food samples. The multiplex immunoassay could be expanded to detect more target pathogens, depending on the availability of specific antibodies and QDs with different emission wavelengths.

In this study, we explored the use of semiconductor quantum dots (QDs) as fluorescence labels in immunoassays for simultaneous detection of two species of foodborne pathogenic bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium. QDs with different sizes can be excited with a single wavelength of light, resulting in different emission peaks that can be measured simultaneously. Highly fluorescent semiconductor quantum dots with different emission wavelengths (525 nm and 705 nm) were conjugated to anti-E. coli O157 and anti-Salmonella antibodies, respectively. Target bacteria were separated from samples by using specific antibody coated magnetic beads. The bead-cell complexes reacted with QD-antibody conjugates to form bead-cell-QD complexes. Fluorescent microscopic images of QD labeled E. coli and Salmonella cells demonstrated that QD-antibody conjugates could evenly and completely attach to the surface of bacterial cells, indicating that the conjugated QD molecules still retain their effective fluorescence, while the conjugated antibody molecules remain active and are able to recognize their specific target bacteria in a complex mixture. The intensities of fluorescence emission peaks at 525 nm and 705 nm of the final complexes were measured for quantitative detection of E. coli O157:H7 and S. Typhimurium simultaneously. The fluorescence intensity (FI) as a function of cell number (N) was found for Salmonella and E. coli, respectively. The regression models can be expressed as: FI = 60.6 log N- 250.9 with R(2) = 0.97 for S. Typhimurium, and FI = 77.8 log N- 245.2 with R(2) = 0.91 for E. coli O157:H7 in the range of cell numbers from 10(4) to 10(7) cfu ml(-1). The detection limit of this method was 10(4) cfu ml(-1). The detection could be completed within 2 hours. The principle of this method could be extended to detect multiple species of bacteria (3-4 species) simultaneously, depending on the availability of each type of QD-antibody conjugates with a unique emission peak and the antibody coated magnetic beads specific to each species of bacteria.

In this study, we demonstrated the use of a general medium--brain heart infusion (BHI) broth that is not specifically formulated for impedance measurement, to achieve detectable impedance signals by using an interdigitated microelectrode (IME) with capacitance measurement at low frequencies. Anti-Salmonella antibody coated immunomagnetic beads were used to separate S. typhimurium from samples to provide the selectivity to this method. From analysis based on the equivalent circuit of the IME system, we found that the impedance change in BHI broth resulting from the growth of Salmonella was indeed the change in the double layer capacitance and could be monitored at 10 Hz using the IME. The results indicated that medium modification to improve impedance signal is not necessary with this IME system. However, effective immunological separation for the target organism is required for the selectivity when non-selective media are used. This finding provides a more flexible option of medium in impedance methods, which may provide opportunities to test those species of bacteria that have no suitable conductance growth medium. The detection time, t(d), was obtained from the impedance growth curve (impedance against bacterial growth time) at 10 Hz at the point where the impedance started to change. A linear relationship between the detection time and the logarithmic value of the initial cell number (N) was found in the Salmonella cell number ranging from 10(1) to 10(6) cfu/ml. The regression equation was t(d) = -1.22Log N + 8.90, with R2 = 0.95. The detection times for the initial cell number of 10(1) CFU/ml and 10(6) CFU/ml are 8 h and 1.5 h, respectively. This method is more sensitive than impedance methods using conventional electrodes.

A capillary immunoassay system was constructed and optimized for detection of Salmonella Typhimurium. The system consisted of a capillary bioseparator-bioreactor and a flow-injection electrochemical detector. Three methods were compared for immobilizing antibodies on the inner surface of silica capillary columns; these methods were based on the use of a homobifunctional cross-linker glutaraldehyde, a heterobifunctional cross-linker N-succinimidyl-4-maleimidobutyrate, and biotin-streptavidin chemistry, respectively. The glutaraldehyde method gave the best reproducibility with a relative standard deviation of 1 to 6% for detection of Salmonella Typhimurium. The optimized immunoassay system could detect Salmonella Typhimurium in chicken breast and ground turkey meats with a detection limit of 2.4 x 10(3) and 2.4 x 10(4) CFU/ml, respectively. The total detection time was less than 2.5 h without any preenrichment. When stored at 4 degrees C, the immunocolumns could retain their activities for at least 3 months.

