Organophosphate vapor detection on gold electrodes using peptide nanotubes

Advancements in Biosensors Based on the Assembles of Small Organic Molecules and Peptides

Over the past few decades, molecular self-assembly has witnessed tremendous progress in a variety of biosensing and biomedical applications. In particular, self-assembled nanostructures of small organic molecules and peptides with intriguing characteristics (e.g., structure tailoring, facile processability, and excellent biocompatibility) have shown outstanding potential in the development of various biosensors. In this review, we introduced the unique properties of self-assembled nanostructures with small organic molecules and peptides for biosensing applications. We first discussed the applications of such nanostructures in electrochemical biosensors as electrode supports for enzymes and cells and as signal labels with a large number of electroactive units for signal amplification. Secondly, the utilization of fluorescent nanomaterials by self-assembled dyes or peptides was introduced. Thereinto, typical examples based on target-responsive aggregation-induced emission and decomposition-induced fluorescent enhancement were discussed. Finally, the applications of self-assembled nanomaterials in the colorimetric assays were summarized. We also briefly addressed the challenges and future prospects of biosensors based on self-assembled nanostructures.

Carbon nanomaterials for the detection of pesticide residues in food: A review

In agricultural fields, pesticides are widely used, but their residual presence in the environment poses a threat to humans, animals, insects, and ecosystems. The overuse of pesticides for pest control, enhancement of crop yield, etc. leaves behind a significant residual amount in the environment. Various robust, reliable, and reusable methods using a wide class of composites have been developed for the monitoring and controlling of pesticides. Researchers have discovered that carbon nanomaterials have a wide range of characteristics such as high porosity, conductivity and easy electron transfer that can be successfully used to detect pesticide residues from food. This review emphasizes the role of carbon nanomaterials in the field of pesticide residue analysis in different food matrices. The carbon nanomaterials including carbon nanotubes, carbon dots, carbon nanofibers, graphene/graphene oxides, and activated carbon fibres are discussed in the review. In addition, the review examines future prospects in this research area to help improve detection techniques for pesticides analysis.

Identification of Two Commercial Pesticides by a Nanoparticle Gas-Sensing Array

This study presents the experimental testing of a gas-sensing array, for the detection of two commercially available pesticides (i.e., Chloract 48 EC and Nimrod), towards its eventual use along a commercial smart-farming system. The array is comprised of four distinctive sensing devices based on nanoparticles, each functionalized with a different gas-absorbing polymeric layer. As discussed herein, the sensing array is able to identify as well as quantify three gas-analytes, two pesticide solutions, and relative humidity, which acts as a reference analyte. All of the evaluation experiments were conducted in close to real-life conditions; specifically, the sensors response towards the three analytes was tested in three relative humidity backgrounds while the effect of temperature was also considered. The unique response patterns generated after the exposure of the sensing-array to the two gas-analytes were analyzed using the common statistical analysis tool Principal Component Analysis (PCA). The sensing array, being compact, low-cost, and highly sensitive, can be easily integrated with pre-existing crop-monitoring solutions. Given that there are limited reports for effective pesticide gas-sensing solutions, the proposed gas-sensing technology would significantly upgrade the added-value of the integrated system, providing it with unique advantages.

A sensing approach for automated and real-time pesticide detection in the scope of smart-farming

The increased use of pesticides across the globe has a major impact on public health. Advanced sensing methods are considered of significant importance to ensure that pesticide use on agricultural products remains within safety limits. This study presents the experimental testing of a hybrid, nanomaterial based gas-sensing array, for the detection of a commercial organophosphate pesticide, towards its integration in a holistic smart-farming tool such as the "gaiasense" system. The sensing array utilizes nanoparticles (NPs) as the conductive layer of the device while four distinctive polymeric layers (superimposed on top of the NP layer) act as the gas-sensitive layer. The sensing array is ultimately called to discern between two gas-analytes: Chloract 48 EC (a chlorpyrifos based insecticide) and Relative Humidity (R.H.) which acts as a reference analyte since is anticipated to be present in real-field conditions. The unique response patterns generated after the exposure of the sensing-array to the two gas-analytes were analysed using a common statistical analysis tool, namely Principal Component Analysis (PCA). PCA has validated the ability of the array to detect, quantify as well as to differentiate between R.H. and Chloract. The sensing array being compact, low-cost and highly sensitive (LOD in the order of ppb for chlorpyrifos) can be effectively integrated with pre-existing crop-monitoring solutions such as the gaiasense.

