Electrochemical immunoassay for the carcinoembryonic antigen based on the use of a glassy carbon electrode modified with an octahedral Cu2O-gold nanocomposite and staphylococcal protein for signal amplification

Detection of receptor tyrosine kinase-orphan receptor-2 using an electrochemical immunosensor modified with electrospun nanofibers comprising polyvinylpyrrolidone, soy, and gold nanoparticles

An electrochemical immunosensing platform was developed for the detection of receptor tyrosine kinase-orphan receptor-2 (ROR2) at a glassy carbon electrode (GCE) modified with the electrospun nanofiber containing polyvinylpyrrolidone (PVP), soy, and Au nanoparticles (AuNPs). The PVP/soy/AuNP nanofiber exhibited good electrochemical behavior due to synergistic effects between PVP, soy, and AuNPs. The PVP/soy in the modified film provided good mechanical strength, high porosity, flexible structures, and high specific surface area. On the other hand, the presence of AuNPs effectively improved conductivity, as well as the immobilization of anti-ROR2 on the modified GCE, leading to enhanced sensitivity. Various characterization approaches such as FE-SEM, FTIR, and EDS were used for investigating the morphological and structural features, and the elemental composition. The designed immunosensor performance was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Under optimum conditions with a working potential range from -0.2 to 0.6 V (vs. SCE), sensitivity, linear range (LR), limit of detection (LOD), and correlation coefficient (R2) were acquired at 122.26 μA/cm2 dec, 0.01-1000 pg/mL, 3.39 fg/mL, and 0.9974, respectively. Furthermore, the determination of ROR2 in human plasma samples using the designed immunosensing platform was examined and exhibited satisfactory results including good selectivity against other proteins, reproducibility, and cyclic stability.

Electrogenerated chemiluminescence resonance energy transfer between luminol and MnO2 nanosheets decorated with Cu2O nanoparticles for sensitive detection of RNase H

In the present work, a novel approach was developed for the preparation of Cu₂O nanoparticle decorated MnO₂ nanosheets (Cu₂O@MnO₂). Uniformly dispersed Cu₂O nanocrystals were produced on the surface of MnO₂ nanosheets by in situ reduction under refluxing conditions. The unique structure of the used MnO₂ nanosheet support played a vital role in the preparation of such Cu₂O@MnO₂ nanocomposites. The electrogenerated chemiluminescence (ECL) resonance energy transfer can occur between the luminol/H₂O₂ system and Cu₂O@MnO₂ nanocomposites, resulting in a decrease of the ECL intensity, which can be used to fabricate an ECL sensor. Cu₂O@MnO₂ nanocomposite modified heterologous DNA/RNA duplexes were modified on the GCE to construct an ECL-RET system, leading to the decrease of ECL intensity. As a highly conserved damage repair protein, RNase H can specifically hydrolyze RNA in DNA/RNA strands to release Cu₂O@MnO₂ nanocomposites and recover the ECL signal. As a result, an "off-on" mode ECL sensor for sensitive RNase H assay was fabricated. Under the optimal conditions, the detection limit of RNase H is 0.0005 U mL^-1, which is superior to other approaches. The proposed method provides a universal platform for monitoring RNase H, and exhibits great potential in bioanalysis.

Highly Sensitive Detection of Carcinoembryonic Antigen via an Electrochemical Platform Fabricated by AuNPs/Streptavidin/Reduced Graphene Oxide

Tumor markers are one of the important indicators for early cancer diagnosis. As a new analytical method, electrochemical immunosensing analysis has the advantages of high sensitivity, good selectivity, and rapid detection, which is of great significance for the detection of tumor markers. In this work, an AuNP/reduced graphene oxide (AuNP/rGO) composite was synthesized. We used it for electrochemical sensor fabrication with the assistance of the biotin–streptavidin protein (SA) system to further amplify the signal to achieve sensitive detection of carcinoembryonic antigen (CEA). In addition, AuNPs have been incorporated due to their good electrical conductivity and biocompatibility, which can accelerate electron transfer at the electrode interface and improve the loading capacity to capture antibodies. The fabricated AuNPs/SA/rGO has a large working surface area and high material utilization ratio, which improves the catalytic capacity of H₂O₂ reduction and effectively amplifies the current signal. The linear range of the response current signal of the sensor toward the CEA concentration is 20 fg/ml to 200 ng/ml, and the limit of detection can achieve 6.2 fg/ml. In addition, the fabricated immunosensor has good reproducibility, selectivity, and stability.

