Porous platinum nanoparticles and PdPt nanocages for use in an ultrasensitive immunoelectrode for the simultaneous determination of the tumor markers CEA and AFP

3-Polythiophene Acetic Acid Nanosphere Anchored Few-Layer Graphene Nanocomposites for Label-Free Electrochemical Immunosensing of Liver Cancer Biomarker

This study devised a label-free electrochemical immunosensor for the quantitative detection of alpha-fetoprotein (AFP). 3-Polythiophene acetic acid (3-PTAA) nanoparticles were anchored onto a few-layer graphene (FLG) nanosheet, and the resulting nanocomposite was utilized as the immunosensor platform. The AFP antibody (anti-AFP) was immobilized on 3-PTAA@FLG via a covalent interaction between the amine group of anti-AFP and the carboxylic group of 3-PTAA via ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling. FLG is largely responsible for providing electrochemical signals, whereas 3-PTAA nanoparticles are well-known for their ability to be compatible with biological molecules in neutral aqueous solutions. Moreover, the carboxyl group present in 3-PTAA effectively binds anti-AFP through EDC/NHS conjugation. Owing to good dispersibility and higher surface area of 3-PTAA, it is very convenient for casting the polymer directly on the electrode substrate followed by immobilization of anti-AFP. Thus, it is feasible to regulate the activity of AFP proteins and control the spatial distribution of the immobilized anti-AFP proteins. The electrochemical sensing performance was assessed via cyclic voltammetry and electrochemical impedance spectroscopy. For an increase in the bioconjugate concentration, the results demonstrated a surge in charge-transfer resistance and a consequent decline in the current response. This approach effectively detected AFP at an extended dynamic range of 0.0001-250 ng/mL with a detection limit of 0.047 pg/mL. Furthermore, the sensing capacity of the immunosensor for AFP detection has been demonstrated to be steady in real human serum cultures. Our approach exhibits good electrochemical performance in terms of reproducibility, selectivity, and stability, which would surely impart budding applications in the clinical diagnosis of several other tumor markers.

Performance Enhancement of Electrochemiluminescence with the Immunosensor Controlled Using Magnetized Masks for the Determination of Epithelial Cancer Biomarker EpCAM

The performance of an electrochemiluminescence (ECL) immunosensor was improved with a particle gradient. SiO₂-coated magnetic beads were adopted as nanocarriers for gradient manipulation and immobilized with the primary antibody. Cadmium telluride quantum dots were coated with a layer of protein G for conjugation and orientation of the secondary antibody as signal labels. ECL immunosensor gradients on the electrode were formed by magnetolithography (ML) with magnetized nickel masks of column and stripe arrays. The immunosensor generally aggregated as an island on the substrate, leading to a decrease of efficiency in the characteristic signals. Stripe arrays of magnetized nickel were designed to generate cylindrical magnetic flux on the substrate to improve the particle manipulation with the gradient. Various gradients of the sandwich-structured immunosensor substantially affected the electrochemical performance. Compared to the gradient-free immunosensor, the gradient of the immunosensor generated by ML using a 3 μm stripe array mask enhanced the ECL intensity ∼2.2 times. The results of quantification of epithelial cell adhesion molecules (EpCAM) with the gradient immunosensor showed a broad linear range (15-420 pg mL^-1), a low limit of detection (5.5 pg mL^-1), and high reliability for EpCAM-spiked serum samples, indicating that the immunosensor gradient substantially enhances the performance of the ECL assay.

Ultrasensitive multiplex SERS immunoassay based on porous Au-Ag alloy nanoparticle-amplified Raman signal probe and encoded photonic crystal beads

An ultrasensitive multiplex surface-enhanced Raman scattering (SERS) immunoassay was developed using porous Au-Ag alloy nanoparticles (p-AuAg NPs) as Raman signal amplification probe coupling with encoded photonic crystal microsphere. p-AuAg NPs were synthesized and modified with the second antibody (Ab₂) and Raman tag (mercaptobenzoic acid, MBA) to prepare a Raman signal-amplified probe. The high porosity of the p-AuAg NPs enables significant coupling of the localized surface plasmon resonance and thus abundant inherent hotspots for Raman signal enhancement. 3D-ordered silver nanoparticles-coated silica photonic crystal beads (Ag/SPCBs) were prepared as encoded SERS substrate for multiplex detection using their reflection peaks. The signal-amplified probe was used for multiplex detection of tumor markers carcinoembryonic antigen (CEA) and alpha fetoprotein (AFP). The wide linear ranges of 10^-7-10³ ng/mL for CEA and 10^-4-10³ ng/mL for AFP with detection limits of 1.22 × 10^-8 ng/mL and 2.47 × 10^-5 ng/mL for CEA and AFP at a signal-to-noise ratio of 3 were obtained. The proposed multiplex SERS immunoassay method displays ultrahigh sensitivity, wide linear range, and excellent specificity, which can be successfully applied to measure clinical serum samples with satisfactory results. The research provides a novel SERS signal enhancement strategy for the multiplex bioassay.

