Carbon nanomaterial-enabled pesticide biosensors: Design strategy, biosensing mechanism, and practical application

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

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

A method for detecting perfluorooctanoic acid and perfluorooctane sulfonate in water samples using genetically engineered bacterial biosensor

A simple, reagent and pre-treatment (i.e. dilution, sample purification and pH adjustment) free approach based genetically engineered bacterial biosensor is developed and demonstrated for the detection of perfluorinated compounds in water samples. The bacterial biosensor was developed by integrating two genes called regulatory (defluorinase gene) and reporter gene (green fluorescence gene) through genetic engineering techniques. The as-developed bacterial biosensor was employed to detect perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in water samples upon induction of regulatory gene and expression of green fluorescence protein. The induced fluorescence emission by the biosensor was visualized using fluorescence microscopic images. The specificity of biosensor was evaluated with different types of organic pollutants such as chlorinated compounds, polyaromatic hydrocarbons and pesticides etc., in both presence and absence of PFOA and PFOS. The biosensor was employed to detect the perfluorinated compounds at nano gram level in both standard solutions and natural water samples like river water, wastewater and drinking water with an analysis time of 24 h. The detection of PFOA and PFOS by the developed-bacterial sensor is validated by liquid chromatography coupled with mass spectrometer. The developed biosensor has demonstrated a rapid and sensitive detection of PFOA and PFOS in various water samples.

Graphene/MoS2 Nanohybrid for Biosensors

Graphene has been studied a lot in different scientific fields because of its unique properties, including its superior conductivity, plasmonic property, and biocompatibility. More recently, transition metal dicharcogenide (TMD) nanomaterials, beyond graphene, have been widely researched due to their exceptional properties. Among the various TMD nanomaterials, molybdenum disulfide (MoS2) has attracted attention in biological fields due to its excellent biocompatibility and simple steps for synthesis. Accordingly, graphene and MoS2 have been widely studied to be applied in the development of biosensors. Moreover, nanohybrid materials developed by hybridization of graphene and MoS2 have a huge potential for developing various types of outstanding biosensors, like electrochemical-, optical-, or surface-enhanced Raman spectroscopy (SERS)-based biosensors. In this review, we will focus on materials such as graphene and MoS2. Next, their application will be discussed with regard to the development of highly sensitive biosensors based on graphene, MoS2, and nanohybrid materials composed of graphene and MoS2. In conclusion, this review will provide interdisciplinary knowledge about graphene/MoS2 nanohybrids to be applied to the biomedical field, particularly biosensors.

Biosensors for rapid detection of Salmonella in food: A review

Salmonella is one of the main causes of foodborne infectious diseases, posing a serious threat to public health. It can enter the food supply chain at various stages of production, processing, distribution, and marketing. High prevalence of Salmonella necessitates efficient and effective approaches for its identification, detection, and monitoring at an early stage. Because conventional methods based on plate counting and real-time polymerase chain reaction are time-consuming and laborious, novel rapid detection methods are urgently needed for in-field and on-line applications. Biosensors provide many advantages over conventional laboratory assays in terms of sensitivity, specificity, and accuracy, and show superiority in rapid response and potential portability. They are now recognized as promising alternative tools and one of the most on-site applicable and end user-accessible methods for rapid detection. In recent years, we have witnessed a flourishing of studies in the development of robust and elaborate biosensors for detection of Salmonella in food. This review aims to provide a comprehensive overview on Salmonella biosensors by highlighting different signal-transducing mechanisms (optical, electrochemical, piezoelectric, etc.) and critically analyzing its recent trends, particularly in combination with nanomaterials, microfluidics, portable instruments, and smartphones. Furthermore, current challenges are emphasized and future perspectives are discussed.

