Paper-based fluorescent sensor via aggregation induced emission fluorogen for facile and sensitive visual detection of hydrogen peroxide and glucose

NFC-enabled photothermal-based microfluidic paper analytical device for glucose detection

This study introduces the development of a photothermal-based microfluidic paper analytical device (PT-µPAD) integrated with near-field communication (NFC) technology and smartphone readout for enzyme-free glucose quantification in human samples. With the properties of gold nanoparticles (AuNPs) both as a nanozyme and as a photothermal substrate, there is no need for costly reagents like enzymes or a readout instrumentation for the selective and sensitive detection of glucose. In PT-µPADs, AuNPs are etched by hydrogen peroxide (H2O2) generated from glucose catalysis. Photothermal detection from the plasmonic heating of these AuNPs when illuminated by a 533nm LED light source is achieved by inserting the PT-µPAD sensor into a portable NFC platform suitable for smartphone readout. Temperature variation is directly proportional to the glucose concentration. After optimization, we acquired a linear range between 5.0 and 20.0 µmol L-1 (R2 = 0.9967) and a limit of detection (LOD) of 25.0 nmol L-1 for glucose. Additionally, while our sensor does not utilize any enzyme, it is remarkably selective to glucose with no effects from interferences. Recovery studies in various human control samples indicated a range of 99.73-102.66% with the highest RSD of 3.53%, making it highly accurate and precise. Moreover, our method is more sensitive than other methods relying on conventional µPADs for glucose sensing. By integrating the potential benefits of microfluidics, nanomaterials as nanozymes, and NFC technology for wireless readout, our sensor demonstrates great promise as an accessible, affordable, and shelf-stable device for glucose quantification. Moreover, this concept can be extended to detect other molecules of interest as a point-of-care (POC) diagnostics device.

Construction of an autofluorescence interference-free phosphorescence biosensor for the specific detection of TK1 mRNA

The anti-interference ability of biosensors is critical for detection in biological samples. Fluorescence-based sensors are subject to interference from self-luminescent substances in biological matrices. Therefore, phosphorescent sensors stand out among biosensors due to their lack of self-luminescence background. In this study, a phosphorescent sensor was constructed, which can accurately detect thymidine kinase 1 (TK1) mRNA in biological samples and avoid autofluorescence interference. When there is no target, polydopamine (PDA) is used as the phosphorescence resonance energy transfer (PRET) acceptor to quench the phosphorescence of the persistently luminescent (PL) nanomaterial. When there is a target, the DNA modified by the PL nanomaterial is replaced by the hairpin H and removed away from the PDA, resulting in a rebound in phosphorescence. The phosphorescent sensor exhibits a good linear relationship in the TK1 mRNA concentration range of 0-200 nM, and the detection limit was 1.74 nM. The sensor fabricated in this study can effectively avoid interference from spontaneous fluorescence in complex biological samples, and sensitively and precisely detect TK1 mRNA in serum samples, providing a powerful tool to more accurately detect biomarkers in biological samples.

A coronene diimide based radical anion for detection of picomolar H2O2: a biochemical assay for detection of picomolar glucose in aqueous medium

Coronene diimide functionalized with 4-(2-nitrovinyl)phenyl (CDI 2) serves as a precursor for generating a stable radical anion (CDI 2˙-) using H2S as a reductant in 40% H2O-THF solution in the NIR region with stability up to >50 min. The optical, cyclic voltammetry (CV), current-voltage (I-V) and electron paramagnetic resonance (EPR) studies revealed the formation of the radical anion (CDI 2˙-). The addition of a strong oxidant NOBF4 quenches the radical anion (CDI 2˙-). The aggregation studies revealed that CDI 2 exists in the aggregated state in 40% H2O-THF solution, which points to the possibility of stabilization of the radical anion in the aggregates. The radical anion (CDI 2˙-) was explored for the detection of 58.27 pM H2O2 in aqueous medium with the naked eye colour change from green to light yellow. The biochemical assay involving the radical anion (CDI 2˙-) and glucose oxidase (GOx) enzyme can be used for the detection of 16 pM (UV-vis method) and 82.4 pM (fluorescence method) glucose. The naked eye colour change from green to light yellow (daylight) and a colorless non-fluorescent solution to a green fluorescent solution (365 nm) allow the detection of 1 nM glucose.

Unique development of a new dual application probe for selective detection of antiparallel G-quadruplex sequences

G-Quadruplex (G4) structures play vital roles in many biological processes; consequently, they have been implicated in various human diseases like cancer, Alzheimer's disease etc. The selective detection of G4 DNA structures is of great interest for understanding their roles and biological functions. Hence, development of multifunctional fluorescent probes is indeed essential. In this investigation, we have synthesized a quinolinium based dual application probe (QnMF) that presents molecular rotor properties. This dual application molecular rotor is able to detect selectively antiparallel G4 sequences (22AG in 100 mM NaCl) through a turn-on response over other G4 topologies. The QnMF also contains a distinct fluorine-19 that undergoes a significant chemical shift in response to microenvironmental changes around the molecule when bound to G4 structures. The probe QnMF exhibits significantly brighter fluorescence emissions in glycerol (ε × ϕ = 2800 cm-1 M-1) and relatively less brighter fluorescence emissions in methanol (ε × ϕ = 40.5 cm-1 M-1). The restricted rotation inherent property of the QnMF molecular rotor is responsible for brighter fluorescence and leads to enhancement in the fluorescence upon binding to the G4 structure. Overall, the probe's dual detection method makes it useful for monitoring the G4 structures that are abundant and plays a vital role in living organisms.

