Quantum dot-DNA aptamer conjugates coupled with capillary electrophoresis: A universal strategy for ratiometric detection of organophosphorus pesticides

Advances in Aptamer-Based Conjugate Recognition Techniques for the Detection of Small Molecules in Food

Small molecules are significant risk factors for causing food safety issues, posing serious threats to human health. Sensitive screening for hazards is beneficial for enhancing public security. However, traditional detection methods are unable to meet the requirements for the field screening of small molecules. Therefore, it is necessary to develop applicable methods with high levels of sensitivity and specificity to identify the small molecules. Aptamers are short-chain nucleic acids that can specifically bind to small molecules. By utilizing aptamers to enhance the performance of recognition technology, it is possible to achieve high selectivity and sensitivity levels when detecting small molecules. There have been several varieties of aptamer target recognition techniques developed to improve the ability to detect small molecules in recent years. This review focuses on the principles of detection platforms, classifies the conjugating methods between small molecules and aptamers, summarizes advancements in aptamer-based conjugate recognition techniques for the detection of small molecules in food, and seeks to provide emerging powerful tools in the field of point-of-care diagnostics.

A photoelectrochemical aptasensor for omethoate determination based on a photocatalysis of CeO2@MnO2 heterojunction for glucose oxidation

In the present work, we developed a photoelectrochemical aptasensor to determine omethoate (OMT) based on the dual signal amplification of CeO2@MnO2 photocatalysis for glucose oxidation and exonuclease I-assisted cyclic catalytic hydrolysis. CeO2@MnO2 heterojunction material prepared by hydrothermal method was linked with captured DNA (cDNA) and then assembled on the ITO conductive glass to form ITO/CeO2@MnO2-cDNA, which exhibited significant photocurrent response and good photocatalytic performance for glucose oxidation under visible light irradiation, providing the feasibility for sensitive determining OMT. After binding with the aptamer of OMT (apt), the formation of rigid double stranded cDNA/apt kept CeO2@MnO2 away from ITO surface, which ensured a low photocurrent background for the constructed ITO/CeO2@MnO2-cDNA/apt aptasensor. In the presence of target OMT, the restoration of the cDNA hairpin structure and the exonuclease I-assisted cyclic catalytic hydrolysis led to the generation and amplification of measurement photocurrent signals, and allowed the aptasensor to have an ideal quantitative range of 0.01-10.0 nM and low detection limit of 0.0027 nM. Moreover, the aptasensor has been applied for selective determination of OMT in real samples with good precision of the relative standard deviation less than 6.2 % and good accuracy of the recoveries from 93 % to 108 %. What's more, the aptasensor can be used for other target determination only by replacing the captured DNA and corresponding aptamer.

A Review of in vivo Toxicity of Quantum Dots in Animal Models

Tremendous research efforts have been devoted to nanoparticles for applications in optoelectronics and biomedicine. Over the past decade, quantum dots (QDs) have become one of the fastest growing areas of research in nanotechnology because of outstanding photophysical properties, including narrow and symmetrical emission spectrum, broad fluorescence excitation spectrum, the tenability of the emission wavelength with the particle size and composition, anti-photobleaching ability and stable fluorescence. These characteristics are suitable for optical imaging, drug delivery and other biomedical applications. Research on QDs toxicology has demonstrated QDs affect or damage the biological system to some extent, and this situation is generally caused by the metal ions and some special properties in QDs, which hinders the further application of QDs in the biomedical field. The toxicological mechanism mainly stems from the release of heavy metal ions and generation of reactive oxygen species (ROS). At the same time, the contact reaction with QDs also cause disorders in organelles and changes in gene expression profiles. In this review, we try to present an overview of the toxicity and related toxicity mechanisms of QDs in different target organs. It is believed that the evaluation of toxicity and the synthesis of environmentally friendly QDs are the primary issues to be addressed for future widespread applications. However, considering the many different types and potential modifications, this review on the potential toxicity of QDs is still not clearly elucidated, and further research is needed on this meaningful topic.

Fluorescent nanostructured carbon dot-aptasensor for chlorpyrifos detection: Elucidating the interaction mechanism for an environmentally hazardous pollutant

Chlorpyrifos (CPF) is a commonly used insecticide found in many water sources and is related to several health and environmental effects. Biosensors based on aptamers (single-stranded nucleic acid oligonucleotides) are promising alternatives to achieve the detection of CPF and other pesticides in natural waters. However, several challenges need to be addressed to promote the real application of functional aptasensing devices. In this work, an ssDNA aptamer (S1) is combined with carbon quantum dots (CD) and graphene oxide (GO) to produce a stable fluorescent aptasensor characterized through spectrophotometric and electrophoretic techniques. For a deeper understanding of the system, the mechanism of molecular interaction was studied through docking modeling using free bioinformatic tools like HDOCK, showing that the stem-loops and the higher guanine (G) content are crucial for better interaction. The model also suggests the possibility of generating a truncated aptamer to improve the binding affinity. The biosensor was evaluated for CPF detection, showing a low LOD of 0.01 μg L-1 and good specificity in tap water, even compared to other organophosphates pesticides (OPs) like profenofos. Finally, the recovery of the proposed aptasensor was evaluated in some natural water using spiked samples and compared with UPLC MS-MS chromatography as the gold standard, showing a good recovery above 2.85 nM and evidencing the need of protecting ssDNA aptamers from an erratic interaction with the aromatic groups of dissolved organic matter (humic substances). This work paves the way for a better aptasensors design and the on-site implementation of novel devices for environmental monitoring.

