On-Site Fluorescent Detection of Sepsis-Inducing Bacteria using a Graphene-Oxide CRISPR-Cas12a (GO-CRISPR) System

Sepsis is an extremely dangerous medical condition that emanates from the body's response to a pre-existing infection. Early detection of sepsis-inducing bacterial infections can greatly enhance the treatment process and potentially prevent the onset of sepsis. However, current point-of-care (POC) sensors are often complex and costly or lack the ideal sensitivity for effective bacterial detection. Therefore, it is crucial to develop rapid and sensitive biosensors for the on-site detection of sepsis-inducing bacteria. Herein, we developed a graphene oxide CRISPR-Cas12a (GO-CRISPR) biosensor for the detection of sepsis-inducing bacteria in human serum. In this strategy, single-stranded (ssDNA) FAM probes were quenched with single-layer graphene oxide (GO). Target-activated Cas12a trans-cleavage was utilized for the degradation of the ssDNA probes, detaching the short ssDNA probes from GO and recovering the fluorescent signals. Under optimal conditions, we employed our GO-CRISPR system for the detection of Salmonella Typhimurium (S. Typhimurium) with a detection sensitivity of as low as 3 × 103 CFU/mL in human serum, as well as a good detection specificity toward other competing bacteria. In addition, the GO-CRISPR biosensor exhibited excellent sensitivity to the detection of S. Typhimurium in spiked human serum. The GO-CRISPR system offers superior rapidity for the detection of sepsis-inducing bacteria and has the potential to enhance the early detection of bacterial infections in resource-limited settings, expediting the response for patients at risk of sepsis.

Polyethersulfone-Based Microfluidic Device Integrated with DNA Extraction on Paper and Recombinase Polymerase Amplification for the Detection of Salmonella enterica

Rising consumption, large-scale production, and widespread distribution have been accompanied by an increase in the number of Salmonella infections reported to implicate contaminated food products. We developed a portable origami microfluidic device that enabled rapid detection of S. enterica from sample preparation to end-point detection, including nucleic acid extraction on paper dipstick without pipetting, nucleic acid amplification using isothermal recombinase polymerase amplification (RPA), and lateral flow assay for results readout. We also explored the feasibility of the polyethersulfone (PES) membrane as a new reaction matrix against the widely used chromatography paper to optimize nucleic acid amplification. Nucleic acid amplification was achieved within 20 min and demonstrated 100% specificity to S. enterica. The limit of detection of this PES-based microfluidic device was 260 CFU/mL and equivalent to RPA reaction in tube. A chromatography paper-based microfluidic device was found 1-log less in sensitivity for Salmonella detection compared to the use of PES. This PES-based microfluidic device could detect S. enterica in lettuce, chicken breast, and milk at concentrations of 6 CFU/g, 9 CFU/g, and 58 CFU/mL, respectively, after 6 h enrichment. PES has shown high compatibility to isothermal nucleic acid amplification and great potential to be implemented as an integrated sample-to-answer microfluidic device for the detection of pathogens in various food commodities.

Facial Preparation of Cyclometalated Iridium (III) Nanowires as Highly Efficient Electrochemiluminescence Luminophores for Biosensing

In this study, highly efficient ECL luminophores composed of iridium complex-based nanowires (Ir-NCDs) were synthesized via covalently linking bis(2-phenylpyridine)-(4-carboxypropyl-2,2'-bipyridyl) iridium(III) hexafluorophosphate with nitrogen-doped carbon quantum dots (NCDs). The ECL intensity of the nanowires showed a five-fold increase in ECL intensity compared with the iridium complex monomer under the same experimental conditions. A label-free ECL biosensing platform based on Ir-NCDs was established for Salmonella enteritidis (SE) detection. The ECL signal was quenched linearly in the range of 10²-10⁸ CFU/mL for SE with a detection limit of 10² CFU/mL. Moreover, the relative standard deviations (RSD) of the stability within and between batches were 0.98% and 3.9%, respectively. In addition, the proposed sensor showed high sensitivity, selectivity and stability towards SE in sheep feces samples with satisfactory results. In summary, the excellent ECL efficiency of Ir-NCDs demonstrates the prospects for Ir(III) complexes in bioanalytical applications.

A rapid and facile analytical approach to detecting Salmonella Enteritidis with aptamer-based surface-enhanced Raman spectroscopy

Salmonella should be absence in pharmaceutical preparations and foods according to regulations in many countries. Up to now, rapidly detecting Salmonella at 1 CFU·[10 g (mL) ]^-1 in pharmaceutical preparation or 1 CFU·[25 g (mL) ]^-1 in food samples is still a challenge. Herein, we present an aptamer-based surface-enhanced Raman spectroscopy (SERS) method for rapidly detecting Salmonella Enteritidis by using a handheld Raman instrument. The aptamer could specifically recognize S. Enteritidis, and 4-MBA self-assembled on the surface of Au@Ag NPs was used as a Raman reporter molecule. The method was validated to be high specific with no interference from other five pathogenic bacteria. It could identify S. Enteritidis contaminant at ∼ 1 CFU·(10 g)^-1 spiked level in a real sample (Wenxin granule, a botanical drug) after 6 h of enrichment. The detection time was much shorter than that of the methods (more than 54 ∼ 96 h) in the standards of pharmaceutical preparations and foods. In addition, the method could quantitatively determinate S. Enteritidis with satisfactory results. The SERS peak intensities of 4-MBA at 1072 cm^-1 showed a good linear correlation (R² = 0.9873) with the logarithms of S. Enteritidis concentrations ranging from 4.17 × 10² to 1.39 × 10⁷ CFU·mL^-1. T-test result (P = 0.425) revealed that there was no significant difference between the determination results obtained by the SERS method and the plate counting method. Therefore, the study indicated that the method was practical and reliable, and it could be a promising alternative for the on-site detection of S. Enteritidis.

