Instrument-free and visual detection of organophosphorus pesticide using a smartphone by coupling aggregation-induced emission nanoparticle and two-dimension MnO2 nanoflake

A ratiometric fluorescence and visual sensor based on conjugated polymer nanoparticles@MnO2 probe for organophosphorus pesticides detection

Organophosphorus (OPs) pesticide residues pose significant threats to human health and the environment. To tackle this issue, we synthesized water-soluble fluorescent conjugated polymer nanoparticles (WSCPNs), which offer high fluorescence intensity, simple preparation methods, and ease of functionalization, making them ideal candidates for fluorescent sensing applications. These WSCPNs were subsequently used to prepare a WSCPNs@MnO2 probe via in situ synthesis, resulting in efficient fluorescence resonance energy transfer between WSCPNs and MnO₂. This system effectively oxidizes non-fluorescent o-Phenylenediamine (OPD) into 2,3-diaminophenazine (DAP). In the absence of OPs, acetylthiocholine (ATCh) is catalyzed by acetylcholinesterase (AChE) to produce thiocholine (TCh), which reduces MnO₂ on the surface of the probe, restoring the fluorescence intensity. When OPs are present, AChE's catalytic pathway is inhibited, limiting the recovery of fluorescence intensity in WSCPNs. The remaining MnO₂ can further oxidize OPD to DAP, allowing quantitative analysis by monitoring changes in fluorescence signal ratios, achieving a detection limit of 0.0139 ng/mL. Additionally, color changes can be captured and analyzed using a smartphone, facilitating fluorescence visualization for OPs detection, achieving a detection limit of 0.025 ng/mL. This method exhibits excellent anti-interference capabilities and has been successfully applied to detect organophosphorus pesticides in leaves and soil, demonstrating the effectiveness of our ratiometric fluorescence and fluorescence visualization dual-mode sensing platform for monitoring OPs.

Nanomaterials-Enabled Sensors for Detecting and Monitoring Chemical Warfare Agents

Despite their restrictions under international treaties, many chemical warfare agents (CWAs) and their toxic analogues are still used in various industrial sectors such as agriculture and chemical manufacturing. Thus, the need for sensitive and selective CWA detection remains critical. Commercially available detection methods, while accurate, are often bulky, expensive, and require specialized personnel. Sensors incorporating nanomaterials present a promising alternative, offering rapid, portable, and cost-effective detection due to their unique properties, such as high surface area and tunable reactivity. This review covers the four main CWA categories: nerve agents, blister agents, blood agents, and choking agents, highlighting recent progress in nanosensor development for each category. It discusses various sensing mechanisms employed, including fluorescence, colorimetry, chemiresistivity, electrochemistry, and Raman spectroscopy. Despite these advancements, challenges remain, particularly regarding the scalability, stability, and selectivity of nanomaterials-based sensors in complex environments. The review concludes by emphasizing the need to address these challenges and explore novel nanomaterials, the development of scalable nanomanufacturing techniques, and the integration of artificial intelligence to fully unlock the potential of nanomaterials in CWA sensing for homeland security and personal safety.

In-situ synthesis of 2D nanozymes-coated cellulose nanofibers on paper-based chips for portable detection of biothiols

BACKGROUND

Simple, fast and low-cost paper-based analytical devices (PADs) have a good application prospect for point-of-care detection of GSH. However, effective immobilization of functional nanomaterials onto cellulose, as a critical factor in the construction of PADs, presents numerous difficulties and challenges.

RESULTS

In this study, we have developed an exceptionally straightforward and environmentally friendly synthetic approach by using ovalbumin (OVA) as a bio-mineralization template for the preparation of MnO2 nanosheets. The MnO2 nanosheets produced in the solution phase exhibited excellent intrinsic nano-enzyme activity and biodegradability. The OVA-MnO2 nanosheets can effectively oxidize Amplex red in the absence of H2O2, enabling sensitive detection of GSH with a linear range of 5 nM-10 μM and a detection limit as low as 2.8 nM. Furthermore, we utilized this method to facilitate in situ synthesis of OVA-MnO2 nanosheets directly on paper substrates. This approach eliminates the need for conventional stirring and centrifugation steps, greatly simplifying the fabrication process while reducing material usage and time expenditure. Characterization of the chemical composition and morphology confirmed the intimate growth of the 2D nano-enzymes on the cellulose fibers. Utilizing smartphone capabilities, the OVA-MnO2 nanosheet-modified PAD enabled instrument-free detection of GSH, demonstrating high sensitivity (0.74 μM) and a wide linear response range (1-1000 μM).

