Inhibition of the acetycholine esterase-stimulated growth of Au nanoparticles: nanotechnology-based sensing of nerve gases

Fabrication of a re-useable ionic liquid-based colorimetric organo nanosensor for detection of nerve agents' stimulants

Nerve agents are highly poisonous organophosphorus chemicals, and the possibility of being used in terrorist attacks seriously threatens public safety. Thus, developing quick and straightforward detection techniques for these dangerous substances is paramount for the scientific communities. In this contribution, we have fabricated a sensitive and easily applicable ionic liquids (ILs) based colorimetric sensor for detecting various nerve agents' stimulants in solution and gas phases, respectively, based on methyl orange (MO)-based IL ([P66614]+[MO]-) derived from MO dye and trihexyltetradecylphosphonium chloride (P66614Cl) by a simple ion exchange mechanism. The developed [P66614]+[MO]- and water-suspended [P66614]+[MO]- nanoparticles are found to be very much sensitive to detecting various nerve agents' stimulants having detection limits in the μM range in any medium and could be identified based on the response times which is found to be superior to many chemosensors available in the literature. The naked eye observed a distinct color change from yellow to fuchsia in the presence of nerve agents' stimulants, which shows better sensitivity than the free organic indicator. Furthermore, a facile test strip with [P66614]+[MO]- and water-suspended [P66614]+[MO]- NPs has been fabricated that can achieve visual detection of various nerve agents' stimulants within the stockpiles of other analogous harmful analytes. Also, a dip-stick experiment has been performed to detect harmful toxic analytes vapor. The effectiveness of [P66614]+[MO]- and water-suspended [P66614]+[MO]- NPs in identifying and quantifying various nerve agents' stimulants demonstrated its potential for usage as a signal tool for real sample analysis.

Gold nanoparticles as colorimetric probes in food analysis: Progress and challenges

The rapid, sensitive and reliable food safety control is urgently needed due to the harmful effects of the food contaminants on human health. Colorimetric approach has exhibited promising potential for the detection of food contaminants due to their easy preparation, rapid detection, high sensitivity, and naked-eye sensing. In recent years, AuNPs-based colorimetric probes have been extensively explored for food analysis. The present article reviews the development of AuNPs-based colorimetric probes for colorimetric sensing and their applications in food analysis. It generally summarizes the properties of AuNPs and introduces the preparation and functionalization methods of AuNPs. An overview of the colorimetric sensing mechanisms of AuNPs-based probes and their applications in analysis of food contaminants are also provided. Although AuNPs-based colorimetric probes show many advantages in detection of food contaminants, challenges remain in terms of complexity of food matrices, multiple analytes detection in a single go, and testing conditions interference.

Ultrathin C3N4 nanosheets-based oxidase-like 2D fluorescence nanozyme for dual-mode detection of organophosphorus pesticides

Engineering efficient dual-mode portable sensor with built-in cross reference correction is of great significance for onsite reliable and precise detection of organophosphorus pesticides (OPs) and evading the false-positive outputs, especially in emergency case. Currently, most nanozyme-based sensors for OPs monitoring primarily replied on the peroxidase-like activity, which involved unstable and toxic H₂O₂. In this scenario, a hybrid oxidase-like 2D fluorescence nanozyme (PtPdNPs@g-C₃N₄) was yielded by in situ growing PtPdNPs in the ultrathin two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanosheet. When acetylcholinesterase (AChE) hydrolyzed acetylthiocholine (ATCh) to thiocholine (TCh), it ablated O₂^-• from the dissolved O₂ catalyzed by PtPdNPs@g-C₃N₄'s oxidase-like activity, hampering the oxidation of o-phenylenediamine (OPD) into 2,3-diaminophenothiazine (DAP). Consequently, with the increasing concentration of OPs which inhibited the blocking effect by inactivating AChE, the produced DAP caused an apparent color change and a dual-color ratiometric fluorescence change in the response system. Through integrating into a smartphone, a H₂O₂-free 2D nanozyme-based onsite colorimetric and fluorescence dual-mode visual imaging sensor for OPs was proposed with acceptable results in real samples, which holds vast promise for further development of commercial point-of-care testing platform in early warning and controlling of OPs pollution for safeguarding environmental health and food safety.

