Novel Single-Cell Analysis Platform Based on a Solid-State Zinc-Coadsorbed Carbon Quantum Dots Electrochemiluminescence Probe for the Evaluation of CD44 Expression on Breast Cancer Cells

Quantum Dot Research in Breast Cancer: Challenges and Prospects

The multifaceted role of quantum dots (QDs) in breast cancer research highlights significant advancements in diagnostics, targeted therapy, and drug delivery systems. This comprehensive review addresses the development of precise imaging techniques for early cancer detection and the use of QDs in enhancing the specificity of therapeutic delivery, particularly in challenging cases like triple-negative breast cancer (TNBC). The paper also discusses the critical understanding of QDs' interactions with cancer cells, offering insights into their potential for inducing cytotoxic effects and facilitating gene therapy. Limitations such as biocompatibility, toxicity concerns, and the transition from laboratory to clinical practice are critically analyzed. Future directions emphasize safer, non-toxic QD development, improved targeting mechanisms, and the integration of QDs into personalized medicine, aiming to overcome the current challenges and enhance breast cancer management.

Tumor diagnosis using carbon-based quantum dots: Detection based on the hallmarks of cancer

Carbon-based quantum dots (CQDs) have been shown to have promising application value in tumor diagnosis. Their use, however, is severely hindered by the complicated nature of the nanostructures in the CQDs. Furthermore, it seems impossible to formulate the mechanisms involved using the inadequate theoretical frameworks that are currently available for CQDs. In this review, we re-consider the structure-property relationships of CQDs and summarize the current state of development of CQDs-based tumor diagnosis based on biological theories that are fully developed. The advantages and deficiencies of recent research on CQDs-based tumor diagnosis are thus explained in terms of the manifestation of nine essential changes in cell physiology. This review makes significant progress in addressing related problems encountered with other nanomaterials.

Application and outlook of electrochemical technology in single-cell analysis

Cellular heterogeneity, especially in some important diseased cells like tumor cells, acts as an invisible driver for disease development like cancer progression in the tumor ecosystem, contributing to differences in the macroscopic and microscopic detection of disease lesions like tumors. Traditional analysis techniques choose group information masked by the mean as the analysis sample, making it difficult to achieve precise diagnosis and target treatment, on which could be shed light via the single-cell level determination/bioanalysis. Hence, in this article we have reviewed the special characteristic differences among various kinds of typical single-cell bioanalysis strategies and electrochemical techniques, and then focused on the recent advance and special bio-applications of electrochemiluminescence and micro-nano electrochemical sensing mediated in single-cell bioimaging & bioanalysis. Especially, we have summarized the relevant research exploration of the possibility to establish the in-situ single-cell electrochemical methods to detect cell heterogeneity through determination of specific biomolecules and bioimaging of some important biological processes. Eventually, this review has explored some important advances of electrochemical single-cell detection techniques for the real-time cellular bioimaging and diagnostics of some disease lesions like tumors. It raises the possibility to provide the specific in-situ platform to exploit the versatile, sensitive, and high-resolution electrochemical single-cell analysis for the promising biomedical applications like rapid tracing of some disease lesions or in vivo bioimaging for precise cancer theranostics.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

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.

Electrochemically Exfoliated Graphene Quantum Dots Based Biosensor for CD44 Breast Cancer Biomarker

An innovative electrochemical biosensor based on graphene quantum dots (GQDs) is developed for a simple, rapid, and highly sensitive primary diagnosis of the breast cancer biomarker cluster of differentiation-44 (CD44) antigen. Herein, electrochemical exfoliation of waste dry batteries provides facile, eco-friendly, and cost-effective synthesis of GQDs. Transmission electron microscopy (TEM) analysis reveals that GQDs exhibit spherical shapes with an average diameter of 4.75 nm. Further, electrochemical analysis through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) reveals that the electrochemical properties of GQDs are suitable for biosensing applications. Subsequently, GQDs have a large electroactive surface area that has been utilized for the immobilization of CD44 antibodies to fabricate the electrochemical biosensor. The electroanalytical performance of GQDs for CD44 biosensing capabilities is studied by differential pulse voltammetry (DPV). The developed electrochemical biosensor has high sensitivity with the lowest detection limit (LOD) of 2.11 fg/mL in the linear range of 0.1 pg/mL to 100.0 ng/mL in phosphate buffer saline (PBS). Further, the linear response of the electrochemical biosensor for CD44 antigen concentration is in the range of 1.0 pg/mL to 100.0 ng/mL with a LOD of 2.71 fg/mL in spiked serum samples. The outcomes suggest that the synthesized GQDs demonstrate promising attributes to be utilized as a viable nanomaterial in biosensing applications.

