Ni(OH)2/NGQDs-based electrochemiluminescence immunosensor for prostate specific antigen detection by coupling resonance energy transfer with Fe3O4@MnO2 composites

One-step electrodeposited hybrid nanofilms in amperometric biosensor development

This review summarizes recent developments in amperometric biosensors, based on one-step electrodeposited organic-inorganic hybrid layers, used for analysis of low molecular weight compounds. The factors affecting self-assembly of one-step electrodeposited films, methods for verifying their composition, advantages, limitations and approaches affecting the electroanalytical performance of amperometric biosensors based on organic-inorganic hybrid layers were systemized. Moreover, issues related to the formation of one-step organic-inorganic hybrid functional layers with different structures in biosensors produced under the same electrodeposition parameters are discussed. The systemized dependencies can support the preliminary choice of functional sensing layers with architectures tuned for specific biotechnology and life science applications. Finally, the capabilities of one-step electrodeposition of organic-inorganic hybrid functional films beyond amperometric biosensors were highlighted.

Electrochemical Detection of Cd2+, Pb2+, Cu2+ and Hg2+ with Sensors Based on Carbonaceous Nanomaterials and Fe3O4 Nanoparticles

Two electrochemical sensors were developed in this study, with their preparations using two nanomaterials with remarkable properties, namely, carbon nanofibers (CNF) modified with Fe3O4 nanoparticles and multilayer carbon nanotubes (MWCNT) modified with Fe3O4 nanoparticles. The modified screen-printed electrodes (SPE) were thus named SPE/Fe3O4-CNF and SPE/Fe3O4-MWCNT and were used for the simultaneous detection of heavy metals (Cd2+, Pb2+, Cu2+ and Hg2+). The sensors have been spectrometrically and electrochemically characterized. The limits of detection of the SPE/Fe3O4-CNF sensor were 0.0615 μM, 0.0154 μM, 0.0320 μM and 0.0148 μM for Cd2+, Pb2+, Cu2+ and Hg2+, respectively, and 0.2719 μM, 0.3187 μM, 1.0436 μM and 0.9076 μM in the case of the SPE/ Fe3O4-MWCNT sensor (following optimization of the working parameters). Due to the modifying material, the results showed superior performance for the SPE/Fe3O4-CNF sensor, with extended linearity ranges and detection limits in the nanomolar range, compared to those of the SPE/Fe3O4-MWCNT sensor. For the quantification of heavy metal ions Cd2+, Pb2+, Cu2+ and Hg2+ with the SPE/Fe3O4-CNF sensor from real samples, the standard addition method was used because the values obtained for the recovery tests were good. The analysis of surface water samples from the Danube River has shown that the obtained values are significantly lower than the maximum limits allowed according to the quality standards specified by the United States Environmental Protection Agency (USEPA) and those of the World Health Organization (WHO). This research provides a complementary method based on electrochemical sensors for in situ monitoring of surface water quality, representing a useful tool in environmental studies.

Ultrasensitive Detection of SARS-CoV-2 Nucleocapsid Protein Based on Porphyrin-Based Metal-Organic Gels with Highly Efficient Electrochemiluminescence at Low Potential

Metal-organic gels (MOGs) are a new type of intelligent soft material, which are bridged by metal ions and organic ligands through noncovalent interactions. In this paper, we prepared highly stable P-MOGs, using the classical organic electrochemiluminescence (ECL) luminescence meso-tetra(4-carboxyphenyl)porphine as the organic ligand and Fe3+ as the metal ion. Surprisingly, P-MOGs can stably output ECL signals at a low potential. We introduced P-MOGs into the ECL resonance energy transfer strategy (ECL-RET) and constructed a quenched ECL immunosensor for the detection of the SARS-CoV-2 nucleocapsid protein (SARS-CoV-2-N). In the ECL-RET system, P-MOGs were used as energy donors, and Au@Cu2O@Fe3O4 were selected as energy acceptors. The ultraviolet-visible spectrum of Au@Cu2O@Fe3O4 partially overlaps with the ECL spectrum of P-MOGs, which can effectively touch off the ECL-RET behavior between the donors and receptors. Under the ideal experimental situation, the linear detection range of the SARS-CoV-2-N concentration was 10 fg/mL to 100 ng/mL, and the limit of detection was 1.5 fg/mL. This work has broad application prospects for porphyrin-MOGs in ECL sensing.

