Salmonella detection using 16S ribosomal DNA/RNA probe-gold nanoparticles and lateral flow immunoassay

Metal and metal oxide nanoparticle-assisted molecular assays for the detection of Salmonella

This paper provides a comprehensive overview of the diverse applications and innovations of nanoparticles in the detection of Salmonella. It encompasses a comprehensive range of novel methods, including efficient enrichment, nucleic acid extraction, immunoassays, nucleic acid tests, biosensors, and emerging strategies with the potential for future applications. The surface modification of specific antibodies or ligands enables nanoparticles to achieve highly selective capture of Salmonella, while optimizing the nucleic acid extraction process and improving detection efficiency. The employment of nanoparticles in immunological and nucleic acid tests markedly enhances the specificity and sensitivity of the reaction, thereby optimizing the determination of detection results. Moreover, the distinctive physicochemical properties of nanoparticles enhance the sensitivity, selectivity, and stability of biosensors, thereby facilitating the rapid advancement of bio-detection technologies. It is particularly noteworthy that there has been significant advancement in the application and innovative research of nanozymes in molecular assays. This progress has not only resulted in enhanced detection efficiency but has also facilitated innovation and improvement in detection technologies. As nanotechnologies continue to advance, the use of metal and metal oxide nanoparticles in Salmonella detection is likely to become a more promising and reliable strategy for ensuring food safety and public health.

Enhancing antibody detection sensitivity in lateral flow immunoassays using endospores of Bacillus subtilis as signal amplifiers

Antibody detection is the critical first step for tracking the spread of many diseases including COVID-19. Lateral flow immunoassay (LFIA) is the most commonly used method for rapid antibody detection because it is easy-to-use and inexpensive. However, LFIA has limited sensitivity when gold nanoparticles (AuNPs) are used as the signals. In this study, the endospores of Bacillus subtilis were used in combination with AuNP in a LFIA to detect antibodies. The endospores serve as a signal amplifier. The detection limit was about 10-8 M for anti-beta galactosidase antibody detection whereas the detection limit of conventional LFIA is about 10-6 M. Furthermore, the proposed methods have no additional user steps compared with the traditional LFIA. This method, therefore, improved the sensitivity 100-fold without compromising any advantages of LFIA. We believe that the proposed method will be useful for detection of antibodies against HIV, Zika virus, SARS-CoV-2, and so on.

Development of nucleic acid lateral flow immunoassay for molecular detection of Entamoeba moshkovskii and Entamoeba dispar in stool samples

Entamoeba moshkovskii, recently known as a possible pathogenic amoeba, and the non-pathogenic Entamoeba dispar are morphologically indistinguishable by microscopy. Although PCR was used for differential diagnosis, gel electrophoresis is labor-intensive, time-consuming, and exposed to hazardous elements. In this study, nucleic acid lateral flow immunoassay (NALFIA) was developed to detect E. moshkovskii and E. dispar by post-PCR amplicon analysis. E. moshkovskii primers were labeled with digoxigenin and biotin whereas primers of E. dispar were lebeled with FITC and digoxigenin. The gold nanoparticles were labeled with antibodies corresponding to particular labeling. Based on the established assay, NALFIA could detect as low as 975 fg of E. moshkovskii target DNA (982 parasites or 196 parasites/microliter), and 487.5 fg of E. dispar target DNA (444 parasites or 89 parasites/microliter) without cross-reactivity to other tested intestinal organisms. After testing 91 stool samples, NALFIA was able to detect seven E. moshkovskii (87.5% sensitivity and 100% specificity) and eight E. dispar samples (66.7% sensitivity and 100% specificity) compared to real-time PCR. Interestingly, it detected three mixed infections as real-time PCR. Therefore, it can be a rapid, safe, and effective method for the detection of the emerging pathogens E. moshkovskii and E. dispar in stool samples.

Disposable and instrument-free nucleic acid lateral flow cassette for rapid and on-site identification of adulterated goat milk

Species identification has become a significant concern due to the growing use of food alternatives that may cause allergies and reduce nutritional value. To address the issue of fraudulent adulteration of goat milk products with cow milk, we have developed an affordable, portable, and user-friendly platform called microfluidic-integrated nucleic acid lateral flow strips (LFS). This platform enables simultaneous detection of components derived from both goats and cows in goat milk. In this study, we have introduced an innovative nucleic acid labeling method. The loop primers of loop-mediated isothermal amplification (LAMP) have been modified with amplification terminator spacer C3 and an oligonucleotide sequence, thus eliminating the requirement for costly antibodies in traditional nucleic acid LFS. This modification not only lowers costs but also enables multiple detections. Additionally, we have integrated the LAMP and LFS assay steps into a microfluidic chip, allowing convenient on-site detection while effectively preventing aerosol contamination of LAMP products. The testing process includes rapid DNA extraction, followed by a short nucleic acid addition and incubation for visualized results in about 50 min. This platform is user-friendly, requiring no specialized equipment or extensive training, making it suitable for rapid on-site detection of dairy products by personnel in diverse fields.

Lateral flow assay of pathogenic viruses and bacteria in healthcare

Healthcare-associated pathogenic viruses and bacteria can have a serious impact on human health and have attracted widespread global attention. The lateral flow assay is a unidirectional detection based on the binding of a target analyte and a bioreceptor on the device via lateral flow. With incredible advantages over traditional chromatographic methods, such as rapid detection, ease of manufacture and cost effectiveness, these test strips are increasingly considered the ideal form for point-of-care applications. This review explores lateral flow assays for pathogenic viruses and bacteria, with a particular focus on methodologies, device components, construction methods, and applications. We anticipate that this review could provide exciting opportunities for developing new lateral flow devices for pathogens and advance related healthcare applications.

