A Controlled Release Aptasensor Utilizing AIE-Active MOFs as High-Efficiency ECL Nanoprobe for the Sensitive Detection of Adenosine Triphosphate

Aggregation-induced emission-based aptasensors for the detection of various targets: Recent progress

The advancement of aptasensors utilizing aggregation-induced emission (AIE) has progressed remarkably in recent years, owing to various unique benefits provided by aggregation-induced emission luminogens (AIEgens) as a novel category of fluorescent substances and aptamers as exceptional recognition components. AIE refers to a photophysical phenomenon identified in certain luminogens that show minimal or absent emission in dilute solutions, yet display considerable emission when in aggregate or solid states. Fluorescent sensing is an effective technique for the detection of various targets; however, many traditional dyes frequently demonstrate an aggregation-caused quenching (ACQ) effect in solid form, which limits their applicability on a larger scale. In contrast, fluorescent probes that leverage AIE characteristics have garnered considerable interest, owing to their elevated fluorescence quantum yields and ease of fabrication. This review discusses the application of various AIEgens in the design of diverse sensitive and selective AIE-based aptasensors for monitoring various targets, with a particular focus on recent advances. The AIE-based aptasensors exploit the supreme affinity of the aptamers to their targets and the remarkable properties of AIEgen, including its photostability and high quantum yield, and the interaction between AIEgen and DNA. The objective is to acquaint researchers with the various categories of materials exhibiting AIE characteristics and their potential applications in the creation of different aptasensors, enabling them to introduce novel kinds of innovative AIEgens and AIE-integrated aptasensors.

CRISPR/Cas12a trans-cleavage cascading dual-template exponential amplification reaction for electrochemiluminescent detection of 17β-estradiol in milk

17β-Estradiol (E2) is a common environmental estrogen that can interfere with the endocrine systems of humans and animals, and poses a carcinogenic risk even at picomolar concentrations. In this study, a functionalized Ru(bpy)32+-embedded metal-organic framework (ZnRuMOF) is synthesized, in which Ru(bpy)32+ served as an electrochemiluminescence (ECL) indicator and the porous structure of ZnRuMOF acts as a nanoreactor to enhance the ECL signal. Based on this, we developed an E2 detection method combining a highly specific CRISPR-Cas12a system and dual-template exponential amplification. This method utilizes the trans-cleavage activity of CRISPR-Cas12a to control a light switch, achieving precise and ultra-sensitive detection of E2. The sensing platform demonstrates excellent performance in detecting E2 concentrations ranging from 1 fg mL-1 to 150 ng mL-1, with a detection limit of 0.27 fg mL-1 (S/N = 3). This study provides a reliable approach for diagnosing and treating diseases related to E2, aiming to protect environmental quality and human health.

Sensitive electrochemiluminescent detection of hydroquinone using silver/luminol-functionalized carbon microspheres

The detection of organic pollutants in water was deemed critical for safeguarding aquatic ecosystems, maintaining human health, and upholding water quality standards. In this study, a novel electrochemiluminescence (ECL) sensor was proposed for the sensitive detection of hydroquinone (HQ) in lake water, utilizing a glassy carbon electrode (GCE) modified with silver/luminol-functionalized carbon microspheres (GCE/CM@Ag/Lu). Due to the consumption of H2O2 by HQ, the ECL signal was attenuated, enabling the quantitative detection of HQ. Under optimized conditions, the linear range for HQ ranged from 1.0 × 10-4-1.0 × 10-10 mol L-1, with a limit of detection (LOD) of 3.3 × 10-11 mol L-1 (S/N = 3). The proposed ECL sensor shows promising potential to open new avenues for water quality assessment.

An intelligent hydrogel detection platform based on colorimetric and SERS techniques for real-time and sensitive detection of kanamycin

Excessive use of kanamycin (KAN) in food can lead to ototoxicity, nephrotoxicity, and antibiotic resistance in humans. Therefore, developing a rapid and sensitive detection method to accurately identify KAN is urgent. In this study, we propose a sensitive and convenient detection technique based on an intelligent color-changing hydrogel. This hydrogel incorporates coral-shaped prussian blue (C-PB) nanozymes and Au polyhedra to achieve dual detection of KAN through colorimetric and Raman techniques. We first combined aptamer chains with DNA single strands to construct a "lock" structure within porous metal-organic frameworks, encapsulating numerous 3,3',5,5'-tetramethylbenzidine (TMB) molecules. In the presence of KAN, because of the higher affinity between the aptamer chain and KAN, the "lock" structure is disrupted, releasing a large amount of TMB. Subsequently, TMB is absorbed by the C-PB-based hydrogel and catalyzed into oxidized TMB with the assistance of hydrogen peroxide. Consequently, the hydrogel changes from pink to blue, accompanied by a significant Raman signal. This intelligent hydrogel platform enables ultrasensitive identification of KAN through both colorimetric and Raman modes with a detection limit of 1.58 × 10-13 mol/L and a linear range from 1.0 × 10-12 to 1.0 × 10-3 mol/L. We believe this dual-mode strategy offers a promising pathway for real-time detection and monitoring of actual samples.

