A novel sandwich electrochemiluminescence immunosensor for ultrasensitive detection of carbohydrate antigen 19-9 based on immobilizing luminol on Ag@BSA core/shell microspheres

CRET-based immunoassay on magnetic beads for selective and sensitive detection of Nanog antigen as a key cancer stem cell marker

A method is presented for chemiluminescence resonance energy transfer (CRET) using APTES-Fe3O4 as a highly efficient energy acceptor with strong magnetic effectiveness over extended distances, while an Au@BSA-luminol composite acts as the donor. In order to boost the chemiluminescence reactions, CuO nanoparticles were successfully employed. The distance between the donor and acceptor is a crucial factor in the occurrence of the CRET phenomenon. A sensitive and high-throughput sandwich chemiluminescence immunosensor has been developed accordingly with a linear range of 1.0 × 10-7 g/L to 6.0 × 10-5 g/L and a limit of detection of 0.8 × 10-7 g/L. The CRET-based sandwich immunosensor has the potential to be implemented to early cancer diagnosis because of its high sensitivity in detecting Nanog, fast analysis (30 min), and simplicity. Furthermore, this approach has the potential to be adapted for the recognition of other antigen-antibody immune complexes by utilizing the corresponding antigens and their selective antibodies.

Confined growth of Ag nanogap shells emitting stable Raman label signals for SERS liquid biopsy of pancreatic cancer

To develop a reliable surface-enhanced Raman scattering (SERS) immunoassay as a new liquid biopsy modality, SERS nanoprobes emitting strong and stable signals are necessary. However, Ag nanoparticles used as SERS nanoprobes are prone to rapid fading of SERS signals by oxidation. This has driven the development of a new strategy for Ag-based SERS nanoprobes emitting stable and strong SERS signals over time. Herein, Ag nanogap shells entrapping Raman labels are created in the confined pores of mesoporous silica nanoparticles (AgNSM) through a rapid single-step reaction for SERS liquid biopsy. Each AgNSM nanoprobe possesses multiple nanogaps of 1.58 nm to entrap Raman labels, allowing superior long-term SERS signal stability and large enhancement of 1.5 × 106. AgNSM nanoprobes conjugated with an antibody specific for carbohydrate antigen (CA)19-9 are employed in the SERS sandwich immunoassay including antibody-conjugated magnetic nanoparticles for CA19-9 detection, showing a two orders of magnitude lower limit of detection (0.025 U mL-1) than an enzyme-linked immunosorbent assay (0.3 U mL-1). The AgNSM nanoprobe immunoassay accurately quantifies CA19-9 levels from clinical serum samples of early and advanced pancreatic cancer. AgNSM nanoprobes with stable SERS signals provide a new route to SERS liquid biopsy for effective detection of blood biomarkers.

Competitive ECL immunosensor for ultrasensitive 17β-estradiol detection based on synergistic promotion strategy using CdSe-ZnSe nanocomposites

A novel competitive ECL immunosensor for detection of 17β-Estradiol (E2) has been fabricated successfully. CdSe-ZnSe nanocomposites (CdSe-ZnSe NCs) with high catalytic properties, large surface area and good conductivity were used synergistically as the ECL nanocarriers of Pt nanoparticles (PtNPs). The ECL intensity of CdSe-ZnSe NCs increased and stabilized with luminol-PtNPs (luminol-PtNPs@CdSe-ZnSe NCs) because of electron transfer. To achieve the successful assembling of competitive ultrasensitive ECL immunosensor with high sensitivity and synergistic effect, Ag@TiO2 core-shell was introduced as label. Ag@TiO2 acted as a signal amplifier and also exhibited the high catalytic activity towards H2O2. This firmly anchored the E2 Antigen with covalent bond and converted the longer wavelength radiations to shorter wavelength. Under optimized conditions, our proposed strategy quantify the selective and reliable analysis of E2 with detection limit of 2.51 fg/mL (S/N = 3) within the linear range of 0.0001-30 ng/mL. The assembled synergistic strategy-based ECL immunosensor manifested the promising sensitivity, selectability along with high level of repeatability. Thus, the fabricated ECL immunosensor has potential valuable application for E2 detection along with many other environmental pollutants.

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.

