A novel fluorescence aptasensor based on mesoporous silica nanoparticles for selective and sensitive detection of aflatoxin B1

A lipoprotein complex conjugated mesoporous silica as potent antibiotic adjuvant for synergistic antibacterial therapy of MRSA

Nowadays, the emergence of antibiotic-resistant bacteria has posed a global threat to public health. However, the deployment of alternative antibiotics is lagging far behind the fast evolving antibiotic resistance, which demands effective strategies to restore drug-resistance sensitivity to available antibiotics. Here, a well-known antitumor lipoprotein complex consisted of bovine α-lactalbumin and oleic acid (BAMLET) was electrostatically adsorbed on the surface of mesoporous silica nanomaterials (MSN), forming an antibiotic adjuvant to re-sensitize methicillin-resistant Staphylococcus aureus (MRSA) to aminoglycoside antibiotics. It was found MSN of distinctive particle size may cause conformational changes of bound lipoprotein complex affecting the bactericidal performance of formed BAMLET@MSN conjugates (BMSN). Moreover, MSN was loaded with curcumin to endow obtained BMSN improved bioavailability and antioxidant capacity. The mechanistic studies revealed that antibacterial activities of BMSN originated from bacterial cell membrane disruption and biofilm inhibition, which promoted antibiotic entry and restored antibiotic bactericidal efficacy in the cell. Finally, transcriptomic analysis of MRSA indicated that BMSN interfered with bacterial amino acid metabolism, carbohydrate synthesis, and ATP translocation in bacteria. Therefore, the constructed BMSN/curcumin as potent antibiotic adjuvant provided a manipulable nanoplatform to tackle the antibiotic resistance crisis.

Highly sensitive fluorescent aptasensor based on magnetic metal-organic framework for aflatoxin B1 detection

Aflatoxin B1 (AFB1) has strong carcinogenicity, mutagenicity, and teratogenicity even at low concentrations, presenting a major risk to food safety and human health, hence, it is crucial to develop a sensitive detection technique for AFB1. Consequently, cadmium telluride (CdTe) quantum dots conjugated with AFB1 aptamers serve as fluorescent signal probes, whereas Fe3O4@UiO-66-NH2 nanocomplexes are employed as magnetic carriers and fluorescence quenchers. Fe3O4@UiO-66-NH2 reduces background signal interference, thereby enhancing detection sensitivity and Förster Resonance Energy Transfer (FRET) efficiency. We have developed a highly sensitive and selective magnetron fluorescence aptasensor based on FRET for the specific detection of AFB1. Under the ideal experimental conditions, the linear range of AFB1 is 0.001-200 ng/mL, with a linear equation of y = 0.16x+0.65 (R2 = 0.996), and the detection limit is 0.012 ng/mL. The aptasensor demonstrated superior selectivity, reproducibility, and stability for AFB1, the recoveries for real samples of corn and wheat ranged from 95 % to 103 %, demonstrating the feasibility and practicality of the sensor. Furthermore, the accuracy of the aptasensor was verified by comparison with the results of high performance liquid chromatography, indicating that the aptasensor holds significant potential for practical detection applications.

Light-activated aptasensor for plug-and-play detection of Aflatoxin B1 in food samples

BACKGROUND

AFB1 contamination in food samples is a global concern, threatening food safety and human health. Numerous assays have been developed for AFB1 detection. Among them, fluorescent aptasensors are of great interest due to their simplicity of operation, easy to read signal output. Nevertheless, these aptasensors are "passive-type", means the target AFB1 bind with the aptamer directly and cause fluorescent signal response. They are "always active", may result in undesired signal generation and the process is hard to control. Generally, the "activable-type" aptasensor would avoid these defects.

RESULTS

Here we demonstrate a light activated aptasensor for plug-and-play detection of AFB1. The aptasensor is constructed by integrating an AFB1-specific aptamer with a complementary DNA strand (PC-strand) that incorporates a photocleavable o-nitrobenzyl group. The AFB1 aptamer is locked by PC-strand preventing it binding to target AFB1. With ultraviolet (UV) light irradiation, the o-nitrobenzyl group cleaves and releases the PC-strand to two short DNA fragments. This fragmentation reduces the hybridization stability with AFB1 aptamer, allowing target AFB1 to bind efficiently to AFB1 aptamer and accompanied by increasing in fluorescence signal. The aptasensor could be activated at desired time, provides a sensitive (0.074 ng/mL) and specific method for AFB1 detection. It has been demonstrated to be a reliable tool for the analysis of AFB1 in food samples (rice, corn, and soybean), yielding satisfactory results.

SIGNIFICANCE AND NOVELTY

The aptasensor is insert to the target AFB1, while its activity could be restored in a time-resolved manner by cleaving the PC-strand to two short strands using UV light irradiation. This approach provides a promising platform for the rapid screening of AFB1 contamination in food samples, contributing to food safety and quality control.