Advanced electrochemiluminescent approaches for contaminant detection in food matrices using metal-organic framework composites

Metal-organic frameworks (MOFs) are highly valued for their electronic and optical capabilities in food sample analysis. Implementing MOF-based sensors is crucial for public health safety. This review centers on electrochemiluminescence (ECL) MOFs for monitoring food samples, highlighting signal changes from combining MOFs with Ru(bpy)32+, TPrA, nanomaterials, and biomolecules. It systematically reviews the development, mechanisms, signal pathways, and findings related to ECL MOF food sensors. Notably, immobilizing ZIF-8 and various metals with transducers like gold nanoparticles enhances ECL signals, enabling effective monitoring across media types. Moreover, MOFs excel in co-reactant processes, resonance energy transfer, and catalytic redox reactions for detecting analytes in food, presenting opportunities for advanced sensory analysis and the creation of cost-effective, sensitive signal transducers for food safety and quality control.

Endogenous Free-Electron-Involved Coreactant-Free Electrochemiluminescence from Nanoclusters and Its Immunoassay Application

All of the commercialized electrochemiluminescence (ECL) immunoassays are automatically conducted at +1.40 V (vs Ag/AgCl) in the coreactant route. To alleviate the exogenous effect of coreactants and simplify the operation procedures, herein, a sulfur-vacancy-involved and free electron strategy is proposed to exploit Au nanoclusters (NCs) as anodic electrochemiluminophores and perform a coreactant-free immunoassay. The deficient coordination between the sulfhydryl of Met and the Au core might induce the departure of partial S atoms and enable Met-capped AuNCs (Met-AuNCs) with a sulfur-vacancy-involved electron-rich nature. The electron-rich nature tends to endow Met-AuNCs with unpaired endogenous free electrons, which can directly combine exogenous holes for light emitting. Coreactant-free ECL at around +0.86 V is consequently and conveniently achieved by merely oxidizing Met-AuNCs at the anode. The coreactant-free ECL is qualified to determine human carcinoembryonic antigen from 10 to 5000 pg/mL with a limit of detection of 5 pg/mL. Electron paramagnetic resonance provides clear evidence that endogenous free electrons within Met-AuNCs play an important role in the generation of coreactant-free ECL. This sulfur-vacancy-involved and free electron strategy is promising for designing nanoelectrochemiluminophores with improved immunoassay performance.

Operando Photoelectrochemical Surface-Enhanced Raman Spectroscopy: Interfacial Mechanistic Insights and Simultaneous Detection of Patulin

Comprehending the biosensing mechanism of the biosensor interface is crucial for sensor development, yet accurately reflecting interfacial interactions within actual detection environments remains an unsolved challenge. An operando photoelectrochemical surface-enhanced Raman spectroscopy (PEC-SERS) biosensing platform was developed, capable of simultaneously capturing photocurrent and SERS signals, allowing operando characterization of the interfacial biosensing behavior. Porphyrin-based MOFs (Zr-MOF) served as bifunctional nanotags, providing a photocurrent and stable Raman signal output under 532 nm laser irradiation. Aptamer was used to bridge the Zr-MOF and the silver-encased gold nanodumbbells (AuNDs@AgNPs). The simultaneous in situ acquisition of target-induced PEC and SERS signal responses facilitated the correlation of electron transfer information from the photocurrent with the distance information from the SERS signal. It revealed the biosensing mechanism in which target-induced aptamer conformational bending drove the Zr-MOF to approach the electrode. However, the increase in charge transfer observed through conventional electrochemical methods contradicts the conclusions drawn from the operando PEC-SERS analysis. Comprehensive analysis indicated that redox probes introduced during the non-in-situ measurement process became adsorbed within the MOF pores, potentially affecting the judgment of the biosensing mechanism. In addition, the operando PEC-SERS biosensor simultaneously obtained two independent signals, providing self-verification to improve the accuracy and reliability of patulin detection. The linear ranges were 1 pg mL-1-10 ng mL-1 for the PEC method and 1 pg mL-1-100 ng mL-1 for the SERS method, respectively. This work provides a powerful tool for determining the interface characteristics of biosensors.