A method for the rapid determination of pesticides coupling thin-layer chromatography and enzyme inhibition principles

Herein, we developed a method coupling TLC and enzyme inhibition principles to rapidly detect OPs (dichlorvos, paraoxon and parathion). After the removal of the organic solvent from the samples using TLC and paper-based chips, the enzyme was added to the detection system. The results showed that the current method effectively reduced the effects of solvents on enzyme behavior. Moreover, the pigments could be successfully retained on TLC with 40% ddH₂O/ACN solution (v/v) as a developing solvent. Additionally, the detection limits (LODs) were 0.002 µg/mL for dichlorvos, 0.006 µg/mL for paraoxon, and 0.003 µg/mL for parathion. Finally, the method was applied to spiked cabbage, cucumber, and spinach and showed good average recoveries ranging between 70.22% and 119.79%. These results showed that this paper-based chip had high sensitivity, precleaning, and elimination of organic solvent properties. Furthermore, it provides a valuable idea for sample pretreatment and rapid determination of pesticide residues in food.

Facile colorimetric smartphone-based biosensor for rapid detection of organophosphorus pesticides residues in environment using the aptamer-enhanced oxidase activity of octahedral Ag2O particles

The long-term and excessive use of organophosphorus pesticides (OPs) leads to hazardous residues in the environment, which threatens human health to a considerable extent. Colorimetric methods can quickly and readily identify pesticide residue, but they still have various challenges in accuracy and stability. Herein, a smartphone-assisted and non-enzymatic colorimetric biosensor was constructed for rapid monitoring of multiple OPs based on the enhanced effect of aptamer on the catalytic ability of octahedral Ag₂O. It was demonstrated that the aptamer sequence could enhance the affinity of colloidal Ag₂O to chromogenic substrates, and accelerate the generation of oxygen radicals such as superoxide radical (·O₂^-) and singlet oxygen (¹O₂) from dissolved oxygen, thereby significantly increasing the oxidase activity of octahedral Ag₂O. The color change of the solution can be easily converted to the corresponding RGB values by a smartphone for quantitative and rapid detection of multiple OPs. Hence, the smartphone-based and visual biosensor of multiple OPs was acquired with limit of detection of 10 μg L^-1, 28 μg L^-1 and 40 μg L^-1 for isocarbophos, profenofos and omethoate, respectively. The colorimetric biosensor also exhibited good recoveries in several environmental and biological samples, showing that it may have broad application prospects for detecting OPs residues.

Implications of biosensors and nanobiosensors for the eco-friendly detection of public health and agro-based insecticides: A comprehensive review

Biosensors, in particular nanobiosensors, have brought a paradigm shift in the detection approaches involved in healthcare, agricultural, and industrial sectors. In accordance with the global expansion in the world population, there has been an increase in the application of specific insecticides for maintaining public health and enhancing agriculture, such as organophosphates, organochlorines, pyrethroids, and carbamates. This has led to the contamination of ground water, besides increasing the chances of biomagnification as most of these insecticides are non-biodegradable. Hence, conventional and more advanced approaches are being devised for the routine monitoring of such insecticides in the environment. This review walks through the implications of biosensors and nanobiosensors, which could offer a wide range of benefits for the detection of the insecticides, quantifying their toxicity status, and versatility in application. Unique eco-friendly nanobiosensors such as microcantilevers, carbon nanotubes, 3D printing organic materials and nylon nano-compounds are some advanced tools that are being employed for the detection of specific insecticides under different conditions. Furthermore, in order to implement a smart agriculture system, nanobiosensors could be integrated into mobile apps and GPS systems for controlling farming in remote areas, which would greatly assist the farmer remotely for crop improvement and maintenance. This review discusses about such tools along with more advanced and eco-friendly approaches that are on the verge of development and could offer a promising alternative for analyte detection in different domains.

Ultrasensitive electrochemiluminescence aptasensor based on ABEI reduced silver nanoparticles for the detection of profenofos

An ultrasensitive electrochemiluminescence (ECL) aptasensor for detection of profenofos was constructed by the reducibility and chemiluminescence property of N-(aminobutyl)-N-(ethylisoluminol) (ABEI). ABEI was used to reduce silver nitrate (AgNO₃) to silver nanoparticles (AgNPs), which could be adsorbed on the lattice of graphene oxide (GO) to form ABEI-AgNPs-GO complex. This compound could achieve excellent luminescence. The aptamer (Apt) modified (5') by sulfhydryl groups could be immobilized on AgNPs to capture profenofos. When profenofos was present, the ECL signal of the aptasensor would be weakened. To further demonstrate the successful construction of the aptasensor, cyclic voltammetry tests were performed on an electrochemical workstation and an ECL analyzer, respectively. The standard curve and specificity experiment both showed that the sensor had the advantages of low limit of detection (LOD) and good specificity. Under the optimal conditions, the aptasensor had a good linear response for profenofos in the range of 1 × 10^-1-1 × 10⁴ ng/mL. It also had a LOD of 6.7 × 10^-2 ng/mL and a correlation coefficient (R²) of 0.9991. The aptasensor had been successfully applied to the detection of profenofos in vegetables. The recovery range of the proposed ECL aptasensor was 98 % ~ 107.4 %.

