Amphiphile-Mediated Ultrasmall Aggregation Induced Emission Dots for Ultrasensitive Fluorescence Biosensing

Multiple DNA cycle amplification for highly efficient detection of mercury pollution in food

Mercury ion (Hg2+), a highly toxic metal pollutant, is widely found in the environment and can enter the human body through the food chain, causing various health issues. Sensitive and accurate methods for monitoring Hg2+ are highly desirable for ensuring food safety. Herein, we propose a self-sustainable multiple amplification system (MAS) for Hg2+ determination through the reciprocal activation between catalytic hairpin assembly (CHA) and rolling circle amplification (RCA). The thymine-encoded recognition element specifically recognizes Hg2+, triggering the exposure of the initiator. The initiator then motivates the mutual activation of CHA and RCA to accelerate the production of an exponentially amplified signal. The MAS method achieved a low detection limit of 11 pM. Due to its reliable target recognition and robust amplification efficiency, the MAS circuit facilitated the highly efficient and accurate analysis of low-abundance Hg2+ in milk and snakehead samples, thus providing a potentially new tool for food safety control.

Recent Development on Sensing Strategies for Small Molecules Detections

Sensors play a critical role in the detection and monitoring of various substances present in our environment, providing us with valuable information about the world around us. Within the field of sensor development, one area that holds particular importance is the detection of small molecules. Small molecules encompass a wide range of organic or inorganic compounds with low molecular weight, typically below 900 Daltons including gases, volatile organic compounds, solvents, pesticides, drugs, biomarkers, toxins, and pollutants. The accurate and efficient detection of these small molecules has attracted significant interest from the scientific community due to its relevance in diverse fields such as environmental pollutants monitoring, medical diagnostics, industrial optimization, healthcare remedies, food safety, ecosystems, and aquatic and terrestrial life preservation. To meet the demand for precise and efficient monitoring of small molecules, this summary aims to provide an overview of recent advancements in sensing and quantification strategies for various organic small molecules including Hydrazine, Glucose, Morpholine, Ethanol amine, Nitrosamine, Oxygen, Nitro-aromatics, Phospholipids, Carbohydrates, Antibiotics, Pesticides, Drugs, Adenosine Triphosphate, Aromatic Amine, Glutathione, Hydrogen Peroxide, Acetone, Methyl Parathion, and Thiophenol. The focus is on understanding the receptor sensing mechanism, along with the electrical, optical, and electrochemical response. Additionally, the variations in UV-visible spectral properties of the ligands upon treatment with the receptor, fluorescence and absorption titration analysis for limit of detection (LOD) determination, and bioimaging analysis are discussed wherever applicable. It is anticipated that the information gathered from this literature survey will be helpful for the perusal of innovation regarding sensing strategies.

Recent Advances in Electrochemiluminescence Biosensors for MicroRNA Detection

Electrochemiluminescence (ECL) as an analytical technology with a perfect combination of electrochemistry and spectroscopy has received considerable attention in bioanalysis due to its high sensitivity and broad dynamic range. Given the selectivity of bio-recognition elements and the high sensitivity of the ECL analysis technique, ECL biosensors are powerful platforms for the sensitive detection of biomarkers, achieving the accurate prognosis and diagnosis of diseases. MicroRNAs (miRNAs) are crucial biomarkers involved in a variety of physiological and pathological processes, whose aberrant expression is often related to serious diseases, especially cancers. ECL biosensors can fulfill the highly sensitive and selective requirements for accurate miRNA detection, prompting this review. The ECL mechanisms are initially introduced and subsequently categorize the ECL biosensors for miRNA detection in terms of the quenching agents. Furthermore, the work highlights the signal amplification strategies for enhancing ECL signal to improve the sensitivity of miRNA detection and finally concludes by looking at the challenges and opportunities in ECL biosensors for miRNA detection.

Self-Assembled Tetraphenylethene-Based Nanoaggregates with Tunable Electrochemiluminescence for the Ultrasensitive Detection of E. coli

As an effective ECL emitter, tetraphenylethene (TPE)-based molecules have recently been reported with aggregation-induced electrochemiluminescence (AIECL) property, while it is still a big challenge to control its aggregation states and obtain uniform aggregates with intense ECL emission. In this study, we develop three TPE derivatives carrying a pyridinium group, an alkyl chain, and a quaternary ammonium group via the Menschutkin reaction. The resulting molecules exhibit significantly red-shifted FL and enhanced ECL emissions due to the tunable reduction of the energy gap between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs). More importantly, the amphiphilicity of the as-developed molecules enables their spontaneous self-assembly into well-controlled spherical nanoaggregates, and the ECL intensity of nanoaggregates with 3 -CH2- (named as C3) is 17.0-fold higher compared to that of the original 4-(4-(1,2,2-triphenylvinyl)phenyl)pyridine (TPP) molecule. These cationic nanoaggregates demonstrate a high affinity toward bacteria, and an ECL sensor for the profiling of Escherichia coli (E. coli) was developed with a broad linear range and good selectivity in the presence of an E. coli-specific aptamer. This study provides an effective way to enhance the ECL emission of TPE molecules through their derivatization and a simple way to prepare well-controlled AIECL nanoaggregates for ECL application.

Aggregation-induced emission for the detection of peptide ligases with improving ligation efficiency

BACKGROUND

Monitoring peptide ligase activity is of great significance for biological research, medical diagnosis, and drug discovery. The current methods for the detection of peptide ligases suffer from the limitations of high background signal, elaborate design of substrate, and high reversibility of ligation reaction. In this work, we proposed a simple and sensitive method for ligase detection with reducing ligation reversibility on the basis of aggregation-induced emission (AIE) mechanism.

