Label free structure-switching fluorescence polarization detection of chloramphenicol with truncated aptamer

Ultrasensitive detection strategy for CAP by molecularity imprinted SERS sensor based on multiple synergistic enhancement of SiO2@AuAg with MOFs@Au signal carrier

Chloramphenicol (CAP) residue in food can cause great harm to human health, it is important to develop a rapid and sensitive method to detect CAP. Here, molecularly imprinted polymer (MIP) was combined with metal-organic frameworks@Au (MOFs@Au) collaborative construction surface-enhanced Raman spectroscopy (SERS) based aptasensor for CAP ultrasensitive detection. MOFs@Au first carried the Raman signal molecule toluidine blue (TB) and aptamer to form MOFs@Au@TB@Apt. In addition, rMIP (CAP was removed) was dropped onto the uniform three-dimensional (3D) SERS substrate SiO2@AuAg to form SiO2@AuAg@rMIP. In the presence of target CAP, it could be specifically captured with rMIP by covalent interaction and was recognised by the aptamer. During this time, SiO2@AuAg@rMIP@CAP could selectively connect MOFs@Au@TB@Apt to realise synergistic enhance the Raman signal. Based on this principle, the proposed SERS aptasensor exhibits excellent sensitivity with a detection limit of 7.59×10-13 M for CAP, providing a new strategy for trace detection in food.

A reusable screen-printed carbon electrode-based aptasensor for the determination of chloramphenicol in food and environment samples

An electrochemical aptasensor was developed for the determination of chloramphenicol (CAP) in fresh foods and food products. The aptasensor was developed using Prussian blue (PB) and chitosan (CS) film. PB acts as a redox probe for detection and CS acts as a sorption material. The aptamer (Apt) was immobilized on a screen-printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs). Under optimum conditions, the linearity of the aptasensor was between 1.0 and 6.0 × 106 ng L-1 with a detection limit of 0.65 and a quantification limit of 2.15 ng L-1. The electrode could be regenerated up to 24 times without the use of chemicals. The aptasensor showed good repeatability (RSD <11.2%) and good reproducibility (RSD <7.7%). The proposed method successfully quantified CAP in milk, shrimp pond water and shrimp meat with good accuracy (recovery = 88.0 ± 0.6% to 100 ± 2%). The proposed aptasensor could be especially useful in agriculture to ensure the quality of food and the environment and could be used to determine other antibiotics.

Dual-Track Multifunctional Bimetallic Metal-Organic Frameworks for Antibiotic Enrichment and Detection

The improper use and overuse of antibiotics have led to significant burdens and detrimental effects on the environment, food supply, and human health. Herein, a magnetic solid-phase extraction program and an optical immunosensor based on bimetallic Ce/Zr-UiO 66 for the detection of antibiotics are developed. A magnetic Fe3O4@SiO2@Ce/Zr-UiO 66 metal-organic framework (MOF) is prepared to extract and enrich chloramphenicol from fish, wastewater, and urine samples, and a horseradish peroxidase (HRP)-Ce/Zr-UiO 66@bovine serum protein-chloramphenicol probe is used for the sensitive detection of chloramphenicol based on the dual-effect catalysis of Ce and HRP. In this manner, the application of Ce/Zr-UiO 66 in integrating sample pretreatment and antibiotic detection is systematically investigated and the associated mechanisms are explored. It is concluded that Ce/Zr-UiO 66 is a versatile dual-track material exhibiting high enrichment efficiency (6.37 mg g-1) and high sensitivity (limit of detection of 51.3 pg mL-1) for chloramphenicol detection and serving as a multifunctional MOF for safeguarding public health and hygiene.

Selection and characterization of ssDNA aptamer targeting Macrobrachium rosenbergii nodavirus capsid protein: A potential capture agent in gold-nanoparticle-based aptasensor for viral protein detection