Development of a colorimetric/fluorescence dual-mode immunoassay for aflatoxin B1 based on streptavidin-induced gold nanoparticle aggregation

A dual-mode immunoassay method was developed for colorimetric and fluorescence detection of aflatoxin B1 (AFB1) based on streptavidin-induced gold nanoparticle aggregation (AuNP@SA). AuNP-modified streptavidin-biotin labeling AFB1 complete antigen aggregations (AuNP@SA@Bio-BSA-AFB1) were synthesized as the competitive binding and dual-mode probe. AuNP@SA@Bio-BSA-AFB1 aggregations possessed high colorimetric and fluorescence quenching intensities. AFB1 antibodies modified immunomagnetic microspheres were used as the capture probe. The competitive binding between AFB1 and AuNP@SA@Bio-BSA-AFB1 leads to changes in color and fluorescence intensity. The detection limit of the colorimetric method is 6.95 ng·mL-1, while that of the fluorescence method is 0.07 ng·mL-1. The practicality of the proposed strategy was demonstrated by determining AFB1 in spiked peanut samples.

Establishment of an amplification strategy - specific binding - convenient processing integrated aflatoxin B1 detection method based on Fe3O4-NH4/AuNPs/apt-S1

Aflatoxin B1 (AFB1) is a potent toxin in food, necessitating rapid, instant, and sensitive detection. We have engineered an electrochemical sensor to monitor AFB1 using a system composed of Fe3O4-NH4/AuNPs/apt-S1. The aptamer specifically recognizes AFB1, while 'S1' is functionalized with methylene blue to enhance the current. The RecJf exonuclease promotes the formation of the electrochemical strategy. The Fe3O4 component, with its magnet properties, enables a rapid separation of solids and liquids without the need for instrumentation. The sensor exhibits a linear range for AFB1 ranging from 1 ng to 10 μg. The regression equation is I(nA) = 446.8 × logc+2085 (where I and c represent the peak current and AFB1 concentration, respectively). The correlation coefficient is 0.9508, and the detection limit is 3.447 nM. The relative standard deviation of AFB1 in peanut oil ranges from 4.80% to 6.80%. These results demonstrate that the sensor has high sensitivity, stability, repeatability, and specificity for AFB1 detection.

Triple-helix molecular-switch-actuated rolling circle amplification and catalytic hairpin assembly multistage signal amplified fluorescent aptasensor for detection of aflatoxin B1

BACKGROUND

Mycotoxins, a class of secondary metabolites produced by molds, are widely distributed in nature and are very common in food contamination. Aflatoxin B1 (AFB1) is a highly stable natural mycotoxin, and many agricultural products are easily contaminated by AFB1, it is important to establish a sensitive and efficient AFB1 detection method for food safety. The fluorescence aptamer sensor has shown satisfactory performance in AFB1 detection, but most of the fluorescence aptasensors are not sensitive enough, so improving the sensitivity of the aptasensor becomes the focus of this work.

RESULTS

Herein, an innovative fluorescent aptasensor for AFB1 detection which is based on catalytic hairpin assembly (CHA) and rolling circle amplification (RCA) driven by triple helix molecular switch (THMS) is proposed. A functional single-strand with an AFB1 aptamer, here called an APF, is first designed to lock onto the signal transduction probe (STP), which separates from THMS when target AFB1 is present. Subsequently, STP initiates the RCA reaction along the circular probe, syntheses macro-molecular mass products through repeated triggering sequences, triggers the CHA reaction to produce a large number of H1-H2 structures, which causes FAM to move away from BHQ-1 and recover its fluorescence signal. The fluorescence signal from FAM at 520 nm was collected as the signal output of aptasensor in this work. With high amplification efficiency of RCA and CHA of the fluorescence sensor, resulting in a low LOD value of 2.95 pg mL-1(S/N = 3).

SIGNIFICANCE

The successful establishment of the sensor designed in this work shows that the cascade amplification reaction is perfectly applied in the fluorescent aptamer sensor, and the signal amplification through the reaction between DNA strands is a simple and efficient method. In addition, it's also important to remember that the aptasensor can detect other targets only by changing the sequence of the aptamer, without redesigning other DNA sequences in the reaction system.

A dual-mode fluorescence and colorimetric sensing platform for efficient detection of ofloxacin in aquatic products using iron alkoxide nanozyme

Trace detection of ofloxacin (OFL) with high sensitivity, reliability, and visual clarity is challenging. To address this, a novel dual-modal aptasensor with fluorescence-colorimetric capabilities was designed that exploit the target-induced release of 3,3',5,5'-tetramethylbenzidine (TMB) molecules from aptamer-gated mesoporous silica nanoparticles (MSNs), the oxidase-like activity of iron alkoxide (IA) nanozyme, and the fluorescence attributes of core-shell upconversion nanoparticles. Therefore, the study reports a dual mode detection, with a fluorescence detection range for OFL spanning from 0.1 μg/kg to 1000 μg/kg (and a detection limit of 0.048 μg/kg). Additionally, the colorimetric method offered a linear detection range of 0.3 μg/kg to 1000 μg/kg, with a detection limit of 0.165 μg/kg. The proposed biosensor had been successfully applied to the determination of OFL content in real samples with satisfactory recoveries (78.24-96.14 %).

