Lateral Flow Strip Biosensors for Foodborne Pathogenic Bacteria via Direct and Indirect Sensing Strategies: A Review

UIO66 low background signal and fluorescence synergism strategy for highly sensitive detection of Salmonella typhimurium

Successful construction of a detection method for Salmonella typhimurium (S. typhimurium) based on the synergy of hybridization chain reaction (HCR) and fluorescence was realized in this paper. First, the aptamer modified with the quenching group Black Hole Quencher-1 acid (BHQ1) was immobilized on the magnetic beads in combination with the complementary chain of the aptamer modified with 6-carboxyfluorescein (6-FAM). Second, S. typhimurium and cDNA-6-FAM immobilized on magnetic beads competitively bound to the aptamer. Finally, the cDNA-6-FAM was released after magnetic separation acted as a promoter to trigger HCR amplification when the target presented. The fluorescence signal could be significantly improved by the combination of green SYBR Green I (SGI) and HCR long double-stranded DNA and the fluorescent synergy of 6-FAM and SGI. Because of the separation of target and its aptamer, the trigger strand was abstracted by magnetic separation. There was no HCR to generate long double-stranded DNA, and the fluorescence of excess hairpin/SGI could be adsorbed through UIO66 so that only a very low background signal was detected. This fluorescent sensor was capable of monitoring S. typhimurium in the range of 10-3.2 × 107 CFU mL-1 with a limit of detection as low as 1.5 CFU mL-1. Because of the excellent properties of the aptasensor and the validity of SGI fluorescence synergy, this HCR enzyme-free amplification strategy could be generalized to other areas.

Sensitive and on-Site Detection of Staphylococcus aureus Based on CRISPR/Cas 13a-Assisted Chemiluminescence Resonance Energy Transfer

Developing a specific, sensitive, rapid, and on-site method for detecting pathogenic bacteria in food samples is critical to ensuring public safety. This article demonstrates a CRISPR/Cas13a system and a chemiluminescence resonance energy transfer (CRET) (CRISPR/Cas 13a-assisted CRET)-based strategy for sensitive and on-site detection of pathogenic bacteria in real samples. Once the hybrid double strand of aptamerS. aureus-cRNA recognizes the target model bacteria of Staphylococcus aureus (S. aureus), the released cRNA would bind with CRISPR/Cas 13a to form a complex of cRNA-CRISPR/Cas 13a, which could cleave the RNA molecule in the detecting probe of horseradish peroxidase (HRP) modified-gold nanoparticles (AuNPs) linked by RNA (AuNPs-RNA-HRP), resulting in an enhanced chemiluminescence signal due to the CRET "OFF" phenomenon after introducing the chemiluminescence substrate of luminol. The CRISPR/Cas 13a-assisted CRET strategy successfully detected S. aureus in drinking water and milk with detection limits of 20 and 30 cfu/mL, respectively, within the recovery of 90.07-105.50%. Furthermore, after integrating with an immunochromatographic test strip (ICTS), the CRISPR/Cas 13a-assisted CRET strategy achieved the on-site detection of as low as 102 cfu/mL of S. aureus in drinking water and milk via a smartphone, which is about 10 times lower than that in the previously reported AuNPs-based colorimetric ICTS, demonstrating a convenient and sensitive detection method for S. aureus in real samples.

Double-Enhanced Photothermal Lateral Flow Biosensor Based on Dual Gold Nanoparticle Conjugates