Ionic liquids functionalized Fe3O4-based colorimetric biosensor for rapid determination of ochratoxin A

A stainless steel mesh (SSM) with the feature of flexibility was employed as the colorimetric biosensor substrate, and aptamer was bond onto the surface of the SSM. Through the cross-linking of ionic liquids (ILs), AuPt nanoparticles were deposited  onto the surface of Fe3O4 material to obtain a magnetic nanozyme with high peroxidase catalytic activity and rapid color change. Through the competing interaction of OTA and cDNA with aptamer, AuPt@IL@Fe3O4 signal probe was separated to catalyze the 3,3',5,5'-tetramethylbenzidine/hydrogen peroxide (TMB/H2O2) system to observe the color by bare eye and record the absorbance at 652 nm using a UV-spectrophotometer. Through the study of the catalytic properties on the basis of the Michaelis equation, AuPt@IL@Fe3O4 nanozyme presented a Vmax of 3.85 × 10-8 M s-1 and Km of 0.01 mM. Under the optimized conditions, the linear range of the colorimetric biosensor towards OTA was 5-100 ng mL-1, and the detection limit was 0.078 ng mL-1. This biosensor was applied to beer and corn samples with recoveries of 70.4-102.6% and 93.3-104.7%, respectively. Results showed that this sensor is a portable, rapid, economical, sensitive visual sensing platform towards mycotoxin in real samples.

A portable paper-based testing device for fast and on-site determination of nitroxynil in food

Nitroxynil (NTX) is a common anthelmintic veterinary drug for the management of fascioliasis in food-producing sheep and cattle. Since excessive NTX residue in food can lead to several adverse side effects, such as allergic skin reaction and respiratory irritation, it is of great importance to develop an efficient analytical method for NTX determination. Herein, we report a simple fluorescent detection method based on a novel supramolecular probe capable of detecting NTX with a fast response (5 s), high sensitivity (107 nM), high selectivity, and acceptable anti-interference property. Moreover, the portable paper-based test strips were facilely prepared and successfully realized on-site determination of NTX in real edible animal products simply with the aid of a smartphone. To the best of our knowledge, this is the very first report on the portable detection of NTX. This study also provides a promising strategy for the fast and portable detection of analyte based on the host-guest system, which will lead to improved fluorescent probe design for food analysis.

Tumor cell membrane-coated continuous electrochemical sensor for GLUT1 inhibitor screening

Glucose transporter 1 (GLUT1) overexpression in tumor cells is a potential target for drug therapy, but few studies have reported screening GLUT1 inhibitors from natural or synthetic compounds. With current analysis techniques, it is difficult to accurately monitor the GLUT1 inhibitory effect of drug molecules in real-time. We developed a cell membrane-based glucose sensor (CMGS) that integrated a hydrogel electrode with tumor cell membranes to monitor GLUT1 transmembrane transport and screen for GLUT1 inhibitors in traditional Chinese medicines (TCMs). CMGS is compatible with cell membranes of various origins, including different types of tumors and cell lines with GLUT1 expression knocked down by small interfering RNA or small molecules. Based on CMGS continuous monitoring technique, we investigated the glucose transport kinetics of cell membranes with varying levels of GLUT1 expression. We used CMGS to determine the GLUT1-inhibitory effects of drug monomers with similar structures from Scutellaria baicalensis and catechins families. Results were consistent with those of the cellular glucose uptake test and molecular-docking simulation. CMGS could accurately screen drug molecules in TCMs that inhibit GLUT1, providing a new strategy for studying transmembrane protein-receptor interactions.

pH-responsive dual-enzyme mimics based on hollow metal organic framework-derivatives β-Co(OH)2 for multiple colorimetric assays

A hollow metal organic framework derivative β-Co(OH)₂ has been prepared, which possesses oxidase and peroxidase-like activities. Oxidase-like activity is derived from the generation of free radicals, and peroxidase-like activity is related to the electron transfer process. Unlike other nanozymes with dual enzyme-like activities, β-Co(OH)₂ possesses pH-responsive enzyme-like activities, among which the β-Co(OH)₂ exhibits superior oxidase and peroxidase-like activities under pH of 4 and 6, respectively, which could avoid mutual interference between multiple enzymes. Based on the phenomenon that enzyme-like activities of β-Co(OH)₂ can catalyze colorless TMB to generate blue oxidized TMB (oxTMB) with absorption peak at 652 nm, the sensors integrating total antioxidant capacity and H₂O₂ quantification were developed. The oxidase-like activity-based colorimetric system has a sensitive response to ascorbic acid, Trolox, and gallic acid, in which the limit of detection for those antioxidant substances was 0.54 μM, 1.26 μM, and 14.34 μM, respectively. The sensors based on peroxidase-like activity had low limit of detection of 1.42 μM for H₂O₂ and a linear range of 5-1000 μM. The proposed method can be well applied to the detection of the total antioxidant capacity of kiwi, Vc tables, orange and tea extract with high accuracy, and H₂O₂ determination in milk and glucose detection in beverages with satisfactory recovery (within 97-106%).