A review of rapid food safety testing: using lateral flow assay platform to detect foodborne pathogens

The detrimental impact of foodborne pathogens on human health makes food safety a major concern at all levels of production. Conventional methods to detect foodborne pathogens, such as live culture, high-performance liquid chromatography, and molecular techniques, are relatively tedious, time-consuming, laborious, and expensive, which hinders their use for on-site applications. Recurrent outbreaks of foodborne illness have heightened the demand for rapid and simple technologies for detection of foodborne pathogens. Recently, Lateral flow assays (LFA) have drawn attention because of their ability to detect pathogens rapidly, cheaply, and on-site. Here, we reviewed the latest developments in LFAs to detect various foodborne pathogens in food samples, giving special attention to how reporters and labels have improved LFA performance. We also discussed different approaches to improve LFA sensitivity and specificity. Most importantly, due to the lack of studies on LFAs for the detection of viral foodborne pathogens in food samples, we summarized our recent research on developing LFAs for the detection of viral foodborne pathogens. Finally, we highlighted the main challenges for further development of LFA platforms. In summary, with continuing improvements, LFAs may soon offer excellent performance at point-of-care that is competitive with laboratory techniques while retaining a rapid format.

Colorimetric and photothermal dual-mode lateral flow immunoassay based on Au-Fe3O4 multifunctional nanoparticles for detection of Salmonella typhimurium

Au-Fe3O4 multifunctional nanoparticles (NPs) were synthesized and integrated with lateral flow immunoassay (LFIA) for dual-mode detection of Salmonella typhimurium. The Au-Fe3O4 NPs not only combined excellent local surface plasmon resonance characteristics and superparamagnetic properties, but also exhibited good photothermal effect. In the detection, antibody-conjugated Au-Fe3O4 NPs first captured S. typhimurium from complex matrix, which was then loaded on the LFIA strip and trapped by the T-line. By observing the color bands with the naked eyes, qualitative detection was performed free of instrument. By measuring the photothermal signal, quantification was achieved with a portable infrared thermal camera. The introduction of magnetic separation achieved the enrichment and purification of target bacteria, thus enhancing the detection sensitivity and reducing interference. This dual-mode LFIA achieved a visual detection limit of 5 × 105 CFU/mL and a photothermal detection limit of 5 × 104 CFU/mL. Compared with traditional Au-based LFIA, this dual-mode LFIA increased the detection sensitivity by 2 orders of magnitude and could be directly applied to unprocessed milk sample. Besides, this dual-mode LFIA showed good reproducibility and specificity. The intra-assay and inter-assay variation coefficients were 3.0% and 7.9%, and with this dual-mode LFIA, other bacteria hardly produced distinguishable signals. Thus, the Au-Fe3O4 NPs-based LFIA has potential to increase the efficiency of pandemic prevention and control. Au-Fe3O4 nanoparticle proved to be a promising alternative reporter for LFIA, achieving multifunctions: target purification, target enrichment, visual qualitation, and instrumental quantification, which improved the limitations of traditional LFIA.

Magnetic Control-Enhanced Lateral Flow Technique for Ultrasensitive Nucleic Acid Target Detection

In this work, a lateral flow (LF)-based detection strategy termed magnetic control-enhanced LFA (MCLF) was proposed to detect nucleic acid sequences at attomolar sensitivity. In the proposed MCLF method, magnetic controllers which are magnetic nanoparticles modified with antibodies against the labels on capture sequences were used to interact with the unreacted labeled capture sequence (CS-label) to improve the detection limit. By regulating the movement of magnetic probes (magnetic controllers) with a simple magnet under the lateral flow strip, the movement of magnetic probes bounded with unreacted CS-label in the sample flow could be reduced. Therefore, the target sequence-containing sandwich structures will arrive at the test zone prior, to interact with the recognition ligands, whereby the capture efficiency of the sandwich structures could be increased because the unreacted capture sequences at the test zone will be reduced. With the colorimetric signal from gold nanoparticle-based probes, the proposed MCLF technique could recognize as low as 100 aM of DNA target sequences by naked eyes, and the responding range of MCLF is from 100 aM to 10 pM.

An ultra-fast, one-step RNA amplification method for the detection of Salmonella in seafood

Salmonella is one of the most common pathogens associated with food-borne illness resulting from seafood consumption. Herein, an accelerated strand exchange amplification (ASEA) requiring only a pair of primers and one polymerase was first reported for ultra-fast, one-step RNA amplification detection of Salmonella in seafood. The ASEA method could detect Salmonella typhimurium DNA in dilutions as low as 10 copies per reaction and displayed good specificity for Salmonella under the interference of a variety of food-borne pathogens. In particular, ASEA could detect RNA in one step without additional reverse transcription. The detection limit for Salmonella in artificially contaminated oyster was 1 CFU mL^-1 following 12 h of enrichment. Moreover, excellent performance of this assay was observed with 99.02% consistency relative to real-time PCR through actual sample detection. Combined with the rapid nucleic acid extraction method, the entire detection process could be completed within 20 min. Therefore, this assay opens up new prospects for the detection of food-borne pathogens in seafood with its rapidity, which would be very beneficial for food safety supervision and pathogen detection of high-throughput samples.

Single-tube analysis for ultra-fast and visual detection of Salmonella

Herein, we developed an ultra-fast and visual single-tube nucleic acid detection approach, which combined the advantages of self-settling characteristics of chitosan-functionalized diatomaceous earth (CDE) and accelerated PCR (AC-PCR). DNA was rapidly extracted by CDE within 3 min for the next nucleic acid amplification based on the nucleic acid attached on the chitosan in pH = 5.0. Under the action of gravity, the DNA-enriched CDE self-sediments to the bottom of the tube could be directly used for AC-PCR to achieve single-tube extraction and amplification. Our method detected Salmonella culture fluids with a detection limit of 1 CFU/mL, which was 100-fold more sensitive than conventional method that have not undergone nucleic acid enrichment. Furthermore, it also displayed high specificity and sensitivity for a variety of spiked samples. The entire process could be completed within 17 min in a single tube, and in particular, the result was visualized by the naked eyes. Overall, it is an all-in-one detection strategy without the requirement of redundant procedure, which greatly improved the detection efficiency, and saved the time and the cost. With these advantages, the approach will supply a promising tool in the field of point-of-care testing for Salmonella and other foodborne pathogens.

