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

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.

Nucleic Acid Aptamer-Based Sensors for Bacteria Detection: A Review

Bacteria have a significant impact on human production and life, endangering human life and health, so rapid detection of infectious agents is essential to improve human health. Aptamers, which are pieces of oligonucleotides (DNA or RNA) have been applied to biosensors for bacteria detection due to their high affinity, selectivity, robust chemical stability, and their compatibility with various signal amplification and signal transduction mechanisms. In this review, we summarize the different bacterial aptamers selected in recent years using SELEX technology and discuss the differences in optical and electrochemical bacterial aptamer sensors. In addition the technological developments and innovations in bacterial aptamer sensor technology are introduced. Combining new materials and methods, the efficiency and stability of the sensors have also been improved. This review summarizes the progress of current bacterial aptamer sensors based on their practical application status and provides an outlook on their future development.

Gold nanoparticle-mediated fluorescence resonance energy transfer for analytical applications in the fields of life health and safety

Fluorescence Resonance Energy Transfer (FRET) has emerged as a predominant, highly sensitive, and homogeneous optical analytical technique in the realm of analytical testing and bio-imaging. Gold nanoparticles (AuNPs) demonstrate a size-dependent, broader absorption range within visible wavelengths owing to the phenomenon of surface plasmon resonance. As a result, they can effectively act as light acceptors, enabling the creation of a donor-acceptor system crucial for achieving precise target analyte analysis. In this comprehensive review, we present an extensive survey of recent research advancements in the field of FRET techniques based on AuNPs for the analytical detection of a wide range of entities, including some biomolecules, pesticides, enzymes, microorganisms, food safety and environmental pollutants. Additionally, we elucidate the procedural strategies and underlying mechanisms involved. Finally, we provide perspectives on the current issues and future efforts surrounding the FRET applications of AuNPs in biological analysis. Overall, this review aims to provide a holistic comprehension of gold nanoparticle applications in life analysis using FRET, while also presenting a promising vision for future endeavors in this domain.

Using gold-based nanomaterials for fighting pathogenic bacteria: from detection to therapy

Owing to the unique quantum size effect and surface effect, gold-based nanomaterials (GNMs) are promising for pathogen detection and broad-spectrum antimicrobial activity. This review summarizes recent research on GNMs as sensors for detecting pathogens and as tools for their elimination. Firstly, the need for pathogen detection is briefly introduced with an overview of the physicochemical properties of gold nanomaterials. And then strategies for the application of GNMs in pathogen detection are discussed. Colorimetric, fluorescence, surface-enhanced Raman scattering (SERS) techniques, dark-field microscopy detection and electrochemical methods can enable efficient, sensitive, and specific pathogen detection. The third section describes the antimicrobial applications of GNMs. They can be used for antimicrobial agent delivery and photothermal conversion and can act synergistically with photosensitizers to achieve the precise killing of pathogens. In addition, GNMs are promising for integrated pathogen detection and treatment; for example, combinations of colorimetric or SERS detection with photothermal sterilization have been demonstrated. Finally, future outlooks for the applications of GNMs in pathogen detection and treatment are summarized.

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.

Bacterial detection based on Förster resonance energy transfer

The huge economic loss and threat to human health caused by bacterial infection have attracted the public's concern, and there is an urgent need to relieve and improve the tough problem. Therefore, it is significant to establish a facile, rapid, and sensitive method for bacterial detection considering the shortcomings of existing methods. Förster resonance energy transfer (FRET)-based sensors have exhibited immense potential and applicability for bacterial detection given their high signal-to-noise ratio and high sensitivity. This review focuses on the development of FRET-based fluorescence assays for bacterial detection. We summarize the principle of FRET-based assays, discuss the commonly used recognition molecules and further introduce three frequent construction strategies. Based on the strategies and materials, relevant applications are presented. Moreover, some restrictions of FRET fluorescence sensors and development prospects are discussed. Suitable donor-acceptor pairs and stable recognition molecules are the essential conditions for sensors to play their roles, and there is still some room for development. Besides, applying FRET fluorescence sensors to point-of-care detection is still difficult. Future developments could focus on near-infrared fluorescent dyes and simultaneous detection of multiple analytes.