A Paper-Based Fluorescent Sensor for Rapid Early Screening of Oral Squamous Cell Carcinoma

Various types of sensors play an irreplaceable role in the detection of biomarkers, but their high cost and complicated operation make it difficult to benefit ordinary people. Herein, we develop a low-cost, double-layered, paper-based fluorescent sensor (CP/HQ) structurally consisting of the upper reaction layer loaded with two oxidases (lactate oxidase and choline oxidase) and the bottom fluorescent layer that physically associates with the porphine-grafted composite fluorescent polymer colloids (PF-PDMTP/HQ). Based on the dramatic and rapid fluorescence decrease of porphine induced by the oxidation between saliva and oxidases and subsequent fluorescence resonance energy transfer from oxidized hydroquinone, the resultant fluorescent paper sensor enables us to achieve visual detection of OSCC, which was further recognized by smartphone scanning as the grayscale variation. It was found that the linear sensing range of grayscale value are 10-200 μM for lactic acid and 10-100 μM for choline, with LODs of 5.7 and 8.9 μM, respectively. More importantly, the sensor can achieve a powerful detection capability comparable to that of high-performance liquid chromatography (HPLC) in clinical settings with simple operation, demonstrating its great application potential. Our proposed sensor not only improves the accuracy of OSCC diagnosis but also provides a valuable attempt for the device modification of polymer-sensing systems and the development of non-invasive and easy-to-operate disease screening methods.

Sensitive and specific detection of saccharide species based on fluorescence: update from 2016

Increasing evidence supports the critical role of saccharides in various pathophysiological steps of tumor progression, where they regulate tumor proliferation, invasion, hematogenic metastasis, and angiogenesis. The identification and recognition of these saccharides provide a solid foundation for the development of targeted drug preparations, which are however not fully understood due to their complex and similar structures. In order to achieve fluorescence sensing of saccharides, extensive research has been conducted to design molecular probes and nanoparticles made of different materials. This paper aims to provide in-depth discussion of three main topics that cover the current status of the carbohydrate sensing based on the fluorescence sensing mechanism, including a phenylboronic acid-based sensing platform, non-boronic acid entities, as well as an enzyme-based sensing platform. It also highlights efforts made to understand the recognition mechanisms and improve the sensing properties of these systems. Finally, we present the challenge of achieving high selectivity and sensitivity recognition of saccharides, and suggest possible future avenues for exploration.

Silk fibroin-based colorimetric microneedle patch for rapid detection of spoilage in packaged salmon samples

Spoiled salmon can cause foodborne diseases and severely affects human health. Herein, we report a pH-responsive colorimetric microneedle (MN) patch fabricated from bromothymol blue (BTB) and silk fibroin meth acryloyl (SilMA) (BTB/SilMA@MN patch) for sensing salmon spoilage. The needle tips of MN could penetrate food cling film and insert into fish to extract tissue fluids directly and transport the extracted fluids to the backing layer for color displaying. The color change of BTB/SilMA@MN patches depended on the pH variation resulting from the increase of total volatile basic nitrogen in salmon during storage. The color of MN patches changed from yellow to yellowish green and to final green, indicating salmon changed from fresh to medium fresh and then to putrefied, respectively. Salmon spoilage can be rapidly determined via naked eye recognition and also analyzed on a smartphone in a nondestructive way, allowing consumers to estimate food quality easily and reliably.

Plasmonic Array at the Liquid-Liquid Interface: A Dual-Mode Optical Sensing Platform for Multianalytes

Analyte-triggered nanoparticle (NP) assemblies in bulk colloidal suspension have been extensively utilized in various optical sensors. Nevertheless, the assembling process is still limited by the slow diffusion dynamics of NPs and the low concentration of analytes in trace detections, which hinders further improvement of the sensitivity and repeatability of the sensors. In this work, by functionalizing the gold NPs with specific ligands, we constructed a dual-mode optical sensing platform for multianalytes based on the plasmonic NP array at the liquid-liquid interface. Through emulsification, the NP diffusion kinetics are boosted for several orders, and the NPs are condensed from the bulk aqueous phase to the liquid-liquid interface as a plasmonic array. The as-formed metasurface generates major reflectance and surface-enhanced Raman scattering changes in response to analytes, providing two optical sensing modes. As prototypes, cysteine and glucose are selected as the target molecules, achieving the limit of detection as 193 ± 2 and 297 ± 12 pM, respectively.

Colorimetric and electrochemical integrated dual-mode detection of glucose by utilizing CoOOH@Cu nanosheets as peroxidase mimetics

Herein, we developed a colorimetric and electrochemical integrated dual-mode assay for glucose detection by utilizing CoOOH@Cu nanosheets as peroxidase mimetics. With the advantages of self-calibration, sensitivity and lower sample cost, this designed dual-mode assay offers great potential in blood glucose analysis.

A Core–Shell Au@TiO2 and Multi-Walled Carbon Nanotube-Based Sensor for the Electroanalytical Determination of H2O2 in Human Blood Serum and Saliva

A hydrogen peroxide (H₂O₂) sensor was developed based on core–shell gold@titanium dioxide nanoparticles and multi-walled carbon nanotubes modified glassy carbon electrode (Au@TiO₂/MWCNTs/GCE). Core–shell Au@TiO₂ material was prepared and characterized using a scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD) and Zeta-potential analyzer. The proposed sensor (Au@TiO₂/MWCNTs/GCE) was investigated electrochemically using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The analytical performance of the sensor was evaluated towards H₂O₂ using differential pulse voltammetry (DPV). The proposed sensor exhibited excellent stability and sensitivity with a linear concentration range from 5 to 200 µM (R² = 0.9973) and 200 to 6000 µM (R² = 0.9994), and a limit of detection (LOD) of 1.4 µM achieved under physiological pH conditions. The practicality of the proposed sensor was further tested by measuring H₂O₂ in human serum and saliva samples. The observed response and recovery results demonstrate its potential for real-world H₂O₂ monitoring. Additionally, the proposed sensor and detection strategy can offer potential prospects in electrochemical sensors development, indicative oxidative stress monitoring, clinical diagnostics, general cancer biomarker measurements, paper bleaching, etc.