Analyte-mediated formation and growth of nanoparticles for the development of chemical sensors and biosensors

The cornerstone of nanomaterial-based sensing systems is the synthesis of nanoparticles with appropriate surface functionalization that ensures their stability and determines their reactivity with organic or inorganic analytes. To accomplish these requirements, various compounds are used as additives or growth factors to regulate the properties of the synthesized nanoparticles and their reactivity with the target analytes. A different rationale is to use the target analytes as additives or growth agents to control the formation and properties of nanoparticles. The main difference is that the analyte recognition event occurs before or during the formation of nanoparticles and it is based on the reactivity of the analytes with the precursor materials of the nanoparticles (e.g., metal ions, reducing agents, and coatings). The transition from the ionic (or molecular) state of the precursor materials to ordered nanostructured assemblies is used for sensing and signal transduction for the qualitative detection and the quantitative determination of the target analytes, respectively. This review focuses on assays that are based on analyte-mediated regulation of nanoparticles' formation and differentiate them from standard nanoparticle-based assays which rely on pre-synthesized nanoparticles. Firstly, the principles of analyte-mediated nanomaterial sensors are described and then they are discussed with emphasis on the sensing strategies, the signal transduction mechanisms, and their applications. Finally, the main advantages, as well as the limitations of this approach, are discussed and compared with assays that rely on pre-synthesized nanoparticles in order to highlight the major advances accomplished with this type of nano-sensors and elucidate challenges and opportunities for further evolving new nano-sensing strategies.

Highly sensitive visual colorimetric sensor for trichlorfon detection based on the inhibition of metallization of gold nanorods

In this study, a highly sensitive visual colorimetric sensor was designed for the detection of trichlorfon based on inhibiting ascorbate oxidase (AAO)-induced metallization of gold nanorods (Au NRs). Ascorbic acid (AA) can reduce silver ion (Ag⁺) to metal silver (Ag) that will be deposited on the surface of Au NRs, which results in the blue shift of longitudinal localized surface plasmon resonance (LSPR) peak of Au NRs, accompanying by perceptible color changes from red to cyan to red to yellow. In the presence of trichlorfon, the activity of AAO will be inhibited, resulting in less AA is hydrolyzed to dehydroascorbic acid (DHA), and therefore more Ag⁺ is reduced to Ag by AA. Under the optimized conditions, detection of trichlorfon has a wide linear range of 27.8-11111.1 μg/L with a limit of detection as low as 132.6 ng/L. Moreover, the sensor has a good sample spiked recovery (84.7-96.8%) for the determination of trichlorfon in lake water samples. The proposed method can achieve rapid analysis (about 10 min) of trichlorfon with simple operation when there are no other types of organophosphorus pesticides in the real samples.

Bioremediation and decontamination potentials of metallic nanoparticles loaded nanohybrid matrices - A review

The current nanotechnological advancements provide an astonishing insight to fabricate nanomaterials for nano-bioremediation purposes. Exciting characteristics possessed by hybrid matrices at the nanoscale knock endless opportunities to nano-remediate environmentally-related pollunanomaterials tants of emerging concern. Nanometals are considered among the oldest generation of the world has ever noticed. These tiny nanometals and nanometal oxides showed enormous potential in almost every extent of industrial and biotechnological domains, including their potential multipurpose approach to deal with water impurities. In this manuscript, we discussed their role in the diversity of water treatment technologies used to remove bacteria, viruses, heavy metals, pesticides, and organic impurities, providing an ample perspective on their recent advances in terms of their characteristics, attachment strategies, performance, and their scale-up challenges. Finally, we tried to explore their futuristic contribution to nano-remediate environmentally-related pollutants of emerging concern aiming to collect treated yet safe water that can be reused for multipurpose.

Nanoparticle-based colorimetric sensors to detect neurodegenerative disease biomarkers

Neurodegenerative disorders (NDDs) are progressive, incurable health conditions that primarily affect brain cells, and result in loss of brain mass and impaired function. Current sensing technologies for NDD detection are limited by high cost, long sample preparation, and/or require skilled personnel. To overcome these limitations, optical sensors, specifically colorimetric sensors, have garnered increasing attention towards the development of a cost-effective, simple, and rapid alternative approach. In this review, we evaluate colorimetric sensing strategies of NDD biomarkers (e.g. proteins, neurotransmitters, bio-thiols, and sulfide), address the limitations and challenges of optical sensor technologies, and provide our outlook on the future of this field.