Highly electroactive thiazolium [5,4-d]thiazol-2,5-dicarboxylic acid-silver electrochemiluminescent metal-organic frameworks: synthesis, properties and application in glutathione detection

Thiazolo[5,4-d]thiazole-2,5-dicarboxylic acid (H2Thz), a thiazolothiazole (TTz) derivative with carboxylic acid groups, was synthesized as a ligand for the creation of five MOFs, each associated with distinct metal ions including Ag+, Mn2+, Co2+, Zn2+, and Cu2+. The cathodic electrochemiluminescence (ECL) of H2Thz and the resulting MOFs was investigated. H2Thz was found to generate ECL signals, but this process was heavily reliant on potassium persulfate (K2S2O8) as a co-reactant. However, the Ag-MOF, formed with H2Thz as the ligand, exhibited substantial ECL signals without the need for any co-reactant, which is different from other metal-containing MOFs. The smaller band gap, higher electron mobility and the unique electrocatalytic activity of Ag+ ions were confirmed to be the reasons for the excellent ECL performance of Ag-MOF. The interaction between thiol group of glutathione (GSH) and Ag-MOF suppressed the ECL signal of the Ag-MOF-K2S2O8 system. Based on this, a sensitive ECL method for GSH was developed and effectively utilized for GSH quantification in cell lysates.

A novel electrochemiluminescence aptasensor for ultrasensitive lincomycin detection using Ti3C2-TiO2-Ru probe

The presence of lincomycin (LIN) residues in food poses significant health risks to humans, necessitating a highly sensitive and specific detection method for LIN. This study used a self-enhancing Ti3C2-TiO2-Ru probe to develop an electrochemiluminescence aptasensor to detect LIN. The Ti3C2-TiO2 was synthesized in situ by harnessing the unique reducibility of Ti3C2, with TiO2 serving as a co-reaction accelerator. Moreover, Ti3C2-TiO2 served as a carrier with an excellent negative charge, allowing for the immobilization of a substantial amount of Ru(bpy)32+ through electrostatic adsorption, thus forming a self-enhancing Ti3C2-TiO2-Ru probe. Furthermore, the specific affinity of LIN toward the aptamer and the chelating interaction between the Ti and phosphate groups ensured highly precise LIN detection. This sensor demonstrated excellent performance, with a detection limit of 0.025 ng mL-1 and a detection range of 1.0 × 10-1-1.0 × 104 ng mL-1. The LIN detection in milk showed commendable recovery rates, ranging from 94.4% to 106.0%.

A Review of Current Developments in Functionalized Mesoporous Silica Nanoparticles: From Synthesis to Biosensing Applications

Functionalized mesoporous silica nanoparticles (MSNs) have been widely investigated in the fields of nanotechnology and material science, owing to their high surface area, diverse structure, controllable cavity, high biocompatibility, and ease of surface modification. In the past few years, great efforts have been devoted to preparing functionalized MSNs for biosensing applications with satisfactory performance. The functional structure and composition in the synthesis of MSNs play important roles in high biosensing performance. With the development of material science, diverse functional units have been rationally incorporated into mesoporous structures, which endow MSNs with design flexibility and multifunctionality. Here, an overview of the recent developments of MSNs as nanocarriers is provided, including the methodologies for the preparation of MSNs and the nanostructures and physicochemical properties of MSNs, as well as the latest trends of MSNs and their use in biosensing. Finally, the prospects and challenges of MSNs are presented.

Metal-Organic Frameworks (MOFs): Classification, Synthesis, Modification, and Biomedical Applications

Metal-organic frameworks (MOFs) are a new variety of solid crystalline porous functional materials. As an extension of inorganic porous materials, it has made important progress in preparation and application. MOFs are widely used in various fields such as gas adsorption storage, drug delivery, sensing, and biological imaging due to their high specific surface area, porosity, adjustable pore size, abundant active sites, and functional modification by introducing groups. In this paper, the types of MOFs are classified, and the synthesis methods and functional modification mechanisms of MOFs materials are summarized. Finally, the application prospects and challenges of metal-organic framework materials in the biomedical field are discussed, hoping to promote their application in multidisciplinary fields.