The giant freshwater prawn holds a significant position as a valuable crustacean species cultivated in the aquaculture industry, particularly well-known and demanded among the Southeast Asian countries. Aquaculture production of this species has been impacted by Macrobrachium rosenbergii nodavirus (MrNV) infection, which particularly affects the larvae and post-larvae stages of the prawn. The infection has been recorded to cause mortality rates of up to 100% among the affected prawns. A simple, fast, and easy to deploy on-site detection or diagnostic method is crucial for early detection of MrNV to control the disease outbreak. In the present study, novel single-stranded DNA aptamers targeting the MrNV capsid protein were identified using the systematic evolution of ligands by exponential enrichment (SELEX) approach. The aptamer was then conjugated with the citrate-capped gold nanoparticles (AuNPs), and the sensitivity of this AuNP-based aptasensor for the detection of MrNV capsid protein was evaluated. Findings revealed that the aptamer candidate, APT-MrNV-CP-1 was enriched throughout the SELEX cycle 4, 9, and 12 with the sequence percentage of 1.76%, 9.09%, and 12.42%, respectively. The conjugation of APT-MrNV-CP-1 with citrate-capped AuNPs exhibited the highest sensitivity in detecting the MrNV capsid protein, where the presence of 62.5 nM of the viral capsid protein led to a significant agglomeration of the AuNPs. This study demonstrated the practicality of an AuNP-based aptasensor for disease diagnosis, particularly for detecting MrNV infection in giant freshwater prawns.

A novel Recjf Exo signal amplification strategy based on bioinformatics-assisted truncated aptamer for efficient fluorescence detection of AFB1

Aflatoxin B1 (AFB1) is a typical mycotoxin that signifacntly endangers public health and economy. In this study, we systematically studied the interaction of aptamers with AFB1 using circular dichroism, molecular dynamics, molecular docking, and fluorescence analysis. The truncated sequence aptamers were screened using molecular docking. We successfully obtained the AFB1 aptamer with higher affinity and its truncated form was enhanced by 5.2-fold compared to the initial AFB1 aptamer. In addition, for rapid detection of AFB1, we designed a fluorescent nano-adaptor sensing platform using RecJf exonuclease signal amplification strategy based on the optimal aptamer. The aptasensor showed satisfactory sensitivity towards AFB1 with a linear detection range of 1-400 ng/mL and a detection limit of 0.57 ng/mL. The aptasensor was successfully applied to the determination of AFB1 in soybean oil and corn oil with recoveries of 91.02 %-106.59 % and 87.39 %-110.61 %, respectively. The successful application of the AFB1 aptasensor, developed through bioinformatics truncation of the aptamer, provides a novel approach to creating a cost-effective, eco-friendly, and rapid aptamer sensing platform.

An electrochemical aptasensor for the detection of chloramphenicol based on ultra-small Au-inserted hollow PCN-222 MOF

The excessive utilization of antibiotics has led to significant water contamination and posed severe threats to human well-being. Consequently, the pressing imperative to identify antibiotics in the environment arises. In this study, we have successfully synthesized a hollow PCN-222 MOF distinguished by its substantial surface area and abundant functional groups, particularly the porphyrin cores. To augment the electrical conductivity of the hollow PCN-222 (HPCN-222), gold (Au) particles were incorporated within the porphyrin core using a fundamental hydrothermal method. This modification facilitated the effective immobilization of aptamer strands through π-π stacking and electrostatic interactions. As a result, the Au@HPCN-222 composite demonstrated exceptional efficacy as a substrate for immobilizing the aptamer (Apt) onto the GCE surface. By employing differential pulse voltammetry (DPV) we successfully achieved the detection of chloramphenicol (CAP) with a remarkably low limit of detection of 0.0138 ng mL-1 and the peak DPV currents at 0.18 V (vs. Ag/AgCl) were used for calibration. Furthermore, this aptasensor exhibited high selectivity and reproducibility.

Construction of a nanoscale metal-organic framework aptasensor for fluorescence ratiometric sensing of AFB1 in real samples

Aflatoxins B1 (AFB1) that could contaminate agricultural products has received sustained attention due to its high toxicity and wide distribution. Therefore, sensitive and facile detection method for AFB1 is significant for food safety and control. In this work, a ratiometric fluorescence NMOFs-Aptasensor was developed based on the combination of Cy3-modified aptamer and zirconium-based nanoscale metal-organic frameworks (NMOFs). NMOFs served as energy donors, and Cy3 labeled on the AFB1 aptamer was used as an acceptor. An energy donor-acceptor pair was fabricated in the NMOFs-Aptasensor. With AFB1 selectively caught by the AFB1 aptamer, the fluorescence of the NMOFs-Aptasensor changed via fluorescence resonance energy transfer (FRET), and the fluorescence spectra changed accordingly. The ratiometric fluorescence signal was utilized to quantitatively measure AFB1. The reported NMOFs-Aptasensor presented great detection performance from 0 to 3.33 ng mL^-1, with an LOD of 0.08 ng mL^-1. Moreover, the fluorescence sensor was successfully applied to detect AFB1 in real samples.