SIGNIFICANCE

The synthesis of MnO2 nanosheets directly on cellulose substrates substantially streamlines the modification workflow of PADs and reduces detection costs, offering new avenues for clinical diagnostics of relevant diseases.

Peptide-Based Flavivirus Biosensors: From Cell Structure to Virological and Serological Detection Methods

In tropical and developing countries, mosquito-borne diseases by flaviviruses pose a serious threat to public health. Early detection is critical for preventing their spread, but conventional methods are time-consuming and require skilled technicians. Biosensors have been developed to address this issue, but cross-reactivity with other flaviviruses remains a challenge. Peptides are essentially biomaterials used in diagnostics that allow virological and serological techniques to identify flavivirus selectively. This biomaterial originated as a small protein consisting of two to 50 amino acid chains. They offer flexibility in chemical modification and can be easily synthesized and applied to living cells in the engineering process. Peptides could potentially be developed as robust, low-cost, sensitive, and selective receptors for detecting flaviviruses. However, modification and selection of the receptor agents are crucial to determine the effectiveness of binding between the targets and the receptors. This paper addresses two potential peptide nucleic acids (PNAs) and affinity peptides that can detect flavivirus from another target-based biosensor as well as the potential peptide behaviors of flaviviruses. The PNAs detect flaviviruses based on the nucleotide base sequence of the target's virological profile via Watson-Crick base pairing, while the affinity peptides sense the epitope or immunological profile of the targets. Recent developments in the functionalization of peptides for flavivirus biosensors are explored in this Review by division into electrochemical, optical, and other detection methods.

Manganese dioxide nanosheet-modulated ratiometric fluoroprobe based on carbon quantum dots from okra for selective and sensitive dichlorvos detection in foods

Herein, we developed a ratiometric fluoroprobe by integrating okra-derived carbon quantum dots (CQDs) with amplex red (AR) using manganese dioxide nanosheets (MnO2 NSs) as a medium. Fluorescence intensities (FIs) of CQDs were sharply quenched by MnO2 NSs via an inner-filter effect processes, whereas the FIs of AR were significantly enhanced due to oxidation of AR to AR-ox by the oxidase-mimetic activity of MnO2 NSs. Acetyrylcholinesterase hydrolyzed acetylthiocholine to produce thiocholine, and the decomposition of MnO2 NSs to Mn2+ by thiocholine led to the FI recovery of CQDs, but decreased FIs of AR-ox. Based on the above phenomenon and the inhibitory effect of dichlorvos (DDVP) on acetyrylcholinesterase activity, a novel ratiometric fluoroprobe for DDVP quantification was pioneered. Under optimized conditions, this fluoroprobe gave a wide linear range (4-120 μg/L), low detection limit (1.2 μg/L), and satisfactory fortification recoveries (90.0-110.0%), thereby providing good prospects for routine DDVP monitoring in foods.

Active site engineering of Zn-doped mesoporous ceria toward highly efficient organophosphorus hydrolase-mimicking nanozyme

Hydrolase-mimicking nanozymes have received increasing attention in recent years, but the effective rational design and development of these materials has not been realized, as they are not at present considered a critical research target. Herein, we report that Zn-doped mesoporous ceria (Zn-m-ceria) engineered to have an abundance of two different active sites with different functions-one that allows both co-adsorption binding of organophosphate (OP) and water and another that serves as a general base-has significant organophosphorus hydrolase (OPH)-like catalytic activity. Specifically, Zn-m-ceria exhibits a catalytic efficiency over 75- and 25-fold higher than those of m-ceria and natural OPH, respectively. First-principles calculations reveal the importance of Zn for the OPH-mimicking activity of the material, promoting substrate adsorption and proton-binding. The OPH-like Zn-m-ceria catalyst is successfully applied to detect a model OP, methyl paraoxon, in spiked tap water samples with excellent sensitivity, stability, and detection precision. We expect that these findings will promote research based on the rational engineering of the active site of nanozymes and efficient strategies for obtaining a diverse range of catalysts that mimic natural enzymes, and hence the utilization in real-world applications of enzyme-mimicking catalysts with properties superior to their natural analogs should follow.

