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

Multimodal nanoenzyme-linked aptamer assay for Salmonella typhimurium based on catalysis and photothermal effect of PB@Au

A composite nanomaterial of Prussian blue@gold nanoparticles (PB@Au) with catalytic and photothermal properties was proposed, which combined with anti-matrix interference aptamers to achieve robust specificity and sensitivity in the detection of Salmonella typhimurium (S. typhimurium). The detection probe, PB@Au-Aptamer (PB@Au-Apt), was designed to exhibit high specificity for the target and catalyze the signal generation to produce a color change, thereby enabling rapid detection. Additionally, the excellent photothermal performance of the PB@Au catalytic system was utilized for multimodal sensitive detection in the multimodal nanoenzyme-linked aptamer assay. Moreover, the utilization of both catalytic and photothermal dual-mode detection was mutually verified to enhance detection accuracy. Under optimal conditions, the detection of S. typhimurium in a sample can be completed in 2 h. The developed assay exhibited exceptional specificity in detecting S. typhimurium, with an impressive detection limit down to 23 CFU·mL-1. Furthermore, the assay exhibited excellent repeatability and stability. Real sample analyses have proven the high reliability and practicality of this assay, highlighting its significant potential for applications in food safety testing.

Highly sensitive detection of Staphylococcus aureus α-hemolysin protein (Hla or α-toxin) by apta-qPCR

Alpha-toxin of Staphylococcus aureus belongs to the pore-forming toxin (PFT) family, which can lyse red and white blood cells. In addition to the existence of the hla gene in the majority of S. aureus strains (about 95 %), higher expression exhibits enhanced pathogenicity to the bacteria. Various methods, such as antibodies and aptamers, could serve to detect this toxin. In the current study, for the first time, an improved sandwich aptamer-antibody-based method was developed using specific murine polyclonal antibodies and a specific aptamer to detect a wide range of α-toxin levels. Denatured recombinant α-toxin was administered to mice to trigger the production of specific antibodies, which were subsequently purified from immune sera. These antibodies served as capturers in the designed apta-qPCR assay, with an aptamer employed as a detector. The results showed that spiked α-toxin in the undiluted serum samples could detect α-toxin between 300 and 0.5 ng/mL with no cross-reactivity. The coefficient of variation (CV) percent of intra- and inter-assays were 0.84 and 1.06, respectively. Since in the apta-qPCR assay, a combination of specific polyclonal antibodies as capture and specific aptamer along with real-time PCR (qPCR) sensitivity is used, this robust method could be used in diagnostic laboratories to detect various levels of the toxin in human serum samples.

Biotemplated Janus Magnetic Microrobots Based on Diatomite for Highly Efficient Detection of Salmonella

Foodborne illnesses caused by Salmonella bacteria pose a significant threat to public health. It is still challenging to detect them effectively. Herein, biotemplated Janus disk-shaped magnetic microrobots (BJDMs) based on diatomite are developed for the highly efficient detection of Salmonella in milk. The BJDMs were loaded with aptamer, which can be magnetically actuated in the swarm to capture Salmonella in a linear range of 5.8 × 102 to 5.8 × 105 CFU/mL in 30 min, with a detection limit as low as 58 CFU/mL. In addition, the silica surface of BJDMs exhibited a large specific surface area to adsorb DNA from captured Salmonella, and the specificity was also confirmed via tests of a mixture of diverse foodborne bacteria. These diatomite-based microrobots hold the advantages of mass production and low cost and could also be extended toward the detection of other types of bacterial toxins via loading different probes. Therefore, this work offers a reliable strategy to construct robust platforms for rapid biological detection in practical applications of food safety.

Ultra-sensitive electrochemical immunosensor based on 2D vanadium diselenide (VSe2) for efficient detection of pathogens: Salmonella Typhimurium

Layered transition metal dichalcogenides (TMDs), with an extensive surface area, intriguing tunable electrical and optical features, and a distinctive Van der Waals layered structure, yield outstanding sensing properties. Essentially, most TMDs originally existed in the crystallographic phase of a 2H trigonal prismatic structure, which is semiconducting in nature with poor electrocatalytic activity. In contrast, vanadium diselenide (VSe2) with its metastable metallic 1 T octahedral crystal structure has been proven to be an outstanding electrode material, embracing exceptional electrocatalytic behavior for various electrochemical (EC) applications. However, practically, VSe2 has hardly ever been explored in the field of biosensing technology. This study presents a novel EC biosensor based on the antibody of Salmonella Typhimurium (Anti-ST) immobilized on VSe2-supported Indium tin oxide (Anti-ST/VSe2/ITO) for quantitative and efficient Salmonella Typhimurium (ST) detection. The Anti-ST/VSe2/ITO bioelectrode displayed a linear relationship with ST concentration (1.3 × 10-107 CFU/ml) with a limit of detection (LOD) (0.096 CFU/ml) that is lower than previously reported ST biosensors and impressively high sensitivity (0.001996 μA.mL/CFU). Furthermore, the proposed electrode's electroanalytical activity was evaluated in spiked sugarcane juice, demonstrating distinguished applicability for specific ST detection in real samples.