Characterization of chicken meat contaminated with Salmonella by fluorescence spectroscopy

Contaminated poultry products as eggs and meat are the primary vehicles of Salmonella infection. Conventional methods for microorganisms detections involve multiple steps, and despite its accuracy, these assays are time-consuming. Biosensing methods have shown great potential for the rapid detection of foodborne pathogens. Some of the biosensors are based on fluorescence. Various fluorophores such as collagen, elastin, NAD(P)H, and porphyrins can be used to evaluate possible chemical changes in meat. In this manuscript, the fluorescence properties of chicken meat contaminated with Salmonella enterica (ATCC 14028) cell suspensions (500; 5000; 50,000 and 500,000 cells/mL) were obtained and compared with non-contaminated control, for meat kept at 25 °C for 24 and 48 h. The effects of ambient light were also considered. Our results indicated that free NAD(P)H and coproporphyrin emission bands present in contaminated meat, increased over time, and can provide access to valuable information for the detection of Salmonella in chicken meat.

Advancement in Salmonella Detection Methods: From Conventional to Electrochemical-Based Sensing Detection

Large-scale food-borne outbreaks caused by Salmonella are rarely seen nowadays, thanks to the advanced nature of the medical system. However, small, localised outbreaks in certain regions still exist and could possess a huge threat to the public health if eradication measure is not initiated. This review discusses the progress of Salmonella detection approaches covering their basic principles, characteristics, applications, and performances. Conventional Salmonella detection is usually performed using a culture-based method, which is time-consuming, labour intensive, and unsuitable for on-site testing and high-throughput analysis. To date, there are many detection methods with a unique detection system available for Salmonella detection utilising immunological-based techniques, molecular-based techniques, mass spectrometry, spectroscopy, optical phenotyping, and biosensor methods. The electrochemical biosensor has growing interest in Salmonella detection mainly due to its excellent sensitivity, rapidity, and portability. The use of a highly specific bioreceptor, such as aptamers, and the application of nanomaterials are contributing factors to these excellent characteristics. Furthermore, insight on the types of biorecognition elements, the principles of electrochemical transduction elements, and the miniaturisation potential of electrochemical biosensors are discussed.

Single-digit Salmonella detection with the naked eye using bio-barcode immunoassay coupled with recombinase polymerase amplification and a CRISPR-Cas12a system

The ability to visually detect low numbers of Salmonella in food samples is highly valuable but remains a challenge. Here we present a novel platform for ultrasensitive and visual detection of Salmonella Typhimurium by integrating the bio-barcode immunoassay (BCA), recombinase polymerase amplification (RPA), and CRISPR-Cas12a cleavage in a single reaction system (termed as BCA-RPA-Cas12a). In the system, the target bacteria were separated by immunomagnetic nanoparticles and labeled with numerous barcode AuNPs, which carry abundant bio-barcode DNA molecules to amplify the signal. Afterwards, the bio-barcode DNA molecules were amplified by RPA and subsequently triggered the cleavage activity of Cas12a to generate the fluorescence signal. Due to this triplex signal amplification, the BCA-RPA-Cas12a system can selectively detect Salmonella Typhimurium at the single-digit level with the naked eye under blue light within 60 min. Meanwhile, this novel platform was successfully applied to detect Salmonella Typhimurium in spiked milk samples with a similar sensitivity and satisfactory recovery, indicating its potential application in real samples. Furthermore, in virtue of the versatility of the antibody in the stage of BCA, the BCA-RPA-Cas12a system can be extended to further application in other bacteria detection and food safety monitoring.

An Aggregation-Induced Emission Material Labeling Antigen-Based Lateral Flow Immunoassay Strip for Rapid Detection of Escherichia coli O157:H7

Escherichia coli O157:H7 (E. coli O157:H7) is a dangerous foodborne pathogen, mainly found in beef, milk, fruits, and their products, causing harm to human health or even death. Therefore, the detection of E. coli O157:H7 in food is particularly important. In this paper, we report a lateral flow immunoassay strip (LFIS) based on aggregation-induced emission (AIE) material labeling antigen as a fluorescent probe for the rapid detection of E. coli O157:H7. The detection sensitivity of the strip is 10⁵ CFU/mL, which is 10 times higher than that of the colloidal gold test strip. This method has good specificity and stability and can be used to detect about 250 CFU of E. coli O157:H7 successfully in 25 g or 25 mL of beef, jelly, and milk. AIE-LFIS might be valuable in monitoring food pathogens for rapid detection.