Ultrasensitive Detection and Separation of Pancreatic Cancer Biomarker CA 19-9 Using a Multiphoton Laser Wave-Mixing Detector Interfaced to Capillary Electrophoresis

The carbohydrate antigen 19-9 (CA 19-9) is the most commonly used biomarker in the clinical diagnosis of pancreatic cancer. Multiphoton nonlinear laser wave-mixing spectroscopy is presented as an ultrasensitive detection method for CA 19-9. Wave mixing is an optical absorption-based method, and hence, one can detect CA 19-9 without labels in their native form using compact ultraviolet (UV) lasers or labeled samples using a visible laser. The wave-mixing signal exhibits a quadratic dependence on the sample concentration, and hence, it is an ideal sensor to monitor small changes in the sample. Wave mixing has inherent advantages over other absorption-based detection methods, including short optical path length (micrometer-thin samples instead of 1 cm cuvette) and excellent spatial resolution (micrometer probe). Since the laser wave-mixing probe volume is small (picoliter), it is convenient to interface to microfluidics or capillary-based electrophoresis systems to enhance chemical specificity. Our wave-mixing detectors could be configured as portable battery-powered devices suitable for field use. Laser wave-mixing spectroscopy offers enhanced selectivity levels for protein detection when coupled with capillary electrophoresis (CE). We report a concentration detection limit of 0.16 U/mL, and a corresponding mass detection limit of 1.2 × 10-8 U, and these detection limits are better than those of chemiluminescence- or ELISA- based methods.

Ultrasensitive immunosensor for monitoring of CA 19-9 pancreatic cancer marker using electrolyte-gated TiS3 nanoribbons field-effect transistor

Measuring CA 19-9 antigen level is critical for early diagnosis of pancreatic cancer, monitoring the treatment process, and predicting disease recurrence. The purpose of this research is to assess the application of novel few-layered TiS₃ nanoribbons material as a channel material in electrolyte-gated field-effect transistor immunosensor for rapid detection of CA 19-9 antigen as a cancer marker. Accordingly, TiS₃ nanoribbons were produced through liquid-phase exfoliation of as-synthesized TiS₃ whiskers in N, N-dimethylformamide. Then, dispersed TiS₃ nanoribbons were drop cast onto the FET surface to form an active channel material between source and drain electrodes. Subsequently, the channel surface was modified by utilizing 1-naphthylamine (NA) and glutaraldehyde (GA) to strengthen the binding of monoclonal antibody 19-9 to TiS₃ nanoribbons. Spectroscopic and microscopic methods were utilized for comprehensive characterizations. Electrical characterization of electrolyte-gated TiS₃ nanoribbons field-effect transistor represented a depletion-mode n-type behavior with field-effect mobility of 0.059 cm²/Vs, current on/off ratio of 10.88 and subthreshold swing (SS) of 450.9 mV/decade. With increasing in CA 19-9 antigen concentration from 1.0 × 10^-12 U/mL to 1.0 × 10^-5 U/mL, a decrease in the drain current occurred with high sensitivity of 0.04 μA/decade and a detection limit of 1.3 × 10^-13 U/mL. Additionally, the proposed TiS₃ nanoribbons FET immunosensor exhibited outstanding selectivity, and its good performance was compared with an enzyme-linked immunosorbent assay (ELISA) for spiked real human serum samples. The good and satisfactory obtained results of the proposed immunosensor suggest that the developed platform can be a superb candidate for cancer diagnosis and therapeutic monitoring.

Washing-free electrogenerated chemiluminescence magnetic microbiosensors based on target assistant proximity hybridization for multiple protein biomarkers