Nucleic acid aptamer-based biosensors and their application in thrombin analysis

Thrombin is a multifunctional serine protease that plays an important role in coagulation and anticoagulation processes. Aptamers have been widely applied in biosensors due to their high specificity, low cost and good biocompatibility. This review summarizes recent advances in thrombin quantification using aptamer-based biosensors. The primary focus is optical sensors and electrochemical sensors, along with their applications in thrombin analysis and disease diagnosis.

Improving aptamer performance: key factors and strategies

Aptamers are functional single-stranded oligonucleotide fragments isolated from randomized libraries by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), exhibiting excellent affinity and specificity toward targets. Compared with traditional antibody reagents, aptamers display many desirable properties, such as low variation and high flexibility, and they are suitable for artificial and large-scale synthesis. These advantages make aptamers have a broad application potential ranging from biosensors, bioimaging to therapeutics and other areas of application. However, the overall performance of aptamer pre-selected by SELEX screening is far from being satisfactory. To improve aptamer performance and applicability, various post-SELEX optimization methods have been developed in the last decade. In this review, we first discuss the key factors that influence the performance or properties of aptamers, and then we summarize the key strategies of post-SELEX optimization which have been successfully used to improve aptamer performance, such as truncation, extension, mutagenesis and modification, splitting, and multivalent integration. This review shall provide a comprehensive summary and discussion of post-SELEX optimization methods developed in recent years. Moreover, by discussing the mechanism of each approach, we highlight the importance of choosing the proper method to perform post-SELEX optimization.

Study of binding mechanism of aptamer to kanamycin and the development of fluorescent aptasensor in milk detection

Aptasensors being versatile sensing platforms presented higher sensitivity toward target detection. However, lacking theoretical basis of recognition between most targets and their corresponding aptamers has impeded their applications. Herein, we conducted a study to explore the binding mechanism of aptamer to kanamycin (Kana) and developed rapid fluorescent aptasensing methods. Based on the fluorescence polarization results, base mutations were performed at different sites of the aptamer. The key binding nucleotides of Kana was identified as T7, T8, C13 and A15 by using isothermal titration calorimetry (ITC). The Kmut3 (2.18 μM) with lower dissociation constants (Kd), one-third of the native aptamer (6.91 μM), was also obtained. In addition, the lower K⁺ concentration and temperature were found to be conducive to Kana binding. Circular dichroism (CD) results revealed that the binding of Kana can trigger the change of base stacking force and helix force. On the aforementioned basis, a fluorescent sensor was designed with the native aptamer and Kmut3 as recognition elements. The comparison results proved that the Kmut3 presented a 3 times lower limit of detection of 59 nM compared to the native aptamer (148 nM). Notably, this developed aptasensor can be finished in 45 min and was convenient to operate.

A tag-free fluorescent aptasensor for tobramycin detection using a hybridization of three aptamer strands and SYBR Green I dye

In this study, a sensitive fluorescent method is designed to detect tobramycin (TOB) drug applying a hybrid structure of three aptamer strands and SYBR Green I (SGI) fluorescent dye as the bioreceptor segment and signal indicator, respectively. The preferential binding of the aptamers to TOB resulted in the collapse of the hybridized aptamer skeleton to the single strands. So, the intercalation of SGI molecules reduced that quenched the fluorescence response. The aptasensing assay provided the superior target specificity with a detection limit (LOD) of 0.153 pM and a wide linear dynamic range over 0.5 pM-300 μM. The aptasensor could successfully quantify TOB in human serum samples. The tag-free sensor with the remarkable advantages of simplicity, easy-to-use, cost-effectiveness, and high sensitivity is superior to be applicable for clinical samples.

Optimization of an aptamer against Prorocentrum minimum - A common harmful algae by truncation and G-quadruplex-forming mutation