Cell Membrane and V2C MXene-Based Electrochemical Immunosensor with Enhanced Antifouling Capability for Detection of CD44

The inactive adsorption and interference of biomolecules in electrochemical biosensors is a topic of intense interest. Directly utilizing native cell membranes to endow electrochemical surfaces with antifouling and biocompatible features is a promising strategy, rather than attempting to synthetically replicate complex biological interface properties. In this study, we present a facial and sensitive sandwich-type antifouling immunoassay through platelet membrane/Au nanoparticle/delaminated V₂C nanosheet (PM/AuNPs/d-V₂C)-modified electrode as the substrate of sensing interface and methylene blue/aminated metal organic framework (MB@NH₂-Fe-MOF-Zn) as an electrochemical signal probe. The biosensor perfectly integrates the high conductivity of AuNPs-loaded V₂C MXene with the excellent loading property of NH₂-Fe-MOF-Zn to improve the electrochemical sensing performance. In addition, the excellent antifouling properties of the homogeneous cell membrane can effectively prevent the non-specific adsorption of model proteins. The obtained antifouling biosensor possesses the capability of ultrasensitive detection of CD44 and CD44-positive cancer cell in complex liquids and exhibits good analytical performance for the analysis of CD44 with a linear range from 0.5 ng/mL to 500 ng/mL. This strategy of developing cell membrane-based biosensing systems with enhanced antifouling capability can be easily expanded to the construction of other complex biosensors, and the advanced biological probes and analytical methods provide a favorable means to accurately quantify biomarkers associated with tumor progression.

PNA-ATP aptamer-capped doxorubicin-loaded silica nanoparticles for targeted cancer therapy

Nanomaterial-based drug delivery has opened new horizons in cancer therapy. This study aimed to investigate the in vitro and in vivo anti-cancer effects of a hyaluronic acid (HA)-targeted nanocarrier based on hollow silica nanoparticles (HSNPs), gated with peptide nucleic acid (PNA) and ATP aptamer (ATP_Apt) and loaded with doxorubicin (DOX). After formulation of a smart drug delivery nanosystem (HSNPs/DOX/ATP_Apt/PNA/HA), drug release, cytotoxicity, uptake, and in vivo anti-tumor properties were studied. Drug release test showed the controlled release of encapsulated DOX in response to ATP content. MTT and flow cytometry indicated that HA could improve both cytotoxicity and cellular uptake of the formulation. Moreover, HA-targeted formulation enhanced both the survival rate and tumor inhibition in the tumor-bearing mice compared with free DOX (P < 0.05). Our findings confirmed that HA-targeted nanoformulation, gated with PNA/aptamer and loaded with DOX can provide a novel therapeutic platform with great potential for cancer therapy.

Recent Advances in Single Cell Analysis by Electrochemiluminescence

Understanding biological mechanisms operating in cells is one of the major goals of biology. Since heterogeneity is the fundamental property of cellular systems, single cell measurements can provide more accurate information about the composition, dynamics, and regulatory circuits of cells than population-averaged assays. Electrochemiluminescence (ECL), the light emission triggered by electrochemical reactions, is an emerging approach for single cell analysis. Numerous analytes, ranging from small biomolecules such as glucose and cholesterol, proteins and nucleic acids to subcellular structures, have been determined in single cells by ECL, which yields new insights into cellular functions. This review aims to provide an overview of research progress on ECL principles and systems for single cell analysis in recent years. The ECL reaction mechanisms are briefly introduced, and then the advances and representative works in ECL single cell analysis are summarized. Finally, outlooks and challenges in this field are addressed.

A mass-tagged MOF nanoprobe approach for ultra-sensitive protein quantification in tumor-educated platelets

A mass-tagged metal-organic framework (MOF) nanoprobe approach was developed for ultra-sensitive quantification of platelet protein CD44 by integrating activable aptamer recognition and MOF nanoprobe signal amplification with mass spectrometric detection. This approach offered high sensitivity and quantitative capability for low abundant protein analysis in tumor-educated platelets (TEPs), exhibiting great potential in cancer diagnosis and management.