Voltammetric Detection of Glucose-The Electrochemical Behavior of the Copper Oxide Materials with Well-Defined Facets

Cu₂O nanomaterials with well-defined facets and uniform size were synthesized by a wet-chemical method. Regardless of the additive composition, powders crystallize mostly in cuprite form. To compare their electrochemical behavior, the obtained materials were deposited on carbon glassy electrodes. The response to glucose from the materials with different exposed facets was recorded with a delay at the anodic curve. The chronoamperometric analyses (AMP) exhibited a lower signal in contrast to the cyclic voltammetry data (CV), indicating that the number of active sites involved in glucose oxidation processes resulting from the structure of the material is insufficient. For samples with dominant (100) or (111) planes, a typical characteristic was observed, however, with an additional peak at the anodic curve. The location of the peaks is approximately the same and no significant differences from the AMP and CV analysis were observed. The sample enclosed by the (111) facets exhibited higher activity; however, as a result of the redox reaction with glucose molecules, the surface state is changing. Cu₂O materials enclosed by (100) planes exhibited optimal sensitivity as well as a large detective range. Samples with differential facet exposition present various current-potential profiles, as the effect of binder-particle interaction with Nafion.

L-Selenocysteine induced HepG-2 cells apoptosis through reactive oxygen species-mediated signaling pathway

BACKGROUND

Currently, Liver cancer is the fifth most common tumor and the second most important reason for cancer-related death in the world. However, there are still many limitations of the clinical treatment of liver cancer, and new treatment options are clearly needed. Fortunately, studies have shown that L-Selenocysteine has a certain effect on cancer. This study was to investigate the effects of L-Selenocysteine on the inhibition of cell proliferation and the promotion of apoptosis of HepG-2 cells through ROS mediated fine signaling pathway.

MATERIALS AND METHODS

CCK-8 assay was applied to evaluating the cytotoxic effect of L-Selenocysteine on HepG-2 cells. Electron microscopy, flow cytometry and Western Blot was utilization in further researching cells signaling pathways.

RESULTS

The growth of HepG-2 cells was inhibited by L-selenocysteine ​​treatment in a dose-dependent manner. The cell viability decreased to 52.20%, 43.20% and 30.83% under the treatment of 4, 8, 16 µM L-selenocysteine, respectively. L-Selenocysteine had higher cytotoxicity towards HepG-2 cells than normal cells. L-Selenocysteine can induce the apoptosis of HepG-2 cells by increasing the DNA fragmentation, and activating the Caspase-3. In addition, it was found that the mechanism of the induction to HepG-2 cell apoptosis by L-Selenocysteine was closely related to the overproduction of ROS and promoted apoptosis through the Bcl-2 signaling pathway.

CONCLUSIONS

Our data suggest that L-selenocysteine ​​may cause mitochondrial damage and subsequently stimulate ROS production. ROS can damage cellular DNA and mediate the production of Casapase-8, Bid, Bcl-2 and other proteins, affecting downstream signaling pathways, and ultimately induced apoptosis.

Polyoxometalate-based materials in extraction, and electrochemical and optical detection methods: A review

Polyoxometalates (POMs) as metal-oxide anions have exceptional properties like high negative charges, remarkable redox abilities, unique ligand properties and availability of organic grafting. Moreover, the amenability of POMs to modification with different materials makes them suitable as precursors to further obtain new composites. Due to their unique attributes, POMs and their composites have been utilized as adsorbents, electrodes and catalysts in extraction, and electrochemical and optical detection methods, respectively. A survey of the recent progress and developments of POM-based materials in these methods is therefore desirable, and should be of great interest. In this review article, POM-based materials, their properties as well as their identification methods, and analytical applications as adsorbents, electrodes and catalysts, and corresponding mechanisms of action, where relevant, are reviewed. Some current issues of the utilization of these materials and their future prospects in analytical chemistry are discussed.

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

Structure engineering of silicon nanoparticles with dual signals for hydrogen peroxide detection

Fluorescent silicon nanoparticles (SiNPs) were synthesized by a one-step, simple, and green method with 3-Aminopropyltriethoxysilane (APTES) and ascorbic acid (AA) as reaction agents. Subsequently, the SiNPs and AgNPs nanocomplex (SiNPs@AgNPs) was constructed as the probe for hydrogen peroxide (H₂O₂) detection. The fluorescence of SiNPs was quenched due to the surface plasmonic-enhanced energy transfer between SiNPs and AgNPs. Meanwhile, the color tends to be yellow due to the existence of AgNPs. As the AgNPs were etched by H₂O₂, the fluorescence recovers and color fadings. Based on the well-designed structure, the "off-on" fluorescence sensing and "on-off" color sensing platforms for H₂O₂ were fabricated. The as-synthesized materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Fluorescence and UV-vis absorption spectra were used to evaluate the optical performance. The fabricated sensor exhibited a linear range of 1.0-100.0 μM, with a limit of detection of 0.36 μM for the fluorescence sensing of H₂O₂. Additionally, a linear range of 1.0-50.0 μM and a limit of detection of 0.45 μM were displayed for the detection of H₂O₂ by colorimetric assay. The feasibility in complex medium of the fabricated fluorescent and colorimetric dual-signal sensor was evaluated by the detection of H₂O₂ in phosphate buffer saline (PBS) and lake water samples.