RESULTS

The peptide probes labeled with AIE luminogens (AIEgens) were water-soluble and emitted weak fluorescence. After ligation reaction, the enzymatic products with AIEgens showed high hydrophobicity and could readily assembly into aggregates, thus lighting up the fluorescence. More interestingly, the formation of aggregates pushed the equilibrium to the generation of the desired ligation products, thus improving the catalytic efficiency by driving the reaction towards completion. The ligation reaction conversion rate (>80 %) is significantly higher than that without blocking the reversibility with additional treatment. With sortase A (SrtA) as the analyte example, the detection limit of this method was found to be 0.01 nM with a linear range of 0-50 nM. The system was applied to evaluate the inhibition efficiency of berberine chloride and quercetin and determine the activity of SrtA in serum, lysate and Staphylococcus aureus with satisfactory results.

SIGNIFICANCE

This study indicated that the ligation efficiency and detection sensitivity can be improved by reducing ligation reversibility through AIE phenomenon. The proposed strategy could be used for the detection of other peptide ligases by adopting sequence-specific peptide substrates.

Ultrasound-enhanced catalytic hairpin assembly capable of ultrasensitive microRNA biosensing for the early screening of Alzheimer's disease

Catalytic hairpin assembly (CHA) is a promising enzyme-free, isothermal signal amplification strategy, but the relatively time-consuming strand replacement limits its application scenarios. Here, we developed an ultrasound-enhanced catalytic hairpin assembly (UECHA) biosensing platform for early screening of Alzheimer's disease by introducing a portable acoustic-drive platform with functionalized microspheres for effective biomarkers enrichment and fluorescence enhancement. By constructing a gradient ultrasonic field in a microcavity, the platform concentrates the functionalized microspheres in a central position, accompanied by an enhanced fluorescence signal with a specific release. In addition, the programmable frequency modulation can also modify the acoustic potential well and effectively promote non-equilibrium chemical reactions such as CHA (25 min). Compared with the conventional catalytic hairpin assembly (CHA), UECHA allows for direct and quantitative measurement of AD miRNAs down to 3.55 × 10-15 M in 1 μL samples. This visual analysis of ultra-trace biomarkers based on acoustic enrichment and promotion provides a new perspective for the rapid and highly sensitive clinical detection of Alzheimer's disease.

Naphthalimide-Based AIEgens for Sensing Protein Disulfide Isomerase through Thiol-Disulfide Redox Exchange

Aggregation-induced emission (AIE)-based fluorescent organic nanoparticles (FONPs) with distinctive characteristics are emerging as superior sensors due to their facile fabrication, high signal-to-noise ratio, and good biocompatibility. The present article delineates the detection and analysis of the redox behavior of the protein disulfide isomerase (PDI) enzyme by exploitation of the AIE of novel naphthalimide (NI) derivatives having thiol (-SH) and disulfide (-S-S-) moieties. Self-aggregated spherical-shaped organic nanoparticles were prepared by synthesized NI-based amphiphiles (NISH, NISS, NINSS, and TNINSH) through J-type aggregation in DMSO-water (fw = 99 vol %). Naphthyl residue containing NI-derived amphiphiles (NINSS and TNINSH) exhibited AIE (blue and yellow) at 470 and 550 nm, respectively, in DMSO-water (fw = 99 vol %). NINSS and TNINSH FONPs were suitably utilized in sensing PDI through their redox nature of thiol-disulfide exchange. Fluorescence quenching of NINSS FONPs was observed due to reduction of disulfide to thiol by PDI, whereas emission intensity was progressively red-shifted and enhanced ("Dual-AIE") for TNINSH (containing ER-targeting N-tosylethylenediamine), owing to oxidation of thiol to disulfide by PDI. NINSS and TNINSH FONPs were found to be highly efficient in sensing PDI through the AIE-based "fluorescence off/on" mechanism having limits of detection of ∼12.6-17.7 and ∼11.7-16.5 ng/mL, respectively. In vitro cell imaging for NIH3T3 (noncancer) and B16F10 (melanoma) cells with NINSS and TNINSH FONPs displayed excellent diagnosis of eukaryotic cells upon interaction with indigenous PDI. Notably, detection of cancer cells was more sensitive over the noncancerous cells by these FONPs due to overexpression of PDI within cancer cells.

Overview on the Development of Alkaline-Phosphatase-Linked Optical Immunoassays

The drive to achieve ultrasensitive target detection with exceptional efficiency and accuracy requires the advancement of immunoassays. Optical immunoassays have demonstrated significant potential in clinical diagnosis, food safety, environmental protection, and other fields. Through the innovative and feasible combination of enzyme catalysis and optical immunoassays, notable progress has been made in enhancing analytical performances. Among the kinds of reporter enzymes, alkaline phosphatase (ALP) stands out due to its high catalytic activity, elevated turnover number, and broad substrate specificity, rendering it an excellent candidate for the development of various immunoassays. This review provides a systematic evaluation of the advancements in optical immunoassays by employing ALP as the signal label, encompassing fluorescence, colorimetry, chemiluminescence, and surface-enhanced Raman scattering. Particular emphasis is placed on the fundamental signal amplification strategies employed in ALP-linked immunoassays. Furthermore, this work briefly discusses the proposed solutions and challenges that need to be addressed to further enhance the performances of ALP-linked immunoassays.

