Power-free colorimetric biosensing of foodborne bacteria in centrifugal tube.

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.

Simple and rapid separation of Haematococcus pluvialis and ciliate based on the dean-coupled inertial microfluidics.

Astaxanthin with high antioxidant activity is of great practical value and Haematococcus pluvialis is recognized as the best natural astaxanthin producer. The yield of Haematococcus pluvialis was often affected by the ciliate during its production, however, the use of biochemical pesticides might have a great impact on Haematococcus pluvialis. Therefore, a simple microfluidic chip with the spiral microchannel was developed for continuous-flow physical separation of ∼10 µm ciliate from ∼30 µm Haematococcus pluvialis since their different sizes resulted in different equilibrium positions in the channel due to the Dean-coupled inertial migration. First, a spiral microchannel with a width of 700 µm and a height of 130 µm in the microfluidic chip was developed using three-dimensional printing and verified to completely separate polystyrene particles of 10 µm from those of 30 µm. Then, this microfluidic chip was used to separate the actual sample, and experimental results showed that ∼80% of ciliate was continuously separated from Haematococcus pluvialis at a flow rate of 2.8 ml/min. More importantly, no additional biochemical reagents were used and the activity of Haematococcus pluvialis was not affected. This microfluidic chip featured with simple design, automatic operation, and small size is promising for purification and breeding of Haematococcus pluvialis.

A lab-on-a-tube biosensor for automatic detection of foodborne bacteria using rotated Halbach magnetic separation and Raspberry Pi imaging.

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.

Combining impedance biosensor with immunomagnetic separation for rapid screening of Salmonella in poultry supply chains.

Salmonella screening is a key to ensure food safety in poultry supply chains. Currently available Salmonella detection methods including culture, polymerase chain reaction and enzyme-linked immuno-sorbent assay could not achieve rapid, sensitive, and in-field detection. In this study, different strategies for separation and detection of Salmonella were proposed, compared, and improved based on our previous studies on immunomagnetic separation and impedance biosensor. First, the coaxial capillary for immunomagnetic separation of target bacteria was improved with less contamination, and 3 strategies based on the improved capillary and immunomagnetic nanoparticles were compared to separate the target bacteria from sample and form the magnetic bacteria. The experimental results showed that the strategy of capture in tube and separation in capillary was the most suitable with separation efficiency of approximately 88%. Then, the immune gold nanoparticles coated with urease were used to label the magnetic bacteria, resulting in the formation of enzymatic bacteria, which were injected into the capillary. After the urea was catalyzed by the urease on the enzymatic bacteria in the capillary, different electrodes were compared to measure the impedance of the catalysate and the screen-printed electrode with higher sensitivity and better stability was the most suitable. This impedance biosensor-based bacterial detection strategy was able to detect Salmonella as low as 102 CFU/mL in 2 h without complex operations. Compared to the gold standard culture method for practical screening of Salmonella in poultry supply chains, this proposed strategy had an accuracy of approximately 90% for 75 real poultry samples.

Rapid and sensitive detection of Salmonella Typhimurium using nickel nanowire bridge for electrochemical impedance amplification.

Rapid detection of foodborne pathogens is crucial to prevent the outbreaks of foodborne illnesses. In this study, a sensitive electrochemical aptasensor was developed using aptamer coated gold interdigitated microelectrode for target capture and impedance measurement, and antibody modified nickel nanowires (NiNWs) for target separation and impedance amplification. First, the interdigitated microelectrode was modified with the biotinylated aptamers against Salmonella typhimurium through electrostatic absorption of streptavidin onto the microelectrode and streptavidin-biotin binding. Then, the target Salmonella cells were magnetically separated and concentrated using the NiNWs modified with the anti-Salmonella typhimurium antibodies to form the bacteria-NiNW complexes, and incubated on the microelectrode to form the aptamer-bacteria-NiNW complexes. After an external arc magnetic field was developed and applied to control the NiNWs to form conductive NiNW bridges across the microelectrode, the enhanced impedance change of the microelectrode was measured and used to determine the amount of target bacteria. This electrochemical aptasensor was able to quantitatively detect Salmonella ranging from 102 to 106 CFU/mL in 2 h with the detection limit of 80 CFU/mL. The mean recovery for the spiked chicken samples was 103.2%.

An ultrasensitive biosensor for colorimetric detection of Salmonella in large-volume sample using magnetic grid separation and platinum loaded zeolitic imidazolate Framework-8 nanocatalysts.