State of the art: Lateral flow assays toward the point-of-care foodborne pathogenic bacteria detection in food samples

Diverse chemicals and some physical phenomena recently introduced in nanotechnology have enabled scientists to develop useful devices in the field of food sciences. Concerning such developments, detecting foodborne pathogenic bacteria is now an important issue. These kinds of bacteria species have demonstrated severe health effects after consuming foods and high mortality related to acute cases. The most leading path of intoxication and infection has been through food matrices. Hence, quick recognition of foodborne bacteria agents at low concentrations has been required in current diagnostics. Lateral flow assays (LFAs) are one of the urgent and prevalently applied quick recognition methods that have been settled for recognizing diverse types of analytes. Thus, the present review has stressed on latest developments in LFAs-based platforms to detect various foodborne pathogenic bacteria such as Salmonella, Listeria, Escherichia coli, Brucella, Shigella, Staphylococcus aureus, Clostridium botulinum, and Vibrio cholera. Proper prominence has been given on exactly how the labels, detection elements, or procedures have affected recent developments in the evaluation of diverse bacteria using LFAs. Additionally, the modifications in assays specificity and sensitivity consistent with applied food processing techniques have been discussed. Finally, a conclusion has been drawn for highlighting the main challenges confronted through this method and offered a view and insight of thoughts for its further development in the future.

Convenient and ultrasensitive detection of live Salmonella using ratiometric electrochemical molecular substrates

Salmonella contamination is a major concern in food and public health safety, and carrying out episodic monitoring of Salmonella contamination in food and water bodies is essential for safeguarding public health and the economy. Therefore, there is an urgent need to develop an easy-to-operate Salmonella-targeting point-of-care detection platform. To this end, we designed two activity-based latent ratiometric electrochemical molecular substrates, denoted as Sal-CAF and Sal-NBAF, specifically for achieving easy, rapid, and selective profiling of Salmonella esterase (a Salmonella biomarker) under physiological conditions. The octyl esters of the substrates were cleaved by the esterase and triggered the trimethyl lock to eject the electron-rich aminoferrocene derivatives (CAF and NBAF), and the corresponding electrochemical signals were tracked at the negative region (-0.08 V vs Ag/AgCl) of the voltammetric spectrum. The Sal-CAF substrate was used to determine the concentration of Salmonella in a wide dynamic range (1.03 × 10⁵-1.1 × 10¹⁰ CFU mL^-1) with a low detection limit of 39.27 × 10³ CFU mL^-1. The developed probes were tested against various bacteria but were only activated by live Salmonella. Furthermore, the Sal-CAF probe was used directly in quantifying spiked live Salmonella spiked in milk samples and also used to effectively monitor and quantify Salmonella production in real-time. These achievements indicated the Sal-CAF probe to be a promising platform for point-of-care Salmonella analysis.

New analytical methods using carbon-based nanomaterials for detection of Salmonella species as a major food poisoning organism in water and soil resources

Salmonella is one of the most prevalent causing agents of food- and water-borne illnesses, posing an ongoing public health threat. These food-poisoning bacteria contaminate the resources at different stages such as production, aggregation, processing, distribution, as well as marketing. According to the high incidence of salmonellosis, effective strategies for early-stage detection are required at the highest priority. Since traditional culture-dependent methods and polymerase chain reaction are labor-intensive and time-taking, identification of early and accurate detection of Salmonella in food and water samples can prevent significant health economic burden and lessen the costs. The immense potentiality of biosensors in diagnosis, such as simplicity in operation, the ability of multiplex analysis, high sensitivity, and specificity, have driven research in the evolution of nanotechnology, innovating newer biosensors. Carbon nanomaterials enhance the detection sensitivity of biosensors while obtaining low levels of detection limits due to their possibility to immobilize huge amounts of bioreceptor units at insignificant volume. Moreover, conjugation and functionalization of carbon nanomaterials with metallic nanoparticles or organic molecules enables surface functional groups. According to these remarkable properties, carbon nanomaterials are widely exploited in the development of novel biosensors. To be specific, carbon nanomaterials such as carbon nanotubes, graphene and fullerenes function as transducers in the analyte recognition process or surface immobilizers for biomolecules. Herein the potential application of carbon nanomaterials in the development of novel Salmonella biosensors platforms is reviewed comprehensively. In addition, the current problems and critical analyses of the future perspectives of Salmonella biosensors are discussed.

Lateral flow device for water fecal pollution assessment: from troubleshooting of its microfluidics using bioluminescence to colorimetric monitoring of generic Escherichia coli

Water is the most important ingredient of life. Water fecal pollution threatens water quality worldwide and has direct detrimental effects on human health and the global economy. Nowadays, assessment of water fecal pollution relies on time-consuming techniques that often require well-trained personnel and highly-equipped laboratories. Therefore, faster, cheaper, and easily-used systems are needed to in situ monitor water fecal pollution. Herein, we have developed colorimetric lateral flow strips (LFS) able to detect and quantify Escherichia coli species in tap, river, and sewage water samples as an indicator of fecal pollution. The combination of LFS with a simple water filtration unit and a commercially available colorimetric reader enhanced the assay sensitivity and enabled more accurate quantification of bacteria concentration down to 104 CFU mL-1 in 10 minutes, yielding recovery percentages between 80% and 90% for all water samples analyzed. Overall, this system allows for monitoring and assessing water quality based on E. coli species as a standard microbiological indicator of fecal pollution. Furthermore, we have developed a novel bioluminescent, bacteria-based method to quickly characterize the performance of a great variety of LFS materials. This new method allows evaluating the flow rate of big analytes such as bacteria through the LFS materials, as a suggestive means for selecting the appropriate materials for fabricating LFS targeting big analytes (≈2 μm). As a whole, the proposed approach can accelerate and reduce the costs of water quality monitoring and pave the way for further improvement of fecal pollution detection systems.