Carboxylic acid-tethered polyaniline as a generic immobilization matrix for electrochemical bioassays

Polyaniline (PANI) was functionalized by thiol-ene click chemistry to obtain carboxylic acid-tethered polyaniline (PCOOH). The versatility of PCOOH as an immobilization matrix was demonstrated by constructing four different biosensors for detection of metabolites and cancer biomarker. Immobilization efficiency of PCOOH was investigated by surface plasmon resonance and fluorescence microscopic analysis which revealed dense immobilization of biomolecules on PCOOH as compared to conventional PANI. A sandwich electrochemical biosensor was constructed using PCOOH for detection of liver cancer biomarker, α-fetoprotein (AFP). The sensor displayed sensitivity of 15.24 µA (ng mL^-1)^-1 cm^-2, with good specificity, reproducibility (RSD 3.4%), wide linear range (0.25-40 ng mL^-1) at - 0.1 V (vs. Ag/AgCl), and a low detection limit of 2 pg mL^-1. The sensor was validated by estimating AFP in human blood serum samples where the AFP concentrations obtained are consistent with the values estimated using ELISA. Furthermore, utilization of PCOOH for construction of enzymatic biosensor was demonstrated by covalent immobilization of glucose oxidase, uricase, and horseradish peroxidase (HRP) for detection of glucose, uric acid, and H₂O₂, respectively. The biosensors displayed reasonable sensitivity (50, 148, 127 µA mM^-1 cm^-2), and linear ranges (0.1-5, 0.1-6, 0.1-7 mM) with a detection limit of 10, 1, and 8 µM for glucose, uric acid, and H₂O₂, respectively. The present study demonstrates the capability of PCOOH to support and enable oxidation of H₂O₂ generated by oxidase enzymes as well as HRP enzyme catalyzed reduction of H₂O₂. Thus, PCOOH offers a great promise as an immobilization matrix for development of high-performance biosensors to quantify a variety of other disease biomarkers. Carboxylic acid-tethered polyaniline synthesized by thiol-ene click chemistry was used as matrix to construct four different electrochemical biosensors for detection of cancer biomarker α-fetoprotein, glucose, uric acid, and H₂O₂.

Multiplex bioassaying of cancer proteins and biomacromolecules: Nanotechnological, structural and technical perspectives

Since the specific proteins (carbohydrate antigens, ligands and interleukins) get raised up in body tissue or fluids in cancer cases, early detection of them will provide an effective treatment and survival rate. Sensitive and accurate determination of multiple cancer proteins can be engaged in chorus by simultaneous/multiplex detection in the biomedical fields. Bioassaying technology is one of the non-invasive, high-sensitive, and economical methods. Currently, extensive application of nanomaterial (biocompatible polymers, metallic and metal oxide) in bioassays resulted in ultra-high sensitive and selective diagnosis. This review article focuses on types of multiplex bioassays for delicate and specific determination of cancer proteins for diagnostic aims. It also covers two modes of multiplex bioassays as multi labeled bioassays and spatially-separated test zones (multi-electrode mode). In this review, the nanotechnological, structural, and technical perspectives in the multiplex analysis of cancer proteins were discussed. Finally, the use of different types of nanomaterials, polysaccharides, biopolymers and their advantages in signal amplification are discussed.

An Electrochemical Immunosensor for Sensitive Detection of the Tumor Marker Carcinoembryonic Antigen (CEA) Based on Three-Dimensional Porous Nanoplatinum/Graphene

Carcinoembryonic antigen (CEA) is an important broad-spectrum tumor marker. The quantitative detection of a low concentration of CEA has important medical significance. In this study, three-dimensional porous graphene-oxide-supported platinum metal nanoparticles (3DPt/HGO) composites were prepared by a wet chemical method and modified on an electrode with enhanced conductivity, a large surface area, and good adsorption of immobilizing antibodies (Ab₁). Horseradish peroxidase (HRP)-functionalized Au nanoparticles were fabricated to label the secondary antibodies (Ab₂). The proposed immunosensor showed a good linear relationship in the range of 0.001–150 ng/mL for CEA and a detection limit of 0.0006 ng/mL. The immunosensor had high sensitivity, good stability and reproducibility, and has great application prospects for the clinical diagnosis of cancer.

