Nanoelectrode ensembles as recognition platform for electrochemical immunosensors

A D-Shaped Polymer Optical Fiber Surface Plasmon Resonance Biosensor for Breast Cancer Detection Applications

Fiber-optic biosensors have garnered significant attention and witnessed rapid development in recent years owing to their remarkable attributes such as high sensitivity, immunity to electromagnetic interference, and real-time monitoring. They have emerged as a potential tool in the realm of biomarker detection for low-concentration and small molecules. In this paper, a portable and cost-effective optical fiber biosensor based on surface plasmon resonance for the early detection of breast cancer is demonstrated. By utilizing the aptamer human epidermal growth factor receptor 2 (HER2) as a specific biomarker for breast cancer, the presence of the HER2 protein can be detected through an antigen-antibody binding technique. The detection method was accomplished by modifying a layer of HER2 aptamer on the flat surface of a gold-coated D-shaped polymer optical fiber (core/cladding diameter 120/490 μm), of which the residual thickness after side-polishing was about 245 μm, the thickness of the coated gold layer was 50 nm, and the initial wavelength in pure water was around 1200 nm. For low-concentration detection of the HER2 protein, the device exhibited a wavelength shift of ~1.37 nm with a concentration of 1 μg/mL (e.g., 5.5 nM), which corresponded to a limit of detection of ~5.28 nM. Notably, the response time of the biosensor was measured to be as fast as 5 s. The proposed biosensor exhibits the potential for early detection of HER2 protein in initial cancer serum and offers a pathway to early prevention of breast cancer.

Development of Electrochemical Immunosensors for HER-1 and HER-2 Analysis in Serum for Breast Cancer Patients

In this work, two human epidermal growth factor receptors, HER-1 and HER-2, were selected as biomarkers to enable the detection of breast cancer. Therefore, two biosensors were developed using gold sensor chips coupled with amperometric detection of the enzyme label horse radish peroxidase (HRP). The biosensors/immunosensors relied on indirect sandwich enzyme-linked immunosorbent assays with monoclonal antibodies (Ab) against HER-1 and HER-2 attached to the sensors to capture the biomarkers. Detection polyclonal antibodies followed by secondary anti-rabbit (for HER-1) and anti-goat (for HER-2) IgG antibody-HRP were then applied for signal generation. In buffer, the developed sensors showed limits of detections (LOD) of 1.06 ng mL^-1 and 0.95 ng mL^-1 and limits of quantification (LOQ) of 2.1 ng mL^-1 and 1.5 ng mL^-1 for HER-1 and HER-2, respectively. In 100% (undiluted) serum, LODs of 1.2 ng mL^-1 and 1.47 ng mL^-1 and LOQs of 1.5 ng mL^-1 and 2.1 ng mL^-1 were obtained for HER-1 and HER-2, respectively. Such limits of detections are within the serum clinical range for the two biomarkers. Furthermore, gold nanoparticles (AuNP) labelled with secondary anti-rabbit and anti-goat IgG antibody-HRP were then used to enhance the assay signal and increase the sensitivity. In buffers, LODs of 30 pg mL^-1 were seen for both sensors and LOQs of 98 pg mL^-1 and 35 pg mL^-1 were recorded for HER-1 and HER-2, respectively. For HER-2 the AuNPs biosensor was also tested in 100% serum obtaining a LOD of 50 pg mL^-1 and a LOQ of 80 pg mL^-1. The HER-2 AuNP electrochemical immunosensor showed high specificity with very low cross-reactivity to HER-1. These findings demonstrate that the two developed sensors can enable early detection as well as monitoring of disease progression with a beneficial impact on patient survival and clinical outcomes.