New modes of converting chemical information with colloidal photonic crystal sensing units

Photonic crystal is a kind of device which can convert a chemical signal into an optical signal and is commonly used in sensing and detection. The maximum reflection wavelength representing the photonic band gap has been the most common converting mode in analytical usage which however discard too much valuable chemical information. In this work, we established two additional modes for mining chemical information more deeply in time and space as the sensing information to distinguish analytes. They are respectively based on dynamic analysis of the spectrum shift and the distinction of the RGB partition block value information of optical image. The molecular imprinting sensing mechanism worked well on three organophosphorus compounds to the detection limit of 10-4 M. The principle component analysis of above data did present a good discrimination of organophosphorus analytes from interfering counter anions to a low detection limit of 10-6 M. To make the detection more convenient and to achieve real-time on-site detection, we have designed the portable photonic crystal signal acquisition kit. Together with the mobile terminal, the kit connects the optical image collected on site, the algorithm working on the cloud and the input/output interactive interface of users in detection. The methods were constructed on an example made of a three-dimensional molecularly imprinted photonic crystal hydrogels sensing unit targeting on organo-phosphides.

Exploring Various Photochemical Processes in Optical Sensing of Pesticides by Luminescent Nanomaterials: A Concise Discussion on Challenges and Recent Advancements

Food safety is a burning global issue in this present era. The prevalence of harmful food additives and contaminants in everyday food is a significant cause for concern as they can adversely affect human health. More particularly, among the different food contaminants, the use of excessive pesticides in agricultural products is severely hazardous. So, the optical detection of residual pesticides is an effective strategy to counter the hazardous effect and ensure food safety. In this perspective, nanomaterials have played a leading role in defending the open threat against food safety instigated by the reckless use of pesticides. Now, nanomaterial-based optical detection of pesticides has reached full pace and needs an inclusive discussion. This Review covers the advancement of photoprocess-based optical detection of pesticides categorically using nanomaterials. Here, we have thoroughly dissected the photoprocesses (aggregation and aggregation-induced emission (AIE), charge transfer and intramolecular charge transfer (ICT), electron transfer and photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), hydrogen bonding, and inner filter effect) and categorically demarcated their significant role in the optical detection of pesticides by luminescent nanomaterials over the last few years.

Illuminating the path: aggregation-induced emission for food contaminants detection

Food safety is a global concern that deeply affects human health. To ensure the profitability of the food industry and consumer safety, there is an urgent need to develop rapid, sensitive, accurate, and cost-effective detection methods for food contaminants. Recently, the Aggregation-Induced Emission (AIE) has been successfully used to detect food contaminants. AIEgens, fluorescent dyes that cause AIE, have several valuable properties including high quantum yields, photostability, and large Stokes shifts. This review provides a detailed introduction to the principles and advantages of AIE-triggered detection, followed by a focus on the past five years' applications of AIE in detecting various food contaminants including pesticides, veterinary drugs, mycotoxins, food additives, ions, pathogens, and biogenic amines. Each detection principle and component is comprehensively covered and explained. Moreover, the similarities and differences among different types of food contaminants are summarized, aiming to inspire future researchers. Finally, this review concludes with a discussion of the prospects for incorporating AIEgens more effectively into the detection of food contaminants.

