Flexible Aggregation-Induced Emission-Active Hydrogel for On-Site Monitoring of Pesticide Degradation

Carbon dots-based stimuli-responsive hydrogel for in-situ detection of thiram on fruits and vegetables

Stimuli-responsive hydrogel possesses a strong loading capacity to embed luminescent indicators for constructing food safety sensors, which are suitable for field application. In this work, a fluorescent hydrogel sensor was fabricated by incorporating Ag+-modified carbon dots (CDs-Ag+) into a sodium alginate (SA) hydrogel for in-situ detection of thiram. The fluorescence of CDs was quenched due to the combined effects of electrostatic adsorption and electron transfer between Ag+ and CDs. The formation of an AgS bond between thiram and Ag+ facilitates the release of CDs, causing subsequently fluorescence recovery. Combined with smartphone and analysis software, the fluorescence color change of the hydrogel sensor was converted into data information for quantitative detection of thiram. Such a sample-to-result step is completed within 10 min. Notably, the in-situ detection experiment of thiram in fruit and vegetable samples confirmed the practical application of the hydrogel sensor. Therefore, the hydrogel sensor provides a new research direction for the in-situ detection of pesticide residues in the monitoring of food safety.

Construction of portable hydrogel kits with self-ratio optical bimodal detection and smartphone imaging for on-site nitrite screening

Accurate on-site detection of nitrite in complex matrices remains a significant challenge. Herin, we construct a self-ratio optical bimodal portable kit via co-assembling NaErF4:0.5%Tm@NaYF4@NaYbF4:0.5%Tm@NaYF4 (Er:Tm@Yb:Tm) and nitrogen-doped carbon platinum nanomaterials (Pt/CN) in sodium alginate (SA) hydrogel. Pt/CN nanomaterials are synthesized by high-temperature sintering using a zinc-based zeolite imidazolium framework as a sacrificial template. The Pt/CN nanozyme possesses excellent oxidase-like activity to produce the oxidation state 3,3',5,5'-tetramethylbenzidine (oxTMB). Nitrite mediates diazotization of oxTMB to trigger the change of absorption signals, accompanying the ratio fluorescence response of the Er:Tm@Yb:Tm. Crucially, Er:Tm@Yb:Tm and Pt/CN are embedded in SA hydrogel to fabricate a portable kit with efficient and sensitive performance. An image processing algorithm is used to analyze the nitrite-induced signal change of the portable hydrogel kit, resulting in detection limits of 0.63 μM. This method has great potential for point-of-care applications due to its reliability, long-term stability, accuracy, sensitivity, and portability.

Dual-enhanced enzyme cascade hybrid hydrogel for the construction of optical biosensor

The biomimetic enzyme cascade system plays a key role in biosensing as a sophisticated signal transduction and amplification strategy. However, constructing a regulated enzyme cascade sensing system remains challenging due to the mismatch of multiple enzyme activities and poor stability. Herein, we design an efficient dual-enhanced enzyme cascade hybrid system (UFD-DEC) containing DNA-controlled nanozymes (Fe-cdDNA) and enzyme (urease) via combining the electrostatic contact effect with the hydrogel-directed confinement effect. Precise modulation of Fe-cdDNA nanozyme by DNA offers a means to control its catalytic efficiency. This regulated UFD-DEC system accelerates the reaction rate and provides remarkable stability compared with the free enzyme system. Benefiting from the plasticity properties of hydrogels, a "lab-in-a-tube" platform was constructed by encapsulating UFD-DEC in a microcentrifuge tube. Such a UFD-DEC-based hydrogel tube exhibits sufficient adaptability to profile urea when used in conjunction with a smartphone-assisted image processing algorithm, which on-site delivers urea information with a detection limit of 0.12 mmol L-1. This customizable and inexpensive miniaturized biosensor platform for monitoring urea may facilitate point-of-care testing applications.

A handheld fluorescent platform integrated with a Sm(III)-CdTe quantum dot-based ratiometric nanoprobe for point-of-use determination of phosphate