A comprehensive review on electrochemical and optical aptasensors for organophosphorus pesticides

There has been a rise in pesticide use as a result of the growing industrialization of agriculture. Organophosphorus pesticides have been widely applied as agricultural and domestic pest control agents for nearly five decades, and they remain as health and environmental hazards in water supplies, vegetables, fruits, and processed foods causing serious foodborne illness. Thus, the rapid and reliable detection of these harmful organophosphorus toxins with excellent sensitivity and selectivity is of utmost importance. Aptasensors are biosensors based on aptamers, which exhibit exceptional recognition capability for a variety of targets. Aptasensors offer numerous advantages over conventional approaches, including increased sensitivity, selectivity, design flexibility, and cost-effectiveness. As a result, interest in developing aptasensors continues to expand. This paper discusses the historical and modern advancements of aptasensors through the use of nanotechnology to enhance the signal, resulting in high sensitivity and detection accuracy. More importantly, this review summarizes the principles and strategies underlying different organophosphorus aptasensors, including electrochemical, electrochemiluminescent, fluorescent, and colorimetric ones.

Advanced screening and tailoring strategies of pesticide aptamer for constructing biosensor

The rapid development of aptamers has helped address the challenges presented by the wide existed pesticides contaminations. Screening of aptamers with excellent performance is a prerequisite for successfully constructing biosensors, while further tailoring of aptamers with enhanced activity greatly improved the assay performance. Firstly, this paper reviewed the advanced screening strategies for pesticides aptamers, including immobilization screening that preserves the native structures of targets, non-immobilized screening based on nanomaterials, capillary electrophoresis-systematic evolution of ligands by exponential enrichment (CE-SELEX), virtual screening in silico, high-throughput selection, and rational secondary library generation methods, which contributed significantly to improve the success rate of screening, reduce the screening time, and ensure aptamer binding affinity. Secondly, the precise tailoring strategies for pesticides aptamers were modularly elaborated, containing deletion, splitting, elongation, and fusion, which provided various advantages like cost-efficiency, enhanced binding affinity, and new derived functional motifs. Thirdly, the developed aptamer-based biosensors (aptasensors) for pesticide detection were systematically reviewed according to the different signal output modes. Finally, the challenges and future perspectives of pesticide detection are discussed comprehensively.

β-Cyclodextrin Polymer-Based Host-Guest Interaction and Fluorescence Enhancement of Pyrene for Sensitive Isocarbophos Detection

The extensive use of organophosphorus pesticides in agriculture poses a high risk to human health and has boosted the demands for developing sensitive monitoring methods. Herein, we developed a facile and sensitive method for isocarbophos detection based on the remarkable fluorescence enhancement of pyrene during host-guest interaction of β-cyclodextrin polymer (β-CDP) and pyrene. The 3'-pyrene-labeled isocarbophos aptamer could be cleaved by exonuclease I to obtain free pyrene that was tagged on mononucleotides, which could enter the hydrophobic cavity of β-CDP, resulting in a prominent fluorescence enhancement. While the target isocarbophos was added, aptamer could undergo a conformational change into a hairpin complex, which prevented the cleavage and host-guest interaction because of the steric hindrance, leading to a weak fluorescence. The isocarbophos has been sensitively and selectively analyzed by detecting the system fluorescence intensity with a detection limit as low as 1.2 μg/L. In addition, we have verified the ability of our proposed method in real sample detection from fruit extract.

Metal-Organic Frameworks-Based Sensors for Food Safety

Food contains a variety of poisonous and harmful substances that have an impact on human health. Therefore, food safety is a worldwide public concern. Food detection approaches must ensure the safety of food at every step of the food supply chain by monitoring and evaluating all hazards from every single step of food production. Therefore, early detection and determination of trace-level contaminants in food are one of the most crucial measures for ensuring food safety and safeguarding consumers' health. In recent years, various methods have been introduced for food safety analysis, including classical methods and biomolecules-based sensing methods. However, most of these methods are laboratory-dependent, time-consuming, costly, and require well-trained technicians. To overcome such problems, developing rapid, simple, accurate, low-cost, and portable food sensing techniques is essential. Metal-organic frameworks (MOFs), a type of porous materials that present high porosity, abundant functional groups, and tunable physical and chemical properties, demonstrates promise in large-number applications. In this regard, MOF-based sensing techniques provide a novel approach in rapid and efficient sensing of pathogenic bacteria, heavy metals, food illegal additives, toxins, persistent organic pollutants (POPs), veterinary drugs, and pesticide residues. This review focused on the rapid screening of MOF-based sensors for food safety analysis. Challenges and future perspectives of MOF-based sensors were discussed. MOF-based sensing techniques would be useful tools for food safety evaluation owing to their portability, affordability, reliability, sensibility, and stability. The present review focused on research published up to 7 years ago. We believe that this work will help readers understand the effects of food hazard exposure, the effects on humans, and the use of MOFs in the detection and sensing of food hazards.

Aptamer-binding zirconium-based metal-organic framework composites prepared by two conjunction approaches with enhanced bio-sensing for detecting isocarbophos

A novel label-free and enzyme-free detection strategy has been developed for the electrochemical biosensor detection of isocarbophos (ICP) using UiO-66-NH₂ and aptamer as the signal transducers. In this work, the ICP aptamers were attached to UiO-66-NH₂ through physical mixing and chemical combination methods. In the presence of ICP, the aptamers could undergo conformational change and bind to them, which prevent the electron transfer to the surface of electrode. By comparing the two conjunction approaches of aptasensors, these proposed strategies could selectively and sensitively detect ICP with a detection limit of 6 ng mL^-1 (20.74 nM) and 0.9 ng mL^-1 (3.11 nM). Furthermore, we have also demonstrated the capability of this strategy in the detection of ICP in real samples from vegetable and fruit extract, indicating the potential application of this strategy in food safety issues.