Aptamer recognition-promoted hybridization chain reaction for amplified label-free and enzyme-free fluorescence analysis of pesticide

Development of high-performance fluorescence sensors for pesticide is highly urgent but remains a grand challenge. It is due to that most of known fluorescence sensors detect pesticides based on enzyme-inhibited strategy, which requires high-price cholinesterase, suffers from serious interference of reductive materials, and can't difference pesticides with each other; the known aptamer-based fluorescence ones entail tool enzymes or nanomaterials to transducer/amplify the signal and demand signalers to be tagged in nucleic acid, which are expensive and intricate. Herein, we develop a novel aptamer-based fluorescence system for label-free, enzyme-free and highly sensitive detection of pesticide (profenofos) based on target-initiated hybridization chain reaction (HCR)-assisted signal amplification and specific intercalation of N-methylmesoporphyrin IX (NMM) in G-quadruplex DNA. Hairpin probe ON1 recognizes profenofos to generate profenofos@ON1 complex, which switches the HCR to yield multiple G-quadruplex DNA, consequently making large numbers of NMM be locked. In comparison with profenofos absence, a sharply improved fluorescence signal was recorded and it was dependent on profenofos dose. Hence, label-free, enzyme-free and highly sensitive detection of profenofos is achieved with limit of detection of 0.085 nM, which compared favorably with or superior to those of known fluorescence methods. Furthermore, the present method was applied to determine the profenofos residue in rice with agreeable result, and will provide more valuable information for guaranteeing the pesticide-related food safety.

Achieving broad availability of SARS-CoV-2 detections via smartphone-based analysis

With the development of COVID-19, widely available tests are in great demand. Naked-eye SARS-CoV-2 test kits have recently been developed as home tests, but their sensitivity and accuracy are sometimes limited. Smartphones can convert various signals into digital information, potentially improving the sensitivity and accuracy of these home tests. Herein, we summarize smartphone-based detections for SARS-CoV-2. Optical detections of non-nucleic acids using various sensors and portable imaging systems, as well as nucleic acid analyses based on LAMP, CRISP, CATCH, and biosensors are discussed. Furthermore, different electrochemical detections were compared. We show results obtained using relatively complex equipment, complicated programming procedures, or custom smartphone apps, and describe methods for obtaining information with only simple setups and free software on smartphones. Then, the combined costs of typical smartphone-based detections are evaluated. Finally, the prospect of improving smartphone-based strategies to achieve broad availability of SARS-CoV-2 detection is proposed.

A Cationic Amphiphilic AIE Polymer for Mitochondrial Targeting and Imaging

Mitochondria are important organelles that play key roles in generating the energy needed for life and in pathways such as apoptosis. Direct targeting of antitumor drugs, such as doxorubicin (DOX), to mitochondria into cells is an effective approach for cancer therapy and inducing cancer cell death. To achieve targeted and effective delivery of antitumor drugs to tumor cells, to enhance the therapeutic effect, and to reduce the side effects during the treatment, we prepared a cationic amphiphilic polymer with aggregation-induced emission (AIE) characteristic. The polymer could be localized to mitochondria with excellent organelle targeting, and it showed good mitochondrial targeting with low toxicity. The polymer could also self-assemble into doxorubicin-loaded micelles in phosphate buffer, with a particle size of about 4.3 nm, an encapsulation rate of 11.03%, and micelle drug loading that reached 0.49%. The results of in vitro cytotoxicity experiments showed that the optimal dosage was 2.0 μg/mL, which had better inhibitory effect on tumor cells and less biological toxicity on heathy cells. Therefore, the cationic amphiphilic polymer can partially replace expensive commercial mitochondrial targeting reagents, and it can be also used as a drug loading tool to directly target mitochondria in cells for corresponding therapeutic research.

Enhanced detection of ascorbic acid with cascaded fluorescence recovery of a dual-nanoquencher system

An innovative strategy with target-triggered cascade fluorescence recovery of a dual-nanoquencher system was developed to detect ascorbic acid (AA). Herein, manganese dioxide (MnO₂) nanosheets and gold nanoparticles (AuNPs) were used as nanoquenchers simultaneously. Owing to their synergistic effects, the fluorescence of 2,3-diaminophenazine (DAP) was decreased efficiently, thus minimizing the background fluorescence. The introduction of AA triggered the decomposition of MnO₂ into Mn²⁺, which induced the aggregation of AuNPs. Both the decomposed MnO₂ and aggregated AuNPs possess weak quenching abilities towards DAP. Such a cascade amplification strategy enhanced the detection sensitivity for AA with a LOD as low as 6.7 nM, which was two orders of magnitude lower than that of MnO₂-based fluorescence assay. Furthermore, this amplification strategy was successfully applied to detect AA in food samples.

