Quantum dots for electrochemiluminescence bioanalysis - A review

Research progress on electrochemiluminescence nanomaterials and their applications in biosensors - A review

BACKGROUND

Electrochemiluminescence (ECL) is a promising analytical technique that combines electrochemistry with chemiluminescence. The performance of ECL systems depends on luminophores. Nonetheless, conventional luminophores present certain limitations. At first, their ECL efficiencies often fall short of the requirements for accurate detection. Moreover, in complex environments, traditional materials struggle to selectively identify target compounds and are prone to interference. Furthermore, these materials exhibit a deficiency in flexibility and tunability, attributed to their rigid structure and inherent characteristics. Advancing ECL technology necessitates the creation of novel materials that improve efficiency, selectivity, stability, and flexibility.

RESULTS

This review emphasizes the recent advances in ECL nanomaterials and their applications in biosensors. The discussion starts with a comprehensive examination of two main mechanisms of ECL emission: quenching ECL and co-reactant ECL. Various nanomaterials are then discussed, including semiconductor nanomaterials, metal nanoclusters, carbon nanomaterials, nanoscale aggregation-induced emission materials, organic nanomaterials, and composite nanomaterials, with emphasis on their unique ECL properties. Examples illustrate specific applications in disease diagnosis, environmental monitoring, and food safety testing. The review further examines the structural and luminescent characteristics of nanomaterials, which facilitate the advancement of novel ECL detection methodologies. Finally, we examine the existing challenges and propose possible avenues for the future advancement of innovative ECL nanomaterials.

SIGNIFICANCE

ECL nanomaterials possess unique quantum sizes and surface effects. Through the design and selection of appropriate nanomaterials, extremely sensitive, selective, and stable ECL biosensors may be developed for the detection of particular targets, applicable in disease diagnostics, food safety, and environmental monitoring.

Synthesis of AgInS2 quantum dots loaded with celastrol for induction of apoptosis and autophagy in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is a predominant form of liver cancer and one of the leading causes of cancer-related death globally. Therefore, there is an urgent need for innovative therapeutic strategies that target the molecular mechanisms underlying HCC progression and metastasis, aiming to improve treatment efficacy and patient survival. The natural product celastrol (Cel) has demonstrated inhibitory effects in various cancer cell lines. However, its clinical application has been hindered by high toxicity and a low safety threshold. Metal-free quantum dots (QDs), AgInS2 (AIS QDs) not only eliminate toxic risks associated with heavy metals but also exhibit high biocompatibility in the biomedical field. By developing AIS QD@Cel, an AIS QDs nano-delivery system for Cel, the cell selectivity and inhibitory effects of Cel on HCC were enhanced. Fourier-transform infrared spectroscopy (FTIR) analysis revealed that AIS QDs can interact with Cel via amide bonds. The encapsulation rate of AIS QDs to Cel reached 27.5%. AIS QD@Cel eliminated toxicity on 293T and enhanced inhibition on HCC cells by over 10 times. Furthermore, the western blotting and flow cytometry experiments showed that AIS QD@Cel promoted apoptosis and autophagy signal pathway. Finally, transcriptome sequencing revealed that AIS QD@Cel effect on HCC by regulating gene expression involved in critical signaling pathways that are implicated in the progression of cancer. This strategy holds the potential to increase safety threshold and clinical applicability of Cel, offering significant clinical value for the treatment of HCC patients.

Engineered MXene Biomaterials for Regenerative Medicine

MXene-based materials have attracted significant interest due to their distinct physical and chemical properties, which are relevant to fields such as energy storage, environmental science, and biomedicine. MXene has shown potential in the area of tissue regenerative medicine. However, research on its applications in tissue regeneration is still in its early stages, with a notable absence of comprehensive reviews. This review begins with a detailed description of the intrinsic properties of MXene, followed by a discussion of the various nanostructures that MXene can form, spanning from 0 to 3 dimensions. The focus then shifts to the applications of MXene-based biomaterials in tissue engineering, particularly in immunomodulation, wound healing, bone regeneration, and nerve regeneration. MXene's physicochemical properties, including conductivity, photothermal characteristics, and antibacterial properties, facilitate interactions with different cell types, influencing biological processes. These interactions highlight its potential in modulating cellular functions essential for tissue regeneration. Although the research on MXene in tissue regeneration is still developing, its versatile structural and physicochemical attributes suggest its potential role in advancing regenerative medicine.

A mini-review on the research progress and application of nanomaterials in electrochemiluminescent sensors in the detection of water environmental pollutants

With the increasingly serious problem of environmental pollution, the development of new and efficient detection technology has become an urgent need. Electrochemiluminescence (ECL) sensors have attracted wide attention in environmental pollution detection due to their advantages of low cost, fast analysis speed, high sensitivity, and good selectivity. At the same time, with the rapid development of nanotechnology, nanomaterials are widely used to construct ECL sensors. Based on the different roles of nanomaterials in the construction of ECL sensors, they can be summarized as (1) nanomaterials for signal amplification; (2) ECL nanoemitters; (3) Nanomaterials as receptors for ECL resonance energy transfer. In this paper, the construction and luminescence mechanism of ECL sensors are discussed from the above three aspects. Finally, the challenges and prospects of nanomaterials ECL sensors in the field of environmental pollution detection in the future are discussed.