Electrochemiluminescence nanoemitters for immunoassay of protein biomarkers

The family of electrochemiluminescent luminophores has witnessed quick development since the electrochemiluminescence (ECL) phenomenon of silicon nanoparticles was first reported in 2002. Moreover, these developed ECL nanoemitters have extensively been applied in sensitive detection of protein biomarker by combining with immunological recognition. This review firstly summarized the origin and development of various ECL nanoemitters including inorganic and organic nanomaterials, with an emphasis on metal-organic frameworks (MOFs)-based ECL nanoemitters. Several effective strategies to amplify the ECL response of nanoemitters and improve the sensitivity of immunosensing were discussed. The application of ECL nanoemitters in immunoassay of protein biomarkers for diagnosis of cancers and other diseases, especially lung cancer and heart diseases, was comprehensively presented. The recent development of ECL imaging with the nanoemitters as ECL tags for detection of multiplex protein biomarkers on single cell membrane also attracted attention. Finally, the future opportunities and challenges in the ECL biosensing field were highlighted.

Applications of Carbon Dots for the Treatment of Alzheimer's Disease

There are currently approximately 50 million victims of Alzheimer's disease (AD) worldwide. The exact cause of the disease is unknown at this time, but amyloid plaques and neurofibrillary tangles in the brain are hallmarks of the disease. Current drug treatments for AD may slow the progression of the disease and improve the quality of life of patients, but they are often only minimally effective and are not cures. A major obstacle to developing and delivering more effective drug therapies is the presence of the blood-brain barrier (BBB), which prevents many compounds with therapeutic potential from reaching the central nervous system. Nanotechnology may provide a solution to this problem. Among the medical nanomaterials currently being studied, carbon dots (CDs) have attracted widespread attention because of their ability to cross the BBB, non-toxicity, and potential for drug/gene delivery.

Coupled electrochemiluminescent and resonance energy transfer determination of microRNA-141 using functionalized Mxene composite

The electrochemiluminescence and resonance energy transfer (ECL-RET) method was adopted to detect miRNAs, in which the two-dimensional Ti₃C₂ Mxenes with high surface area modified with CdS:W nanocrystals (CdS:W NCs) were used as ECL signal emitter. Mxenes with a specific surface area of 5.2755 m²/g carried more emitters and promote ECL intensity. As an energy acceptor, BiOCl nanosheets (BiOCl NSs) have a wide UV-Vis absorption peak in the range 250 nm-700 nm, including the emission band of CdS:W NCs with 520 nm emission wavelength. Hence, BiOCl NSs are covalently bound to hairpin DNA 2 by amide bond to quench the ECL signal of CdS:W NCs. In the presence of miRNA-141, the hairpin DNA 1 modified on the GCE was unfold and then paired with hairpin DNA 2 to release miRNA-141 and quench the signal of the ECL biosensor. Then, the concentration signal of miRNA-141 was amplified by catalytic hairpin assembly. The novel specific biosensor demonstrated a satisfactory linear relationship with miRNA-141 in the range 0.6 pM to 4000 pM; the detection limit was as low as 0.26 pM (3 s/m) under the potential of 0 ~ -1.3 V and showed outstanding RSD of 1.19%. The findings of the present work with high accuracy and sensitivity will be of positive significance for the clinical diagnosis of miRNA in the future work. The construction process of the biosensor and electrochemiluminescence mechanism.

Organic quantum dots: An ultrasmall nanoplatform for cancer theranostics

Tumours are the second leading cause of death globally, generating alterations in biological interactions and, as a result, malfunctioning of crucial genetic traits. Technological advancements have made it possible to identify tumours at the cellular level, making transcriptional gene variations and other genetic variables more easily investigated. Standard chemotherapy is seen as a non-specific treatment that has the potential to destroy healthy cells while also causing systemic toxicity in individuals. As a result, developing new technologies has become a pressing necessity. QDs are semiconductor particles with diameters ranging from 2 to 10 nanometers. QDs have grabbed the interest of many researchers due to their unique characteristics, including compact size, large surface area, surface charges, and precise targeting. QD-based drug carriers are well known among the many nanocarriers. Using QDs as a delivery approach enhances solubility, lengthens retention time, and reduces the harmful effects of loaded medicines. Several varieties of quantum dots used in drug administration are discussed in this article, along with their chemical and physical characteristics and manufacturing methods. Furthermore, it discusses the role of QDs in biological, medicinal, and theranostic applications.