This work reports washing-free electrogenerated chemiluminescence (ECL) magnetic microbiosensors based on target assistant proximity hybridization (TAPH) for multiple protein biomarkers for the first time. As a principle-of-proof, alpha-fetoprotein (AFP) was chosen as a model analyte, and biotin-DNA1 bound streptavidin-coated magnetic microbeads (MMB@SA⋅biotin-DNA1) were designed as the universal capture MMB, while the corresponding two antibodies tagged with DNA2 or DNA3 were utilized as hybrid recognition probes, and ruthenium complex-tagged DNA4-10A was designed as a universal ECL signal probe. When the capture MMB was added into the mixture solution (containing the analyte, hybrid recognition probes, signal probe and tri-n-propylamine), biocomplexes were formed on the MMB. After the resulting MMB was efficiently brought to the surface of a magnetic glassy carbon electrode (MGCE), ECL measurement was performed without a washing step, resulting in an increase in the ECL intensity. A model for ECL measuring the second-order rate constants of hybridization reactions on MMB was derived. It was found that the rate constants for hybridization reactions on MMB in rotating mode are 1.6-fold higher than those in shaking mode, and a suitable DNA length of the signal probe can improve the signal-to-noise ratio. The washing-free ECL method was developed for the determination of AFP with a much lower detection limit (LOD) of 0.04 ng mL^-1. The developed flexible strategy has been extended to determine D-dimer with an LOD of 0.1 ng mL^-1 and myoglobinglobin with an LOD of 1.1 ng mL^-1. This work demonstrated that the proposed strategy of ECL TAPH on MMB at MGCE is a washing-free and flexible promising strategy, and can be extended to qualify other multiple protein biomarkers in real clinical assays.

An electrochemiluminescence immunosensor based on signal magnification of luminol using OER-activated NiFe2O4@C@CeO2/Au as effective co-reaction accelerator

In this work, a novel, label-free electrochemiluminescence (ECL) immunosensor was constructed for the ultrasensitive detection of carbohydrate antigen 15-3 (CA15-3) by the combined use of NiFe₂O₄@C@CeO₂/Au hexahedral microbox and luminol luminophore. The synthesis of the co-reaction accelerator (NiFe₂O₄@C@CeO₂/Au) was related to the calcination of FeNi-based metal-organic framework (MOF), as well as the ingrowth of CeO₂ nanoparticles and modification of Au nanoparticles. To be specific, the electrical conductivity will be boosted due to the Au nanoparticles, the synergetic effect generated between CeO₂ and calcination FeNi-MOF could offer better activity of oxygen evolution reaction (OER). Herein, the NiFe₂O₄@C@CeO₂/Au hexahedral microbox as a co-reaction accelerator has excellent OER activity and production of reactive oxygen species (ROS), thus increasing the ECL intensity of luminol in a neutral medium without other co-reactants such as H₂O₂. Because of these benefits, the constructed ECL immunosensor was applied to detect CA15-3 as an example under optimum conditions, the designed ECL immunosensor exhibited high-level selectivity and sensitivity for CA15-3 biomarker within a linear response range of 0.01-100 U mL^-1 and an ultralow detection limit of 0.545 mU mL^-1 (S/N = 3), demonstrating its potentially valuable application in the area of clinical analysis.

Development of sandwich electrochemiluminescence immunosensor for COVID-19 diagnosis by SARS-CoV-2 spike protein detection based on Au@BSA-luminol nanocomposites

Coronavirus disease (COVID-19) is a new and highly contagious disease posing a threat to global public health and wreaking havoc around the world. It's caused by the Coronavirus that causes severe acute respiratory syndrome (SARS-CoV-2). In the current pandemic situation, rapid and accurate SARS-CoV-2 diagnosis on a large scale is critical for early-stage diagnosis. Early detection and monitoring of viral infections can aid in controlling and preventing infection in large groups of people. Accordingly, we developed a sensitive and high-throughput sandwich electrochemiluminescence immunosensor based on antigen detection for COVID-19 diagnosis (the spike protein of SARS-CoV-2). For the spike protein of SARS-CoV-2, the ECL biosensor had a linear range of 10 ng mL^-1 to 10 µg mL^-1 with a limit of detection of 1.93 ng mL^-1. The sandwich ECL immunosensor could be used in early clinical diagnosis due to its excellent recovery in detecting SARS-CoV-2, rapid analysis (90 min), and ease of use.