Fluorescent semiconductor quantum dots have recently emerged as a novel and promising class of fluorescent labels for biological detection. In this study, quantum dots were used as fluorescent labels in immunoassays for quantitative detection of foodborne pathogenic bacteria. Salmonella Typhimurium cells were separated from chicken carcass wash water using anti-Salmonella antibody coated magnetic beads and reacted to secondary biotin-labeled anti-Salmonella antibody. Quantum dots coated with streptavidin were added to react with biotin on the secondary antibody. Measurement of the intensity of fluorescence produced by quantum dots provided a quantitative method for microbial detection. A linear relationship between Salmonella Typhimurium cell number (log N) in the samples of chicken carcass wash water and the fluorescence intensity (FI) was found for the cell numbers ranging from 10(3) to 10(7) CFU/ml. The regression model can be expressed as FI = 198.6 Log N - 639.03 with R2 = 0.96. The detection limit of this method was 10(3) CFU/ml.

Interdigitated microelectrodes (IMEs) were used as impedance sensors for rapid detection of viable Salmonella typhimurium in a selective medium and milk samples. The impedance growth curves, impedance against bacterial growth time, were recorded at four frequencies (10Hz, 100Hz, 1kHz, and 10kHz) during the growth of S. typhimurium. The impedance did not change until the cell number reached 10(5)-10(6) CFUml(-1). The greatest change in impedance was observed at 10Hz. To better understand the mechanism of the IME impedance sensor, an equivalent electrical circuit, consisting of double layer capacitors, a dielectric capacitor, and a medium resistor, was introduced and used for interpreting the change in impedance during bacterial growth. Bacterial attachment to the electrode surface was observed with scanning electron microscopy, and it had effect on the impedance measurement. The detection time, t(D), defined as the time for the impedance to start change, was obtained from the impedance growth curve at 10Hz and had a linear relationship with the logarithmic value of the initial cell number of S. typhimurium in the medium and milk samples. The regression equations for the cell numbers between 4.8 and 5.4 x 10(5) CFUml(-1) were t(D) = -1.38 log N + 10.18 with R(2) = 0.99 in the pure medium and t(D) = -1.54 log N + 11.33 with R(2) = 0.98 in milk samples, respectively. The detection times for 4.8 and 5.4 x 10(5) CFUml(-1) initial cell numbers were 9.3 and 2.2 h, respectively, and the detection limit could be as low as 1 cell in a sample.

Three-electrode electrochemical impedance technique was investigated for detection of Salmonella typhimurium by monitoring the growth of bacteria in selenite cystine (SC) broth supplemented with trimethylamine oxide hydrochloride (TMAO.HCl) and mannitol (M). The change in the system impedance during the growth of bacteria was studied using frequency spectral scanning. It was found that the impedance at low frequencies (<10 kHz) mainly came from the double-charged layer capacitance, reflecting the changes at the electrode interface and the adsorption on the electrode surface. While at high frequencies (>10 kHz), the system impedance mainly depended on the medium resistance. The adsorption of bacteria on the electrode surface was detected by measuring low frequency impedance, and verified with Faradic impedance spectroscopy. Enumeration of S. typhimurium using a low frequency (1 Hz) capacitance measurement and a high frequency (1 MHz) resistance measurement were compared. The detection times were determined for quantitative analysis based on the growth curves of bacteria referring to either the medium resistance or electrode capacitance. The regression equations for the detection times (t(d), h) and the initial cell number (N, cells.ml(-1)) were t(d)=-1.24logN+13.4 with R(2)=0.98 and t(d)=-1.40logN+14.46 with R(2)=0.97 for the medium resistance and electrode capacitance methods, respectively.

