Electrochemical Signal Substance for Multiplexed Immunosensing Interface Construction: A Mini Review

Appropriate labeling method of signal substance is necessary for the construction of multiplexed electrochemical immunosensing interface to enhance the specificity for the diagnosis of cancer. So far, various electrochemical substances, including organic molecules, metal ions, metal nanoparticles, Prussian blue, and other methods for an electrochemical signal generation have been successfully applied in multiplexed biosensor designing. However, few works have been reported on the summary of electrochemical signal substance applied in constructing multiplexed immunosensing interface. Herein, according to the classification of labeled electrochemical signal substance, this review has summarized the recent state-of-art development for the designing of electrochemical immunosensing interface for simultaneous detection of multiple tumor markers. After that, the conclusion and prospects for future applications of electrochemical signal substances in multiplexed immunosensors are also discussed. The current review can provide a comprehensive summary of signal substance selection for workers researched in electrochemical sensors, and further, make contributions for the designing of multiplexed electrochemical immunosensing interface with well signal.

A label-free multiplex electrochemical biosensor for the detection of three breast cancer biomarker proteins employing dye/metal ion-loaded and antibody-conjugated polyethyleneimine-gold nanoparticles

A new electrochemical immunosensor is developed for the label-free simultaneous detection of mucin1 (MUC1), cancer antigen 15-3 (CA15-3), and human epidermal growth factor receptor 2 (HER2) early breast cancer biomarkers. The biosensor is simply designed using the deposition of three different systems of redox species-antibody-conjugated polyethylenimine coated-gold nanoparticles (PEI-AuNPs), for the first time. The screen-printed carbon electrode (SPCE) comprising a three-working electrode array is modified with the conjugated PEI-AuNPs. Multiplex sensing is performed by utilizing the distinguishable electrochemical responses of the redox-active species; anthraquinone-2-carboxylic acid (AQ), thionine chloride (TH), and AgNO3 (Ag+) on the PEI-AuNPs conjugates for the detection of MUC1, CA15-3, and HER2, respectively. The single-run determination of the biomarkers by the proposed immunosensor is carried out by measuring the decrease (%) in the oxidation peak currents due to the formation of three kinds of antibody-antigen complexes. The decreased currents are logarithmically proportional to the antigen concentrations in the ranges of 0.10-100 U mL-1 CA15-3 and 0.10-100 ng mL-1 MUC1 and HER2 with detection limits of 0.21 U mL-1, 0.53 ng mL-1 and 0.50 ng mL-1, respectively, which are significantly lower than the clinically relevant cut-off levels. The sensor reveals high selectivity and satisfactory reproducibility. After storing for two weeks, the sensor retains the responses with ca. 90% of the initial currents. The immunosensor is successfully applied to detect three tumor markers in human serum and can provide a new technological platform for the development of low-cost, highly stable, sensitive, selective, and point-of-care (POC) diagnosis.

A Portable Microfluidic System for Point-of-Care Detection of Multiple Protein Biomarkers

Protein biomarkers are indicators of many diseases and are commonly used for disease diagnosis and prognosis prediction in the clinic. The urgent need for point-of-care (POC) detection of protein biomarkers has promoted the development of automated and fully sealed immunoassay platforms. In this study, a portable microfluidic system was established for the POC detection of multiple protein biomarkers by combining a protein microarray for a multiplex immunoassay and a microfluidic cassette for reagent storage and liquid manipulation. The entire procedure for the immunoassay was automatically conducted, which included the antibody–antigen reaction, washing and detection. Alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA) and carcinoma antigen 125 (CA125) were simultaneously detected in this system within 40 min with limits of detection of 0.303 ng/mL, 1.870 ng/mL, and 18.617 U/mL, respectively. Five clinical samples were collected and tested, and the results show good correlations compared to those measured by the commercial instrument in the hospital. The immunoassay cassette system can function as a versatile platform for the rapid and sensitive multiplexed detection of biomarkers; therefore, it has great potential for POC diagnostics.

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.