Phosphate (Pi) is crucial for various physiological processes and aquatic environments, which emphasizes the need for a simple, on-site sensor to promptly detect Pi for human health and environmental conservation. In this study, we propose a dual-emission ratiometric fluorescence sensor for highly sensitive and visual Pi detection. The sensor employs samarium ions (Sm3+) as a core component, with cadmium telluride quantum dots (CdTe QDs) and ofloxacin (OFL) serving as signal carriers. The CdTe-Sm(III)-OFL nanoprobe emits a purple fluorescence resulting from the red fluorescence of CdTe QDs and the blue-green fluorescence of OFL. The fluorescence of OFL is quenched by Sm3+ through fluorescence resonance energy transfer (FRET). Upon Pi interaction, the FRET process is disrupted due to the competitive Pi-Sm3+ binding, which leads to the fluorescence recovery of OFL while the red fluorescence of CdTe remains steady. This enables the construction of a ratiometric fluorescent sensor for Pi detection, manifesting as a color change from purple to blue. The sensor demonstrated a linear response for Pi detection within the range of 0.1-75 μM, with a low detection limit of 17.0 nM. By utilizing the distinct fluorescence responses of various physiological phosphates and employing chemometrics, this innovative dual-emission sensor accurately distinguishes among different physiological phosphates. Furthermore, a portable lab-on-paper device based on CdTe-Sm(III)-OFL, coupled with a smartphone-integrated mini-device, is developed for swift Pi detection using an ordinary smartphone. Analytical performance validated on environmental and biological samples demonstrates the sensor's excellent robustness and adaptability. This study introduces a pioneering approach to fabricate ratiometric fluorescence sensors and customize portable, cost-effective mini-devices for precise target detection, thus opening avenues for advanced sensing strategies in various applications.

Upconversion-based hydrogel kit with Python-assisted analysis platform for sample-to-result detection of organophosphorus pesticide

On-site quantitative analysis of pesticide residues is crucial for monitoring environmental quality and ensuring food safety. Herein, we have developed a reliable hydrogel portable kit using NaYbF4@NaYF4: Yb, Tm upconversion nanoparticles (UCNPs) combined with MnO2 nanoflakes. This portable kit is integrated with a smartphone reader and Python-assisted analysis platform to enable sample-to-result analysis for chlorpyrifos. The novel UCNPs maximizes energy donation to MnO2 acceptor by employing 100 % of activator Yb3+ in the nucleus for NIR excitation energy collection and confining emitter Tm3+ to the surface layer to shorten energy transfer distance. Under NIR excitation, efficient quenching of upconversion blue-violet emission by MnO2 nanoflakes occurs, and the quenched emission is recovered with acetylcholinesterase-mediated reactions. This process allows for the determination of chlorpyrifos by inhibiting enzymatic activity. The UCNPs/MnO2 were embedded to fabricate a hydrogel portable kit, the blue-violet emission images captured by smartphone were converted into corresponding gray values by Python-assisted superiority chart algorithm which achieves a real-time rapid quantitative analysis of chlorpyrifos with a detection limit of 0.17 ng mL-1. At the same time, pseudo-color images were also added by Python in "one run" to distinguish images clearly. This sensor detection with Python-assisted analysis platform provides a new perspective on pesticide monitoring and broadens the application prospects in bioanalysis.

Glutathione‑iron hybrid nanozyme-based colorimetric sensor for specific and stable detection of thiram pesticide on fruit juices

Given the potential dangers of thiram to food safety, constructing a facile sensor is significantly critical. Herein, we presented a colorimetric sensor based on glutathione‑iron hybrid (GSH-Fe) nanozyme for specific and stable detection of thiram. The GSH-Fe nanozyme exhibits good peroxidase-mimicking activity with comparable Michaelis constant (Km = 0.551 mM) to the natural enzyme. Thiram pesticides can specifically limit the catalytic activity of GSH-Fe nanozyme via surface passivation, causing the change of colorimetric signal. It is worth mentioning that the platform was used to prepare a portable hydrogel kit for rapid qualitative monitoring of thiram. Coupling with an image-processing algorithm, the colorimetric image of the hydrogel reactor is converted into the data information for accurate quantification of thiram with a detection limit of 0.3 μg mL-1. The sensing system has good selectivity and high stability, with recovery rates in fruit juice samples ranging from 92.4% to 106.9%.

Metal nanostructures in polymeric matrices for optical detection and removal of heavy metal ions, pesticides and dyes from water

Water pollutants such as heavy metal ions, pesticides, and dyes pose a worldwide issue. Their presence in water resources interferes with the normal growth mechanisms of living beings and causes long or short-term diseases. For this reason, research continuously tends to develop innovative, selective, and efficient processes or technologies to detect and remove pollutants from water. This review provides an up-to-date overview on metal nanoparticles loaded in polymeric matrices, such as hydrogels and membranes, and employed as optical sensors and as removing materials for water pollutants. The synthetic pathways of nanomaterials loading into polymeric matrices have been analyzed, particularly focusing on noble metal nanoparticles, noble metal nanoclusters, and metal oxide nanoparticles. Moreover, the sensing properties of modified matrices towards water pollutants have been discussed in addition to the interaction mechanisms between the sensors and the toxic compounds. The last part of the review has been devoted to illustrating the separation mechanism and removal performance of membranes loaded with nanomaterials in the treatment and purification of water streams from different contaminants (heavy metals, dyes and pesticides).

