Instrument-Free and Visual Detection of Salmonella Based on Magnetic Nanoparticles and an Antibody Probe Immunosensor

Ultrasensitive and point-of-care detection of plasma phosphorylated tau in Alzheimer's disease using colorimetric and surface-enhanced Raman scattering dual-readout lateral flow assay

Phosphorylation of tau at Ser (396, 404) (p-tau396,404) is one of the earliest phosphorylation events, and plasma p-tau396,404 level appears to be a potentially promising biomarker of Alzheimer's disease (AD). The low abundance and easy degradation of p-tau in the plasma make the lateral flow assay (LFA) a suitable choice for point-of-care detection of plasma p-tau396,404 levels. Herein, based on our screening of a pair of p-tau396,404-specific antibodies, we developed a colorimetric and surface-enhanced Raman scattering (SERS) dual-readout LFA for the rapid, highly sensitive, and robust detection of plasma p-tau396,404 levels. This LFA realized a detection limit of 60 pg/mL by the naked eye or 3.8 pg/mL by SERS without cross-reacting with other tau species. More importantly, LFA rapidly and accurately differentiated AD patients from healthy controls, suggesting that it has the potential for clinical point-of-care application in AD diagnosis. This dual-readout LFA has the advantages of simple operation, rapid, and ultra-sensitive detection, providing a new way for early AD diagnosis and intervention, especially in primary and community AD screening.

Electronic Supplementary Material

Supplementary material (characterization of AuNPs and 4-MBA@AuNP probe; the optimal 4-MBA load for AuNPs; the optimal K2CO3 volumes for 4-MBA@AuNP-3G5 conjugates; the optimal 3G5 load for 4-MBA@AuNP conjugates; effect of NaCl concentration on 4-MBA@AuNP-3G5 stability; the linear curve of T-line color and SERS intensity versus different p-tau396,404 concentrations; the comparison of colorimetric-based LFA test results and the diagnosis results; Raman intensities and antibody activity of 4-MBA@AuNP-3G5 before and after storage; colorimetric intensity of dual-readout LFA detecting different concentrations of p-tau396,404 protein; sequence of synthesized peptides used in this study; information of the participants in this study; the information of antibodies used in this study) is available in the online version of this article at 10.1007/s12274-022-5354-4.

Molecular Targets for Foodborne Pathogenic Bacteria Detection

The detection of foodborne pathogenic bacteria currently relies on their ability to grow on chemically defined liquid and solid media, which is the essence of the classical microbiological approach. Such procedures are time-consuming and the quality of the result is affected by the selectivity of the media employed. Several alternative strategies based on the detection of molecular markers have been proposed. These markers may be cell constituents, may reside on the cell envelope or may be specific metabolites. Each marker provides specific advantages and, at the same time, suffers from specific limitations. The food matrix and chemical composition, as well as the accompanying microbiota, may also severely compromise detection. The aim of the present review article is to present and critically discuss all available information regarding the molecular targets that have been employed as markers for the detection of foodborne pathogens. Their strengths and limitations, as well as the proposed alleviation strategies, are presented, with particular emphasis on their applicability in real food systems and the challenges that are yet to be effectively addressed.

Rapid, Sensitive, Specific, and Visual Detection of Salmonella in Retail Meat with Loop-Mediated Isothermal Amplification, Targeting the invA Gene

ABSTRACT

Salmonella is one of the major pathogenic bacteria causing foodborne diseases. The rapid detection of Salmonella in food is of great significance to food safety. In this study, the loop-mediated isothermal amplification (LAMP) method was developed, and primers were designed targeting the invA gene of Salmonella. Standard samples of recombinant invA-plasmid and 100 retail meat samples were tested by LAMP and compared with the results tested by conventional PCR and the routine Chinese National Food Safety Standard-Microbiological Examination of Food-Examination of Salmonella, respectively. The results showed that Salmonella strains of eight different serotypes were amplified successfully by the developed LAMP assay, and it was 1,000-fold more sensitive than conventional PCR, with the analytical sensitivity of 8 × 102 copies per μL of the standard sample of invA-plasmid. The results were visualized directly by adding calcein and MnCl2 in the LAMP reaction tube, and the positively amplified products turned green after an incubation of 2 min. In parallel detection, the positive rate of Salmonella by the LAMP assay was highly correlated with the routine Chinese national standard method. The results of the study demonstrated that the developed LAMP assay is a simple, rapid, strongly specific, highly sensitive, and visual detection method for Salmonella.