Mechanochemical synthesis of an AIE-TICT-ESIPT active orange-emissive chemodosimeter for selective detection of hydrogen peroxide in aqueous media and living cells, and solid-phase quantitation using a smartphone

We report herein the design and mechanochemical synthesis of a chemodosimeter, benzothiazole-derived unsymmetrical azine protected by 4-bromomethylphenylboronic acid (BTPAB), an orange aggregation-induced emission (AIE), for the selective detection of H2O2 in a turn-on manner.

Phenothiazine and triphenylamine-based fluorescent Schiff bases for the dual application of white light generation and H2O2 sensing

Two simple Schiff bases applied for white light emission in an ionic liquid medium and peroxide sensing with an exceptional LOD.

Recent Advances in Aggregation-Induced Emission Active Materials for Sensing of Biologically Important Molecules and Drug Delivery System

The emergence and development of aggregation induced emission (AIE) have attracted worldwide attention due to its unique photophysical phenomenon and for removing the obstacle of aggregation-caused quenching (ACQ) which is the most detrimental process thereby making AIE an important and promising aspect in various fields of fluorescent material, sensing, bioimaging, optoelectronics, drug delivery system, and theranostics. In this review, we have discussed insights and explored recent advances that are being made in AIE active materials and their application in sensing, biological cell imaging, and drug delivery systems, and, furthermore, we explored AIE active fluorescent material as a building block in supramolecular chemistry. Herein, we focus on various AIE active molecules such as tetraphenylethylene, AIE-active polymer, quantum dots, AIE active metal-organic framework and triphenylamine, not only in terms of their synthetic routes but also we outline their applications. Finally, we summarize our view of the construction and application of AIE-active molecules, which thus inspiring young researchers to explore new ideas, innovations, and develop the field of supramolecular chemistry in years to come.

Carbon dot based nucleus targeted fluorescence imaging and detection of nuclear hydrogen peroxide in living cells

Investigation of the intracellular generation of H₂O₂, one of the most important reactive oxygen species (ROS), is crucial for preventing various diseases since it is closely linked with different physiological and complex cell signaling pathways. Despite the development of various fluorescent probes, the majority of the fluorescent probes cannot move across the nuclear membrane. However, detection of the nuclear level of H₂O₂ is very important since it can directly cause oxidative DNA damage which ultimately leads to various diseases. Therefore, in this study, p-phenylenediamine based carbon quantum dots (B-PPD CDs) have been synthesized and integrated with 4-formylbenzeneboronic acid as a doping agent for the detection of H₂O₂. The detection mechanism showed that, upon exposure to H₂O₂, the fluorescence of the B-PPD CDs was immediately quenched. Further investigation has been done in the in vitro RAW 264.7 cell line by both exogenous and endogenous exposure of H₂O₂ to demonstrate the feasibility of the method. It is shown successfully that the exogenous presence and endogenous generation of H₂O₂ in RAW 264.7 cells can be detected using B-PPD CDs. The limit of detection (LOD) was determined to be 0.242 μM. The development of such imaging probes using carbon quantum dots will lead to live-cell imaging as well as ROS detection.

Portable and Intelligent Urine Glucose Analyzer Based on a CdTe QDs@GOx Aerogel Circular Array Sensor

Diabetes is a public health problem characterized by hyperglycemia, high mortality, and morbidity. A simple, rapid, and sensitive glucose detection method for diabetes screening and health self-management of patients with diabetes is of great significance. Therefore, an attractive urine glucose (UG) analyzer with advantages of fastness, sensitivity, and portability was developed. A cadmium telluride quantum dots (CdTe QDs)@glucose oxidase (GOx) aerogel circular array sensor can emit visible red fluorescence when excited by a 365 nm ultraviolet light source inside the analyzer. When urine samples containing glucose were dropped onto the sensor, glucose was oxidized by GOx to produce hydrogen peroxide (H₂O₂), which quenched the red fluorescence of CdTe QDs. The fluorescence images of the sensor were obtained using a CCD camera, and the linear relationship between the glucose concentration and the gray value of the fluorescence image was established. The analyzer shows good sensitivity (LOD, 0.12 mM) with a wide linear range of 0.12-26 mM. Based on the linear relation, the software of the analyzer was written in the C++ language, which can automatically give the gray value of the image and the corresponding glucose concentration. The UG analyzer was used for the detection of a large number clinical samples and compared with a variety of UG test papers, which all showed good detection performance. The novel analyzer we proposed has an important significance in the screening of diabetes and the self-management of diabetic patients.