Recent advances in gold nanoparticle-based lateral flow immunoassay for the detection of bacterial infection

Diagnosis of bacterial infections (BI) is becoming an increasingly difficult task in clinical practice due to their high prevalence and frequency, as well as the growth of antibiotic resistance worldwide. World Health Organization (WHO) reported antibiotic resistance is a major public health problem. BI becomes difficult or impossible to treat when the bacteria acquire immunity against antibiotics. Thus, there is a need for a quick and accurate technique to detect infection. Lateral flow immunoassay (LFIA) is an ideal technique for point-of-care testing of a disease or pathological changes inside the human body. In recent years, several LFIA based strips are being used for the detection of BI by targeting specific analytes which may range from the causative bacterium, whole-cell, DNA, or biomarker. Numerous nanoparticles like lipid-based nanoparticles, polymeric nanoparticles, and inorganic nanoparticles such as quantum dots, magnetic, ceramic, and metallic nanoparticles (copper, silver gold, iron) are widely being used in the advanced treatment of BI. Out of these gold nanoparticle (AuNPs), is being used for detection BI more effectively than other nanoparticles due to their surface functionalization, extraordinary chemical stability, biorecognition, and signal amplification properties and help to improve in conjugation with capture antibodies, and act as a color marker with unique optical properties on LFIA strips. Herein, a review that provides an overview of the principle of LFIA, how LFIA based strip is developed, and how it is helpful to detect a specific biomarker for bedside detection of the BI.

A strip of lateral flow gene assay using gold nanoparticles for point-of-care diagnosis of African swine fever virus in limited environment

Recombinase polymerase amplification (RPA) was combined with lateral flow to develop a gold nanoparticles test strip for point-of-care diagnosis of African swine fever virus (ASFV), which is called lateral flow gene assay (LFGA). Common diagnostic techniques, including polymerase chain reaction (PCR) and immunochromatography, are time-consuming and labor-intensive, and generally require costly instruments. For improvement, this assay used tailed primers to produce DNA duplexes with a single-stranded tail at one end which can hybridize with a gold nanoparticle (AuNP)-labeled oligonucleotide detection probe. And then, biotin attached to the other end of the product bound to streptavidin, which previously fixed to the test line. Therefore, there would form a sandwich structure, and gold nanoparticles labeled on the detection probe would show a red band on the test line of strip. With the low reaction temperature (37~42 °C) and short reaction time (30 min), LFGA can specifically identify ASFV in blood samples infected with ASFV and classical swine fever virus (CSFV), and the LOD was 10² copies/μL, which was comparable to that of agarose gel electrophoresis. In addition, blood samples infected with ASFV and CSFV were tested, and it was found that the LFGA can specifically identify ASFV DNA. In conclusion, LFGA achieves visual observation of the product after rapid RPA amplification and does not require any expensive instruments during the entire process, which is very helpful for early diagnosis of ASFV. Combined recombinase polymerase amplification (RPA) with lateral flow, we developed a gold nanoparticles test strip for point-of-care diagnosis of African swine fever virus. The upstream primers of RPA were modified with biotin, and the downstream primers were modified with a C3 spacer and an oligonucleotide tail that can be hybridized to a gold nanoparticle-labeled oligonucleotide detection probe. On the strip, the test line and control line were sprayed with streptavidin and an oligonucleotide control probe. In the presence of positive products, RPA products can form a sandwich structure on the test line. Therefore, two red lines will be displayed both on the test line and control line. When there is no positive product, only the control line is shown in red. Its low reaction temperature (37~42 °C) and short time of amplification and detection (30 min) make ASFV realizing point-of-care diagnosis in limited environment.

16S rRNA Monitoring Point-of-Care Magnetic Focus Lateral Flow Sensor

The detection and profiling of pathogenic bacteria is critical for human health, environmental, and food safety monitoring. Herein, we propose a highly sensitive colorimetric strategy for naked eye screening of 16S ribosomal RNA (16S rRNA) from pathogenic agents relevant to infections, human health, and food safety monitoring with a magnetic focus lateral flow sensor (mLFS) platform. The method developed was demonstrated in model 16S rRNA sequences of the pathogen Escherichia coli O157:H7 to detect as low as 1 fM of targets, exhibiting a sensitivity improved by ∼5 × 10⁵ times compared to the conventional GNP-based colorimetric lateral flow assay used for oligonucleotide testing. Based on the grayscale values, semi-quantitation of up to 1 pM of target sequences was possible in ∼45 min. The methodology could detect the target 16S rRNA from as low as 32 pg/mL of total RNA extracted from pathogens. Specificity was demonstrated with total RNA extracted from E. coli K-12 MG1655, Bacillus subtilis (B. subtilis), and Pseudomonas aeruginosa (P. aeruginosa). No signal was observed from as high as 320 pg/mL of total RNA from the nontarget bacteria. The recognition of target 16S rRNA from 32 pg/mL of total RNA in complex matrices was also demonstrated. The proposed mLFS method was then extended to monitoring B. subtilis and P. aeruginosa. Our approach highlights the possibility of extending this concept to screen specific nucleic acid sequences for the monitoring of infectious pathogens or microbiome implicated in a range of diseases including cancer.