Nanotechnology‐based electrochemical biosensors for monitoring breast cancer biomarkers

Breast cancer is categorized as the most widespread cancer type among women globally. On-time diagnosis can decrease the mortality rate by making the right decision in the therapy procedure. These features lead to a reduction in medication time and socioeconomic burden. The current review article provides a comprehensive assessment for breast cancer diagnosis using nanomaterials and related technologies. Growing use of the nano/biotechnology domain in terms of electrochemical nanobiosensor designing was discussed in detail. In this regard, recent advances in nanomaterial applied for amplified biosensing methodologies were assessed for breast cancer diagnosis by focusing on the advantages and disadvantages of these approaches. We also monitored designing methods, advantages, and the necessity of suitable (nano) materials from a statistical standpoint. The main objective of this review is to classify the applicable biosensors based on breast cancer biomarkers. With numerous nano-sized platforms published for breast cancer diagnosis, this review tried to collect the most suitable methodologies for detecting biomarkers and certain breast cancer cell types.

Electrochemical Profiling of Plants

The profiling, or fingerprinting, of distinct varieties of the Plantae kingdom is based on the bioactive ingredients, which are systematically segregated to perform their detailed analysis. The secondary products portray a pivotal role in defining the ecophysiology of distinct plant species. There is a crucial role of the profiling domain in understanding the various features, characteristics, and conditions related to plants. Advancements in variable technologies have contributed to the development of highly specific sensors for the non-invasive detection of molecules. Furthermore, many hyphenated techniques have led to the development of highly specific integrated systems that allow multiplexed detection, such as high-performance liquid chromatography, gas chromatography, etc., which are quite cumbersome and un-economical. In contrast, electrochemical sensors are a promising alternative which are capable of performing the precise recognition of compounds due to efficient signal transduction. However, due to a few bottlenecks in understanding the principles and non-redox features of minimal metabolites, the area has not been explored. This review article provides an insight to the electrochemical basis of plants in comparison with other traditional approaches and with necessary positive and negative outlooks. Studies consisting of the idea of merging the fields are limited; hence, relevant non-phytochemical reports are included for a better comparison of reports to broaden the scope of this work.

Current Approaches to Monitor Macromolecules Directly from the Cerebral Interstitial Fluid

Gaining insights into the pharmacokinetic and pharmacodynamic properties of lead compounds is crucial during drug development processes. When it comes to the treatment of brain diseases, collecting information at the site of action is challenging. There are only a few techniques available that allow for the direct sampling from the cerebral interstitial space. This review concerns the applicability of microdialysis and other approaches, such as cerebral open flow microperfusion and electrochemical biosensors, to monitor macromolecules (neuropeptides, proteins, …) in the brain. Microdialysis and cerebral open flow microperfusion can also be used to locally apply molecules at the same time at the site of sampling. Innovations in the field are discussed, together with the pitfalls. Moreover, the ‘nuts and bolts’ of the techniques and the current research gaps are addressed. The implementation of these techniques could help to improve drug development of brain-targeted drugs.

Electrogenerated Chemiluminescence Immunoassays on Nanoelectrode Ensembles Platform with Magnetic Microbeads for the Determination of Carbohydrate Antigen

This work reports a gold nanoelectrode ensembles (Au-NEE) platform taken as a disposable electrogenerated chemiluminescence (ECL) platform with immunomagnetic microbeads for ECL immunoassays for the first time. The peak-shaped voltammograms were obtained at the Au-NEE, attributed to the total diffusional overlap. The ECL intensity at Au-NEE was 12.9 folds in the Ru(bpy)₃²⁺-tri-n-propylamine (TPA) ECL system and 19.6 folds in the luminol-H₂O₂ system, compared with that at the Au macroelectrode using the normalized active area of the electrodes, mainly attributed to the diffusion overlap of the Au-NEE and the edge effect of the individual gold nanodisks of the Au-NEE. The ECL immunoassay on the Au-NEE platform with magnetic microbeads for the determination of cancer biomarkers was developed. Carbohydrate antigen 19-9 (CA 19-9) was chosen as a model analyte while CA 19-9 antibody on the magnetic microbeads was taken as the capture probe, and ruthenium complex-labeled CA 19-9 antibody was used as the signal probe. A "sandwich" bioconjugates on the magnetic beads were transferred onto the ECL platform, and then the ECL measurements were performed in TPA solution. The developed method showed that the ECL peak intensity was directly in proportion to the concentration of CA 19-9 in the range from 0.5 to 20 U/mL with a limit of detection of 0.4 U/mL. This work demonstrates that the Au-NEE can be employed as a useful disposable ECL platform with the merits of cheapness, low nonspecific adsorption and practical application. The proposed approach will open a new avenue in the point-of-care test for the determination of protein biomarkers.