Nitrogen, boron-doped Ti3C2 MXene quantum dot-based ratiometric fluorescence sensing platform for point-of-care testing of tetracycline using an enhanced antenna effect by Eu3

The Ti₃C₂ MXene quantum dots (Ti₃C₂ MQDs) derived from Ti₃C₂ MXene have received much attention because of their remarkable advantages in biosensing. Nevertheless, the functionalization of Ti₃C₂ MQDs to improve their properties is just in its infant stage. Herein, we firstly synthesized nitrogen and boron co-doped Ti₃C₂ MQDs (N, B-Ti₃C₂ MQDs) with good water solubility, strong stability, and high optical characteristics. The N, B-Ti₃C₂ MQDs exhibit excitation wavelength-dependent blue photoluminescence with optimal excitation/emission peaks at 335/439 nm. Nowadays, the development of fast and real-time detection of tetracycline (TC) in animal derived food is very essential. In this work, a novel point-of-care testing (POCT) platform was established based on ratiometric fluorescence method using N, B-Ti₃C₂ MQDs coupled with Eu³⁺. Upon addition of TC in the Eu³⁺/N, B-MQDs system, blue fluorescence emission of N, B-Ti₃C₂ MQDs was quenched and red fluorescence emission of Eu³⁺ was enhanced gradually, which was ascribed to the synergistic inner filter effect and antenna effect. Moreover, we prepared test papers with N, B-Ti₃C₂ MQDs and Eu³⁺ for TC detection based on the change of fluorescence color, which could be recognized by color recognizer app installed in the smartphone. Therefore, great promise for POCT of TC is given with the merits of simplicity and visible detection possibility. The proposed method demonstrated a low detection limit of 20 nM. Application of the platform for TC quantification in milk samples opened a novel means for the potential use of N, B-Ti₃C₂ MQDs in food safety.

Hydrogel-assisted paper-based lateral flow sensor for the detection of trypsin in human serum

The detection of trypsin and its inhibitor is significantly important for both clinical diagnosis and disease treatment. Herein, we demonstrate a hydrogel-assisted paper-based lateral flow sensor for the detection of trypsin and its inhibitor for the first time. The gelatin hydrogel is hydrolyzed based on the gel-to-sol transition in the presence of trypsin, which results in the release of the trapped water molecules in the gelatin hydrogel. By placing one end of a pH indicator strip onto the hydrolyzed gelatin hydrogel, water is flowing along the pH indicator strip. However, in the absence of trypsin, water cannot flow along the pH indicator strip as the water molecules are trapped in the gelatin hydrogel. The detection limit of the system reaches as low as 1.0 × 10^-6 mg/mL, and it is also applied to the quantitative detection of trypsin in human serum. In addition, the detection of a clinical drug aprotinin that is an inhibitor of trypsin is also successfully achieved. Noteworthy, only the gelatin hydrogel, pH indicator strip, and PS substrate are needed to fulfill the detection of trypsin without the need of other chemicals or reagents. Overall, we develop a particularly simple, elegant, robust, competitive, high-throughput, and low-cost approach for the rapid and label-free detection of trypsin and its inhibitor, which is very promising in the development of commercial products for sensing, diagnostic, and pharmaceutical applications. Besides, the hydrogel-assisted paper-based lateral flow sensor can also be employed to detect other analytes of interest by use of different stimuli-responsive hydrogel systems.

Confining copper nanoclusters on exfoliation-free 2D boehmite nanosheets: Fabrication of ultra-sensitive sensing platform for α-glucosidase activity monitoring and natural anti-diabetes drug screening

α-Glucosidase (α-Glu) and its inhibitors play critical roles in diabetes therapy. Herein, a simple and ultra-sensitive fluorescence sensing approach was fabricated for α-Glu activity monitoring and natural inhibitor screening by electrostatically confining negatively charged glutathione-capped copper nanoclusters (GSH-CuNCs) on exfoliation-free and positively charged 2D boehmite (Boe) nanosheets. Boe significantly improved the fluorescence emission/stability of GSH-CuNCs and simultaneously led to an obvious blue-shift of the excitation peak of CuNCs from 365 nm to 330 nm. As a result, the fluorescence emission of Boe@GSH-CuNCs was efficiently quenched by 4-nitrophenyl-α-D-glucopyranoside (PNPG) with a maximum absorbance peak (λ_max) at 310 nm via inner filter effect, and sequentially recovered by α-Glu through the hydrolysis of PNPG to p-nitrophenol (λ_max = 410 nm). Accordingly, an ultra-sensitive fluorescence assay for the determination of α-Glu activity was proposed by using Boe@GSH-CuNCs as fluorescence probes. The detection limit of 0.43 U/L was achieved, which was lower than most of other α-Glu activity assays. Furthermore, this method was capable of screening α-Glu inhibitors originated from actinomycetes, peanut, sophora flower, celery, and orange as potential anti-diabetes drugs. Taken together, this work provided a promising strategy for clinical treatment of diabetes and discovery of anti-diabetes drugs.

A lanthanide-based ratiometric fluorescent biosensor for the enzyme-free detection of organophosphorus pesticides

Organophosphorus pesticides (OPs) residues have caused great concern as they cause great harm to public health. Herein, a ratiometric fluorescent sensing system was developed for the OPs detection with the merits of enzyme-free, simple operation, short-time and sensitivity. The change in the fluorescence signal in the sensing system was provided by guanine-rich DNA (G-DNA) and silver nanoparticles (AgNPs) with terbium ion (Tb3+) and dured. Tb3+ coordinated with the G-DNA to form a DNA-Tb complex to emit green fluorescence, which can be significantly enhanced by AgNPs based on the mechanism of metal enhanced fluorescence. Dured embedded into the G-DNA emits red fluorescence as the built-in fluorescence signal. After adding OPs into the DNA-Tb-dured-AgNPs sensing system, the fluorescence of Tb3+ quenched, while the fluorescence of dured remained unchanged. The OPs detection is implemented enzyme-free or label-free and has the advantage of high sensitivity and reliability. The limit of detection reaches as low as 0.034 μg L-1, and good recoveries are obtained for the OPs detection in tap water and apple. Moreover, the developed sensing system is simple in preparation and low cost, exhibiting an efficient platform to meet the requirement for in situ application in food safety and environmental monitoring.