Electrochemiluminescence Imaging for the Morphological and Quantitative Analysis of Living Cells under External Stimulation

In this work, a simple electrochemiluminescence (ECL) imaging method based on the cell shield of the ECL emission was developed for the morphological and quantitative analysis of living cells under external stimulation. ECL images of MCF-7 cells cultured on or captured at the glassy carbon electrode (GCE) surface in a solution of tris(2,2'-bipyridyl)ruthenium(II)-tri-n-propylamine were recorded. Important morphological characteristics of living cells, including cell shape, cell area, average cell boundary, and junction distance between two adjacent cells, were directly obtained using the developed negative ECL imaging method. The ECL images revealed gradual morphological changes in cells on the GCE surface. During the course of H₂O₂ stimulation of cells on the GCE surface, cells shrunk, rounded up, disengaged from surrounding cells, and finally detached from the electrode surface. During the course of electrical stimulation (0.8 V), the cells on the GCE surface exhibited aggregation as demonstrated by increases in the average cell boundary and decreases in the junction distance between two adjacent cells. Additionally, a quantitative method for the sensitive determination of MCF-7 cells with a limit of detection of 29 cells/mL was developed using the negative ECL imaging strategy. This work demonstrates that the proposed negative ECL imaging strategy is a promising approach to assess important morphological characteristics of living cells during the course of external stimulation and to obtain quantitative information on cell concentrations in solution.

Preparation of a novel sandwich-type electrochemical immunosensor for AFP detection based on an ATRP and click chemistry technique

It is extremely important to explore the synthesis methodology and application scope of functional polymer brush-based nanocomposites.

Suppressing Non-Specific Binding of Proteins onto Electrode Surfaces in the Development of Electrochemical Immunosensors

Electrochemical immunosensors, EIs, are systems that combine the analytical power of electrochemical techniques and the high selectivity and specificity of antibodies in a solid phase immunoassay for target analyte. In EIs, the most used transducer platforms are screen printed electrodes, SPEs. Some characteristics of EIs are their low cost, portability for point of care testing (POCT) applications, high specificity and selectivity to the target molecule, low sample and reagent consumption and easy to use. Despite all these attractive features, still exist one to cover and it is the enhancement of the sensitivity of the EIs. In this review, an approach to understand how this can be achieved is presented. First, it is necessary to comprise thoroughly all the complex phenomena that happen simultaneously in the protein-surface interface when adsorption of the protein occurs. Physicochemical properties of the protein and the surface as well as the adsorption phenomena influence the sensitivity of the EIs. From this point, some strategies to suppress non-specific binding, NSB, of proteins onto electrode surfaces in order to improve the sensitivity of EIs are mentioned.

Integrated Affinity Biosensing Platforms on Screen-Printed Electrodes Electrografted with Diazonium Salts

Adequate selection of the electrode surface and the strategies for its modification to enable subsequent immobilization of biomolecules and/or nanomaterials integration play a major role in the performance of electrochemical affinity biosensors. Because of the simplicity, rapidity and versatility, electrografting using diazonium salt reduction is among the most currently used functionalization methods to provide the attachment of an organic layer to a conductive substrate. This particular chemistry has demonstrated to be a powerful tool to covalently immobilize in a stable and reproducible way a wide range of biomolecules or nanomaterials onto different electrode surfaces. Considering the great progress and interesting features arisen in the last years, this paper outlines the potential of diazonium chemistry to prepare single or multianalyte electrochemical affinity biosensors on screen-printed electrodes (SPEs) and points out the existing challenges and future directions in this field.

Magnetofluorescent nanocomposites and quantum dots used for optimal application in magnetic fluorescence-linked immunoassay

Magnetofluorescent nanocomposites with optimal magnetic and fluorescent properties were prepared and characterized by combining magnetic nanoparticles (iron oxide@polymethyl methacrylate) with fluorescent nanoparticles (rhodamine 6G@mSiO₂). Experimental parameters were optimized to produce nanocomposites with high magnetic susceptibility and fluorescence intensity. The detection of a model biomarker (alpha-fetoprotein) was used to demonstrate the feasibility of applying the magnetofluorescent nanocomposites combined with quantum dots and using magnetic fluorescence-linked immunoassay. The magnetofluorescent nanocomposites enable efficient mixing, fast re-concentration, and nanoparticle quantization for optimal reactions. Biofunctional quantum dots were used to confirm the alpha-fetoprotein (AFP) content in sandwich immunoassay after mixing and washing. The analysis time was only one third that required in ELISA. The detection limit was 0.2 pg mL^-1, and the linear range was 0.68 pg mL^-1-6.8 ng mL^-1. This detection limit is lower, and the linear range is wider than those of ELISA and other methods. The measurements made using the proposed method differed by less than 13% from those obtained using ELISA for four AFP concentrations (0.03, 0.15, 0.75, and 3.75 ng mL^-1). The proposed method has a considerable potential for biomarker detection in various analytical and biomedical applications. Graphical abstract Magnetofluorescent nanocomposites combined with fluorescent quantum dots were used in magnetic fluorescence-linked immunoassay.