A self-enhanced electrochemiluminescence aptasensor Zr-porphyrin modified with polyamidoamine for sensitive detection of lincomycin

Exploring novel and sensitive analysis methods for monitoring lincomycin (Lin) residues is of great significance since overuse of it would cause a serious threat to public health. Herein, a Zr-porphyrin metal-organic frameworks (Zr-TCPP) with covalently modified polyamidoamine (PAMAM) dendrimers was synthesized as a novel intramolecular self-enhanced ECL reagent, which exhibited greatly improved ECL response due to the promotion of SO4•- generation and the shortening of the electron transfer distance. Graphene oxide modified with gold nanoparticles (Au@GO) was synthesized as the quencher for the ECL sensor construction based on the quenching strategy. The present aptasensor achieved a wide linear range of 1.0 × 10-14 - 5.0 × 10-9 g/mL and a low detection limit of 1.7 fg/mL, which was applied for the determination of Lin in different real samples with satisfactory results.

Recent advances and future prospects in oxidative-reduction low-triggering-potential electrochemiluminescence strategies based on nanoparticle luminophores

The oxidative-reduction electrochemiluminescence (ECL) potential of a luminophore is one of the most significant parameters during light generation processes when considering the growing demand for anti-interference analysis techniques, electrode compatibility and the reduction of damage to biological molecules due to excessive excitation potential. Nanoparticle luminophores, including quantum dots (QDs) and metal nanoclusters (NCs), possess tremendous potential for forming various ECL sensors due to their adjustable surface states. However, few reviews focused on nanoparticle luminophore-based ECL systems for low-triggering-potential (LTP) oxidative-reduction ECL to avoid the possible interference and oxidative damage of biological molecules. This review summarizes the recent advances in the LTP oxidative-reduction ECL potential strategy with nanoparticle luminophores as ECL emitters, including matching efficient coreactants and nanoparticle luminophores, doping nanoparticle luminophores, constructing donor-acceptor systems, choosing suitable working electrodes, combining multiplex nanoparticle luminophores, and employing surface-engineering strategies. In the context of the different LTP ECL systems, potential-lowering strategies and bio-related applications are discussed in detail. Additionally, the future trends and challenges of low ECL-triggering-potential strategies are discussed.

Quantitative fluorescent detection of tetracycline in animal-derived foods using quantum dots

Tetracycline (Tc) antibiotics, a class of synthetically produced broad-spectrum antimicrobial drugs, have been widely used in animal husbandry, leading to their widespread presence in animal-derived foods. However, misuse, overuse, and non-compliance with withdrawal periods in animal farming have resulted in excessive Tc residues in these foods, which can cause various adverse reactions in humans, induce bacterial resistance, and pose a significant threat to public health. Consequently, the detection of Tc antibiotic residues in animal-derived food has become a critical issue. This study aims to establish a novel method for quantifying Tc residues in animal-derived food using quantum dots (QDs) fluorescence immunoassay (FLISA). The developed method was optimized to achieve a detection limit of 0.69 ng/mL and a quantitative detection range of 1.30 ~ 59.22 ng/mL. The applicability of the method was demonstrated by successfully determining Tc residues in pork, chicken, fish, milk, eggs, and honey samples spiked with Tc standard solutions, yielding recoveries ranging from 94.01% to 110.19% and relative standard deviations between 1.10% and 11.39%. The significance of this study lies in its potential to provide a rapid and reliable approach for monitoring Tc residues in animal-derived food products, thereby contributing to the enhancement of food safety monitoring practices. KEY POINTS: • Screen out tetracycline-specific blocking monoclonal antibodies • The quantitative detection has high specificity and sensitivity • This method can be a useful tool for laboratories or testing facilities.

Highly Sensitive Electrochemiluminescence Biosensing Method for SARS-CoV-2 N Protein Incorporating the Micelle Probes of Quantum Dots and Dibenzoyl Peroxide Using the Screen-Printed Carbon Electrode Modified with a Carboxyl-Functionalized Graphene

