Magnetic Nanoseparation Technology for Efficient Control of Microorganisms and Toxins in Foods: A Review

Quartz crystal microbalance-based aptasensor integrated with magnetic pre-concentration system for detection of Listeria monocytogenes in food samples

A fast and accurate identification of Listeria monocytogenes. A new quartz crystal microbalance (QCM) aptasensor was designed for the specific and rapid detection of L. monocytogenes. Before detection of the target bacterium from samples in the QCM aptasensor, a magnetic pre-enrichment system was used to eliminate any contaminant in the samples. The prepared magnetic system was characterized using ATR-FTIR, SEM, VSM, BET, and analytical methods. The saturation magnetization values of the Fe3O4, Fe3O4@PDA, and Fe3O4@PDA@DAPEG particles were 57.2, 40.8, and 36.4 emu/g, respectively. The same aptamer was also immobilized on the QCM crystal integrated into QCM flow cell and utilized to quantitatively detect L. monocytogenes cells from the samples. It was found that a specific aptamer-magnetic pre-concentration system efficiently captured L. monocytogenes cells in a short time (approximately 10 min). The Fe3O4@PDA@DA-PEG-Apt particles provided selective isolation of L. monocytogenes from the bacteria-spiked media up to 91.8%. The immobilized aptamer content of the magnetic particles was 5834 µg/g using 500 ng Apt/mL. The QCM aptasensor showed a very high range of analytical performance to the target bacterium from 1.0 × 102 and 1.0 × 107 CFU/mL. The limit of detection (LOD) and limit of quantitation (LOQ) were 148 and 448 CFU/mL, respectively, from the feeding of the QCM aptasensor flow cell with the eluent of the magnetic pre-concentration system. The reproducibility of the aptasensor was more than 95%. The aptasensor was very specific to L. monocytogenes compared to the other Listeria species (i.e., L. ivanovii, L. innocua, and L. seeligeri) or other tested bacteria such as Staphylococcus aureus, Escherichia coli, and Bacillus subtilis. The QCM aptasensor was regenerated with NaOH solution, and the system was reused many times.

Specific separation and sensitive detection of foodborne pathogens by phage-derived bacterial-binding protein-nano magnetic beads coupled with smartphone-assisted paper sensor

Foodborne pathogen infection poses a significant threat to public health and is considered as one of the most serious hazards in global food safety. Herein, a sensitive and efficient method for on-site monitoring of foodborne pathogens was developed by using a smartphone-assisted paper-sensor combined with phage-derived bacterial-binding proteins-nano magnetic beads (PBPs-MBs). PBPs including tail fiber protein (TFP:gp13), cell-wall binding domain (CBD) of endolysin and tailspike protein (TSP) coated on the surface of MBs were applied for rapid separation and enrichment of targeted bacteria (Escherichia coli O157:H7, Staphylococcus aureus and Salmonella typhimurium, respectively) from food samples in 20 min before detection on paper-based sensors. The paper-based sensor was loaded with the lytic agent (polymyxin B) to induce bacterial lysis and release specific endogenous enzymes. Subsequently, three distinct chromogenic substrates were hydrolyzed by their corresponding enzymes, resulting in characteristic color changes on the paper, respectively. In addition, a smartphone APP for red-green-blue (RGB) color analysis of paper was able to directly detect three foodborne pathogens. As a result, the limit of detection (LOD) values for three foodborne pathogens were found to be 2.44 × 102, 2.68 × 104 and 4.62 × 103 CFU/mL, respectively, which were much lower than other studies (106-108 CFU/mL) based on enzymes. Moreover, the feasibility of this approach was further assessed through the successful detection of targeted bacteria in real samples with satisfactory recovery rates. In conclusion, this smartphone-assisted biosensor offers promising application potential for point-of-care testing (POCT) of foodborne pathogens in resource-scarce areas.

Nanomagnetic tetraaza (N4 donor) macrocyclic Schiff base complex of copper(ii): synthesis, characterizations, and its catalytic application in Click reactions