Salmonella is the leading risk factor in food safety. Rapid, sensitive and accurate detection of Salmonella is a key to prevent and control the outbreaks of foodborne diseases caused by Salmonella. In this study, we reported a colorimetric biosensor for ultrasensitive detection of Salmonella Typhimurium using a magnetic grid separation column to efficiently separate target bacteria from large volume of sample and platinum loaded zeolitic imidazolate framework-8 (Pt@ZIF-8) nanocatalysts to effectively amplify biological signal. The target Salmonella cells in large volume of sample were first separated and concentrated using the magnetic grid separation column with immune magnetic particle chains, then conjugated with the immune Pt@ZIF-8 nanocatalysts to mimic peroxidase for catalysis of hydrogen peroxide-3,3',5,5'-tetramethylbenzidine, and finally determined by measuring the catalysate at characteristic wavelength of 450 nm. This proposed biosensor was able to separate ∼70% of target Salmonella cells from 50 mL of bacterial sample and quantitatively detect Salmonella from 101 to 104 CFU/mL in 2.5 h with the lower detection limit of 11 CFU/mL. The mean recovery for Salmonella in spiked chicken carcass was about 109.8%. This new magnetic grid separation method was first time reported for efficient separation of target bacteria from very large volume of sample to greatly improve the sensitivity of this biosensor and could be used with various biosensing assays for practical applications in routine detection of foodborne pathogens without any bacterial pre-enrichment.

Continuous-Flow Separation and Efficient Concentration of Foodborne Bacteria from Large Volume Using Nickel Nanowire Bridge in Microfluidic Chip.

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 ≤102 CFU/mL in 3 h, and has the potential to separate other pathogenic bacteria from large volumes of food samples by changing the antibodies.

Exploring Protein-Inorganic Hybrid Nanoflowers and Immune Magnetic Nanobeads to Detect Salmonella Typhimurium.

Early screening of pathogenic bacteria is key to preventing and controlling outbreaks of foodborne diseases. In this study, protein-inorganic hybrid nanoflowers were synthesized for signal amplification and used with a calcium ion selective electrode (Ca-ISE) to establish a new enzyme-free assay for rapid and sensitive detection of Salmonella. Calcium hydrophosphate crystals were first conjugated with polyclonal antibodies against Salmonella to synthesize immune calcium nanoflowers (CaNFs), and streptavidin modified magnetic nanobeads (MNBs) were conjugated with biotinylated monoclonal antibodies against Salmonella to form immune MNBs. After target bacteria were separated using immune MNBs to form magnetic bacteria, immune CaNFs were conjugated with magnetic bacteria to form nanoflower conjugated bacteria. Then, hydrogen chloride was used to release calcium ions from nanoflower conjugated bacteria. After magnetic separation, the supernatant was finally injected as a continuous-flow to fluidic chip with Ca-ISE for specific detection of calcium ions. The supernatant's potential had a good linear relationship with bacteria concentration, and this assay was able to detect the S. Typhimurium cells as low as 28 colony forming units/mL within two hours. The mean recovery of target bacteria in spiked chicken samples was 95.0%. This proposed assay shows the potential for rapid, sensitive, and on-line detection of foodborne pathogens.

The Diagnostic Ability of rs-DWI to Detect Subtle Acute Infarction Lesion in the Different Regions of the Brain and the Comparison between Different b-Values.

OBJECTIVE: To evaluate the diagnostic ability of rs-DWI to detect subtle acute infarction lesion in the different regions of the brain in comparison to routine DWI and the comparison between different b-values. METHOD: 35 acute brain infarction patients were included. The subtle acute infarction lesions in ss-DWI and rs-DWI sequence were evaluated in 9 anatomical regions of the brain, and the ss-EPI DWI was also acquired with different b-values of 0, 1000, 2000, and 3000s/mm2. The McNemar test was performed for comparing the diagnostic ability of ss-DWI and rs-DWI and different b-values. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for the whole brain and in each anatomical region were calculated. RESULT: A total of 406 subtle acute infarction lesions were confirmed. The ss-DWI detected 338 subtle lesions, out of which 318 were true positive and 20 were false positive lesions. The rs-DWI detected 386 subtle lesions, out of which 385 were true positive lesions and 1 was true negative lesion. Sensitivity, specificity, positive predictive value, and negative predictive value in rs-DWI were better than ss-DWI in all anatomical regions of the brain. In the comparison of different b-values, b2000 was found better among b1000, b2000, and b3000. CONCLUSION: The rs-DWI offers a useful alternative to routine DWI for detecting the subtle acute infarctions, especially in the regions that are susceptible to distortion as in frontal cortex. In addition, high b-value can also provide benefit by increasing diffusion weighting but further raising can deteriorate image quality as SNR is decreased.