Immunomagnetic bead-based bioassay for the voltammetric analysis of the breast cancer biomarker HER2-ECD and tumour cells using quantum dots as detection labels

An electrochemical magnetic immunosensing strategy was developed for the determination of HER2-ECD, a breast cancer biomarker, and breast cancer cells in human serum. A sandwich assay was performed on carboxylic acid-functionalized magnetic beads (MBs) using a screen-printed carbon electrode (SPCE) as transducer surface. The affinity process was detected using electroactive labels; core/shell streptavidin-modified CdSe@ZnS Quantum Dots (QDs). Cd²⁺ ions, released from the QDs, were determined by differential pulse anodic stripping voltammetry (DPASV). An assay time of 90 min, with an actual hands-on time of about 20 min, a linear range between 0.50-50 ng·mL^-1 of HER2-ECD and a limit of detection of 0.29 ng·mL^-1 were achieved. Analysis of live breast cancer cells was also performed using the optimized assay. Breast cancer cell lines SK-BR-3 (a HER2-positive cell line), MDA-MB-231 (a HER2-negative cell line) and MCF-7 (a cell line with low HER2 expression) were tested. The selectivity of the assay towards SK-BR-3 cells was confirmed. A concentration-dependent signal that was 12.5× higher than the signal obtained for the HER2-negative cells (MDA-MB-231) and a limit of detection of 2 cells·mL^-1 was obtained. Graphical abstractSchematic representation of the electrochemical immunomagnetic assay for the determination of the breast cancer biomarker HER2-ECD and cancer cells using magnetic beads (MBs), a screen-printed carbon electrode (SPCE) as transducer surface and quantum dots (QD) as electroactive labels.

Quantum dots as nanolabels for breast cancer biomarker HER2-ECD analysis in human serum

Early detection of cancer increases the possibility for an adequate and successful treatment of the disease. Therefore, in this work, a disposable electrochemical immunosensor for the front-line detection of the ExtraCellular Domain of the Human Epidermal growth factor Receptor 2 (HER2-ECD), a breast cancer biomarker, in a simple and efficient manner is presented. Bare screen-printed carbon electrodes were selected as the transducer onto which a sandwich immunoassay was developed. The affinity process was detected through the use of an electroactive label, core/shell CdSe@ZnS Quantum Dots, by differential pulse anodic stripping voltammetry in a total time assay of 2 h, with an actual hands-on time of less than 30 min. The proposed immunosensor responded linearly to HER2-ECD concentration within a wide range (10-150 ng/mL), showing acceptable precision and a limit of detection (2.1 ng/mL, corresponding to a detected amount (sample volume = 40 μL) of 1.18 fmol) which is about 7 times lower than the established cut-off value (15 ng/mL). The usefulness of the developed methodology was tested through the analysis of spiked human serum samples. The reliability of the presented biosensor for the selective screening of HER2-ECD was confirmed by analysing another breast cancer biomarker (CA15-3) and several human serum proteins.