Obtaining stable electrochemiluminescence (ECL) emissions from a hydrophobic luminophore in aqueous solutions and designing a method without the use of an exogenous coreactant are promising for ECL biosensing. Here, a highly sensitive signal-on ECL immunoassay for the SARS-CoV-2 N protein was developed using micelles as an ECL tag. The micelles were prepared by coencapsulating the luminophore hydrophobic CdSe/ZnS quantum dots and coreactant dibenzoyl peroxide within the hydrophobic core of micelles. The ECL probe was obtained by covalently bonding a SARS-CoV-2 N protein-binding aptamer onto the micelle surface. The construction of the immunosensor was initiated by the immobilization of the anti-SARS-CoV-2 N protein antibody onto the screen-printed carbon electrode (SPCE) with a -COOH-functionalized surface. The surface functionalization of SPCEs was achieved through paste-exfoliated graphene, which was modified with a -COOH group through supramolecular-covalent scaffolds on SPCE. Upon achieving sandwich complexes on the immunosensor, an efficient ECL signal response at -1.4 V versus Ag/AgCl was obtained in phosphate buffer solution. The ECL assay was used for the sensitive determination of SARS-CoV-2 N protein with the linear range from 0.01 to 50 ng mL-1, and the detection limit was 3.0 pg mL-1. The immunosensor showed good reproducibility and stability, and the ECL immunoassay was used to determine the SARS-CoV-2 N protein in serum samples. The proposed approach to obtain micelles is versatile for the preparation of stable ECL luminophores by using hydrophobic materials, and the strategy provides an alternative for ECL bioassays based on the coreactant route.

Aptamer responsive DNA Functionalized hydrogels electrochemiluminescence biosensor for the detection of adenosine triphosphate

DNA hydrogel represents a noteworthy biomaterial. The preparation of biosensors by combining DNA hydrogel with electrochemiluminescence can simplify the modification process and raise the experimental efficiency. In this study, an electrochemiluminescence (ECL) biosensor based on DNA hydrogel was fabricated to detect adenosine triphosphate (ATP) simply and quickly. CdTe-Ru@SiO2 nanospheres capable of ECL resonance energy transfer (RET) were synthesized and encapsulated CdTe-Ru@SiO2 in the DNA hydrogel to provide strong and stable ECL signals. DNA hydrogel avoided the labeling of ECL signal molecules. The aptamer of ATP as the linker of the hydrogel for the specificity of ATP detection. The cross-linked structure of the aptamer and the polymer chains was opened by ATP, and then the decomposition of the DNA hydrogel initiated the escape of CdTe-Ru@SiO2 to generate an ECL signal. The designed biosensor detected ATP without too much modification and complex experimental steps on the electrode surface, with good specificity and stability, and a wide linear range. The detection range was 10-5000 nM, and the detection limit was 6.68 nM (S/N = 3). The combination of DNA hydrogel and ECL biosensor provided a new way for clinical detection of ATP and other biomolecule.

A smartphone-assisted electrochemiluminescent biosensor for highly sensitive detection of miRNA-21 based on Ru(bpy)2(L)4+@MOF-5

A smartphone-assisted electrochemiluminescence (ECL) strategy based on Ru(bpy)2(L)4+ as chromophores confined with metal - organic frameworks (Ru(bpy)2(L)4+@MOF-5) for the signal-amplified detection of miRNA-21 was developed. We synthesized a derivative of tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)2(L)4+) with high charges, which can be loaded into the MOF-5 by strong electrostatic interaction to prevent from leakage. In addition, nucleic acid cycle amplification was used to quench the signal of Ru(bpy)2(L)4+@MOF-5 by ferrocene. This method was applied to detect the concentration of miRNA-21 ranging from 1.0 × 10-14-1.0 × 10-9 M with a low LOD of 7.2 fM. This work demonstrated the construction of a signal quenching strategy ECL biosensor for miRNA using Ru(bpy)2(L)4+@MOF-5 systems and its application in smartphone-assisted ECL detection.

Magnetic N-doped carbon derived from mixed ligands MOF as effective electrochemiluminescence coreactor for performance enhancement of SARS-CoV-2 immunosensor

COVID-19 as an infectious disease with rapid transmission speed is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), so, early and accurate diagnostics of COVID-19 is quite challenging. In this work, the selective and sensitive self-enhanced ECL method to detect of SARS-CoV-2 protein was designed with magnetic N-doped carbon derived from dual-ligand metal-organic frameworks (MOF) (CoO@N-C) with the primary and tertiary amino groups as a novel coreactant that covalently combined with Ru(bpy)2(phen-NH2)2+ as electrochemiluminescence (ECL) emitter. Mixed-ligand strategy and selected nitrogen-containing ligands, 4,4',4''-((1,3,5-triazine-2,4,6-triyl) tris-(azanediyl)) tribenzoic acid (H3TATAB) with 2-aminoterephthalic acid (BDC-NH2) were used for synthesis of the proposed MOF. Also, magnetic CoO@N-C with high synergistically charge transfer kinetics and good stability can be used as an effective platform/coreactor on the ITO electrode which load more Ru-complex as signal producing compound and SARS-CoV-2 N protein antibody to increase the sensitivity of the immunosensor. Furthermore, (CoO@N-C) as coreactor improved the ECL signal of the Ru (II)-complex more than 2.1 folds compared to tripropylamine. In view of these competences, the novel "on-off" ECL biosensor performed with great stability and repeatability for detection of SARS-CoV-2 protein, which exhibited a broad linearity from 8 fg. mL-1 to 4 ng. mL-1 (6 order of magnitude) and an ultra-low limit of detection 1.6 fg. mL-1. Finally, this proposed method was successfully applied to detect of SARS-CoV-2 N protein in serum sample with satisfactory results, indicating the proposed immunosensor has the potential for quick analysis of SARS-CoV-2.