Screening and Identification of DNA Nanostructure Aptamer Using the SELEX Method for ‎Detection of Epsilon Toxin

Background

Epsilon toxin (ETX), produced by Clostridium perfringens, is one of the most potent toxins known, with a lethal potency approaching that of botulinum neurotoxins. Epsilon toxin is responsible for enteritis. Therefore, the development of rapid and simple methods to detect ETX is imperative. Aptamers are single-stranded oligonucleotides that can bind tightly to specific target molecules with an affinity comparable to that of monoclonal antibodies (mAbs). DNA aptamers can serve as tools for the molecular identification of organisms, such as pathogen subspecies.

Objectives

This study aimed to isolate high-affinity single-stranded DNA (ssDNA) aptamers against ETX.

Methods

This study identified aptamers using the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) method, enzyme-linked apta-sorbent assay (ELASA), and surface plasmon resonance (SPR) to determine the affinity and specificity of the newly obtained aptamers targeting ETX.

Results

Several aptamers obtained through the SELEX process were studied. Among them, 2 aptamers, ETX clone 3 (ETX3; dissociation constant (Kd = 8.4 ± 2.4E-9M) and ETX11 (Kd = 6.3 ± 1.3E-9M) had favorable specificity for ETX. The limits of detection were 0.21 and 0.08 μg/mL for ETX3 and ETX11, respectively.‎.

Conclusions

The discovered aptamers can be used in various aptamer-based rapid diagnostic tests for the detection of ETX.

Ultrasensitive Fluorescence Lateral Flow Assay for Simultaneous Detection of Pseudomonas aeruginosa and Salmonella typhimurium via Wheat Germ Agglutinin-Functionalized Magnetic Quantum Dot Nanoprobe

Point-of-care testing methods for the rapid and sensitive screening of pathogenic bacteria are urgently needed because of the high number of outbreaks of microbial infections and foodborne diseases. In this study, we developed a highly sensitive and multiplex lateral flow assay (LFA) for the simultaneous detection of Pseudomonas aeruginosa and Salmonella typhimurium in complex samples by using wheat germ agglutinin (WGA)-modified magnetic quantum dots (Mag@QDs) as a universal detection nanoprobe. The Mag@QDs-WGA tag with a 200 nm Fe3O4 core and multiple QD-formed shell was introduced into the LFA biosensor for the universal capture of the two target bacteria and provided the dual amplification effect of fluorescence enhancement and magnetic enrichment for ultra-sensitivity detection. Meanwhile, two antibacterial antibodies were separately sprayed onto the two test lines of the LFA strip to ensure the specific identification of P. aeruginosa and S. typhimurium through one test. The proposed LFA exhibited excellent analytical performance, including high capture rate (>80%) to the target pathogens, low detection limit (<30 cells/mL), short testing time (<35 min), and good reproducibility (relative standard deviation < 10.4%). Given these merits, the Mag@QDs-WGA-based LFA has a great potential for the on-site and real-time diagnosis of bacterial samples.

Oligonucleotide aptamers for pathogen detection and infectious disease control

During an epidemic or pandemic, the primary task is to rapidly develop precise diagnostic approaches and effective therapeutics. Oligonucleotide aptamer-based pathogen detection assays and control therapeutics are promising, as aptamers that specifically recognize and block pathogens can be quickly developed and produced through simple chemical synthesis. This work reviews common aptamer-based diagnostic techniques for communicable diseases and summarizes currently available aptamers that target various pathogens, including the SARS-CoV-2 virus. Moreover, this review discusses how oligonucleotide aptamers might be leveraged to control pathogen propagation and improve host immune system responses. This review offers a comprehensive data source to the further develop aptamer-based diagnostics and therapeutics specific for infectious diseases.