Simple synthesis of PtRu nanoassemblies as signal amplifiers for electrochemical immunoassay of carbohydrate antigen 19-9

In clinical analysis, carbohydrate antigen 19-9 (CA199) is a gold standard for pancreatic cancer diagnosis. Herein, PtRu nanoassemblies (NAs) were synthesized via a facile one-step solvothermal approach, with the help of octylphenoxypolye thoxyethanol (NP-40) acted as a growth-directing molecule, and triethylene glycol (TEG) worked as a reductant and solvent. During the assembly process of small particles, a large number of voids were formed, which significantly increase the specific surface area of the PtRu NAs exhibiting excellent electrocatalytic performance. Incorporating the PtRu NAs as signal amplifiers for potassium ferrocyanide oxidation into the specific molecular recognition of proteins, a facile signal-enhanced electrochemical (EC) immunosensor was developed. Verified by a series of experiments, the proposed immunosensor presented a wide linear range (10^-4-70 U mL^-1) and a low detection limit (3.3 × 10^-5 U mL^-1), accompanied by good reproducibility, selectivity, and stability, which could be applied in human serum samples for the determination of CA199, and was comparable to commercial electrochemiluminescence (ECL) immunoassay. Feasibility of batch fabrication of PtRu NAs makes nanomaterial-based EC immunoassay promising for the determination of similar cancer markers in future.

Nanotechnology-based approaches for effective detection of tumor markers: A comprehensive state-of-the-art review

As well-appreciated biomarkers, tumor markers have been spotlighted as reliable tools for predicting the behavior of different tumors and helping clinicians ascertain the type of molecular mechanism of tumorigenesis. The sensitivity and specificity of these markers have made them an object of even broader interest for sensitive detection and staging of various cancers. Enzyme-linked immunosorbent assay (ELISA), fluorescence-based, mass-based, and electrochemical-based detections are current techniques for sensing tumor markers. Although some of these techniques provide good selectivity, certain obstacles, including a low sample concentration or difficulty carrying out the measurement, limit their application. With the advent of nanotechnology, many studies have been carried out to synthesize and employ nanomaterials (NMs) in sensing techniques to determine these tumor markers at low concentrations. The fabrication, sensitivity, design, and multiplexing of sensing techniques have been uplifted due to the attractive features of NMs. Various NMs, such as magnetic and metal nanoparticles, up-conversion NPs, carbon nanotubes (CNTs), carbon-based NMs, quantum dots (QDs), and graphene-based nanosensors, hyperbranched polymers, optical nanosensors, piezoelectric biosensors, paper-based biosensors, microfluidic-based lab-on-chip sensors, and hybrid NMs have proven effective in detecting tumor markers with great sensitivity and selectivity. This review summarizes various categories of NMs for detecting these valuable markers, such as prostate-specific antigen (PSA), human carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), human epidermal growth factor receptor-2 (HER2), cancer antigen 125 (CA125), cancer antigen 15-3 (CA15-3, MUC1), and cancer antigen 19-9 (CA19-9), and highlights recent nanotechnology-based advancements in detection of these prognostic biomarkers.

Graphdiyne nanosheet as a novel sensing platform for self-enhanced electrochemiluminescence of MOF enriched ruthenium (II) in the presence of dual co-reactants for detection of tumor marker

Graphdiyne (GDY) is a new two-dimensional carbon material with high charge carrier mobility, excellent conductivity, more suitable band gap, and natural pores was introduced as a new electrochemiluminescent sensing platform. Herein, the metal organic framework (MOFs) used for enrichment of luminophore with grafting Ru(bpy)₂(phen-NH₂)²⁺(Ru-complex) and Ru-complex amine-rich nitrogen-doped carbon nanodots(Ru-NCNDs) via both encapsulating and external decoration and decoration of SmS₂ QDs as coreactant. Then, the MOF enriched Ru-complex (Ru@MOF@NCNDs-Ru@SmS₂ QD) located on a GDY modified ITO electrode developed as a novel and efficient ECL platform. According to the Density Functional Theory (DFT) calculation, the band gap of graphdiyne/Ru(bpy)₂(phen-NH₂)²⁺ system decreased compared to graphdiyne, Ru-complex and also graphene oxide/Ru(bpy)₂(phen-NH₂)²⁺system, which enhanced (2 folds) the signal response of the presented ECL platform. The ECL response signal of the suggested emitter with high ECL efficiency (13.34%) increased 8 and 4 folds compared to GDY/Ru-NCNDs and GDY/Ru@MOF@NCNDs-Ru as platforms, respectively. The proposed ECL platform applied for CA19-9 antigens detection at concentration range 0.0005 UmL^-1 to 200 UmL^-1 and detection limit of 0.00013 UmL^-1.The development of GDY based platform for decorating nano luminophores, not only provides the design of ECL luminophores with high performance but also promises the application of the presented strategy for fabrication of ultrasensitive bio affinity sensors as candidates in clinical monitoring and diseases diagnostics.