Electrochemical immunosensor with surface-confined probe for sensitive and reagentless detection of breast cancer biomarker

Sensitive and reliable detection of tumour markers is of great significance for early diagnosis and monitoring recurrence of cancers. Herein, a simple electrochemical immunosensor is developed with an integrated electrochemical probe on the sensing surface, which is able to sensitively and reagentlessly detect the breast cancer biomarker, human epidermal growth factor receptor 2 (ErbB2). Ferrocene (Fc) is chosen as the signal indicator and covalently grafted on cationic polyelectrolyte poly(ethylene imine) (Fc-PEI). The redox Fc-PEI could alternately assemble with carboxyl functionalized single-walled carbon nanotubes (SWNTs) on an indium tin oxide electrode through layer-by-layerelectrostatic assembly. After Anti-ErbB2 antibody is covalently immobilized onto the outermost SWNTs layer followed by blocking the electrode with bovine serum albumin, a sensing interface with recognitive probe and electrochemical probe is obtained. In the presence of ErbB2, the formed antigen–antibody complex makes a barrier to inhibit electro-transfer of inner Fc, leading to a decreased electrochemical response. Owing to the SWNTs-facilitated charge transfer and abundant surface-bound probes, the developed sensor demonstrates outstanding performance for reagentless detection of ErbB2 in terms of wide detection range (1.0–200.0 ng mL⁻¹) and low detection limit (0.22 ng mL⁻¹). The developed immunosensor also exhibits good selectivity, reproducibility and stability. Real analysis of ErbB2 in human serum samples is also demonstrated.

An electrochemical immunosensor with surface-confined redox probes as signal indicators was developed via LBL self-assembly technique for sensitive and reagentless detection of ErbB2.

An aptamer-based colorimetric lateral flow assay for the detection of human epidermal growth factor receptor 2 (HER2)

An aptamer-based colorimetric lateral flow assay was developed for the detection of human epidermal growth factor receptor 2 (HER2). In this study, two approaches were examined using HER2 binding aptamers and gold nanoparticles. The first method used was a solution-based adsorption-desorption colorimetric approach wherein aptamers were adsorbed onto the gold nanoparticle surface. Upon the addition of HER2, HER2 binds specifically with its aptamer, releasing the gold nanoparticles. Addition of NaCl then induces the formation of gold nanoparticle aggregates. This leads to a color change from red to blue and a detection limit of 10 nM was achieved. The second method used an adsorption-desorption colorimetric lateral flow assay approach wherein biotin-modified aptamers were adsorbed onto the gold nanoparticle surface in the absence of HER2. In the presence of HER2, HER2 specifically binds with its aptamer leading to release of the gold nanoparticles. These solutions were applied to the lateral flow assay format and a detection limit of 20 nM was achieved. Both colorimetric and lateral flow assays are inexpensive, simple, rapid to perform and produce results visible to the naked-eye.

Electrochemical Immunosensor Based on Nanoelectrode Ensembles for the Serological Analysis of IgG-type Tissue Transglutaminase

Celiac disease (CD) is a gluten-dependent autoimmune disorder affecting a significant percentage of the general population, with increasing incidence particularly for children. Reliable analytical methods suitable for the serological diagnosis of the disorder are urgently required for performing both the early diagnosis and the follow-up of a patient adhering to a gluten-free diet. Herein we report on the preparation and application of a novel electrochemical immunosensor based on the use of ensembles of gold nanoelectrodes (NEEs) for the detection of anti-tissue transglutaminase (anti-tTG), which is considered one reliable serological marker for CD. To this end, we take advantage of the composite nature of the nanostructured surface of membrane-templated NEEs by functionalizing the polycarbonate surface of the track-etched membrane with tissue transglutaminase. Incubation of the functionalized NEE in anti-tTG samples results in the capture of the anti-tTG antibody. Confirmation of the recognition event is achieved by incubating the NEE with a secondary antibody labelled with horseradish peroxidase (HRP): in the presence of H₂O₂ as substrate and hydroquinone as redox mediator, an electrocatalytic current is indeed generated whose increment is proportional to the amount of anti-tTG captured from the sample. The optimized sensor allows a detection limit of 1.8 ng mL⁻¹, with satisfactory selectivity and reproducibility. Analysis of serum samples from 28 individuals, some healthy and some affected by CD, furnished analytical results comparable with those achieved by classical fluoroenzyme immunoassay (FEIA). We note that the NEE-based immunosensor developed here detects the IgG isotype of anti-tTG, while FEIA detects the IgA isotype, which is not a suitable diagnostic marker for IgA-deficient patients.