An aptamer biosensor based dual signal amplification system for the detection of salmonella typhimurium

Salmonella, a typical foodborne pathogen, always seriously threatens the health and even life of both humans and animals. However, highly sensitive and fast quantitative methods for its detection are remaining to be challenged. Herein, we presented an efficient method with dual signal amplification strategy by combining immune hybridization chain reaction (HCR) with surface enhanced Raman scattering (SERS) to high sensitively detect Salmonella typhimurium in food. After sample preparation, S. typhimurium were specifically captured by immunomagnetic beads (IMBs), then aptamers and hairpin-probes were added to trigger HCR to form nicked dsDNA, finally 4',6-Diamidino-2-phenylindole dihydrochloride (DAPI) was incubated with HCR products and then the whole system was mixed with AgNP colloid to detect the SERS intensity at 1610 cm^-1. As a result, a good linear relationship was achieved between SERS intensities and corresponding concentrations of S. typhimurium ranging from 10 to 10⁵ CFU/mL, with a limit of detection (LOD) of 6 CFU/mL in 3.5 h. The proposed method has been successfully applied to capture and detect the S. typhimurium in spiked milk samples, and the results were consistent with those of the traditional plate counting method. The method, with combination of HCR and SERS, achieves double amplification of the detection signal and significantly improves the detection sensitivity of S. typhimurium. And it also shows good application potential for the highly sensitive detection of other contaminants in food.

Salmonella typhimurium detector based on the intrinsic peroxidase-like activity and photothermal effect of MoS2

A multimode dot-filtration immunoassay (MDFIA) was established for rapid and accurate detection of the target (Salmonella typhimurium), which was based on the intrinsic color, peroxidase-like activity and photothermal effect of molybdenum disulfide (MoS₂). Obviously, multimode detection can improve detection accuracy compared to the direct visual detection in test strips. A thermal imaging camera was used as detector to record the temperature change (ΔT) of MoS₂ and establish the standard curve of ΔT and the concentration of Salmonella typhimurium to realize quantitative determination. The main parameters that affect the analytical performance of MDFIA were optimized. Under the optimal experimental conditions, the limit of detection (LOD) of photothermal detection reached 10² CFU mL^-1 and was one order of magnitude lower than the limit of direct visual detection and catalytic color development detection (10³ CFU mL^-1). The accuracy and analytical sensitivity were enhanced by intrinsic peroxidase-like activity and the huge photothermal effect of MoS₂. Moreover, this method exhibited high selectivity, good repeatability, and acceptable stability and the entire process was simple to be accomplished in 30 min, which generally meets the need of rapid detection. The successful implementation in real samples with the recovery being between 99.5 and 119.2% showed that it could be used as a promising quality control strategy for detection of other foodborne pathogens. The peroxidase-like activity and excellent photothermal effect of MoS₂ was used to develop a multimode dot-filtration immunoassay for rapid detection of Salmonella typhimurium.

Immunomagnetic separation: An effective pretreatment technology for isolation and enrichment in food microorganisms detection

The high efficiency and accurate detection of foodborne pathogens and spoilage microorganisms in food are a task of great social, economic, and public health importance. However, the contamination levels of target bacteria in food samples are very low. Owing to the background interference of food ingredients and negative impact of nontarget flora, the establishment of efficient pretreatment techniques is very crucial for the detection of food microorganisms. With the significant advantages of high specificity and great separation efficiency, immunomagnetic separation (IMS) assay based on immunomagnetic particles (IMPs) has been considered as a powerful system for the separation and enrichment of target bacteria. This paper mainly focuses on the development of IMS as well as their application in food microorganisms detection. First, the basic principle of IMS in the concentration of food bacteria is presented. Second, the effect of different factors, including the sizes of magnetic particles (MPs), immobilization of antibody and operation parameters (the molar ratio of antibody to MPs, the amount of IMPs, incubation time, and bacteria concentration) on the immunocapture efficiency of IMPs are discussed. The performance of IMPs in different food samples is also evaluated. Finally, the combination of IMS and various kinds of detection methods (immunology-based methods, nucleic acid-based methods, fluorescence methods, and biosensors) to detect pathogenic and spoilage organisms is summarized. The challenges and future trends of IMS are also proposed. As an effective pretreatment technique, IMS can improve the detection sensitivity and shorten their testing time, thus exhibiting broad prospect in the field of food bacteria detection.

Rapid and sensitive detection of Salmonella Typhimurium using nickel nanowire bridge for electrochemical impedance amplification

Rapid detection of foodborne pathogens is crucial to prevent the outbreaks of foodborne illnesses. In this study, a sensitive electrochemical aptasensor was developed using aptamer coated gold interdigitated microelectrode for target capture and impedance measurement, and antibody modified nickel nanowires (NiNWs) for target separation and impedance amplification. First, the interdigitated microelectrode was modified with the biotinylated aptamers against Salmonella typhimurium through electrostatic absorption of streptavidin onto the microelectrode and streptavidin-biotin binding. Then, the target Salmonella cells were magnetically separated and concentrated using the NiNWs modified with the anti-Salmonella typhimurium antibodies to form the bacteria-NiNW complexes, and incubated on the microelectrode to form the aptamer-bacteria-NiNW complexes. After an external arc magnetic field was developed and applied to control the NiNWs to form conductive NiNW bridges across the microelectrode, the enhanced impedance change of the microelectrode was measured and used to determine the amount of target bacteria. This electrochemical aptasensor was able to quantitatively detect Salmonella ranging from 10² to 10⁶ CFU/mL in 2 h with the detection limit of 80 CFU/mL. The mean recovery for the spiked chicken samples was 103.2%.