Sensitivity Dependence on the Crystal Forms of a Fluorescence Quencher for Silicon Quantum Dots and Its Use in Acetylcholinesterase Assay

Acetylcholinesterase (AChE) plays crucial roles in the nervous system, and thus the reliable assay of its activity is of great significance for the diagnosis of nervous diseases. In this work, we report a fluorescent sensing platform with silicon quantum dots (Si-QDs) as a fluorescence oscillator and nano iron oxyhydroxide (α-, β-, and γ-FeOOH) as a quencher for the assay of AChE. FeOOH with α-, β-, and γ-crystal forms quenches the fluorescence of Si-QDs at λ_ex/λ_em = 350/438 nm, which is retrieved in the presence of AChE and its substrate acetylthiocholine (ATCh) to provide an off-on strategy with a high signal/noise ratio. It is interesting that the sensitivity of AChE sensing is closely related to the crystal forms of FeOOH, with the highest sensitivity by adopting α-FeOOH as the quencher. A linear calibration is achieved within 0.02-1.4 U/L along with a limit of detection of 0.016 U/L. The sensing strategy was demonstrated by the AChE assay in human blood, plasma, and hemocytes.

3D-Printed, Portable, Fluorescent-Sensing Platform for Smartphone-Capable Detection of Organophosphorus Residue Using Reaction-Based Aggregation Induced Emission Luminogens

Development of an easy-to-use, low-cost, household device can help the consumer quickly identify an organophosphorus (OP) residue concentration level. In this work, we demonstrate a 3D-printed, portable, fluorescent-sensing platform for smartphone-capable detection of OPs in vegetables. For development of the proposed device, we utilize the smartphone for capturing the strong thiol-activated fluorescence, which was produced by hydrolysis of OPs in the presence of alkali. The thiol-responsive AIEgen (maleimide-functionalized tetraphenylethylene) was non-emissive in both solution and the solid state but could be readily lighted up by the click addition of thiol to its MI pendant. An android application "Detection" has been developed on the basis of the gray value to analyze the different concentration levels of OPs in vegetable samples. The gray value was linearly related with the concentration of five kinds of organophosphorus residue, ranging from 0 to 20 μg/mL. It was also applied for determination of OPs residue in the leaves of cowpea, celery, and Chinese cabbage. Different from acetylcholinesterase enzyme-based sensors for poor stability under high temperature, the proposed method was a direct detection method for OPs and can be used for rapid monitoring of OPs residue concentration levels before LC-MS analysis.

Ultrasensitive zero-background photoelectrochemical biosensor for analysis of organophosphorus pesticide based on in situ formation of DNA-templated Ag2S photoactive materials

Herein, a novel signal-on photoelectrochemical (PEC) biosensor with nearly zero background noise (ZBN) was first fabricated to determine the presence of organophosphorus pesticide based on in situ formation of DNA-templated Ag₂S photoactive materials, accompanied by hybridization chain reaction (HCR) signal amplification. The capture probe (S1) on the gold nanoparticle-modified electrode can hybridize with the aptamer molecule to generate a simple PEC biosensor. In the presence of a target molecule, the aptamer molecule is released on the double-stranded DNA (dsDNA)-modified PEC biosensor. Meanwhile, the capture probe remains on the electrode and can open the DNA hairpins (H1, H2) which are rich in cytosine, to trigger the HCR reaction. The rich "C" strands are uncovered after formation of a long dsDNA polymer strand, which can assemble multiple silver ions (Ag⁺) by means of by C-Ag⁺-C chelation. Then, a large number of Ag₂S can be generated by challenging with S^2- solution, producing a satisfactory photocurrent signal. The photoactive material is formed in situ, which eliminates the laborious operation. Moreover, the signal can be highly amplified with nearly zero background noise and HCR signal amplification. Under optimal conditions, the ZBN aptasensor exhibited high sensitivity and selectivity, with a low detection limit of 2 pg mL^-1 for malathion. Importantly, the sensing platform can also be applied to determine the presence of malathion in real samples. In this assay, a novel signal-on photoelectrochemical biosensor with nearly zero background noise was first fabricated to determine the presence of organophosphorus pesticide based on in situ formation of DNA-templated Ag₂S photoactive materials, accompanied by hybridization chain reaction signal amplification.