A novel electrochemiluminescence biosensor based on Ru(bpy)32+-functionalized MOF composites and cycle amplification technology of DNAzyme walker for ultrasensitive detection of kanamycin

An electrochemiluminescence (ECL) sensing platform for ultrasensitive and highly selective detection of kanamycin (KANA) was developed based on the prepared Ru(bpy)32+-functionalized MOF (Ru@MOF) composites by hydrothermal synthesis and Ag+-dependent DNAzyme. In this sensor, the stem-loop DNA (HP) with the ferrocene (Fc) was used as substrate chain to quench the ECL emission generated by the Ru@MOF. Using the specific recognition effect between KANA and the KANA aptamer (Apt) and the DNAzyme dependence on Ag+, the KANA aptamer as the pendant strand of the DNAzyme was assembled on Ru@MOF/GCE with the aptamer. When both Ag+ and KANA were present simultaneously, KANA specifically was binded to KANA aptamer as a pendant chain. Subsequently, Ag+-dependent DNAzyme walker continuously cleaved the HP chain and released the modified end of Fc to restore the ECL signal of Ru@MOF composites, thus achieving selective and ultrasensitive detection of KANA. The constructed KANA biosensor exhibits a wide detection range (30 pM to 300 μM) accompanied by a low detection limit (13.7 pM). The KANA in seawater and milk samples are determined to evalute the practical application results of the sensor. This ECL detection strategy could be used for detecting other similar analytes and has broad potential application in biological analysis.

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

Efficient Electrochemiluminescence Sensing in Microfluidic Biosensors: A Review

Microfluidic devices are capable of handling 10-9 L to 10-18 L of fluids by incorporating tiny channels with dimensions of ten to hundreds of micrometers, and they can be fabricated using a wide range of materials including glass, silicon, polymers, paper, and cloth for tailored sensing applications. Microfluidic biosensors integrated with detection methods such as electrochemiluminescence (ECL) can be used for the diagnosis and prognosis of diseases. Coupled with ECL, these tandem devices are capable of sensing biomarkers at nanomolar to picomolar concentrations, reproducibly. Measurement at this low level of concentration makes microfluidic electrochemiluminescence (MF-ECL) devices ideal for biomarker detection in the context of early warning systems for diseases such as myocardial infarction, cancer, and others. However, the technology relies on the nature and inherent characteristics of an efficient luminophore. The luminophore typically undergoes a redox process to generate excited species which emit energy in the form of light upon relaxation to lower energy states. Therefore, in biosensor design the efficiency of the luminophore is critical. This review is focused on the integration of microfluidic devices with biosensors and using electrochemiluminescence as a detection method. We highlight the dual role of carbon quantum dots as a luminophore and co-reactant in electrochemiluminescence analysis, drawing on their unique properties that include large specific surface area, easy functionalization, and unique luminescent properties.

Optical nanosensors based on noble metal nanoclusters for detecting food contaminants: A review

Food contaminants present a significant threat to public health. In response to escalating global concerns regarding food safety, there is a growing demand for straightforward, rapid, and sensitive detection technologies. Noble metal nanoclusters (NMNCs) have garnered considerable attention due to their superior attributes compared to other optical materials. These attributes include high catalytic activity, excellent biocompatibility, and outstanding photoluminescence properties. These features render NMNCs promising candidates for crafting nanosensors for food contaminant detection, offering the potential for the development of uncomplicated, swift, sensitive, user-friendly, and cost-effective detection approaches. This review investigates optical nanosensors based on NMNCs, including the synthesis methodologies of NMNCs, sensing strategies, and their applications in detecting food contaminants. Furthermore, it involves a comparative assessment of the applications of NMNCs in optical sensing and their performance. Ultimately, this paper imparts fresh perspectives on the forthcoming challenges. Hitherto, optical (particularly fluorescent) nanosensors founded on NMNCs have demonstrated exceptional sensing capabilities in the realm of food contaminant detection. To enhance sensing performance, future research should prioritize atomically precise NMNCs synthesis, augmentation of catalytic activity and optical properties, development of high-throughput and multimode sensing, integration of NMNCs with microfluidic devices, and the optimization of NMNCs storage, shelf life, and transportation conditions.