Development of a label-free, sensitive gold nanoparticles-poly(adenine) aptasensing platform for colorimetric determination of aflatoxin B1 in corn

In this work, a sensitive colorimetric bioassay method based on a poly(adenine) aptamer (polyA apt) and gold nanoparticles (AuNPs) was developed for the determination of aflatoxin B1 (AFB1). The polyA apt, adsorbed on the AuNPs, especially can bind to the analyte while deterring non-specific interactions. This nano aptasensor uses cationic polymer poly(diallyl dimethyl ammonium chloride) (PDDA), as an aggregating agent, to aggregate gold nanoparticles. PolyA apt-decorated gold nanoparticles (AuNPs/polyA apt) show resistance to PDDA-induced aggregation and maintains their dispersed state (red color) with the optical absorbance signal at λ = 520 nm. However, in the presence of AFB1 in the assay solution, the specific aptamer reacts with high affinity and folds into its three-dimensional form. Aggregation of AuNPs induced by PDDA caused their optical signal shift to λ = 620 nm (blue color). AFB1 concentration in the bioassay solution determines the amount of optical signal shift. Therefore, optical density ratio in two wavelengths (A620/520) can be used as a sturdy colorimetric signal to detect the concentration of aflatoxin B1. AFB1 was linearly detected between 0.5 and 20 ng mL-1, with a detection limit of 0.09 ng mL-1 (S/N = 3). The fabricated aptasensor was applied to the detection of AFB1 in real corn samples.

An ultra-sensitive SARS-CoV-2 antigen optical biosensor based on angiotensin converting enzyme 2 (ACE-2) functionalized magnetic-fluorescent silica nanoparticles

This work reports on the design and synthesis of an angiotensin-converting enzyme 2 (ACE-2) functionalized magnetic fluorescent silica nanoparticles (Fe-FSNP) as a biosensing platform to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen. Iron oxide (Fe3O4) nanoparticles were synthesized via ultrasonic-assisted coprecipitation and then coated with fluorescent silica nanoparticles (FSNP) through thesol-gelmethod forming the Fe-FSNP samples. Silica obtained from local geothermal powerplant was used in this work and Rhodamine B was chosen as the incorporated fluorescent dye, hence this reports for the first time ACE-2 was immobilized on the natural silica surface. The Fe-FSNP nanoparticle consists of a 18-25 nm magnetic core and a silica shell with a thickness of 30 nm as confirmed from the transmission electron microscopy image. Successful surface functionalization of the Fe-FSNP with ACE-2 as bioreceptor was conducted through hydrosylilation reaction and confirmed through the Fourier transform infrared spectroscopy. The detection of SARS-Cov-2 antigen by Fe-FSNP/ACE2 was measured through the change in its maximum fluorescence intensity at 588 nm where fluorescence- quenching had occurred. The biosensing platform showed a rapid response at 30 min with a linear range of 10-6to 10-2μg ml-1. The magnetic-fluorescent properties of the nanoparticle enables an ultra-sensitive detection of SARS-Cov-2 antigen with the limit of detection as low as 2 fg ml-1.

Cas12a-based direct visualization of nanoparticle-stabilized fluorescence signal for multiplex detection of DNA methylation biomarkers

The CRISPR-Cas12a RNA-guided complexes hold immense promise for nucleic acid detection. However, limitations arise from their specificity in detecting off-targets and the stability of the signal molecules. Here, we have developed a platform that integrates multiplex amplification and nanomolecular-reporting signals, allowing us to detect various clinically relevant nucleic acid targets with enhanced stability, sensitivity, and visual interpretation. Through the electrostatic co-assembly of the Oligo reporter with oppositely charged nanoparticles, we observed a significant enhancement in its stability in low-pollution environments, reaching up to a threefold increase compared to the original version. Additionally, the fluorescence efficiency was expanded by three orders of magnitude, broadening the detection range considerably. Utilizing a multiplex strategy, this assay can accomplish simultaneous detection of multiple targets and single-point indication detection of nine specific targets. This significant advancement heightened the sensitivity of disease screening and improved the accuracy of diagnosing disease-related changes. We tested this assay in a colorectal cancer model, demonstrating that it can identify DNA methylation features at the aM-level within 40-60 min. Validation using clinical samples yielded consistent results with qPCR and bisulfite sequencing, affirming the assay's reliability and potential for clinical applications.

A Fluorescence Resonance Energy Transfer Aptasensor for Aflatoxin B1 Based on Ligand-Induced ssDNA Displacement

In this study, a fluorescence resonance energy transfer (FRET)-based aptasensor for the detection of aflatoxin B1 (AFB1) was designed using a carboxyfluorescein (FAM)-labeled aptamer and short complementary DNA (cDNA) labeled with low molecular quencher RTQ1. The sensing principle was based on the detection of restored FAM-aptamer fluorescence due to the ligand-induced displacement of cDNA in the presence of AFB1, leading to the destruction of the aptamer/cDNA duplex and preventing the convergence of FAM and RTQ1 at the effective FRET distance. Under optimal sensing conditions, a linear correlation was obtained between the fluorescence intensity of the FAM-aptamer and the AFB1 concentration in the range of 2.5-208.3 ng/mL with the detection limit of the assay equal to 0.2 ng/mL. The assay time was 30 min. The proposed FRET aptasensor has been successfully validated by analyzing white wine and corn flour samples, with recovery ranging from 76.7% to 91.9% and 84.0% to 86.5%, respectively. This work demonstrates the possibilities of labeled cDNA as an effective and easily accessible tool for sensitive AFB1 detection. The homogeneous FRET aptasensor is an appropriate choice for contaminant screening in complex matrices.