Dual-Mode Immunosensor for Electrochemiluminescence Resonance Energy Transfer and Electrochemical Detection of Rabies Virus Glycoprotein Based on Ru(bpy)32+-Loaded Dendritic Mesoporous Silica Nanoparticles

Rabies is a serious zoonotic disease in almost all warm-blooded animals and causes fatal encephalitis. The detection of rabies virus (RABV) is critical and remains a significant challenge. Herein, an electrochemiluminescence resonance energy transfer (ECL-RET) and electrochemical (EC) dual-mode immunosensor was developed for highly sensitive detection of RABV glycoprotein. Dendritic mesoporous silica nanoparticles (DMSNs) were employed to load Ru(bpy)₃²⁺ and to obtain ECL probes (Ru@DMSNs). Ru@DMSNs were decorated on the electrode surface, followed by the modification of the RABV antibody (Ab₁). RABV was specifically recognized and captured by Ab₁, causing the decline of the ECL signal due to the obstruction of electron transfer. Additionally, manganese oxide nanoparticles (MnO_x) modified with Ab₂ can further quench the ECL signal of Ru@DMSNs via the RET between Ru@DMSNs and MnO_x. Meanwhile, MnO_x can catalyze the oxidation of o-phenylenediamine (o-PD), generating a significant differential pulse voltammetry (DPV) signal as a second signal to monitor RABV glycoprotein concentration. Consequently, an immunosensor was developed to achieve dual-signal detection of RABV and improve reliability. Under the optimal conditions, detection ranges of 0.10 pg·mL^-1 to 10 ng·mL^-1 for ECL (with an 88 fg·mL^-1 detection limit) and 1 pg·mL^-1 to 2 ng·mL^-1 for EC (with a 0.1 pg·mL^-1 detection limit) were obtained for RABV detection. The reliability of this immunoassay was validated by eight brain tissue samples. The results were found to be compatible with the results of the real-time reverse transcription-polymerase chain reaction (RT-PCR) assay, indicating the potential applicability of this method for RABV diagnosis.

Ultrasensitive Immunosensor for Prostate-Specific Antigen Based on Enhanced Electrochemiluminescence by Vertically Ordered Mesoporous Silica-Nanochannel Film

Ultrasensitive and specific detection of prostate-specific antigen (PSA) in complex biological samples is crucial for early diagnosis and treatment of prostate-related diseases. Immunoassay with a simple sensing interface and ultrahigh sensitivity is highly desirable. Herein, a novel electroluminescence (ECL) immunosensing platform is demonstrated based on the equipment of vertically ordered mesoporous silica-nanochannel films (VMSFs) with PSA antibody, which is able to realize ultrasensitive detection of PSA in human serum. Through the electrochemically assisted self-assembly (EASA) method, the VMSF is easily grown on an indium tin oxide (ITO) electrode in a few seconds. Owing to a large surface area and the negatively charged surface, VMSF nanochannels display strong electrostatic attraction to the positively charged ECL luminophores (tris(2,2-bipyridyl) dichlororuthenium (II), (Ru(bpy)₃²⁺), leading to two orders-of-magnitude enhancement of ECL emission compared with that of the bare ITO electrode. The outer surface of the VMSF is functionalized with reactive epoxy groups, which further allows covalent attachment of PSA antibody (Ab) on the entry of nanochannels. As the combination of PSA with Ab decreases the ECL signal by hindering the mass transfer of ECL luminophores and coreactant, the developed immunosensor can achieve ultrasensitive detection of PSA ranging from 1 pg ml⁻¹ to 100 ng ml⁻¹ with a limit of detection (LOD) of 0.1 pg ml⁻¹. Considering the antifouling ability of the VMSF, sensitive detection of PSA in human serum is also realized. The proposed nanochannel-based immunosensor may open up a new way for the facile development of the universal immunosensing platform for rapid and ultrasensitive detection of disease markers.