Rapid detection and discrimination of food-related bacteria using IR-microspectroscopy in combination with multivariate statistical analysis

Spoilage microorganisms are of great concern for the food industry. While traditional culturing methods for spoilage microorganism detection are laborious and time-consuming, the development of early detection methods has gained a lot of interest in the last decades. In this work a rapid and non-destructive detection and discrimination method of eight important food-related microorganisms (Bacillus subtilis DSM 10, Bacillus coagulans DSM 1, Escherichia coli K12 DSM 498, Escherichia coli TOP10, Micrococcus luteus DSM 20030, Pseudomonas fluorescens DSM 4358, Pseudomonas fluorescens DSM 50090 and Bacillus thuringiensis israelensis DSM 5724) based on IR-microspectroscopy and chemometric evaluation was developed. Sampling was carried out directly from the surface to be tested, without the need for sample preparation such as purification, singulation, centrifugation and washing steps, as an efficient and inexpensive blotting technique using the sample carrier. IR spectra were recorded directly after the blotting from the surface of the sample carrier without any further pretreatments. A combination of data preprocessing, principal component analysis and canonical discriminant analysis was found to be suitable. The spectral range from 400 to 1750 cm^-1 of the IR-microspectrosopic data was determined to be highly sensitive to the time after incubation and sample thickness, resulting in a high standard deviation. Therefore, this area was excluded from the evaluation in favor of the meaningfulness of the chemometric model and, thus, only the spectral range of specific -CH/-NH/-OH excitations (2815-3680 cm^-1) was used for model development. This study showed that the differentiation of food-related microorganisms on genera, species and strain level is feasible. A leave-one-out cross-validation of the training data set showed 100% accuracy. The classification of the ungrouped test data showed with an accuracy of 94.5% that, despite the large biological variance of the analytes such as different times after incubation and the presented sampling (including its variance), a robust and meaningful model for the differentiation of food-related bacteria could be developed by data preprocessing and subsequent chemometric evaluation.

Development of Electrochemical DNA Biosensor for Equine Hindgut Acidosis Detection

The pH drop in the hindgut of the horse is caused by lactic acid-producing bacteria which are abundant when a horse’s feeding regime is excessively carbohydrate rich. This drop in pH below six causes hindgut acidosis and may lead to laminitis. Lactic acid-producing bacteria Streptococcus equinus and Mitsuokella jalaludinii have been found to produce high amounts of L-lactate and D-lactate, respectively. Early detection of increased levels of these bacteria could allow the horse owner to tailor the horse’s diet to avoid hindgut acidosis and subsequent laminitis. Therefore, 16s ribosomal ribonucleic acid (rRNA) sequences were identified and modified to obtain target single stranded deoxyribonucleic acid (DNA) from these bacteria. Complementary single stranded DNAs were designed from the modified target sequences to form capture probes. Binding between capture probe and target single stranded deoxyribonucleic acid (ssDNA) in solution has been studied by gel electrophoresis. Among pairs of different capture probes and target single stranded DNA, hybridization of Streptococcus equinus capture probe 1 (SECP1) and Streptococcus equinus target 1 (SET1) was portrayed as gel electrophoresis. Adsorptive stripping voltammetry was utilized to study the binding of thiol modified SECP1 over gold on glass substrates and these studies showed a consistent binding signal of thiol modified SECP1 and their hybridization with SET1 over the gold working electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to examine the binding of thiol modified SECP1 on the gold working electrode and hybridization of thiol modified SECP1 with the target single stranded DNA. Both demonstrated the gold working electrode surface was modified with a capture probe layer and hybridization of the thiol bound ssDNA probe with target DNA was indicated. Therefore, the proposed electrochemical biosensor has the potential to be used for the detection of the non-synthetic bacterial DNA target responsible for equine hindgut acidosis.

Highly sensitive protein detection using recombinant spores and lateral flow immunoassay

Lateral flow immunoassays (LFIs) can be used to detect intact bacteria or spores; when gold nanoparticles (AuNPs) are used as the signal reporters, the detection limits are very low. Spore-based surface display has been widely studied for enzyme immobilization and live-nontoxic oral vaccines. In this study, recombinant spores were used to improve the sensitivity of a LFI. We developed a test kit that combines streptavidin-displayed spores with a LFI assay for rapid protein detection. The recombinant spores served as a signal amplifier and AuNPs were used as the signal reporters. For detection of β-galactosidase, which was used as the model protein, the detection limit was about 10^-15 mol, while that of the conventional LFI is about 10^-12 mol. In both methods, nanogold was used as the colorimetric signal and could be observed with the naked eye. This method improved LFI sensitivity without sacrificing its advantages. Furthermore, enhanced green fluorescent protein (eGFP) was also displayed on the surface of the streptavidin-displayed spores. Without AuNPs, the fluorescent recombinant spores acted as the signal, which could be detected by a fluorescence detector, such as a fluorescence microscope. The detection limit was 10^-16 mol under fluorescence microscopy whose magnification was 25-fold. Therefore, in conclusion, in this proof of concept study, the detection limits of both proposed methods were far superior to those of traditional LFI assay.

Rapid on-site detection of Salmonella pullorum based on lateral flow nucleic acid assay combined with recombinase polymerase amplification reaction

Caused by Salmonella pullorum, pullorosis is a bacterial disease threatening the poultry industry and has been listed as the bacterial disease to be eliminated by the government. However, antibiotic treatment of pullorosis has become increasingly difficult, resulting in severe influences on the sustainable development of poultry. Abuse of antibiotics may cause global drug-resistant problems. Hence, early diagnosis of young chickens and accurate treatment of sick chickens are urgently needed. Traditional serotyping for Salmonella detection is costly and labor-intensive, whereas other commonly used plate agglutination test methods often cause physical injury of chickens. Therefore, a rapid and nondamaging detection method is of great significance for early diagnosis, which is the key step in accurate medication and elimination of pullorosis. In this study, we propose a novel lateral flow nucleic acid assay (LFNAA) system combining recombinase polymerase amplification (RPA) for the detection of S. pullorum. In this method, the DNA of S. pullorum strains was quickly amplified by RPA under 37°C, and then, the RPA products were added onto the LFNAA sample pad until the final results could be observed by naked eyes within 3 min. The proposed assay is fast and delivers visible results to naked eyes in field test. The limit of detection for genomic DNA was 5 × 10^-3 ng/μL, indicating high sensitivity. In addition, the proposed LFNAA system is cost-effective, efficient, and nondamaging to chicks in the field test. This system provides technical support for early diagnosis of S. pullorum in the poultry and paves a way for future precision medicine to avoid the global drug-resistance issues.