A Novel Fluorescent Aptasensor Based on Mesoporous Silica Nanoparticles for Selective and Sensitive Detection of Saxitoxin in Shellfish

Background:

Saxitoxin (STX) stands as one of the most potent marine biotoxins, exhibiting high lethality. Despite its severity, current treatments remain ineffective, and existing detection techniques are limited due to ethical concerns and technical constraints.

Methods:

Herein, an innovative approach was constructed for STX detection, utilizing mesoporous silica nanoparticles (MSN) as a foundation. This innovative, easy, and label-free aptamer (Apt)- sensor was fabricated. Apts were employed as molecular identification probes and "gated molecules," while rhodamine 6G was encapsulated within particles to serve as a signal probe. In a lack of STX, Apts immobilized on an MSN surface kept a "gate" closed, preventing signal probe leakage. Upon the presence of STX, the "gate" opened, allowing a particular binding of Apts to STX and a subsequent release of a signal probe.

Results:

Experimental results demonstrated a positive correlation between fluorescence intensity and concentrations of STX within a range of 1 to 80 nM, with an exceptional limit of detection of 0.12 nM. Furthermore, the selectivity and stability of a biosensor were rigorously evaluated, validating its reliability.

Conclusion:

This newly developed sensing strategy exhibits remarkable performance in STX detection. Its success holds significant promise for advancing portable STX detection equipment, thereby addressing a pressing need for efficient and ethical detection methods in combating marine biotoxin contamination.

Recent Advances in Biological Applications of Aptamer-Based Fluorescent Biosensors

Aptamers have been spotlighted as promising bio-recognition elements because they can be tailored to specific target molecules, bind to targets with a high affinity and specificity, and are easy to chemically synthesize and introduce functional groups to. In particular, fluorescent aptasensors are widely used in biological applications to diagnose diseases as well as prevent diseases by detecting cancer cells, viruses, and various biomarkers including nucleic acids and proteins as well as biotoxins and bacteria from food because they have the advantages of a high sensitivity, selectivity, rapidity, a simple detection process, and a low price. We introduce screening methods for isolating aptamers with q high specificity and summarize the sequences and affinities of the aptamers in a table. This review focuses on aptamer-based fluorescence detection sensors for biological applications, from fluorescent probes to mechanisms of action and signal amplification strategies.

Meeting Contemporary Challenges: Development of Nanomaterials for Veterinary Medicine

In recent decades, nanotechnology has been rapidly advancing in various fields of human activity, including veterinary medicine. The review presents up-to-date information on recent advancements in nanotechnology in the field and an overview of the types of nanoparticles used in veterinary medicine and animal husbandry, their characteristics, and their areas of application. Currently, a wide range of nanomaterials has been implemented into veterinary practice, including pharmaceuticals, diagnostic devices, feed additives, and vaccines. The application of nanoformulations gave rise to innovative strategies in the treatment of animal diseases. For example, antibiotics delivered on nanoplatforms demonstrated higher efficacy and lower toxicity and dosage requirements when compared to conventional pharmaceuticals, providing a possibility to solve antibiotic resistance issues. Nanoparticle-based drugs showed promising results in the treatment of animal parasitoses and neoplastic diseases. However, the latter area is currently more developed in human medicine. Owing to the size compatibility, nanomaterials have been applied as gene delivery vectors in veterinary gene therapy. Veterinary medicine is at the forefront of the development of innovative nanovaccines inducing both humoral and cellular immune responses. The paper provides a brief overview of current topics in nanomaterial safety, potential risks associated with the use of nanomaterials, and relevant regulatory aspects.

Progress in Fluorescence Biosensing and Food Safety towards Point-of-Detection (PoD) System

The detection of pathogens in food substances is of crucial concern for public health and for the safety of the natural environment. Nanomaterials, with their high sensitivity and selectivity have an edge over conventional organic dyes in fluorescent-based detection methods. Advances in microfluidic technology in biosensors have taken place to meet the user criteria of sensitive, inexpensive, user-friendly, and quick detection. In this review, we have summarized the use of fluorescence-based nanomaterials and the latest research approaches towards integrated biosensors, including microsystems containing fluorescence-based detection, various model systems with nano materials, DNA probes, and antibodies. Paper-based lateral-flow test strips and microchips as well as the most-used trapping components are also reviewed, and the possibility of their performance in portable devices evaluated. We also present a current market-available portable system which was developed for food screening and highlight the future direction for the development of fluorescence-based systems for on-site detection and stratification of common foodborne pathogens.