Two-dimensional nanocomposite-based electrochemical sensor for rapid determination of trans-resveratrol

A two-dimensional nanocomposite-based disposable electrochemical sensor was fabricated for the rapid analysis of trans-resveratrol (TRA) in red wine. The sensor was prepared by modifying graphene-molybdenum disulfide (Gr-MoS₂) nanocomposite on the surface of screen-printed electrode (SPE). Results show that the Gr-MoS₂ nanocomposite with sheet-on-sheet structure can accelerate the oxidation reaction kinetics of TRA due to its large effective electrochemical surface area and high electron transfer rate. As a result, the Gr-MoS₂ nanocomposite appears the synergistic effects, making the highly sensitive detection of TRA come true. The prepared sensor showed a linear response in TRA concentration from 1.0 to 200 μmol L^-1 (with a limit of detection of 0.45 μmol L^-1). After validating the accuracy with high performance liquid chromatography (HPLC), this nanocomposite-based electrochemical sensor can be applied for the detection of TRA in real red wine samples.

Chemically synthesized chevron-like graphene nanoribbons for electrochemical sensors development: determination of epinephrine

We employ chevron-like graphene nanoribbons (GNRs) synthesized by a solution-based chemical route to develop a novel electrochemical sensor for determination of the neurotransmitter epinephrine (EPI). The sensor surface, a glassy carbon electrode modified with GNRs, is characterized by atomic force microscopy, scanning electron microscopy and Raman spectroscopy, which show that the electrode surface modification comprises of bi-dimensional multilayer-stacked GNRs that retain their molecular structure. The charge transfer process occurring at the electrode interface is evaluated by electrochemical impedance spectroscopy. The sensor is applied to the determination of EPI, employing as an analytical signal the reduction peak corresponding to the epinephrinechrome–leucoepinephrinechrome transition (E = − 0.25 V) instead of the oxidation peak usually employed in the literature (E =  + 0.6 V) in order to minimize interferences. The results obtained demonstrate that chevron-like nanoribbons synthesized by solution methods exhibit reliable electrocatalytic activity for EPI determination. Using differential pulse voltammetry, we obtain a linear concentration range from 6.4 × 10^–6 to 1.0 × 10^–4 M and a detection limit of 2.1 × 10^–6 M. The applicability of the sensor was evaluated by determining EPI in pharmaceutical samples with satisfactory results.

Nanobioconjugates for Signal Amplification in Electrochemical Biosensing

Nanobioconjugates are hybrid materials that result from the coalescence of biomolecules and nanomaterials. They have emerged as a strategy to amplify the signal response in the biosensor field with the potential to enhance the sensitivity and detection limits of analytical assays. This critical review collects a myriad of strategies for the development of nanobioconjugates based on the conjugation of proteins, antibodies, carbohydrates, and DNA/RNA with noble metals, quantum dots, carbon- and magnetic-based nanomaterials, polymers, and complexes. It first discusses nanobioconjugates assembly and characterization to focus on the strategies to amplify a biorecognition event in biosensing, including molecular-, enzymatic-, and electroactive complex-based approaches. It provides some examples, current challenges, and future perspectives of nanobioconjugates for the amplification of signals in electrochemical biosensing.

A disposable molecularly imprinted electrochemical sensor for the ultra-trace detection of the organophosphorus insecticide phosalone employing monodisperse Pt-doped UiO-66 for signal amplification

In this work, a disposable molecularly imprinted electrochemical sensor was developed towards the highly sensitive and selective detection of the organophosphorus insecticide phosalone (PAS), employing a home-made carbon paste microelectrode (CPME) modified with a Zr-based metal-organic framework catalyst (Pt-UiO-66) and a mesoporous structured conductive molecularly imprinted polymer (MIP). Pt-UiO-66 octahedra with isolated dispersed Pt nanoparticle active sites were firstly incorporated into the CPME to provide a remarkably amplified signal for voltammetric determination. The mesoporous MIP was then synthesized onto the Pt-UiO-66/CPME via electropolymerization and a subsequent sol-gel process, which could bind the PAS template molecules through hydrogen bond, coordinate bonding, hydrophobic interaction, and π-π stacking interaction. Morphological, structural, and electrochemical characterization studies revealed that this nano-sized MIP provided excellent features for PAS detection, including high porosity, large surface area, enhanced electron-transport ability, greatly improved diffusion capacity, and strong recognition specificity. Therefore, the resulting sensor exhibited an outstanding linearly proportional concentration domain of 0.50 nM-20 μM, low detection limit of 0.078 nM, marked selectivity over certain interferences with similar configurations, considerable repeatability, reproducibility, and stability for the analysis of PAS. Moreover, the sensor was successfully applied for the determination of PAS in agricultural products and environmental samples with results in good compatibility with a chromatographic method, indicative of the high reliability and practicability. Such an electrochemical sensor might open a novel window for the investigation of selective sensing of small organic species from their analogues coupled with the molecular imprinting technique.

