Electrochemiluminescence immunosensor based on graphene oxide nanosheets/polyaniline nanowires/CdSe quantum dots nanocomposites for ultrasensitive determination of human interleukin-6

Graphene Nanocomposite Ink Coated Laser Transformed Flexible Electrodes for Selective Dopamine Detection and Immunosensing

Novel and flexible disposable laser-induced graphene (LIG) sensors modified with graphene conductive inks have been developed for dopamine and interleukin-6 (IL-6) detection. The LIG sensors exhibit high reproducibility (relative standard deviation, RSD = 0.76%, N = 5) and stability (RSD = 4.39%, N = 15) after multiple bendings, making the sensors ideal for wearable and stretchable bioelectronics applications. We have developed electrode coatings based on graphene conductive inks, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (G-PEDOT:PSS) and polyaniline (G-PANI), for working electrode modification to improve the sensitivity and limit of detection (LOD). The selectivity of LIG sensors modified with the G-PANI ink is 41.47 times higher than that of the screen-printed electrode with the G-PANI ink modification. We have compared our fabricated bare laser-engraved Kapton sensor (LIG) with the LIG sensors modified with G-PEDOT (LIG/G-PEDOT) and G-PANI (LIG/G-PANI) conductive inks. We have further compared the performance of the fabricated electrodes with commercially available screen-printed electrodes (SPEs) and screen-printed electrodes modified with G-PEDOT:PSS (SPE/G-PEDOT:PSS) and G-PANI (SPE/G-PANI). SPE/G-PANI has a lower LOD of 0.632 μM compared to SPE/G-PEDOT:PSS (0.867 μM) and SPE/G-PANI (1.974 μM). The lowest LOD of the LIG/G-PANI sensor (0.4084 μM, S/N = 3) suggests that it can be a great alternative to measure dopamine levels in a physiological medium. Additionally, the LIG/G-PANI electrode has excellent LOD (2.6234 pg/mL) to detect IL-6. Also, the sensor is successfully able to detect ascorbic acid (AA), dopamine (DA), and uric acid (UA) in their ternary mixture. The differential pulse voltammetry (DPV) result shows peak potential separation of 229, 294, and 523 mV for AA-DA, DA-UA, and UA-AA, respectively.

An electrochemical molecularly imprinted microfluidic paper-based chip for detection of inflammatory biomarkers IL-6 and PCT

Based on surface biomolecular imprinting technology, a rotary microfluidic electrochemical paper-based chip (MIP-ePADs) was proposed for sensitive and selective detection of human interleukin 6 (IL-6) and procalcitonin (PCT). Compared with the traditional method, the sample can be added directly on the MIP-ePAD by rotating the working electrode, which avoids the loss of the liquid to be tested and greatly simplifies the process of electropolymerization imprinting and template elution. Our experimental results show that linear concentration ranges of IL-6 and PCT in the electrochemical molecularly imprinted microfluidic paper-based chip ranged from 0.01 to 5 ng mL-1, with their detection limits being 3.5 and 2.1 pg mL-1, respectively. For the detection of actual serum samples, there was no significant difference between the results of MIP-ePADs and the traditional electrochemiluminescence method used in hospitals, indicating that the paper-based chip can be used for stable and accurate analysis and detection. The chip greatly reduces the cost of clinical trials due to its advantages of easy preparation and low cost. The chip can be used for the analysis of non-antibody inflammation markers and can be widely used in home and hospital treatment detection. This method will not only play an important role in rapid detection, but also provide new ideas for the improvement of rapid detection technology.

Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines

Cytokines are a large group of small proteins secreted by immune and non-immune cells in response to external stimuli. Much attention has been given to the application of cytokines' detection in early disease diagnosis/monitoring and therapeutic response assessment. To date, a wide range of assays are available for cytokines detection. However, in specific applications, multiplexed or continuous measurements of cytokines with wearable biosensing devices are highly desirable. For such efforts, various nanomaterials have been extensively investigated due to their extraordinary properties, such as high surface area and controllable particle size and shape, which leads to their tunable optical emission, electrical, and magnetic properties. Different types of nanomaterials such as noble metal, metal oxide, and carbon nanoparticles have been explored for various biosensing applications. Advances in nanomaterial synthesis and device development have led to significant progress in pushing the limit of cytokine detection. This article reviews currently used methods for cytokines detection and new nanotechnology-based biosensors for ultrasensitive cytokine detection.

A critical review on quantum dots: From synthesis toward applications in electrochemical biosensors for determination of disease-related biomolecules

Fluorescent quantum dots (QDs), defined by a diameter size of <10 nm, have been the core concept of nanoscience and nanotechnology since their inception. QDs possess many unique structural, electrochemical and photochemical properties that render them a promising platform for sensing applications. These nanomaterials can greatly enhance the analytical performances of biosensors, namely detection limit, sensitivity and selectivity. QDs are being developed not only because of their ability for signal enhancement but also because of their high capacity for fuctionalization with bioreceptors. In this review, we summarize a basic knowledge of QDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into the sensing field. Due to the nature of QDs, especially their ability to combine nanotechnology and biotechnology, they possess the potential to open a novel paradigm on early diagnosis of diseases using the electrochemical biosensors. Therefore, we try to give a comprehensive view of the role of these zero-dimensional (0D) nanomaterials in the designing electrochemical sensors for determination of disease-related biomolecules, including tumor markers, inflammatory biomarkers, depression markers and archetypal biomarker in diabetes diagnosis. Considering the high potential of QDs for the electrochemistry-based biosensing strategies, the authors suggest that more research is needed on understanding their electronic properties and why synthesis and surface modification methods can affect these properties.

PANI/PbS QD nanocomposite structure for visible light driven photocatalytic degradation of rhodamine 6G

Among conducting polymers, polyaniline (PANI) is one of the most widely used materials due to its unique properties (e.g., high electrical conductivity, outstanding electrochemical properties, easy polymerization, high stability, and low-cost synthesis). In this study, we report the synthesis of a composite of polyaniline with lead sulfide quantum dots (PbS QDs), which was subsequently employed for photocatalysis of a dye, rhodamine 6G (Rh-6G). This PANI/PbS composite was prepared by employing the chemical oxidative polymerization of aniline monomer in the presence of PbS QDs. The composite has been characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and ultraviolet-visible spectroscopy. The composite formation turned out to be beneficial not only for the dispersion of PbS QDs but also for increasing the conductivity of the whole catalyst. They exhibited ~87% degradation of the dye content for 50 min. The kinetic rate for its destruction is 5.03 mmol g^-1 h^-1 with the quantum efficiency (QE) of 7.98E-06 molec/photon. Due to enhanced charge transfer characteristics, the PANI/PbS photocatalyst was capable of efficiently degrading the dye molecules across varying concentrations. The electron-hole pair generated after the visible light irradiation on the PANI/PbS composite led to an efficient oxidative degradation of Rh 6G.

The development of an ultra-sensitive electrochemical immunosensor using a PPyr-NHS functionalized disposable ITO sheet for the detection of interleukin 6 in real human serums

A label-free biosensor based on poly(pyrrole N-hydroxy succinimide) polymer modified ITO electrode was developed for sensitive detection of interleukin 6 antigen. Under optimized conditions, it had a wide detection range (0.03–22.5 pg mL⁻¹).

Recent Advances in Electrochemiluminescence Sensors for Pathogenic Bacteria Detection

Pathogenic bacterial contamination greatly threats human health and safety. Rapidly biosensing pathogens in the early stage of infection would be helpful to choose the correct drug treatment, prevent transmission of pathogens, as well as decrease mortality and economic losses. Traditional techniques, such as polymerase chain reaction and enzyme-linked immunosorbent assay, are accurate and effective, but are greatly limited because they are complex and time-consuming. Electrochemiluminescence (ECL) biosensors combine the advantages of both electrochemical and photoluminescence analysis and are suitable for high sensitivity and simple pathogenic bacteria detection. In this review, we summarize recent advances in ECL sensors for pathogenic bacteria detection and highlight the development of paper-based ECL platforms in point of care diagnosis of pathogens.