Palladium encapsulated mesoporous silica nanoparticles for the rapid detection of analytes

We designed a simple, inexpensive, and user-friendly assay using mesoporous silica nanoparticles to detect analytes.

Dual fluorescent aptasensor for simultanous and quantitative detection of sulfadimethoxine and oxytetracycin residues in animal-derived foods tissues based on mesoporous silica

Herein, we developed a dual fluorescent aptasensor based on mesoporous silica to simultaneously detect sulfadimethoxine (SDM) and oxytetracycline (OTC) in animal-derived foods. We immobilized two types of aptamers modified with FAM and CY5 on the silica surface by base complementary pairing reaction with the cDNA modified with a carboxyl group and finally formed the aptasensor detection platform. Under optimal conditions, the detection range of the aptasensor for SDM and OTC was 3-150 ng/mL (R ² = 0.9831) and 5-220 ng/mL (R ² = 0.9884), respectively. The limits of detection for SDM and OTC were 2.2 and 1.23 ng/mL, respectively. The limits of quantification for SDM and OTC were 7.3 and 4.1 ng/mL, respectively. Additionally, the aptasensor was used to analyze spiked samples. The average recovery rates ranged from 91.75 to 114.65% for SDM and 89.66 to 108.94% for OTC, and all coefficients of variation were below 15%. Finally, the performance and practicability of our aptasensor were confirmed by HPLC, demonstrating good consistency. In summary, this study was the first to use the mesoporous silica-mediated fluorescence aptasensor for simultaneous detection of SDM and OTC, offering a new possibility to analyze other antibiotics, biotoxins, and biomolecules.

Chitosan coated fluorescent mesoporous silica for the sensitive and selective detection of H2O2

A novel turn-on fluorescent sensor for hydrogen peroxide (H₂O₂) was prepared from chitosan (CS) coating mesoporous silica nanoparticles (MSNs) loaded with 1-(4-Aminophenyl)-1,2,2-triphenylethene (TPE-NH₂) and silver nanoparticles (AgNCs). The surface of MSNs was coated by CS as the gatekeeper and the template for loading of AgNCs. Because of the surface plasmon-enhanced energy transfer (SPEET), AgNCs effectively quenched the fluorescence emission of nanoparticles. In the presence of H₂O₂, AgNCs can be oxidized to Ag⁺, resulting in the recovery of fluorescence. This fluorescent sensor was characterized with respect to its chemical composition, morphological features and optical properties by means of FTIR, XRD, TGA, SEM, TEM, XPS, UV-Vis and fluorescence spectroscopy. The MSN/TPE-CS@Ag nanoparticles showed good sensitivity and selectivity for H₂O₂ even with various interfering ions and agents. Under optimized conditions, the detection limit for H₂O₂ was 0.64 μM in the rage of 1-300 μM. The feasibility of the practical application of this probe was confirmed by accurate quantitative of H₂O₂ in practical samples.

Recent Progress on Techniques in the Detection of Aflatoxin B1 in Edible Oil: A Mini Review

Contamination of agricultural products and foods by aflatoxin B1 (AFB1) is becoming a serious global problem, and the presence of AFB1 in edible oil is frequent and has become inevitable, especially in underdeveloped countries and regions. As AFB1 results from a possible degradation of aflatoxins and the interaction of the resulting toxic compound with food components, it could cause chronic disease or severe cancers, increasing morbidity and mortality. Therefore, rapid and reliable detection methods are essential for checking AFB1 occurrence in foodstuffs to ensure food safety. Recently, new biosensor technologies have become a research hotspot due to their characteristics of speed and accuracy. This review describes various technologies such as chromatographic and spectroscopic techniques, ELISA techniques, and biosensing techniques, along with their advantages and weaknesses, for AFB1 control in edible oil and provides new insight into AFB1 detection for future work. Although compared with other technologies, biosensor technology involves the cross integration of multiple technologies, such as spectral technology and new nano materials, and has great potential, some challenges regarding their stability, cost, etc., need further studies.

Oxygen Free Radical Scavenger PtPd@PDA as a Dual-Mode Quencher of Electrochemiluminescence Immunosensor for the Detection of AFB1

Here, a dual-mode quenched electrochemiluminescence (ECL) immunosensor based on PtPd@PDA was proposed. Among them, nitrogen-doped hydrazide conjugated carbon dots (NHCDs), as an ECL emitter and a donor of resonance energy transfer, were quenched by PtPd@PDA (receptor). At the same time, PDA in PtPd@PDA, as an oxygen radical scavenger, completed the further quenching of the ECL signal by consuming O₂^•- generated by the decomposition of co-reactant H₂O₂. The dual-mode quenching from the above two channels was achieved. In addition, compared with the traditional carbon quantum dots, NHCDs as ECL emitters had lower excitation potential. Moreover, a large number of amino groups provided by aminated MWCNTs could capture more antibodies while connecting with NHCDs. Under the optimum experimental conditions, taking aflatoxin B1 as the target, the proposed sensor with good specificity, stability, and reproducibility had good linearity when the concentration of AFB1 was 0.01-100 ng/mL, with the detection limit of 2.63 pg/mL (S/N = 3). This strategy provided more possibilities for the application of dopamine metal nanocomposites in electrochemiluminescence analysis and offered a new approach to detect AFB1.