Recent advances in nanomaterials for prostate cancer detection and diagnosis

Despite the significant progress in the discovery of biomarkers and the exploitation of technologies for prostate cancer (PCa) detection and diagnosis, the initial screening of these PCa-related biomarkers using current...

Electrochemiluminescence biosensor for cardiac troponin I with signal amplification based on a MoS2@Cu2O–Ag-modified electrode and Ce:ZnO-NGQDs

A sensitive sandwiched electrochemiluminescence (ECL) immunosensor was built for the detection of cTnI. The ECL immunosensor had a low detection limit (2.90 fg mL−1) and wide detection range (10 pg mL−1 to 100 ng mL−1).

Proximity binding induced nucleic acid cascade amplification strategy for ultrasensitive homogeneous detection of PSA

In this work, based on the powerful cycle amplification cascades of proximity hybridization-induced hybridization chain reaction and catalyzed hairpin assembly, we engineered a nonenzymatic and ultrasensitive method which combined the Mg²⁺-DNAzyme recycling signal amplification for the analysis of the human prostate specific antigen. Herein, we adopted PSA-conjugates as triggers in the self-assembly process of two hairpin DNAs (H1, H2) into the products of the CHA which could activate the HCR to induce repeated hybridization. And both ends of each adjacent sequence of the HCR products could form a unit of Mg²⁺-DNAzyme which in presence of cofactor Mg²⁺ could recognize and cyclically cleave the hairpin probes in the solution and thus generate observably enhanced fluorescent signal. Benefit from the nucleic acid circuit amplification strategy, PSA of concentration low to 0.73 pg mL^-1 was detected in this system. This homogeneous sensing method in solution avoid the use of the sophisticated equipment and complex operation, as well as addition of artificial enzyme, thus greatly reducing the constraints and complexity of experimental conditions. Moreover, considering most protein biomarkers in serum don't have their corresponding aptamers, this sensing method provide a general sensing approach for homogeneous sensitive detection of these important protein biomarkers which transfer rough antigen-antibody interactivity to smart signal amplification sensing strategies, thus exhibiting a remarkable prospect in clinical application.

Novel dual-sensitization electrochemiluminescence immunosensor using photopermeable Ru(bpy)3 2+ -doped chitosan/SiO2 nanoparticles as labels and chitosan-decorated Nafion/MWNTs composites as enhancer

A novel dual-sensitization electrochemiluminescence (ECL) immunosensor for the detection of tumour protein prostate specific antigen (PSA) at trace level using Ru(bpy)₃ ²⁺ -doped chitosan/SiO₂ nanoparticles (Ru(bpy)₃ ²⁺ /chitosan/SiO₂ NPs) as the first signal enhancers was fabricated. Due to chitosan with excellent pore forming capacity, these nanoparticles possess porous structures and better photopermeability, and therefore have higher luminescence efficiencies compared with Ru(bpy)₃ ²⁺ /SiO₂ NPs reported in previous publications. Conversely, chitosan with good biocompatibility and high hydrophilicity was electrochemically decorated onto a Nafion/multiwall carbon nanotubes (Nafion/MWNTs) modified electrode surface and used as the second sensitizing matrix to seize large amounts of prostate specific capture antibody (Ab₁ ). The chitosan-decorated Nafion/MWNTs composites exhibited a 5.5-times higher ECL intensity than the unadorned Nafion/MWNTs films. Also, without additional reagents, such as (3-aminopropyl)triethoxysilane (APTS), the one-step functionalized Ru(bpy)₃ ²⁺ /chitosan/SiO₂ NPs provided a large number of active arms to connect with PSA-detected antibodies (Ab₂ ) through the amino groups in chitosan. After a sandwich immunoreaction, the PSA antigen and Ru(bpy)₃ ²⁺ /chitosan/SiO₂ NPs-labelled Ab₂ were sequentially captured onto the Ab₁ /chitosan/Nafion/MWNTs-modified electrode surface. The ECL signal increases were linearly related to the PSA antigen concentrations and ranged from 0.01 pg·mLl^-1 to 10.0 pg·mLl^-1 . Under the optimized experimental conditions, the immunosensor displayed excellent sensitivity and selectivity. The detection limit was as low as 3.4 fg·mLl^-1 , equivalent to, or better than, those of the reported ECL immunosensors for PSA.