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.

Combined Detection of CA19-9 and MUC1 Using a Colorimetric Immunosensor Based on Magnetic Gold Nanorods for Ultrasensitive Risk Assessment of Pancreatic Cancer

We herein report a facile approach for developing an enzyme-free colorimetric immunosensor based on a magnetic iron oxide (IO)-coated gold nanorod (MGNR) nanocomposite with high electron transfer ability to accelerate the color bleaching reaction of methyl orange (MO) in the presence of NaBH₄ for ultrasensitive detection of cancer antigens. In the case of MO, the reaction rate of MGNRs showed approximately 45.6-fold and 1520.8-fold higher than that of Cys-GNRs and NaBH₄, respectively. The proposed colorimetric immunosensor was demonstrated to enable simple, cost-effective, sensitive, and specific carbohydrate antigen 19-9 (CA19-9) and mucin 1 (MUC1) detection for risk evaluation of pancreatic cancer (PC) with a small volume of serum sample without the use of any enhancing solutions or enzymes. By increasing the concentration of CA19-9 and MUC1, more MGNRs remained in the plate well to enhance the color bleaching of MO. As a proof-of-concept, the limit of detection (LOD) of 3.5 × 10^-5 U/mL for CA19-9 and 5.2 × 10^-6 U/mL for MUC1 was obtained with a wide linear quantification range from 8.6 × 10^-5 U/mL to 1.4 × 10^-2 U/mL for CA19-9 and 1.3 × 10^-5 U/mL to 2.1 × 10^-3 U/mL for MUC1, suggesting potential clinical applications for the early risk evaluation of PC.

In situ H2O2 generation with gold nanoflowers as the coreactant accelerator for enzyme-free electrochemiluminescent immunosensing

In traditional electrochemiluminescence (ECL) analysis, gold nanomaterials are commonly used as a tool for signal amplification and linking antibodies due to their good electrical conductivity and biocompatibility. Here, we found that multitipped gold nanoparticles-gold nanoflowers (AuNFs) as coreactant accelerator have good catalytic activity for the reduction of dissolved oxygen (O₂) to hydrogen peroxide (H₂O₂) using tris (hydroxymethyl) aminomethane (Tris) as electron donor. Based on this, a new enzyme-free and label-free ECL immunosensor have been constructed for the detection of α-fetoprotein (AFP). In this system, due to the unique geometric and spatial effects of AuNFs, the dissolved O₂ as endogenous coreactant was catalyzed by AuNFs to produce H₂O₂ using Tris as an electron donor. The in situ generated H₂O₂ can more efficiently produce various electrogenerated reactive oxygen species (ROSs) as the important intermediates on the electrode surface. Then, oxidation of luminol reacts with ROSs significantly amplifies the luminol ECL signal. Under optimal experimental conditions, the proposed ECL immunosensor was able to detect the AFP concentration from 0.01 to 100 ng mL^-1, with a low detection limit of 3.4 pg mL^-1 (S/N = 3). In addition, the prepared ITO-based sensor is similar to a micro-test chip and convenient to use, thus making it suitable for clinical use as a disposable device in point-of-care tests (POCTs).

Bimetallic cerium and ferric oxides nanoparticles embedded within mesoporous carbon matrix: Electrochemical immunosensor for sensitive detection of carbohydrate antigen 19-9

A label-free electrochemical immunosensor was successfully developed for sensitively detecting carbohydrate antigen 19-9 (CA19-9) as a cancer marker. To achieve this, a series of bimetallic cerium and ferric oxide nanoparticles embedded within the mesoporous carbon matrix (represented by CeO₂/FeO_x@mC) was obtained from the bimetallic CeFe-based metal organic framework (CeFe-MOF) by calcination at different high temperatures. The formed CeO₂ or FeO_x nanoparticles were uniformly distributed within the highly graphitized mesoporous carbon matrix at the calcination temperature of 500 °C (represented by CeO₂/FeO_x@mC₅₀₀). However, the obtained nanoparticles were aggregated into large size when calcined at the temperatures of 700 and 900 °C. The CA 19-9 antibody can be anchored to the CeO₂/FeO_x@mC network through chemical absorption between carboxylic groups of antibody and CeO₂ or FeO_x by ester-like bridging. The CeO₂/FeO_x@mC₅₀₀-based immunosensor displayed superior sensing performance to the pristine CeFe-MOF, CeO₂/FeO_x@mC₇₀₀- and CeO₂/FeO_x@mC₉₀₀-based ones. Electrochemical impedance spectroscopy results showed that the developed immunosensor exhibited an extremely low detection limit of 10 μU·mL^-1 (S/N = 3) within a wide range from 0.1 mU·mL^-1 to 10 U·mL^-1 toward CA 19-9. It also illustrated excellent specificity, good reproducibility and stability, and acceptable application analysis in the human serum solution which was diluted 100-fold with 0.01 M PBS solution (pH 7.4) and spiked with different amounts of CA19-9. Consequently, the proposed electrochemical immunosensor is capable enough of determining CA 19-9 in clinical diagnostics.

