Aptasensor for paraquat detection by gold nanoparticle colorimetric method

Selection of aptamers targeting small molecules by capillary electrophoresis: Advances, challenges, and prospects

Aptamers, as novel recognition molecules, hold immense potential across various domains such as biosensing, nucleic acid drugs, medical diagnostics, as well as environmental and food analysis. The majority of aptamer selection processes targeting small molecules and protein commonly employ magnetic bead-based methodologies, wherein the target is initially immobilized on magnetic beads, followed by magnetic separation. The Evolutionary Systematic Evolution of Ligands by Exponential Enrichment technique based on capillary electrophoresis (CE-SELEX) is acknowledged as one of the most efficient screening methods. Our research group has achieved breakthroughs in employing CE-SELEX for the selection of aptamers targeting small molecules. This paper outlines specific methodologies utilized from 2005 to 2023 for CE-SELEX screening for small-molecule targets. It summarizes the methods for the separation of small molecules and oligonucleotide complexes, as well as the identification of candidate aptamers. Drawing upon our research group's extensive experience in CE-SELEX for selecting aptamers targeting multi-scale targets, we offer strategic guidance specifically tailored to the screening of aptamers for small-molecule targets using CE-SELEX. This includes systematic insights into each technical aspect of the screening process: analysis of the structure of small-molecule targets and characteristics of ssDNA libraries, patterns of CE separation and collection of complexes, screening strategies, and CE-based methods for the affinity and specificity characterization of aptamers. This comprehensive review aims to contribute to the widespread adoption of CE-SELEX technology, enhancing the efficiency and success rate of selecting aptamers for small-molecule targets.

Portable label-free electrochemical aptasensor for sensitive detection of paraquat herbicide mediated by oxygen reduction reaction

Paraquat (PQ) is a highly toxic herbicide that has been prohibited in almost 70 countries, but remains in use worldwide. Thus, routine on-site PQ monitoring is a key mechanism to ensure safety and efficiently enforce regulations. Herein, a label-free portable electrochemical aptasensor for the detection of PQ was developed by utilizing aptamer designed to specifically recognize PQ. The aptasensor employs square-wave voltammetry (SWV) to quantify PQ binding on the aptamer-functionalized electrode surface by tracking the downstream oxygen reduction reaction. It provided a detection range spanning from 0.01 to 100.0 μg mL-1 PQ with a limit of detection (LOD) of 8.9 ng mL-1. Validation against spiked tap water, pomegranate juice, and orange juice revealed recovery rate performances of 75 %-130 %. The aptasensor demonstrates promising feasibility for PQ detection in real-world applications, offering remarkable portability and operational simplicity. Notably, it can operate without supplementary redox agents, requiring only sample incubation and subsequent washing steps.

A new colorimetric aptasensor for paraquat detection based on the designed aptamer with multiple paraquat binding sites in combination with gold nanoparticles

The presence of paraquat in the environment poses a danger to human health, leading to a growing demand for an uncomplicated and highly responsive method to detect paraquat. This work reports a new, simple, and sensitive colorimetric aptasensor based on the designed aptamers containing 1-5 paraquat binding sites (R1-R5) in combination with gold nanoparticles (AuNPs). Although the aptamers with more binding sites exhibited greater paraquat interaction capability, the aptasensor based on the R3 aptamer showed the highest detection sensitivity for paraquat in a linear range of 5-50 nM with a limit of detection of 1.29 nM, meaning that it is 2.14 fold more sensitive than the R1-aptasensor. This R3-aptasensor selectively detected paraquat but not the other tested herbicides, including difenzoquat, 2,4-D, ametryn, atrazine, and glufosinate. Also, it efficiently detected paraquat spiked in water samples within the precision acceptance criterion of recovery rates (96.8-105.0%) and the relative standard deviations (1.50-3.81%). These results demonstrated the development of a new aptasensor for paraquat detection, in which the multiple paraquat binding sites of the aptamers could enhance detection sensitivity.

Pesticide residue detection technology for herbal medicine: current status, challenges, and prospects

The domains of cancer therapy, disease prevention, and health care greatly benefit from the use of herbal medicine. Herbal medicine has become the mainstay of developing characteristic agriculture in the planting area increasing year by year. One of the most significant factors in affecting the quality of herbal medicines is the pesticide residue problem caused by pesticide abuse during the cultivation of herbal medicines. It is urgent to solve the problem of detecting pesticide residues in herbal medicines efficiently and rapidly. In this review, we provide a comprehensive description of the various methods used for pesticide residue testing, including optical detection, the enzyme inhibition rate method, molecular detection methods, enzyme immunoassays, lateral immunochromatographic, nanoparticle-based detection methods, colorimetric immunosensor, chemiluminescence immunosensor, smartphone-based immunosensor, etc. On this basis, we systematically analyze the mechanisms and some of the findings of the above detection strategies and discuss the challenges and prospects associated with the development of pesticide residue detection tools.