Synthesis and modification of carbon dots for advanced biosensing application

There has been an explosion of interest in the use of nanomaterials for biosensing applications, and carbonaceous nanomaterials in particular are at the forefront of this explosion. Carbon dots (CDs), a new type of carbon material, have attracted extensive attention due to their fascinating properties, such as small particle size, tunable optical properties, good conductivity, low cytotoxicity, and good biocompatibility. These properties have enabled them to be highly promising candidates for the fabrication of various high-performance biosensors. In this review, we summarize the top-down and bottom-up synthesis routes of CDs, highlight their modification strategies, and discuss their applications in the fields of photoluminescence biosensors, electrochemiluminescence biosensors, chemiluminescence biosensors, electrochemical biosensors and fluorescence biosensors. In addition, the challenges and future prospects of the application of CDs for biosensors are also proposed.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Bio-nanocomposite based highly sensitive and label-free electrochemical immunosensor for endometriosis diagnostics application

In this research, for the first time, a bio-nanocomposites based highly sensitive and label-free electrochemical immunosensor is reported with the aim of endometriosis diagnostics application. Multiwalled carbon nanotube and magnetite nanoparticle (MWCNT-Fe₃O₄) was dispersed in chitosan (CS) to fabricate a bio-nanocomposite to immobilize very monoclonal specific antibody (via cross-linking using glutaraldehyde) for selective electrochemical immuno-sensing of carbohydrate antigen 19-9 (CA19-9), a potential biomarker for endometriosis diagnostics. Well-characterized Anti-Abs_CA19-9/CS-MWCNT-Fe₃O₄ immune-electrode fabricated on glassy carbon electrode (GCE) successfully detect CA 19-9 and exhibited a high sensitivity as (2.55 µA pg^-1 cm^-1), a detection limit of 0.163 pg mL^-1, detection range from 1.0 pg mL^-1 to 100 ng mL^-1. Our fabricated electrochemical Abs_CA19-9/CS-MWCNT-Fe₃O₄ immunosensor performed CA19-9 sensing in physiological range and at a very level which suggest it application for early-stage diagnostics, diseases monitoring, and optimization of therapy. To claim the clinical application, our sensor was tested using real samples and sensing performance was validated using enzyme-linked immune-sorbent assay (ELISA). The results of the studies projected Abs_CA19-9/CS-MWCNT-Fe₃O₄ electrochemical CA19-9 immunosensor as a potential and affordable alternate of conventional techniques like ELISA. We believe that our fabricated sensor can be the plane of a disease's management program due to affordable, rapid, label-free, and sensitive detection of a targeted biomarker.

Advances in prostate specific antigen biosensors-impact of nanotechnology

Prostate cancer is one of the most dangerous and deadly cancers in elderly men. Early diagnosis using prostate-specific antigen (PSA) facilitates disease detection, management and treatment. Biosensors have recently been used as sensitive, selective, inexpensive and rapid diagnostic tools for PSA detection. In this review, a variety of PSA biosensors such as aptasensors, peptisensors and immunesensors are highlighted. These use aptamers, peptides and antibodies in the biorecognition element, respectively, and can detect PSA with very high sensitivity via electrochemical, electrochemiluminescence, fluorescence and surface-enhanced Raman spectroscopy. To improve the sensitivity of most of these PSA biosensors, different nanostructured materials have played a critical role.

Morphology-dependent MnO2/nitrogen-doped graphene nanocomposites for simultaneous detection of trace dopamine and uric acid

Four nanostructured MnO₂ with various controllable morphologies, including nanowires, nanorods, nanotubes and nanoflowers were synthesized, and then further composited with nitrogen-doped graphene (NG) with the assistance of ultrasonication. The surface morphologies, phase structures, and electrochemical performances of the proposed MnO₂/NG nanohybrids were investigated by various techniques, and their catalytic activities on the electrooxidation of dopamine (DA) and uric acid (UA) were compared systematically. The sensing performances were found to be highly correlated with their morphologies. Among these morphologies, the nanoflower-like MnO₂, composited with NG, displayed the most sensitive response signals for DA and UA. The boosted electrocatalytic activity was ascribed to the unique porous structure, large electroactive area, and low charge transfer resistance (R_ct), which facilitated the electron transfer between electrode and analytes. Two linear response ranges (0.1 μM-10 μM and 10 μM-100 μM) were accompanied with very low detection limits of 34 nM and 39 nM for DA and UA, respectively. Moreover, the successful application of the MnO₂NFs/NG composites for the simultaneous detection of DA and UA in human serum was realized using second-derivative linear sweep voltammetry (SDLSV). These findings give valuable insights for understanding the morphology-dependent sensing properties of MnO₂ based nanomaterials, which is conducive to the rapid development of ubiquitous MnO₂-based electrochemical sensors.