Recent Advances in Electrochemical Immunosensors

Immunosensors have experienced a very significant growth in recent years, driven by the need for fast, sensitive, portable and easy-to-use devices to detect biomarkers for clinical diagnosis or to monitor organic pollutants in natural or industrial environments. Advances in the field of signal amplification using enzymatic reactions, nanomaterials such as carbon nanotubes, graphene and graphene derivatives, metallic nanoparticles (gold, silver, various oxides or metal complexes), or magnetic beads show how it is possible to improve collection, binding or transduction performances and reach the requirements for realistic clinical diagnostic or environmental control. This review presents these most recent advances; it focuses first on classical electrode substrates, then moves to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials, metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, to finish, explore the use of ionic liquids. Analytical performances are systematically covered and compared, depending on the detection principle, but also from a chronological perspective, from 2012 to 2016 and early 2017.

Recent Advances in the Fabrication and Application of Screen-Printed Electrochemical (Bio)Sensors Based on Carbon Materials for Biomedical, Agri-Food and Environmental Analyses

This review describes recent advances in the fabrication of electrochemical (bio)sensors based on screen-printing technology involving carbon materials and their application in biomedical, agri-food and environmental analyses. It will focus on the various strategies employed in the fabrication of screen-printed (bio)sensors, together with their performance characteristics; the application of these devices for the measurement of selected naturally occurring biomolecules, environmental pollutants and toxins will be discussed.

A review on amperometric-type immunosensors based on screen-printed electrodes

In this brief review, we summarize the recent research activities involved in the development of amperometric-type immunosensors based on screen-printed electrodes (SPEs). We focus on the underlying principle involved in these types of sensors, their fabrication and electrode surface modification. We also discuss the various factors involved in the designing of such immunosensors and how they affect their performances. Finally we provide an insight into the drawbacks associated with these SPEs.

Simultaneous fluoroimmunoassay of two tumor markers based on CdTe quantum dots and gold nanocluster coated-silica nanospheres as labels

Fluoroimmunoassay for simultaneous detection of CEA and AFP.

Gold nanorods-paper electrode based enzyme-free electrochemical immunoassay for prostate specific antigen using porous zinc oxide spheres–silver nanoparticles nanocomposites as labels

Gold nanorods-modified paper electrode and porous zinc oxide spheres–silver nanoparticles nanocomposites were used to construct an enzyme-free immunosensor.

A reliable self-assembled peptide based electrochemical biosensor for detection of caspase 3 activity and apoptosis

A sensitive electrochemical self-assembled peptide based biosensor was developed for the detection of caspase 3 activity and apoptosis using a Asp-Glu-Val-Asp (DEVD) modified peptide and horseradish peroxidase (HRP) as cleaving and electron transfer agents, respectively.

Hollow AuPt alloy nanoparticles as an enhanced immunosensing platform for detection of multiple analytes

Hollow AuPt alloy nanoparticles with a rough surface were prepared by one-step galvanic displacement reaction and were used to fabricate enhanced immunoprobes for detection of multiple analytes.

Single electrode biosensor for simultaneous determination of interferon gamma and lysozyme

Simultaneous detection of multiple biomarkers holds great promise for acute leukemia evaluation. Here, a novel biosensor is developed for simultaneous electrochemical detection of interferon gamma (IFN-γ) and lysozyme (Lys) based on aptamer recognition by coupling "signal-on" and "signal-off" modes. On one Au electrode, two kinds of signaling probes labeled by the thiolated ferrocene (Fc)- and methy blue (MB)- were designed to hybridize with IFN-γ and Lys aptamers respectively to form partial complementary DNA duplexes. In the presence of IFN-γ and Lys, the target-aptamer interaction led to the release of aptamer from duplex DNA structure. The single-stranded signaling probes thus suffered from the conformation changes, which resulted in the decreased (or increased) oxidation peak current of Fc (or MB) according to the "signal-off (or signal-on)" mode. Electrodes were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimized conditions, the signal changes were quantified using square wave voltammetry (SWV). This proposed biosensor for IFN-γ and Lys possessed linear detection range from 0.01 to 10 nM and 0.1 to 100 nM, with the detection limits of 1.14×10(-3) nM and 0.0164 nM, respectively. Moreover, this biosensor was readily regenerated and proved successful toward the practical analysis. The proposed strategy could provide more integrated and reliable information for acute leukemia evaluation.