A novel electrochemiluminescence aptasensor based on copper-gold bimetallic nanoparticles and its applications

In this work, a novel electrochemiluminescence (ECL) aptasensor was structured for the detection of four organophosphorus pesticides (OPs). Firstly, multi-walled carbon nanotubes (MWCNTs) were used to create a favorable loading interface for the fixation of tris (2, 2'-bipyridyl) ruthenium (II) (Ru (bpy)₃²⁺). At the same time, copper (core)-gold (shell) bimetallic nanoparticles (Cu@Au NPs) were synthesized in the aqueous phase for the sensor construction. Gold nanoparticles (Au NPs) could promote the electrochemiluminescence intensity of Ru (bpy)₃²⁺ with high efficiency by catalyzing the oxidation process of tri-n-propylamine (TPrA). Compared with the Au NPs, Cu@Au NPs increased the solid loading of Au NPs by virtue of the large specific surface area of copper nanoparticles (Cu NPs), which could further improve the sensitivity of aptasensor. When OPs were added, the ECL intensity was significantly reduced, and the concentration of OPs could be detected through the ECL intensity. Under the optimum conditions, the aptasensor had a wider dynamic range and ultra-low detection limit for the detection of four pesticides: profenofos, isocarbophos, phorate, and omethoate, and their detection limits were 3 × 10^-4 ng/mL, 3 × 10^-4 ng/mL, 3 × 10^-3 ng/mL, and 3 × 10^-2 ng/mL respectively (S/N = 3). The aptasensor had the merits of good stability, reproducibility, and specificity, and had a favorable recovery rate in detecting OPs residues in vegetables. This work provided an effective method for the construction of a simple, rapid, and sensitive biosensor.

Peptide nanotube functionalized molecularly imprinted polydopamine based single-use sensor for impedimetric detection of malathion

In the present study, a peptide nanotube functionalized polydopamine (p-Dop) based molecularly imprinted (MIP) sensor system was constructed, characterized, and studied for the impedimetric sensing of an organophosphorus pesticide, malathion (MLT). Electropolymerization in the presence of a template (MLT) was utilized as a convenient and effective strategy to generate imprinted p-Dop films on peptide nanotubes (PNTs) modified graphite electrodes (PGEs). Upon the removal of template, the adsorption of MLT on the specific cavities formed in the MIP film was tracked using electrochemical impedance spectroscopy (EIS). To attain optimal sensor response, experimental conditions, such as film thickness, analyte/functional monomer ratio, and desorption/adsorption time, were analyzed. The obtained MIP(p-Dop)-PNT-PGE sensor exhibited high sensitivity for electrochemical MLT analysis with a wide dynamic detection range of 13 pg mL^-1 - 1.3 µg mL^-1 and a LOD of 1.39 pg mL^-1. The combination of a bio-inspired p-Dop-based MIP with the EIS technique allowed excellent sensitivity and selectivity toward MLT sensing which also yielded high recoveries in real samples. The success of this research strategy in real samples revealed its potential for various future environmental applications.

Activity of CdTe Quantum-Dot-Tagged Superoxide Dismutase and Its Analysis in Capillary Electrophoresis

Quantum dots (QDs) have a broad range of applications in cell biolabeling, cancer treatment, metastasis imaging, and therapeutic drug monitoring. Despite their wide use, relatively little is known about their influence on other molecules. Interactions between QDs and proteins can influence the properties of both nanoparticles and proteins. The effect of mercaptosuccinic acid-capped CdTe QDs on intercellular copper–zinc superoxide dismutase (SOD1)—one of the main enzymatic antioxidants—was investigated. Incubation of SOD1 with QDs caused an increase in SOD1 activity, unlike in the case of CdCl₂, which inhibited SOD1. Moreover, this effect on SOD1 increased with the size and potential of QDs, although the effect became clearly visible in higher concentrations of QDs. The intensity of QD-SOD1 fluorescence, analyzed with the use of capillary electrophoresis with laser-induced fluorescence detection, was dependent on SOD1 concentration. In the case of green QDs, the fluorescence signal decreased with increasing SOD1 concentration. In contrast, the signal strength for Y-QD complexes was not dependent on SOD1 dilutions. The migration time of QDs and their complexes with SOD1 varied depending on the type of QD used. The migration time of G-QD complexes with SOD1 differed slightly. However, in the case of Y-QD complexes with SOD1, the differences in the migration time were not dependent on SOD concentration. This research shows that QDs interact with SOD1 and the influence of QDs on SOD activity is size-dependent. With this knowledge, one might be able to control the activation/inhibition of specific enzymes, such as SOD1.