Development of ZnCdSe/ZnS quantum dot-based fluorescence immunochromatographic assay for the rapid visual and quantitative detection 25⁃hydroxyvitamins D in human serum

Vitamin D deficiency is associated with various diseases such as obesity, digestive problems, osteoporosis, depression, and infections, and has therefore emerged as a topic of great interest in public healthcare. The quantitative assessment of 25-hydroxyvitamin D (25-OH VD) in human serum may accurately reflect the nutritional status of vitamin D in the human body, which is significant for the prevention and treatment of vitamin D-deficient patients. In this study, we developed an assay for quantitative detection of 25-OH VD based on the 25-OH VD monoclonal antibody (mAb), and identified the optimal process parameters. The following process settings were found to be suitable for the test strips: pH of 7.6, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) ratio of 1:2000, and the anti-25-OH VD mAb ratio was 1:8. The equilibration time of the immune dynamic assay was 15 min. Under optimal conditions, the quantum dot nanoparticle-based fluorescent immunochromatographic assay (QDs-FICA) exhibited dynamic linear detection of 25-OH VD in PBS, from 5 ng/mL to 100 ng/mL, and the strip quantitative curve could be represented by the following regression equation: y = -0.02088 logx)+1.444 (R2 = 0.9050). The IC50 of the QDs-FICA was 39.6 ± 1.33 ng/mL. The specificity of the QDs-FICA was evaluated by running several structurally related analogues, including 25-OH VD2, 25-OH VD3, 1,25-OH2VD3, 1,25-OH2VD2, VD2, and VD3. The coefficients of variation were all below 10%. The shelf life of the test strips in this study was about 160 days at room temperature. Briefly, this study is the first to perform QDs-FICA for the rapid visual and quantitative detection of 25-OH VD, with great potential significance for clinical diagnosis of vitamin D-associated diseases.

Nano-matrixes propped self-enhanced electrochemiluminescence biosensor for microRNA detection

MicroRNAs (miRNA) are the potential biomarker for breast cancer, a biosensor for detecting miRNA-21 was successfully prepared by covalently linking carbohydrazide (CON4H6) and tris (4,4 '- dicarboxylic acid-2,2' - bipyridyl) ruthenium dichloride (Ru (dcbpy)32+) as a self-enhanced emitter (Ru-CON4H6). The biosensor was prepared by coating the electrode with mesoporous silica encapsulated Ru-CON4H6 as luminophores (RMSNs) to covalently link a couple of DNA strands (Q1-H2). The RMSNs coated electrode exhibited strong ECL emission due to the intramolecular electron transfer between the electrochemically oxidized Ru (dcbpy)32+ and co-reactant CON4H6. In the presence of target miRNA-21 and an assistant hairpin H1, H2 could be released from the surface through a strand displacement reaction (SDR), and the reserved Q1 could form G-quadruplex upon the addition of K+. The formed G-quadruplex then interacted with Q2-Fc in the presence of Mg2+ to form a DNA complex on the biosensor surface, which quenched the nano-matrixes propped self-enhanced ECL emission through the electron exchange between Fc and electrode or oxidized ECL intermediates. Under optimal conditions, the ECL decrease showed a correlation with target concentration, leading to a biosensing method for sensitive detection of miRNA-21. The proposed ECL method demonstrated a detectable concentration range from 0.1 fM to 1 nM along with a detection limit of 0.03 fM, good accuracy, and acceptable reproducibility, showing that the self-enhanced ECL biosensing strategy supported by nano-matrix provided a new way for the ultrasensitive detection of miRNA, and promoted the development of breast cancer diagnosis.

Potential-Resolved Electrochemiluminescence Multiplex Immunoassay for Florfenicol and Chloramphenicol in a Single Sample

The simultaneous detection of multiple antibiotic residues in food is of great significance for food safety. In this work, a novel dual-potential electrochemiluminescence (ECL) immunoassay was designed for the simultaneous detection of chloramphenicol and fluorfenicol residues in food. Ru@MOF was used as an anodic probe, and SnS2 QDs-PEI-Au-MoS2 was used as a cathodic probe. Notably, the coreactant for both luminophores was K2S2O8, avoiding interactions caused by different kinds of coreactants. Au nanoparticles functionalized with a nitrogen- and sulfur-doped graphene oxide-modified glassy carbon electrode to improve the electron transfer efficiency and provide a larger surface area for immobilization of antigen. The linear range for the detection of florfenicol was determined to be 0.1-1000 ng mL-1 with a detection limit of 0.03 ng mL-1, and the linear range for the detection of chloramphenicol was 0.01-1000 ng mL-1 with a detection limit of 3.2 pg mL-1 by recording the ECL responses at two different excitation potentials. The proposed immunoassay achieved a more stable recovery in the detection of actual samples and provided a new analytical method for the simultaneous detection of florfenicol and chloramphenicol residues with high sensitivity and specificity.