Green approach for simultaneous determination of multi-pesticide residue in environmental water samples using excitation-emission matrix fluorescence and multivariate calibration

Pesticides are among the most widespread organic contaminants in aquatic environments. In this work, a new green fluorescence application was proposed for the simultaneous determination of four widely employed pesticides in environmental water samples. To overcome the highly overlapped spectra within the analytes, and with the tissue matrix interferences in complex solutions, we have used the multivariate calibration methods such as parallel factor analysis (PARAFAC) and unfolded partial least squares coupled to residual bilinearization (U-PLS/RBL). These four pesticides can be identified simultaneously, and the correlation coefficients between resolved and actual spectra are all above 0.95. The second-order advantage allowed the determination of four pesticides at the ng mL^-1 level, even in the presence of humic acid (HA). The best results were obtained with the limits of detection of 1.72-18.69 for Carbendazim (CBZ), 0.30-5.19 for carbaryl (CAR), 0.35-6.32 for chlorothalonil (CHL), and 4.92-29.96 for tsumacide (TSU) (ng mL^-1), which can fully meet the quantitative detection and analysis requirements of trace pesticides in water samples. The real water sample of Bohai Seawater was used to check the performance of this approach in practical applications, which have achieved good prediction results of U-PLS/RBL. This study demonstrated the proposed method is rapid, accurate, sensitive, low detection limit, and environmentally friendly to determinate multi-pesticide residues in environmental water samples.

Self-reduction bimetallic nanoparticles on ultrathin MXene nanosheets as functional platform for pesticide sensing

Two-dimensional (2D) transition metal carbides and nitrides, named MXene, appear promising application prospects in sensor filed. Metal nanoparticles, especially bimetallic nanoparticles, are the superior nanocatalyst, which process excellent features due to the high specific surface area and synergistic catalytic capacity. Using ultrathin MXene nanosheets as the natural reducing agent and support, we prepare the shape-controlled Au-Pd bimetallic nanoparticles via a self-reduction process at room temperature in a short time, which can well enhance the catalytic performance and are benefit for the acetylcholinesterase immobilization. Based on their desired properties, we propose a disposable electrochemical biosensor for the detection of organophosphorus pesticide using the multi-dimensional nanocomposites (MXene/Au-Pd) as the functional platform. Under the optimized conditions, our fabricated biosensor exhibits a favorable linear relationship with the concentration of paraoxon from 0.1 to 1000 μg L^-1, with a low detection limit of 1.75 ng L^-1. Furthermore, the biosensor can be applied for paraoxon detection in pear and cucumber samples, providing an effective and useful avenue for the applicability of novel 2D nanomaterials in biosensing field.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Recent Advances in Functionalized Carbon Dots toward the Design of Efficient Materials for Sensing and Catalysis Applications

Since the past decade, enormous research efforts have been devoted to the detection/degradation and quantification of environmental toxic pollutants and biologically important molecules due to their ubiquitous necessity in the fields of environmental protection and human health. These fields of sensor and catalysis are advanced to a new era after emerging of nanomaterials, especially, carbon nanomaterials including graphene, carbon nanotube, carbon dots (C-dots), etc. Among them, the C-dots in the carbon family are rapidly boosted in the aspect of synthesis and application due to their superior properties of chemical and photostability, highly fluorescent with tunable, non/low-toxicity, and biocompatibility. The C-dot-based functional materials have shown great potential in sensor and catalysis fields for the detection/degradation of environmental pollutants. The major advantage of C-dots is that they can be easily prepared from numerous biomass/waste materials which are inexpensive and environment-friendly and are suitable for a developing trend of sustainable materials. This review is devoted to the recent development (since 2017) in the synthesis of biomass- and chemical-derived C-dots as well as diverse functionalization of C-dots. Their capability as a sensor and catalyst and respective mechanism are summarized. The future perspectives of C-dots are also discussed.