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

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

Stimuli-responsive aggregation-induced emission of molecular probes by electrostatic and hydrophobic interactions: Effect of organic solvent content and application for probing of alkaline phosphatase activity

We suggest that aggregation-induced emission (AIE) molecular probes with single charged/reactive group can exist in the formation of nanostructures but not monomers at extremely low organic solvent content. The nanoaggregates show good dispersivity and emit week emission. Stimuli-responsive assembly of nanoaggregates by electrostatic interactions can turn on the fluorescence, facilitating the design of biosensors with single-charged molecular probes as the AIE fluorogens. To prove the concept, tetraphenylethene-substituted pyridinium salt (TPE-Py) was used as the AIE fluorogen for probing of alkaline phosphatase (ALP) activity with pyrophosphate ion (PPi) as the enzyme substrate. The dynamic light scattering and transmission electron microscope experiments demonstrated that TPE-Py probes existed in aqueous solution at nanometer size and morphology. Stimuli such as the negatively charged PPi, citrate, ATP, ADP, NADP and DNA could trigger the aggregation of the positively charged TPE-Py nanoparticles, thus enhancing the fluorescence via AIE effect. ALP-enzymatic hydrolysis of PPi into two phosphate ions (Pi) limited the aggregation of TPE-Py nanoparticles. The strategy was used for the assay of ALP with a low detection limit (1 U/L) and wide linear range (1-200 U/L). We also investigated the effect of organic solvent content on the AIE process and found that high concentration of organic solvent can prevent the hydrophobic interaction between AIE molecules but show no essential influence on the electrostatic interaction-mediated assembly. The work should be evaluable for understanding AIE phenomenon and developing novel, simple and sensitive biosensors using a molecular probe with single charged/reactive group as the signal reporter.

Background-Quenched Aggregation-Induced Emission through Electrostatic Interactions for the Detection of Poly(ADP-ribose) Polymerase-1 Activity

Poly(ADP-ribose) polymerase-1 (PARP1) is a potential biomarker and therapeutic target for cancers that can catalyze the poly-ADP-ribosylation of nicotinamide adenine dinucleotide (NAD⁺) onto the acceptor proteins to form long poly(ADP-ribose) (PAR) polymers. Through integration with aggregation-induced emission (AIE), a background-quenched strategy for the detection of PARP1 activity was designed. In the absence of PARP1, the background signal caused by the electrostatic interactions between quencher-labeled PARP1-specitic DNA and tetraphenylethene-substituted pyridinium salt (TPE-Py, a positively charged AIE fluorogen) was low due to the fluorescence resonance energy transfer effect. After poly-ADP-ribosylation, the TPE-Py fluorogens were recruited by the negatively charged PAR polymers to form larger aggregates through electrostatic interactions, thus enhancing the emission. The detection limit of this method for PARP1 detection was found to be 0.006 U with a linear range of 0.01~2 U. The strategy was used to evaluate the inhibition efficiency of inhibitors and the activity of PARP1 in breast cancer cells with satisfactory results, thus showing great potential for clinical diagnostic and therapeutic monitoring.

Polyethyleneimine-induced fluorescence enhancement strategy for AIEgen: the mechanism and application

Aggregation-induced emission luminogens (AIEgens) are attracting extensive research attention in the biosensor fields. Herein, we report a new polyethyleneimine (PEI)-induced strategy for enhancing luminescence of TCBPE (an AIEgen) to promote its development in biosensor. The copolymer dots (TCBPE-PEI) with high quantum yield (39.7%) and outstanding stability were synthesized via a one-pot method. The fluorescence enhancement mechanism based on the PEI strategy originated from the restriction of intramolecular motions of TCBPEs and the form of donor-acceptor structures to decrease the inherent energy bandgap. Benefiting from chelating property of TCBPE-PEI by Cu²⁺, a fluorescence-quenching sensor for Cu²⁺ detection was developed based on the fluorescence quenching of the electron transfer effect. Especially, a good linear range of 10-250 nM with a low limit of detection 1.1 nM was achieved, and it was further applied in samples successfully. The current work provides a novel approach to fabricate AIEgen biosensors and shows great potential in Cu²⁺ detection.

In situ coordination interactions between metal-organic framework nanoemitters and coreactants for enhanced electrochemiluminescence in biosensing

Coreactant electrochemiluminescence (ECL) is one of the most popular pathways in commercial analysis, which can provide simplicity and convenience for getting intense ECL emission. However, the low efficiency of intermolecular electron transfer could weaken ECL intensity. In this work, we developed an enhanced ECL strategy through in situ coordination interactions between metal-organic framework emitters and coreactants. First, a metal-organic framework (MOF) emitter was synthesized with 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethane (TPPE) as aggregation-induced emission linkers and Zn as nodes. Interestingly, compared to TPPE ligand, the resulted MOF nanoemitters demonstrated 49.5 folds enhancement of ECL emission in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) as the coreactant. More significantly, different from the constant ECL intensity using TPrA coreactant, DABCO exhibited time-dependent ECL intensity due to the intrareticular electron transfer through coordination interaction between DABCO and Zn²⁺, which was confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectral experiments. The enhanced ECL was then applied to construct a sensitive ECL method to detect dopamine in serum samples. The coordination interaction between emitters and coreactants not only provides a universal way to enhance ECL, but also expands the applications of coreactant ECL system in convenience route.