A differential strategy to enhance the anti-interference ability of molecularly imprinted electrochemiluminescence sensor with a semi-logarithmic calibration curve

The non-specific adsorption behaviors of various interferents on the surface of a molecularly imprinted polymer (MIP) are adverse for the selectivity of an MIP-based sensor, which can be overcome via a differential strategy by using the differential signal between MIP- and non-imprinted polymer (NIP)-based sensors. However, the normal differential mode is not suitable for the MIP-based sensors with non-linear calibration curves. Herein, an improved differential strategy is reported for an MIP-based sensor with a semi-logarithmic calibration curve, demonstrated by an electrochemiluminescence (ECL) sensor for dopamine (DA). Glassy carbon electrode (GCE) was modified by the mixture of g-C3N4, TiO2 nanoparticles (NPs) and carbon nanotubes (CNTs). MIP membrane for DA was fabricated on the surface of g-C3N4/TiO2NPs/CNTs/GCE using chitosan for film-forming, obtained MIP@GCE. To enhance the anti-interference ability of the MIP-based DA sensor, the difference between exponential functions ECL intensities of MIP@GCE and NIP@GCE is used as the analytical signal in the improved differential strategy. The differential signal was increased linearly with increasing DA concentration ranging from 10 pM to 0.10 μM, with the detection limit of 5.6 pM. The interference level of Cu2+ on DA determination in the improved differential mode is only 9.7% of that in the normal MIP mode. The improved differential strategy can be used in other MIP-based sensors with semi-logarithmic calibration curves.

Dual-template imprinted polymer electrochemical sensor for simultaneous determination of malathion and carbendazim using graphene quantum dots

Malathion (MAL) and carbendazim (CBZ) are organophosphate pesticides and fungicides, respectively. They are often used simultaneously in agriculture, and both have been shown to have harmful effects on humans and animals. Therefore, it is important to be able to measure both of these toxins simultaneously in order to assess their potential risks. This study aims to design a dual template electrochemical sensor using a cost-effective graphite-epoxy composite electrode (GECE) modified with molecularly imprinted polymers (MIPs) coated on graphene quantum dots (GQDs) for simultaneous detection of MAL and CBZ in real samples. GQDs were synthesized initially, and their surface was coated with MIPs that were formed using MAL and CBZ as the template molecules, ethylene glycol dimethyl acrylate as the cross-linker, and methacrylic acid as the functional monomer. The GQDs@MIP were characterized using Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and X-ray scattering spectroscopy. Parameters affecting the sensor response, such as the percentage of GQDs@MIP in the fabricated electrode, the pH of the rebinding solution and analysis solution, and the incubation time, were optimized. The optimum pH values of the rebinding solution were verified using density functional theory (DFT) calculations. Under the optimized conditions, differential pulse voltammetry (DPV) response calibration curves of MAL and CBZ were generated, and the results showed that the sensor had a linear response to MAL in the range of 0.02-55.00 μM with a limit of detection (LOD) of 2 nM (S/N = 3) and to CBZ in the range of 0.02-45.00 μM with a low LOD of 1 nM (S/N = 3). The results also demonstrated the proposed sensor's long-term stability and anti-interference capability. The practical applicability of the fabricated electrode was evaluated for real sample analysis, and good recovery values were obtained.

An "on-off-on" electrochemiluminescence aptasensor based on a self-enhanced luminophore for ochratoxin A detection

A highly selective and sensitive "on-off-on" electrochemiluminescence (ECL) aptasensor based on a self-enhanced luminophore was developed for the detection of ochratoxin A (OTA). Specifically, polyethyleneimine functionalized multi-walled carbon nanotubes decorated with gold nanoparticles (AuNPs-PEI-MWCNTs) were used as the electrode matrix to accelerate electron transfer and provide a favorable microenvironment for self-enhanced luminophore loading and ECL signal enhancement. In addition, black phosphorus quantum dots (BPQDs) were used as co-reactants of the ECL reagent tris (2,2'-bipyridyl) ruthenium(II) (Ru(bpy)32+) in ECL experiments, and the reaction mechanism was investigated. The self-enhanced luminophore Ru@SiO2-BPQDs was obtained by encapsulating Ru(bpy)32+ in silica (SiO2) nanoparticles and then combining it with BPQDs through electrostatic interaction. In conventional ECL systems, the emitter and its co-reactants reacted via the inter-nanoparticle pathway, leading to long distance electron transfer. However, the electron transfer distance in the self-enhanced luminophore was significantly shortened due to the intra-nanoparticle electron transfer pathway because BPQDs and oxidized Ru(bpy)32+ were bound within one nanoparticle, thereby improving ECL efficiency to achieve the first "switch-on" state. Then, the luminophore was quenched using ferrocenes (Fc) modified on an aptamer to achieve the "switch-off" state. Finally, OTA was specifically identified by the adapter, causing Fc to be released from the sensor interface, restoring the ECL intensity to achieve the second "switch-on" state. Under optimal conditions, the aptasensor exhibited good sensitivity, stability, and reproducibility, with a linear detection range from 0.1 to 320 ng/mL and a detection limit of 0.03 ng/mL. The novel ECL aptasensor provided a common analytical tool for the detection of mycotoxins and other small molecules.