Ratiometric electrochemical aptasensor for ultrasensitive detection of Ochratoxin A based on a dual signal amplification strategy: Engineering the binding of methylene blue to DNA

A novel ratiometric electrochemical aptasensor was developed for Ochratoxin A (OTA) detection based on the binding of methylene blue (MB) to DNA with a dual signal amplification strategy. The formation of dsDNA structures between ferrocene-labeled complementary DNA (Fc-cDNA), the OTA aptamer, and complementary helper DNA (hDNA) caused Fc away from the electrode, and allowed dsDNA to bind with a certain amount of MB. Here, a small oxidation current of Fc (I_Fc) and a large oxidation current of MB (I_MB) were obtained. In the presence of OTA, its specific recognition with the aptamer induced the release of aptamer and hDNA from the electrode and subsequently the formation of hairpin structure for cDNA, which caused Fc close to the electrode and a weaker binding ability with MB. Then, an increased I_Fc and a decreased I_MB were obtained. Based on this principle, OTA could be accurately quantified by measuring the ratiometric signal of I_Fc/I_MB. Herein, the dual signal amplification strategy of the introduction of hDNA and the binding with MB after the OTA recognition was exploited to amplify the response signal. The obtained aptasensor showed a linear detection range from 10 pg mL^-1 to 10 ng mL^-1 and a detection limit of 3.3 pg mL^-1. The aptasensor was successfully applied to determine OTA in wheat, and the results were validated through HPLC-MS. Furthermore, by changing the target aptamers, this strategy could be universally used for the determination of various mycotoxins, showing promising potential applications for mycotoxins monitoring in agricultural products and foods.

Integrating Target-Responsive Hydrogels with Smartphone for On-Site ppb-Level Quantitation of Organophosphate Pesticides

Precise on-site profiling of organophosphate pesticides (OPs) is of significant importance for monitoring pollution and estimating poisoning. Herein, we designed a simple and convenient portable kit based on Ag⁺-responsive hydrogels for accurate detection of OPs. The newly developed hydrogels employed o-phenylenediamine (OPD) and silicon quantum dots (SiQDs) as indicator, which possessed ratiometric response. In this sensor, OPs as inhibitor of acetylcholinesterase prevented the generation of thiocholine, which blocked the formation of metal-polymer with Ag⁺, further triggered the oxidation of OPD to yield yellow 2,3-diaminophenazine (DAP) with fluorescence emission at 557 nm. The fluorescence intensity of SiQDs (444 nm) was quenched by DAP through inner filter effect (IFE) process, emerging a typical ratiometric response. Interestingly, the ratiometric signal of kit, which was recorded by smartphone's camera, can be transduced by ImageJ software into the hue parameter that was linearly proportional to the concentration of OPs. The simplicity of portable kit combined with smartphone operation, which possessed high sensitivity (detection limit <10 ng mL^-1) and rapid sample-to-answer detection time (45 min) in agricultural sample, indicating that the methodology offered a new sight for portable monitoring of food safety and human health.

A Water-Stable Luminescent Metal-Organic Framework for Rapid and Visible Sensing of Organophosphorus Pesticides

Metal-organic frameworks (MOFs) have shown considerable prospects for sensing pesticide residues. However, the low stability of MOFs in water hinders them from testing food and environmental samples. Herein, we report an easy and cost-efficient synthesis of a water-stable zirconium luminescent MOF (Zr-LMOF) and its application for rapid, sensitive, and in situ detection of organophosphorous pesticides (OPPs). The Zr-MOF is prepared using Zr(IV) and 1,2,4,5-tetrakis(4-carboxyphenyl)benzene. The synthesized Zr-LMOF rapidly absorbs trace amounts of OPP parathion-methyl and indicates its presence. A low limit of detection of 0.115 μg kg^-1 (0.438 nM) with a wide linear range from 70 μg kg^-1 to 5.0 mg kg^-1 was achieved. Satisfactory recoveries ranging from 78% to 107% were obtained for spiked food and environmental samples. Further, the Zr-LMOF was applied to imitate rapid and in situ imaging detection of pesticide residue on fresh produce nondestructively; visual signals appeared under ultraviolet light within 5 min. These results suggest that the Zr-LMOF has the potential for low-cost, rapid, and in situ imaging detection of OPPs contamination via easy-to-read visual signal.