Inner-filter effect induced fluorescent sensor based on fusiform Al-MOF nanosheets for sensitive and visual detection of nitrofuran in milk

Developing highly sensitive and visual methods for rapid detection of antibiotics is significant to ensure food quality and safety. To meet the requirement of nitrofuran antibiotics detection, luminescent fusiform Al(III)-containing metal-organic frameworks (Al-MOF) nanosheets were successfully synthesized by one-step hydrothermal method. And then, the nanosheet served as a fluorescent probe to detect nitrofuran via the inner-filter effect mechanism. The developed sensor allowed sensitive and selective detection of nitrofuran with good linear relationships. And, the detection limit (LOD) values were estimated to be 0.53, 0.838 and 0.583 μM for nitrofurazone, nitrofurantoin and furazolidone detection, respectively. The practical application of the proposed system was verified by HPLC in spiked milk samples with satisfying recoveries ranging from 88.14 to 126.21% and low relative standard deviations of 2.85 ~ 8.13%. Moreover, we designed fluorescent test papers for semi-quantitative detection of nitrofuran via naked-eye colorimetric assay. The established method provides an alternative strategy for semiquantitative detection of nitrofuran.

Label-free immunosensor for cardiac troponin I detection based on aggregation-induced electrochemiluminescence of a distyrylarylene derivative

Herein, the aggregation-induced electrochemiluminescence (AIECL) of a distyrylarylene derivative, 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DPVBi), was investigated for the first time. This luminophore exhibits significantly enhanced photoluminescence (PL) and electrochemiluminescence (ECL) emission with the increases of water content in organic/water mixtures. This high luminescence efficiency of DPVBi in aggregate state is due to the fact that the aggregates can reduce the energy loss by restricting the intramolecular motions. The ECL behavior of DPVBi in acetonitrile was investigated by ECL transients and so-called "half-scan" technology, where singlet-singlet annihilation ECL was generated under continuous potential switching. The DPVBi nanobulks (DPVBi NBs) were prepared to improve its application in aqueous media, which could be conveniently cast on electrode surface for developing sensing platform due to its good film-forming nature. The constructed heterogeneous AIECL platform can produce reductive-oxidative and oxidative-reductive ECL by using trimethylamine (TEA) and potassium peroxodisulfate (K₂S₂O₈) as coreactant. On the basis of the higher ECL efficiency of DPVBi NBs/TEA system, a label free immunosensor for cardiac troponin I (cTnI) was developed with the assistance of electrodeposited gold nanoparticles, and it showed a wide linear range of 20 ng/mL~100 fg/mL and low detection limit of 43 fg/mL. Moreover, the constructed immunosensor also exhibited good specificity, stability and satisfied performance in practical sample analysis.

Optical-Based Biosensors and Their Portable Healthcare Devices for Detecting and Monitoring Biomarkers in Body Fluids

The detection and monitoring of biomarkers in body fluids has been used to improve human healthcare activities for decades. In recent years, researchers have focused their attention on applying the point-of-care (POC) strategies into biomarker detection. The evolution of mobile technologies has allowed researchers to develop numerous portable medical devices that aim to deliver comparable results to clinical measurements. Among these, optical-based detection methods have been considered as one of the common and efficient ways to detect and monitor the presence of biomarkers in bodily fluids, and emerging aggregation-induced emission luminogens (AIEgens) with their distinct features are merging with portable medical devices. In this review, the detection methodologies that use optical measurements in the POC systems for the detection and monitoring of biomarkers in bodily fluids are compared, including colorimetry, fluorescence and chemiluminescence measurements. The current portable technologies, with or without the use of smartphones in device development, that are combined with optical biosensors for the detection and monitoring of biomarkers in body fluids, are also investigated. The review also discusses novel AIEgens used in the portable systems for the detection and monitoring of biomarkers in body fluid. Finally, the potential of future developments and the use of optical detection-based portable devices in healthcare activities are explored.