Ultrasensitive and label free electrochemical immunosensor for detection of ROR1 as an oncofetal biomarker using gold nanoparticles assisted LDH/rGO nanocomposite

In the present article, we developed a highly sensitive label-free electrochemical immunosensor based on NiFe-layered double hydroxides (LDH)/reduced graphene oxide (rGO)/gold nanoparticles modified glassy carbon electrode for the determination of receptor tyrosine kinase-like orphan receptor (ROR)-1. In this electrochemical immunoassay platform, NiFe-LDH/rGO was used due to great electron mobility, high specific surface area and flexible structures, while Au nanoparticles were prepared and coated on the modified electrodes to improve the detection sensitivity and ROR1 antibody immobilizing (ROR1Ab). The modification procedure was approved by using cyclic voltammetry and differential pulse voltammetry based on the response of peak current to the step by step modifications. Under optimum conditions, the experimental results showed that the immunosensor revealed a sensitive response to ROR1 in the range of 0.01-1 pg mL^-1, and with a lower limit of quantification of 10 attogram/mL (10 ag mL^-1). Furthermore, the designed immunosensor was applied for the analysis of ROR1 in several serum samples of chronic lymphocytic leukemia suffering patients with acceptable results, and it also exhibited good selectivity, reproducibility and stability.

A novel electrochemical immunosensor for the sensitive detection of tiamulin based on staphylococcal protein A and silver nanoparticle-graphene oxide nanocomposites

Tiamulin (TML) is a pleuromutilin antibiotic and mainly used to treat pulmonary and gastrointestinal infections. However, excessive use of TML can bring health threats to consumers. In this work, a label-free electrochemical immunosensor was proposed for sensitive detection of TML in pork and pork liver. Silver nanoparticles (AgNPs) were synthesized in situ on graphene oxide (GO), in which GO acted as a carrier for loading more AgNPs and AgNPs exhibited both strong conductivity and good redox property. In addition, staphylococcal protein A (SPA) was applied to oriented immobilization of fragment crystallizable (Fc) region of the TML monoclonal antibody. Under the optimal condition, the developed electrochemical immunosensor exhibited a good linear response with a concentration of TML ranging from 0.05 ng mL^-1 to 100 ng mL^-1 and the limit of detection (LOD) was 0.04 ng mL^-1. Furthermore, the designed immunosensor was applied to detect TML in real samples with a good accuracy. Therefore, the label-free electrochemical immunosensor could be used as a potential method to detect TML and other antibiotic residues in animal derived foods.

Construction of electrochemical aptasensor of carcinoembryonic antigen based on toehold-aided DNA recycling signal amplification

Carcinoembryonic antigen (CEA), serves as a broad-spectrum tumor marker, and plays an important role in reflecting the existence, therapeutic evaluation, development, monitoring and prognosis of many types of cancer. An electrochemical aptasensor was designed for CEA detection based on toehold-aided DNA recycling. A partially hybridized Probe-4 (i.e. P2/P3/P4) was self-assembled on the surface of a gold electrode serving as the sensing platform. For CEA detection, CEA can bind with aptamer and free probe-1 (P1) can hybridize with P4, triggering toehold-aided DNA recycling. This enables the hybridization of more probe-5 (P5) (labeled with methylene blue (MB)) with P4, causing more methylene blue (MB) to be brought close to the electrode surface. An amplified current signal was thus generated due to more MB in the electrode surface. The proposed design showed good linearity between current response and log CEA concentration ranging from 0.1 to 50 ng·mL^-1, with a detection limit of 20 pg mL^-1. This aptasensor also showed high specificity for CEA detection, and was successfully used in spiked biological samples.