Spatially confined dual-emission nanoprobes assembled from silicon nanoparticles and gold nanoclusters for ratiometric biosensing

Gold nanoclusters (AuNCs) possess weak intrinsic fluorescence, limiting their sensitivity in biosensing applications. This study addresses these limitations by developing a spatially confined dual-emission nanoprobe composed of silicon nanoparticles (SiNPs) and AuNCs. This amplified and stabilized fluorescence mechanism overcomes the limitations associated with using AuNCs alone, achieving superior sensitivity in the sensing platform. The nanoprobe was successfully employed for ratiometric detection of bleomycin (BLM) in serum samples, operating at an excitation wavelength of 365 nm, with emission wavelengths at 480 nm and 580 nm. The analytical performance of the system is distinguished by a linear detection range of 0-3.5 μM, an impressive limit of detection (LOD) of 35.27 nM, and exceptional recoveries ranging from 96.80 to 105.9%. This innovative approach significantly enhances the applicability and reliability of AuNC-based biosensing in complex biological media, highlighting its superior analytical capabilities.

Advancing abiotic stress monitoring in plants with a wearable non-destructive real-time salicylic acid laser-induced-graphene sensor

Drought and salinity stresses present significant challenges that exert a severe impact on crop productivity worldwide. Understanding the dynamics of salicylic acid (SA), a vital phytohormone involved in stress response, can provide valuable insights into the mechanisms of plant adaptation to cope with these challenging conditions. This paper describes and tests a sensor system that enables real-time and non-invasive monitoring of SA content in avocado plants exposed to drought and salinity. By using a reverse iontophoretic system in conjunction with a laser-induced graphene electrode, we demonstrated a sensor with high sensitivity (82.3 nA/[μmol L-1⋅cm-2]), low limit of detection (LOD, 8.2 μmol L-1), and fast sampling response (20 s). Significant differences were observed between the dynamics of SA accumulation in response to drought versus those of salt stress. SA response under drought stress conditions proved to be faster and more intense than under salt stress conditions. These different patterns shed light on the specific adaptive strategies that avocado plants employ to cope with different types of environmental stressors. A notable advantage of the proposed technology is the minimal interference with other plant metabolites, which allows for precise SA detection independent of any interfering factors. In addition, the system features a short extraction time that enables an efficient and rapid analysis of SA content.

Self-ratiometric fluorescent platform based on upconversion nanoparticles for on-site detection of chlorpyrifos

Monitoring organophosphorus pesticides is significant for food safety assessment. Herein, we developed upconversion nanoparticles (UCNPs)-based self-ratiometric fluorescent platform for the detection of chlorpyrifos. The UCNPs have the ability to confine the detection and reference functions in one nanoparticle. Specifically, the blue upconversion (UC) emission (448 nm) in the shell layer of UCNPs is quenched by the product of the acetylcholinesterase-mediated reaction, while the red UC emission (652 nm) from the core remains constant as a self-calibrated reference signal. Employing the inhibition property of chlorpyrifos, self-proportional fluorescence is employed to detect chlorpyrifos. As proof-of-concept, test strips are fabricated by loading the UCNPs onto filter paper. Combined with the smartphone and image-processing algorithm, chlorpyrifos quantitative testing is achieved with a detection limit of 14.4843 ng mL-1. This portable platform displays anti-interference capability and high stability in the complicated matrix, making it an effective candidate for on-site application.

CRISPR/Cas12a-derived ratiometric fluorescence sensor for high-sensitive Pb2+ detection based on CDs@ZIF-8 and DNAzyme

Benefiting from specific target recognition and trans-cleavage capabilities, the CRISPR/Cas12a system has great application prospects in the design of highly sensitive and rapid fluorescence biosensors. The CRISPR/Cas12a-based fluorophore-quencher molecular beacons exhibit single-color emission and are easily exposed to interference from environmental factors. Herein, we design a CRISPR/Cas12a-derived ratiometric fluorescence sensor for Pb2+ detection based on embedded carbon dots@zeolitic imidazolate framework-8 (CDs@ZIF-8) composites and DNAzyme. The functions of ZIF-8 about encapsulating red emissive CDs in the inner cavity and adsorbing DNA on the outer surface are integrated to establish dual fluorescence signals, thereby reducing the possibility of interference and improving sensing accuracy. The presence of Pb2+ is converted into the change of activator by the GR5 DNAzyme to activate the CRISPR/Cas12a system, which provides signal amplification through multiple turnovers of side branch cutting, achieving highly sensitive detection of Pb2+ with a low detection limit of 18 pM. This method has the advantages of simplicity, universality, and excellent quantitative ability, and has broad prospects in sensing applications.