A novel Zn2+-coordination fluorescence probe for sensing HPPD inhibitors and its application in environmental media and biological imaging

Mesotrione, topramezone, tembotrione, and sulcotrione are four types of 4-hydroxyphenylpyruvate dioxidase (HPPD) inhibitor herbicides that are extensively employed in agricultural practices, but their usage also leads to environmental pollution and poses risks to human health. A probe (E)-1-((2-(pyridin-2-yl) hydrazineylidene) methyl) naphthalen-2-ol (CHMN) based on chelation enhancement (CHEF) effect synthesized. CHMN was first chelated with Zn2+ to form a probe system with green, which can be further used to detect mesotrione, topramezone, tembotrione and sulcotrione in complicated environment. CHMN-Zn2+ detection of four pesticides was accurate, with an excellent linear relationship between 0 and 100 μM. The detection limits were LODmesotrione = 7.79 μM, LODtopramezone = 1.91 μM, LODtembotrione = 1.38 μM and LODsulcotrione = 2.43 μM. The detection time is 1 min, and it is successfully applied in real water sample and bioimaging. This work can provide a novel method for studying the migration and behavior of environmental pollutants.

3D nanocake-like Au-MXene/Au pallet structure-based label-free electrochemical aptasensor for paraquat determination

3D nanocake-like Au-MXene and Au pallet (Au-MXene/AuP) nanocomposite-modified screen-printed carbon electrodes (SPCEs) were utilized to construct an ultrasensitive label-free electrochemical aptasensor through a self-assembly procedure for trace paraquat (PQ) residue detection. Benefiting from the excellent electrochemical (EC) performances (e.g., high conductivity and large surface area) of Au-MXene nanocomposites and AuP substrate, the developed Apt/Au-MXene/AuP/SPCE-based EC aptasensor displayed excellent specificity and anti-interference ability, good repeatability, and stability. A linear relationship between the log value of the change in current intensity [lg (ΔI)] and the log value of the concentration of PQ [lg (CPQ)] was obtained in the range 0.05-1000 ng/mL. The limit of detection was 0.028 ng/mL, and the sensitivity was 255.5 μA/(μM·cm2). Practical applications in malt and mint samples confirmed the accuracy of the EC aptasensor in complex matrices for PQ detection, providing a universal analytical tool for other trace pesticides in different food samples by simply replacing the corresponding aptamers.

Copper nanoparticle-decorated nitrogen-doped carbon nanosheets for electrochemical determination of paraquat

A new strategy to prepare copper (Cu) nanoparticles anchored in nitrogen-doped carbon nanosheets (Cu@CN) has been designed and the nanomaterial applied to the determination of paraquat (PQ). The nanocomposite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and several other techniques. We found that the Cu nanoparticles are uniformly distributed on the carbon materials, providing abundant active sites for electrochemical detection. The electrochemical behavior of the Cu@CN-based PQ sensor was investigated by square-wave voltammetry (SWV). Cu@CN exhibited excellent electrochemical activity and PQ detection performance. The Cu@CN-modified glassy carbon electrode (Cu@CN/GCE) exhibited excellent stability, favorable sensitivity, and high selectivity under optimized conditions (enrichment voltage -0.1 V and enrichment time 400 s) of the SWV test. The detection range reached 0.50 nM to 12.00 μM, and the limit of detection was 0.43 nM with high sensitivity of 18 μA·μM^-1·cm^-2. The detection limit is 9 times better than that of the high-performance liquid chromatography method. The Cu@CN electrochemical sensor demonstrated excellent sensitivity and selectivity also in environmental water and fruit samples enabling its use in practical, rapid trace-level detection of PQ in environmental samples.