Faraday cage-type ECL biosensor for the detection of circulating tumor cell MCF-7

Herein, a Faraday cage-type electrochemiluminescence biosensor was designed for the detection of human breast cancer cell MCF-7. Two kinds of nanomaterials, Fe₃O₄-APTs and GO@PTCA-APTs, were synthesized as capture unit and signal unit, respectively. In presence of the target MCF-7, the Faraday cage-type electrochemiluminescence biosensor was constructed by forming a complex "capture unit-MCF-7-signal unit". In this case, lots of electrochemiluminescence signal probes were assembled and could participate in the electrode reaction, achieving a significant increase in sensitivity. In addition, the double aptamer recognition strategy was adopted to improve the capture, enrichment efficiency and detection reliability. Under optimal experimental conditions, the limit of detection was 3 cells/mL. And, the sensor could afford the detection of actual human blood samples, which is the first report on the detection of intact circulating tumor cells by the Faraday cage-type electrochemiluminescence biosensor.

Nanobiosensing Based on Electro-Optically Modulated Technology

At the nanoscale, metals exhibit special electrochemical and optical properties, which play an important role in nanobiosensing. In particular, surface plasmon resonance (SPR) based on precious metal nanoparticles, as a kind of tag-free biosensor technology, has brought high sensitivity, high reliability, and convenient operation to sensor detection. By applying an electrochemical excitation signal to the nanoplasma device, modulating its surface electron density, and realizing electrochemical coupling SPR, it can effectively complete the joint transmission of electrical and optical signals, increase the resonance shift of the spectrum, and further improve the sensitivity of the designed biosensor. In addition, smartphones are playing an increasingly important role in portable mobile sensor detection systems. These systems typically connect sensing devices to smartphones to perceive different types of information, from optical signals to electrochemical signals, providing ideas for the portability and low-cost design of these sensing systems. Among them, electrochemiluminescence (ECL), as a special electrochemically coupled optical technology, has good application prospects in mobile sensing detection due to its strong anti-interference ability, which is not affected by background light. In this review, the SPR is introduced using nanoparticles, and its response process is analyzed theoretically. Then, the mechanism and sensing application of electrochemistry coupled with SPR and ECL are emphatically introduced. Finally, it extends to the relevant research on electrochemically coupled optical sensing on mobile detection platforms.

Current Trends in Nanomaterials-Based Electrochemiluminescence Aptasensors for the Determination of Antibiotic Residues in Foodstuffs: A Comprehensive Review

Veterinary pharmaceuticals have been recently recognized as newly emerging environmental contaminants. Indeed, because of their uncontrolled or overused disposal, we are now facing undesirable amounts of these constituents in foodstuff and its related human health concerns. In this context, developing a well-organized environmental and foodstuff screening toward antibiotic levels is of paramount importance to ensure the safety of food products as well as human health. In this case, with the development and progress of electric/photo detecting, nanomaterials, and nucleic acid aptamer technology, their incorporation-driven evolving electrochemiluminescence aptasensing strategy has presented the hopeful potentials in identifying the residual amounts of different antibiotics toward sensitivity, economy, and practicality. In this context, we reviewed the up-to-date development of ECL aptasensors with aptamers as recognition elements and nanomaterials as the active elements for quantitative sensing the residual antibiotics in foodstuff and agriculture-related matrices, dissected the unavoidable challenges, and debated the upcoming prospects.

Recent advances and challenges in developing electrochemiluminescence biosensors for health analysis

This Feature Article simply introduces principles and mechanisms of electrochemiluminescence (ECL) biosensors for the determination of biomarkers and highlights recent advances of ECL biosensors on key aspects including new ECL reagents and materials, new biological recognition elements, and emerging construction biointerfacial strategies with illustrative examples and a critical eye on pitfalls and discusses challenges and perspectives of ECL biosensors for health analysis.

Advances in electrochemiluminescence for single-cell analysis

Recent years have witnessed the emergence of innovative analytical methods with high sensitivity and spatiotemporal resolution that allowed qualitative and quantitative analysis to be carried out at single-cell and subcellular levels. Electrochemiluminescence (ECL) is a unique chemiluminescence of high-energy electron transfer triggered by electrical excitation. The ingenious combination of electrochemistry and chemiluminescence results in the distinct advantages of high sensitivity, a wide dynamic range and good reproducibility. Specifically, single-cell ECL (SCECL) analysis with excellent spatiotemporal resolution has emerged as a promising toolbox in bioanalysis for revealing individual cells' heterogeneity and stochastic processes. This review focuses on advances in SCECL analysis and bioimaging. The history and recent advances in ECL probes and strategies for system design are briefly reviewed. Subsequently, the latest advances in representative SCECL analysis techniques for bioassays, bioimaging and therapeutics are also highlighted. Then, the current challenges and future perspectives are discussed.