Recent advances in designing nanomaterial based biointerfaces for electrochemical biosensing cardiovascular biomarkers

Early diagnosis of cardiovascular disease (CVD) is critically important for successful treatment and recovery of patients. At present, detection of CVD at early stages of its progression becomes a major issue for world health. The nanoscale electrochemical biosensors exhibit diverse outstanding properties, rendering them extremely suitable for the determination of CVD biomarkers at very low concentrations in biological fluids. The unique advantages offered by electrochemical biosensors in terms of sensitivity and stability imparted by nanostructuring the electrode surface together with high affinity and selectivity of bioreceptors have led to the development of new electrochemical biosensing strategies that have introduced as interesting alternatives to conventional methodologies for clinical diagnostics of CVD. This review provides an updated overview of selected examples during the period 2005-2018 involving electrochemical biosensing approaches and signal amplification strategies based on nanomaterials, which have been applied for determination of CVD biomarkers. The studied CVD biomarkers include AXL receptor tyrosine kinase, apolipoproteins, cholesterol, C-reactive protein (CRP), D-dimer, fibrinogen (Fib), glucose, insulin, interleukins, lipoproteins, myoglobin, N-terminal pro-B-type natriuretic peptide (BNP), tumor necrosis factor alpha (TNF-α) and troponins (Tns) on electrochemical transduction format. Identification of new specific CVD biomarkers, multiplex bioassay for the simultaneous determination of biomarkers, emergence of microfluidic biosensors, real-time analysis of biomarkers and point of care validation with high sensitivity and selectivity are the major challenges for future research.

Combined electrochemiluminescent and electrochemical immunoassay for interleukin 6 based on the use of TiO2 mesocrystal nanoarchitectures

A dual-responsive sandwich-type immunosensor is described for the detection of interleukin 6 (IL-6) by combining electrochemiluminescent (ECL) and electrochemical (EC) detection based on the use of two kinds of TiO₂ mesocrystal nanoarchitectures. A composite was prepared from TiO₂ (anatase) mesocages (AMCs) and a carboxy-terminated ionic liquid (CTIL) and then placed on a glassy carbon electrode (GCE). In the next step, the ECL probe Ru(bpy)₃(II) and antibody against IL-6 (Ab₁) were immobilized on the GCE. Octahedral anatase TiO₂ mesocrystals (OAMs) served as the matrix for immobilizing acid phosphatase (ACP) and secondary antibody (Ab₂) labeled with horseradish peroxidase (HRP) to form a bioconjugate of type Ab₂-HRP/ACP/OAMs. It was self-assembled on the GCE by immunobinding. 1-Naphthol, which is produced in-situ on the surface of the GCE due to the hydrolysis of added 1-naphthyl phosphate by ACP, is oxidized by HRP in the presence of added H₂O₂. This results in an electrochemical signal (typically measured at 0.4 V vs. Ag/AgCl) that increases linearly in the 10 fg·mL^-1 to 90 ng·mL^-1 IL-6 concentration range with a detection limit of 0.32 fg·mL^-1. Secondly, the oxidation product of 1-naphthol quenches the ECL emission of Ru(bpy)₃²⁺. This leads to a decrease in ECL intensity which is linear in the 10 ag·mL^-1 to 90 ng·mL^-1 concentration range, with a detection limit of 3.5 ag·mL^-1. The method exhibits satisfying selectivity and good reproducibility which demonstrates its potential in clinical testing and diagnosis. Graphical abstract A dual-responsive sandwich-type immunosensor was fabricated for the detection of interleukin 6 by combining electrochemiluminescence and electrochemical detection based on the use of two kinds of TiO₂ mesocrystal nanoarchitectures.