Quantum dots for electrochemiluminescence bioanalysis - A review

Electrochemiluminescence (ECL) bioanalysis has become increasingly important in various fields from bioanalysis to clinical diagnosis due to its outstanding merits, including low background signal, high sensitivity, and simple instrumentation. Quantum dots (QDs) are a significant theme in ECL bioanalysis since their excellent optical, electrochemical properties, and ease of functionalization endow them with versatile roles and new mechanisms of signal transduction in ECL. Herein, this review details recent advances of QDs-based ECL bioanalysis by using QDs as ECL emitters, coreactants, or ECL resonance energy transfer donors/acceptors, mainly focused on their optical and electrochemical properties and ECL reaction mechanism. In the end, we will discuss the current limitations and future developments in QDs ECL bioanalysis to address the requirement about selectivity, sensitivity, toxicity, and emerging applications.

Recent progress in the early detection of cancer based on CD44 biomarker; nano-biosensing approaches

CD44 is a cell matrix adhesion molecule overexpressed on the cell surfaces of the major cancers. CD44 as a cancer-related biomarker has an essential role in the invasion and metastasis of cancer. The detection and quantification of CD44 can provide essential information useful for clinical cancer diagnosis. In this regard, biosensors with sensitive and specific properties, give prominence to the development of CD44 detection platforms. To date, various aptamer-based sensitive-enhancers together with nanoparticles (NPs) have been combined into the biosensors systems to provide an innovative biosensing method (aptasensors/nano-aptasensors) with substantially improved detection limit. This review article discusses the recent advances in the field of biosensors, nanobiosensors, and aptasensors for the quantitative determination of CD44 and the detection of CD44-expressing cancer cells.

Recent Advances in Functional Carbon Quantum Dots for Antitumour

Carbon quantum dots (CQDs) are an emerging class of quasi-zero-dimensional photoluminescent nanomaterials with particle sizes less than 10 nm. Owing to their favourable water dispersion, strong chemical inertia, stable optical performance, and good biocompatibility, CQDs have become prominent in biomedical fields. CQDs can be fabricated by “top-down” and “bottom-up” methods, both of which involve oxidation, carbonization, pyrolysis and polymerization. The functions of CQDs include biological imaging, biosensing, drug delivery, gene carrying, antimicrobial performance, photothermal ablation and so on, which enable them to be utilized in antitumour applications. The purpose of this review is to summarize the research progress of CQDs in antitumour applications from preparation and characterization to application prospects. Furthermore, the challenges and opportunities of CQDs are discussed along with future perspectives for precise individual therapy of tumours.

A ratiometric electrochemiluminescent cytosensor based on polyaniline hydrogel electrodes in spatially separated electrochemiluminescent systems

Here, we proposed a ratiometric electrochemiluminescent (ECL) strategy in spatially multiplied ECL systems. By the specific recognition of hyaluronic acid with proteoglycan CD44 and epidermal growth factor with epidermal growth factor receptor on the cell surface, the cells were labelled with potential-resolved ECL probes, namely Ru(bpy)₃²⁺ and g-C₃N₄, respectively. The as-proposed cytosensor provides a multichannel ECL protocol to improve the throughput, which may push the application of ECL for the cellular immunoanalysis.

Electrogenerated chemiluminescence detection of single entities

Electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), is an electrochemically induced production of light by excited luminophores generated during redox reactions. It can be used to sense the charge transfer and related processes at electrodes via a simple visual readout; hence, ECL is an outstanding tool in analytical sensing. The traditional ECL approach measures averaged electrochemical quantities of a large ensemble of individual entities, including molecules, microstructures and ions. However, as a real system is usually heterogeneous, the study of single entities holds great potential in elucidating new truths of nature which are averaged out in ensemble assays or hidden in complex systems. We would like to review the development of ECL intensity and imaging based single entity detection and place emphasis on the assays of small entities including single molecules, micro/nanoparticles and cells. The current challenges for and perspectives on ECL detection of single entities are also discussed.

