A Turn-on Biosensor-Based Aptamer-Mediated Carbon Quantum Dots Nanoaggregate for Acetamiprid Detection in Complex Samples

Aptamer-based biosensors for the detection of neonicotinoid insecticides in environmental samples: A systematic review

Neonicotinoids, sometimes abbreviated as neonics, represent a class of neuro-active insecticides with chemical similarities to nicotine. Neonicotinoids are the most widely adopted group of insecticides globally since their discovery in the late 1980s. Their physiochemical properties surpass those of previously established insecticides, contributing to their popularity in various sectors such as agriculture and wood treatment. The environmental impact of neonicotinoids, often overlooked, underscores the urgency to develop tools for their detection and understanding of their behavior. Conventional methods for pesticide detection have limitations. Chromatographic techniques are sensitive but expensive, generate waste, and require complex sample preparation. Bioassays lack specificity and accuracy, making them suitable as preliminary tests in conjunction with instrumental methods. Aptamer-based biosensor is recognized as an advantageous tool for neonicotinoids detection due to its rapid response, user-friendly nature, cost-effectiveness, and suitability for on-site detection. This comprehensive review represents the inaugural in-depth analysis of advancements in aptamer-based biosensors targeting neonicotinoids such as imidacloprid, thiamethoxam, clothianidin, acetamiprid, thiacloprid, nitenpyram, and dinotefuran. Additionally, the review offers valuable insights into the critical challenges requiring prompt attention for the successful transition from research to practical field applications.

Developments in food neonicotinoids detection: novel recognition strategies, advanced chemical sensing techniques, and recent applications

Neonicotinoid insecticides (NEOs) are a new class of neurotoxic pesticides primarily used for pest control on fruits and vegetables, cereals, and other crops after organophosphorus pesticides (OPPs), carbamate pesticides (CBPs), and pyrethroid pesticides. However, chronic abuse and illegal use have led to the contamination of food and water sources as well as damage to ecological and environmental systems. Long-term exposure to NEOs may pose potential risks to animals (especially bees) and even human health. Consequently, it is necessary to develop effective, robust, and rapid methods for NEOs detection. Specific recognition-based chemical sensing has been regarded as one of the most promising detection tools for NEOs due to their excellent selectivity, sensitivity, and robust interference resistance. In this review, we introduce the novel recognition strategies-enabled chemical sensing in food neonicotinoids detection in the past years (2017-2023). The properties and advantages of molecular imprinting recognition (MIR), host-guest recognition (HGR), electron-catalyzed recognition (ECR), immune recognition (IR), aptamer recognition (AR), and enzyme inhibition recognition (EIR) in the development of NEOs sensing platforms are discussed in detail. Recent applications of chemical sensing platforms in various food products, including fruits and vegetables, cereals, teas, honey, aquatic products, and others are highlighted. In addition, the future trends of applying chemical sensing with specific recognition strategies for NEOs analysis are discussed.

Green Synthesis for Carbon Quantum Dots via Opuntia ficus-indica and Agave maximiliana: Surface-Enhanced Raman Scattering Sensing Applications

In this study, we present an alternative method for synthesizing carbon quantum dots (CQDs) using a green synthesis approach via extracts from Agave maximiliana and Opuntia ficus-indica(Ofi). The extracts from both plants were used as the carbon source for the CQDs. The synthesis method employs mesoporous zeolite 4A as a refractory for the thermal treatment of the samples. Transmission electron microscopy analysis established that the size of the CQDs shows a narrow distribution centered around 2 nm with a maximum size of less than 3 nm for both cases. The CQDs exhibit absorption bands associated with π-π* transitions located around 220 nm. In both cases, photoluminescence (PL) phenomenon was detected by irradiating the samples with a UV wavelength and detecting emissions close to the blue wavelength. Additionally, both kinds of CQDs were tested as surface-enhanced Raman scattering (SERS) substrates against methylene blue (MB), indicating an enhancement associated with ring deformation and stretching modes of the v(C-C) and v(C-N) bonds located around 1400 and 1620 cm-1, respectively. Complementarily, in the framework of density functional theory, H2nC2(2m+1) structures (with n = 3-5 and m = 1-3) were used as a theoretical representation of CQDs in interaction with the MB molecule. It is used for developing the analysis of charge transfer effects between both systems and for specifying elements that generate the SERS effect associated with the chemical enhancement mechanism.