Aggregation-induced emission luminogen@manganese dioxide core-shell nanomaterial-based paper analytical device for equipment-free and visual detection of organophosphorus pesticide

Organophosphorus pesticide (OP) residues have gathered considerable attention because of their significant threat to society development and healthy life. Developing a sensitive and practical OPs sensor is highly urgent, whereas remains a huge challenge. To this end, we fabricated a high-performance fluorescence paper analytical device (PAD) for apparatus-free and visual sensing of OPs based on aggregation-induced emission (AIE) luminogen's bright emission in aggregated state, unique response of MnO₂ to thiol compounds, and difference of MnO₂ and Mn²⁺ in quenching fluorescence. AIE nanoparticles PTDNPs-0.10 and MnO₂ respectively acted as core and shell to prepare PTDNPs@MnO₂, which possessed high stability and were dripped on cellulose paper's surface to fabricate AIE-PAD. The sensing mechanism is that OPs-treated acetylcholinesterase (AChE) prevents the formation of thiocholine, thereby minimizing the reduction of MnO₂ into Mn²⁺ and changing the output signal. As a result, equipment-free and visual sensing of OPs was acquired with limit of detection of 1.60 ng/mL. This work justifies the feasibility of applying core-shell material to develop high-performance sensor and substituting complex/expensive solution-phase sensor with PAD, providing a new avenue to bring OPs analysis out of the lab and into the world.

Inorganic Recognizer-Assisted Homogeneous Electrochemiluminescence Determination of Organophosphorus Pesticides via Target-Controlled Emitter Release

Given the relevance of organophosphorus pesticides (OPs) with food safety, it is highly urgent to develop sensitive and reliable sensors for OPs. However, most of the OP sensors are developed based on colorimetric and fluorescent techniques, which are limited to severe interference of color and fluorescence from pigments and organic acids in agricultural crops. Herein, we develop an inorganic recognizer-based homogeneous electrochemiluminescence (ECL) sensor for the highly sensitive and credible determination of OPs based on manganese dioxide and tris(2,2'-bipyridine)ruthenium [Ru(bpy)₃]²⁺. Through electrostatic interaction, manganese dioxide nanoflakes-[Ru(bpy)₃]²⁺ nanocomposites (MnNFs-Ru) are formed and exhibit a weak ECL signal due to the confinement of [Ru(bpy)₃]²⁺ in MnNFs-Ru. Interestingly, MnNFs-Ru are capable of recognizing thiols due to the analyte-initiated reduction of MnNFs into Mn²⁺ and release of [Ru(bpy)₃]²⁺ from MnNFs-Ru into solution. Further, MnNFs-Ru are employed for the homogeneous ECL determination of OPs, where acetylcholinesterase (AChE) catalyzes the hydrolysis of acetylthiocholine (ATCh) into thiocholine, which in turn decomposes MnNFs of MnNFs-Ru into Mn²⁺, and OPs inhibit AChE activity. This study widens the application of inorganic recognizers from colorimetry/fluorescence to homogeneous ECL and effectively avoids the interference of color and fluorescence, opening up a new path to the development of high-performance OP sensors and supplying a promising tool for guaranteed OP-related food safety.

Aptamer Recognition-Driven Homogeneous Electrochemical Strategy for Simultaneous Analysis of Multiple Pesticides without Interference of Color and Fluorescence

Credible and simultaneous determination of multiple pesticides is highly desirable for guaranteeing food safety. However, the current methods are limited to significant interference of color and fluorescence or electrode's modification and mainly focus on the analysis of a single pesticide. Herein, we proposed a novel aptamer-based homogeneous electrochemical system for highly sensitive and simultaneous analysis of multiple pesticides based on target pesticide-switched exonuclease III (Exo III)-assisted signal amplification. The recognition of hairpin probes by target pesticides impels the production of pesticide-DNA complexes, which hybridize with electroactive dye-labeled DNA to form double-stranded DNA, subsequently initiating an Exo III-assisted digestion reaction to generate abundant electroactive dye-tagged mononucleotides. In comparison with pesticide deficiency, two higher differential pulse voltammetry (DPV) currents are measured, which rely on the amount of target pesticides. Therefore, simultaneous analysis of two pesticides is realized with limits of detection of 0.0048 and 0.0089 nM, respectively, comparable or superior to those of known methods that focused on a single pesticide. Moreover, the proposed system is successfully employed to simultaneously evaluate the residual level of acetamiprid and profenofos in Brassica chinensis and thus will find more useful applications for pesticide-related food safety.