Photoelectrochemical aptasensor with low background noise

In photoelectrochemical (PEC) detection, enhancing the PEC signal and depressing the blank signal are conducive to improve the sensitivity. Because the carbon nanotube (CNT) effectively transfers photogenerated electrons from SnSe to the electrode, the composite nanomaterial CNTs/SnSe generates a strong PEC signal. Methionine (Met), AuNPs, and probe DNA are woven together forming a nanoprobe which is used as a quencher to quench the PEC signal of CNTs/SnSe. When the nanoprobe and CNTs/SnSe are modified onto the electrode, there is a low blank signal. In the presence of metastatic breast cancer cells, the cells interact with the aptamer of dsDNA; concomitantly, cDNA is released to trigger catalytic hairpin assembly (CHA). As a result, a new dsDNA which has an overhang is formed. The nanoprobe on the surface of the electrode hybridizes with the newly formed dsDNA. Subsequently, the nanoprobe is released from the surface of the electrode and the quenching effect between the nanoprobe and the CNTs/SnSe disappears. The PEC aptasensor is linear in the concentration range of 300-5,000 cells/mL, and the detection limit is 180 cells/mL under optimized conditions. The relative standard deviation (RSD) is 3.6% at 10,000 cells/mL. This work demonstrates a promising strategy using CNTs/SnSe as the photoactive material and Met-AuNPs as the quencher to establish a PEC aptasensor with a high PEC response and low blank signal. It can be used to detect bioactive substances at ultralow levels prospectively. Graphical abstract.

Cancer Stem Cells-Origins and Biomarkers: Perspectives for Targeted Personalized Therapies

The use of biomarkers in diagnosis, therapy and prognosis has gained increasing interest over the last decades. In particular, the analysis of biomarkers in cancer patients within the pre- and post-therapeutic period is required to identify several types of cells, which carry a risk for a disease progression and subsequent post-therapeutic relapse. Cancer stem cells (CSCs) are a subpopulation of tumor cells that can drive tumor initiation and can cause relapses. At the time point of tumor initiation, CSCs originate from either differentiated cells or adult tissue resident stem cells. Due to their importance, several biomarkers that characterize CSCs have been identified and correlated to diagnosis, therapy and prognosis. However, CSCs have been shown to display a high plasticity, which changes their phenotypic and functional appearance. Such changes are induced by chemo- and radiotherapeutics as well as senescent tumor cells, which cause alterations in the tumor microenvironment. Induction of senescence causes tumor shrinkage by modulating an anti-tumorigenic environment in which tumor cells undergo growth arrest and immune cells are attracted. Besides these positive effects after therapy, senescence can also have negative effects displayed post-therapeutically. These unfavorable effects can directly promote cancer stemness by increasing CSC plasticity phenotypes, by activating stemness pathways in non-CSCs, as well as by promoting senescence escape and subsequent activation of stemness pathways. At the end, all these effects can lead to tumor relapse and metastasis. This review provides an overview of the most frequently used CSC markers and their implementation as biomarkers by focussing on deadliest solid (lung, stomach, liver, breast and colorectal cancers) and hematological (acute myeloid leukemia, chronic myeloid leukemia) cancers. Furthermore, it gives examples on how the CSC markers might be influenced by therapeutics, such as chemo- and radiotherapy, and the tumor microenvironment. It points out, that it is crucial to identify and monitor residual CSCs, senescent tumor cells, and the pro-tumorigenic senescence-associated secretory phenotype in a therapy follow-up using specific biomarkers. As a future perspective, a targeted immune-mediated strategy using chimeric antigen receptor based approaches for the removal of remaining chemotherapy-resistant cells as well as CSCs in a personalized therapeutic approach are discussed.

Electrochemiluminescence immunoassay of human chorionic gonadotropin using silver carbon quantum dots and functionalized polymer nanospheres

A composite, reduced graphene oxide (rGO) doped with silver nanoparticles (Ag NPs), was prepared by using binary reductants of sodium citrate and hydrazine hydrate. Carbon quantum dots (CQDs) synthesized by papaya peel combined with silver ions to form a CQDs-loaded silver nanoparticle (AgCQDs) nanocomposite. Polymer nanospheres (PNS) were generated via the infinite coordination polymer of ferrocene dicarboxylic acid and employed as carriers to load AgCQDs. The prepared AgCQDs@PNS-PEI has good biocompatibility and electrical conductivity and can be used as a matrix for the immobilization of a secondary antibody (Ab2). A sandwich-type electrochemiluminescence (ECL) immunosensor using AgCQDs@PNS-PEI nanocomposite as probe has been developed for the detection of human chorionic gonadotropin (HCG). The proposed immunosensor exhibits a linear range from 0.00100 to 500 mIU mL^-1 and the detection limit is 0.33 μIU mL^-1 (S/N = 3) under optimal conditions. The sensor exhibits excellent selectivity, good reproducibility, and high stability. These features demonstrate that the proposed method has promising potential for clinical protein detection and displays a new strategy to fabricate an immunosensor. Graphical abstract.