Recent Advances on Detection of Insecticides Using Optical Sensors

Insecticides are enormously important to industry requirements and market demands in agriculture. Despite their usefulness, these insecticides can pose a dangerous risk to the safety of food, environment and all living things through various mechanisms of action. Concern about the environmental impact of repeated use of insecticides has prompted many researchers to develop rapid, economical, uncomplicated and user-friendly analytical method for the detection of insecticides. In this regards, optical sensors are considered as favorable methods for insecticides analysis because of their special features including rapid detection time, low cost, easy to use and high selectivity and sensitivity. In this review, current progresses of incorporation between recognition elements and optical sensors for insecticide detection are discussed and evaluated well, by categorizing it based on insecticide chemical classes, including the range of detection and limit of detection. Additionally, this review aims to provide powerful insights to researchers for the future development of optical sensors in the detection of insecticides.

How does DNA 'meet' capillary-based microsystems?

DNA possesses various chemical and physical properties which make it important in biological analysis. The opportunity for DNA to 'meet' capillary-based microsystems is rapidly increasing owing to the expanding development of miniaturization. Novel capillary-based methods can provide favourable platforms for DNA-ligand interaction assay, DNA translocation study, DNA separation, DNA aptamer selection, DNA amplification assay, and DNA digestion. Meanwhile, DNA exhibits great potential in the fabrication of new capillary-based biosensors and enzymatic bioreactors. Moreover, DNA has received significant research interest in improving capillary electrophoresis (CE) performance. We focus on highlighting the advantages of combining DNA and capillary-based microsystems. The general trend presented in this review suggests that the 'meeting' has offered a stepping stone for the application of DNA and capillary-based microsystems in the field of analytical chemistry.

Recent developments in non-enzymatic (bio)sensors for detection of pesticide residues: Focusing on antibody, aptamer and molecularly imprinted polymer

The utilization of pesticides has been increased in recent years due to population growth and increasing urbanization. The constant use of pesticides has resulted in contamination of the environment and agricultural products with serious human health concerns associated with their use. Therefore, detection and quantification of pesticides by sensitive and selective methods is highly required in food safety management. Traditional detection methods cannot realize highly sensitive, selective and on-site detection, which limits their application. (Bio)sensors and (bio)assays are emerging tools with unique properties such as rapid, sensitive, efficient and portable detection. Among them, enzyme-based biosensors have been widely developed and some have even been commercialized. However, they suffer from some limitations such as instability and low reproducibility that originate from the nature of enzyme. Non-enzymatic (bio)sensors overcome the current limitations of enzyme-based detection methods and provide great potential for efficient, highly sensitive and low-cost detection assays using smart and miniaturized devices. In this study, we provide an overview of recent advances and new trends in optical and electrochemical non-enzymatic (bio)sensors for the detection of pesticides by focusing on antibody, aptamer and molecularly imprinted polymer (MIP) as recognition elements. Performance, advantages and drawbacks of the developed (bio)sensors are discussed well. The main advantage these recognition elements is their stability over an extended period of time compared to the enzymes. Furthermore, the combination of nanomaterials in these (bio)sensors can significantly improve their performance.

Pesticide Aptasensors-State of the Art and Perspectives

Contamination by pesticides in the food chain and the environment is a worldwide problem that needs to be actively monitored to ensure safety. Unfortunately, standard pesticide analysis based on mass spectrometry takes a lot of time, money and effort. Thus, simple, reliable, cost-effective and field applicable methods for pesticide detection have been actively developed. One of the most promising technologies is an aptamer-based biosensor or so-called aptasensor. It utilizes aptamers, short single-stranded DNAs or RNAs, as pesticide recognition elements to integrate with various innovative biosensing technologies for specific and sensitive detection of pesticide residues. Several platforms for aptasensors have been dynamically established, such as colorimetry, fluorometry, electrochemistry, electrochemiluminescence (ECL) and so forth. Each platform has both advantages and disadvantages depending on the purpose of use and readiness of technology. For example, colorimetric-based aptasensors are more affordable than others because of the simplicity of fabrication and resource requirements. Electrochemical-based aptasensors have mainly shown better sensitivity than others with exceedingly low detection limits. This paper critically reviews the progression of pesticide aptasensors throughout the development process, including the selection, characterization and modification of aptamers, the conceptual frameworks of integrating aptamers and biosensors, the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to end users) criteria of different platforms and the future outlook.

Bioactive microfluidic paper device for pesticide determination in waters

This work presents a new optical microfluidic paper biosensor for the detection of organophosphate pesticides and carbamate pesticides. The assay strip is composed of a paper support (1 × 17.6 mm) onto which acetylcholine esterase (AChE) and acetylcholine chloride (AChCl) are deposited, in such a way that there is a small hole between them that ensures that they only come into contact in the reaction zone when they are carried by a solution of the sample by lateral flow to the reaction zone containing bromocresol purple (BCP) as the pH indicator, immobilized by sol-gel. The sensor operates at room temperature and the rate of the inhibited reaction serves as an analytical signal, which is measured using a camera by quantifying the appropriate colour coordinate. Calibration curves were obtained for chlorpyrifos and carbaryl, with a useful concentration range from 0.24 to 20 μg L^-1 for carbaryl and from 2.00 to 45 μg L^-1 for chlorpyrifos. The detection limits were 0.24 and 2.00 μg L^-1, respectively, and with reproducibility around 4.2-5.5%. The method was applied to the determination of pesticides in different water samples, with no sample preparation.