A Colorimetric/Fluorescent Dual-Mode Aptasensor for Salmonella Based on the Magnetic Separation of Aptamers and a DNA-Nanotriangle Programmed Multivalent Aptamer

Salmonella infection has emerged as a global health threat, causing death, disability, and socioeconomic disruption worldwide. The rapid and sensitive detection of Salmonella is of great significance in guaranteeing food safety. Herein, we developed a colorimetric/fluorescent dual-mode method based on a DNA-nanotriangle programmed multivalent aptamer for the sensitive detection of Salmonella. In this system, aptamers are precisely controlled and assembled on a DNA nanotriangle structure to fabricate a multivalent aptamer (NTri-Multi-Apt) with enhanced binding affinity and specificity toward Salmonella. The NTri-Multi-Apt was designed to carry many streptavidin-HRPs for colorimetric read-outs and a large load of Sybr green I in the dsDNA scaffold for the output of a fluorescent signal. Therefore, combined with the magnetic separation of aptamers and the prefabricated NTri-Multi-Apt, the dual-mode approach achieved simple and sensitive detection, with LODs of 316 and 60 CFU/mL for colorimetric and fluorescent detection, respectively. Notably, the fluorescent mode provided a self-calibrated and fivefold-improved sensitivity over colorimetric detection. Systematic results also revealed that the proposed dual-mode method exhibited high specificity and applicability for milk, egg white, and chicken meat samples, serving as a promising tool for real bacterial sample testing. As a result, the innovative dual-mode detection method showed new insights for the detection of other pathogens.

Joint concanavalin A-aptamer enabled dual recognition for anti-interference visual detection of Salmonella typhimurium in complex food matrices

Given that food poisoning and infectious diseases caused by Salmonella typhimurium (S. typhimurium) draw intensive public health concerns, developing rapid, accurate, and cost-effective approaches to detect the pathogen is of crucial importance. Herein, we proposed a concanavalin A (Con A)-aptamer joint strategy to realize dual recognition for the strongly specific, visual, and highly sensitive determination of S. typhimurium. Compared with currently used single identification strategies, Con A and aptamer could recognize different sites of S. typhimurium to enhance the utilization rate of these sites for better sensing. The developed assay offered specific detection of S. typhimurium against other bacteria in a remarkably wide concentration range of 7.0 × 10¹ ∼ 7.0 × 10⁹ CFU/mL, along with a detection limit as low as 23 CFU/mL. Real sample analyses of milk and pork demonstrated the excellent reliability and practicability of our assay, providing great potential for food safety analysis.

A facile aptamer-based sensing strategy for dopamine detection through the fluorescence energy transfer between dye and single-wall carbon nanohorns

Dopamine (DBA) as an important biomarker, plays a crucial role in disease diagnosis. In this study, we have developed a fast and simple aptamer-based fluorescence strategy which used single-wall carbon nanohorns (SWCNHs) as a quencher for dopamine detection. SWCNHs were negatively charged after pretreated, which improved its dispersion in solution. 5-carboxy-fluorescein (FAM) was used to label dopamine aptamer. In the absence of dopamine, FAM-modified aptamer could be absorbed onto the SWCNHs surface due to π-π interaction, resulting in the fluorescence intensity decreased. Dopamine could specifically bind with FAM-DNA to form G-quadruplex, which could not be absorbed onto the surface of SWCNHs. Hence, the fluorescence of FAM-DNA recovered, and the fluorescent intensity as a function of different concentrations of dopamine was measured. We obtained a detection limit of 5 μM for this detection system with a linear detection range of 0.02-2.20 mM. Furthermore, the feasibility of the innovative detection system has been verified by detecting dopamine in spiked serum samples.

Recent Advances in Electrochemical Biosensors for the Detection of Salmonellosis: Current Prospective and Challenges

Salmonellosis is a major cause of foodborne infections, caused by Salmonella, posing a major health risk. It possesses the ability to infiltrate the food supply chain at any point throughout the manufacturing, distribution, processing or quality control process. Salmonella infection has increased severely and requires effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction and culture plate, consume a lot of time and are labor-intensive. Therefore, new quick detection methods for on-field applications are urgently needed. Biosensors provide consumer-friendly approaches for quick on-field diagnoses. In the last few years, there has been a surge in research into the creation of reliable and advanced electrochemical sensors for the detection of Salmonella strains in food samples. Electrochemical sensors provide extensive accuracy and reproducible results. Herein, we present a comprehensive overview of electrochemical sensors for the detection of Salmonella by focusing on various mechanisms of electrochemical transducer. Further, we explain new-generation biosensors (microfluidics, CRISPR- and IOT-based) for point-of care applications. This review also highlights the limitations of developing biosensors in Salmonella detection and future possibilities.