Recent developments in electrochemiluminescence nanosensors for cancer diagnosis applications

In recent years, electrochemiluminescence (ECL) nanosensing systems have undergone rapid development and made significant progress in ultrasensitive analysis and cell imaging. Because of the unique advantages of high selectivity, ultra-sensitivity, and good reproducibility, ECL nanosensors can open new paths for cancer diagnosis. With the development of ECL nanosensors, high-throughput analysis, visual detection and spatially resolved ECL imaging of single cells are being realized. The innovations of ECL nanosensors consist of electrochemical excitation, coreactant catalysis, light radiation and luminescence signal amplification, which involve several fields such as nanotechnology, catalysis, optics, and electrochemistry. The developments of ECL instruments also relate to imaging technology. Herein, we review the construction modes, sensing strategies and cancer diagnosis applications of ECL nanosenors. Firstly, the nano-components of the ECL sensing system are discussed. The construction and signal amplification methods of the nanosensing system are emphasized. Secondly, the high-efficiency cancer identification strategies are presented, including protein tumor marker detection, nucleic acid assay, cancer cell identification and exosome detection. The recent advances in representative examples of ECL nanosenors in cancer diagnosis are highlighted, including high-throughput ECL analysis, in situ assay, visual ECL detection, single-cell imaging diagnosis, and so on. Finally, the challenges are featured based on the recent development of the ECL nanosensing system in the clinical diagnosis. The ECL nanosensors provide effective and reliable analytical methods and open new paths for cancer diagnosis. It is noteworthy that the prospects of the ECL nanosensing system in clinical diagnosis are instructive to the developments of other nanosensor research.

Formation of a Photoelectrochemical Z-Scheme Structure with Inorganic/Organic Hybrid Materials for Evaluation of Receptor Protein Expression on the Membrane of Cancer Cells

Quantitative analysis of receptor protein expression is essential to give new insights into tumor-related research. Benefitting from their high sensitivity and low background, photoelectrochemical (PEC) platforms are considered as powerful tools for evaluating the expression of receptor proteins. Herein, to reduce the cytotoxicity and facilitate the subsequent assembly, l-cysteine-modified Ag-ZnIn₂S₄ quantum dots (l-Cys AZIS QDs) are prepared and PEC responses under the irradiation of long wavelength light are obtained. To further improve the PEC behavior, iron phthalocyanine (FePc) is employed to form a Z-scheme structure with l-Cys AZIS QDs. The Z-scheme structure based on l-Cys AZIS QDs/FePc hybrid materials exhibits high photo-to-electric conversion efficiency and can be excited with near-infrared range light. Because hyaluronic acid linked to photoactive materials can recognize CD44 expressed on the membrane of cancer cells, cancer cells are immobilized onto l-Cys AZIS QDs/FePc hybrid materials, inducing a decrease of the photocurrent intensity. Consequently, a PEC cytosensor is constructed to quantify cancer cells expressing CD44. The PEC analytical platform is able to determine A549 cells in the range of 2 × 10² to 4.5 × 10⁶ cells/mL, and a detection limit of 15 cells/mL is realized in the case of S/N = 3. In addition, the expression of CD44 in A549 and other five cancer cells is measured with this PEC method. Depending on our data, the expression of CD44 in different cancer cells is distinct, indicating great potential of this method in receptor protein-related studies.

Recent Advances in Electrochemiluminescence-Based Systems for Mammalian Cell Analysis

Mammalian cell analysis is essential in the context of both fundamental studies and clinical applications. Among the various techniques available for cell analysis, electrochemiluminescence (ECL) has attracted significant attention due to its integration of both electrochemical and spectroscopic methods. In this review, we summarize recent advances in the ECL-based systems developed for mammalian cell analysis. The review begins with a summary of the developments in luminophores that opened the door to ECL applications for biological samples. Secondly, ECL-based imaging systems are introduced as an emerging technique to visualize single-cell morphologies and intracellular molecules. In the subsequent section, the ECL sensors developed in the past decade are summarized, the use of which made the highly sensitive detection of cell-derived molecules possible. Although ECL immunoassays are well developed in terms of commercial use, the sensing of biomolecules at a single-cell level remains a challenge. Emphasis is therefore placed on ECL sensors that directly detect cellular molecules from small portions of cells or even single cells. Finally, the development of bipolar electrode devices for ECL cell assays is introduced. To conclude, the direction of research in this field and its application prospects are described.