Electrochemiluminescence Aptasensor Based on Gd(OH)3 Nanocrystalline for Ochratoxin A Detection in Food Samples

In the present study, the electrochemiluminescence (ECL) properties of Gd(OH)₃ nanocrystals with K₂S₂O₈ as the cathode coreactant were studied for the first time. Based on the prominent ECL behavior of this material and the excellent specificity of the aptamer technique, an ECL aptasensor for the detection of ochratoxin A (OTA) was formulated successfully. Over an OTA concentration range of 0.01 pg mL^-1 to 10 ng mL^-1, the change in the ECL signal was highly linear with the OTA concentration, and the limit of detection (LOD) was 0.0027 pg mL^-1. Finally, the ECL aptasensor was further used to detect OTA in real samples (grapes and corn) and satisfactory results were obtained, which indicated that the built method is expected to be applied in food detection.

Nanomaterials-Based Electrochemiluminescence Biosensors for Food Analysis: Recent Developments and Future Directions

Developing robust and sensitive food safety detection methods is important for human health. Electrochemiluminescence (ECL) is a powerful analytical technique for complete separation of input source (electricity) and output signal (light), thereby significantly reducing background ECL signal. ECL biosensors have attracted considerable attention owing to their high sensitivity and wide dynamic range in food safety detection. In this review, we introduce the principles of ECL biosensors and common ECL luminophores, as well as the latest applications of ECL biosensors in food analysis. Further, novel nanomaterial assembly strategies have been progressively incorporated into the design of ECL biosensors, and by demonstrating some representative works, we summarize the development status of ECL biosensors in detection of mycotoxins, heavy metal ions, antibiotics, pesticide residues, foodborne pathogens, and other illegal additives. Finally, the current challenges faced by ECL biosensors are outlined and the future directions for advancing ECL research are presented.

Strategies for Enhancing the Sensitivity of Electrochemiluminescence Biosensors

Electrochemiluminescence (ECL) has received considerable attention as a powerful analytical technique for the sensitive and accurate detection of biological analytes owing to its high sensitivity and selectivity and wide dynamic range. To satisfy the growing demand for ultrasensitive analysis techniques with high efficiency and accuracy in complex real sample matrices, considerable efforts have been dedicated to developing ECL strategies to improve the sensitivity of bioanalysis. As one of the most effective approaches, diverse signal amplification strategies have been integrated with ECL biosensors to achieve desirable analytical performance. This review summarizes the recent advances in ECL biosensing based on various signal amplification strategies, including DNA-assisted amplification strategies, efficient ECL luminophores, surface-enhanced electrochemiluminescence, and ratiometric strategies. Sensitivity-enhancing strategies and bio-related applications are discussed in detail. Moreover, the future trends and challenges of ECL biosensors are discussed.

Chitosan-CdS Quantum Dots Biohybrid for Highly Selective Interaction with Copper(II) Ions

Cadmium sulfide (CdS) quantum dots (QDs) were homogeneously embedded into chitosan (CTS), denoted as CdS@CTS, via an in situ hydrothermal method. The intact structure of the synthesized materials was preserved using freeze-drying. The materials were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscopy, high-resolution TEM, scanning TEM, dispersive energy X-ray (EDX) for elemental analysis and mapping, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption isotherms, thermogravimetric analysis, UV-vis spectroscopy, and diffuse reflectance spectroscopy (DRS). The synthesis procedure offered CdS QDs of 1-7 nm (average particle size of 3.2 nm). The functional groups of CTS modulate the in situ growth of CdS QDs and prevent the agglomeration of CdS QDs, offering homogenous distribution inside CTS. CdS@CTS QDs can also be used for naked-eye detection of heavy metals with high selectivity toward copper (Cu2+) ions. The mechanism of interactions between Cu2+ ions and CdS@CTS QDs were further studied.

Electrochemiluminescence with semiconductor (nano)materials

Electrochemiluminescence (ECL) is the light production triggered by reactions at the electrode surface. Its intrinsic features based on a dual electrochemical/photophysical nature have made it an attractive and powerful method across diverse fields in applied and fundamental research. Herein, we review the combination of ECL with semiconductor (SC) materials presenting various typical dimensions and structures, which has opened new uses of ECL and offered exciting opportunities for (bio)sensing and imaging. In particular, we highlight this particularly rich domain at the interface between photoelectrochemistry, SC material chemistry and analytical chemistry. After an introduction to the ECL and SC fundamentals, we gather the recent advances with representative examples of new strategies to generate ECL in original configurations. Indeed, bulk SC can be used as electrode materials with unusual ECL properties or light-addressable systems. At the nanoscale, the SC nanocrystals or quantum dots (QDs) constitute excellent bright ECL nano-emitters with tuneable emission wavelengths and remarkable stability. Finally, the challenges and future prospects are discussed for the design of new detection strategies in (bio)analytical chemistry, light-addressable systems, imaging or infrared devices.