A simple and sensitive AuNPs-based colorimetric aptasensor for specific detection of azlocillin

A new colorimetric biosensor for specific detection of azlocillin was developed by using DNA aptamer as recognition element and unmodified gold nanoparticles (AuNPs) as colorimetric indicator. In the absence of azlocillin, the AuNPs were protected by the aptamer and stabilized at high NaCl concentrations, displaying a red solution. In the presence of azlocillin, the aptamer reacts specifically with azlocillin, resulting in the aggregation of AuNPs and an apparent red to blue color change. The characteristic change can be easily observed by the naked eye and quantitatively detected by an ultraviolet-visible (UV-Vis) spectrometer. Under the optimal conditions, the absorbance variation at 522 nm (ΔA₅₂₂) of AuNPs changed proportionally with increasing concentration of azlocillin, which exhibited a linear relationship in the concentration range of 50 nM to 500 nM, with a detection limit of 11.6 nM. Furthermore, the aptasensor was successfully used to detect azlocillin in milk and tap water samples, with recoveries ranging from 97.64% to 102.21% and a relative standard deviation (RSD) less than 3.81%.

Nucleic Acid-Based Nanobiosensor (NAB) Used for Salmonella Detection in Foods: A Systematic Review

Salmonella bacteria is a foodborne pathogen found mainly in food products causing severe symptoms in the individual, such as diarrhea, fever, and abdominal cramps after consuming the infected food, which can be fatal in some severe cases. Rapid and selective methods to detect Salmonella bacteria can prevent outbreaks when ingesting contaminated food. Nanobiosensors are a highly sensitive, simple, faster, and lower cost method for the rapid detection of Salmonella, an alternative to conventional enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) techniques. This study systematically searched and analyzed literature data related to nucleic acid-based nanobiosensors (NABs) with nanomaterials to detect Salmonella in food, retrieved from three databases, published between 2010 and 2021. We extracted data and critically analyzed the effect of nanomaterial functionalized with aptamer or DNA at the limit of detection (LOD). Among the nanomaterials, gold nanoparticles (AuNPs) were the most used nanomaterial in studies due to their unique optical properties of the metal, followed by magnetic nanoparticles (MNPs) of Fe₃O₄, copper nanoparticles (CuNPs), and also hybrid nanomaterials multiwalled carbon nanotubes (c-MWCNT/AuNP), QD/UCNP-MB (quantum dotes upconverting nanoparticle of magnetic beads), and cadmium telluride quantum dots (CdTe QDs@MNPs) showed excellent LOD values. The transducers used for detection also varied from electrochemical, fluorescent, surface-enhanced Raman spectroscopy (SERS), RAMAN spectroscopy, and mainly colorimetric due to the possibility of visualizing the detection result with the naked eye. Furthermore, we show the magnetic separation system capable of detecting the target amplification of the genetic material. Finally, we present perspectives, future research, and opportunities to use point-of-care (POC) diagnostic devices as a faster and lower cost approach for detecting Salmonella in food as they prove to be viable for resource-constrained environments such as field-based or economically limited conditions.

A Novel Fluorescence Aptasensor Based on Magnetic Beads/Gold Nanoparticles/DNA-Stabilized Silver Nanoclusters for Detection of Salmonella Typhimurium

Salmonella Typhimurium (S. Typhimurium) is a globally distributed foodborne pathogen, which can lead to outbreaks of foodborne infectious diseases. It is essential to guarantee food safety by timely and correct detection of S. Typhimurium. In this investigation, an original fluorescence aptasensor was constructed to detect S. Typhimurium rapidly and sensitively. Through the coupling of magnetic beads, aptamer, and gold nanoparticles (AuNPs), a fluorescence quenching system with a "sandwich structure" was established. The aptamer acted as a link, and its specific binding to S. Typhimurium could release AuNPs from the system. Meanwhile, fluorescent DNA-stabilized silver nanoclusters (DNA-AgNCs) were synthesized. The fluorescence intensity changes caused by the fluorescence resonance energy transfer between DNA-AgNCs and AuNPs were utilized to detect S. Typhimurium. The purposed aptasensor exhibited high selectivity and sensitivity with a linear response to S. Typhimurium, ranging from 3.7 × 10² to 3.7 × 10⁵ cfu/mL. The limit of detection (LOD) was estimated to be 98 cfu/mL within 2 h 10 min. In addition, this method showed excellent application for detection of S. Typhimurium in artificially contaminated milk, with LOD reaching 3.4 × 10² cfu/mL. Therefore, the developed fluorescence aptasensor has great potential to identify S. Typhimurium in foodstuffs.

Biosensor Technologies in Medicine: from Detection of Biochemical Markers to Research into Molecular Targets (Review)

Infections are a major cause of premature death. Fast and accurate laboratory diagnostics of infectious diseases is a key condition for the timely initiation and success of treatment. Potentially, it can reduce morbidity, as well as prevent the outbreak and spread of dangerous epidemics. The traditional methods of laboratory diagnostics of infectious diseases are quite time- and labour-consuming, require expensive equipment and trained personnel, which is crucial within limited resources. The fast biosensor-based methods that combine the diagnostic capabilities of biomedicine with modern technological advances in microelectronics, optoelectronics, and nanotechnology make an alternative.