A simple aptamer/gold nanoparticle aggregation-based colorimetric assay for oxidized low-density lipoprotein determination

Oxidized low-density lipoprotein (oxLDL) is the leading cause of atherosclerosis and cardiovascular diseases. Here, we created a simple colorimetric assay for sensitive and specific determination of oxLDL using a selective aptamer coupled with salt-induced gold nanoparticle (AuNP) aggregation. The aptamer was chosen by Systematic Evolution of Ligands by Exponential Enrichment to obtain a novel selective sequence towards oxLDL (as 5'-CCATCACGGGGCAGGCGGACAAGGGGTAAGGGCCACATCA-3'). Mixing a 5 μM aptamer solution with an aliquot of a sample containing oxLDL followed by adding AuNP solution (OD = 1) and 80 mmol L^-1 NaCl achieved rapid results within 19 min: linear response to oxLDL from 0.002 to 0.5 μmol L^-1 with high selectivity, a recovery accuracy of 100-111% at the 95% confidence interval, and within-run and between-run precision of 1-6% and 1-5% coefficient variations, respectively. Artificial serum diluted at least 1:8 with distilled water, analyzed by the aptamer-based colorimetric assay, showed excellent correlation with conventional thiobarbituric acid reactive substances (TBARS) (R² = 0.9792) as a rapid colorimetric method without the need for sample preparation other than dilution.

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

Aptamer-enhanced the Ag(I) ion-3,3',5,5'-tetramethylbenzdine catalytic system as a novel colorimetric biosensor for ultrasensitive and selective detection of paraquat

A facile and simple colorimetric biosensor was first established for paraquat (PQ) detection based on the aptamer-enhanced oxidation process of 3,3',5,5'-tetramethylbenzidine (TMB) by Ag⁺. The study confirmed that the interaction of PQ-15 aptamer with Ag⁺ accelerates the electron transfer from the aptamer-Ag⁺ complex to dissolved oxygen, which enhances the release of superoxide anion radicals (O₂̇^-) and facilitates the catalytic oxidation of the chromogenic substrate. PQ-15 aptamer will preferentially bind to PQ molecules, resulting in no further enhancement of the catalytic activity of Ag⁺. Molecular docking results revealed that the PQ molecules are attached to the stem-loop region of the PQ-15 aptamer through σ-π conjugation interactions. The proposed method is simple that only contains Ag⁺ and corresponding aptamer. The limit of detection (LOD) of the constructed colorimetric biosensor for PQ detection was determined to be 16.5 μg·L^-1, belowing the maximum residue limit in fruits and vegetables set by the EU. Moreover, the colorimetric biosensor showed excellent selectivity and anti-interference properties, which was validated for detecting PQ residues in several typical agricultural and water samples.

Development of sensitive colorimetric aptasensor based on short DNA aptamer and its application to screening for paraquat residues in agricultural soil

Paraquat is a widely used herbicide for controlling weeds and grasses in agriculture, and its contaminated residues in agricultural areas are of increasing concern. This work reports the development of the sensitive and easy-to-use colorimetric aptasensor for screening paraquat residues in agricultural soil. The short DNA fragments derived from the original aptamer were analyzed for their capability to interact with paraquat by molecular dynamic simulation. The paraquat-aptasensor was developed using the selected DNA fragment and gold nanoparticles. Its limit of detection (LOD) for paraquat is 2.76 nM, which is more sensitive than the aptasensor with long-length aptamer (LOD = 12.98 nM). The developed aptasensor shows the selectivity to paraquat, but not to other tested herbicides; ametryn, atrazine, difenzoquat, 2,4-D-dimethyl ammonium, and glufosinate. The recovery rates of paraquat detection in the spiked soil samples were in a range of 99.5%-105.1%, with relative standard deviation values of <4%. The developed aptasensor was used to screen for paraquat residues in agricultural soils, and three out of 23 soil samples were tested positive for paraquat, which was confirmed by a high-performance liquid chromatography analysis. These results suggested the potential application of the developed aptasensor to detect paraquat residues in agricultural sites.

A Label-Free Electrochemical Aptasensor Based on Zn/Fe Bimetallic MOF Derived Nanoporous Carbon for Ultra-Sensitive and Selective Determination of Paraquat in Vegetables