Dual Electrochemiluminescence Signal System for In Situ and Simultaneous Evaluation of Multiple Cell-Surface Receptors

A mutiplex cytosensor based on a dual electrochemiluminescence (ECL) signal system was fabricated for in situ and simultaneous detection of the expression levels of multiple cell-surface receptors, mannose and epidermal growth factor receptor (EGFR), using luminol-capped gold nanoparticles (Au@luminol) and CdS quantum dots (CdS QDs) as potential-resolved ECL nanoprobes. Two spatially resolved areas on indium tin oxide (ITO) electrodes were modified with polyaniline (PANI) by electropolymerization, on which gold nanoparticles (AuNPs) were attached to strengthen conductivity and stability of the sensing interface. Human mucin1 protein (MUC1) aptamer was immobilized onto AuNPs for capturing MUC1-positive MCF-7 cells. Au@luminol and CdS QDs as ECL nanoprobes were covalently linked with concanavalin A (ConA) and epidermal growth factor (EGF) to label MCF-7 cells on the two areas of the cytosensor separately. Compared to conventional multiplex biosensor, we demonstrated a novel analysis platform for the simultaneous detection of multiple cell-surface receptors; it could provide two sensitive and potential-resolved ECL signals during one potential scanning and avoid cross-reactivity between the two nanoprobes. The quantification of MCF-7 cells on the two spatially resolved areas could be achieved over the linear range from 10² to 1.0 × 10⁶ cells mL^-1 with a detection limit of 20 cells mL^-1. This multiplex cytosensor was further applied for simultaneous quantitative evaluation of the expression levels of mannose and EGFR on MCF-7 cells, revealed that the average numbers of mannose and EGFR per captured MCF-7 cell were 1.2 × 10⁶ and 0.86 × 10⁵ with the relative standard deviation of 5.3% and 4.2%, respectively. The multiplex cytosensor was capable of evaluating multiple cell-surface receptors, which would be beneficial to developing a better diagnostic tool for diseases.

Critical overview on the application of sensors and biosensors for clinical analysis

Sensors and biosensors have been increasingly used for clinical analysis due to their miniaturization and portability, allowing the construction of diagnostic devices for point-of-care testing. This paper presents an up-to-date overview and comparison of the analytical performance of sensors and biosensors recently used in clinical analysis. This includes cancer and cardiac biomarkers, hormones, biomolecules, neurotransmitters, bacteria, virus and cancer cells, along with related significant advances since 2011. Some methods of enhancing the analytical performance of sensors and biosensors through their figures of merit are also discussed.

Electrogenerated Chemiluminescence Resonance Energy Transfer between Ru(bpy)3(2+) Electrogenerated Chemiluminescence and Gold Nanoparticles/Graphene Oxide Nanocomposites with Graphene Oxide as Coreactant and Its Sensing Application

In the present work, strong anodic electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) was observed at a graphene oxide modified glassy carbon electrode (GO/GCE) in the absence of coreactants. The electrocatalytical effect of GO on the oxidation of Ru(bpy)3(2+) suggested that GO itself can act as the coreactant of Ru(bpy)3(2+) ECL, which can be used to fabricate the ECL biosensor. Thiol group terminated adenosine triphosphate (ATP) aptamer was immobilized on the GO film via DNA hybridization. When gold nanoparticles/graphene oxide (AuNPs/GO) nanocomposites were modified on the aptamer through the S-Au bond to form a sandwich-like structure, the ECL resonance energy transfer (ECL-RET) could occur between Ru(bpy)3(2+) and AuNPs/GO nanocomposites, resulting in an apparent decrease of ECL signal. After the ECL sensor was incubated in ATP solution, the AuNPs/GO nanocomposites were released from the electrode due to the specific interaction between aptamer and ATP, leading to the increased ECL signal. On the basis of these results, an ECL aptasensor was fabricated and could be used in the sensitive and selective detection of ATP in the range of 0.02-200 pM with a detection limit of 6.7 fM (S/N = 3). The proposed ECL aptasensor can be applied in the detection of ATP in real samples with satisfactory results.