Enzyme inhibition methods based on Au nanomaterials for rapid detection of organophosphorus pesticides in agricultural and environmental samples: A review

•

The review systematically and completely collated the enzyme inhibition method based on Au nanomaterials for organophosphorus pesticide detection method in the last 20 years.

•

The significance of the optical properties of Au nanomaterials is outlined with different shapes, sizes, and surface modifiers in enzyme inhibition methods.

•

The principles, classification and application of enzyme inhibition methods based on Au nanomaterials are comprehensively summarized from a new perspective in agricultural and environmental samples, including colorimetric method, fluorometric method, electrochemical biosensor method.

•

Unlike traditional enzyme inhibition method, the merits of enzyme inhibition method based on Au nanomaterials were elaborated in this review.

•

Combined with the research progress of enzyme inhibition method, this review predicts the future research direction of enzyme inhibition method, providing a theoretical reference for researchers.

Background

Organophosphorus pesticides (OPs), as insecticides or acaricides, are widely used in agricultural products to ensure agricultural production. However, widespread use of OPs leads to environmental contamination and significant negative consequences on biodiversity, food security, and water resources. Therefore, developing a sensitive and rapid method to determine OPs residues in different matrices is necessary. Originally, the enzyme inhibition methods are often used as preliminary screens of OPs in crops. Many studies on the characteristic of Au nanomaterials have constantly been emerging in the past decade. Combined with anisotropic Au nanomaterials, enzyme inhibition methods have the advantages of high sensitivity, durability, and high stability.

Aim of Review

This review aims to summarize the principles and strategies of gold (Au) nanomaterials in enzyme inhibition methods, including colorimetric (dispersion, particle size of Au nanomaterials) and fluorometric (fluorescence energy transfer, internal filtration effect) detection, and electrochemical sensing system (shape of Au nanomaterials, Au nanomaterials combined with other nanomaterials). The application of enzyme inhibition in agricultural products and research progress was also outlined. Next, this review illustrates the advantages of Au nanomaterial-based enzyme inhibition methods compared with conventional enzyme inhibition methods. The detection limits and linear range of colorimetric and fluorometric detection and electrochemical biosensors have also been provided. At last, key perspectives, trends, gaps, and future research directions are proposed.

Key Scientific Concepts of Review

Herein, we introduced the technology of enzyme inhibition method based on Au nanomaterials for onsite and infield rapid detection of organophosphorus pesticide.

Recent progress in plasmonic nanoparticle-based biomarker detection and cytometry for the study of central nervous system disorders

Neurological disorders affect hundreds of millions of people around the world, are often life-threatening, untreatable, and can result in debilitating symptoms. The high prevalence of these disorders, which feature biochemical or structural abnormalities in neuronal systems, has spurned innovations in both rapid and early detection to assist in the selection of appropriate treatment strategies to improve the patients' quality of life. Plasmonic nanoparticles (PNPs), a versatile and promising class of nanomaterials, are widely utilized in numerous imaging techniques, drug delivery systems, and biomarker detection methods. Recently, PNP-based nanoprobes have attracted considerable attention for the early diagnosis of neurological disorders. Gold nanoparticles (AuNPs), with high local surface plasmon resonance (LSPR) signals, have been particularly well exploited as probes for dynamic biomarker detection, with quantification sensitivity demonstrated down to the single-molecule level. In this review, we will discuss the possibilities of PNPs in the methodological development for rapid neurological disease identification. In addition, we will also describe a new digital cytometry method that combines dark-field imaging and machine learning for precise biomarker enumeration on single cells. The aim of this review is to attract researchers working on the future development of new plasmonic nanoprobe-based strategies for the diagnosis of neurological disorders.

Application of gold nanoparticles for improvement of analytical characteristics of conductometric enzyme biosensors

In the work, the possibility of using nanoparticles of gold (AuNPs) to upgrade bioselective elements of biosensors in order to improve their analytical characteristics is considered. The bioselective elements of biosensors based on acetylcholinesterase (AChE), butyryl cholinesterase (BuChE) and glucose oxidase (GOD) were used as an experimental model. Immobilization of enzymes on the surfaces of conductometric transducers was performed by the crosslinking of corresponding enzymes using glutaraldehyde. The conditions of immobilization of AChE with gold nanoparticles were optimized. Thus, we determined the optimal values of concentration of crosslinking agent (glutaraldehyde), duration of immobilization, the enzyme to AuNPs ratio, the AuNPs concentration and size. The performance characteristics of the biosensors based on enzymes and AuNPs were investigated and compared with the characteristics of biosensors based on enzymes only. It was also examined how the addition of AuNPs to the bioselective element of biosensors affects the biosensor stability. In particular, the reproducibility of preparation and continuous operation of biosensors was tested as well as their stability at storage. It was shown that the presence of AuNPs in the composition of bioselective elements can improve some characteristics of biosensors, which may be promising for further study and use.