Nanotechnology and nanomaterial-based no-wash electrochemical biosensors: from design to application

Nanotechnology and nanomaterial based electrochemical biosensors (ECBs) have achieved great development in many fields, such as clinical diagnosis, food analysis, and environmental monitoring. Nowadays, the single-handed pursuit of sensitivity and accuracy cannot meet the demands of detection in many in situ and point-of-care (POC) circumstances. More and more attention has been focused on simplifying the operation procedure and reducing detection time, and thus no-wash assay has become one of the most effective ways for the continuous development of ECBs. However, there are many challenges to realize no-wash detection in the real analysis, such as redox interferences, multiple impurities, non-conducting protein macromolecules, etc. Furthermore, the complex detection circumstance in different application fields makes the realization of no-wash ECBs more complicated and difficult. Thanks to the updated nanotechnology and nanomaterials, in-depth analysis of the obstacles in the detection process and various methods for fabricating no-wash ECBs, most issues have been largely resolved. In this review, we have systematically analyzed the nanomaterial based design strategy of the state-of-the-art no-wash ECBs in the past few years. Following that, we summarized the challenges in the detection process of no-wash ECBs and their applications in different fields. Finally, based on the summary and analysis in this review, we also evaluated and discussed future prospects from the design to the application of ECBs.

Colorimetric immunosensor for determination of prostate specific antigen using surface plasmon resonance band of colloidal triangular shape gold nanoparticles

In this work, we demonstrated the development of a colorimetric immunosensor using surface plasmon resonance band of gold nanoparticles for the detection of prostate specific antigen (PSA). To develop this biosensing tool, triangular gold nanoparticles (AuNPs) were synthesized using Tween-20 as a nonionic surfactant and then, conjugated with PSA capture antibody (Ab₁-AuNPs). When exposed to Ab₁-AuNPs, PSA antigens were found to be successfully captured by nanosystem (PSA)-Ab₁-AuNPs. Next, (PSA)-Ab₁-AuNPs were incubated with second PSA antibody (2)-decorated magnetite (Fe₃O₄-Ab₂) and separated by an external magnetic force to leave Ab₁-AuNPs in the supernatant solution to be directly analyzed using UV-Vis spectroscopy. It was found that the absorption intensity was directly proportional to the PSA concentration. As a result, the linear range for PSA detection was found to be 0.01-20 ng mL^-1 with a detection limit of 0.009 ng mL^-1. Because of significant stability of the prepared Ab₁-AuNPs and excellent selectivity to the PSA antigen, this simple and sensitive sensing system is proposed to be potentially effective in the fast and real-time analysis of clinical samples from prostate cancer patients. We believe that the simple platform of this immunosensor to be useful in the development of future point-of-care sensing tools, working on the quantification of biomarkers in a drop of blood.

Distance-dependent plasmon-enhanced electrochemiluminescence biosensor based on MoS2 nanosheets

Nonmetallic plasmonic MoS₂ nanosheets were synthesized by hydrothermal top-down method. MoS₂ nanosheets had shown strong surface plasmon coupling (SPC) light absorption in the visible and near-infrared region. Herein, the nonmetallic plasmonic MoS₂ nanosheets were employed to enhance the electrochemiluminescence (ECL) signal of sulfur doped boron nitrogen QDs (S-BN QDs) in this work. It is important to regulate the distance between ECL luminophore and plasmonic nanoparticles. On one hand, too closed distance can cause energy or electron transfer, which could quench the ECL intensity of nano-luminophore. On the other hand, plasmonic nanostructure cannot significantly affect the luminescence in the far distance. Therefore, we discussed the distance-dependent plasmon-enhanced ECL in detail with different length DNA chains. Furthermore, we constructed a hybridization chain reaction (HCR) amplification ECL sensing mode with the SPC-ECL strategy. The proposed DNA sensor can quantify hepatitis C virus (HCV) gene from 0.5 pmoL/L to 1 nmoL/L with a limit of detection (LOD) of 0.17 pmoL/L.