Capillary electrophoresis-based immunoassay and aptamer assay: A review

Over the last two decades, the group of techniques called affinity probe CE has been widely used for the detection and the determination of several types of biomolecules with high sensitivity. These techniques combine the low sample consumption and high separation power of CE with the selectivity of the probe to the target molecule. The assays can be defined according to the type of probe used: CE immunoassays, with an antibody as the probe, or aptamer-based CE, with an aptamer as the probe. Immunoassays are generally divided into homogeneous and heterogeneous groups, and homogeneous variant can be further performed in competitive or noncompetitive formats. Interacting partners are free in solution at homogeneous assay, as opposed to heterogeneous analyses, where one of them is immobilized onto a solid support. Highly sensitive fluorescence, chemiluminescence or electrochemical detections were typically used in this type of study. The use of the aptamers as probes has several advantages over antibodies such as shorter generation time, higher thermal stability, lower price, and lower variability. The aptamer-based CE technique was in practice utilized for the determination of proteins in biological fluids and environmentally or clinically important small molecules. Both techniques were also transferred to microchip. This review is focused on theoretical principles of these techniques and a summary of their applications in research.

β-cyclodextrin modified quantum dots as pseudo-stationary phase for direct enantioseparation based on capillary electrophoresis with laser-induced fluorescence detection

In recent years, quantum dots (QDs) have attracted a tremendous amount of attention due to their compelling features. In this work, a kind of composite QDs based on β-cyclodextrin (β-CD) and its derivatives modification was prepared, and for the first time utilized to separate and determine enantiomers in the combined system of capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). By taking advantages of the inclusion complexation of β-CD and the fluorescence property of QD core, the composite QDs were added into the running buffer as pseudo-stationary phase. The resultant CE-LIF method accomplished enantioseparation for six groups of model analytes without need of capillary preparation and analyte derivatization. The effects of composite QDs concentration, the pH value and concentration of the running buffer on resolution have been investigated individually. The RSDs of interday and intraday repeatability were in the range of 2.7-8.1%, 0.7-3.9%, and 1.5-3.8% for the peak area, migration time and resolution, respectively. The theoretical calculation results of the binding energies and binding constant further validated the interaction mechanism of composite QDs and target analytes. Furthermore, this developed method was successfully applied to the analysis of the active components (catechin and epicatechin) in Chinese herb Catechu, and the recoveries were in the range of 92.2-108%. The experimental results suggested that the preparation strategy of the composite QDs is appropriate for enantioseparation of more enantiomers by adjusting the modifiers on the surface of QDs, which is particularly promising for electrophoretic enantioseparation based on fluorescence detection, especially for those analytes lacking proper derivative functional groups.

Voltammetric determination of organophosphorus pesticides using a hairpin aptamer immobilized in a graphene oxide-chitosan composite

An aptasensor is described for electrochemical determination of organophosphorus pesticides (OPPs), specifically of profenofos, phorate, isocarbophos, and omethoate. The method uses a hairpin aptamer as signalling donor. Its 5' and 3' ends were modified with amino groups and the redox probe ferrocene (Fc), respectively. A nanocomposite consisting of graphene oxide and chitosan (GO-chit) was used to immobilize the aptamer via formation of an amide link. Its good conductivity facilitates monitoring of the electrochemical responses. Upon addition of an OPP, it will be bound by the aptamer. This results in an opening of the hairpin structure. Thus, Fc is shifted away from the surface of the electrode. As a result, the impedance increases and the redox signal of Fc decreases. The electrochemical performance, binding capacity and response of the aptasensor for profenofos, phorate, isocarbophos and omethoate were studied. The limits of detection are as low as 0.01, 0.1, 0.01 and 0.1 nM, respectively. Graphical abstract Schematic representation of an electrochemical aptasensor prepared by immobilizing ferrocene (Fc) labeled hairpin aptamer (HP) on the surface of graphene oxide-chitosan (GO-chit) modified electrode, and its application to the determination of organophosphorus pesticides (OPPs) by voltammetry.

Computationally Designed Peptides for Zika Virus Detection: An Incremental Construction Approach

Herein, and in contrast to current production of anti-Zika virus antibodies, we propose a semi-combinatorial virtual strategy to select short peptides as biomimetic antibodies/binding agents for the detection of intact Zika virus (ZIKV) particles. The virtual approach was based on generating different docking cycles of tetra, penta, hexa, and heptapeptide libraries by maximizing the discrimination between the amino acid motif in the ZIKV and dengue virus (DENV) envelope protein glycosylation site. Eight peptides, two for each length (tetra, penta, hexa, and heptapeptide) were then synthesized and tested vs. intact ZIKV particles by using a direct enzyme linked immunosorbent assay (ELISA). As a reference, we employed a well-established anti-ZIKV antibody, the antibody 4G2. Three peptide-based assays had good detection limits with dynamic range starting from 10⁵ copies/mL of intact ZIKV particles; this was one order magnitude lower than the other peptides or antibodies. These three peptides showed slight cross-reactivity against the three serotypes of DENV (DENV-1, -2, and -3) at a concentration of 10⁶ copies/mL of intact virus particles, but the discrimination between the DENV and ZIKV was lost when the coating concentration was increased to 10⁷ copies/mL of the virus. The sensitivity of the peptides was tested in the presence of two biological matrices, serum and urine diluted 1:10 and 1:1, respectively. The detection limits decreased about one order of magnitude for ZIKV detection in serum or urine, albeit still having for two of the three peptides tested a distinct analytical signal starting from 10⁶ copies/mL, the concentration of ZIKV in acute infection.