Optimising electrogenerated chemiluminescence of quantum dots via co-reactant selection

We demonstrate that for quantum dot (QD) based electrochemiluminescence (ECL), the commonly used co-reactant does not perform as effectively as potassium persulfate. By exploiting this small change in co-reactant, ECL intensity can be enhanced dramatically in a cathodic-based ECL system. However, TPA remains the preferential co-reactant-based system for anodic ECL. This phenomenon can be rationalised through the relative energy-level profiles of the QD to the co-reactant in conjunction with the applied potential range. This work highlights the importance of understanding the co-reactant pathway for optimising the application of ECL to bioanalytical analysis, in particular for near-infrared (NIR) QDs which can be utilised for analysis in blood.

Graphical Abstract

Synthesis and sensing applications of polyaniline nanocomposites: a review

A comprehensive review on the synthesis of PANI nanocomposites and their applications as gas sensors and biosensors has been presented.

Immunosensors in Clinical Laboratory Diagnostics

The application of simple, cost-effective, rapid, and accurate diagnostic technologies for detection and identification of cardiac and cancer biomarkers has been a central point in the clinical area. Biosensors have been recognized as efficient alternatives for the diagnostics of various diseases due to their specificity and potential for application on real samples. The role of nanotechnology in the construction of immunological biosensors, that is, immunosensors, has contributed to the improvement of sensitivity, since they are based in the affinity between antibody and antigen. Other analytes than biomarkers such as hormones, pathogenic bacteria, and virus have also been detected by immunosensors for clinical point-of-care applications. In this chapter, we first introduced the various types of immunosensors and discussed their applications in clinical diagnostics over the recent 6 years, mainly as point-of-care technologies for the determination of cardiac and cancer biomarkers, hormones, pathogenic bacteria, and virus. The future perspectives of these devices in the field of clinical diagnostics are also evaluated.

Recent advance in fabricating monolithic 3D porous graphene and their applications in biosensing and biofuel cells

Graphene shows great potential in biosensing and bioelectronics. To facilitate graphene's applications and enhance its performance, recently, three-dimensional (3D) graphene-based materials especially free-standing porous graphene with tunable pore size and void space, have attracted increasing attention for bio-related applications owing to their special features. 3D graphene usually shows the following merits such as an interconnected porous network, a high electronic conductivity, a large active surface area, good chemical/thermal stability and can be more easily handled compared with dispersed graphene sheets. With modified surface properties, graphene can also be bio-friendly. These properties make 3D graphene a perfect candidate as high-performance electrode materials in bioelectronics devices. In this review, we discuss recent advance in fabricating monolithic 3D graphene and their applications in biosensing and biofuel cells.

Polyaniline/graphene quantum dot-modified screen-printed carbon electrode for the rapid determination of Cr(VI) using stopped-flow analysis coupled with voltammetric technique

Polyaniline/graphene quantum dots (PANI/GQDs) were used to modify a screen-printed carbon electrode (SPCE) in a flow-based system. A method for rapidly determining the Cr(VI) concentrations by using stopped-flow analysis has been developed using an Auto-Pret system coupled with linear-sweep voltammetry using the PANI/GQD-modified SPCE. The GQDs, synthesized in a botton-up manner from citric acid, were mixed with aniline monomer in an optimized ratio. The mixture was injected into an electrochemical flow cell in which electro-polymerization of the aniline monomer occurred. Under conditions optimized for determining Cr(VI), wide linearity was obtained in the range of 0.1-10 mg L(-1), with a detection limit of 0.097 mg L(-1). For a sample volume of 0.5 m L, the modified SPCE can be used continuously with a sample-throughput of more than 90 samples per hour. In addition, this proposed method was successfully applied to mineral water samples with acceptable accuracy, and the quantitative agreement was accomplished in deteriorated Cr-plating solutions with a standard traditional method for Cr(VI) detection.