Paraquat (PQ) has high acute toxicity, even at low concentrations. For most people, the main pathway of exposure to PQ is through the diet. Therefore, the development of simple and efficient methods for PQ testing is critical for ensuring food safety. In this study, a new electrochemical detection strategy for paraquat is proposed based on the specific binding of PQ to its nucleic acid aptamer. Firstly, the Zn/Fe bimetallic ZIF derived nanoporous carbon (Zn/Fe-ZIF-NPC) and nickel hexacyanoferrate nanoparticles (NiHCF-NPs) were sequentially modified onto the glassy carbon electrode (GCE). NiHCF-NPs served as the signal probes, while Zn/Fe-ZIF-NPC facilitated electron transfer and effectively enhanced the sensing signal of NiHCF-NPs. Au nanoparticles (AuNPs) were then electrodeposited on the NiHCF-NPs/Zn/Fe-ZIF-NPC/GCE and then the thiolated aptamer was assembled on the AuNPs/NiHCF-NPs/Zn/Fe-ZIF-NPC/GCE via Au-S bonding. When incubated with PQ, the formation of PQ–aptamer complexes delayed the interfacial electron transport reaction of NiHCF-NPs, which caused a decrease in the current signals. As a result, simple and highly sensitive detection of PQ can be readily achieved by detecting the signal changes. A linear range was obtained from 0.001 to 100 mg/L with a detection limit as low as 0.34 μg/L. Due to the recognition specificity of the aptamer to its target molecule, the proposed method has excellent anti-interference ability. The prepared electrochemical aptasensor was successfully used for PQ assay in lettuce, cabbage and agriculture irrigation water samples with recoveries ranging from 96.20% to 104.02%, demonstrating the validity and practicality of the proposed method for PQ detection in real samples.

Identification of Mycoplasma pneumoniae by DNA-modified Gold Nanomaterials in a Colorimetric Assay

Mycoplasma pneumoniae (M. pneumoniae) is a highly infectious bacterium and the major cause of pneumonia, especially in school children. Mycoplasma pneumoniae affects the respiratory tract, and 25% of patients experience health-related problems. It is important to have a suitable method to detect M. pneumoniae, and gold nanoparticle (GNP)-based colorimetric biosensing was used in this study to identify the specific target DNA for M. pneumoniae. The color of GNPs changes due to negatively charged GNPs in the presence of positively charged monovalent (Na⁺ ) ions from NaCl. This condition is reversed in the presence of a single-stranded oligonucleotide, as it attracts GNPs, but not in the presence of double-stranded DNA. Single standard capture DNA was mixed with optimal target DNA that cannot be adsorbed by GNPs; under this condition, GNPs are not stabilized and aggregate at high ionic strength (from 100 mM). Without capture DNA, the GNPs were stabilized by capture DNA (from 1 μM), becoming more stable under high ionic conditions and retaining their red color. The GNPs turned blue in the presence of target DNA at concentrations of 1 pM, and the GNPs retained a red color when there was no target in the solution. This method is useful for the simple, easy, and accurate identification of M. pneumoniae target DNA at higher discrimination and without involving sophisticated equipment, and this method provides a diagnostic for M. pneumoniae. This article is protected by copyright. All rights reserved.

The Integration of Gold Nanoparticles with Polymerase Chain Reaction for Constructing Colorimetric Sensing Platforms for Detection of Health-Related DNA and Proteins

Polymerase chain reaction (PCR) is the standard tool in genetic information analysis, and the desirable detection merits of PCR have been extended to disease-related protein analysis. Recently, the combination of PCR and gold nanoparticles (AuNPs) to construct colorimetric sensing platforms has received considerable attention due to its high sensitivity, visual detection, capability for on-site detection, and low cost. However, it lacks a related review to summarize and discuss the advances in this area. This perspective gives an overview of established methods based on the combination of PCR and AuNPs for the visual detection of health-related DNA and proteins. Moreover, this work also addresses the future trends and perspectives for PCR-AuNP hybrid biosensors.

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.

Gold nanoparticle functionalized nanopipette sensors for electrochemical paraquat detection

A sensitive nanopipette sensor is established through a unique design of host-guest recognition, which could be further enhanced by the introduction of gold nanoparticles (Au NPs). Generally, the nanopipette is conjugated with caboxylatopillar[5]arenes (CP[5]) or carboxylated leaning pillar[6]arene (CLP[6]) to generate recognition sites. After the addition of pesticide molecules, they would be captured by CP[5] (or CLP[6]), resulting in a significant electronegativity change on the nanopipette's inner surface, which could be determined by the ionic current change. The CP[5]-modified nanopipette exhibited reliable selectivity for paraquat, while the CLP[6]-modified nanopipette showed an ability of detection for both paraquat and diquat. The addition of Au NPs improved the selectivity and sensitivity of the CP[5]-Au NP-modified nanopipette for paraquat sensing. After optimization by lowering the size of the Au NPs, CP[5]-Au NPs (3 nm)-modified nanopipettes achieved lower detection limits of 0.034 nM for paraquat. Furthermore, in real sample analysis, this sensor demonstrates exceptional sensitivity and selectivity. This study provides a new strategy to develop nanopipette sensors for practical small molecule detection. The gold nanoparticles enhanced quartz nanopipette sensor based on host-guest interaction was firstly established, which could achieve an excellent limit of detection of 3.4 × 10^-11 mol/L for paraquat.