The modern achievements in the development of label-free biosensors make them promising diagnostic tools that combine rapid detection of specific molecular markers, simplicity, ease-of-use, efficiency, accuracy, and cost-effectiveness with the tendency to the development of portable platforms. These qualities exceed the generally accepted standards of microbiological and immunological diagnostics and open up broad prospects for using these analytical systems in clinical practice directly at the site of medical care provision (point-of-care, POC concept).

A wide variety of modern biosensor designs are based on the use of diverse formats of analytical and technological strategies, identification of various regulatory and functional molecular markers associated with infectious pathogens. The solution to the existing problems in biosensing will open up great prospects for these rapidly developing diagnostic biotechnologies.

A novel fluorescent platform of DNA-stabilized silver nanoclusters based on exonuclease III amplification-assisted detection of Salmonella Typhimurium

A novel fluorescent platform of DNA-stabilized silver nanoclusters (DNA-AgNCs) has been developed based on exonuclease III (Exo III) amplification-assisted for simple and sensitive detection of Salmonella Typhimurium (S. Typhimurium). The platform was designed by using magnetic beads, aptamer, its complementary DNA, hairpin probe (HP), Exo III, AgNO₃, and NaBH₄. The functionalized HP contained a cytosine-rich oligonucleotide loop (C-rich loop), which served as an effective template for the chemical reduction of Ag⁺ with NaBH₄ to synthesize DNA-AgNCs. In the presence of S. Typhimurium, the C-rich loop was converted into an open form of ssDNA by the recycle digestion of Exo III, leading to a corresponding decrease in fluorescence intensity. Based on the fluorescence changes of the formed DNA-AgNCs, the sensitive detection of S. Typhimurium was achieved. Under the optimal conditions, a wide linear relationship was observed in the concentration of S. Typhimurium ranging from 4.6 × 10² to 4.6 × 10⁷ cfu mL^-1 with the limit of detection (LOD) being 82 cfu mL^-1. The method showed good selectivity for detecting S. Typhimurium. In addition, the platform could be used for the detection of S. Typhimurium in milk samples. The LOD reached 6.6 × 10² cfu mL^-1 with a good linear range, indicating that the method had excellent practicability in complex food samples.

A detection method of Escherichia coli O157:H7 based on immunomagnetic separation and aptamers-gold nanoparticle probe quenching Rhodamine B's fluorescence: Escherichia coli O157:H7 detection method based on IMS and Apt-AuNPs probe quenching Rho B' s fluorescence

This research aimed to detect Escherichia coli O157:H7 in milk based on immunomagnetic probe separation technology and quenching effect of gold nanoparticles to Rhodamine B. Streptavidin-modified magnetic beads (MBs) were combined with biotin-modified antibodies to capture E. coli O157:H7 specifically. Gold nanoparticle (AuNPs) was incubated with sulfhydryl-modified aptamers (SH-Aptamers) to obtain the Aptamers-AuNPs probe. After magnetic beads captured target bacteria and formed a sandwich structure with the gold nanoprobe, Rhodamine B was added into complex to obtain fluorescent signal changes. Our results demonstrated that the established method could detect E. coli O157:H7 in the range of 101-107 CFU/mL, and the limit of detection (LOD) was 0.35 CFU/mL in TBST buffer (pH = 7.4). In milk simulation samples, the LOD of this method was 1.03 CFU/mL. Our research provides a promising approach on the detection of E. coli O157:H7.

Recent progress in the optical detection of pathogenic bacteria based on noble metal nanoparticles

Pathogenic bacteria have become a huge threat to social health and economy for their frighteningly infectious and lethal capacity. It is quite important to make a diagnosis in advance to prevent infection or allow a rapid treatment after infection. Noble metal nanoparticles, due to their unique physicochemical properties, especially optical properties, have drawn a great attention during the past decades and have been widely applied into all kinds of fields related to human health. By utilizing these noble metal nanoparticles, optical diagnosis platforms towards pathogenic bacteria have emerged continually, providing highly sensitive, selective, and particularly facile detection tools for clinic or point-of-care diagnosis. This review summarizes the recent development in this field. It begins with a brief introduction of pathogenic bacteria and noble metal nanoparticles. And then, optical detection methods are systematically discussed in three distinct aspects. In addition to these proof-of-concept methods, corresponding algorithms and point-of-care detection devices are also described. Finally, the review ends up with subjective views on present limitations and some appropriate advice for future research directions.