Background: Foodborne pathogenic bacteria threaten worldwide public health, and simple bacterial detection methods are in urgent need. Here, we established a lab-on-a-tube biosensor for simple, rapid, sensitive, and specific detection of foodborne bacteria. Methods: A rotatable Halbach cylinder magnet and an iron wire netting with magnetic silica beads (MSBs) were used for simple and effective extraction and purification of DNA from the target bacteria, and recombinase-aided amplification (RAA) was combined with clustered regularly interspaced short palindromic repeats/CRISPR-associated proteins12a(CRISPR-Cas12a) to amplify DNA and generate fluorescent signal. First, 15 mL of the bacterial sample was centrifuged, and the bacterial pellet was lysed by protease to release target DNA. Then, DNA-MSB complexes were formed as the tube was intermittently rotated and distributed uniformly onto the iron wire netting inside the Halbach cylinder magnet. Finally, the purified DNA was amplified using RAA and quantitatively detected by the CRISPR-Cas12a assay. Results: This biosensor could quantitatively detect Salmonella in spiked milk samples in 75 min, with a lower detection limit of 6 CFU/mL. The fluorescent signal of 102 CFU/mL Salmonella Typhimurium was over 2000 RFU, while 104 CFU/mL Listeria monocytogenes, Bacillus cereus, and E. coli O157:H7 were selected as non-target bacteria and had signals less than 500 RFU (same as the negative control). Conclusions: This lab-on-a-tube biosensor integrates cell lysis, DNA extraction, and RAA amplification in one 15 mL tube to simplify the operation and avoid contamination, making it suitable for low-concentration Salmonella detection. [ABSTRACT FROM AUTHOR]

Abstract: A quartz crystal microbalance (QCM) immunosensor was described for the detection of Salmonella Typhimurium with simultaneous measurements of the resonant frequency and motional resistance. The immunosensor was fabricated using protein A for the antibody immobilization. High-frequency impedance analysis indicated that the changes in resonant frequency and motional resistance (ΔF and ΔR) of the QCM were significant while the changes in static capacitance, motional capacitance, and motional inductance were insignificant. In the direct detection of S. Typhimurium in chicken meat sample, ΔF and ΔR were proportional to the cell concentration in the range of 105–108 and 106–108 cells/ml, respectively. Using anti-Salmonella-magnetic beads as a separator/concentrator for sample pretreatment as well as a marker for signal amplification, the detection limit was lowered to 102 cells/ml based on the ΔR measurement; however, ΔF was not related to the cell concentration. No interference was observed from E. coli K12 or the sample matrix. [Copyright &y& Elsevier]

Investigates the combined effect of electrical stimulation with several food additive salt solutions on Salmonella typhirium attached to chicken skin. Transmitted of S. typhirium from contaminated to uncontaminated carcasses of poultry products during processing; Summary of cell numbers of S. typhimurium in solution and on chicken skin.

Cites a study which investigated the use of chemical sprays on the Salmonella typhimurium bacteria found on the skin of chicken. What chemical spray parameters include; Details on the effects spraying temperature, pressure and exposure on the bacterium; Results of the study.

A new method for in situ monitoring Salmonella typhimurium in a selective medium was developed by measuring the cathodic peak current of oxygen in cyclic voltammograms during bacterial proliferation with an electrochemical voltammetric analyzer. The rapid oxygen consumption at a time during the growth of bacteria resulted in a sharp decline of the curves. The detection times (threshold values) obtained from the oxygen consumption curve were inversely related to the concentrations of S. typhimurium in the medium. This method for detection of S. typhimurium is more sensitive than nucleic acid-based polymerase chain reaction (PCR) methods and any of the antibody-based methods such as enzyme-linked immunosorbent assay (ELISA) technology, electrochemical immunoassays, immunosensors, and it has a sensitivity similar to conventional culture methods and impedimetric methods but is more rapid than either of them. A calibration curve was obtained by plotting initial cell concentrations (CFU ml−1) determined by conventional plate counting, as a function of the detection time. A linear response was found on the calibration curve for S. typhimurium between 1–2×100 and 1–2×106 cells per ml. The detection time for 1–2×100 and 1–2×106 cells per ml of viable S. typhimurium in the medium was 10 and 2.1 h, respectively. [Copyright &y& Elsevier]