A New Portable Colorimetric Sensor Based on RGB Chromaticity for Quantitative Determination of Sarin in Water

Background:

Sarin is a nerve agent which is lethal to people due to its high toxicity. According to its extreme toxicity, sarin, relatively lack of color, highly toxic, miscible in water, poses viable threats to potable water sources. Therefore, there is an urgent need for portable, rapid and yet reliable methods to monitor for adulteration of potable water sources by sarin on spot.

Methods:

A stock solution of 30 mg/L sarin was prepared daily by dissolving 300 μg of sarin in 10 mL isopropanol. A certain amount of sarin was added to the glass tube, and then o-dianisidine and hydrogen peroxide were added. The pH value of the solution was adjusted to 9.8. The solution was transferred to the test tube after 10 minutes. A test tube of 2 mL was placed between the light source and the RGB color sensor. The LED light source illuminates directly over the test tube while the RGB sensor obtained the generated spectral response. This RGB voltage output is connected to the ADC and microcontroller to convert these analog voltages to three digital data. This RGB digital data is linked to the microcomputer through the serial port that is interfaced with the user interface. The data thus obtained in the sensor can be processed to display the sarin concentration.

Results:

Under the optimum conditions as described above, the calibration curve of chromaticity value versus sarin concentration was linear in the range of 0.15 mg/L to 7.8 mg/L. According to the IUPAC definition, theoretical detection limits of this method were 0.147 mg/L and 0.140 mg/L for R and B values, respectively. The practical detection limit was 0.15 mg/L. The sensor was successfully applied to the determination of sarin in artificial water samples and the recoveries were between 86.0% to 95.9%.

Conclusion:

The results in the present work have demonstrated the feasibility to design a new portable colorimetric sensor based on the RGB chromaticity method for quantitative determination of sarin in water. The influences of chromogenic reagent, oxidant, reaction time, o-dianisidine concentration, hydrogen peroxide concentration, reaction temperature, pH on the chromaticity values were investigated. The results showed that the sensor possessed high selectivity, sensitivity and good repeatability. The method would be potentially applied to the analysis of other toxic compounds in environment, such as other chemical warfare agents.

Acetylcholinesterase biosensors based on ionic liquid functionalized carbon nanotubes and horseradish peroxidase for monocrotophos determination

Long-term and excessive use of monocrotophos (MPs) pesticide leads to an accumulation of MPs residues in agricultural products. Electrochemical biosensor technology was developed as a simple and efficient method for detecting MPs. However, commercial acetylcholinesterase (AChE) sensors are not applied in practical MPs detection due to poor stability and reliability. In this study, the advantages of functionalized carbon nanotubes (Cl/MWCNTs) and a bi-enzyme system (horseradish peroxidase (HRP)/AChE) were combined, a novel bi-enzyme electrode (Cl/MWCNTs/HRP/AChE/GCE) was constructed. Under optimal conditions, the bi-enzyme sensor had a wide detection range of 1.0 × 10^-11 to 1.0 × 10^-7 mol/L and low detection limit of 4.5 × 10^-12 mol/L. The proposed AChE biosensor exhibited excellent stability and sensitivity for MPs determination and presented a promising tool for monitoring food safety.

Peptide Nanotube Encapsulated Enzyme Biosensor for Vapor Phase Detection of Malathion, an Organophosphorus Compound

This study explores the use of a butyrylcholinesterase (BChE)-based, reversible reaction biosensor using screen-printed electrodes (SPEs) having a smaller working surface area than the single-use electrodes previously studied. Previous research demonstrated the prospective application of a single-use biosensor fabricated with an acetylcholinesterase (AChE) enzyme encapsulated in peptide nanotubes (PNTs) and enhanced with horseradish peroxidase (HRP) to detect organophosphorus compounds (OPCs) in aqueous and gas phases. In the current study, potential improvements to the biosensor are investigated. BChE-based biosensors were fabricated using PNTs, HRP, and Nafion in combination to increase the reactive surface area, enhance sensitivity, and maintain enzyme stability. Cyclic voltammetry (CV) was used along with the new modified sensor to measure malathion concentration in the gas phase. The results show that a BChE-based biosensor could reliably measure gas phase malathion concentrations between 6–25 ppbv by CV with the extent of inhibition linearly proportional to the malathion concentration (R² = 0.941). This research demonstrated that fabricated BChE-based biosensors could be stored without cold storage requirement for up to six weeks with minimal performance degradation. Moreover, the sensor electrodes were each reused several times, and were still useable at the conclusion of the research. This research demonstrates the potential of fabricating a reusable, inexpensive biosensor that is capable of OPC detection with high sensitivity and a low detection limit without a long-term cold storage requirement.