A Fluidics-Based Biosensor to Detect and Characterize Inhibition Patterns of Organophosphate to Acetylcholinesterase in Food Materials

A chip-based electrochemical biosensor is developed herein for the detection of organophosphate (OP) in food materials. The principle of the sensing platform is based on the inhibition of dimethoate (DMT), a typical OP that specifically inhibits acetylcholinesterase (AChE) activity. Carbon nanotube-modified gold electrodes functionalized with polydiallyldimethylammonium chloride (PDDA) and oxidized nanocellulose (NC) were investigated for the sensing of OP, yielding high sensitivity. Compared with noncovalent adsorption and deposition in bovine serum albumin, bioconjugation with lysine side chain activation allowed the enzyme to be stable over three weeks at room temperature. The total amount of AChE was quantified, whose activity inhibition was highly linear with respect to DMT concentration. Increased incubation times and/or DMT concentration decreased current flow. The composite electrode showed a sensitivity 4.8-times higher than that of the bare gold electrode. The biosensor was challenged with organophosphate-spiked food samples and showed a limit of detection (LOD) of DMT at 4.1 nM, with a limit of quantification (LOQ) at 12.6 nM, in the linear range of 10 nM to 1000 nM. Such performance infers significant potential for the use of this system in the detection of organophosphates in real samples.

Near-infrared fluorescent probe for evaluating the acetylcholinesterase effect in the aging process and dietary restriction via fluorescence imaging

Dietary restriction (DR), as a natural intervention, not only benefits the neuroendocrine system, but also has an antiaging action. Acetylcholinesterase (AChE) is one of the most important bioactive substances and plays a major part in choline changes in the aging process. Thus, we aim to evaluate the effect of DR on AChE in the brains of aging animals. In this study, we synthesize a NIR fluorescent probe BD-AChE for the real-time and in situ monitoring of AChE level changes in living cells and living mice, notably in brains. In situ visualization with BD-AChE verified a decrease in the AchE level in the brains of mice aging models. Evidently, the prepared probe has the excellent capability of measuring AChE variation in the brains of aging mice with DR via NIR fluorescence bioimaging, indicating that long-term DR can effectively affect AChE levels in the brain. The attenuation of AChE level in the brain of aging mice after DR could be helpful in infering the advantageous impact of DR on age-related neurodegenerative disease, as a better treatment alternative in the future.

Biothiol modulated growth and aggregation of gold nanoparticles and their determination in biological fluids using digital photometry

This work describes a novel and easy to use method for the determination of biologically important thiols that relies on their ability to inhibit the catalytic enlargement of AuNP seeds in the presence of ACl₄^- ions and trigger their aggregation. UV-vis spectroscopic monitoring of the plasmon resonance bands of the formed AuNPs showed that the spectral and color transitions depend both on the concentration and the structure of biothiols. The colorimetric changes induced by biothiols were quantified in the concentration range from 5 to 300 μM in the RGB color system with digital photometry using a commercially available flatbed scanner as detector. On the basis of these results, the applicability of the method was tested to the determination of glutathione in red blood cells and cysteine in blood plasma with satisfactory recoveries (88.7-96.5%), low detection limits (1.0 μM), good selectivity against major biomolecules under physiologically relevant conditions and satisfactory reproducibility (<8%). The method requires minimum technical expertise, is easy to use and is performed without scientific equipment, holding promise as a simple assay of biothiol testing even by non-experts.

