Immunomagnetic nanoparticle based quantitative PCR for rapid detection of Salmonella

Application of Nanomaterials to Enhance Polymerase Chain Reaction

Polymerase Chain Reaction (PCR) is one of the most common technologies used to produce millions of copies of targeted nucleic acid in vitro and has become an indispensable technique in molecular biology. However, it suffers from low efficiency and specificity problems, false positive results, and so on. Although many conditions can be optimized to increase PCR yield, such as the magnesium ion concentration, the DNA polymerases, the number of cycles, and so on, they are not all-purpose and the optimization can be case dependent. Nano-sized materials offer a possible solution to improve both the quality and productivity of PCR. In the last two decades, nanoparticles (NPs) have attracted significant attention and gradually penetrated the field of life sciences because of their unique chemical and physical properties, such as their large surface area and small size effect, which have greatly promoted developments in life science and technology. Additionally, PCR technology assisted by NPs (NanoPCR) such as gold NPs (Au NPs), quantum dots (QDs), and carbon nanotubes (CNTs), etc., have been developed to significantly improve the specificity, efficiency, and sensitivity of PCR and to accelerate the PCR reaction process. This review discusses the roles of different types of NPs used to enhance PCR and summarizes their possible mechanisms.

Rapid determination of aflatoxin B1 by an automated immunomagnetic bead purification sample pretreatment method combined with high-performance liquid chromatography

We aimed to establish an automated versatile sample preconcentration method based on the modified immunomagnetic beads, which was utilized to enrich for aflatoxin B1 from the matrices. The critical main parameters affecting the extraction efficiency, such as usage amount of immunomagnetic beads, reaction time, elution time, and blending way were investigated. Under the optimized conditions, the content of aflatoxin B1 was analyzed by high-performance liquid chromatography, the mobile phase consists of water-acetonitrile-methanol (42:18:10, v/v/v), and fluorescence detection was performed with excitation and emission wavelengths at 360 and 440 nm, respectively. Moreover, the performance of preconcentration method was compared with the conventional method based on the immunoaffinity column. The accuracy of two clean-up methods was within the error range. In addition, the stability and recyclability of the immunomagnetic beads was studied by recycling them five times. The results for the respective analysis in various samples demonstrated that the developed extraction platform provides a promising approach that is simple, rapid, sensitive, and easy to use.

Aptamer-based fluorometric determination of Salmonella Typhimurium using Fe3O4 magnetic separation and CdTe quantum dots

Based on the high sensitivity and stable fluorescence of CdTe quantum dots (QDs) in conjunction with a specific DNA aptamer, the authors describe an aptamer-based fluorescence assay for the determination of Salmonella Typhimurium. The fluorescence detection and quantification of S. Typhimurium is based on a magnetic separation system, a combination of aptamer-coated Fe₃O₄ magnetic particles (Apt-MNPs) and QD-labeled ssDNA2 (complementary strand of the aptamer). Apt-MNPs are employed for the specific capture of S. Typhimurium. CdTe QD-labeled ssDNA2 was used as a signaling probe. Simply, the as-prepared CdTe QD-labeled ssDNA2 was first incubated with the Apt-MNPs to form the aptamer-ssDNA2 duplex. After the addition of S. Typhimurium, they could specifically bind the DNA aptamer, leading to cleavage of the aptamer-ssDNA2 duplex, accompanied by the release of CdTe QD-labeled DNA. Thus, an increased fluorescence signal can be achieved after magnetic removal of the Apt-MNPs. The fluorescence of CdTe QDs (λexc/em = 327/612 nm) increases linearly in the concentration range of 10 to 10¹⁰ cfu•mL^-1, and the limit of detection is determined to be 1 cfu•mL^-1. The detection process can be performed within 2 h and is successfully applied to the analysis of spiked food samples with good recoveries from 90% to 105%.