Nanoscale dynamic chemical, biological sensor material designs for control monitoring and early detection of advanced diseases

Early detection and easy continuous monitoring of emerging or re-emerging infectious, contagious or other diseases are of particular interest for controlling healthcare advances and developing effective medical treatments to reduce the high global cost burden of diseases in the backdrop of lack of awareness regarding advancing diseases. Under an ever-increasing demand for biosensor design reliability for early stage recognition of infectious agents or contagious diseases and potential proteins, nanoscale manufacturing designs had developed effective nanodynamic sensing assays and compact wearable devices. Dynamic developments of biosensor technology are also vital to detect and monitor advanced diseases, such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), diabetes, cancers, liver diseases, cardiovascular diseases (CVDs), tuberculosis, and central nervous system (CNS) disorders. In particular, nanoscale biosensor designs have indispensable contribution to improvement of health concerns by early detection of disease, monitoring ecological and therapeutic agents, and maintaining high safety level in food and cosmetics. This review reports an overview of biosensor designs and their feasibility for early investigation, detection, and quantitative determination of many advanced diseases. Biosensor strategies are highlighted to demonstrate the influence of nanocompact and lightweight designs on accurate analyses and inexpensive sensing assays. To date, the effective and foremost developments in various nanodynamic designs associated with simple analytical facilities and procedures remain challenging. Given the wide evolution of biosensor market requirements and the growing demand in the creation of early stage and real-time monitoring assays, precise output signals, and easy-to-wear and self-regulating analyses of diseases, innovations in biosensor designs based on novel fabrication of nanostructured platforms with active surface functionalities would produce ​remarkable biosensor devices. This review offers evidence for researchers and inventors to focus on biosensor challenge and improve fabrication of nanobiosensors to revolutionize consumer and healthcare markets.

Highly sensitive bioaffinity electrochemiluminescence sensors: Recent advances and future directions

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) has attracted much attention in various fields of analysis due to the potential remarkably high sensitivity, extremely wide dynamic range and excellent controllability. Electrochemiluminescence biosensor, by taking the advantage of the selectivity of the biological recognition elements and the high sensitivity of ECL technique was applied as a powerful analytical device for ultrasensitive detection of biomolecule. In this review, we summarize the latest sensing applications of ECL bioanalysis in the field of bio affinity ECL sensors including aptasensors, immunoassays and DNA analysis, cytosensor, molecularly imprinted sensors, ECL resonance energy transfer and ratiometric biosensors and give future perspectives for new developments in ECL analytical technology. Furthermore, the results herein discussed would demonstrate that the use of nanomaterials with unique chemical and physical properties in the ECL biosensing systems is one of the most interesting research lines for the development of ultrasensitive electrochemiluminescence biosensors. In addition, ECL based sensing assays for clinical samples analysis and medical diagnostics and developing of immunosensors, aptasensors and cytosensor for this purpose is also highlighted.

Lanthanide terbium complex: synthesis, electrochemiluminescence (ECL) performance, and sensing application

In this study, a new lanthanide terbium complex, Tb(pzda)3(NO3)3·nH2O, was synthesized by a hydrothermal method and characterized by Fourier transform infrared spectroscopy (FT-IR) and energy-dispersive X-ray spectroscopy (EDS). It was found that the as-synthesized Tb-complex exhibited good electrochemiluminescence (ECL) behavior in the presence of triethanolamine (TEOA) in a HAc-NaAc buffer solution on a glassy carbon electrode. The possible reaction mechanism has been discussed based on the fluorescence spectra and ECL spectra. For sensing applications, it was found that protocatechuic acid (PCA) had an obvious quenching effect on the ECL signal of the Tb-complex, and this resulted in a decreased ECL signal associated with the concentration of PCA. Therefore, a highly sensitive method for the detection of PCA was established with a linear range of 1.283 × 10-10 M to 3.845 × 10-4 M and a detection limit of 0.085 nM at an S/N ratio of 3. This novel ECL assay strategy with an outstanding ECL efficiency offers great potential for pharmaceutical analyses.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

A high precision MUA-spaced single-cell sensor for cellular receptor assay based on bifunctional Au@Cu-PbCQD nanoprobes