Bacterial toxins emerge as the primary triggers of foodborne illnesses, posing a significant threat to human health. To ensure food safety, it is imperative to implement point-of-care testing methods. Lateral flow biosensors (LFBs) based on gold nanoparticles (GNPs) have been commonly used for rapid detection, but their applicationis limited by low sensitivity. Based on the localized surface plasmon resonance and photothermal effect of dual gold nanoparticle conjugates (DGNPs), we developed a smartphone-integrated photothermal LFB (PLFB) with double-enhanced colorimetric and photothermal sensitivity. Through numerical simulations, we verified that DGNPs have significantly enhanced photothermal performance compared to single 15 nm GNPs (SGNPs), and applied DGNPs in PLFB for the detection of staphylococcus enterotoxin A (SEA). The colorimetric and photothermal limits of detection of DGNPs-based PLFB for SEA were 0.091 and 0.0038 ng mL-1, respectively. Compared with the colorimetric detection of the SGNPs-based LFB, the colorimetric detection sensitivity of the DGNPs-based PLFB was increased by 10.7 times, and the photothermal detection sensitivity was further improved by 255.3 times. Moreover, the PLFB exhibits robust reproducibility and exceptional specificity and is applicable for detecting SEA in milk samples. This smartphone-integrated PLFB based on DGNPs allows users to detect toxins simply, conveniently, and quickly and has huge application potential in the field of food safety.

Simultaneous Electrochemical Detection of Multiple Bacterial Species Using Metal-Organic Nanohybrids

Organic metallic nanohybrids (NHs), in which many small metal nanoparticles are encapsulated within a conductive polymer matrix, are useful as sensitive electrochemical labels because the constituents produce characteristic oxidation current responses. Gold NHs, consisting of gold nanoparticles and poly(m-toluidine), and copper NHs, consisting of copper nanoparticles and polyaniline, did not interfere with each other in terms of the electrochemical signals obtained on the same electrode. Antibodies were introduced into these NHs to function as electrochemical labels for targeting specific bacteria. Electrochemical measurements using screen-printed electrodes dry-fixed with NH-labeled bacterial cells enabled the estimation of bacterial species and number within minutes, based on the distinct current response of the labels. Our proposed method achieved simultaneous detection of enterohemorrhagic Escherichia coli and Staphylococcus aureus in a real sample. These NHs will be powerful tools as electrochemical labels and are expected to be useful for rapid testing in food and drug-related manufacturing sites.

Dual-mode colorimetric and fluorescence biosensors for the detection of foodborne bacteria

Due to the growing demand for detection technologies, there has been significant interest in the development of integrated dual-modal sensing technologies, which involve combining two signal transduction channels into a single technique, particularly in the context of food safety. The integration of two detection signals not only improves diagnostic performance by reducing assumptions, but also enhances diagnostic functions with increased application flexibility, improved accuracy, and a wider detection linear range. The top two output signals for emerging dual-modal probes are fluorescent and colorimetric, due to their exceptional advantages for real-time sensitive sensing and point-of-care applications. With the rapid progress of nanotechnology and material chemistry, the integrated colorimetric/fluorimetric dual-mode systems show immense potential in sensing foodborne pathogenic bacteria. In this comprehensive review, we present a detailed summary of various colorimetric and fluorimetric dual-modal sensing methods, with a focus on their application in detecting foodborne bacteria. We thoroughly examine the sensing methodologies and the underlying principles of the signal transduction systems, and also discuss the challenges and future prospects for advancing research in this field.

A novel photothermal sensing probe based on violet phosphorus for sensitive immunochromatographic sensing detection

Photothermal immunochromatographic sensor is an emerging detection technology, and it is important to develop new sensing probes with excellent photothermal performance to improve its detection performance. In the present study, a novel photothermal sensing probe based on violet phosphorus nanosheets with satisfactory photothermal conversion efficiency (31.1 %) was reported for the first time. A photothermal immunochromatographic sensor using the above probe was applied for visual and photothermal detection of diethylstilbestrol. The diethylstilbestrol concentration was inversely proportional to photothermal sensing signal and showed a good linear correlation in the range of 0.75 ∼ 50 μg·L-1. After optimizing, the visual and photothermal detection limits were 6 μg·L-1 and 0.56 μg·L-1, respectively. The recovery rates in tap water, milk and pork samples ranged from 82.2 % to 115.2 %, with a coefficient of variation (CV) ranging from 2.0 % to 10.8 %. This work not only structured a new type of photothermal probe, but also expanded the application range of violet phosphorus.