A fluorescence biosensor for Salmonella typhimurium detection in food based on the nano-self-assembly of alendronic acid modified upconversion and gold nanoparticles

A simple and quick-response fluorescent biosensor for Salmonella typhimurium detection based on the recognition of an aptamer coupled with alendronic acid (ADA)@upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) has been developed. Briefly, the aptamer can adsorb on the surfaces of the AuNPs via a "Au-S" bond to protect the AuNPs from aggregation in highly concentrated salt solution. Then, the AuNPs and UCNPs are linked by electrostatic adsorption, which leads to a decrease in the fluorescence peak at 541 nm based on fluorescence resonance energy transfer (FRET) between the UCNPs and AuNPs. In the presence of Salmonella typhimurium, the "Au-S" bond was broken, and the fluorescence intensity at 541 nm was recovered. Under optimal conditions, the correlation between the concentration of S. typhimurium and the intensity of the fluorescent biosensor signals was observed to be linear within the range of 1.16 × 10² to 1.16 × 10⁷ CFU mL^-1 (R² = 0.9912), and the detection limit of the developed biosensor was observed to be 36 CFU mL^-1. Furthermore, the proposed method was successfully used to detect the Salmonella typhimurium pathogen in food samples with satisfactory results.

Gold Nanomaterials as a Promising Integrated Tool for Diagnosis and Treatment of Pathogenic Infections-A Review

This review summarizes research on functionalized gold nanomaterials as pathogen detection sensors and pathogen elimination integrated tools. After presenting the challenge of current severe threat from pathogenic bacteria and the increasingly serious growth rate of drug resistance, the first section mainly introduces the conspectus of gold nanostructures from synthesis, characterization, physicochemical properties and applications of gold nanomaterials. The next section deals with gold nanomaterials-based pathogen detection sensors such as colorimetric sensors, fluorescence sensors and Surface-Enhanced Raman Scattering sensors. We then discuss strategies based on gold nanomaterials for eliminating pathogenic infections, such as the dual sterilization strategy for grafting gold nanomaterials with antibacterial substances, photothermal antibacterial and photodynamic antibacterial methods. The fourth part briefly introduces the comprehensive strategy for diagnosis and sterilization of pathogen infection based on gold nanomaterials, such as the diagnosis and treatment strategy for pathogen infection using Roman signals real-time monitoring and photothermal sterilization. A concluding section that summarizes the current status and challenges of the novel diagnosis and treatment integrated strategy for pathogenic infections, gives an outlook on potential future perspectives.

Rapid Detection of Salmonella typhimurium in Drinking Water by a White Light Reflectance Spectroscopy Immunosensor

Biosensors represent an attractive approach for fast bacteria detection. Here, we present an optical biosensor for the detection of Salmonella typhimurium lipopolysaccharide (LPS) and Salmonella bacteria in drinking water, based on white light reflectance spectroscopy. The sensor chip consisted of a Si die with a thin SiO₂ layer on top that was transformed into a biosensor through the immobilization of Salmonella LPS. The optical setup included a reflection probe with seven 200 μm fibers, a visible and near-infrared light source, and a spectrometer. The six fibers at the reflection probe circumference were coupled with the light source and illuminated the biosensor chip vertically, whereas the central fiber collected the reflected light and guided it to the spectrometer. A competitive immunoassay configuration was adopted for the analysis. Accordingly, a mixture of LPS or bacteria solution, pre-incubated for 15 min, with an anti-Salmonella LPS antibody was pumped over the chip followed by biotinylated secondary antibody and streptavidin for signal enhancement. The binding of the free anti-Salmonella antibody to chip-immobilized LPS led to a shift of the reflectance spectrum that was inversely related to the analyte concentration (LPS or bacteria) in the calibrators or samples. The total assay duration was 15 min, and the detection limits achieved were 4 ng/mL for LPS and 320 CFU/mL for bacteria. Taking into account the low detection limits, the short analysis time, and the small size of the chip and instrumentation employed, the proposed immunosensor could find wide application for bacteria detection in drinking water.

A microfluidic biosensor for rapid and automatic detection of Salmonella using metal-organic framework and Raspberry Pi

Rapid screening of pathogenic bacteria contaminated foods is crucial to prevent food poisoning. However, available methods for bacterial detection are still not ready for in-field screening because culture is time-consuming; PCR requires complex DNA extraction and ELISA lacks sensitivity. In this study, a microfluidic biosensor was developed for rapid, sensitive and automatic detection of Salmonella using metal-organic framework (MOF) NH₂-MIL-101(Fe) with mimic peroxidase activity to amplify biological signal and Raspberry Pi with self-developed App to analyze color image. First, the target bacteria were separated and concentrated with the immune magnetic nanobeads (MNBs), and labeled with the immune MOFs to form MNB-Salmonella-MOF complexes. Then, the complexes were used to catalyze colorless o-phenylenediamine and H₂O₂ to produce yellow 2,3-diaminophenazine (DAP). Finally, the image of the catalysate was collected under the narrow-band blue light and analyzed using the Raspberry Pi App to determine the bacterial concentration. The experimental results showed that this biosensor was able to detect Salmonella Typhimurium from 1.5 × 10¹ to 1.5 × 10⁷ CFU/mL in 1 h with the lower detection limit of 14 CFU/mL. The mean recovery for Salmonella in spiked chicken meats was ~112%. This biosensor integrating mixing, separation, labelling and detection onto a single microfluidic chip has demonstrated the merits of automatic operation, fast reaction, less reagent and small size, and is promising for in-field detection of foodborne bacteria.