An esterase-sensitive AIEgen probe targeting mitochondria and lipid droplets for assessing cell viability

In order to conduct in-depth research on the mechanisms of cancer diagnosis and treatment, it is very important to develop fluorescent probes to study the interactions between different organelles and understand the relationship between various organelles and cell viability. However, the lack of fluorescent probes to visualize two or more targets has resulted in limited studies of intracellular interactions between different organelles. To this end, in this work, we developed a near-infrared (NIR) AIE probe with dual-color emission, NAP-Py-E, for mitochondria and lipid droplets imaging. The probe NAP-Py-E consists of lipophilic fraction, pyridine cation structure and esterase hydrolysis site. Interestingly, NAP-Py-E first targets mitochondria and emits red fluorescence; after partially hydrolyed by esterase in living cells, the hydrolysate NAP-Py accumulates in lipid droplets and emits green fluorescence. The probe has been successfully used to assess cell viability due to its dual-color emission and dual-organelle targeted changes.

Novel Polarity Fluorescent Probe for Dual-Color Visualization of Lysosomes and Plasma Membrane during Apoptosis

Apoptosis plays a crucial role in the occurrence of cancer and other diseases. Real-time monitoring of the cell apoptosis process has great significance for cell viability and drug screening. Herein, a novel fluorescent probe was constructed based on the fluorescence resonance energy transfer mechanism, which track the sensitivity of polarity changes, as well as detect the drug-induced cell apoptosis process in a dual-color mode. Importantly, the change of cellular microenvironmental polarity makes it possible to dynamically visualize the process of drug-induced cell apoptosis. More significantly, the designed probe targeted the lysosomes in the living cells to give a blue emission, and it accumulated on the plasma membrane to display red fluorescence during the drug-induced cell apoptosis process. Thus, cell viability could be monitored by both the localization and emission colors of the robust probe. We expect that the unique probe can provide a new blueprint for evaluating and screening apoptosis-related drugs.

Sensitive CTC analysis and dual-mode MRI/FL diagnosis based on a magnetic core-shell aptasensor

Synergizing the sensitive circulating tumor cell (CTC) capture, detection, release and the specific magnetic resonance/fluorescence (MR/FL) imaging for accurate cancer diagnosis is of great importance for cancer treatment. Herein, EcoR1-responsive complementary pairing of two ssDNA with a fluorescent P₀ aptamer, which can specifically bind with the overexpressed MUC1 protein on cancer cells, was covalently modified to SiO₂@C-coated magnetic nanoparticles for preparing a special nanoparticle-mediated FL turn-on aptasensor (FSC-D-P₀). This aptasensor can selectively capture/enrich CTC and thus achieve sensitive CTC detection/imaging in even the blood due to its stable targeting, unique magnetic properties and the regulated interactions between the quencher and the fluorescent groups. Meanwhile, FSC-D-P₀ can release the captured CTC for further downstream analysis upon the EcoR1 enzyme-triggered cleavage of the double-stranded DNA (dsDNA). Most importantly, this aptasensor can distinctly avoid false positivity of MRI via multiple targeting mechanisms. Thus, the sensitive CTC capture, detection, release and accurate MR/FL imaging were synergistically combined into a single platform with good biocompatibility, promising a robust pattern for clinical tumor diagnosis in vitro and in vivo.

Dual-QDs ratios fluorescent probe for sensitive and stable detection of insulin

In this work, immune modified graphene quantum dot (GQD) and semiconductor quantum dot (SQD) with blue and red emission respectively were synthesized to assemble a dual-QDs ratios fluorescent probe, which could be efficient used for insulin determination. There may be the dynamic equilibrium of förster resonance energy transfer (FRET) and aggregation-induced emission (AIE) in the internal of the probe, thus emitted special dual fluorescent lights. However, this sate of probe was cleaved upon exposure to target insulin, resulting in changing of the dual fluorescent lights. The resulting ratios response can be correlated quantitatively to the concentration of insulin, and was found to have a detection limit (as low as 0.045 ng mL^-1) and rapid response time (as short as 5 min). It has been preliminarily used for ratiometric sensing of insulin in biological samples and exhibited consistency of the insulin detected results and higher stability compared with conventional ELISA. Therefore, this sensitive, rapid and stable detection system has great potential for next generation of the bioassay platform for clinical diagnosis and other applications.

A conveniently synthesized redox-active fluorescent covalent organic framework for selective detection and adsorption of uranium

Uranium is a key element in the nuclear industry and also a global environmental contaminant with combined highly toxic and radioactive. Currently, the materials based on post-modification of amidoxime have been developed for uranium detection and adsorption. However, the affinity of amidoxime group for vanadium is stronger than that of uranium, which is the main challenge hindering the practical application of amidoxime-based adsorbents. Herein, we synthesized a fluorescent covalent organic framework (TFPPy-BDOH) through integrating biphenyl diamine and pyrene unit into the π-conjugated framework. TFPPy-BDOH has an excellent selectivity to uranium due to the synergistic effect of nitrogen atom in the imine bond and hydroxyl groups in conjugated framework. It can achieve ultra-fast fluorescence response time (2 s) and ultra-low detection limit (8.8 nM), which may be attributed to its intrinsic regular porous channel structures and excellent hydrophilicity. More excitingly, TFPPy-BDOH can chemically reduce soluble U (VI) to insoluble U (IV), and release the binding site to adsorb additional U (VI), achieving high adsorption capacity of 982.6 ± 49.1 mg g^-1. Therefore, TFPPy-BDOH can overcome the challenges faced by current amidoxime-based adsorbents, making it as a potential adsorbent in practical applications.