Zeolitic Imidazolate-Framework-Engineered Heterointerface Catalysis for the Construction of Plant-Wearable Sensors

Plant-wearable sensors provide real-time information that enables pesticide inputs to be finely tuned and play critical roles in precision agriculture. However, tracking pesticide information in living plants remains a formidable challenge owing to inadequate shape adaptabilities and low in-field sensor sensitivities. In this study, plant-wearable hydrogel discs are designed by embedding a dual-shelled upconversion-nanoparticles@zeolitic-imidazolate-framework@polydopamine (UCNPs@ZIF@PDA) composite in double-network hydrogels to deliver on-site pesticide-residue information. Benefiting from the enzyme-mimetic catalytic activity of ZIFs and enzyme triggered-responsive property of PDA shell, the hydrogel discs are endowed with high sensing sensitivity toward 2,4-dichlorophenoxyacetic acid pesticide at the nanogram per milliliter level via boosting fluorescence quenching efficiency. Notably, hydrogel discs mounted on tomato plants exhibit sufficient adaptability to profile dynamic pesticide degradation when used in conjunction with an ImageJ processing algorithm, which is practically applicable. Such hydrogel discs form a noninvasive and low-cost toolkit for the on-site acquisition of pesticide information, thereby contributing to the precise management of the health status of a plant and the judicious development of precision agriculture.

Signal Amplification by Spatial Concentration for Immunoassay on Cellulose Media

Immunoassay is one of the most common bioanalytical techniques from lab-based to point-of-care settings. Over time, various approaches have been developed to amplify signals for greater sensitivity. However, the need for effective, versatile, and simple signal amplification methods persists yet. This paper presents a novel signal amplification method for immunoassay that utilizes spatial concentration of a cellulose-based plate possessing sensor transducers, specifically gold nanoparticles. By modifying the dimensions of the plate, the density of nanoparticles increased, resulting in intensified color signals. The coating material, polydopamine, which is utilized to protect the gold nanoparticles. Chemical changes in nanocomposites are characterized using scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The application of this method to colorimetric quantification demonstrated great consistency across various concentrations of nanoparticles, with better reliability at lower concentration ranges. A model immunoassay is designed to evaluate the analytical performance. As a result, this method successfully corrected a false-negative result with a lowered Kd of 0.509 pmol per zone. This method shows strong signal enhancement capability that can correct false-negative signals in the immunoassays, with potential benefits including versatility, simplicity, low cost, and the ability to operate multiple plates simultaneously.

In Situ Fabrication of Photoluminescent Hydrogen-Bonded Organic Framework-Functionalized Ca (II) Hydrogel Film for the Tetracyclines Visual Sensor and Information Security

A facilely in situ fabricated hydrogen-bonded organic framework (HOF) hydrogel film with perfect photoluminescent performance was designed for visual sensing of tetracycline antibiotics (TCs) and information security. Luminescent HOF (MA-IPA) was combined with sodium alginate (SA) through hydrogen bonding actions and electrostatic interactions, then cross-linked with Ca2+ ions to form HOF hydrogel film (Ca@MA-IPA@SA). The HOF hydrogel film exhibited exceptional mechanical robustness along with stable blue fluorescence and ultralong green phosphorescence. After exposure to TCs, Ca2+ was combined with TCs to generate a new green fluorescence exciplex (TC-Ca2+) in hydrogel films. Due to fluorescence resonance energy transfer, the fluorescence of MA-IPA was quenched, and the fluorescent color of the HOF hydrogel film was changed from blue to green. This dichromatic fluorescent response is convenient for the visual and rapid detection of TCs. The detection limits of tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) were 5.1, 7.7, and 32.7 ng mL-1, respectively. Importantly, this hydrogel sensing platform was free of tedious operation and enabled the ultrasensitive and selective detection of TCs within 6 min. It has been successfully applied to TC detection in pork and milk samples. Based on the stable photoluminescence performance of HOF hydrogel films and fluorescent-responsive properties to TCs, two types of anticounterfeiting arrays were fabricated for information encryption and decryption. This work provides a novel approach for on-site detection of TCs and offers valuable insights into information security.