Smartphone-based optical analysis systems

During the past few decades, there has been a growing trend towards the use of smartphone-based analysis systems. This is mainly due to its ubiquity, its increasing computing capacity, its relatively low cost and the ability to acquire and process data at the same time. Furthermore, there are many sensors integrated into a smartphone, for example a complementary metal-oxide semiconductor (CMOS) sensor. A CMOS sensor enables optical analysis for example by using it as a colorimeter, photometer or spectrometer. This review explores the current state-of-the-art smartphone-based optical analysis systems in various areas of application. It is organized into three sections, each of which investigates one class of smartphone-based devices: (i) smartphone-based colorimeters (ii) smartphone-based photo- and spectrometers and (iii) smartphone-based fluorimeters.

Fluorescence-Based Sensing of Pesticides Using Supramolecular Chemistry

The detection of pesticides in real-world environments is a high priority for a broad range of applications, including in areas of public health, environmental remediation, and agricultural sustainability. While many methods for pesticide detection currently exist, the use of supramolecular fluorescence-based methods has significant practical advantages. Herein, we will review the use of fluorescence-based pesticide detection methods, with a particular focus on supramolecular chemistry-based methods. Illustrative examples that show how such methods have achieved success in real-world environments are also included, as are areas highlighted for future research and development.

pH-Response Quantum Dots with Orange-Red Emission for Monitoring the Residue, Distribution, and Variation of an Organophosphorus Pesticide in an Agricultural Crop

Development of simple, sensitive, and reliable fluorescence sensors for monitoring the residue, distribution, and variation of organophosphorus pesticides (OPs) in agricultural crops is highly urgent but remains challenging, which is ascribed to deprivation of an ideal fluorophore and ingenious detection strategy. Herein, we report the fabrication of cadmium telluride quantum dots (CdTe QDs) with bright emission, good water dispersion, and long emission wavelength for OP screening based on the unique response of CdTe QDs to pH and the inhibition of OPs on acetylcholinesterase (AChE) activity. AChE catalyzed hydrolysis of acetylcholine (ACh) into CH₃COOH, which protonated CdTe QDs to decline the fluorescence, whereas target OP impeded AChE from catalyzing hydrolysis of ACh into CH₃COOH, making little influence in fluorescence of CdTe QDs. On the basis of the change in fluorescence, sensitive detection of OP was acquired, with the limit of detection at 0.027 ng/mL, which was comparable or lower than that of most known OP sensors. Furthermore, the CdTe-QD-based sensor was successfully applied for precisely monitoring the residue, distribution, and variation of methidathion in Chinese cabbage and cultivated soil. Therefore, the proposed sensor was anticipated to supply a promising alternative for food safety guarantee and was an valuable application for OP screening.

Detection of organophosphorus pesticides by nanogold/mercaptomethamidophos multi-residue electrochemical biosensor

Based on the successful synthesis of mercaptomethamidophos as a substrate, a novel nanogold/mercaptomethamidophos multi-residue electrochemical biosensor was designed and fabricated by combining nanoscale effect, strong Au-S bonds as well as interaction between acetylcholinesterase (AChE) and mercaptomethamidophos, which can simultaneously detect 11 kinds of organophosphorus pesticides (OPPs) and total amount of OPPs using indirect competitive method. Electrochemical behavior of the modified electrode was characterized by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The AChE concentration and incubation time were optimized at 37.4 °C to achieve the best detection effect. This biosensor exhibits excellent electrochemical properties with a wider linear range of 0.1 ~ 1500 ng·mL^-1, lower detection limit of 0.019 ~ 0.077 ng·mL^-1, better stability and repeatability, which realizes the rapid detection of total amount of OPPs, and can simultaneously detect a large class of OPPs rather than one kind of OPP. Two OPPs (trichlorfon, dichlorvos) were detected in actual samples of apple and cabbage and achieved satisfactory test results.