Insight into the charge transfer behavior of an electrochemiluminescence sensor based on porphyrin-coumarin derivatives with a donor-acceptor configuration

The excellent photophysical and electrochemical properties of porphyrins have inspired widespread interest in the realm of electrochemiluminescence (ECL). The aggregation-caused deficiency of ECL emission in aqueous solution, however, still severely impedes further applications. Herein, a molecule with a donor-acceptor (D-A) configuration, ATPP-Cou, consisting of monoaminoporphyrin as an electron donor and coumarin as an electron acceptor, was designed as an ECL luminophore to address the susceptibility of the porphyrin to aggregation-caused quenching (ACQ) in aqueous solution. ATPP-Cou demonstrated a three-fold enhanced ECL signal compared to pristine ATPP. Despite the acknowledged significance of intramolecular charge transfer (ICT) in generating excited states in ECL, there is a lack of quantitative descriptions. Herein, intensity-modulated photocurrent spectroscopy (IMPS) and scanning photoelectrochemical microscopy (SPECM) were utilized to validate the influence of ICT on the enhancement performance of D-A type ECL molecules. Additionally, ATPP-Cou was also developed as a probe for the successful detection of Cu2+ in aqueous solution. The present study not only enriches the repertoire of efficient porphyrin-based ECL luminophores applicable in aqueous environments but also exemplifies the successful integration of novel measurement techniques to provide more comprehensive insights into the underlying mechanisms responsible for improved ECL performance.

Framework-Induced Electrochemiluminescence Enhancement of an AIEgen-Based MOF Coupled with Heterostructured TiO2@Ag NPs as an Efficient Coreaction Accelerator for Sensitive Biosensing

In conventional metal-organic framework (MOF) luminophore-involved electrochemiluminescence (ECL) systems, the aggregation-caused quenching commonly exists for the organic luminescent ligands, limiting the ECL efficiency and detection sensitivity. Herein, by employing the aggregation-induced emission luminogen (AIEgen) 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene (H4TCBPE) as a ligand, one high-efficiency ECL emitter (Zr-MOF) was synthesized through a simple hydrothermal reaction. Compared with H4TCBPE monomers and their aggregates, the resultant Zr-MOF possesses the strongest ECL emission, which is mainly attributed to the framework-induced ECL enhancement. Specifically, the heterostructure was prepared by the deposition of silver nanoparticles on TiO2 microflowers and utilized as an efficient coreaction accelerator. Remarkably, the formative heterojunction can increase the interfacial charge transfer efficiency and promote the carrier separation, facilitating the oxidation of coreactant tripropylamine. In this way, a novel aptamer-mediated ECL sensing platform is constructed, achieving the sensitive analysis of adenosine triphosphate with a low detection limit of 0.17 nM. As a proof-of-concept study, this work may enlighten the rational design of new-type MOF-based ECL materials and expand the application scope of the ECL technology.

High-Sensitivity Homogeneous Detection of miRNA-155 Governed by DNA Walker-Regulated Surface DNA Density of Magnetic Electrochemiluminescence Nanoparticles

Homogeneous electrochemiluminescence (ECL) has gained attention for its simplicity and stability. However, false positives due to solution background interference pose a challenge. To address this, magnetic ECL nanoparticles (Fe3O4@Ru@SiO2 NPs) were synthesized, offering easy modification, magnetic separation, and stable luminescence. These were utilized in an ECL sensor for miRNA-155 (miR-155) detection, with locked DNAzyme and substrate chain (mDNA) modified on their surface. The poor conductivity of long-chain DNA significantly impacts the conductivity and electron transfer capability of Fe3O4@Ru@SiO2 NPs, resulting in weaker ECL signals. Upon target presence, unlocked DNAzyme catalyzes mDNA cleavage, leading to shortened DNA chains and reduced density. In contrast, the presence of short-chain DNA has minimal impact on the conductivity and electron transfer capability of Fe3O4@Ru@SiO2 NPs. Simultaneously, the material surface's electronegativity decreases, weakening the electrostatic repulsion with the negatively charged electrode, resulting in the system detecting stronger ECL signals. This sensor enables homogeneous ECL detection while mitigating solution background interference through magnetic separation. Within a range of 100 fM to 10 nM, the sensor exhibits a linear relationship between ECL intensity and target concentration, with a 26.91 fM detection limit. It demonstrates high accuracy in clinical sample detection, holding significant potential for clinical diagnostics. Future integration with innovative detection strategies may further enhance sensitivity and specificity in biosensing applications.