An aptamer assay for aflatoxin B1 detection using Mg2+ mediated free zone capillary electrophoresis coupled with laser induced fluorescence

We described an aptamer based and Mg²⁺ mediated free zone capillary electrophoresis-laser induced fluorescence (CE-LIF) assay for aflatoxin B1 (AFB1) detection. This CE-LIF assay applied an anti-AFB1 aptamer with a single fluorescein (FAM) label at 5' end and a short complementary DNA (cDNA). In the absence of AFB1, the cDNA hybridized with the aptamer probe and formed a duplex DNA. The use of running buffer containing MgCl₂ allowed good isolation of the duplex DNA from the single stranded DNA in CE. We found introducing a biotin label on the cDNA further improved the isolation. When AFB1 existed in sample solution, the aptamer probe bound with AFB1, dissociating from the duplex DNA. Thus, the duplex DNA peak decreased, while the aptamer probe peak increased during CE-LIF analysis. We achieved detection of AFB1 by measuring the aptamer probe peak. The length of cDNA, the ratio of aptamer to cDNA, and the concentration of MgCl₂ in sample buffer and separation buffer had great effect on the aptamer based CE-LIF assay. Under optimized conditions, the detection limit of AFB1 was 0.2 nM, and the dynamic range was from 0.2 nM to 500 nM. Limit of quantitation was 0.5 nM. This CE-LIF assay enabled detection of AFB1 spiked in diluted human serum, diluted human urine, and corn flour samples. This assay exhibits potential for wide application as it integrates the rapidity, high sensitivity, low sample consumption of CE-LIF analysis and the strengths of aptamer.

Microfluidic-based graphene field effect transistor for femtomolar detection of chlorpyrifos

Chlorpyrifos is one of the most widely used pesticides that acts on the nervous system by inhibiting acetylcholinesterase. Prolonged use of chlorpyrifos causes severe neurological, autoimmune, and persistent developmental disorders in humans. Therefore, in this study, a highly sensitive and robust biosensor platform was devised by fabricating graphene field effect transistors (graFET) on Si/SiO2 substrate for the detection of chlorpyrifos in real samples. Anti-chlorpyrifos antibodies were immobilized successfully on the graphene surface. Under optimal conditions, graFET sensor showed an excellent response for chlorpyrifos detection in the linear range of 1 fM to 1 µM with a limit of detection up to 1.8 fM in spiked samples. The developed graFET biosensor is highly stable, sensitive, and specific for chlorpyrifos as confirmed by its significant ability to detect changes in electrostatic potential. These findings signify useful efficacy of immunobiosensors for the detection of chlorpyrifos and other organophosphates in fruits and vegetables.

Aptasensors for pesticide detection

Pesticide contamination has become one of the most serious problems of public health in the world, due to their wide application in agriculture industry to guarantee the crop yield and quality. The detection of pesticide residues plays an important role in food safety management and environment protection. However, the conventional detection methodologies cannot realize highly sensitive, selective and on-site detection, which limits their applications. Aptamers are short single-stranded oligonucleotides (RNA or DNA) selected by SELEX method, which can selectively bind to their targets with high affinity. Compared with the commonly used antibodies or enzymes in designing biosensors, aptamers exhibit better stability, low molecular weight, easy modification and low cost, and were regarded as excellent candidates for developing aptasensors for pesticide detection. In this review, application of aptamers for pesticide detection was reviewed. Firstly, aptamers specifically bind to various pesticides were first summarized. Secondly, the progresses and highlights of developing aptasensors for highly-sensitive and selective detection of pesticide residues were systematically provided. Finally, the present challenges and future perspectives for developing novel highly-effective aptasensor for the detection of pesticide residues were discussed.

Electrochemical determination of methyl parathion based on pillar[5]arene@AuNPs@reduced graphene oxide hybrid nanomaterials

The detection of pesticides has become a very important and critical research area because of the rapid development of agriculture and strict environmental protection regulations.

Advances in aptasensors for the detection of food contaminants

Food safety is a global health objective, and foodborne diseases represent a major crisis in health. Techniques that are simple and suitable for fast screening to detect and identify pathogenic factors in the food chain are vital to ensure food safety. At present, a variety of analytical methods have been reported for the detection of pathogenic agents. Whereas the sensitivity of detection and quantification are still important challenges, we expect major advances from new assay formats and synthetic bio-recognition elements, such as aptamers. Owing to the specific folding capability of aptamers in the presence of an analyte, aptasensors have substantially and successfully been exploited for the detection of a wide range of small and large molecules (e.g., toxins, antibiotics, heavy metals, bacteria, viruses) at very low concentrations. Here, we review the use of aptasensors for the development of highly sensitive and affordable detection tools for food analysis.

Affinity Sensing Strategies for the Detection of Pesticides in Food

This is a review of recent affinity-based approaches that detect pesticides in food. The importance of the quantification and monitoring of pesticides is firstly discussed, followed by a description of the different approaches reported in the literature. The different sensing approaches are reported according to the different recognition element used: antibodies, aptamers, or molecularly imprinted polymers. Schemes of detection and the main features of the assays are reported and commented upon. The large number of affinity sensors recently developed and tested on real samples demonstrate that this approach is ready to be validated to monitor the amount of pesticides used in food commodities.

Critical Review: DNA Aptasensors, Are They Ready for Monitoring Organic Pollutants in Natural and Treated Water Sources?