Rapid and sensitive detection of Staphylococcus aureus assisted by polydopamine modified magnetic nanoparticles

Pathogens cause significant morbidity and mortality to humans. Thus, development of fast and reliable methods for detection and identification of pathogens is urgently needed to increase protection level of public health and ensure the safety of consumers. Herein, a rapid and sensitive method has been developed for Staphylococcus aureus (S. aureus) detection based on the dual role of polydopamine modified magnetic nanoparticles (PDA@Fe₃O₄ NPs) combined with polymerase chain reaction (PCR) and capillary electrophoresis (CE). The core-shell type structure PDA@Fe₃O₄ NPs were prepared, which are spherical, about 152 ± 20 nm in diameter and the PDA shell is about 17.5 ± 1.6 nm. PDA@Fe₃O₄ NPs play a dual role including efficient capture of bacteria and extraction of DNA. In the pH range of 3.0-7.0, the capture efficiency of S. aureus by PDA@Fe₃O₄ NPs was more than 95% in 5 min. The adsorption capacity of the PDA@Fe₃O₄ NPs for S. aureus is 1.2 × 10⁸ cfu mg^-1. The efficient capture and concentration of bacteria from large volumes of samples by PDA@Fe₃O₄ NPs avoids the time-consuming culture-enrichment prior to PCR. Interestingly, PDA@Fe₃O₄ NPs were also found to be efficient adsorbents for extraction of genomic DNA from pathogens based on the electrostatic interaction. The process can be finished in 25 min. The PDA@Fe₃O₄ NPs based solid phase extraction combined with PCR and CE allows for detecting the order of 10² cfu mL^-1S. aureus in tap water and orange juice samples. The whole process takes < 5.5 h. The developed method would provide a promising platform for rapid and sensitive detection of pathogens.

An aptamer-based PCR method coupled with magnetic immunoseparation for sensitive detection of Salmonella Typhimurium in ground turkey

Aptamers are single-stranded oligonucleotide ligands that can bind to targets with high affinity and specificity. They have been widely studied in the field of diagnostics as alternatives to antibodies due to their favorable features such as easy labeling, temperature tolerance, lower cost and recognition of a wide variety of targets. In this study, an aptamer-based PCR method coupled with magnetic immunoseparation was developed to detect S. Typhimurium from ground turkey. Firstly, biotinylated polyclonal anti-S. Typhimurium antibody was immobilized on streptavidin-coated magnetic nanobeads to capture S. Typhimurium. Secondly, the aptamers were added and bound to the surface of S. Typhimurium after blocking the magnetic nanobeads with short ssDNA. Finally, the aptamers were released by heating and amplified by PCR. After optimization, this assay was able to detect 10² CFU/mL of S. Typhimurium in pure culture, and 10³ CFU/mL of S. Typhimurium in ground turkey. This study demonstrated the feasibility and application of an aptamer-based PCR method coupled with magnetic immunoseparation for sensitive detection of S. Typhimurium in ground turkey.

Preparation of amino-functionalized magnetic nanoparticles for enhancement of bacterial capture efficiency

PEI-MNPs were successfully fabricated, which showed higher bacterial capture ability than the triaminopropylalkoxysilane directly modified NH-MNPs at low concentration.

Quaternized magnetic nanoparticles-fluorescent polymer system for detection and identification of bacteria

Nanomaterial-based 'chemical nose' sensor with sufficient sensing specificity is a useful analytical tool for the detection of toxicologically important substances in complicated biological systems. A sensor array containing three quaternized magnetic nanoparticles (q-MNPs)-fluorescent polymer systems has been designed to identify and quantify bacteria. The bacterial cell membranes disrupt the q-MNP-fluorescent polymer, generating unique fluorescence response array. The response intensity of the array is dependent on the level of displacement determined by the relative q-MNP-fluorescent polymer binding strength and bacteria cells-MNP interaction. These characteristic responses show a highly repeatable bacteria cells and can be differentiated by linear discriminant analysis (LDA). Based on the array response matrix from LDA, our approach has been used to measure bacteria with an accuracy of 87.5% for 10(7) cfu mL(-1) within 20 min. Combined with UV-vis measurement, the method can be successfully performed to identify and detect eight different pathogen samples with an accuracy of 96.8%. The measurement system has a potential for further applications and provides a facile and simple method for the rapid analysis of protein, DNA, and pathogens.