A Novel Carbon Quantum Dots Signal Amplification Strategy Coupled with Sandwich Electrochemiluminescence Immunosensor for the Detection of CA15-3 in Human Serum

A sensitive sandwich electrochemiluminescence immunosensor was established by employing graphene oxide-PEI-carbon quantum dots (CQDs)-Au nanohybrid as probe to measure carbohydrate antigen 15-3 (CA15-3), a breast cancer biomarker. In this work, nanocomposites of Ag nanoparticles and polydopamine (AgNPs-PDA) were synthesized by redox reaction between dopamine and Ag⁺. The nanocomposite with high surface area can provide an efficient substrate for immobilizing initial antibody (Ab1). Carbon quantum dots (CQDs) are fixed on polyethylenimine-functionalized graphene oxide (PEI-GO) by amide bonds. Au nanoparticles are modified on CQDs-decorated PEI-GO substrates. The secondary antibody (Ab2) was immobilized by AuNPs/CQDs-PEI-GO composite. CQDs can be assembled onto the surface of an electrode by incorporation of CA15-3 with Ab1 and Ab2. Under the synergistic action of AgNPs, polydopamine, AuNPs, and PEI-GO, the ECL signal of CQDs is greatly amplified as an excellent conductive material to facilitate electron transfer rate and further increase electrochemical detection capability. Under optimal conditions, the fabricated immunosensor showed a linear concentration range from 0.005 to 500 U mL^-1, with a detection limit of 0.0017 U mL^-1 (signal-to-noise ratio of 3) for CA15-3. The designed ECL immunosensor displayed receivable accuracy, excellent stability, and high specificity. The results of the detection of human serum samples are satisfactory, revealing that the method offers a potential application for the clinical diagnosis of tumor markers.

A simple and sensitive electrochemiluminescence aptasensor for determination of ochratoxin A based on a nicking endonuclease-powered DNA walking machine

Ochratoxin A (OTA) poses a serious threat to the health of human beings and animals. In this paper, a simple and sensitive electrochemiluminescence (ECL) aptasensor was constructed to detect OTA based on electrochemiluminescence resonance energy transfer (ECL-RET) and a nicking endonuclease-powered DNA walking machine. Originally, the signal of cadmium sulfide semiconductor quantum dots (CdS QDs) was quenched efficiently by Cy5. After the addition of OTA, the walker autonomously hybridized with Cy5-labeled DNA and released plenty of Cy5-DNA from the electrode surface with the help of a nicking endonuclease. As a result, the signal of CdS QDs recovered efficiently. As an artificial and popular signal amplification technique, the DNA walking machine greatly improved the sensitivity. Under optimal conditions, the aptasensor not only detected OTA in a linear range from 0.05 nM to 5 nM with a detection limit of 0.012 nM (S/N = 3), but also showed an excellent selectivity for OTA over other mycotoxins.