Paper and Other Fibrous Materials-A Complete Platform for Biosensing Applications

Paper-based analytical devices (PADs) and Electrospun Fiber-Based Biosensors (EFBs) have aroused the interest of the academy and industry due to their affordability, sensitivity, ease of use, robustness, being equipment-free, and deliverability to end-users. These features make them suitable to face the need for point-of-care (POC) diagnostics, monitoring, environmental, and quality food control applications. Our work introduces new and experienced researchers in the field to a practical guide for fibrous-based biosensors fabrication with insight into the chemical and physical interaction of fibrous materials with a wide variety of materials for functionalization and biofunctionalization purposes. This research also allows readers to compare classical and novel materials, fabrication techniques, immobilization methods, signal transduction, and readout. Moreover, the examined classical and alternative mathematical models provide a powerful tool for bioanalytical device designing for the multiple steps required in biosensing platforms. Finally, we aimed this research to comprise the current state of PADs and EFBs research and their future direction to offer the reader a full insight on this topic.

Optical glucose biosensor built-in disposable strips and wearable electronic devices

On-demand screening, real-time monitoring and rapid diagnosis of ubiquitous diseases, such as diabetes, at early stages are indispensable in personalised treatment. Emerging impacts of nano/microscale materials on optical and portable biosensor strips and devices have become increasingly important in the remarkable development of sensitive visualisation (i.e. visible inspection by the human eye) assays, low-cost analyses and personalised home testing of patients with diabetes. With the increasing public attention regarding the self-monitoring of diabetes, the development of visual readout, easy-to-use and wearable biosensors has gained considerable interest. Our comprehensive review bridges the practical assessment gap between optical bio-visualisation assays, disposable test strips, sensor array designs and full integration into flexible skin-based or contact lens devices with the on-site wireless signal transmission of glucose detection in physiological fluids. To date, the fully modulated integration of nano/microscale optical biosensors into wearable electronic devices, such as smartphones, is critical to prolong periods of indoor and outdoor clinical diagnostics. Focus should be given to the improvements of invasive, wireless and portable sensing technologies to improve the applicability and reliability of screen display, continuous monitoring, dynamic data visualisation, online acquisition and self and in-home healthcare management of patients with diabetes.

A ferrocene-linked metal-covalent organic polymer as a peroxidase-enzyme mimic for dual channel detection of hydrogen peroxide

A novel ferrocene-linked metal-covalent organic polymer (MCOP-NFC) was synthesized through the Claisen-Schmidt condensation reaction of 1,1'-diacetyl ferrocene and tris(4-formylphenyl)amine. MCOP-NFC acts as a highly efficient artificial enzyme for mimicking peroxidase, and shows good stability in harsh chemical environments including strong bases and acids, and boiling water. Based on the peroxidase-like activity of MCOP-NFC, a highly sensitive dual channel detection method for hydrogen peroxide was developed. For the colorimetric detection strategy, the limit of detection (LOD) reached 2.1 μM, while the limit of detection was found to be as low as 0.08 μM based on the electrochemical detection channel. This study offers a new strategy for the development of an enzyme mimetic on the basis of the covalent assembly of nanostructures, and the proposed electrochemical-colorimetric sensor for H₂O₂ detection has great potential for applications in biology and biomedicine.

Four xanthene–fluorene based probes for the detection of Hg2+ ions and their application in strip tests and biological cells

Four new fluorescent probes based on the xanthene structure to detect mercury ions with different colors of fluorescence have been reported.

A Facile Strategy for Immobilizing GOD and HRP onto Pollen Grain and Its Application to Visual Detection of Glucose

Pollen grain was explored as a new carrier for enzyme immobilization. After being modified with boric acid-functionalized titania, the pollen grain was able to covalently immobilize glycosylated enzymes by boronate affinity interaction under very mild experimental conditions (e.g., pH 7.0, ambient temperature and free of organic solvent). The glucose oxidase and horse radish peroxidase-immobilized pollen grain became a bienzyme system. The pollen grain also worked as an indicator of the cascade reaction by changing its color. A rapid, simple and cost-effective approach for the visual detection of glucose was then developed. When the glucose concentration exceeded 0.5 mM, the color change was observable by the naked eye. The assay of glucose in body fluid samples exhibited its great potential for practical application.