Biosensors for rapid detection of Salmonella in food: A review

Salmonella is one of the main causes of foodborne infectious diseases, posing a serious threat to public health. It can enter the food supply chain at various stages of production, processing, distribution, and marketing. High prevalence of Salmonella necessitates efficient and effective approaches for its identification, detection, and monitoring at an early stage. Because conventional methods based on plate counting and real-time polymerase chain reaction are time-consuming and laborious, novel rapid detection methods are urgently needed for in-field and on-line applications. Biosensors provide many advantages over conventional laboratory assays in terms of sensitivity, specificity, and accuracy, and show superiority in rapid response and potential portability. They are now recognized as promising alternative tools and one of the most on-site applicable and end user-accessible methods for rapid detection. In recent years, we have witnessed a flourishing of studies in the development of robust and elaborate biosensors for detection of Salmonella in food. This review aims to provide a comprehensive overview on Salmonella biosensors by highlighting different signal-transducing mechanisms (optical, electrochemical, piezoelectric, etc.) and critically analyzing its recent trends, particularly in combination with nanomaterials, microfluidics, portable instruments, and smartphones. Furthermore, current challenges are emphasized and future perspectives are discussed.

A carbon nanoparticle-peptide fluorescent sensor custom-made for simple and sensitive detection of trypsin

Herein, we report a novel sensor to detect trypsin using a purpose-designed fluorescein-labelled peptide with negatively charged carbon nanoparticles (CNPs) modified by acid oxidation. The fluorescence of the fluorescein-labelled peptide was quenched by CNPs. The sensor reacted with trypsin to cleave the peptide, resulting in the release of the dye moiety and a substantial increase in fluorescence intensity, which was dose- and time-dependent, and trypsin could be quantified accordingly. Correspondingly, the biosensor has led to the development of a convenient and efficient fluorescent method to measure trypsin activity, with a detection limit of 0.7 μg/mL. The method allows rapid determination of trypsin activity in the normal and acute pancreatitis range, suitable for point-of-care testing. Furthermore, the applicability of the method has been demonstrated by detecting trypsin in spiked urine samples.

A dual-function oligonucleotide-based ratiometric fluorescence sensor for ATP detection

Adenosine triphosphate (ATP) is the main energy currency of life that plays a vital role in supporting physiological activities in living organisms, including humans. Therefore, accurate and sensitive detection of ATP concentration is necessary in biochemical research and clinical diagnosis. Herein, a ratiometric fluorescence aptasensor was developed for ATP detection. A dual-function DNA strand comprising an ATP-binding aptamer (ABA) and berberine-binding aptamer (BBA) was designed and optimized, in which ABA can capture ATP and thioflavin T (ThT), whereas BBA can capture berberine. Interestingly, the fluorescence intensity of both berberine and ThT were enhanced as they were captured by this dual-function DNA strand. In the presence of ATP, the ABA on the 3'-end of the DNA bound specifically to its target, causing ThT release and a significant drop in ThT fluorescence. However, ATP had no significant effect on the interaction between berberine and DNA, remaining the enhanced fluorescence intensity of berberine stable. Based on this interesting phenomenon, a ratiometric fluorescence sensor was constructed that used the enhanced fluorescence intensity of berberine as reference to measure the fluorescence intensity of ThT for ATP detection. This ratiometric fluorescence strategy had excellent selectivity and high sensitivity towards ATP with a detection limit (3σ) as low as 24.8 nM. The feasibility of application of this method in biological samples was evaluated in human serum and urine samples, where it exhibited a good detection performance.