There is a growing need to monitor anthropogenic organic contaminants detected in water sources. DNA aptamers are synthetic single-stranded oligonucleotides, selected to bind to target contaminants with favorable selectivity and sensitivity. These aptamers can be functionalized and are used with a variety of sensing platforms to develop sensors, or aptasensors. In this critical review, we (1) identify the state-of-the-art in DNA aptamer selection, (2) evaluate target and aptamer properties that make for sensitive and selective binding and sensing, (3) determine strengths and weaknesses of alternative sensing platforms, and (4) assess the potential for aptasensors to quantify environmentally relevant concentrations of organic contaminants in water. Among a suite of target and aptamer properties, binding affinity is either directly (e.g., organic carbon partition coefficient) or inversely (e.g., polar surface area) correlated to properties that indicate greater target hydrophobicity results in the strongest binding aptamers, and binding affinity is correlated to aptasensor limits of detection. Electrochemical-based aptasensors show the greatest sensitivity, which is similar to ELISA-based methods. Only a handful of aptasensors can detect organic pollutants at environmentally relevant concentrations, and interference from structurally similar analogs commonly present in natural waters is a yet-to-be overcome challenge. These findings lead to recommendations to improve aptasensor performance.

Interaction between polymorphisms in cell-cycle genes and environmental factors in regulating cholinesterase activity in people with exposure to omethoate

Cholinesterase activity (ChA), the effective biomarker for organophosphate pesticide exposure, is possibly affected by single nucleotide polymorphisms (SNPs) in cell-cycle-related genes. One hundred and eighty workers with long-term exposure to omethoate and 115 healthy controls were recruited to explore the gene-gene and gene-environment interactions. The acetylthiocholine and dithio-bis-(nitrobenzoic acid) method was used to detect the cholinesterase activities in whole blood, erythrocytes and plasma. Genetic polymorphisms were determined by the PCR-RFLP and direct PCR electrophoresis methods. Statistical results showed that the cholinesterase activities of whole blood, erythrocytes and plasma in the exposure group were significantly lower than those in the control group (p < 0.001), and erythrocyte cholinesterase activities were associated with gender, smoking and drinking in the exposure group (p < 0.05). Single-locus analyses showed that there is a statistically significant difference in the ChA among the genotypes CC, CA and AA of the p21 rs1801270 locus in the control group (p = 0.033), but not in the exposure group. A significant interaction between genes and environmental factors (i.e. p53, p21, mdm2, gender, smoking and drinking) affecting ChA was found through a generalized multifactor dimensionality reduction analysis. These obtained markers will be useful in further marker-assisted selection in workers with exposure to omethoate.

Label-free aptamer-based sensor for specific detection of malathion residues by surface-enhanced Raman scattering

A novel label-free aptamer surface-enhanced Raman scattering (SERS) sensor for trace malathion residue detection was proposed. In this process, the binding of malathion molecule with aptamer is identified directly. The silver nanoparticles modified with positively charged spermine served as enhancing and capture reagents for the negatively charged aptamer. Then, the silver nanoparticles modified by aptamer were used to specifically capture the malathion. The SERS background spectra of spermine, aptamer, and malathion were recorded and distinguished with the spectrum of malathion-aptamer. To enhance the characteristic peak signal of malathion captured by the aptamer, the aggregate reagents (NaCl, KCl, MgCl₂) were compared and selected. The selectivity of this method was verified in the mixed-pesticide standard solution, which included malathion, phosmet, chlorpyrifos-methyl, and fethion. Results show that malathion can be specifically identified when the mixed-pesticide interferences existed. The standard curve was established, presenting a good linear range of 5×10^-7 to 1×10^-5mol·L^-1. The spiked experiments for tap water show good recoveries from 87.4% to 110.5% with a relative standard deviation of less than 4.22%. Therefore, the proposed label-free aptamer SERS sensor is convenient, specifically detects trace malathion residues, and can be applied for qualitative and quantitative analysis of other pesticides.

Ultrasensitive electrochemical immuno-sensing platform based on gold nanoparticles triggering chlorpyrifos detection in fruits and vegetables

Chlorpyrifos (chl) is an organophosphate pesticide extensively used in agriculture and highly toxic for human health. Fluorine doped tin-oxide (FTO) based electrochemical nanosensor was developed for chlorpyrifos detection with gold nanoparticles (AuNPs) and anti-chlorpyrifos antibodies (chl-Ab). AuNPs provides high electrical conductivity and specific resistivity, thus increases the sensitivity of immunoassay. High electrical conductivity of AuNPs reveals that it promotes the redox reaction for better cyclic voltammetry. Based on the intrinsic conductive properties of FTO-AuNPs complex, chl-Ab was immobilized onto AuNPs surface. Under optimized conditions, the proposed FTO based nanosensor exhibited high sensitivity and stable response for the detection of chlorpyrifos, ranging from 1fM to 1µM with limit of detection (LOD) up to 10fM. The FTO-AuNPs sensor was successfully employed for the detection of chlorpyrifos in standard as well in real samples up to 10nM for apple and cabbage, 50nM for pomegranate. The proposed FTO-AuNPs nanosensor can be used as a quantitative tool for rapid, on-site detection of chlorpyrifos traces in real samples when miniaturized due to its excellent stability, sensitivity, and simplicity.

A fluorescent dual aptasensor for the rapid and sensitive onsite detection ofE. coliO157:H7 and its validation in various food matrices

The speedy analysis of food products remains a keen area of concern; thus, rapid, highly efficient and robust on-site detection platforms are essential.