FRET-Based Host-Guest Supramolecular Probe for On-Site and Broad-Spectrum Detection of Pyrethroids in the Environment

The massive use of pyrethroid pesticides in agriculture has brought growing concerns about food safety due to their several harmful effects on human health, especially through the accumulation of the food chain. To date, most of the available analytical methods for pyrethroids still suffer from insufficient detection universality, complicated sample pretreatment, and detection processes, which severely limit their practical applications. Herein, a novel Förster resonance energy transfer (FRET)-assisted host-guest supramolecular nanoassembly is reported, for the first time, successfully realizing ratiometric fluorescent detection of pyrethroids in real samples through the indicator displacement assay (IDA) mechanism. This method is capable of detecting a broad spectrum of pyrethroids, including bifenthrin, cyfluthrin, cypermethrin, deltamethrin, etofenprox, fenvalerate, and permethrin, with ultrahigh detection sensitivity, great selectivity, high anti-interference ability, and, in particular, distinct emission color response from red to green. Such a large chromatic response makes this method available for fast and on-site detection of pyrethroids in real samples with the aid of several simple portable analytical apparatuses.

Bioinspired Multifunctional Self-Sensing Actuated Gradient Hydrogel for Soft-Hard Robot Remote Interaction

The development of bioinspired gradient hydrogels with self-sensing actuated capabilities for remote interaction with soft-hard robots remains a challenging endeavor. Here, we propose a novel multifunctional self-sensing actuated gradient hydrogel that combines ultrafast actuation and high sensitivity for remote interaction with robotic hand. The gradient network structure, achieved through a wettability difference method involving the rapid precipitation of MoO2 nanosheets, introduces hydrophilic disparities between two sides within hydrogel. This distinctive approach bestows the hydrogel with ultrafast thermo-responsive actuation (21° s-1) and enhanced photothermal efficiency (increase by 3.7 °C s-1 under 808 nm near-infrared). Moreover, the local cross-linking of sodium alginate with Ca2+ endows the hydrogel with programmable deformability and information display capabilities. Additionally, the hydrogel exhibits high sensitivity (gauge factor 3.94 within a wide strain range of 600%), fast response times (140 ms) and good cycling stability. Leveraging these exceptional properties, we incorporate the hydrogel into various soft actuators, including soft gripper, artificial iris, and bioinspired jellyfish, as well as wearable electronics capable of precise human motion and physiological signal detection. Furthermore, through the synergistic combination of remarkable actuation and sensitivity, we realize a self-sensing touch bioinspired tongue. Notably, by employing quantitative analysis of actuation-sensing, we realize remote interaction between soft-hard robot via the Internet of Things. The multifunctional self-sensing actuated gradient hydrogel presented in this study provides a new insight for advanced somatosensory materials, self-feedback intelligent soft robots and human-machine interactions.

Recent Studies and Applications of Hydrogel-Based Biosensors in Food Safety

Food safety has increasingly become a human health issue that concerns all countries in the world. Some substances in food that can pose a significant threat to human health include, but are not limited to, pesticides, biotoxins, antibiotics, pathogenic bacteria, food quality indicators, heavy metals, and illegal additives. The traditional methods of food contaminant detection have practical limitations or analytical defects, restricting their on-site application. Hydrogels with the merits of a large surface area, highly porous structure, good shape-adaptability, excellent biocompatibility, and mechanical stability have been widely studied in the field of food safety sensing. The classification, response mechanism, and recent application of hydrogel-based biosensors in food safety are reviewed in this paper. Furthermore, the challenges and future trends of hydrogel biosensors are also discussed.

Dual-mode supramolecular fluorescent probe for rapid and on-site detection of chlorpyrifos in the environment

Chlorpyrifos (CPF) as a classic organophosphorus pesticide has been widely used in agricultural applications to control insects and worms. CPF in the environment can cause deaths of diverse kinds of aquatic organism and bring a high risk to human health. Therefore, the development of effective analytical method for CPF is of great importance. In this work, a novel dual-mode albumin (ALB)-based supramolecular probe FD@ALB was designed and prepared for rapid detection of CPF in the environment. The limit of detection is 0.57 μM (∼ 0.2 ppm) with a wider detection range up to 200 μM, which is satisfactory for application. The sensing mechanism can be ascribed to CPF-induced phosphorylation of ALB, thus leading to a change in the binding microenvironment of FD dye. Moreover, the paper-based test strips were used in conjunction with the FD@ALB, realizing the portable detection of CPF. This method was demonstrated to be suitable for on-site detection of CPF in various kinds of environmental samples, including water, soil, and food samples, with the aid of a smartphone. To the best of our knowledge, this is the first analytical method achieving a combination of the rapid and ratiometric detection of CPF in the environment.