Dual-Readout Immunochromatographic Assay by Utilizing MnO2 Nanoflowers as the Unique Colorimetric/Chemiluminescent Probe

Manganese dioxide nanoflowers (MnO₂ NFs) were synthesized and used as a dual readout probe to develop a novel immunochromatographic test strip (ITS) for detecting pesticide residues using chlorpyrifos as the model analyte. MnO₂ NFs-labeled antibody for chlorpyrifos was employed as the signal tracer for conducting the ITS. After 10 min competitive immunoreaction, the tracer antibody was captured by the immobilized immunogen in the test strip, resulting in the captured MnO₂ NFs on test line. The captured MnO₂ NFs led to the appearance of brown color on the test line, which could be easily observed by the naked eye as a qualitative readout. Due to the very slight colorimetric difference of chlorpyrifos at trace concentrations, the semiquantitative readout by naked eyes could not meet the demand of quantitative analysis. MnO₂ NFs showed a significant effect on the luminol-H₂O₂ chemiluminescent (CL) system, and the CL signal driven by MnO₂ NFs were used to detect the trace concentration of chlorpyrifos quantitatively. 1,3-Diphenylisobenzofuran quenching studies and TMB-H₂O₂ coloration assays were conducted for studying the enhancing mechanism of MnO₂ NFs, which was based on the oxidant activity to decompose H₂O₂ for forming reactive oxygen species. Under optimal conditions, the linear range of chlorpyrifos was 0.1-50 ng/mL with a low detection limit of 0.033 ng/mL (S/N = 3). The reliability of the dual-readout ITS was successfully demonstrated by the application on traditional Chinese medicine and environmental water samples. Due to the simultaneous rapid-qualitative and sensitive-quantitative detection, the dual-readout protocol provides a promising strategy for rapid screening and field assay on various areas such as environmental monitoring and food safety.

Detection of vapor-phase organophosphate threats using wearable conformable integrated epidermal and textile wireless biosensor systems

Flexible epidermal tattoo and textile-based electrochemical biosensors have been developed for vapor-phase detection of organophosphorus (OP) nerve agents. These new wearable sensors, based on stretchable organophosphorus hydrolase (OPH) enzyme electrodes, are coupled with a fully integrated conformal flexible electronic interface that offers rapid and selective square-wave voltammetric detection of OP vapor threats and wireless data transmission to a mobile device. The epidermal tattoo and textile sensors display a good reproducibility (with RSD of 2.5% and 4.2%, respectively), along with good discrimination against potential interferences and linearity over the 90-300mg/L range, with a sensitivity of 10.7µA∙cm³∙mg^-1 (R² = 0.983) and detection limit of 12mg/L in terms of OP air density. Stress-enduring inks, used for printing the electrode transducers, ensure resilience against mechanical deformations associated with textile and skin-based on-body sensing operations. Theoretical simulations are used to estimate the OP air density over the sensor surface. These fully integrated wearable wireless tattoo and textile-based nerve-agent vapor biosensor systems offer considerable promise for rapid warning regarding personal exposure to OP nerve-agent vapors in variety of decentralized security applications.

Peptide nanostructures in biomedical technology

Nanostructures of peptides have been investigated for biomedical applications due to their unique mechanical and electrical properties in addition to their excellent biocompatibility. Peptides may form fibrils, spheres and tubes in nanoscale depending on the formation conditions. These peptide nanostructures can be used in electrical, medical, dental, and environmental applications. Applications of these nanostructures include, but are not limited to, electronic devices, biosensing, medical imaging and diagnosis, drug delivery, tissue engineering and stem cell research. This review offers a discussion of basic synthesis methods, properties and application of these nanomaterials. The review concludes with recommendations and future directions for peptide nanostructures. WIREs Nanomed Nanobiotechnol 2016, 8:730-743. doi: 10.1002/wnan.1393 For further resources related to this article, please visit the WIREs website.

Nanomaterials-based electrochemical detection of chemical contaminants

Recent advances in the development of nanomaterials-based electrochemical sensors for environmental monitoring and food safety applications are assessed.