Label-Free Biosensors for Laboratory-Based Diagnostics of Infections: Current Achievements and New Trends

Infections pose a serious global public health problem and are a major cause of premature mortality worldwide. One of the most challenging objectives faced by modern medicine is timely and accurate laboratory-based diagnostics of infectious diseases. Being a key factor of timely initiation and success of treatment, it may potentially provide reduction in incidence of a disease, as well as prevent outbreak and spread of dangerous epidemics. The traditional methods of laboratory-based diagnostics of infectious diseases are quite time- and labor-consuming, require expensive equipment and qualified personnel, which restricts their use in case of limited resources. Over the past six decades, diagnostic technologies based on lateral flow immunoassay (LFIA) have been and remain true alternatives to modern laboratory analyzers and have been successfully used to quickly detect molecular ligands in biosubstrates to diagnose many infectious diseases and septic conditions. These devices are considered as simplified formats of modern biosensors. Recent advances in the development of label-free biosensor technologies have made them promising diagnostic tools that combine rapid pathogen indication, simplicity, user-friendliness, operational efficiency, accuracy, and cost effectiveness, with a trend towards creation of portable platforms. These qualities exceed the generally accepted standards of microbiological and immunological diagnostics and open up a broad range of applications of these analytical systems in clinical practice immediately at the site of medical care (point-of-care concept, POC). A great variety of modern nanoarchitectonics of biosensors are based on the use of a broad range of analytical and constructive strategies and identification of various regulatory and functional molecular markers associated with infectious bacterial pathogens. Resolution of the existing biosensing issues will provide rapid development of diagnostic biotechnologies.

An aptamer-based colorimetric lateral flow assay for the detection of human epidermal growth factor receptor 2 (HER2)

An aptamer-based colorimetric lateral flow assay was developed for the detection of human epidermal growth factor receptor 2 (HER2). In this study, two approaches were examined using HER2 binding aptamers and gold nanoparticles. The first method used was a solution-based adsorption-desorption colorimetric approach wherein aptamers were adsorbed onto the gold nanoparticle surface. Upon the addition of HER2, HER2 binds specifically with its aptamer, releasing the gold nanoparticles. Addition of NaCl then induces the formation of gold nanoparticle aggregates. This leads to a color change from red to blue and a detection limit of 10 nM was achieved. The second method used an adsorption-desorption colorimetric lateral flow assay approach wherein biotin-modified aptamers were adsorbed onto the gold nanoparticle surface in the absence of HER2. In the presence of HER2, HER2 specifically binds with its aptamer leading to release of the gold nanoparticles. These solutions were applied to the lateral flow assay format and a detection limit of 20 nM was achieved. Both colorimetric and lateral flow assays are inexpensive, simple, rapid to perform and produce results visible to the naked-eye.

Aptamer and nanomaterial based FRET biosensors: a review on recent advances (2014-2019)

Fluorescence resonance energy transfer, one of the most powerful phenomena for elucidating molecular interactions, has been extensively utilized as a biosensing tool to provide accurate information at the nanoscale. Numerous aptamer- and nanomaterial-based FRET bioassays has been developed for detection of a large variety of molecules. Affinity probes are widely used in biosensors, in which aptamers have emerged as advantageous biorecognition elements, due to their chemical and structural stability. Similarly, optically active nanomaterials offer significant advantages over conventional organic dyes, such as superior photophysical properties, large surface-to-volume ratios, photostability, and longer shelf life. In this report (with 175 references), the use of aptamer-modified nanomaterials as FRET couples is reviewed: quantum dots, upconverting nanoparticles, graphene, reduced graphene oxide, gold nanoparticles, molybdenum disulfide, graphene quantum dots, carbon dots, and metal-organic frameworks. Tabulated summaries provide the reader with useful information on the current state of research in the field. Graphical abstract Schematic representation of a fluorescence resonance energy transfer-based aptamer nanoprobe in the absence and presence of a given target molecule (analyte). Structures are not drawn to their original scales.

A label-free fluorometric aptasensor for adenosine triphosphate (ATP) detection based on aggregation-induced emission probe

Based on Aggregation-Induced Emission (AIE), the development of a label-free, simple and sensitive fluorometric aptasensor for adenosine triphosphate (ATP) detection is described. With ATP present, the aptamers will combine with ATP and the conformation of the aptamer will switch from a random coil to an antiparallel G-quadruplex, which impedes the digestion by exonuclease I (Exo I). Addition of 4,4 -(1E,1E)-2,2-(anthracene-9,10-diyl) bis (ethene-2,1-diyl) bis (N,N, N-trimethyl-benzenaminium iodide) (DSAI) into the solution will cause aggregation of DSAI on the surface of the aptamer/ATP complex and consequently give rise to strong emission. Additionally, a good linear relationship was observed under optimized conditions between the fluorescence intensities and the logarithm of ATP concentrations (R² = 0.9908). The established aptamer sensor was highly sensitive and exhibited a low limit of detection of 32.8 nM, with superior specificity for ATP. It was also used in the quantification of ATP levels in human serum samples and demonstrated satisfactory recoveries in the scope of 93.2%-107.6%. The cellular ATP assay results indicated that the developed method can be used for monitoring ATP concentrations in cell extracts without the interference of other substances in the cells. This method offers several advantages such as simplicity, rapidity, low cost and excellent selectivity, which make it hold great potential for the detection of ATP in bioanalytical and biological studies.