Facile synthesis of CuCo2O4@NiCo2O4 hybrid nanowire arrays on carbon cloth for a multicomponent non-enzymatic glucose sensor

The design of hierarchical heterogeneous structures with rational components is considered as a promising method to enhance the properties of electrocatalyst. Binary metal oxides, with high electrochemical activity, have attracted considerable interest in glucose determination. In this work, we synthesized the CuCo₂O₄@NiCo₂O₄ hybrid structure on conductive carbon cloth (CC) via a simple two-step hydrothermal process and investigated its catalytic ability toward glucose. The two individual components that make up this hybrid electrode have good electrical conductivity and excellent catalytic properties for glucose, so the smart combination of these two active materials can provide more catalytic sites and sufficient redox couples for the glucose oxidation. As a result, the CuCo₂O₄@NiCo₂O₄ modified CC presented superior glucose sensing properties, including ultrahigh sensitivity, fast response time, wide linear range and acceptable detection limit. Besides, the sample also exhibited good selectivity for substances in human blood that interfere with glucose detection, such as UA, AA, fructose, sucrose and KCl. The potential of the CuCo₂O₄@NiCo₂O₄/CC electrode for practical application was investigated by measuring the glucose concentration in real serum samples. These results prove that the construction of hierarchical ordered structure is conducive to the improvement of glucose sensor.

An Adaptable Cryptosystem Enabled by Synergies of Luminogens with Aggregation-Induced-Emission Character

The strong emission in the solid state and the feasibility of introducing stimuli responsiveness make aggregation-induced-emission luminogens promising for optical information encryption. Yet, the vast majority of previous reports rely on subtle changes in the molecular conformation or intermolecular interactions, limiting the robustness, multiplicity, capacity, and security of the resulting cryptosystems. Herein, a versatile cryptographic system is presented based on three interconnected and orthogonal covalent transformations concerning a tetraphenylethylene-maleimide conjugate. The cryptosystem is adapted into four configurations with different functionalities by organizing the reactions and molecules in different ways. These variants either balance the accessibility and security of the encrypted information or improve the security and density in data encryption. Significantly, they allow variable decryption from a single encryption and reconstruction of the chemical nature hidden in the fluorescent pattern can only be accessed through given algorithms. These results highlight the importance of multi-component synergies in advancing information encryption systems, which is enabled by the robustness and diversity stemming from the covalent nature of these transformations.

In situ deposition of MOF-74(Cu) nanosheet arrays onto carbon cloth to fabricate a sensitive and selective electrocatalytic biosensor and its application for the determination of glucose in human serum

A new electrocatalytic biosensor (MOF-74(Cu) NS-CC) based on the in situ deposition of MOF-74(Cu) nanosheet on carbon cloth via a bottom-up synthetic approach in a glass tube was developed. The electrocatalytic activity of the deposited MOF-74(Cu) NS was demonstrated in the oxidation of glucose to gluconate under alkaline conditions. The results revealed that the proposed method of in situ formation of MOF-74(Cu) NS onto a carbon cloth surface in a multi-layer solution is capable to generate a stable MOF-74(Cu) NS-CC electrode with excellent sensing performance. When the as-synthesized MOF-74(Cu) NS-CC was applied directly as the working electrode for glucose sensing, it showed much higher conductivity and redox activity than MOF-74(Cu) NS-GCE. With the potential applied at 0.55 V (vs. Ag/AgCl), this new electrocatalytic biosensor exhibits an excellent linear relationship between current density and concentration of glucose. Moreover, a wide linear range of detection (1.0 to 1000 μM) was observed. The limit of detection was found to be 0.41 μM (S/N = 3). The response sensitivity is 3.35 mA mM^-1 cm^-2 when the concentration of glucose is in the range 1-100 μM and 3.81 mA mM^-1 cm^-2 for the 100-1000 μM concentration range. This study provides a low-cost, easy to prepare, and reproducible methodology for the synthesis of highly redox-active nanomaterials based on the in situ formation of two-dimensional MOF-74(Cu) NS for the development of new electrocatalytic biosensors. Graphical abstract.

Electrochemical Detection of H2O2 Released from Prostate Cancer Cells Using Pt Nanoparticle-Decorated rGO–CNT Nanocomposite-Modified Screen-Printed Carbon Electrodes

In this study, we fabricated platinum nanoparticles (PtNP)-decorated, porous reduced graphene oxide (rGO)–carbon nanotube (CNT) nanocomposites on a PtNP-deposited screen-printed carbon electrode (PtNP/rGO–CNT/PtNP/SPCE) for detection of hydrogen peroxide (H2O2), which is released from prostate cancer cells LNCaP. The PtNP/rGO–CNT/PtNP/SPCE was fabricated by a simple electrochemical deposition and co-reduction method. In addition, the amperometric response of the PtNP/rGO–CNT/PtNP/SPCE electrode was evaluated through consecutive additions of H2O2 at an applied potential of 0.2 V (vs. Ag pseudo-reference electrode). As a result, the prepared PtNP/rGO–CNT/PtNP/SPCE showed good electrocatalytic activity toward H2O2 compared to bare SPCE, rGO–CNT/SPCE, PtNP/SPCE, and rGO–CNT/PtNP/SPCE. In addition, the PtNP/rGO–CNT/PtNP/SPCE electrode exhibited a sensitivity of 206 μA mM−1·cm−2 to H2O2 in a linear range of 25 to 1000 μM (R2 = 0.99). Moreover, the PtNP/rGO–CNT/PtNP/SPCE electrode was less sensitive to common interfering substances, such as ascorbic acid, uric acid, and glucose than H2O2. Finally, real-time monitoring of H2O2 released from LNCaP cells was successfully performed by this electrode. Therefore, we expect that the PtNP/rGO–CNT/PtNP/SPCE can be utilized as a promising electrochemical sensor for practical nonenzymatic detection of H2O2 in live cells or clinical analysis.