CRISPR (Clustered regularly interspaced short palindromic repeats) has been a cutting-edge biotechnology in both gene editing and biosensing due to its desirable features, such as high base resolution and set-and-forget operation. However, as a nucleic acid detection method, an DNA/RNA amplification procedure is still inevitable in CRISPR biosensors. In this study, a highly-ordered nanopore array SERS substrate, coated with silver nanoparticles, was fabricated and utilized as a platform for the specific detection of Salmonella Typhimurium (S. Typhimurium) without the time-consuming DNA amplification step. The smart sensing strategy was established by introducing an ssDNA labeled with a Raman active molecule as a signal report probe to show the changes during target identification and detection. The CRISPR-SERS biosensor was developed by combining the ultra-sensitive sensing mechanism of CRISPR technology with the SERS analytical method, aiming at detecting the invasin A gene (invA) of S. Typhimurium. The sensing materials and operation conditions were optimized to maximize the output signal and minimize the cost. The results showed that the proposed biosensor could specifically detect S. Typhimurium with a limit of detection (LOD) of 110 CFU/mL in poultry samples within 2 h. This CRISPR-SERS sensing strategy could provide an alternative way for pathogen detection in food safety monitoring. • The ultra-sensitivity sensing mechanism of the CRISPR-SERS were fully investigated and the CRISPR-SERS sensor was reported. • The CRISPR-SERS sensor overcomes the drawbacks of the low specificity of SERS sensor in bacteria detection. • The CRISPR-SERS sensor can selectively detect Salmonella typhimurium in complex samples with a LOD of 110 cfu/mL. [ABSTRACT FROM AUTHOR]

• A new nanozyme was synthesized by decorating MIL-88 with Pd and Pt NPs. • The nanozyme was verified to greatly enhance peroxidase-mimic activity. • This biosensor enabled detection of 32 CFU/mL Salmonella in 1 h. Pathogen screening is an important step in preventing foodborne diseases. In this study, a hybrid nanozyme, metal organic framework decorated with palladium (Pd) and platinum (Pt) (MIL-88@Pd/Pt), was innovatively synthesized and used with immune magnetic nanobeads (MNBs) for sensitive biosensing of Salmonella. First, immune MIL-88@Pd/Pt nanozymes and immune MNBs were mixed with target pathogens in a large-volume sample, resulting in effective isolation and specific label of target pathogens to form nanobead- Salmonella -nanozyme conjugates. Then, these conjugates were used to catalyze H 2 O 2 -TMB, and its color was changed from colorless to blue. Finally, catalysate absorption was measured to determine pathogen concentration. This colorimetric immunoassay could determine Salmonella typhimurium from 4 × 101 to 4 × 105 CFU/mL in 60 min with a detection limit of 32 CFU/mL. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Screening of pathogenic bacteria is an essential measure for ensuring food safety. A fast, sensitive and automatic platform for Salmonella determination was presented employing continuous-flow magnetic isolation, enzymatic impedance amplification and smartphone data analysis. First, magnetic nanoparticles coupling with polyclonal antibody, polystyrene spheres coupling with monoclonal antibody and glucose oxidase, and bacterial sample were simultaneously immitted into reaction chamber, and actively mixed for formation of MNP- Salmonella -PS complexes in the microfluidic chip. After the MNP- Salmonella -PS complexes were continuous-flow caught in separation channel using the enhanced magnetic field and successively washed for removing redundant immune PSs and remanent ions, glucose with high impedance was then pumped and catalyzed into hydrogen peroxide and gluconic acid. Finally, impedance change of catalysate was dynamically measured with the on-chip PCB electrode and analyzed by the self-developed smartphone to quantify target bacteria. The microfluidic platform was able to quantitatively detect Salmonella from 1.3 × 102 to 1.3 × 106 CFU/mL in 1.5 h with a detection limit of 53 CFU/mL. The recovery of Salmonella in spiked chicken meats ranged from 88.2% to 112.0%, verifying its good practical applicability. This platform is featured with fast detection, high sensitivity and simple operation, and promising for in-field Salmonella screening. • An active stirring mixer in microfluidic chip was elaborately developed for efficient mixing. • The on-chip PCB electrode was proved for dynamic and accurate measurement of impedance. • Glucose-glucose oxidase-gluconic acid system was employed for effectively signal amplification. • This biosensor integrated whole detection procedures onto a chip to achieve automatic operations. • Salmonella typhimurium was detected to be as few as 53 CFU/mL within 1.5 h. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Salmonella Typhimurium (S. Typhimurium) is regarded as a major cause of foodborne diseases, which has been identified as a server threat to public health. Herein, an electrochemical sensing method was developed to detect S. Typhimurium in combination with polymerase chain reaction (PCR) and CRISPR/Cas12a (E-CRISPR biosensor). The target DNA extracted from the bacteria was amplified by PCR first, followed by the second amplification through the activation of collateral cleavage activity of Cas12a against signaling hairpin DNA probes, causing the release of electrochemical labels and a dramatic current decrease. The design of hairpin DNA on the electrode also reduced the steric hindrance effect for better Cas12a collateral cleavage efficiency, leading to improved detection performance. Under the optimized conditions, the proposed E-CRISPR biosensor allowed the sensitive detection of S. Typhimurium in a linear range from 6.7 × 101 to 6.7 × 105 CFU/mL with a limit of detection of 55 CFU/mL in pure culture. In addition, the E-CRISPR biosensor enables the detection of S. Typhimurium in spiked poultry meat with excellent accuracy and sensitivity. This CRISPR-based biosensor has the potential to provide an alternative way for the detection of foodborne pathogens in the food supply chain. • An E-CRISPR detection platform for Salmonella Typhimurium was developed. • The method could detect Salmonella Typhimurium down to 55 CFU/mL. • The applicability was verified for detection of Salmonella Typhimurium in poultry samples. [ABSTRACT FROM AUTHOR]