Recent progress in fluorescent aptasensors for the detection of aflatoxin B1 in food

Aflatoxin B1 pollution is one of the most critical issues of food safety and has been categorized as a group I carcinogen by the International Agency for Research on Cancer. Aflatoxin B1 exists in various foods and feedstuff products and can be produced and contaminate food products in all processes, including growth, harvest, storage, or processing. Therefore, it is of great value for detecting and on-site monitoring aflatoxin B1. Aptamers are short single-stranded DNA or RNA obtained from the nucleic acid molecular library through SELEX. With advantages of high specificity, large affinity, and easy modification, aptasensors have become popular in a wide range of promising applications. This review focuses on recent advances on fluorescent aptamer sensors for the detection of aflatoxin B1, including their design strategies, working mechanisms, and applications to on-site detection. Finally, the current challenges and prospects are discussed.

Combining Electrochemiluminescence Detection with Aptamer-Gated Indicator Releasing Mesoporous Nanoparticles Enables ppt Sensitivity for Strip-Based Rapid Tests

The combination of electrogenerated chemiluminescence (ECL) and aptamer-gated indicator delivering (gAID) magnetic mesoporous silica nanoparticles embedded into glass fibre paper functionalised with poly(ethyleneglycol) and N-(3-triethoxysilylpropyl)diethanolamine allowed the development of a rapid test that detects penicillin directly in diluted milk down to 50±9 ppt in <5 min. Covalent attachment of the aptamer "cap" to the silica scaffold enabled pore closure through non-covalent electrostatic interactions with surface amino groups, while binding of penicillin led to a folding-up of the aptamer thus releasing the ECL reporter Ru(bpy)32+ previously loaded into the material and letting it be detected after lateral flow by a smartphone camera upon electrochemical excitation with a screen printed electrode inserted into a 3D-printed holder. The approach is simple, generic and presents advantages with respect to sensitivity, measurement uncertainty and robustness compared with conventional fluorescence or electrochemical detection, especially for point-of-need analyses of challenging matrices and analytes at ultra-trace levels.

A signal-enhancement fluorescent aptasensor based on the stable dual cross DNA nanostructure for simultaneous detection of OTA and AFB1

The simultaneous detection of multiple mycotoxins is of great significance for food safety and human health. Herein, a simple, convenient and accurate fluorescent aptasensor was designed based on the dual cross DNA nanostructure for the simultaneous detection of ochratoxin A (OTA) and aflatoxin B₁ (AFB₁), in which the stable dual cross DNA nanostructure provided an assay platform using the fluorescent dye-labeled aptamers as a sensing element. Owing to the higher affinity of aptamers for their target, the aptamer probes were released from the assay platform in the presence of OTA and AFB₁, resulting in an enhanced fluorescence at 570 nm and 670 nm. This "signal-on" fluorescent aptasensor assay system can effectively avoid background signals and minimize false positive. Furthermore, the designed method can realize the simultaneous detection of OTA and AFB₁ during the whole experiment. The limits of detection (LOD) were as low as 0.0058 ng/mL for OTA, ranging from 0.01 to 50 ng/mL and 0.046 ng/mL for AFB₁, ranging from 0.05 to 100 ng/mL. The proposed fluorescent aptasensor exhibits excellent performance in practical application and provides a novel approach for the simultaneous detection of multiple mycotoxins by simply changing the aptamers. A "signal-on" fluorescent aptasensor assay system based on the stable dual cross DNA nanostructure was successfully developed for simultaneous detection of OTA and AFB₁ with lower detection limits in wider linear ranges.

Aptasensors for mycotoxins in foods: Recent advances and future trends

Mycotoxin contamination in foods has posed serious threat to public health and raised worldwide concern. The development of simple, rapid, facile, and cost-effective methods for mycotoxin detection is of urgent need. Aptamer-based sensors, abbreviated as aptasensors, with excellent recognition capacity to a wide variety of mycotoxins have attracted ever-increasing interest of researchers because of their simple fabrication, rapid response, high sensitivity, low cost, and easy adaptability for in situ measurement. The past few decades have witnessed the rapid advances of aptasensors for mycotoxin detection in foods. Therefore, this review first summarizes the reported aptamer sequences specific for mycotoxins. Then, the recent 5-year advancements in various newly developed aptasensors, which, according to the signal output mode, are divided into electrochemical, optical and photoelectrochemical categories, for mycotoxin detection are comprehensively discussed. A special attention is taken on their strengths and limitations in real-world application. Finally, the current challenges and future perspectives for developing novel highly reliable aptasensors for mycotoxin detection are highlighted, which is expected to provide powerful references for their thorough research and extended applications. Owing to their unique advantages, aptasensors display a fascinating prospect in food field for safety inspection and risk assessment.