Harmful algal blooms (HABs) caused by Prorocentrum minimum have seriously posed economic losses and ecological disasters. To reduce these losses, aptamers are used as a new molecular probe to establish rapid methods. Herein, to improve the affinity and application of aptamers in the detection of harmful algae, the optimization was performed on the previously reported aptamers against P. minimum. First, a total of seven candidate aptamers, including three truncated aptamers (TA1, TA2 and TA3) and four mutant aptamers (MA1, MA2, MA3 and MA4), were obtained by truncation and G-quadruplex (GQ)-forming mutation. Next, the specificity and affinity test by flow cytometry revealed that except for TA1 and TA2, all of the candidate aptamers are specific with the equilibrium dissociation constant of (40.4 ± 5.5) nM for TA3, (63.3 ± 24.0) nM for MA1, (71.7 ± 14.6) nM for MA2, (365.9 ± 74.4) nM for MA3, and (21.1 ± 0.5) nM for MA4, respectively. The circular dichroism analysis of the mutant aptamers demonstrated that the GQ structures formed by MA1/MA2, MA3 and MA4 were antiparallel, mixed parallel and parallel, respectively. The affinity of aptamers with various GQ is in the order of parallel structure > antiparallel structure > mixed parallel structure. In addition, to further improve binding ability, the binding conditions of MA4 were optimized as follows: binding time, 60 min; binding temperature, 37 °C; pH of the binding buffer, 7.5; and Na⁺/Mg²⁺ concentration in the binding buffer, 100 mM/0.5 mM. The binding examination by fluorescence microscopy showed that MA4 had a stronger binding ability to P. minimum than the original aptamer. Taken together, this study not only obtained an aptamer with higher affinity than the original aptamer, which laid a good foundation for subsequent application, but also may provide a feasible reference method for aptamer optimization.

Novel Dual-Signal SiO2-COOH@MIPs Electrochemical Sensor for Highly Sensitive Detection of Chloramphenicol in Milk

In view of the great threat of chloramphenicol (CAP) to human health and the fact that a few producers have illegally used CAP in the food production process to seek economic benefits in disregard of laws and regulations and consumer health, we urgently need a detection method with convenient operation, rapid response, and high sensitivity capabilities to detect CAP in food to ensure people's health. Herein, a molecularly imprinted polymer (MIP) electrochemical sensor based on a dual-signal strategy was designed for the highly sensitive analysis of CAP in milk. The NiFe Prussian blue analog (NiFe-PBA) and SnS₂ nanoflowers were modified successively on the electrode surface to obtain dual signals from [Fe(CN)₆]^3-/4- at 0.2 V and NiFe-PBA at 0.5 V. SiO₂-COOH@MIPs that could specifically recognize CAP were synthesized via thermal polymerization using carboxylated silica microspheres (SiO₂-COOH) as carriers. When the CAP was adsorbed by SiO₂-COOH@MIPs, the above two oxidation peak currents decreased at the same time, allowing the double-signal analysis. The SiO₂-COOH@MIPs/SnS₂/NiFe-PBA/GCE sensor used for determining CAP was successfully prepared. The sensor utilized the interactions of various nanomaterials to achieve high-sensitivity dual-signal detection, which had certain innovative significance. At the same time, the MIPs were synthesized using a surface molecular imprinting technology, which could omit the time of polymerization and elution and met the requirements for rapid detection. After optimizing the experimental conditions, the detection range of the sensor was 10^-8 g/L-10^-2 g/L and the limit of detection reached 3.3 × 10^-9 g/L (S/N = 3). The sensor had satisfactory specificity, reproducibility, and stability, and was successfully applied to the detection of real milk samples.

Fluorescence-based aptasensors for small molecular food contaminants: From energy transfer to optical polarization

Small molecular food contaminants, such as mycotoxins, pesticide residues and antibiotics, are highly probable to be passively introduced in food at all stages of its processing, including planting, harvest, production, transportation and storage. Owing to the high risks caused by the unknowing intake and accumulation in human, there is an urgent need to develop rapid, sensitive and efficient methods to monitor them. Fluorescence-based aptasensors provide a promising platform for this area owing to its simple operation, high sensitivity, wide application range and economical practicability. In this paper, the common sorts of small molecular contaminants in foods, namely mycotoxins, pesticides, antibiotics, etc, are briefly introduced. Then, we make a comprehensive review, from fluorescence resonance energy transfer (in turn-on, turn-off, and ratiometric mode, as well as energy upconversion) to fluorescence polarization, of the fluorescence-based aptasensors for the determination of these food contaminants reported in the last five years. The principle of signal generation, the advances of each sort of fluorescent aptasensors, as well as their applications are introduced in detail. Additionally, we also discussed the challenges and perspectives of the fluorescent aptasensors for small molecular food contaminants. This work will offer systematic overview and inspiration for amateurs, researchers and developers of fluorescence-based aptasensors for the detection of small molecules.