An OliGreen-responsive fluorescence sensor for sensitive detection of organophosphorus pesticide based on its specific selectivity towards T-Hg2+-T DNA structure

In this paper, it was found that OliGreen emitted much stronger fluorescence in rigid T-Hg²⁺-T DNA structure than that in the presence of poly T. Thus, an OliGreen-responsive label-free fluorescent sensor was proposed for sensitive detection of organophosphorus pesticides (OPs) by constructing T-Hg²⁺-T DNA structure. OliGreen emits strong fluorescence in T-Hg²⁺-T structures. The rigid DNA structure of T-Hg²⁺-T is prone to be destroyed by thiocholine (TCh) that hydrolyzed by acetylcholinesterase (AChE) because of the high affinity of TCh with Hg²⁺. As a result, T-Hg²⁺-T DNA structure broke down and the fluorescence intensity of OliGreen decreased greatly. With the inhibition of AChE by OPs, fluorescence intensity of OliGreen remained strong because of the rigid T-Hg²⁺-T DNA structure. Thus, a "turn-on" fluorescent sensor which avoids synthesis of nanomaterials and complex label procedures is proposed based on the fluorescence intensity of OliGreen. DDVP were detected with a wide linear range from 0.005 to 25.0 ng/mL and the detection limit was 2.9 pg/mL, which is more sensitive than previously reported methods.

Highly sensitive label-free bio-interfacial colorimetric sensor based on silk fibroin-gold nanocomposite for facile detection of chlorpyrifos pesticide

Herein, the preparation of gold nanoparticles-silk fibroin (SF-AuNPs) dispersion and its label-free colorimetric detection of the organophosphate pesticide, namely chlorpyrifos, at ppb level are reported. The silk fibroin solution was extracted from B. mori silk after performing degumming, dissolving and dialysis steps. This fibroin solution was used for synthesis of gold nanoparticles in-situ without using any external reducing and capping agent. X-ray Diffractometry (XRD), Field Emission Transmission Electron Microscopy (FETEM) along with Surface Plasmon Resonance based optical evaluation confirmed generation of gold nanoparticles within SF matrix. The resultant SF-AuNPs dispersion exhibited rapid and excellent colorimetric pesticide sensing response even at 10 ppb concentration. Effect of additional parameters viz. pH, ionic concentration and interference from other pesticide samples was also studied. Notably, SF-AuNPs dispersion exhibited selective colorimetric pesticide sensing response which can be calibrated. Furthermore, this method was extended to various simulated real life samples such as tap water, soil and agricultural products including plant residues to successfully detect the presence of chlorpyrifos pesticide. The proposed colorimetric sensor system is facile yet effective and can be employed by novice rural population and expert researchers alike. It can be exploited as preliminary tool for label-free colorimetric chlorpyrifos pesticide sensing in water and agricultural products.

A review on colorimetric methods for determination of organophosphate pesticides using gold and silver nanoparticles

This review (with 99 refs.) summarizes the progress that has been made in colorimetric (i.e. spectrophotometric) determination of organophosphate pesticides (OPPs) using gold and silver nanoparticles (NPs). Following an introduction into the field, a first large section covers the types and functions of organophosphate pesticides. Methods for colorimetric (spectrophotometric) measurements including RGB techniques are discussed next. A further section covers the characteristic features of gold and silver-based NPs. Syntheses and modifications of metal NPs are covered in section 5. This is followed by overviews on enzyme inhibition-based assays, aptamer-based assays and chemical (non-enzymatic) assays, and a discussion of specific features of colorimetric assays. Several Tables are presented that give an overview on the wealth of methods and materials. A concluding section addresses current challenges and discusses potential future trends and opportunities. Graphical abstractSchematic representation of organophosphate pesticide determinations based on aggregation of nanoparticles (particular silver or gold nanoparticles). This leads to a color change which can be determined visually and monitored by a red shift in the absorption spectrum.

Advances in nanomaterial application in enzyme-based electrochemical biosensors: a review

Electrochemical enzyme-based biosensors are one of the largest and commercially successful groups of biosensors. Integration of nanomaterials in the biosensors results in significant improvement of biosensor sensitivity, limit of detection, stability, response rate and other analytical characteristics. Thus, new functional nanomaterials are key components of numerous biosensors. However, due to the great variety of available nanomaterials, they should be carefully selected according to the desired effects. The present review covers the recent applications of various types of nanomaterials in electrochemical enzyme-based biosensors for the detection of small biomolecules, environmental pollutants, food contaminants, and clinical biomarkers. Benefits and limitations of using nanomaterials for analytical purposes are discussed. Furthermore, we highlight specific properties of different nanomaterials, which are relevant to electrochemical biosensors. The review is structured according to the types of nanomaterials. We describe the application of inorganic nanomaterials, such as gold nanoparticles (AuNPs), platinum nanoparticles (PtNPs), silver nanoparticles (AgNPs), and palladium nanoparticles (PdNPs), zeolites, inorganic quantum dots, and organic nanomaterials, such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon and graphene quantum dots, graphene, fullerenes, and calixarenes. Usage of composite nanomaterials is also presented.