Multiquenching-Based Aggregation-Induced Electrochemiluminescence Sensing for Highly Sensitive Detection of the SARS-CoV-2 N Protein

The rapid epidemic around the world of coronavirus disease 2019 (COVID-19), caused by the SARS-CoV-2 virus, proves the need and stimulates efforts to explore efficient diagnostic tests for the sensitive detection of the SARS-CoV-2 virus. An aggregation-induced electrochemiluminescence (AIECL) sensor was developed for the ultrasensitive detection of the SARS-CoV-2 nucleocapsid (N) protein in this work. Tetraphenylethylene doped in zeolite imidazole backbone-90 (TPE-ZIF-90) showed highly efficient aggregation-induced emission (AIE) to endow TPE-ZIF-90 with high ECL intensity. Upon the capture of the SARS-CoV-2 N protein by immune recognition, an alkaline phosphatase (ALP)-modified gold nanoparticle (AuNP)-decorated zinc oxide (ZnO) nanoflower (ALP/Au-ZnO) composite was introduced on the sensing platform, which catalyzed L-ascorbate-2-phosphate trisodium salt (AA2P) to produce PO43- and ascorbic acid (AA). Based on a multiquenching of the ECL signal strategy, including resonance energy transfer (RET) between TPE-ZIF-90 and Au-ZnO, disassembly of TPE-ZIF-90 triggered by the strong coordination between PO43- and Zn2+, and RET between TPE-ZIF-90 and AuNPs produced in situ by the AA reductive reaction, the constructed AIECL sensor achieved highly sensitive detection of the SARS-CoV-2 N protein with a low limit of detection of 0.52 fg/mL. With the merits of high specificity, good stability, and proven application ability, the present RET- and enzyme-triggered multiquenching AIECL sensor may become a powerful tool in the field of SARS-CoV-2 virus diagnosis.

Electrochemiluminescence of Ultrasmall Silica Nanoparticles from Size Modulation and Multipath Surface State Adjustment for Ultrasensitive HIV-DNA Fragment Detection

Here, ultrasmall SiO2 nanoparticles (u-SiO2 NPs, <5 nm) with obvious electrochemiluminescence (ECL) phenomenon, which was absent for conventional silica nanoparticles (c-SiO2 NPs), were reported. In a finite ultrasmall volume, the u-SiO2 NPs exhibited increasing ground state energy and higher optical absorption strength due to the electron-hole confinement model and favored catalyzing the reaction through the rapid diffusion of bulk charge, resulting in apparent ECL emission. Then, Zn2+-induced u-SiO2 nanoaggregates (Zn/u-SiO2-Ov nAGG) were synthesized and exhibited improved ECL performance via multipath surface state adjustment of u-SiO2 from several aspects, including aggregation-induced ECL, the generation of oxygen vacancy (Ov), and more positive surface charge. In addition, an ECL biosensor was constructed for ultrasensitive human immunodeficiency virus-related deoxyribonucleic acid detection from 100 aM to 1 nM with a low limit of 50.48 aM, combining the ECL luminescence of Zn/u-SiO2-Ov nAGG with three-dimensional DNA nanomachine-mediated multioutput amplification for enhanced accuracy and sensitivity compared to the single-output method. Therefore, exploring the ECL of ultrasmall nanoparticles via the adjustment of size and surface state provided a valuable indication to a wider investigation and application of novel ECL materials for clinical diagnostic.

Potential-Resolved Ratiometric Aptasensor for Sensitive Acetamiprid Analysis Based on Coreactant-free Electrochemiluminescence Luminophores of Gd-MOF and "Light Switch" Molecule of [Ru(bpy)2dppz]2

For conventional potential-resolved ratiometric electrochemiluminescence (ECL) systems, the introduction of multiplex coreactants is imperative. However, the undesirable interactions between different coreactants inevitably affect analytical accuracy and sensitivity. Herein, through the coordination of aggregation-induced emission ligands with gadolinium cations, the self-luminescent metal-organic framework (Gd-MOF) is prepared and serves as a novel coreactant-free anodic ECL emitter. By the intercalation of [Ru(bpy)2dppz]2+ with light switch effect into DNA duplex, one high-efficiency cathodic ECL probe is obtained using K2S2O8 as a coreactant. In the presence of acetamiprid, the strong affinity between the target and its aptamer induces the release of [Ru(bpy)2dppz]2+, resulting in a decreasing cathode signal and an increasing anode signal owing to the ECL resonance energy transfer from Gd-MOF to [Ru(bpy)2dppz]2+. In this way, an efficient dual-signal ECL aptasensor is constructed for the ratiometric analysis of acetamiprid, exhibiting a remarkably low detection limit of 0.033 pM. Strikingly, by using only one exogenous coreactant, the cross interference from multiple coreactants can be eliminated, thus improving the detection accuracy. The developed high-performance ECL sensing platform is successfully applied to monitor the residual level of acetamiprid in real samples, demonstrating its potential application in the field of food security.