A highly sensitive competitive aptasensor for AFB1 detection based on an exonuclease-assisted target recycling amplification strategy

Aflatoxin B₁ (AFB₁) is a typical mycotoxin found in agricultural products, and poses a huge threat to both humans and animals. Accurate and rapid measurement of AFB₁ is essential for environmental analysis and food safety. Based on molecular docking simulation design and exonuclease-assisted target recycling amplification, we designed a competitive fluorescence aptasensor to detect AFB₁ rapidly and sensitively. According to the molecular docking simulations, a complementary strand (cDNA) was designed by searching for potential binding sites of the aptamer, which had the lowest binding energy. Magnetic beads modified with biotin-Apt were used as the capture probe, while FAM-labeled cDNA acted as the reporter probe. By using EXO I for target recycling amplification, this aptasensor was highly sensitive and selective for AFB₁. The detection limit of the suggested aptasensor under optimal conditions was 0.36 ng mL^-1 (S/N = 3) in the range of 1-1000 ng mL^-1 (R² = 0.991). The developed aptasensor was successfully used to analyze AFB₁ in oil samples.

Highly Sensitive Determination of Antibiotic Residues in Aquatic Products by High-Performance Liquid Chromatography-Tandem Mass Spectrometry

Antibiotic drug residues are crucial to ensure food safety and minimize risk to human health. Herein, a sensitive high-performance liquid chromatography−tandem mass spectrometry (HPLC−MS/MS) method was developed and validated for the determination of antibiotic residues (mainly amphenicols) consisting of chloramphenicol (CAP), thiamphenicol (TAP), florfenicol (FF), and florfenicol amine (FFA) in aquatic products. Amphenicols were well separated on a Kinetex F5 (100 mm × 3.0 mm, 2.6 µm) chromatographic column with the mobile phases of 1 mM ammonium acetate aqueous solution and methanol solution and measured after positive and negative electrospray ionizations using four internal standards. To our knowledge, it was the first time to report the good performance of F5 column and four internal standards for the determination of amphenicols. The established method featured a good linear relationship between chromatographic peak area ratios and the concentrations of amphenicols (R2 > 0.992), a wide and low detection matrix-based range of 0.01−5 μg/L, a low detection limit of 0.01 μg/kg, etc. The spiked assays evidenced the accuracy and reliability of the developed method with the recoveries between 84.0 and 105%, the intraday relative standard deviations (RSDs) over the range of 0.769−13.7%, and the interday RSDs over the range of 0.582−13.3%. Finally, the proposed method was applied to investigate amphenicol residues in various aquatic products, including fish, shrimp, crab, shellfish, and other aquatic species.

Amplification of fluorescence polarization signal based on specific recognition of aptamers combined with quantum quenching effect for ultrasensitive and simple detection of PCB-77

Here, we report a novel aptasensor based on decahedral silver nanoparticles (Ag₁₀NPs) enhanced fluorescence polarization (FP) for detecting PCB-77. Using aptamer modified Ag₁₀NPs hybridized with DNA sequence labeled fluorescent group as an analytical probe, polychlorinated biphenyls (PCB-77) could be detected with high sensitivity and selectivity. The linear range of determination was 0.02 ng/L to 390 ng/L and the limit of detection was 5 pg/L. In addition, through the optimization of the experiment condition and signal probe DNA (pDNA), we found that the maximum FP signal could be generated when the distance between fluorescein and the surface of Ag₁₀NPs was 3 nm. When the aptamer was immobilized on the surface of Ag₁₀NPs could be strengthened the anti-interference performance of aptamer nanoprobe and further improved the detection ability. At the same time, we also compared the detection performance of the traditional FP signal enhancer streptavidin (SA) analysis system. The fluorescence polarization aptasensor could detect PCB-77 samples efficiently in complex environmental water, which shows a good application prospect.

Luminescent Aptamer-Based Bioassays for Sensitive Detection of Food Allergens

The presence of hidden allergens in food products, often due to unintended contamination along the food supply chain (production, transformation, processing, and transport), has raised the urgent need for rapid and reliable analytical methods for detecting trace levels of such species in food products. Indeed, food allergens represent a high-risk factor for allergic subjects due to potentially life-threatening adverse reactions. Portable biosensors based on immunoassays have already been developed as rapid, sensitive, selective, and low-cost analytical platforms that can replace analyses with traditional bench-top instrumentation. Recently, aptamers have attracted great interest as alternative biorecognition molecules for bioassays, since they can bind a variety of targets with high specificity and selectivity, and they enable the development of assays exploiting a variety of transduction and detection technologies. In particular, aptasensors based on luminescence detection have been proposed, taking advantage of the development of ultrasensitive tracers and enhancers. This review aims to summarize and discuss recent efforts in the field of food allergen analysis using aptamer-based bioassays with luminescence detection.