A Novel Colorimetric Nano Aptasensor for Ultrasensitive Detection of Aflatoxin B1 Based on the Exonuclease III-Assisted Signal Amplification Approach

The detection of aflatoxin B1 (AFB1) has recently garnered much attention on the issue of food safety. In this study, a novel and sensitive aptasensor towards AFB1 is proposed using an Exonuclease III (Exo III)-integrated signal amplification strategy. This reported sensing strategy is regulated by aptamer-functionalized nanobeads that can target AFB1; furthermore, complementary DNA (cDNA) strands can lock the immobilized aptamer strands, preventing the signal amplification function of Exo III in the absence of AFB1. The presence of AFB1 triggers the displacement of cDNA, which will then activate the Exo III-integrated signal amplification procedure, resulting in the generation of a guanine (G)-rich sequence to form a G-4/hemin DNAzyme, which can catalyze the substrate of ABTS to produce a green color. Using this method, a practical detection limit of 0.0032 ng/mL and a dynamic range of detection from 0.0032 to 50 ng/mL were obtained. Additionally, the practical application of the established sensing method for AFB1 in complex matrices was demonstrated through recovery experiments. The recovery rate and relative standard deviations (RSD) in three kinds of cereal samples ranged from 93.83% to 111.58%, and 0.82% to 7.20%, respectively, which were comparable with or better than previously reported methods.

Carbon Dots/α-Fe2O3-Fe3O4 nanocomposite: Efficient synthesis and application as a novel electrochemical aptasensor for the ultrasensitive determination of aflatoxin B1

Developing an effective method for the detection of aflatoxin B1 (AFB1) remains an arduous task due to the high toxicity of AFB1 to a health concern. In this study, a sensitive and reliable electrochemical aptasensor based on carbon dots/α-Fe₂O₃-Fe₃O₄ nanocomposite (CDs/α-Fe₂O₃-Fe₃O₄) is constructed for the determination of AFB1. The CDs have good electrical conductivity and large specific surface areas to improve the aptasensor's sensitivity. The α-Fe₂O₃-Fe₃O₄ can not only improve the catalytic performance of the aptasensor but also have magnetism, which can realize the recovery of CDs/α-Fe₂O₃-Fe₃O₄ to avoid material waste and environmental pollution. This electrochemical aptasensor can achieve a good linear (0.001-100.0 nM) and excellent detection limit (0.5 pM) for the determination of AFB1. In addition, the aptasensor was also applied to determine AFB1 in beer, rice, and peanuts, all results were in good agreement with HPLC, indicating that the electrochemical aptasensor has a broad application prospect.

Enhanced Detection of Major Pathogens and Toxins in Poultry and Livestock With Zoonotic Risks Using Nanomaterials-Based Diagnostics

Nanotechnology has gained prominence over the recent years in multiple research and application fields, including infectious diseases in healthcare, agriculture, and veterinary science. It remains an attractive and viable option for preventing, diagnosing, and treating diseases in animals and humans. The apparent efficiency of nanomaterials is due to their unique physicochemical properties and biocompatibility. With the persistence of pathogens and toxins in the poultry and livestock industries, rapid diagnostic tools are of utmost importance. Though there are many promising nanomaterials-based diagnostic tests specific to animal disease-causing agents, many have not achieved balanced sensitivity, specificity, reproducibility, and cost-effectiveness. This mini-review explores several types of nanomaterials, which provided enhancement on the sensitivity and specificity of recently reported diagnostic tools related to animal diseases. Recommendations are also provided to facilitate more targeted animal populations into the development of future diagnostic tools specifically for emerging and re-emerging animal diseases posing zoonotic risks.

An overview of nanomaterial based biosensors for detection of Aflatoxin B1 toxicity in foods

Aflatoxin B1 (AFB1) is one of the most potent mycotoxin contaminating several foods and feeds. It suppresses immunity and consequently increases mutagenicity, carcinogenicity, teratogenicity, hepatotoxicity, embryonic toxicity and increasing morbidity and mortality. Continuous exposure of AFB1 causes liver damage and thus increases the prevalence of cirrhosis and hepatic cancer. This article was planned to provide understanding of AFB1 toxicity and provides future directions for fabrication of cost effective and user-friendly nanomaterials based analytical devices. In the present article various conventional (chromatographic & spectroscopic), modern (PCR & immunoassays) and nanomaterials based biosensing techniques (electrochemical, optical, piezoelectrical and microfluidic) are discussed alongwith their merits and demerits. Nanomaterials based amperometric biosensors are found to be more stable, selective and cost-effective analytical devices in comparison to other biosensors. But many unresolved issues about their stability, toxicity and metabolic fate needs further studies. In-depth studies are needed for development of advanced nanomaterials integrated biosensors for specific, sensitive and fast monitoring of AFB1 toxicity in foods. Integration of biosensing system with micro array technology for simultaneous and automated detection of multiple AFs in real samples is also needed. Concerted efforts are also required to reduce their possible hazardous consequences of nanomaterials based biosensors.