Copper(II) complex as a turn on fluorescent sensing platform for acetylcholinesterase activity with high sensitivity

Acetylcholinesterase (AChE) is an important enzyme associated with many nervous diseases, demonstrating the great need for smarter sensing platform with improved sensitivity, selectivity and simplified operation. A "turn on" fluorometric assay is described herein for AChE activity detection, according to the specific enzyme catalyzed reaction of acetylcholine (ATCh) by AChE, which generates thiocholine (TCh) as the product. The well-designed fluorescent probe HBTP possesses ESIPT (Excited State Intramolecular Proton Transfer) nature, leading to a larger Stokes shift, which could be quenched upon coordination with Cu²⁺. The fluorescence-silent HBTP-Cu²⁺ complex could be broken by TCh generated from reaction of ATCh with AChE, giving rise to HBTP release which originates from competitive coordination of TCh with Cu²⁺. This complex probe HBTP-Cu²⁺ offers a limit detection as low as 0.02 mU mL^-1, which is lower than most reported literatures. Furthermore, both HBTP-Cu²⁺ and HBTP show little toxicity to live cells and is available in visualizing cellular AChE activity.

Nanomaterials-Based Colorimetric Immunoassays

Colorimetric immunoassays for tumor marker detection have attracted considerable attention due to their simplicity and high efficiency. With the achievements of nanotechnology and nanoscience, nanomaterials-based colorimetric immunoassays have been demonstrated to be promising alternatives to conventional colorimetric enzyme-linked immunoassays. This review is focused on the progress in colorimetric immunoassays with the signal amplification of nanomaterials, including nanomaterials-based artificial enzymes to catalyze the chromogenic reactions, analyte-induced aggregation or size/morphology change of nanomaterials, nanomaterials as the carriers for loading enzyme labels, and chromogenic reactions induced by the constituent elements released from nanomaterials.

A Luminescence Turn-On Assay for Acetylcholinesterase Activity and Inhibitor Screening Based on Supramolecular Self-Assembly of Alkynylplatinum(II) Complexes on Coordination Polymer

A new approach toward acetylcholinesterase (AChE) detection has been demonstrated based on the electrostatic interactions between anionic alkynylplatinum(II) complex molecules and cationic coordination polymer, together with the spectroscopic and emission characteristics of alkynylplatinum(II) complexes upon supramolecular self-assembly. This process involves strengthening of distinct noncovalent Pt(II)···Pt(II) and π-π stacking interactions, which is evidenced by UV-vis absorption, emission, and resonance light scattering results. Such a method has been applied to AChE inhibitor screening, which is important as the demand for AChE inhibitor assays arises along with the drug development for Alzheimer's disease. It affords an emission turn-on response and operates in a continuous and label-free fashion. The low-energy red emission and large Stokes shift of alkynylplatinum(II) complexes are advantageous to biological applications.

Visual detection of a nerve agent simulant using chemically modified paper strips and dye-assembled inorganic nanocomposite

Chromogenic probe with oxidized bis-indolyl scaffold has been synthesized for the detection of a nerve gas mimicking agent, DCNP (diethyl cyanophosphonate) at pH 8.0 in water. The mechanism of interaction was proposed as the release of cyanide ion through the indole group mediating the hydrolysis of phosphorous-hetero atom bond and, thereafter, the Michael addition of the liberated CN^- ion to the electron deficient C[double bond, length as m-dash]C bond of the bis-indolyl moiety. The reaction featured a remarkable change in color from red to colorless at ambient condition. Then, low-cost and portable paper strips were designed for a rapid and on-site vapor phase detection of DCNP without involving any sophisticated instrument or skilled personnel. Finally, a dye assembled inorganic nanocomposite material was devised to achieve a more sensitive 'turn-on' detection of DCNP in water.