Aggregates-based fluorescence sensing technology for food hazard detection: Principles, improvement strategies, and applications

Aggregates often exhibit modified or completely new properties compared with their molecular elements, making them an extraordinarily advantageous form of materials. The fluorescence signal change characteristics resulting from molecular aggregation endow aggregates with high sensitivity and broad applicability. In molecular aggregates, the photoluminescence properties at the molecular level can be annihilated or elevated, leading to aggregation-causing quenching (ACQ) or aggregation-induced emission (AIE) effects. This change in photoluminescence properties can be intelligently introduced in food hazard detection. Recognition units can combine with the aggregate-based sensor by joining the aggregation process, endowing the sensor with the high specificity of analytes (such as mycotoxins, pathogens, and complex organic molecules). In this review, aggregation mechanisms, structural characteristics of fluorescent materials (including ACQ/AIE-activated), and their applications in food hazard detection (with/without recognition units) are summarized. Because the design of aggregate-based sensors may be influenced by the properties of their components, the sensing mechanisms of different fluorescent materials were described separately. Details of fluorescent materials, including conventional organic dyes, carbon nanomaterials, quantum dots, polymers and polymer-based nanostructures and metal nanoclusters, and recognition units, such as aptamer, antibody, molecular imprinting, and host-guest recognition, are discussed. In addition, future trends of developing aggregate-based fluorescence sensing technology in monitoring food hazards are also proposed.

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.

Selective detection of nitenpyram by silica-supported carbon quantum dots

In this study, a fluorescent sensor of nitrogen-doped carbon quantum dots (N-CQDs) and silica gel hybrid was developed for the quantitative detection of nitenpyram, a toxic neonicotinoid existing in groundwater and/or surface water.The prepared N-CQDs@SiO₂ sensor exhibited remarkable sensing selectivity and sensitivity towards nitenpyram among the four pesticides and six metal ions. A prominent fluorescence quenching of N-CQDs@SiO₂ at 445 nm was observed in the presence of nitenpyram with a linear response range of 0-300.0 mg L^-1 and an estimated limit of detection of 1.53 mg L^-1. The main cause for selective sensing is that nitenpyram absorbs the excitation light of N-CQDs@SiO₂, leading to fluorescence quenching of the sensor through the inner filter effect.

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.

Developing a DNA logic gate nanosensing platform for the detection of acetamiprid

This paper reports a novel fluorescence and colorimetric dual-signal-output DNA aptamer based sensor for the detection of acetamiprid residue. Acetamiprid is a new systemic broad-spectrum insecticide with high insecticidal efficiency that is widely used worldwide, but there is a risk of adverse neurological reactions in humans and animals. The dual-mode output principle designed in this paper, consisting of a fluorescence signal and colorimetric signal, is based on the relevant reaction of the special domain of a G-quadruplex, bidding farewell to a classical single-signal output, with a target-recognition cycle used to complete signal amplification through a hybridization chain reaction. Upgraded detection sensitivity and the qualitative and semi-quantitative detection of acetamiprid are achieved based on the fluorescence signal output and visual discrimination observations during colorimetric experiments. This model was applied to the determination of acetamiprid residue in fruits and vegetables. The dual-detection platform further reduced systematic error, with a detection limit of 27.7 pM. When applied in a comparative detection study using three different pesticides, the system shows excellent discrimination specificity and it performs well in actual sample detection and has a fast response time. Designing DNA logic gates that operate in the presence of targets and molecular-switch-based detection platforms also involves the intersection of biology and computational modeling, providing new ideas for biological platforms.

Green synthesis of carbon quantum dots and their environmental applications

Green synthesis of scalable, high-quality, fluorescent carbon quantum dots (CQDs) from natural biomass remains attractive due to their outstanding environmental application. CQDs are an emerging class of zero-dimensional carbon nanomaterials (<10 nm) that have recently attracted much attention due to their strong optical properties, biocompatibility, nontoxicity, uniform particle size, high photostability, low-cost synthesis, and highly tunable photoluminescence. The unique properties of CQDs possess a broad range of prospective applications in a number of fields such as metal ions detection, photocatalysis, sensing, medical diagnosis, bioimaging, and drug delivery. CQD nanostructures are synthesized using various techniques such as hydrothermal method, laser ablation, microwave irradiation, electrochemical oxidation, reflux method, and ultrasonication. However, this type of fabrication approach requires several chemical reactions including oxidation, carbonization, and pyrolysis. Green synthesis of CQDs has several advantages such as the use of low-cost and non-toxic raw materials, renewable resources, simple operations, and being environment-friendly. This review article will discuss the physicochemical properties of CQDs techniques used in the production of CQDs, and the stability of CQDs along with their applications in wastewater treatment and biomedical fields.

DNA-Mediated Assembly of Carbon Nanomaterials

Carbon nanomaterials (CNMs) have attracted extensive attentions on account of their superior electrical, mechanical, optical, and biological properties. However, the dimensional limit and irregular arrangement have hampered their further application. It is necessary to find an easy, efficient and controllable way to assemble CNMs into well-ordered array. DNA nanotechnology, owning to the advantages of precise programmability, highly structural predictability and spatial addressability, has been widely applied in the assembly of CNMs. Summarizing the progress and achievements in this field will be of great value to related studies. Herein, based on the different dimensions of CNMs containing 0-dimensional (0D) carbon dots (CDs), fullerenes, 1-dimensional (1D) carbon nanotubes (CNTs) and 2-dimensional (2D) graphene, we introduced the conjugation strategies between DNA and CNMs, their different assembly methods and their applications. In addition, we also discuss the existing challenges and future opportunities in the field.