HIGHLIGHTS

Recombinase Polymerase Amplification Coupled with a Photosensitization Colorimetric Assay for Fast Salmonella spp. Testing

Salmonella spp. is one of the most serious foodborne pathogens causing millions of infection cases annually, especially in resource-limited areas. The standard culture method (2-3 days) and current nucleic acid amplification-based testing are not suitable for on-site testing in rural areas with heavy Salmonella spp. burden. Here, we developed a colorimetric recombinase polymerase amplification (RPA) method for fast and sensitive Salmonella spp. testing in 1 h. Specifically, the invA gene from the genomic DNA of Salmonella spp. was amplified isothermally to produce double-stranded DNA (dsDNA) amplicons, which were directly quantified by a photosensitization colorimetric assay. The proposed method offered the lowest detectable concentration of 5 × 10³ colony-forming units/mL (cfu/mL), which is much lower than that of ELISA (10⁵-10⁷ cfu/mL). The detectable limit could be further pushed down to 3 cfu/mL upon coupling with bacteria pre-enrichment for 6 h. Analysis of synthetic milk samples confirmed the high precision (90%) and specificity (95%) of the method for Salmonella spp. testing. Moreover, use of a DNA releaser could further simplify the whole testing operation. Because RPA features low-temperature amplification (25-42 °C) without the need for specific instruments and the dsDNA-based photosensitization colorimetric assay served as a simple and facile readout for RPA, our method thus allows fast and low-cost Salmonella spp. testing in food samples.

Development and Application of an Immunocapture PCR Diagnostic Assay Based on the Monoclonal Antibody for the Detection of Shigella

Background:

Shigella is among the most important human pathogenic microorganisms, infecting both humans and nonhuman and causing clinically severe diarrhea. Shigella must be enriched before detection, which is time-consuming.

Objectives:

To develop a sensitive, rapid, and specific method for Shigella detection.

Materials and Methods:

Shigella was used as an antigen to generate monoclonal antibodies (mAbs). mAbs were screened via indirect enzyme-linked immunosorbent assay (ELISA) and western blot, and two mAbs were selected. The mAb A3 showed high affinity and specificity and was used to develop immune magnetic beads (IMBs) for Shigella enrichment. An immunocapture (IC)-PCR primer was designed from the ipaH gene, and IC-PCR was developed based on the IMBs and PCR.

Results:

This system shortened the Shigella detection time to 70 min. The sensitivity of the IC-PCR was 9 colony-forming units.mL^-1 in artificial milk. The accuracy of the IC-PCR was confirmed using 46 clinical samples collected from monkeys. The IC-PCR results were consistent with the serological and biochemical assays.

Conclusion:

The IC-PCR described herein accurately detected Shigella from milk samples, monkeys and can thus be used to complement classical detection methods.

Development of a rapid, one-step-visual method to detect Salmonella based on IC-LAMP method

BACKGROUND

Salmonella can cause serious human gastroenteritis and is frequently isolated from various food samples. The cell culturing, immunoassay, and polymerase chain reactions (PCR) are the current methods to detect such pathogenic agents. However, these methods are time-consuming and labor-intensive, and thus unavailable for rapid-monitoring of Salmonella.

AIMS

This study aimed to develop an immunocapture-loop-mediated isothermal amplification (IC-LAMP) for rapid and sensitive detection of Salmonella.

METHODS

Salmonella was used as antigen to produce monoclonal antibody (mAb) and mAbs were prepared via subcloning three times. The mAb 1B12 with high affinity was coated on the surface of the immuno-magnetic beads (IMBs) to capture Salmonella. The enriched products (IMBs-Salmonella) were used for LAMP using the special primers targeted the conserved invA gene of Salmonella.

RESULTS

The IC-LAMP was developed based on mAb 1B12 and LAMP. Targeting the conserved invA gene of Salmonella, the detection time was shortened to 50 min from three days. If the reaction contains Salmonella, the green fluorescence and the trapezoidal strip can be clearly observed. Importantly, the method combines the specificity of antibody and LAMP with a detection limit of 5 CFU/ml in artificially contaminated water and milk. The specificity of this method was demonstrated by testing other similar bacteria. The results indicate that the IC-LAMP reacts only with Salmonella and does not cross-react with other similar bacteria.

CONCLUSION

The IC-LAMP assay developed here is a rapid, sensitive, one-step-visual method to screen for the presence of Salmonella in food samples. This method is faster than traditional PCR, LAMP, and other methods, and can be used as a primary screening method for the detection.

Recombinase Polymerase Amplification (RPA) Combined with Lateral Flow Immunoassay for Rapid Detection of Salmonella in Food

Salmonella can cause serious foodborne diseases. We have developed a lateral flow immunoassay combined with recombinase polymerase amplification (LFD-RPA) for detection of Salmonella in food. The conserved fragment (fimY) was selected as the target gene. Under an optimal condition (37 °C, 10 min), the sensitivity was 12 colony-forming units (CFU)/mL in a pure culture. Testing with 16 non-Salmonella strains as controls revealed that LFD-RPA was specific to the fimY gene of Salmonella. The established assay could detect Salmonella at concentrations as low as 1.29 × 10² CFU/mL in artificially contaminated samples. This detection was at a slightly higher level than that for a pure bacterial culture. Combined with the test strip reader, the LFD-RPA is a feasible method for quantitative detection of Salmonella based on the test line intensity, which was the ratio for the test line and control line of the reflected light. The method could be a potential point-of-care test in limited resource areas and provides a new approach and technical support for the diagnosis of food safety.