A ratiometric fluorescence assay for acetylcholinesterase activity and inhibitor screening based on supramolecular assembly induced monomer-excimer emission transition of a perylene probe

A ratiometric fluorescence assay for acetylcholinesterase activity is established, which is based on controlled perylene probe assembly and monomer-excimer transition. In a buffer solution, a perylene probe with two negatively charged groups (PDI-DHA) mainly exists in monomeric form. In the presence of cationic lauroylcholine and lauric acid, PDI-DHA can form supramolecular assemblies and the perylene excimer emission can be observed. AChE can catalyze the hydrolysis of lauroylcholine to anionic lauric acid and choline. The hydrolysis process can trigger the breakdown of the supramolecular assemblies. The perylene excimer recovers to the monomeric form because of the de-aggregation of the probe. The excimer-monomer transition can be detected, and a ratiometric fluorescence assay for AChE activity and inhibitor screening is therefore established.

Recent Advances in the Development of Chromophore-Based Chemosensors for Nerve Agents and Phosgene

The extreme toxicity and ready accessibility of nerve agents and phosgene has caused an increase in the demand to develop effective systems for the detection of these substances. Among the traditional platforms utilized for this purpose, chemosensors including surface acoustic wave (SAW) sensors, enzymes, carbon nanotubes, nanoparticles, and chromophore based sensors have attracted increasing attention. In this review, we describe in a comprehensive manner recent progress that has been made on the development of chromophore-based chemosensors for detecting nerve agents (mimic) and phosgene. This review comprises two sections focusing on studies of the development of chemosensors for nerve agents (mimic) and phosgene. In each of the sections, the discussion follows a format which concentrates on different reaction sites/mechanisms involved in the sensing processes. Finally, chemosensors uncovered in these efforts are compared with those based on other sensing methods and challenges facing the design of more effective chemosensors for the detection of nerve agents (mimic) and phosgene are discussed.

Biosensing strategies based on enzymatic reactions and nanoparticles

Application of new nanomaterials to detection of enzymatic activities allows the development of new sensitive and selective bioanalytical assays based on enzymes for recognition and signal amplification.

A gold nanoparticle based colorimetric and fluorescent dual-channel probe for acetylcholinesterase detection and inhibitor screening

Based on the competitive host–guest interaction between p-sulfonatocalix[6]arene (p-SC₆A) capped AuNPs and Rhodamine B (RhB)/acetylthiocholine, a fluorescent and colorimetric dual channel probe was developed for rapid detection of AChE with high sensitivity and selectivity. The detection limit was estimated to be 0.16 mU mL⁻¹. Crucially, due to the specific host–guest interaction, the high selectivity of the bioassay permitted the discrimination of AChE from other cations and proteins including biothiols and enzymes. Furthermore, the present method was also successfully applied to determinate AChE levels and screen AChE inhibitors in real cerebrospinal fluid (CSF) samples, which suggested that our proposed method has great potential to be applied in monitoring the disease progression and drug treatment effects of Alzheimer's disease (AD).

A novel colorimetric and fluorescent dual-channel probe was developed for acetylcholinesterase detection and inhibitor screening with high sensitivity and selectivity.

Sensing Chemical Warfare Agent Simulants via Photonic Crystals of the Morpho didius Butterfly

The rapid and portable detection of trace chemical warfare agents (CWAs) remains a challenge for the international security and monitoring community. This work reports the first use of natural photonic crystals (PhCs) as vapor sensors for CWA simulants. Dimethyl methylphosphonate, a nerve agent simulant, and dichloropentane, a mustard gas simulant, were successfully detected at the parts per million level by processing visible light reflected from the PhC inherent to the wing scales of the Morpho didius butterfly. Additionally, modeling of this natural system suggested several parameters for enhancing the sensitivity of a synthetic PhC toward CWA simulants, including materials selection, structure, and spacing of the PhC, and partial functionalization of the PhC toward the analyte of interest. Collectively, this study provides strategies for designing a sensitive, selective, rapid, and affordable means for CWA detection.