Electrochemiluminescent competitive immunoassay for zearalenone based on the use of a mimotope peptide, Ru(II)(bpy)3-loaded NiFe2O4 nanotubes and TiO2 mesocrystals

An ultrasensitive competitive-type electrochemiluminescence immunoassay for the mycotoxin zearalenone is described. The method is based on the use of (a) a mimotope peptide that was selected from a phage displayed peptide library and used to substitute ZEN for designing the competitive assay; (b) NiFe₂O₄ nanotubes with large specific surface area loaded with the ECL probe Ru(bpy)₃²⁺; and (c) poly(vinylpyrrolidone) (PVP)-assisted synthesis of TiO₂ mesocrystals that acts as the sensing platform and support for antibody immobilization. Under the optimized conditions and at an ECL working potential of 1.1 V, a linear response is found for ZEN in the 0.1 to 1.0 × 10^-5 ng·mL^-1 concentration range with a detection limit as low as 3.3 fg·mL^-1. Graphical abstract An ultrasensitive competitive-type electrochemiluminescence (ECL) immunosensor based on mimotope peptide was constructed for the detection of Zearalenone.

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.

Sensitive, selective and simultaneous electrochemical detection of multiple heavy metals in environment and food using a lowcost Fe3O4 nanoparticles/fluorinated multi-walled carbon nanotubes sensor

Multiple heavy metals pollution in environment and food has become an ever-increasing concern and poses a serious threat towards humans and animals. To broad the multiple heavy metals detection, Fe₃O₄ nanoparticles, Fe₃O₄/multi-walled carbon nanotubes (Fe₃O₄/MWCNTs) and Fe₃O₄/fluorinated multi-walled carbon nanotubes (Fe₃O₄/F-MWCNTs) nanocomposites were synthesized by hydrothermal method and constructed as a simultaneous electrochemical sensor, respectively. Compared the catalytic performances of the three electrochemical sensors for the simultaneous detection of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, the results showed that the Fe₃O₄/F-MWCNTs sensor demonstrated preponderant performance. It showed the sensitivity of 108.79, 125.91, 160.85, and 312.65 μA mM^-1 cm^-2 toward Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, which was obviously higher than that of Fe₃O₄/MWCNTs and Fe₃O₄. Additionally, the Fe₃O₄/F-MWCNTs sensor exhibited the wider linear detection ranges of 0.5-30.0, 0.5-30.0, 0.5-30.0, and 0.5-20.0 μM for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively. The limit of detections of the Fe₃O₄/F-MWCNTs sensor were 0.05, 0.08, 0.02, and 0.05 nM (signal to noise ratio of 3) for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, fulfilling the governmental requests of the World Health Organization, China and Indian. The excellent agreement was recorded between the lowcost Fe₃O₄/F-MWCNTs sensor and typical methods (inductively coupled plasma mass spectrometry or atomic fluorescence spectrometry) in river water and soybean samples. Additionally, the sensor also exhibited excellent performances in selectivity, recovery, stability, and reproducibility. This proposal sensor provides a promising strategy to monitor multiple targets in the environment and food.

Electrochemiluminescence "turn-off" detection of curcumin via energy transfer using luminol-doped silica nanoparticles

A method is presented for electrochemiluminescent (ECL) detection of the food additive curcumin via an energy transfer strategy and by using luminol-doped silica nanoparticles (luminol-NPs). The ECL emission of the luminol-NPs (peaking at 425 nm) is reduced in the presence of curcumin due to spectral overlap. The assay can be performed within 1 min, response is linear in the 0.1 to 100 µM curcumin concentration range, and the limit of detection is 32 nM. The method is selective over many ions, adenosine triphosphate, ascorbic acid, cysteine and folic acid. It was successfully applied to the determination of curcumin in spiked human serum and urine. The average recoveries range from 99.0 to 102.6%. Graphical abstract Electrochemiluminescence (ECL) "turn-off" detection of curcumin at levels as low as 32 nM via energy transfer using luminol-doped silica nanoparticles. No hydrogen peroxide (H₂O₂) is used in ECL detection which makes the luminol-NPs ECL system more stable than the conventional luminol-H₂O₂ ECL system.