The response of yeast vacuolar proteins: A novel rapid tool for Salmonella sp. screening

Human health is recently affected by several factors in which food contamination is one of the most dangerous elements that damage directly on our bodies. In this study, we provided a novel approach for the rapid detection of Salmonella sp. at the molecular level using the response of Saccharomyces cerevisiae's vacuoles. First, an augmentation of vacuoles intensity was observed by confocal microscopy after treating Salmonella strains with yeast cells. Second, the vacuolar enzymes were isolated and then analyzed by two-dimensional electrophoresis for the screening of specific biomarkers. After that, various recombinant yeasts containing exclusive biomarkers were constructed by fusing these biomarkers with several fluorescent proteins. Finally, the recombinant strains showed the ability to detect Salmonella strains specifically by appropriate fluorescent signals from 20 CFU/mL after 15 Min of exposure.

Development of a Nucleic Acid Lateral Flow Immunoassay for the Detection of Human Polyomavirus BK

The BK virus (BKV) is an emerging pathogen in immunocompromised individuals and widespread in the human population. Polymerase chain reaction is a simple and highly sensitive method for detecting BKV, but it is time consuming and requires expensive instruments and expert judgment. The lateral flow assay, a rapid, low-cost, minimal-labor, and easy-to-use diagnostic method, was successfully applied for pathogen detection. In this study, we used oligonucleotide probes to develop a simple and rapid sandwich-type lateral flow immunoassay for detecting BKV DNA within 45 minutes. The detection limit for the synthetic single-stranded DNA was 5 nM. The specificity study showed no cross-reactivity with other polyomaviruses, such as JC virus and simian virus 40. For the Escherichia coli containing BKV plasmid cultured samples, the sensitivity was determined to be 107 copies/mL. The approach offers great potential for BKV detection of various target analytes in point-of-care settings.

16S rRNA-functionalized multi-HCR concatemers in a signal amplification nanostructure for visual detection of Salmonella

To prevent foodborne diseases and minimize their impacts, it is extremely important to develop a cost-effective and efficient bacterial detection assay for diagnostics, particularly in resource-poor settings. In this study, 16S rRNA from foodborne Salmonella was coupled with multiple HCR (hybridization chain reaction) concatemers and functionalized in a signal structure for lateral flow nucleic acid biosensor (LFNAB) detection. The 16S rRNA was incubated with two specific capture probes and multiple helper probes carrying the same initiator, to unwind its secondary structure and form an "initiators-on-a-string" complex. Through use of the initiators, each target 16S rRNA yielded multiple HCR concatemers tethered to numerous biotins, and numerous streptavidin-labeled gold nanoparticles were introduced on the LFNAB. The limit of detection was 53.65 CFU/mL for Salmonella. Notably, this method has high specificity and applicability for the detection of Salmonella in food and water samples.

A microfluidic immunosensor for visual detection of foodborne bacteria using immunomagnetic separation, enzymatic catalysis and distance indication

A disposable visual microfluidic immunosensor is described for the determination of foodborne pathogens using immunomagnetic separation, enzymatic catalysis and distance indication. Specifically, a sensor was designed to detect Salmonella typhimurium as a model pathogen. Magnetic nanoparticles (MNPs) were modified with the anti-Salmonella monoclonal antibodies and then used to enrich S. typhimurium from the sample. This is followed by conjugation to polystyrene microspheres modified with anti-Salmonella polyclonal antibodies and catalase to form the MNP-bacteria-polystyrene-catalase sandwich. The catalase on the complexes catalyzes the decomposition of hydrogen peroxide to produce oxygen after passing a micromixer. The generated oxygen gas increases the pressure in the chip and pushes the indicating red dye solution to travel along the channel towards the unsealed outlet. The travel distance of the red dye can be visually read and related to the amount of S. typhimurium using the calibration scale. The sensor can detect as low as 150 CFU·mL^-1 within 2 h. Graphical abstractSchematic representation of the distance-based microfluidic immunosensor for visual detection of foodborne bacteria using immunomagnetic nanoparticles for bacteria separation, catalase for decomposition of hydrogen peroxide to form oxygen which causes a pressure increase, and red dyed particles movement for distance indication.

Single and multiple detections of foodborne pathogens by gold nanoparticle assays

A late detection of pathogenic microorganisms in food and drinking water has a high potential to cause adverse health impacts in those who have ingested the pathogens. For this reason there is intense interest in developing precise, rapid and sensitive assays that can detect multiple foodborne pathogens. Such assays would be valuable components in the campaign to minimize foodborne illness. Here, we discuss the emerging types of assays based on gold nanoparticles (GNPs) for rapidly diagnosing single or multiple foodborne pathogen infections. Colorimetric and lateral flow assays based on GNPs may be read by the human eye. Refractometric sensors based on a shift in the position of a plasmon resonance absorption peak can be read by the new generation of inexpensive optical spectrometers. Surface-enhanced Raman spectroscopy and the quartz microbalance require slightly more sophisticated equipment but can be very sensitive. A wide range of electrochemical techniques are also under development. Given the range of options provided by GNPs, we confidently expect that some, or all, of these technologies will eventually enter routine use for detecting pathogens in food. This article is categorized under: Diagnostic Tools > Biosensing.