Label-Free Homogeneous Electroanalytical Platform for Pesticide Detection Based on Acetylcholinesterase-Mediated DNA Conformational Switch Integrated with Rolling Circle Amplification

This study addresses the need for sensitive pesticide assay by reporting a new label-free and immobilization-free homogeneous electroanalytical strategy, which combines acetylcholinesterase (AChE)-catalyzed hydrolysis product-mediated DNA conformational switch and rolling circle amplification (RCA) to detect organophosphorous and carbamate pesticides in a "signal-on" mode. When target pesticides were present, AChE activity was inhibited and could not trigger the following DNA conformational change and the RCA reaction, which results in numerous methylene blue (MB) molecules in a free state, generating a strong electrochemical response. This proposed strategy was highly sensitive for omethoate detection with a detection limit as low as 2.1 μg/L and a linear range from 10 to 10 000 μg/L. Furthermore, this strategy was demonstrated to be applicable for pesticide detection in real samples. Thus, this novel label-free homogeneous electroanalytical strategy holds great promise for pesticide detection and can be further exploited for sensing applications in the environment and the food safety field.

A novel enzyme-mediated gold nanoparticle synthesis and its application forin situdetection of horseradish peroxidase inhibitor phenylhydrazine

Biocatalyzed gold nanoparticle synthesis for thein situdetection of horseradish peroxidase inhibitor (phenylhydrazine) has been demonstrated.

A chromogenic and ratiometric fluorogenic probe for rapid detection of a nerve agent simulant DCP based on a hybrid hydroxynaphthalene–hemicyanine dye

A new cyanine dye (CYD) has been synthesized for DCP sensing.

Optical Detection of Enzymatic Activity and Inhibitors on Non-Covalently Functionalized Fluorescent Graphene Oxide

It has been of great interest to measure the activity of acetylcholinesterase (AChE) and its inhibitor, as AChE is known to accelerate the aggregation of the amyloid beta peptides that underlie Alzheimer's disease. Herein, we report the development of graphene oxide (GO) fluorescence-based biosensors for the detection of AChE activity and AChE inhibitors. To this end, GO was non-covalently functionalized with phenoxy-modified dextran (PhO-dex-GO) through hydrophobic interaction; the resulting GO showed excellent colloidal stability and intense fluorescence in various aqueous solutions as compared to pristine GO and the GO covalently functionalized with dextran. The fluorescence of PhO-dex-GO remarkably increased as AChE catalyzed the hydrolysis of acetylthiocholine (ATCh) to give thiocholine and acetic acid. It was found that the turn-on fluorescence response of PhO-dex-GO to AChE activity was induced by protonation of carboxyl groups on it from the product of the enzymatic hydrolysis reaction, acetic acid. On the basis of its turn-on fluorescence response, PhO-dex-GO was able to report kinetic and thermodynamic parameters involving a maximum velocity, a Michaelis constant, and an inhibition dissociation constant for AChE activity and inhibition. These parameters enable us to determine the activity of AChE and the efficiency of the inhibitor.

Blocked Enzymatic Etching of Gold Nanorods: Application to Colorimetric Detection of Acetylcholinesterase Activity and Its Inhibitors

The anisotropic morphology of gold nanorods (AuNRs) has been shown to lead to nonuniform ligand distribution and preferential etching through their tips. We have recently demonstrated that this effect can be achieved by biocatalytic oxidation with hydrogen peroxide, catalyzed by the enzyme horseradish peroxidase (HRP). We report here that modification of AuNRs with thiol-containing organic molecules such as glutathione and thiocholine hinders enzymatic AuNR etching. Higher concentrations of thiol-containing molecules in the reaction mixture gradually decrease the rate of enzymatic etching, which can be monitored by UV-vis spectroscopy through changes in the AuNR longitudinal plasmon band. This effect can be applied to develop novel optical assays for acetylcholinesterase (AChE) activity. The biocatalytic hydrolysis of acetylthiocholine by AChE yields thiocholine, which prevents enzymatic AuNR etching in the presence of HRP. Additionally, the same bioassay can be used for the detection of nanomolar concentrations of AChE inhibitors such as paraoxon and galanthamine.

Biosensor: an emerging safety tool for meat industry

The meat industry associated with the health hazards like deadly pathogens, veterinary drugs, pesticide residues, toxins and heavy metals is in need of a tool to tackle the awful situation and ensure safer product to consumer. The growth in the industry, global trade scenario, stringent laws and consumer awareness has placed an extra onus on the meat industry to meet out the expectations and demands. Biosensors are the latest tool of detection in the fast growing industries including the food industry. Hence an attempt is envisaged here to review the possibility of harnessing biosensors as tool of safety to safe guard the consumer health and address safety issues in reference to the common threats of concern in the meat industry.