A gold nanoparticle-based visual aptasensor for rapid detection of acetamiprid residues in agricultural products using a smartphone

Based on the colorimetric analysis of gold nanoparticles and a smartphone readable strategy, a stable, sensitive, and visual method was established for rapid detection of acetamiprid residues in agricultural products. By optimizing the key parameters, the detection process only took 40 minutes with good specificity. The acetamiprid aptamer can help AuNPs to resist salt-induced aggregation. Conversely, in the presence of acetamiprid, the anti-protection is weakened and the AuNPs aggregated with the color change of the solution. The photographs of the solution are recorded by the smartphone and analyzed through image processing. In the range from 25 to 300 μM the method can realize a quantitative analysis of acetamiprid, and the detection limit is about 3.81 μM. Excellent recoveries are taken in samples of cucumber, cabbage, and river water, ranging from 96.78% to 129.95%. These results show no significant difference from the results obtained by the microplate reader. What's more, the method employs a smartphone to read without the assistance of professional equipment, which greatly reduces the cost of detection, and shows a promising application prospect for on-site rapid detection of acetamiprid.

Microbial inhibition and biosensing with multifunctional carbon dots: Progress and perspectives

Carbon dots (CDs) and their doped counterparts including nitrogen-doped CDs (N@CDs) have been synthesized by bottom-up or top-down approaches from different precursors. The attractiveness of such emerging 2D‑carbon-based nanosized materials is attributed to their excellent biocompatibility, preparation, aqueous dispersibility, and functionality. The antimicrobial, optical, and electrochemical properties of CDs have been advocated for two important biotechnological applications: bacterial eradication and sensing/biosensing. CDs as well as N@CDs act as antimicrobial agents as their surfaces encompass functional hydroxyl, carboxyl, and amino groups that generate free radicals. As a new class of photoluminescent nanomaterials, CDs can be employed in diversified analytics. CDs with surface carboxyl or amino groups form nanocomposites with nanomaterials or be conjugated with biorecognition molecules toward the development of sensors/biosensors. The deployment of conductive CDs in electrochemical sensing has also increased significantly because of their quantum size, excellent biocompatibility, enzyme-mimicking activity, and high surface area. The review also addresses the ongoing challenges and promises of CDs in pathogenesis and analytics. Perspectives on the future possibilities include the use of CDs in microbial viability assay, wound healing, antiviral therapy, and medical devices.

Synthesis of Fluorescent Carbon Dots and Their Application in Ascorbic Acid Detection

Water-soluble fluorescent carbon dots (CDs) were synthesized by a hydrothermal method using citric acid as the carbon source and ethylenediamine as the nitrogen source. The repeated and scale-up synthetic experiments were carried out to explore the feasibility of macroscopic preparation of CDs. The CDs/Fe3+ composite was prepared by the interaction of the CDs solution and Fe3+ solution. The optical properties, pH dependence and stability behavior of CDs or the CDs/Fe3+ composite were studied by ultraviolet spectroscopy and fluorescence spectroscopy. Following the principles of fluorescence quenching after the addition of Fe3+ and then the fluorescence recovery after the addition of asorbic acid, the fluorescence intensity of the carbon dots was measured at λex = 360 nm, λem = 460 nm. The content of ascorbic acid was calculated by quantitative analysis of the changing fluorescence intensity. The CDs/Fe3+ composite was applied to the determination of different active molecules, and it was found that the composite had specific recognition of ascorbic acid and showed an excellent linear relationship in 5.0-350.0 μmol·L-1. Moreover, the detection limit was 3.11 μmol·L-1. Satisfactory results were achieved when the method was applied to the ascorbic acid determination in jujube fruit. The fluorescent carbon dots composites prepared in this study may have broad application prospects in a rapid, sensitive and trace determination of ascorbic acid content during food processing.

Carbon-based Nanomaterials and Curcumin: A Review of Biosensing Applications

Curcumin, the main active constituent of turmeric (Curcuma longa L.), is a naturally occurring phenolic compound with a wide variety of pharmacological activities. Although it has multiple pharmaceutical properties, its bioavailability and industrial usage are hindered due to rapid hydrolysis and low water solubility. Due to the growing market of curcumin, exact determination of curcumin in trade and human biological samples is important for monitoring therapeutic actions. Different nanomaterials have been suggested for sensing curcumin; and in this case, carbon-based nanomaterials (CNMs) are one of the most outstanding developments in nanomedicine, biosensing, and regenerative medicine. There are a considerable number of reports which have shown interesting potential of CNMs-based biosensors in the sensitive and selective detection of curcumin. Therefore, this review aims to increase understanding the interaction of curcumin with CNMs in the context of biosensing.