Point-of-care detection of 16S rRNA of Staphylococcus aureus based on multiple biotin-labeled DNA probes

A visual method that combines multiple biotin-labeled DNA probes and lateral-flow nucleic acid biosensor was developed to detect Staphylococcus aureus. The 16S rRNA from Staphyloccocus aureus (S. aureus), coupled with multiple biotin-labeled DNA probes, was functionalized in a signal structure for lateral-flow point-of-care detection. The secondary structure of the 16S rRNA was unwound by two specific capture probes modified by Fam and multiple bridge probes, which extended additional sequences for use as initiators. By utilizing the initiators, each target 16S rRNA with multiple DNA probes could tether a number of biotin molecules, so that a large number of streptavidin-labeled gold nanoparticles could be introduced in the lateral flow assay. The images of the lateral flow detection results obtained using a smartphone were transmitted to a computer via Wi-Fi or Bluetooth connection for quantitative processing by ImageJ. The limit of detection was 10³ cfu/mL without sample enrichment, and decreased to 0.12 cfu/mL following a 3-h enrichment of samples in growth medium. Notably, this method presented high specificity and applicability for the detection of S. aureus in food samples. In short, the developed visual non-specific operation method is very suitable for point-of-care diagnosis of pathogens in resource-limited countries.

Use of nanotechnology for infectious disease diagnostics: application in drug resistant tuberculosis

BACKGROUND

The increased transmission of multidrug-resistant (MDR) tuberculosis (TB) poses a challenge to tuberculosis prevention and control in Sri Lanka. Isoniazid (INH) is a key element of the first line anti tuberculosis treatment regimen. Resistance to INH may lead to development of MDR TB. Therefore, early detection of INH resistance is important to curb spread of resistance. Due to the limited availability of rapid molecular methods for detection of drug resistance in Sri Lanka, this study was aimed at developing a simple and rapid gold nanoparticle (AuNP) based lateral flow strip for the simultaneous detection of the most common INH resistance mutation (katG S315 T, 78.6%) and Mycobacterium tuberculosis (MTb).

METHODS

Lateral flow strip was designed on an inert plastic backing layer containing a sample pad, nitrocellulose membrane and an absorption pad. Biotin labeled 4 capture probes which separately conjugated with streptavidin were immobilized on the nitrocellulose. The test sample was prepared by multiplex PCR using primers to amplify codon 315 region of the katG gene and MTb specific IS6110 region. The two detection probes complementary to the 5' end of each amplified fragment was conjugated with gold nanoparticles (20 nm) and coupled with the above amplified PCR products were applied on the sample pad. The hybridization of the amplified target regions to the respective capture probes takes place when the sample moves towards the absorption pad. Positive hybridization is indicated by red colour lines.

RESULTS

The three immobilized capture probes on the strip (for the detection of TB, katG wild type and mutation) were 100 and 96.6% specific and 100 and 92.1% sensitive respectively.

CONCLUSION

The AuNP based lateral flow assay was capable of differentiating the specific mutation and the wild type along with MTb identification within 3 h.

Visual Detection of Dengue-1 RNA Using Gold Nanoparticle-Based Lateral Flow Biosensor

Dengue is a rapidly spreading mosquito-borne viral disease. Early diagnosis is important for clinical screening, medical management, and disease surveillance. The objective of this study was to develop a colorimetric lateral flow biosensor (LFB) for the visual detection of dengue-1 RNA using dextrin-capped gold nanoparticle (AuNP) as label. The detection was based on nucleic acid sandwich-type hybridization among AuNP-labeled DNA reporter probe, dengue-1 target RNA, and dengue-1 specific DNA capture probe immobilized on the nitrocellulose membrane. Positive test generated a red test line on the LFB strip, which enabled visual detection. The optimized biosensor has a cut-off value of 0.01 µM using synthetic dengue-1 target. Proof-of-concept application of the biosensor detected dengue-1 virus in pooled human sera with a cut-off value of 1.2 × 104 pfu/mL. The extracted viral RNA, when coupled with nucleic acid sequence-based amplification (NASBA), was detected on the LFB in 20 min. This study first demonstrates the applicability of dextrin-capped AuNP as label for lateral flow assay. The biosensor being developed provides a promising diagnostic platform for early detection of dengue infection in high-risk resource-limited areas.

New Functional Tracer-Two-Dimensional Nanosheet-Based Immunochromatographic Assay for Salmonella enteritidis Detection

The rapid monitoring of foodborne pathogens by monoclonal antibody (McAb)-based immunochromatographic tests (ICTs) is desirable but highly challenging as a result of the screening obstacle for a superior performance probe, which will greatly determine the capture efficiency of targets and the sensitivity of the immunoassay. In this work, on the basis of two-dimensional (2D) nanosheets (including MoS₂ and graphene) as the extraordinary capture probe and signal indicator, we fabricated a label-free ICT method for Salmonella enteritidis detection. Especially, without the customarily labeled antibody probe, these 2D versatile probes presented strong capture ability toward bacteria by directly assembling onto the surface of bacteria. An ideal analytical performance with high sensitivity and specificity was achieved by virtue of the novel nanosheet-bacteria-McAb sandwich format. On the basis of MoS₂ 2D nanosheets as a fabulous probe element, the developed ICT exhibited a lowest detectable concentration of 10³ colony-forming units/mL for S. enteritidis and could be well-applied in drinking water and watermelon juice samples. By the smart design, this work removes a series of conditionality issues of traditional double antibody sandwich-based ICTs and can give a new application direction for 2D nanosheet materials in the rapid detection field.