Salt-induced gold nanoparticles aggregation lights up fluorescence of DNA-silver nanoclusters to monitor dual cancer markers carcinoembryonic antigen and carbohydrate antigen 125

In clinical diagnosis of cancer, the monitoring of single tumor marker may result in many false and missed results, while simultaneous detection of multiple tumor markers should be more accuracy and effective. Here, we report a new strategy that salt-induced gold nanoparticles (AuNPs) aggregation lights up fluorescence of dual-color DNA-silver nanoclusters-aptamer (DNA-AgNCs-apta) for the simultaneous monitoring of carcinoembryonic antigen (CEA) and carbohydrate antigen 125 (CA125). The dual-color aptasensor system is composed of green-emitting DNA-AgNCs with CEA aptamer (gDNA₁-AgNCs-apta₁) and red-emitting DNA-AgNCs with CA125 aptamer (rDNA₂-AgNCs-apta₂) in the ratio of 1:1 in volume. Upon addition of AuNPs, gDNA₁-AgNCs-apta₁ and/or rDNA₂-AgNCs-apta₂ are flexibly adsorbed onto the surface of AuNPs by terminal aptamer(s), which prevents salt-induced AuNPs aggregation under high salt condition and results in fluorescence quenching based on surface plasmon enhanced energy transfer (SPEET). With the addition of CEA and/or CA125, the target(s) and corresponding aptamer(s) coordinate to form the complex, keeping DNA-AgNCs-apta(s) far away from the surface of AuNPs and making AuNPs aggregated in high salt medium. The AuNPs aggregation leads to the recovery of fluorescence signals of DNA-AgNCs-apta(s) due to weakened SPEET. Utilizing the fluorescence aptasensor system, the limit of detection of CEA and CA125 are as low as 7.5 pg·mL^-1 and 0.015 U·mL^-1, respectively. The proposed method can be applied to the selective and simultaneous determination of CEA and CA125 in human serum.

A palladium-platinum bimetal nanodendritic melamine network for signal amplification in voltammetric sensing of DNA

A sandwich-type electrochemical DNA sensor is described for the detection of oligonucleotides typical for MECP2 gene mutations. Palladium nanoparticles (PdNPs) and platinum nanoparticles (PtNPs) were used to synthesize flower-like PdPt nanodendrites (NDs) by a one-pot method. The PdPt NDs possess a high specific surface area and excellent catalytic capabilities. They served as the carrier for the signal DNA probe (SP) and simultaneously catalyze the reduction of hydrogen peroxide (H₂O₂). The PdPt NDs were modified with melamine, and this results in the formation of a PdPt-melamine network through stable interactions between the PdPt NDs and the three amino groups of each melamine molecule. The network exhibits excellent catalytic ability in enhancing the current signal response in the voltammetric detection of MECP2 gene mutation, best measured at -0.4 V vs. SCE and using H₂O₂ as the electrochemical probe. In addition, gold nanoflowers were electrodeposited on the electrode interface in order to accelerate electron transfer and to capture the capture probe. The sensor is stable and can detect MECP2 gene mutations in the 1 fmol·L^-1 to 1 nmol·L^-1 concentration range, with a 0.33 fmol·L^-1 lower detection limit at an S/N ratio of 3. Graphical abstract Schematic presentation of electrodes for the determination of the X-linked gene methyl-CpG-binding protein 2 (MECP2). The sensor is based on the electrooxidation of added H₂O₂ by using the melamine modified palladium platinum bimetal nanodendrites as network signal amplification strategy. This versatile platform expands studies on the detection of monogenic disease.

An ultrasensitive enzyme-free electrochemical immunosensor based on redox cycling amplification using methylene blue

We report a new enzyme-free electrochemical sensor for ultrasensitive measurements of protein biomarkers in plasma and whole blood samples based on a unique electrochemical-chemical-chemical (ECC) redox cycling signal amplification scheme. This scheme uses methylene blue (MB) as a redox indicator which undergoes an endergonic reaction with Ru(NH3)63+ and a highly exergonic reaction with tris(2-carboxyethyl)phosphine (TCEP). This approach offers improved detection sensitivity and sensor stability compared with enzyme-based ECC redox cycling techniques, while involving a simpler sensor modification process and detection protocol. This redox cycling scheme was combined with a robust immunosandwich assay for quantitative measurements of protein biomarkers. For proof of principle, Plasmodium falciparum histidine-rich protein 2 (PfHRP2) was measured in human plasma and whole blood samples, which could be detected down to 10 fg mL-1 and 18 fg mL-1, respectively. Furthermore, this immunosensor exhibits high selectivity, excellent reproducibility and good stability for up to 2 weeks, making it a promising platform for point-of-care testing, especially for detecting extremely low biomarker concentrations in raw biofluids.

Design of immunoprobes for electrochemical multiplexed tumor marker detection

Many approaches have been developed for simultaneous detection of multiple tumor markers. Among these approaches, the electrochemical immunoassay has the advantage of high sensitivity and specificity and could be easily expanded into multiplex detection platform. For the simultaneous multianalyte electrochemical immunosensor, performance is closely related with the characteristics of the immunoprobes and substrate. In order to construct a multilabeled immunoprobe platform, the most important issue is how to discriminate each signal for each analyte from the multiple antigen-antibody reactions. Currently, enzyme-based, noble metal nanomaterials, carbonmaterials and polymer-based nanomaterial immunoprobes have been used for dual- or three-analyte detections. However, there are still some challenges in developing sensitive method to detect three or more tumor markers owing to the lack of redox-active species that can produce three or more distinctive peaks. Additionally, for the immunosensing substrate, good conductivity, high specific surface area and good biocompatibility are further necessities.