Magnetic relaxation switching (MRS) biosensors are attractive in the field of food safety owing to their simplicity and high signal-to-noise ratio. But they are less in sensitivity and stability caused by the insufficient crosslinking or non-specific binding of magnetic nanoparticles (MNPs) with targets. To address this problem, the CRISPR-Cas12a system was introduced into an MRS biosensor for the first time, to precisely control the binding of two types of MNPs with sizes of 130 nm (MNP 130) and 30 nm (MNP 30), for the sensitive detection of Salmonella. Delicately, the biosensor was designed based on the different magnetic properties of the two sizes of MNPs. The target Salmonella activated the collateral cleavage activity of the CRISPR-Cas12a system, which inhibited the binding of the two sizes of MNPs, resulting in an increase of unbound MNP 30. After separating MNP 130 -MNP 30 complexes and MNP 130 from MNP 30 , the free MNP 30 left in solution acted as transverse relaxation time (T 2) signal reporters for Salmonella detection. Under optimized conditions, the CRISPR-MRS biosensor presented a limit of detection of 1.3 × 102 CFU mL−1 for Salmonella , which is lower than most MRS biosensor analogues. It also showed satisfactory specificity and performed well in spiked chicken meat samples. This biosensing strategy not only extends the reach of the CRISPR-Cas12a system in biosensors but also offers an alternative for pathogen detection with satisfactory sensitivity. [ABSTRACT FROM AUTHOR]

• This was first time to use HAc to release curcumin as reporter. • ZnO NPs were used to cap MSNs to avoid premature release of curcumin. • Koch fractal mixer was developed and verified with excellent performance. • The biosensor was able to detect Salmonella as low as 101 CFU/mL in 1.5 h. • The mean recovery of the spiked chicken samples was ∼104 %. An acid-responsive microfluidic biosensor using curcumin (CUR) as signal reporter and ZnO-capped mesoporous silica nanoparticles (MSNs) for signal amplification was developed for sensitive and rapid detection of Salmonella in colorimetric and fluorescent modal. The MSNs were first incubated with CUR to obtain MSN@CUR nanoparticles (MC NPs). The MC NPs were then capped with ZnO nanoparticles to form MSN@CUR@ZnO nanoparticles (MCZ NPs) to prevent CUR from premature release, followed by modification with polyclonal antibodies (pAbs) against Salmonella Typhimurium (S. Typhimurium) to obtain immune MSN@CUR@ZnO@pAbs nanoparticles (MCZP NPs). The immune magnetic nanoparticles (MNPs), the S. Typhimurium cells and the MCZP NPs were conjugated in the microfluidic chip with a Koch fractal mixing channel to form MNP-bacteria-MCZP complexes. Finally, the acetic acid (HAc) was first time introduced to release CUR from the complexes, and both the color and fluorescence changes were measured to determine the concentration of Salmonella. This proposed biosensor was able to quantitatively detect S. Typhimurium ranging from 102 to 107 CFU/mL in 1.5 h and the lower detection limits were calculated to be 63 CFU/mL for colorimetric measurement and 40 CFU/mL for fluorescent measurement, respectively. The mean recovery was about 104 % for Salmonella in the spiked chicken samples. [ABSTRACT FROM AUTHOR]