Invited review: Advancements in lateral flow immunoassays for screening hazardous substances in milk and milk powder

Dairy-related food safety outbreaks, such as food-borne pathogen contamination, mycotoxin contamination, and veterinary drug contamination, sometimes happen and have been reported all over the world, affecting human health and, in some cases, leading to death. Thus, rapid yet robust detection methods are needed to monitor milk and milk powder for the presence of hazardous substances. The lateral flow immunoassay (LFI) is widely used in onsite testing because of its rapidity, simplicity, and convenience. In this review, we describe some traditional LFI used to detect hazardous substances in milk and milk powder. Furthermore, we discuss recent advances in LFI that aim to improve sensitivity or detection efficiency. These advances include the use of novel label materials, development of signal amplification systems, design of multiplex detection systems, and the use of nucleic acid-based LFI.

Enlargement of Gold Nanoparticles for Sensitive Immunochromatographic Diagnostics of Potato Brown Rot

Lateral flow immunoassay (LFIA) is a convenient tool for rapid field-based control of various bacterial targets. However, for many applications, the detection limits obtained by LFIA are not sufficient. In this paper, we propose enlarging gold nanoparticles' (GNPs) size to develop a sensitive lateral flow immunoassay to detect Ralstonia solanacearum. This bacterium is a quarantine organism that causes potato brown rot. We fabricated lateral flow test strips using gold nanoparticles (17.4 ± 1.0 nm) as a label and their conjugates with antibodies specific to R. solanacearum. We proposed a signal enhancement in the test strips' test zone due to the tetrachloroauric (III) anion reduction on the GNP surface, and the increase in size of the gold nanoparticles on the test strips was approximately up to 100 nm, as confirmed by scanning electron microscopy. Overall, the gold enhancement approach decreased the detection limit of R. solanacearum by 33 times, to as low as 3 × 10⁴ cells∙mL⁻1 in the potato tuber extract. The achieved detection limit allows the diagnosis of latent infection in potato tubers. The developed approach based on gold enhancement does not complicate analyses and requires only 3 min. The developed assay together with the sample preparation and gold enlargement requires 15 min. Thus, the developed approach is promising for the development of lateral flow test strips and their subsequent introduction into diagnostic practice.

Development of rapid dipstick assay for food pathogens, Salmonella, by optimized parameters

Salmonella is among the very important pathogens threating the human and animal health. Rapid and easy detection of these pathogens is crucial. In this context, antibody (Ab) based lateral flow assays (LFAs) which are simple immunochromatographic point of care test kits were developed by gold nanoparticles (GNPs) as labelling agent for Salmonella detection. For that purpose some critical parameters such as reagent concentrations on the capture zones, conjugate concentrations and ideal membrane type needed for LFAs for whole cell detection were tested for naked eye analysis. Therefore, prepared LFAs were applied to the live and heat inactivated cells when they were used alone or included in different bacterial mixtures. Among the test platforms, membrane 180 (M180) was found as an ideal membrane and 36 nm GNPs showed highly good labelling in the developed LFAs. Diluted conjugates and low concentrations of reagents affected the test signal negatively. Salmonella was detected in different bacterial mixtures, selectively in 4-5 min. The best recognized species by used Ab were S. enteritidis and S. infantis. 5 × 105 S. typhimurium cells were also determined as a limit of detection of this study with mentioned parameters.

Paper-based lateral flow strip assay for the detection of foodborne pathogens: principles, applications, technological challenges and opportunities

As a representative colorimetic biosnesor, paper-based LFSA have emerged as a promising and robust tool that can easily and instansly detect the presence of target biological components in food sample. Recently, LFSAs have gained a considerable attention as an alternative method for rapid diagnosis of foodborne pathogens to the conventional culture-based assays such as plate counting and PCR. One major drawback of the current LFSAs for the detection of pathogenic bacteria is the low sensitivity, limiting its practical applications in POCT. Not like many other protein-based biomarkers that are present in nM or pM range, the number of pathogenic bacteria that cause disease can be as low as few CFU/ml. Here, we review current advances in LFSAs for the detection of pathogenic bacteria in terms of chromatic agents and analyte types. Furthermore, recent approaches for signal enhancement and modifications of the LFSA architecture for multiplex detection of pathogenic bacteria are included in this review, together with the advantages and limitations of each techniques. Finally, the technological challenges and future prospect of LFSA-based POCT for the detection of pathogenic bacteria are discussed.

Label-free aptasensors based on fluorescent screening assays for the detection of Salmonella typhimurium

We report two label-free fluorescent aptasensor methods for the detection of S. typhimurium. In the first method, we have used a ''turn off'' approach in which the aptamer is first intercalated with SYBR Green I (SG), leading to a greatly enhanced fluorescence signal. The addition of S. typhimurium (approximately 1530-96938 CFU/mL), which specifically binds with its aptamer and releases SG, leads to a linear decrease in fluorescence intensity. The lowest detection limit achieved with this approach was in the range of 733 CFU/mL. In the second method, a ''turn on'' approach was designed for S. typhimurium through the Förster resonance energy transfer (FRET) between Rhodamine B (RB) and gold nanoparticles (AuNPs). When the aptamer and AuNPs were mixed with RB, the fluorescence of RB was significantly quenched via FRET. The aptamer adsorbs to the AuNP surface to protect them from salt-induced aggregation, which leads to the fluorescence quenching of RB in presence of AuNPs. Upon the addition of S. typhimurium, S. typhimurium specifically binds with its aptamer and loses the capability to stabilize AuNPs. Thus, the salt easily induces the aggregation of AuNPs, resulting in the fluorescence recovery of the quenched RB. S. typhimurium concentrations ranging from 1530 to 96938 CFU/mL with the detection limit of 464 CFU/mL was achieved with this methodology. Given these data, some insights into the molecular interactions between the aptamer and the bacterial target are provided. These aptasensor methods also may be adapted for the detection of a wide variety of targets.