Design of organic/inorganic nanocomposites for ultrasensitive electrochemical detection of a cancer biomarker protein

A new type of nanocomposite composed of carboxylated single-walled carbon nanotubes (CNTs-COOH), reduced graphene oxide (rGO), bovine serum albumin-Ag hybride (Ag@BSA), and poly(3,4-ethylenedioxythiophene) (PEDOT) was fabricated to develop an ultrasensitive electrochemical platform for the detection of carcinoembryonic antigen (CEA) as a model of biomarkers. Two steps are involved for the fabrication of the organic/inorganic nanocomposites. The Ag@BSA nanoflowers were first synthesized to be doped with CNTs-COOH and rGO followed by the adsorption of PEDOT resulting in CNTs-COOH/rGO/Ag@BSA/PEDOT. The as-prepared nanocomposites were then deposited onto an Au electrode together with subsequent immobilization of CEA antibody (anti-CEA) to construct the electrochemical immunosensor. This unique structure and composition of the developed immunosensor can expect an excellent electrochemical response. The immunosensor offers a linear relationship between the electrochemical responses and the CEA concentrations from 0.002 to 50 ng∙mL^-1 with a detection limit of 1 × 10^-4 ng∙mL^-1. Moreover, the ultrasensitive immunoassay can detect CEA in real human serum samples, and the results are comparable to those obtained from the commercial ELISA. Therefore, this strategy can monitor diseases, offer clinical diagnosis, and may be valuable for the development of new biomedical devices.

Microstructure evolution of sandwich graphite oxide/interlayer-embedded Au nanoparticles induced from γ-rays for carcinoembryonic antigen biosensor

With the capability of inducing small particle sizes of supported metal in graphite oxide (GO), the γ-ray irradiation method applied for preparing graphite oxide-gold (GO-Au) nanocomposites as electrochemical immunosensors has attracted specific attention recently. To study the accurate factors influencing the precise morphology and final performance of the prepared composites in the γ-irradiation system, we proposed a facile method to investigate the evolution of the GO structure, size and dispersion of Au nanoparticles (AuNPs) produced with the addition of isopropyl alcohol to the system. The GO-Au nanocomposites were characterized by Fourier transform infrared spectroscopy, x-ray diffraction spectra, Raman spectra, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. These nanocomposites with sandwich morphology exhibited an excellent immunosensor performance with a low detection limit of 15.8 pg ml^-1 (S/N = 3) and a wide linear range from 1 to 40 ng ml^-1 for detecting carcinoembryonic antigens. The enhanced biosensing performance is attributed to the synergistic effect of γ-irradiation and the precise structure of GO, which endows the smaller size and more uniform distribution of AuNPs on the GO as well as the good signal amplification capability. Furthermore, adopting the γ-irradiation method and use of GO as a precursor is propitious for application in large-scale production because of its high-efficiency and high-yielding characteristics.

Gold/WS2 nanocomposites fabricated by in-situ ultrasonication and assembling for photoelectrochemical immunosensing of carcinoembryonic antigen

Tungsten disulfide (WS₂) nanosheets were obtained by exfoliating WS₂ bulk crystals in N-methylpyrrolidone by ultrasonication. Gold nanoparticles (GNPs) were synthesized by in-situ ultrasonication of sodium citrate and HAuCl₄ while fabricating the WS₂ nanosheets. In this way, the GNPs were self-assembled on WS₂ nanosheets to form a GNPs/WS₂ nanocomposite through interaction between sulfur and gold atoms. The photoelectrochemical response of WS₂ nanosheets is significantly enhanced after integration of the GNPs. The GNPs/WS₂ nanocomposite was coated onto a glassy carbon electrode (GCE) to construct a sensing interface which then was modified with an antibody against the carcinoembryonic antigen (CEA) to obtain a photoelectrochemical immunosensor for CEA. Under optimized conditions, the decline in relative photocurrent is linearly related to the logarithm of the CEA concentration in the range from 0.001 to 40 ng mL^-1. The detection limit is 0.5 pg mL^-1 (at S/N = 3). The assay is sensitive, selective, stable and reproducible. It was applied to the determination of CEA in clinical serum samples. Graphical abstract Schematic presentation of the fabrication of Au/WS₂ nanocomposites by in-situ ultrasonication and the procedure for the CEA photoelectrochemical immunosensor preparation, and the photocurrent response towards the carcinoembryonic antigen.