A concise detection strategy of Staphylococcus aureus using N-Succinyl-Chitosan-dopped bacteria-imprinted composite film and AIE fluorescence sensor

Staphylococcus aureus is one of the major foodborne pathogens. Efficient detection and isolation of Staphylococcus aureus from complex samples are crucial. Herein, we report a concise strategy to detect of Staphylococcus aureus with high sensitivity and specificity, based on N-Succinyl-Chitosan doping bacteria-imprinted composite film and aggregation-induced emission (AIE)-featuring fluorescence sensor. The good shaping and mechanical properties of polydimethylsiloxane provide a specific recognition site suitable for Staphylococcus aureus. For the first time, chitosan derivatives is combined with polydimethylsiloxane to prepare a two-component composite film, which possesses a remarkable absorption performance of Staphylococcus aureus using the natural excellent absorption property of chitosan. The positive charged AIE-featuring Au(I)-disulfide nanoparticles realized the quantitative characterization of Staphylococcus aureus without cooperation with bio-recognition elements. To conclude, this study provides new possibilities for the manufacture of highly efficient bacterial separators with superior performance and facilitates the application of unlabeled nanoparticles in quantitative analysis.

Novel A–D–A structural imidazole derivatives with charge transfer excited states: importance of molecular structure design in obtaining a “turn-on” type fluorescence probe

Two A–D–A structural triphenylamine-imidazole derivatives were designed to provide a potential strategy for the development of turn-on type Fe3+ fluorescent probes.

Highly sensitive fluorescent sensor based on coumarin organic dye for pyrophosphate ion turn-on biosensing in synovial fluid

Highly sensitive fluorescence detection of pyrophosphate ion (PPi) is in urgent demand but remains a great obstacle, ascribing to scarcity of high-performance materials with promising optical property and high affinity. Herein, we report the design and fabrication of a coumarin-based organic dye (DCCH-TPD) containing both hydrazide group and terpyridine moiety for PPi biosensing through Cu²⁺-induced photo-electron transfer (PET) effect and target analyte-switched competitive coordination reaction. Individual DCCH-TPD was found to be highly emissive, and displayed a turn-off response toward Cu²⁺ due to formation of Cu²⁺@DCCH-TPD and PET effect. The recognition of Cu²⁺@DCCH-TPD by PPi leads to generation of Cu²⁺@PPi complex, which greatly reduces the amount of Cu²⁺ coordinated with DCCH-TPD, subsequently decreasing PET effect. Significantly enhanced fluorescence is recorded and the fluorescence intensity is closely relied on PPi concentration. Thus, highly sensitive detection of PPi is achieved, and the detection limit was calculated to be 0.075 μM. Furthermore, the proposed sensor presented good selectivity, and excellent practical ability for application in arthritic fluid.

Highly selective fluorescence probe with peptide backbone for imaging mercury ions in living cells based on aggregation-induced emission effect

Mercury is an anthropogenic toxic heavy metal found in the environment. It is highly desirable to develop a fluorescence probe that can selectively and sensitively detect mercury ions using a turn-on response. This paper reports the successful development of a peptide fluorescence probe, TP-2 (TPE-Trp-Pro-Gln-His-Glu-NH₂), which uses aggregation-induced emission effects and high selectivity to detect Hg²⁺. After fluorescence was activated, Hg²⁺ was efficiently detected using the change in fluorescence intensity. The detection limit for Hg²⁺ in the buffer solution was 41 nM (R² = 0.9952). Owing to its high sensitivity, high cell permeability, and low biotoxicity, the probe could perform live cell imaging under biological conditions. This study demonstrated that TP-2 can detect Hg²⁺ in complex biological environments.

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.

Palladium-Catalyzed Direct Mono- and Diarylation of Diphenydithienylethenes: A Useful Method for Enhancing Fluorescence Intensity and Aggregation-Induced Emission

In this study we report efficient method for the syntheses of mono- and diarylated diphenyldithienylethene (DPDTE) via a palladium-catalyzed C–H arylation reaction. These new derivatives showed amplified luminescent properties thanks to a change in polarity, particularly in the presence of an electron-withdrawing groups (EWG). Moreover, the arylated DPDTEs showed dual-emissive phenomena, including fluorescence in organic solvents and aggregation-induced emission.

A Solid-State Fluorescence Switch Based on Triphenylethene-Functionalized Dithienylethene With Aggregation-Induced Emission

The development of novel dithienylethene-based fluorescence switches in the aggregated state, and the solid state is highly desirable for potential application in the fields of optoelectronics and photopharmacology. In this contribution, three novel triphenylethene-functionalized dithienylethenes (1-3) have been designed and prepared by appending triphenylethene moieties at one end of dithienylethene unit. Their chemical structures are confirmed by 1H NMR, 13C NMR, and HRMS (ESI). They display good photochromic behaviors with excellent fatigue resistance upon irradiation with UV or visible light in Tetrahydrofuran (THF) solution. Before irradiation with UV light, they exhibit Aggregation Induced Emission (AIE) properties and luminescence behaviors in the solid state. Moreover, upon alternating irradiation with UV/visible light, they display effective fluorescent switching behaviors in the aggregated state and the solid state. The experimental results have been validated by the Density Functional Theory (DFT) calculations. Thus, they can be utilized as novel fluorescence switches integrated in smart, solid-state optoelectronic materials and photopharmacology.

Highly selective and sensitive colorimetric/fluorometric dual mode detection of relevant biogenic amines

Biogenic amines are involved in physiological roles in living organisms, but their excessive production or intake can induce undesired toxicological effects. As biogenic amines can be found in the process of food spoilage, they are considered an indicator of food quality and freshness, and their detection is of crucial importance in food safety. In this contribution, we report the fast and direct colorimetric and fluorometric sensing of biogenic amines by means of a dinuclear Zn(ii) Schiff-base complex. The selective and sensitive detection involves the formation of stable adducts between the dinuclear complex, acting as the Lewis acidic molecular tweezer, and biogenic di- or polyamines. The selectivity towards biogenic amines, even in the presence of common aliphatic, primary, secondary, or tertiary monoamines, heterocyclic amines, and amino acids, is demonstrated by competitive experiments. The quantitation of histamine in a fish matrix is easily achieved using a standard extraction procedure followed by simple colorimetric or fluorometric measurements.