Aptamers used for biosensors and targeted therapy

Aptamers are single-stranded nucleic acid sequences that can bind to target molecules with high selectivity and affinity. Most aptamers are screened in vitro by a combinatorial biology technique called systematic evolution of ligands by exponential enrichment (SELEX). Since aptamers were discovered in the 1990s, they have attracted considerable attention and have been widely used in many fields owing to their unique advantages. In this review, we present an overview of the advancements made in aptamers used for biosensors and targeted therapy. For the former, we will discuss multiple aptamer-based biosensors with different principles detected by various signaling methods. For the latter, we will focus on aptamer-based targeted therapy using aptamers as both biotechnological tools for targeted drug delivery and as targeted therapeutic agents. Finally, challenges and new perspectives associated with these two regions were further discussed. We hope that this review will help researchers interested in aptamer-related biosensing and targeted therapy research.

Recent Developments of Carbon Dots in Biosensing: A Review

Early diagnosis of diseases is of great importance because it increases the chance of a cure and significantly reduces treatment costs. Thus, development of rapid, sensitive, and reliable biosensing techniques is essential for the benefits of human life and health. As such, various nanomaterials have been explored to improve performance of biosensors, among which, carbon dots (CDs) have received enormous attention due to their excellent performance. In this Review, the recent advancements of CD-based biosensors have been carefully summarized. First, biosensors are classified according to their sensing strategies, and the role of CDs in these sensors is elaborated in detail. Next, several typical CD-based biosensors (including CD-only, enzymatic, antigen-antibody, and nucleic acid biosensors) and their applications are fully discussed. Last, advantages, challenges, and perspectives on the future trends of CD-based biosensors are highlighted.

MUC-1 aptamer conjugated InP/ZnS quantum dots/nanohydrogel fluorescent composite for mitochondria-mediated apoptosis in MCF-7 cells

The combined use of nanohydrogels (NHGs) and quantum dots (QDs) has resulted in the development of a nanoscaled drug delivery system (DDS) with fluorescence imaging potential. NHG-QDs composite loaded with anti-cancer drugs could be applied as an effective theranostics for simultaneous diagnosis and therapy of cancer cells. Here, we report on the synthesis of NHG-QDs nanosystem (NS) conjugated with an amino-modified MUC-1 aptamer (Ap) and loaded with hydrophobic paclitaxel (PTX). To effectively target and eradicate breast cancer MCF-7 cells, the nanocomposite was further loaded with the inhibitor of lactate dehydrogenase (LDH), sodium oxamate (SO) (Ap-NHG-QDs-PTX-SO) to inhibit the conversion of pyruvate to lactate via LDH and disrupting glycolysis. Results obtained from in vitro analysis (MTT assay, apoptosis/necrosis assessment, evaluation of mitochondria targeting, and gene expression profiling) revealed that Ap-NHG-QDs-PTX-SO NS could significantly target and inhibit MCF-7 cells and also induce mitochondria-mediated apoptosis. Collectively, the Ap-NHG-QDs-PTX-SO NS is proposed to serve as a robust theranostics for simultaneous imaging and therapy of breast cancer and other types of solid tumors.

Arginine-derived carbon nanoparticles for determination of Cr(VI) in water samples

Hexavalent chromium, Cr(VI), is a toxic and carcinogenic ion that poses significant risks toward human health and the environment. Due to its extensive industrial use and high water solubility, Cr(VI) can easily contaminate drinking water sources. Therefore, it is essential to develop methods to detect Cr(VI) in water samples. Recently, carbon quantum dots - being biocompatible, easy to synthesize, and cost-effective fluorophores - have been successfully applied for the determination of different heavy metal ions. In this study, arginine-derived carbon nanoparticles were synthesized using a solvent-free one-pot thermal method. These carbon nanoparticles were characterized using transmission electron microscopy, dynamic light scattering analysis, infrared spectroscopy, ultraviolet-visible (UV-vis) light spectroscopy, fluorescence spectroscopy, and CHNO elemental analysis before being used to design a sensor for Cr(VI). The sensor's signal was optimized and the arginine-derived carbon nanoparticle-based Cr(VI) determination method was shown to have a limit of detection of 18 nM, a limit of quantification of 60 nM, and a linear response range of 0.06-100 μM. The sensor's selectivity toward Cr(VI) was studied and a potential interfering ion was identified and dealt with. Finally, the sensor was successfully applied for the determination of Cr(VI) in tap water and mineral water samples.