Recent advances in aptamer-based sensors for aminoglycoside antibiotics detection and their applications

Aminoglycoside antibiotics (AAs) have been extensively applied in medical field and animal husbandry owing to desirable broad-spectrum antibacterial activity. Excessive AAs residues in the environment can be accumulated in human body through food chain and cause detrimental effect on human health. The establishment of highly specific, simple and sensitive detection methods for monitoring AAs residues is highly in demand. Aptasensor using aptamer as the biological recognition element is the efficient and promising sensing method for detection of AAs. In this review, we have made a summary of specific aptamers sequences against AAs. Subsequently, we provide a systematical and comprehensive overview of modern techniques in aptasensors for detection of AAs according to optical aptasensors as well as electrochemical aptasensors and further summarize their advantages and disadvantages to compare their applications. In addition, we present an overview of practical applications of aptasensors in sample detection of AAs. Moreover, the current challenges and future trends in this field are also included to reveal a promising perspective for developing novel aptasensors for AAs.

Aptasensors for mycotoxin detection: A review

Mycotoxins are toxic compounds produced by fungi, which represent a risk to the food and feed supply chain, having an impact on health and economies. A high percentage of feed samples have been reported to be contaminated with more than one type of mycotoxin. Systematic, cost-effective and simple tools for testing are critical to achieve a rapid and accurate screening of food and feed quality. In this review, we describe the various aptamers that have been selected against mycotoxins and their incorporation into optical and electrochemical aptasensors, outlining the strategies exploited, highlighting the advantages and disadvantages of each approach. The review also discusses the different materials used and the immobilization methods employed, with the aim of achieving the highest sensitivity and selectivity.

Rapid and label free detection of aflatoxin B1 in alcoholic beverages with a microfluid fiber device

A rapid and label free aflatoxin B₁ (AFB₁) microfluid sensor was proposed and tested. The device was fabricated with hollow-core photonics crystal fiber infiltrated with the AFB₁ solution. The autofluorescence emitting from the AFB₁ molecules was detected. The sensor length was optimized. The AFB₁ concentration was tested with a 4 cm long sensor. The best limit of detection was achieved as low as 1.34 ng/ml, which meets the test requirement of the national standards for AFB₁ in food. The effectiveness of this sensor being applied in beer solution was also verified to be a little more sensitive than in aqueous solution. Compared with traditional AFB₁ detection methods, the proposed single-ended device perfectly satisfies the demand of process control in alcoholic beverages manufacture.

Mesoporous Materials-Based Electrochemical Biosensors from Enzymatic to Nonenzymatic

Mesoporous materials have drawn more and more attention in the field of biosensors due to their high surface areas, large pore volumes, tunable pore sizes, as well as abundant frameworks. In this review, the progress on mesoporous materials-based biosensors from enzymatic to nonenzymatic are highlighted. First, recent advances on the application of mesoporous materials as supports to stabilize enzymes in enzymatic biosensing technology are summarized. Special emphasis is placed on the effect of pore size, pore structure, and surface functional groups of the support on the immobilization efficiency of enzymes and the biosensing performance. Then, the development of a nonenzymatic strategy that uses the intrinsic property of mesoporous materials (carbon, silica, metals, and composites) to mimic the behavior of enzymes for electrochemical sensing of some biomolecules is discussed. Finally, the challenges and perspective on the future development of biosensors based on mesoporous materials are proposed.

The pH-triggered drug release and simultaneous carrier decomposition of effervescent SiO2-drug-Na2CO3 composite nanoparticles: to improve the antitumor activity of hydrophobic drugs

To achieve a better release effect of hydrophobic drugs and spontaneous nanocarrier disintegration by dissolution as well as the CO₂ production of Na₂CO₃ further, improving the therapeutic effect of hydrophobic drugs, and thereby avoiding the accumulation of the nanocarrier in vivo to produce organ toxicity, effervescent SiO₂–drug–Na₂CO₃ composite nanoparticles (ESNs) were prepared in this study using a tetraethyl orthosilicate hydrolysis method. Sodium carbonate was used as the effervescent disintegrant to respond to the acidic microenvironment of the tumor. The properties of ESNs were assessed and TEM images were taken to verify the self-disintegration characteristics of nanocarrier materials. The in vitro anticancer efficacy of ESNs was evaluated in human breast cancer MCF-7 cells. ESNs loaded with hydrophobic drugs were successfully constructed, and showed high entrapment efficiency and drug loading. The nanocarrier successfully achieved self-disintegration in a PBS environment of pH value at 5.0, and showed excellent antitumor effect in vitro. ESNs can effectively load hydrophobic drugs and achieve self-disintegration, while avoiding toxicity from the accumulation of the nanocarrier. These results suggest that ESNs are a promising drug delivery system capable of maximizing the anticancer therapeutic efficacy and minimizing the systemic toxicity.

Effervescent SiO₂–drug–Na₂CO₃ composite nanoparticles were prepared in this study using a tetraethyl orthosilicate hydrolysis method to achieve a better release effect of hydrophobic drugs and spontaneous nanocarrier disintegration by dissolution.