An AuNPs-Based Fluorescent Sensor with Truncated Aptamer for Detection of Sulfaquinoxaline in Water

Herein, we developed a novel truncation technique for aptamer sequences to fabricate highly sensitive aptasensors based on molecular docking and molecular dynamics simulations. The binding mechanism and energy composition of the aptamer/sulfaquinoxaline (SQX) complexes were investigated. We successfully obtained a new SQX-specific aptamer (SBA28-1: CCCTAGGGG) with high affinity (K_d = 27.36 nM) and high specificity determined using graphene oxide. This aptamer has a unique stem-loop structure that can bind to SQX. Then, we fabricated a fluorescence aptasensor based on SBA28-1, gold nanoparticles (AuNPs), and rhodamine B (RhoB) that presented a good linear range of 1.25–160 ng/mL and a limit of detection of 1.04 ng/mL. When used to analyze water samples, the aptasensor presented acceptable recovery rates of 93.1–100.1% and coefficients of variation (CVs) of 2.2–10.2%. In conclusion, the fluorescence aptasensor can accurately and sensitively detect SQX in water samples and has good application prospects.

Characterization and Identification of Aptamers against CD49c for the Detection, Capture, and Release of Cancer Cells

As a kind of recognition molecule, aptamers can be inserted into some regulatory sequences for the smart response of their targets. However, the molecular engineering might lead to the change of the binding affinity. Here, we present a stable aptamer ZAJ-2c and an environmentally sensitive aptamer ZAJ-2d optimized from an original cell-binding aptamer ZAJ-2, and the molecular target was further identified as CD49c on the cell membrane. ZAJ-2c was characterized with high binding ability independent of the presence of divalent cations at a temperature range from 4 to 37 °C, showing promise for measuring the expression of CD49c on cancer cells. Moreover, ZAJ-2d had a nanomolar binding affinity in the binding buffer at 4 °C, the same as ZAJ-2c, but lost the binding ability in a PBS buffer supplemented with 5 mM EDTA at 37 °C. This aptamer variant proved to selectively capture and release the CD49c positive cells by simply adjusting the temperatures and divalent cations. This set of aptamers might provide a toolbox for monitoring and operating of a wide range of cancer cells with CD49c expression on the surface, which will be helpful for the studying the heterogeneity of rare cells.

Triple-Helix Molecular Switch Triggered Cleavage Effect of DNAzyme for Ultrasensitive Electrochemical Detection of Chloramphenicol

The abuse of chloramphenicol (CAP) in animal-derived products leads to serious food safety problems, so the sensitive and accurate determination of CAP residues has great noteworthiness for public health. Herein, we present a novel electrochemical aptasensor that incorporates a poly(diallyldimethylammonium chloride) functionalized graphene/Ag@Au nanosheets (PDDA-Gr/Ag@Au NSs) composite modified electrode and a DNAzyme signal amplification effect triggered by a triple-helix molecular switch (THMS) for detecting CAP. The PDDA-Gr/Ag@Au NSs composite has the advantages of high surface area, great conductivity, and dispersibility and has successfully improved the electrochemical performance of the electrode. Specific interaction with CAP will cause the signal transduction probe (STP) to be released from the THMS. After that, the DNAzyme will be activated with the help of Pb²⁺ and remove the immobilized signal probe on the electrode surface. The signal change was recorded by square wave voltammetry (SWV) and led to an accurate quantification of CAP. With all these features, the proposed sensing strategy yielded a satisfactory analytical performance with linearity between 1 pM and 1 μM and a limit of detection of 18.6 fM. Furthermore, the aptasensor shows excellent specificity for CAP in the presence of other antibiotics and resists interference with other common metal ions. Importantly, the performance is not diminished when the constructed aptasensor is applied to measuring CAP in milk powder. This THMS-based method is easy to design, and alteration to different targets can be achieved by simply replacing the aptamer sequence in the THMS. Therefore, this method shows significant prospects as a flexible platform for accurate monitoring of antibiotic residues in foodstuffs.