Bloch Surface Waves Biosensors for High Sensitivity Detection of Soluble ERBB2 in a Complex Biological Environment

We report on the use of one-dimensional photonic crystals to detect clinically relevant concentrations of the cancer biomarker ERBB2 in cell lysates. Overexpression of the ERBB2 protein is associated with aggressive breast cancer subtypes. To detect soluble ERBB2, we developed an optical set-up which operates in both label-free and fluorescence modes. The detection approach makes use of a sandwich assay, in which the one-dimensional photonic crystals sustaining Bloch surface waves are modified with monoclonal antibodies, in order to guarantee high specificity during the biological recognition. We present the results of exemplary protein G based label-free assays in complex biological matrices, reaching an estimated limit of detection of 0.5 ng/mL. On-chip and chip-to-chip variability of the results is addressed too, providing repeatability rates. Moreover, results on fluorescence operation demonstrate the capability to perform high sensitive cancer biomarker assays reaching a resolution of 0.6 ng/mL, without protein G assistance. The resolution obtained in both modes meets international guidelines and recommendations (15 ng/mL) for ERBB2 quantification assays, providing an alternative tool to phenotype and diagnose molecular cancer subtypes.

Reduced graphene oxide-chitosan-aptamer interface as new platform for ultrasensitive detection of human epidermal growth factor receptor 2

The present work describes an ultrasensitive electrochemical aptamer-based assay for detection of human epidermal growth factor receptor 2 protein (HER2) cancer biomarker as a model analyte. Results show that the reduced graphene oxide-chitosan (rGO-Chit) film as a suitable electrode material possesses great favorable properties including high homogeneity, good stability, large surface area and high fraction of amine groups as aptamer binding sites. Various steps of aptasensor fabrication were characterized using microscopic, energy-dispersive X-ray spectroscopy (EDAX), Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques. Using methylene blue (MB) as an electrochemical probe and differential pulse voltammetry (DPV) technique, two linear concentration ranges of 0.5-2ngml^-1 and 2-75ngml^-1 were obtained with a high sensitivity of 0.14μAng^-1ml and a very low detection limit of 0.21ngml^-1 (very lower than the clinical cut-off). The fabricated aptasensor showed excellent selectivity for detection of HER2 in complex matrix of human serum samples. The sensitive detection of HER2 can be attributed to the multiple signal amplification of MB during its accumulation to the modified electrode surface via both affinity interaction to aptamer molecules and electrostatic adsorption to the HER2 analyte as well as high charge transfer kinetic properties of the applied rGO-Chit film. The rapid and simple preparation of the proposed aptasensor as well as its high selectivity, stability and reproducibility provided a promising protocol for non-invasive diagnosis for various points of care application. The proposed aptasensor showed excellent analytical performance in comparison with current HER2 biosensors.

Nanobiosensing with Arrays and Ensembles of Nanoelectrodes

Since the first reports dating back to the mid-1990s, ensembles and arrays of nanoelectrodes (NEEs and NEAs, respectively) have gained an important role as advanced electroanalytical tools thank to their unique characteristics which include, among others, dramatically improved signal/noise ratios, enhanced mass transport and suitability for extreme miniaturization. From the year 2000 onward, these properties have been exploited to develop electrochemical biosensors in which the surfaces of NEEs/NEAs have been functionalized with biorecognition layers using immobilization modes able to take the maximum advantage from the special morphology and composite nature of their surface. This paper presents an updated overview of this field. It consists of two parts. In the first, we discuss nanofabrication methods and the principles of functioning of NEEs/NEAs, focusing, in particular, on those features which are important for the development of highly sensitive and miniaturized biosensors. In the second part, we review literature references dealing the bioanalytical and biosensing applications of sensors based on biofunctionalized arrays/ensembles of nanoelectrodes, focusing our attention on the most recent advances, published in the last five years. The goal of this review is both to furnish fundamental knowledge to researchers starting their activity in this field and provide critical information on recent achievements which can stimulate new ideas for future developments to experienced scientists.