A highly sensitive and reliable detection of CA15-3 in patient plasma with electrochemical biosensor labeled with magnetic beads

An early on-time detection of breast cancer can effectively affect the outcome of the treatment. Here, we developed an ultrasensitive, simple and reliable immunosensor to detect the lowest alteration of CA 15-3, the standard biomarker of breast cancer patients. The proposed immunosensor was achieved by modification of gold electrode by streptavidin to immobilize the biotinylated anti-CA 15-3 monoclonal antibody (mAb). Bovine serum albumin was used to prevent nonspecific binding. To improve the sensitivity of modified immunosensor, the sandwich signal enhancer consisting of streptavidin-coated magnetic beads conjugated with biotinylated horseradish peroxidase (HRP) and anti-CA 15-3 biotinylated mAb was applied. The electrochemical measurements were obtained in the presence of hydroquinone as a redox agent and H₂O₂ as the activating agent of HRP. Under optimized condition and using square wave voltammetry, the lower limit of quantification was obtained as 15 × 10^-6 U/mL and the linear CA 15-3 concentration range was 50-15 × 10^-6 U/mL. While showing significant stability, the immunosensor displayed an excellent sensitivity and specificity for the detection of CA 15-3 even in the human serum as compared to the enzyme-linked immunosorbent assay (ELISA) as a gold standard method. Based on our findings, the engineered immunosensor is proposed as a robust diagnostic tool for the clinical determination of CA 15-3 and other cancer biomarkers.

Immunosensor for Pancreatic Cancer Based on Electrospun Nanofibers Coated with Carbon Nanotubes or Gold Nanoparticles

We report the fabrication of immunosensors based on nanostructured mats of electrospun nanofibers of polyamide 6 and poly(allylamine hydrochloride) coated either with multiwalled carbon nanotubes (MWCNTs) or gold nanoparticles (AuNPs), whose three-dimensional structure was suitable for the immobilization of anti-CA19-9 antibodies to detect the pancreatic cancer biomarker CA19-9. Using impedance spectroscopy, the sensing platform was able to detect CA19-9 with a detection limit of 1.84 and 1.57 U mL-1 for the nanostructured architectures containing MWCNTs and AuNPs, respectively. The high sensitivity achieved can be attributed to the irreversible adsorption between antibodies and antigens, as confirmed with polarization-modulated infrared reflection absorption spectroscopy. The adsorption mechanism was typical Langmuir-Freundlich processes. The high sensitivity and selectivity of the immunosensors were also explored in tests with blood serum from patients with distinct concentrations of CA19-9, for which the impedance spectra data were processed with a multidimensional projection technique. The robustness of the immunosensors in dealing with patient samples without suffering interference from analytes present in biological fluids is promising for a simple, effective diagnosis of pancreatic cancer at early stages.

An ultrasensitive multi-walled carbon nanotube–platinum–luminol nanocomposite-based electrochemiluminescence immunosensor

An ultrasensitive electrochemiluminescence (ECL) immunosensor for carbohydrate antigen 19-9 (CA19-9) detection using multi-walled carbon nanotube–platinum–luminol nanocomposites (MWCNT–Pt–luminol) as nanointerface and signal tags was designed.

Silver-functionalized g-C3N4 nanohybrids as signal-transduction tags for electrochemical immunoassay of human carbohydrate antigen 19-9

A simple and feasible electrochemical immunosensing platform was developed for highly efficient screening of a disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case) using silver-functionalized g-C3N4 nanosheets (Ag/g-C3N4) as signal-transduction tags. Initially, Ag/g-C3N4 nanohybrids were synthesized by combining thermal polymerization of the melamine precursor with the photo-assisted reduction method. Thereafter, the as-synthesized Ag/g-C3N4 nanohybrids were utilized for the labeling of the anti-CA 19-9 detection antibody by using a typical carbodiimide coupling method. The assay was carried out on a capture antibody-modified glassy carbon electrode in a sandwich-type detection mode. The detectable signal mainly derived from the voltammetric characteristics of the immobilized nanosilver particles on the g-C3N4 nanosheets within the applied potentials. Under the optimal conditions, the voltammetric peak currents increased with the increasing amount of target CA 19-9, and exhibited a wide linear range from 5.0 mU mL(-1) to 50 U mL(-1) with a detection limit of 1.2 mU mL(-1). Our strategy also displayed good reproducibility, precision and specificity. The results of the analysis of clinical serum specimens were in good accordance with the results obtained by an enzyme-linked immunosorbent assay (ELISA) method. The newly developed immunosensing system is promising for enzyme-free and cost-effective analysis of low-abundance proteins.

Sensitive electrochemical immunoassay with signal enhancement based on nanogold-encapsulated poly(amidoamine) dendrimer-stimulated hydrogen evolution reaction

A new electrochemical immunosensor with signal enhancement was designed for sensitive detection of disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case).