A single-cell sensor with a spatial architecture was firstly fabricated for realizing high precision single-cell analysis using an 11-mercaptoundecanoic acid (MUA)-spaced sensing interface to prop up single cells and provide a suitable space for effective nanoprobe labeling. Mercapto acids (MA) with different carbon chain lengths were optimized and MUA was selected to provide optimal interspace on the electrodeposited PANI/AuNP substrates, and its carboxyl could couple with folic acid to capture cancer cells. Bifunctional Au@Cu-PbCQD nanoprobes, in which the AuNP cores were linked with lead-coadsorbed carbon quantum dots (PbCQDs) by a copper(ii) ion bridge, were firstly synthesized and applied as highly sensitive electrochemiluminescence (ECL) probes and electrochemical probes. Hyaluronic acid (HA)-functionalized Au@Cu-PbCQD nanoprobes were labelled on MCF-7 cells via specific recognition to the CD44 receptor, which served as the research model. The ECL response of the sensor was applied to evaluate the validity of nanoprobe labeling. With MUA modified, the sensor was able to enhance the ECL intensity by 37.5 ± 3.9%, indicating the remarkable amelioration of the accuracy of single-cell analysis. To take advantage of the bifunctional nanoprobes, differential pulse voltammetry (DPV) was further applied to confirm the feasibility of the proposed single-cell sensor with a spatial architecture. Therefore, the novel strategy provides a single-cell analysis platform to acquire high-precision analytical results, and more accurately to elucidate cellular heterogeneity and biological function.

Cathodic electrochemiluminescence behaviour of MoS2 quantum dots and its biosensing of microRNA-21

The cathodic electrochemiluminescence (ECL) behaviour of nontoxic MoS2 quantum dots (QDs) was studied for the first time using potassium peroxydisulfate as the co-reactant. Ag-PAMAM NCs, serving as difunctional tags for quenching and enhancing ECL of MoS2-reduced graphene oxide composites, were introduced into the ECL detection system for signal amplification. By modulating the interparticle distance between MoS2 QDs and Ag-PAMAM NCs, the ECL quenching from resonance energy transfer and the ECL enhancement from surface plasma resonance were realized. Coupling the good ECL performance of MoS2 QDs with the excellent ECL quenching and enhancement effects of Ag-PAMAM NCs, a novel MoS2 QDs-based ECL biosensing platform for sensitive detection of microRNA-21 was achieved with a detection limit of 0.20 fmol L-1 (S/N = 3). This method was successfully applied to the determination of microRNA-21 in human serum samples with recoveries of 90.0-110.0%, suggesting great potential for its applications in biological and chemical analysis.

A single-cell analysis platform for electrochemiluminescent detection of platelets adhesion to endothelial cells based on Au@DL-ZnCQDs nanoprobes

A novel single-cell analysis platform (SCA) was developed for the investigation of platelets adhesion to single human umbilical vein endothelial cell (HUVEC) via using the adhesion molecule (E-selectin) on the damaged HUVEC as the marker site, and integrating electrochemiluminescence (ECL) with the ultrasensitive Au@DL-ZnCQDs nanoprobes. The Au@DL-ZnCQDs nanocomposite, a kind of double layer zinc-coadsorbed carbon quantum dot (ZnCQDs) core-shell nanoprobe, was firstly constructed by using gold nanoparticles (AuNPs) as the core to load with ZnCQDs and then the citrate-modified silver nanoparticles (AgNPs) as the bridge to link AuNPs-ZnCQDs with ZnCQDs to form the core-shell with double layer ZnCQDs (DL-ZnCQDs) nanoprobe, revealed a 10-fold signal amplification. The H₂O₂-induced oxidative damage HUVECs were utilized as the cellular model on which anti-E-selectin functionalized nanoprobes specially recognized E-selectin, the SCA showed that the ECL signals decreased with platelets adhesion to single HUVEC. The proposed SCA could effectively and dynamically monitor the adhesion between single HUVEC and platelets in the absence and presence of collagen activation, moreover, be able to quantitatively detect the number of platelets adhesion to single HUVEC, and show a good analytical performance with linear range from 1 to 15 platelets. In contrast, the HUVEC was down-regulated the expression of adhesion molecules by treating with quercetin inhibitor, and the SCA also exhibited the feasibility for analysis of platelets adhesion to single HUVEC. Therefore, the single-cell analysis platform provided a novel and promising protocol for analysis of the single intercellular adhesion, and it will be beneficial to elucidate the pathogenesis of cardiovascular diseases.