Modulation of Aggregation-Induced Emission by Excitation Energy Transfer: Design and Application

Excitation energy transfer (EET) as a fundamental photophysical process is well-explored for developing functional materials with tunable photophysical properties. Compared to traditional fluorophores, aggregation-induced emission luminogens (AIEgens) exhibit unique advantages for building EET systems, especially serving as energy donors, due to their outstanding photophysical properties such as bright fluorescence in aggregation state, broad absorption and emission spectra, large Stokes shift, and high photobleaching resistance. In addition, the photophysical properties of AIEgens can be modulated by energy transfer for improved luminescence performance. Therefore, a variety of EET systems based on AIEgens have been constructed and their applications in different areas have been explored. In this review, we summarize recent progress in the design strategy of AIE-based energy transfer systems for light-harvesting, fluorescent probes and theranostic systems, with an emphasis on design strategies to achieve desirable properties. The limitations, challenges and future opportunities of AIE-EET systems are briefly outlined. Design strategies and applications (light-harvesting, fluorescent probe and theranostics) of AIEgen-based excitation energy systems are discussed in this review.

A signal-on fluorescent aptasensor based on gold nanoparticles for kanamycin detection

This study describes the development, verification and practical application of an aptasensor for the fluorometric detection of kanamycin. Using the nucleic acid aptamer with FAM fluorescent group as the conjugate, using gold nanoparticles as the fluorescence dynamic quenching source, a fluorescence sensor was fabricated through the signal-on method for the micro-detection of kanamycin. The nucleic acid chimera is connected to the fluorophore, and the gold nanoparticles are used as the fluorescence dynamic quenching source under actual conditions. The detection limit of kanamycin is 0.1 pM, and the detection range is 0.1 pM to 0.1 μM. This biosensor works satisfactorily in complex samples with no impurities, which gives this method an obvious advantage over other analytical methods. In addition, the mechanism of action between gold nanoparticles/FAM-aptamer/kanamycin is discussed and studied in depth here. It provides a more thorough analysis and more application possibilities for fluorescence-aptamer biosensing.

Highly Efficient Water-Soluble Photosensitizer Based on Chlorin: Synthesis, Characterization, and Evaluation for Photodynamic Therapy

The clinical applications of many photosensitizers (PSs) are limited because of their poor water solubility, weak tissue penetration, low chemical purity, and severe toxicity in the absence of light. We designed a novel chlorin-based PS (designated as HPS) to achieve fluorescence image-guided photodynamic therapy (PDT) with efficient ROS generation. In addition to its simple fabrication process, HPS has other advantages such as excellent water solubility, strong NIR absorption, and high biocompatibility upon chemical functionalization for enhanced phototherapy. HPS exhibited high photodynamic performance against lung cancer and breast cancer cells by generating a large amount of singlet oxygen (¹O₂) under 654 nm laser irradiation. HPS accumulated into multiple organelles such as mitochondria and the endoplasmic reticulum and triggered cell apoptosis by laser exposure. In the tumor-bearing mice, in vivo, HPS showed an optimal half-life in circulation and achieved fluorescence-image-guided PDT within the irradiation window, resulting in effective tumor growth inhibition and the prolonged survival of animals. Moreover, the antitumor PDT effect of HPS was close to the clinical trial phase II stage of HPPH even at the low dosage of 0.32 mg/kg (under 75 J/cm² laser), while the systemic safety of HPS was much higher. In conclusion, HPS is a novel water-soluble chlorin derivative with excellent PDT potential for clinical transformation.

Label-free and enzyme-free fluorescence detection of microRNA based on sulfydryl-functionalized carbon dots via target-initiated hemin/G-quadruplex-catalyzed oxidation

Carbon dots (CDs)-based biosensors have attracted considerable interest in reliable and sensitive detection of microRNA (miRNA) because of their merits of ultra-small size, excellent biosafety and tunable emission, whereas complicated labeling procedure and expensive bioenzyme associated with current strategies significantly limit their practical application. Herein, we developed a label-free and enzyme-free fluorescence strategy based on strand displaced amplification (SDA) for highly sensitive detection of miRNA using sulfydryl-functionalized CDs (CDs-SH) as probe. CDs-SH displayed excellent response to G-quadruplex DNA against other DNAs based on based on the catalytic oxidation of -SH into -S-S- by hemin/G-quadruplex. Further, CDs-SH were employed to detect miRNA, using miRNA-21 as target model, which triggered the SDA reaction of P1 and P2 to generate hemin/G-quadruplex, subsequently making CDs-SH transform from dot to aggresome along with the quenched fluorescence. Therefore, label-free, enzyme-free, and highly sensitive analysis of miRNA-21 was readily acquired with a limit of detection at 0.03 pM. This proposed biosensor couples the advantages of CDs and label-free/enzyme-free strategy, and thus has a significant potential to be used in early and accurate diagnosis of cancer.