Signal enhancing strategies in aptasensors for the detection of small molecular contaminants by nanomaterials and nucleic acid amplification

Small molecular contaminants (such as mycotoxins, antibiotics, pesticide residues, etc.) in food and environment have given rise to many biological and ecological toxicities, which has attracted worldwide attention in recent years. Meanwhile, due to the advantages of aptamers such as high specificity and stability, easy synthesis and modification, as well as low cost and immunogenicity, various aptasensors for the detection of small molecular contaminants have been flourishing. An aptasensor as a whole is composed of an aptamer-based target recognizer and a signal transducer, which are fields of concentrated research. In the practical detection applications, in order to achieve the quantitative detection of small molecular contaminants at low abundance in real samples, a large number of signal enhancing strategies have been utilized in the development of aptasensors. Recent years is a vintage period for efficient signal enhancing strategies of aptasensors by the aid of nanomaterials and nucleic acid amplification that are applied in the elements for target recognition and signal conversion. Therefore, this paper meticulously reviews the signal enhancing strategies based on nanomaterials (including the (quasi-)zero-dimensional, one-dimensional, two-dimensional and three-dimensional nanomaterials) and nucleic acid amplification (including enzyme-assisted nucleic acid amplification and enzyme-free nucleic acid amplification). Furthermore, the challenges and future trends of the abovementioned signal enhancing strategies for application are also discussed in order to inspire the practitioners in the research and development of aptasensors for small molecular contaminants.

A Zeolite Nanoparticle-Modified Anionic Surface for Aptasensing Lipocalin-2 in Ulcerative Colitis by Dual-Electrodes

An aptasensor was developed on an interdigitated microelectrode (IDME) by current-volt sensing for the diagnosis of ulcerative colitis by detecting the biomarker lipocalin-2. Higher immobilization of the anti-lipocalin-2 aptamer as a probe was achieved by using sodium dodecyl benzenesulfonate-aided zeolite particles. FESEM and FETEM observations revealed that the size of the zeolite particles was <200 nm, and they displayed a uniform distribution and spherical shape. XPS analysis attested the occurrence of Si, Al, and O groups on the zeolite particles. Zeolite particles were immobilized on IDME by a (3-aminopropyl)-trimethoxysilane amine linker, and then, the aptamer as the probe was tethered on the zeolite particles through a biotin-streptavidin strategy assisted by a bifunctional aldehyde linker. Due to the high occupancy of the aptamer and the efficient electric transfer from zeolite particles, higher changes in current can be observed upon interaction of the aptamer with lipocalin-2. The lower detection of lipocalin-2 was noted as 10 pg/mL, with a linear range from 10 pg/mL to 1 μg/mL and a linear regression equation of y=8E-07x+8E-08; R² = 0.991. Control experiments with complementary aptamer and matrix metalloproteinase-9 indicate the specific detection of lipocalin-2. Furthermore, spiking lipocalin-2 in human serum does not interfere with the identification.

Simple colorimetric screening of paraquat residue in vegetables evaluated by localized surface plasmon resonance of gold nanoparticles

The contamination of paraquat in vegetables is widely connected with human health risks, leading to the research interest in developing a paraquat sensing system. This work reports a simple detection method of paraquat based on the electrostatic interaction of paraquat and the negatively charged gold nanoparticles (AuNPs), resulting in the changes of colors from red to blue and the shifting of localized surface plasmon resonance (LSPR) peaks of AuNPs. The limit of detection concentration (C_LOD ) of this system was 100 μM paraquat. Moreover, among eight cationic salts tested, NaCl was selective to enhance the detection sensitivity of the system, resulting in the reduction of C_LOD to 0.10 μM. This system selectively detected paraquat, but not other tested herbicides (ametryn, atrazine, glyphosate, and 2,4-D-dimethyl ammonium). The paraquat-spiking experiment in kale demonstrated the significant recovery rate of paraquat at 96.0-103.0%, and the relative standard deviations were less than 4%. The developed system was efficient for screening contaminated paraquat in vegetables under unwashed and washed conditions. Three out of five unwashed vegetables had a significant level of paraquat as determined by LSPR values. These results suggested the potential application of this system for a simple screening of contaminated paraquat in vegetables. Simple paraquat-screening system was developed based on the negatively charged gold nanoparticles. The limit of paraquat detection of this system was 0.10 μM. This system was potentially used for a simple screening of contaminated paraquat in vegetables.