Biosensors for breast cancer diagnosis: A review of bioreceptors, biotransducers and signal amplification strategies

Breast cancer is highly prevalent in females and accounts for second highest number of deaths, worldwide. Cumbersome, expensive and time consuming detection techniques presently available for detection of breast cancer potentiates the need for development of novel, specific and ultrasensitive devices. Biosensors are the promising and selective detection devices which hold immense potential as point of care (POC) tools. Present review comprehensively scrutinizes various breast cancer biosensors developed so far and their technical evaluation with respect to efficiency and potency of selected bioreceptors and biotransducers. Use of glycoproteins, DNA biomarkers, micro-RNA, circulatory tumor cells (CTC) and some potential biomarkers are introduced briefly. The review also discusses various strategies used in signal amplification such as nanomaterials, redox mediators, p19 protein, duplex specific nucleases (DSN) and redox cycling.

Purification and immunodetection of the complete recombinant HER-2[neu] receptor produced in yeast

For the first time, the full length recombinant HER-2[neu] receptor has been produced in a yeast (Arxula adeninivorans). It is one of the most studied membrane receptors in oncology and is involved in aggressive tumor formation. A yeast integration rDNA cassette containing the human gene coding for the HER-2[neu] protein was constructed and a screening procedure was performed to select the most productive transformant. Different detergents were tested for efficient solubilization of the membrane bound protein, with CHAPS giving the best results. To increase the yield of the recombinant protein from HER-2[neu] producing A. adeninivorans, optimal culture parameters were established for cultivation in bioreactor. The recombinant protein was subsequently assayed using ELISA and SPR immunoassays systems with antibodies raised against two different epitopes of the human receptor. In both cases, elution fractions containing the recombinant HER-2[neu] receptor successfully reacted with the immunoassays with limits of quantification below 100ngml(-1). These results demonstrate that the full length recombinant HER-2[neu] reported here has the potential to be a new standard for the detection of HER-2 type cancer.

MultisHRP-DNA-coated CMWNTs as signal labels for an ultrasensitive hepatitis C virus core antigen electrochemical immunosensor

An ultrasensitive and selective electrochemical immunosensor was developed for the detection of hepatitis C virus (HCV) core antigen. The immunosensor consists of graphitized mesoporous carbon-methylene blue (GMCs-MB) nanocomposite as an electrode modified material and a horseradish peroxidase-DNA-coated carboxyl multi-wall carbon nanotubes (CMWNTs) as a secondary antibody layer. After modification of the electrode with GMCs-MB nanocomposite, Au nanoparticles were electrodeposited on to the electrode to immobilize the captured antibodies. The bridging probe and secondary antibodies linked to the CMWNTs, and DNA concatamers were obtained by hybridization of the biotin-tagged signal and auxiliary probes. Finally, streptavidin-horseradish peroxidases (HRP) were labeled on the secondary antibody layer via biotin-streptavidin system. The reduction current of MB were generated in the presence of hydrogen peroxide and monitored by square wave voltammetry. Under optimum conditions, the amperometric signal increased linearly with the core antigen concentration (0.25pgmL(-1) to 300pgmL(-1)). The immunosensor exhibites the detection limit as low as 0.01pgmL(-1) and it has a high selectivity. The new protocol showed acceptable stability and reproducibility, as well as favorable recovery for HCV core antigen in human serum. The proposed immunosensor has great potential for clinical applications.