Porphyrin-based covalent organic framework as bioplatfrom for detection of vascular endothelial growth factor 165 through fluorescence resonance energy transfer

A fluorescent aptasensor based on porphyrin-based covalent organic framework (p-COF) and carbon dots (CDs) was constructed for detecting vascular endothelial growth factor 165 (VEGF₁₆₅) and for imaging of the breast cancer cell line Michigan cancer foundation-7 (MCF-7). CDs synthesized with strong photoluminescence at λ∼380 nm were used as donors to label the VEGF₁₆₅-targeted aptamers (Apt_VEGF/CDs). Additionally, the p-COF nanostructure comprised rich functional groups of CN on the surface and π-stacking planar nanostructure, resulting in the CDs adsorption via weakly π-π stacking, hydrogen bond and the Van der Waals force. Thereby, the fluorescence resonance energy transfer (FRET) occurred due to the close distance between the p-COF network and CDs, leading to the quenching of the fluorescence feature of CDs and p-COF. In the presence of VEGF₁₆₅, the G-quadruplex was formed via the specific binding between VEGF₁₆₅ and aptamer. It impelled that the release of partial VEGF₁₆₅-Apt_VEGF/CDs complex, affording the fluorescence recovery of the sensing system to some extent. Consequently, the proposed Apt_VEGF/CDs/p-COF fluorescence biosensor offered excellent analytical performances for the VEGF₁₆₅ detection, displaying a detection limit of 20.9 fg mL^-1 within a wide linear range of the VEGF₁₆₅ concentration of 1.0 pg mL^-1-100 ng mL^-1. The developed fluorescence biosensor was also used to determine VEGF₁₆₅-overexpressed in MCF-7 cancer cells. Thereby, the present work can greatly widen the application of COFs in the development of aptasensors and cancer diagnosis.

Small Molecular Prodrug Amphiphile Self-Assembled AIE Dots for Cancer Theranostics

A simple and facile one-step method was developed to construct a small molecular prodrug amphiphile self-assembled organic dots CPPG with aggregation-induced emission (AIE) characteristics. Diphenylalanine peptide (FF), which is the essential moiety of the self-assembling peptide-drug conjugate and as its core recognition motifs for molecular self-assembly. In addition, the D-glucose transported protein (GLUT), which is one of the important nutrient transporters and is overexpressed in cancer cells. The conjugation of glycosyl further endues the nanoparticle with good biocompatibility and tumor-targeting ability. Taking advantages of both the cancer cell-targeting capability of small molecular prodrug amphiphile CPPG and the AIE aggregates with strong emission, the prepared CPPG AIE dots can target cancer cells specifically and inhibit the proliferation of cancer cells with good biocompatibility and photostability. Based on the general approach, types of universal organic fluorescent nanoprobes could be facilely constructed for imaging applications and biological therapeutics, which possess the properties of specific recognition and high brightness.

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

Given the importance of food safety, it is highly desirable to develop a convenient, low-cost, and practical sensor for organophosphorus pesticides (OPs) detection. Here, a fluorescent paper analytical device (FPAD) based on aggregation-induced emission (AIE) nanoparticles (PTDNPs-0.10) and two-dimension MnO₂ nanoflakes (2D-MnNFs) was developed for instrument-free and naked-eye analysis of OPs. PTDNP-MnNFs composites were obtained through 2D-MnNFs and PTDNPs-0.10 by electrostatic interaction and the fluorescence emission of PTDNPs-0.10 was quenched through fluorescence resonance energy transfer (FRET). When acetylcholinesterase (AChE) was present, acetylthiocholine (ATCh) was catalytically hydrolyzed into thiocholine, which reduced MnO₂ of PTDNP-MnNFs into Mn²⁺, subsequently blocking the FRET and enhancing the fluorescence. Upon the addition of OP, AChE activity was depressed and thus the FRET between 2D-MnNFs and PTDNPs-0.10 was not affected, resulting in a slight change in fluorescence. On the basis of the variation in fluorescence intensity, highly sensitive detection of OP was readily achieved with a detection limit of 0.027 ng/mL; on the basis of the variation in brightness of FPAD, instrument-free and visual detection of OP was realized using a smartphone with a detection limit of 0.73 ng/mL. The application of FPAD has significantly simplified the detection procedure and decreased the test cost, supplying a new approach for on-site detection of OPs.

Equipment-free and visualized biosensor for transcription factor rapid assay based on dopamine-functionalized cellulose paper

A cellulose paper-based biosensor was developed for the equipment-free and naked-eye detection of a transcription factor (TF) using dopamine as the signal-responsive material based on exonuclease III-assisted cycling amplification. Compared with other TF biosensors, the proposed biosensor demonstrates low-cost, portable, disposable, and naked-eye detection features.

Development of fluorescence oligonucleotide probes based on cytosine- and guanine-rich sequences

The properties of cytosine- and guanine-rich oligonucleotides contributed to employing them as sensing elements in various biosensors. In this paper, we report our current development of fluorescence oligonucleotide probes based on i-motif or G-quadruplex forming oligonucleotides for cellular measurements or bioimaging applications. Additionally, we also focus on the spectral properties of the new fluorescent silver nanoclusters based system (ChONC12-AgNCs) that is able to anchor at the Langmuir monolayer interface, which is mimicking the surface of living cells membrane.

Execution of aggregation-induced emission as nano-sensors for hypochlorite detection and application for bioimaging in living cells and zebrafish

Hypochlorite (ClO^-) could be used as a diagnostic marker for inflammation and related diseases. Although there have been many reports on probes for ClO^- imaging, there was still a lack of specificity and anti-interference ability. Herein, carbazole (NEC) and tetraphenylethylene (TPE) equipped with thiobarbituric acid (TBA), NEC-TBA and TPE-TBA, were synthesized and used as a fluorescence biosensor for monitoring ClO^- with aggregation-induced emission (AIE) effect. we identified that TPE-TBA, with formed nanoparticles in the mean grain size at 76 nm (5 μM), was a superior probe to target ClO^- over other analytes with fluorescence "turn off" strategy. Subsequently, to explore the bioimaging application, TPE-TBA was able to sense exogenous ClO^- in living HeLa cells through fluorescence imaging. In zebrafish model, TPE-TBA effectively captured exogenous ClO^- in the entire organization of zebrafish. Overall, these AIE-based probes merit further development as organism targeting ClO^- sensors.