Magnetic nanoparticles for smart electrochemical immunoassays: a review on recent developments

This review (with 129 refs) summarizes the progress in electrochemical immunoassays combined with magnetic particles that was made in the past 5 years. The specifity of antibodies linked to electrochemical transduction (by amperometry, voltammetry, impedimetry or electrochemiluminescence) gains further attractive features by introducing magnetic nanoparticles (MNPs). This enables fairly easy preconcentration of analytes, minimizes matrix effects, and introduces an appropriate label. Following an introduction into the fundamentals of electrochemical immunoassays and on nanomaterials for respective uses, a large chapter addresses method for magnetic capture and preconcentration of analytes. A next chapter discusses commonly used labels such as dots, enzymes, metal and metal oxide nanoparticles and combined clusters. The large field of hybrid nanomaterials for use in such immunoassays is discussed next, with a focus on MNPs composites with various kinds of graphene variants, polydopamine, noble metal nanoparticles or nanotubes. Typical applications address clinical markers (mainly blood and urine parameters), diagnosis of cancer (markers and cells), detection of pathogens (with subsections on viruses and bacteria), and environmental and food contaminants as toxic agents and pesticides. A concluding section summarizes the present status, current challenges, and highlights future trends. Graphical abstract Magnetic nanoparticles (MNP) with antibodies (Ab) capture and preconcentrate analyte from sample (a) and afterwards become magnetically (b) or immunospecifically (c) bound at an electrode. Signal either increases due to the presence of alabel (b) or decreases as the redox probe is blocked (c).

A novel fluorescence immunosensor based on Förster resonance energy transfer between nitrogen and sulfur co-doped carbon dot functionalized silica nanospheres and Au@Ag NPs

A fluorescence immunosensor for PSA detection was developed based on the FRET between Si/NS-CDs and Au@Ag NPs.

Graphene quantum dots-based electrochemiluminescence detection of DNA using multiple cycling amplification strategy

In this study, a novel strategy for amplified electrochemiluminescence (ECL) detection of DNA was proposed based on excellent ECL activity of graphene quantum dots (GQDs) coupled with multiple cycling amplification technique. A new type of graphene QDs with well ECL property and uniform size were firstly synthesized, then the graphene QDs were assembled on the electrode by poly (diallyldimethylammonium chloride) (PDDA)-graphene oxide (GO) nanocomposites, which could greatly improve ECL signal and stability of QDs. A novel signal-on ECL biosensor for DNA analysis was designed by using ECL quenching of gold nanoparticles (NPs) to graphene QDs combined with endonuclease-aided cyclic amplification strategy. As a result, the proposed strategy can be conveniently expanded to other biosensing application, especially in clinical diagnoses.

Amplified fluorescence detection of serum prostate specific antigen based on metal-dependent DNAzyme assistant nanomachine

An amplified fluorescence biosensing strategy for serum prostate specific antigen (PSA) was developed on the basis of DNAzyme. In presence of cofactor Zn²⁺, Zn²⁺ -dependent DNAzyme could cleave the hairpin substrate probes which were dispersed in solution and generate remarkable fluorescent signal. Taking advantage of the magnetic beads as a carrier, one target protein could bring plentiful hairpin substrate probes on to the electrode through a sandwich structure (Ab₁/PSA/biotin-Ab₂). Moreover, during the cleavage process of as formed DNAzyme, DNAzyme did not be destroyed and could further react with other hairpin probes, then generated continuous fluorescent signal. Benefited by this amplified strategy, the limit of detection (LOD) was low to 0.05 ng mL^-1, which was much lower than our previous reports. This method could be applied to detect different protein biomarkers in serum without corresponding aptamers by changing the corresponding antibodies and thus showed a remarkable prospect in clinical application.

Electrochemiluminescence biosensing based on different modes of switching signals

Electrochemiluminescence (ECL) has attracted much attention in various fields of analysis owing to low background signals, high sensitivity, and excellent controllability.