Formation of thick aminophenyl films from aminobenzenediazonium ion in the absence of a reduction source

Aminophenyl films, electrografted to conducting substrates from a solution of the corresponding diazonium ion, are a useful platform for building up functional surfaces. In our hands, reproducible preparation of aminophenyl films via electrografting is difficult, suggesting competing grafting pathways. To investigate the grafting process without the possibility of reduction of the diazonium ion by the substrate, we have used a spin-coated and cured SU-8 substrate that is nonconducting and very smooth (rms surface roughness 0.43 nm). After in situ formation of the aminobenzenediazonium ion (50 mM) in acidic solution, the substrate was added to the solution in the presence and absence of reducing agents (hypophosphorous acid and iron powder). At short reaction times, the films prepared with and without reducing agent have the same thickness and composition (as revealed by X-ray photoelectron spectroscopy). However, in the presence of a reducing agent, films reach a limiting thickness of 7-8 nm after 10 min, whereas, in the absence of a reducing agent, strong film growth continues, giving a film thickness of 14 nm after 120 min. This behavior contrasts with that of other diazonium ions which, in the absence of an applied potential, a reducing agent, or a reducing substrate, give only very thin films after long reaction times.

Poly(acrylic acid)-grafted fluoropolymer films for highly sensitive fluorescent bioassays

In this study, a facile and effective method for the surface functionalization of inert fluoropolymer substrates using surface grafting was demonstrated for the preparation of a new platform for fluorescence-based bioassays. The surface of perfluorinated poly(ethylene-co-propylene) (FEP) films was functionalized using a 150 keV ion implantation, followed by the graft polymerization of acrylic acid, to generate a high density of carboxylic acid groups on the implanted surface. The resulting functionalized surface was investigated in terms of the surface density of carboxylic acid, wettability, chemical structure, surface morphology, and surface chemical composition. These results revealed that poly(acrylic acid) (PAA) was successfully grafted onto the implanted FEP surface and its relative amount depended on the fluence. To demonstrate the usefulness of this method for the fabrication of bioassays, the PAA-grafted FEP films were utilized for the immobilization of probe DNA for anthrax toxin, followed by hybridization with Cy3-labeled target DNA. Liver cancer-specific α-feto-protein (AFP) antigen was also immobilized on the PAA-grafted FEP films. Texas Red-labeled secondary antibody was reacted with AFP-specific primary antibody prebound to the AFP antigen using an immunoassay method. The results revealed that the fluorescence intensity clearly depended on the concentration of the target DNA hybridized to the probe DNA and the AFP antigen immobilized on the FEP films. The lowest detectable concentrations of the target DNA and the AFP antigen were 10 fg/mL and 10 pg/mL, respectively, with the FEP films prepared at a fluence of 3 × 10(14) ions/cm(2).

Microfluidic beads-based immunosensor for sensitive detection of cancer biomarker proteins using multienzyme-nanoparticle amplification and quantum dots labels

This study reports the development of a microfluidic beads-based immunosensor for sensitive detection of cancer biomarker α-fetoprotein (AFP) that uses multienzyme-nanoparticle amplification and quantum dots labels. This method utilizes microbeads functionalized with the capture antibodies (Ab₁) and modified electron rich proteins as sensing platform that was fabricated within a microfluidic channel, and uses gold nanoparticles (AuNPs) functionalized with the horseradish peroxidase (HRP) and the detection antibodies (Ab₂) as label. Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the large surface area of Au nanoparticle carrier allows several binding events of HRP on each nanosphere. Enhanced sensitivity was achieved by introducing the multi-HRP-antibody functionalized AuNPs onto the surface of microbeads through "sandwich" immunoreactions and subsequently multiple biotin moieties could be deposited onto the surface of beads resulted from the oxidation of biotin-tyramine by hydrogen peroxide. Streptavidin-labeled quantum dots were then allowed to bind to the deposited biotin moieties and displayed the signal. Secondly, enhanced mass transport capability inherent from microfluidics leads to higher capture efficiency of targets because continuous flow within micro-channel delivers fresh analyte solution to the reaction site which maintains a high concentration gradient differential to enhance mass transport. Based on the dual signal amplification strategy, the developed microfluidic bead-based immunosensor could discriminate as low as 0.2 pg mL⁻¹ AFP in 10 μL of undiluted calf serum (0.2 fg/chip), and showed a 500-fold increase in detection limit compared to the off-chip test and 50-fold increase in detection limit compared to microfluidic beads-based immunoassay using single label HRP-Ab₂. The immunosensor showed acceptable repeatability and reproducibility. This microfluidic beads-based immunosensor is a promising platform for disease-related biomolecules at the lowest level at their earliest incidence.