Selection, truncation and fluorescence polarization based aptasensor for Weissella viridescens detection

Weissella viridescens is a spoilage bacterium commonly found in low-temperature meat products. In this work, after fifteen rounds including three counter selection rounds of whole-cell systemic evolution of ligands by exponential enrichment (SELEX) in vitro, a novel aptamer L3 that can specifically recognize W. viridescens was obtained with a dissociation constant (K_d) value of 68.25 ± 5.32 nM. The sequence of aptamer L3 was optimized by truncation and a new aptamer sequence TL43 was obtained with a lower K_d value of 32.11 ± 3.01 nM. Finally, a simple and rapid fluorescence polarization (FP) platform was constructed to detect W. viridescens, in which FAM-labeled complementary sequence (FAM-cDNA) was employed to generate FP signal and streptavidin was used to amplify FP signal. In the presence of target bacteria, FP value decreased owning to the dissociation of FAM-cDNA from streptavidin/biotin-TL43/FAM-cDNA complex. Under optimal conditions, the concentration of W. viridescens and FP value displayed a good linear relationship with the detection range from 10² to 10⁶ cfu/mL. Moreover, the designed detection system had a good recovery rate of 90.6%-107.7% in smoked ham samples compared with classical plate counting method, indicating the great potential of the selected and truncated aptamer in practical biosensing applications.

Utilizing the DNA Aptamer to Determine Lethal α-Amanitin in Mushroom Samples and Urine by Magnetic Bead-ELISA (MELISA)

Amanita poisoning is one of the most deadly types of mushroom poisoning. α-Amanitin is the main lethal toxin in amanita, and the human-lethal dose is about 0.1 mg/kg. Most of the commonly used detection techniques for α-amanitin require expensive instruments. In this study, the α-amanitin aptamer was selected as the research object, and the stem-loop structure of the original aptamer was not damaged by truncating the redundant bases, in order to improve the affinity and specificity of the aptamer. The specificity and affinity of the truncated aptamers were determined using isothermal titration calorimetry (ITC) and gold nanoparticles (AuNPs), and the affinity and specificity of the aptamers decreased after truncation. Therefore, the original aptamer was selected to establish a simple and specific magnetic bead-based enzyme linked immunoassay (MELISA) method for α-amanitin. The detection limit was 0.369 μg/mL, while, in mushroom it was 0.372 μg/mL and in urine 0.337 μg/mL. Recovery studies were performed by spiking urine and mushroom samples with α-amanitin, and these confirmed the desirable accuracy and practical applicability of our method. The α-amanitin and aptamer recognition sites and binding pockets were investigated in an in vitro molecular docking environment, and the main binding bases of both were T3, G4, C5, T6, T7, C67, and A68. This study truncated the α-amanitin aptamer and proposes a method of detecting α-amanitin.

Ultrasensitive and facile detection of multiple trace antibiotics with magnetic nanoparticles and core-shell nanostar SERS nanotags

Ultrasensitive, multiplex, rapid, and accurate quantitative determination of trace antibiotics remains a challenging issue, which is of importance to public health and safety. Herein, we presented a multiplex strategy based on magnetic nanoparticles and surface-enhanced Raman scattering (SERS) nanotags for simultaneous detection of chloramphenicol (CAP) and tetracycline (TTC). In practice, SERS nanotags based on Raman reporter probes (RRPs) encoded gold-silver core-shell nanostars were used as detection labels for identifying different types of antibiotics, and the magnetic nanoparticles could be separated simply by magnetic force, which significantly improves the detection efficiency, reduces the analysis cost, and simplifies the operation. Our results demonstrate that the as-proposed assay possesses the capacities of high sensitivity and multiplexing with the limits of detection (LODs) for CAP and TTC of 159.49 and 294.12 fg mL^-1, respectively, as well as good stability and reproducibility, and high selectivity and reliability. We believe that this strategy holds a great promising perspective for the detection of trace amounts of antibiotics in microsystems, which is crucial to our life. Additionally, the assay can also be used to detect other illegal additives by altering the appropriate antibodies or aptamers.