In this research, a novel nanomagnetic tetra-azamacrocyclic Schiff base complex of copper(ii) was produced via a post-synthetic surface modification of an Fe3O4 surface by a silane-coupling agent that contains acetylacetone functionalities at the end of its chain. Moreover, the target Cu complex that involves a tetradentate Schiff base ligand was obtained from a template reaction with o-phenylenediamine and Cu(NO3)2·3H2O. Furthermore, the prepared complex was nominated as [Fe3O4@TAM-Schiff-base-Cu(II)]. The Fourier-transform infrared (FT-IR) analysis indicates the presence of a Schiff-base-Cu complex in the catalyst. X-ray spectroscopy (EDS) and TGA analysis reveal that approximately 6-7% of the target catalyst comprises hydrocarbon moieties. The scanning electron microscope (SEM) and transmission electron microscopy (TEM) images demonstrate the presence of uniformly shaped particles, nearly spherical in nature, with sizes ranging from 9 to 18 nm. [Fe3O4@TAM-Schiff-base-Cu(II)] was applied as a catalyst for the click synthesis of a diverse range of 5-substituted-1H-tetrazoles in PEG-400 as a green medium. Regarding the electrical properties of the Cu(ii) complex, the presence of a tetra-aza (N4 donor) macrocyclic Schiff base as an N-rich ligand was reasonable - leading to its excellent capacity to catalyze these organic transformations. Finally, the high magnetization value (44.92 emu g-1) of [Fe3O4@TAM-Schiff-base-Cu(II)] enables its recycling at least four times without compromising the catalytic efficiency.

Enhanced detection of Listeria monocytogenes using tetraethylenepentamine-functionalized magnetic nanoparticles and LAMP-CRISPR/Cas12a-based biosensor

BACKGROUND

Listeria monocytogenes is a pathogenic bacterium that can lead to severe illnesses, especially among vulnerable populations. Therefore, the development of rapid and sensitive detection methods is vital to prevent and manage foodborne diseases. In this study, we used tetraethylenepentamine (TEPA)-functionalized magnetic nanoparticles (MNPs) and a loop-mediated isothermal amplification (LAMP)-based CRISPR/Cas12a-based biosensor to concentrate and detect, respectively, L. monocytogenes. LAMP enables DNA amplification at a constant temperature, providing a highly suitable approach for point-of-care testing (POCT). The ability of CRISPR/Cas12a to cleave ssDNA reporter, coupled with TEPA-functionalized MNPs effective attachment to negatively charged bacteria, forms a promising biosensor.

RESULTS

The LAMP assay was meticulously developed by selecting specific primers and designing crRNA sequences targeting a specific region within the hly gene of L. monocytogenes. We selected primer and refined the amplification conditions by systematically exploring a temperature range from 59 °C to 69 °C, ensuring the attainment of optimal performance. This process was complemented by systematic optimization of LAMP-CRISPR/Cas12a system parameters. In particular, we successfully established the optimal ssDNA reporter concentrations (0-1.2 μM) and Cas12a-mediated trans-cleavage times (0-20 min), crucial components that underpin the effectiveness of the LAMP-CRISPR/Cas12a-based biosensor. For optimizing parameters in capturing L. monocytogenes using TEPA-functionalized MNPs, capture efficiency was significantly enhanced through adjustments in TEPA-functionalized MNPs concentration, incubation times, and magnetic separation duration. Large-volume (20 mL) magnetic separation exhibited a 10-fold sensitivity improvement over conventional methods. Utilizing TEPA-functionalized MNPs, the LAMP-CRISPR/Cas12a-based biosensor achieved detection limits of 100 CFU mL-1 in pure cultures and 100 CFU g-1 in enoki mushrooms.

SIGNIFICANCE

The integration of this novel technique with the LAMP-CRISPR/Cas12a-based biosensor enhances the accuracy and sensitivity of L. monocytogenes detection in foods, and it can be a promising biosensor for POCT. The 10-fold increase in sensitivity compared to conventional methods makes this approach a groundbreaking advancement in pathogenic bacteria detection for food safety and public health.

Recent Advances in Polymer-Based Biosensors for Food Safety Detection

The excessive use of pesticides and drugs, coupled with environmental pollution, has resulted in the persistence of contaminants on food. These pollutants tend to accumulate in humans through the food chain, posing a significant threat to human health. Therefore, it is crucial to develop rapid, low-cost, portable, and on-site biosensors for detecting food contaminants. Among various biosensors, polymer-based biosensors have emerged as promising probes for detection of food contaminants in recent years, due to their various functions such as target binding, enrichment, and simple signal reading. This paper aims to discuss the characteristics of five types of food pollutants-heavy metals, pesticide residues, pathogenic bacteria, allergens, and antibiotics-and their adverse effects on human health. Additionally, this paper focuses on the principle of polymer-based biosensors and their latest applications in detecting these five types of food contaminants in actual food samples. Furthermore, this review briefly examines the future prospects and challenges of biosensors for food safety detection. The insights provided in this review will facilitate the development of biosensors for food safety detection.