Electrochemical detection of Salmonella using an invA genosensor on polypyrrole-reduced graphene oxide modified glassy carbon electrode and AuNPs-horseradish peroxidase-streptavidin as nanotag

A rapid and sensitive electrochemical biosensor was constructed to detect Salmonella using invA gene biosensor. The biosensing was based on polyrrole-reduced graphene oxide (PPy-rGO) nanocomposite modified glassy carbon electrode (GCE) and signal amplification with horseradish peroxidase-streptavidin biofunctionalized gold nanoparticles (AuNPs-HRP-SA). PPy-rGO was prepared at 60 °C by chemical reduction of PPy-functionalized graphene oxide (PPy-GO) that was synthesized by in situ polymerization at room temperature. The detection signal was amplified via enzymatic reduction of H₂O₂ in the presence of hydroquinone (HQ) using AuNPs-HRP-SA as nanotag. Under optimal conditions, the differential pulse voltametric (DPV) signal from the biosensor was linearly related to the logarithm of target invA gene concentrations from 1.0 × 10^-16 to 1.0 × 10^-10 M, and the limit of detection (LOD) was 4.7 × 10^-17 M. The biosensor can also detect Salmonella in the range of 9.6 to 9.6 × 10⁴ CFU mL^-1, with LOD of 8.07 CFU mL^-1. The biosensor showed good regeneration ability, acceptable selectivity, repeatability and stability, which bode well as an alternative method for Salmonella screening.

A reduced graphene oxide-titanium dioxide nanocomposite based electrochemical aptasensor for rapid and sensitive detection of Salmonella enterica

Recent foodborne outbreaks in multiple locations necessitate the continuous development of highly sensitive and specific biosensors that offer rapid detection of foodborne biological hazards. This work focuses on the development of a reduced graphene oxide‑titanium dioxide (rGO-TiO₂) nanocomposite based aptasensor to detect Salmonella enterica serovar Typhimurium. A label-free aptamer was immobilized on a rGO-TiO₂ nanocomposite matrix through electrostatic interactions. The changes in electrical conductivity on the electrode surface were evaluated using electroanalytical methods. DNA aptamer adsorbed on the rGO-TiO₂ surface bound to the bacterial cells at the electrode interface causing a physical barrier inhibiting the electron transfer. This interaction decreased the DPV signal of the electrode proportional to decreasing concentrations of the bacterial cells. The optimized aptasensor exhibited high sensitivity with a wide detection range (10⁸ to 10¹ cfu mL^-1), a low detection limit of 10¹ cfu mL^-1 and good selectivity for Salmonella bacteria. This rGO-TiO₂ aptasensor is an excellent biosensing platform that offers a reliable, rapid and sensitive alternative for foodborne pathogen detection.

Development of Structure-Switching Aptamers for Kanamycin Detection Based on Fluorescence Resonance Energy Transfer

The structure-switching aptamers are designed for the simple and rapid detection of kanamycin based on the signal transduction principle of fluorescence resonance energy transfer (FRET). The structure switch is composed of kanamycin-binding aptamers and the complementary strands, respectively labeled with fluorophore and quencher, denoted as FDNA and QDNA. In the absence of kanamycin, FDNA and QDNA form the double helix structure through the complementary pairing of bases. The fluorophore and the quencher are brought into close proximity, which results in the fluorescence quenching because of the FRET mechanism. In the presence of kanamycin, the FDNA specifically bind to the target due to the high affinity of aptamers, and the QDNA are dissociated. The specific recognition between aptamers and kanamycin will obstruct the formation of structure switch and reduce the efficiency of FRET between FDNA and QDNA, thus leading to the fluorescence enhancement. Therefore, based on the structure-switching aptamers, a simple fluorescent assay for rapid detection of kanamycin was developed. Under optimal conditions, there was a good linear relationship between kanamycin concentration and the fluorescence signal recovery. The linear range of this method in milk samples was 100-600 nM with the detection limit of 13.52 nM (3σ), which is well below the maximum residue limit (MRL) of kanamycin in milk. This method shows excellent selectivity for kanamycin over the other common antibiotics. The structure-switching aptamers have been successfully applied to the detection of kanamycin spiked in milk samples with the satisfying recoveries between 101.3 and 109.1%, which is well-consistent with the results from LC-MS/MS. Due to the outstanding advantages of facile operation, rapid detection, high sensitivity, excellent specificity, and low cost, the application and extension of this strategy for rapid determination of antibiotics in food samples may greatly improve the efficiency in food safety and quality supervision.