Rapid detection and prediction of chloramphenicol in food employing label-free HAu/Ag NFs-SERS sensor coupled multivariate calibration

Considering growing food safety issues, hollow Au/Ag nano-flower (HAu/Ag NFs) nanosensor has been synthesized for label-free and ultrasensitive detection of chloramphenicol (CP) via integrating the surface-enhanced Raman scattering (SERS) and multivariate calibration. As the anisotropic plasmonic nanomaterials, HAu/Ag NFs had numerous nano-chink on their surface, which offered huge hotspots for analytes. CP generated a strong SERS signal while adsorbed on the surface of HAu/Ag NFs and noted excellent linearity with 1st derivative-competitive adaptive reweighted sampling-partial least squares (CARS-PLS) in the range of 0.0001-1000 µg/mL among the four applied multivariate calibrations. Additionally, CARS-PLS generated the lowest prediction error (RMSEP) of 0.089 and 0.123 µg/mL for milk and water samples, respectively, and any CARS-PLS model could be used for both samples according to T-test results (P > 0.05). The intra- and interday recovery for both samples were in the range of 92.62-96.74% with CV < 10%, suggested the proposed method has excellent accuracy and precision.

Simultaneous Determination of Amphenicols and Metabolites in Animal-Derived Foods Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry

Amphenicols are widely used to prevent and treat animal diseases. However, amphenicol residues accumulate in livestock and poultry and harm consumers. We hypothesized that one can combine solid-phase extraction (SPE) with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) to simultaneously determine amphenicols and metabolites in pork, beef, lamb, chicken, and their products and meet government regulations for maximum residue limits. We extracted crude samples with ethyl acetate and ammonia water (98:2, v/v), purified the samples with a CNW Si SPE column, defatted the samples with acetonitrile-saturated n-hexane, and then determined the resulting analytes by UHPLC-MS/MS. The limit of detection of the analytes in livestock and poultry meat was 0.03–1.50 μg/kg, and the limit of quantification was 0.05–5.00 μg/kg. Measured chloramphenicol, thiamphenicol, and florfenicol concentrations were linear over the range 0.50–50 μg/kg; and the florfenicol amine concentration was linear over the range 5.00–200 μg/kg (all with correlation coefficients >0.9990). The recovery of the spiked samples was between 72% and 120%. The intraday relative standard deviation (RSD) ranged from 1% to 9%, and the interday RSD ranged from 1% to 12%. Based on the above results, the current method is sensitive, accurate, and reproducible with the detection limits being well below the maximum residue limits as per Chinese standard GB 31650-2019, and thus, our research hypothesis could be confirmed.

Aptamer-Based Fluorescent Biosensor for the Rapid and Sensitive Detection of Allergens in Food Matrices

Food allergies have seriously affected the life quality of some people and even endangered their lives. At present, there is still no effective cure for food allergies. Avoiding the intake of allergenic food is still the most effective way to prevent allergic diseases. Therefore, it is necessary to develop rapid, accurate, sensitive, and reliable analysis methods to detect food allergens from different sources. Aptamers are oligonucleotide sequences that can bind to a variety of targets with high specificity and selectivity, and they are often combined with different transduction technologies, thereby constructing various types of aptamer sensors. In recent years, with the development of technology and the application of new materials, the sensitivity, portability, and cost of fluorescence sensing technology have been greatly improved. Therefore, aptamer-based fluorescence sensing technology has been widely developed and applied in the specific recognition of food allergens. In this paper, the classification of major allergens and their characteristics in animal and plant foods were comprehensively reviewed, and the preparation principles and practical applications of aptamer-based fluorescence biosensors are summarized. In addition, we hope that this article can provide some strategies for the rapid and sensitive detection of allergens in food matrices.

Identification of a novel DNA aptamer that selectively targets lung cancer serum

Lung cancer is the leading cause of cancer-related deaths worldwide. Early diagnosis and treatment is critical to improving the 5 year survival rate of lung cancer. The identification of new options for early-stage diagnosis and therapy of lung cancer still represents a crucial challenge. Therefore, a new diagnostic method is urgently needed. In this study, we used a new modified SELEX, called serum-SELEX, to isolate aptamers that can specifically bind lung cancer serum, without any prior knowledge of their target. Among the obtained candidate aptamer sequences, Ap-LC-19 was identified as the optimal aptamer probe with the lowest dissociation constant (K d) value of 15 ± 8.6 nM and higher affinity assessed by qPCR. Furthermore, this molecule could be a suitable aptamer for lung cancer serum and could be used as a recognition element in aptamer-based biosensors for efficient early diagnosis of lung cancer or as an innovative tool for targeted therapy. In addition, we performed MALDI-TOF MS followed by secondary peptide sequencing MS analysis for the identification of the aptamer targeted proteins. CLEC3B could be useful biomarkers for early detection of lung cancer and in monitoring its evolution.