Amperometric biosensor for glyphosate based on the inhibition of tyrosinase conjugated to carbon nano-onions in a chitosan matrix on a screen-printed electrode

Glyphosate [N-(phosphonomethyl)glycine] is the most frequently used herbicide to date. Due to its indiscriminate use, it has become a globally occurring pollutant of surface waters. A biosensor for glyphosate is described here that consists of a carbon nano-onion/tyrosinase conjugate immobilized in a chitosan matrix on a screen-printed electrode. The analytical principle is based on the inhibition of the enzyme tyrosinase by glyphosate. L-DOPA is used as the enzyme substrate. The presence of the carbon nano-onions has a beneficial effect on the sensitivity of the assay. Glyphosate can be amperometrically quantified in the 0.015 to 10 μM concentration range and with a 6.5 nM (1.1 μg L-1) detection limit. The biosensor is stable more than 2 months at 4 °C. It was applied to the detection of glyphosate in water and soil samples taken from irrigation of a rice field after aerial application. Results were in good agreement with data obtained by a commercial ELISA. Graphical abstract A highly sensitive amperometric biosensor for glyphosate is reported, based on the covalent immobilization of a carbon nano-onion/tyrosinase conjugate on a chitosan matrix.

Tandem catalysis driven by enzymes directed hybrid nanoflowers for on-site ultrasensitive detection of organophosphorus pesticide

Accurate analysis of organophosphate pesticides (OPs) with portable devices remain an elusive goal that have received widespread investigative attention in the areas of environmental contamination and disease prevention. Herein, using all-in-one enzyme-inorganic hybrid nanoflowers (ACC-HNFs) to fabricate high-performance artificial enzyme cascade system, we established a sensitive and affordable lab-on-paper biosensor. This biosensor incorporated disposable screen-printed carbon electrode (SPCE) and colorimetric test strips, which enabled the dual-modal readout (electrochemical and colorimetric signal) for on-site monitoring of OPs, achieving an "on-demand" tuning of the detection performance. Using paraoxon as a model analyte, the ACC-HNFs-based lab-on-paper platform could reach a limit of detection down to the femtogram/mL level (6 fg mL^-1). Meticulous design of ACC-HNFs provided a versatile approach for constructing artificial enzyme as a recognizer and amplifier to fill the gap in constructing robust artificial enzyme systems which can be used for on-site contamination monitoring and biological diagnosis.

Polydopamine-Capped Bimetallic AuPt Hydrogels Enable Robust Biosensor for Organophosphorus Pesticide Detection

Noble metal hydrogels/aerogels with macroscopic nanoassemblies characterized by ultralow density, profuse continuous porosity, and extremely large surface area have gained abundant interest due to not only their tunable physicochemical properties, but also promising applications in catalysis and sensing. Coupling the increased reaction temperature with dopamine-induced effect, herein, a one-step synthetic approach with accelerated gelation kinetics is reported for the synthesis of polydopamine-capped bimetallic AuPt hydrogels. 3D porous nanowire networks with surface functionalization of polydopamine make them a promising biocompatible microenvironment for immobilizing acetylcholinesterase (AChE) and constructing enzyme-based biosensors for sensitive detection of organophosphorus compounds. Taking advantage of their favorable structure and composition, the optimized product exhibits superior electrochemical activity toward thiocholine produced by AChE-catalyzed hydrolysis of acetylthiocholine. Based on the inhibition of organophosphorus pesticide on the enzymatic activity of AChE, the inhibition mode for the detection of paraoxon-ethyl is established, displaying linear regions over the range of 0.5-1000 ng L^-1 with a low detection limit of 0.185 ng L^-1 .

Rapid detection of trichlorfon residues by a microfluidic paper-based phosphorus-detection chip (μPPC)

We propose a novel microfluidic paper-based phosphorus-detection chip (μPPC) for rapid analysis of trichlorfon, one of the most common organophosphate pesticide residues.

Recent developments of photoelectrochemical biosensors for food analysis

Recent developments of photoelectrochemical biosensors for food analysis are summarized and the future prospects in this field are discussed.