Organic Dots Embedded in Mesostructured Silica Xerogel as High-Performance ECL Emitters: Preparation and Application for MicroRNA-126 Detection

Unlike the organic micro/nanocrystals prepared using an emerging reprecipitation method, a novel method of embedding 1-pyrenecarboxaldehyde dots (PycDs) into a mesostructured silica xerogel (PycDs@MSX) for use as electrochemiluminescence (ECL) emitters was first proposed to achieve an extremely strong ECL response, with peroxydisulfate (S₂O₈^2-) used as a coreactant. In this method, (i) PycDs@MSX could ensure the reversal of the PycDs environment from hydrophobic to hydrophilic and (ii) PycDs@MSX could provide massive porous channels, allowing for access of hydrophilic reactive intermediates (i.e., sulfate anion radicals, SO₄^•-), which could accelerate the rate of mass transfer and electron transfer between S₂O₈^2- and PycDs. Using Ag nanoparticles as a coreaction accelerator and a 3D DNA nanomachine as a signal amplification strategy, the proposed ECL biosensing platform was constructed and achieved ultrasensitive detection of microRNA-126 with an excellent linear range (from 100 aM to 100 pM) and a low detection limit (13.0 aM). More importantly, this work not only developed an innovative avenue to improve the ECL efficiency of organic emitters in aqueous phases but also provided a powerful strategy for biochemical analysis and disease diagnosis applications.

Insight into triphenylamine and coumarin serving as copper (II) sensors with "OFF" strategy and for bio-imaging in living cells

Chemosensing is one of the widest and powerful techniques for response to anions and cations in living systems serving as bio-probes. Meanwhile, copper(II) (Cu(II)) widely exists in the environment and the human body as a common trace element, which plays an necessary role in most physiological processes. Thus, it is extremely urgent to explore means for effective, rapid and convenient detection of Cu(II) in living cells. Herein, we introduce a novel strategy for designing triphenylamine (TS) and coumarin-based (CS) functional sensors for Cu(II) detection with fluorescence "OFF" switching mechanism by blocking intramolecular charge transfer (ICT). Based on this design strategy, we have demonstrated two kinds of fluorophores sensors with aunique new fluorescent dye and excellent photophysical properties, which have shown rapid recognition of Cu(II) via a stoichiometric ratio of 2:1 and the proposed binding mode was confirmed by the single-crystal structure of CS-Cu(II) complex. In addition, we have carried out density functional theory (DFT) calculation with the B3LYP exchange functional employing RB3LYP/6-31G basis sets to get insight into the mechanism of Cu(II)-sensors alongside their optical properties. Furthermore, the sensors were capable of bio-imaging Cu(II) in living cancer cells (HepG2, A549 and Hela) with low cytotoxicity and good biocompatibility shown. Taken together, We expect that this novel strategy would provide new insight into the development of Cu(II) detection techniques and could be used more for biomedical applications.

Al3+ triggered aggregation induced emission of an anthracence based azine derivative in SDS medium

Single crystal X-ray structurally characterized anthracene appended unsymmetrical azine derivative, viz. 4-(anthracen-9-ylmethylene-hydrazonomethyl)-2-methoxy-phenol (L5) shows Al³⁺ assisted aggregation induced emission in SDS medium.

In vivo pharmacodynamic evaluation of antidepressants based on flux mitochondrial Cys in living mice via near infrared fluorescence imaging

We proposed a new strategy for in vivo evaluation of antidepressants through NIRF imaging for mitochondrial Cys in the mouse brain.

Dopamine-Based Paper Analytical Device for Truly Equipment-Free and Naked-Eye Biosensing Based on the Target-Initiated Catalyzed Oxidation

The development of low cost, portable, and disposable biosensors for equipment-free and naked-eye biosensing is in eager demand for their widespread application in biomedical field, but it is still a challenge. Herein, we propose a novel paper analytical device (PAD) for truly equipment-free and naked-eye biosensing using dopamine as the chromogenic agent based on target-initiated catalyzed oxidation reaction. The dopamine-functionalized PAD (DPAD) possesses a significant three-dimensional net structure, excellent hydrophilicity, and unique response toward G-quadruplex DNAs against other DNAs, benefiting the bio/chemo reaction occurrence to assay target biomolecules. In light of the exceptional properties, the fabricated DPAD was applied in the analysis of Dam MTase through target-triggered exponential isothermal amplification. The recognition and methylation of H1 by Dam MTase contribute to formation of abundant hemin/G-quadruplexes, which catalyze oxidation of dopamine into dopachrome and reduce the dopamine amount on the DPAD surface. In comparison with the case in which Dam MTase is absent, an evident deep pink signal originating from dopachrome is observed directly by the naked eye and relied on Dam MTase concentrations. Therefore, truly equipment-free and naked-eye detection of Dam MTase is achieved with a detection limit of 1.46 U/mL. The fabricated DPAD not only achieves Dam MTase-visualized detection but also permits the accurate determination of other analytes by varying recognizable DNA's sequences, thus offering a universal biosensor and depicting significant potential for widespread applications in biomedical field.