Facile in situ generation of bismuth tungstate nanosheet-multiwalled carbon nanotube composite as unconventional affinity material for quartz crystal microbalance detection of antibiotics

Overuse and thus a constant presence of antibiotics leads to various environmental hazards and health risks. Thus, accurate sensors are required to determine their presence. In this work, we present a mass-sensitive sensor for the detection of rifampicin. We chose this molecule as it is an important antibiotic for tuberculosis, one of the leading causes of deaths worldwide. Herein, we have prepared a carbon nanotube reinforced with bismuth tungstate nanocomposite material in a well-defined nanosheet morphology using a facile in situ synthesis mechanism. Morphological characterization revealed the presence of bismuth tungstate in the form of square nanosheets embedded in the intricate network of carbon nanotubes, resulting in higher surface roughness of the nanocomposite. The synergy of the composite, so formed, manifested a high affinity for rifampicin as compared to the individual components of the composite. The developed sensor possessed a high sensitivity toward rifampicin with a detection limit of 0.16 μM and excellent specificity, as compared to rifabutin and rifapentine. Furthermore, the sensor yielded statistically good recoveries for the monitoring of rifampicin in human urine samples. This work opens up a new horizon for the exploration of unconventional nanomaterials bearing different morphologies for the detection of pharmaceuticals.

Selection of aptamers against pathogenic bacteria and their diagnostics application

Aptamers are short nucleotide sequences which can specifically bind to a variety of targets with high affinity. They are identified and selected via systematic evolution of ligands by exponential enrichment (SELEX). Compared to antibodies, aptamers offer several advantages including easy labeling, high stability and lower cost. Those advantages make it possible to be a potential for use as a recognition probe to replace antibody in the diagnostic field. This article is intended to provide a comprehensive review, which is focused on systemizing recent advancements concerning SELEX procedures, with special emphasis on the key steps in SELEX procedures. The principles of various aptamer-based detections of pathogenic bacteria and their application are discussed in detail, including colorimetric detection, fluorescence detection, electrochemical detection, lateral flow strip test, mass sensitive detection and PCR-based aptasensor. By discussing recent research and future trends based on many excellent publications and reviews, we attempt to give the readers a comprehensive view in the field of aptamer selection against pathogenic bacteria and their diagnostics application. Authors hope that this review will promote lively and valuable discussions in order to generate new ideas and approaches towards the development of aptamer-based methods for application in pathogenic bacteria diagnosis.

Aptamer based SERS detection of Salmonella typhimurium using DNA-assembled gold nanodimers

The authors describe a surface-enhanced Raman scattering (SERS) based aptasensor for Salmonella typhimurium (S. typhimurium). Gold nanoparticles (AuNPs; 35 nm i.d.) were functionalized with the aptamer (ssDNA 1) and used as the capture probe, while smaller (15 nm) AuNPs were modified with a Cy3-labeled complementary sequence (ssDNA 2) and used as the signalling probe. The asymmetric gold nanodimers (AuNDs) were assemblied with the Raman signal probe and the capture probe via hybridization of the complementary ssDNAs. The gap between two nanoparticles is a "hot spot" in which the Raman reporter Cy3 is localized. It experiences a strong enhancement of the electromagnetic field around the particle. After addition of S. typhimurium, it will be bound by the aptamer which therefore is partially dehybridized from its complementary sequence. Hence, Raman intensity drops. Under the optimal experimental conditions, the SERS signal at 1203 cm^-1 increases linearly with the logarithm of the number of colonies in the 10² to 10⁷ cfu·mL^-1 concentration range, and the limit of detection is 35 cfu·mL^-1. The method can be performed within 1 h and was successfully applied to the analysis of spiked milk samples and performed very well and with high specificity. Graphical abstract DNA-assembled asymmetric gold nanodimers (AuNDs) were synthesized and appllied in a SERS-based aptasensor for S. typhimurium. Capture probe was preferentially combined with S. typhimurium and the structure of the AuNDs was destroyed. The "hot spot" vanished partly, this resulting in the decreased Raman intensity of Cy3.