Label-free Impedimetric Immunosensor Research Articles

A highly sensitive and selective label-free impedimetric immunosensor for the detection of interleukin-6 based on AuNPs@pDA@NiCo2S4@MoS2 nanocomposite.

A highly sensitive and selective label-free impedimetric immunosensor based on AuNPs@pDA@NiCo2S4@MoS2 nanocomposite modified on the surface of a screen-printed electrode (SPE) was designed for the detection of interleukin-6 (IL-6). The distribution of NiCo2S4 nanoparticles on MoS2 nanosheets was able to prevent them from agglomerating. The polydopamine (pDA) layer was coated on the surface of NiCo2S4@MoS2 nanosheets by self-polymerization, which improved the stability and biocompatibility of the nanomaterial. The excellent reduction ability of pDA promoted the synthesis of gold nanoparticles (AuNPs), which increased the amount of antibody adsorption and the conductivity of the material. Finally, the antibody (Ab) of IL-6 was immobilized on the surface of AuNPs@pDA@NiCo2S4@MoS2 nanocomposite. Electrochemical impedance spectroscopy (EIS) was used to detect the change of impedance before and after the immune response between Ab and IL-6 antigen (IL-6). Under the optimal experimental conditions, the relative change in impedance and the logarithmic concentration of IL-6 showed a good linear relationship in the range 1.00 to 1.00 × 106pg/mL, with a low detection limit of 0.97pg/mL. In addition, the proposed immunosensor performed with good reproducibility, stability, and specificity. It was successfully applied to the determination of IL-6 in patient's serum samples of head and neck carcinoma with recoveries of 98.40% to 106.5%. To sum up, the proposed label-free impedimetric immunosensor was successfully constructed for IL-6 detection in real samples.

Development of a label-free impedimetric immunosensor for the detection of respiratory syncytial virus

Development of a label-free impedimetric immunosensor for the detection of respiratory syncytial virus

A disposable impedimetric immunosensor for the analysis of CA125 in human serum samples.

Cancer antigen 125 (CA125) is the most common biomarker used to diagnose and monitor ovarian cancer progression for the last four decades, and precise detection of its levels in blood serum is crucial. In this work, label-free impedimetric CA125 immunosensors were fabricated by using screen-printed carbon electrodes modified with poly toluidine blue (PTB) (in deep eutectic solvent)/gold nanoparticles (AuNP) for the sensitive, environmentally friendly, economical, and practical analysis of CA125. The materials of PTBDES and AuNP were characterized by Fourier Transform Infrared (FT-IR), Scanning Electron Microscope (FE-SEM), and X-ray Diffraction (XRD). The analysis of the CA125 was performed by electrochemical impedance spectroscopy and the developed immunosensor. The immunosensor's repeatability, reproducibility, reusability, selectivity, and storage stability were examined. The developed label-free immunosensor allowed the determination of CA125 in fast, good repeatability and a low limit of detection (1.20pgmL-1) in the linear range of 5-100pgmL-1. The stable surface of the fabricated immunosensor was successfully regenerated ten times. The application of immunosensors in commercial human blood serum was performed, and good recoveries were achieved. The disposable label-free impedimetric CA125 immunosensor developed for the rapid and practical detection of CA125 is a candidate for use in point-of-care tests in clinical applications of ovarian cancer.

Fast analysis of Staphylococcus aureus in food products using disposable label-free nano-electrochemical immunosensor chips

Rapid analysis and early detection of food poisoning has become an important factor for the recognition and prevention of problems associated with food safety and public health. Accordingly, a number of different methods have been developed and applied for the detection and identification ofS. aureus. However, these methods are not suitable for on-site applications as they are time-consuming and laborious. Thus, a label-free impedimetric immunosensor was constructed using the self-assembling monolayer formation of the lipoic at the AuNPs@Fe3O4-screen printed electrode. The formed layer of the lipoic acid supported the covalent immobilization of anti-S. aureusantibody as the selective bio-recognition element. As a result, a specific immune reaction between the whole pathogen cells and the immobilized antibody was monitored under optimized conditions. Electrochemical impedance spectroscopy along with other chemical assessments were used to verify the stepwise assembly of the immunosensor fabrication. Accordingly, the newly developed impedimetric immunosensor showed high sensitivity and selectivity towards the targeting bacterial strain with the limit of detection and limit of quantification of 0.10, and 0.34 CFU/mL, respectively. Eventually, the designed immunosensor was successfully implemented to analyze theS. aureus contamination in milk and meat samples, whereas the obtained results were validated.

A new ITO-based Aβ42 biosensor for early detection of Alzheimer's disease

In this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of Aβ42 protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the Aβ42 protein (anti-Aβ42) was immobilized. The affinity interaction between anti-Aβ42 and Aβ42 in the immobilization steps in immunosensor fabrication and in the quantitation of Aβ42 were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1–100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an Aβ42 biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of Aβ42 in commercially purchased human serum.

Label-free electrochemical immunosensor for Ochratoxin a detection in coffee samples

Ochratoxin A (OTA) is a nephrotoxic and carcinogenic mycotoxin frequently found in coffee, which directly impacts human health and the economy of many countries. For this reason, there has been a growing need for simple and sensitive tools for the on-site detection of this mycotoxin. In this study, we developed a label-free impedimetric immunosensor to detect OTA. The biosensor was built on a thin-film gold electrode evaporated on glass substrtes, modified with a self-assembled cysteamine monolayer and anti-OTA antibodies. Atomic force microscopy and Microspectroscopy RAMAN confirmed the successful functionalization of the electrodes. The biosensor performance was evaluated by electrochemical impedance spectroscopy and the measurements indicated a linear relationship between the change in the impedance values and the OTA concentration in the range from 0.5 to 100 ng mL−1 with a limit of detection of 0.15 ng mL−1. The biosensor was highly selective and did not suffer matrix interference when analyzed in coffee samples. Furthermore, considering the small sample volumes, the short time required for analysis, and the possibility of miniaturization, the developed biosensor represents a promising analytical device for on-site coffee quality analyses.

Label-free impedimetric immunosensor for point-of-care detection of COVID-19 antibodies

The COVID-19 pandemic has posed enormous challenges for existing diagnostic tools to detect and monitor pathogens. Therefore, there is a need to develop point-of-care (POC) devices to perform fast, accurate, and accessible diagnostic methods to detect infections and monitor immune responses. Devices most amenable to miniaturization and suitable for POC applications are biosensors based on electrochemical detection. We have developed an impedimetric immunosensor based on an interdigitated microelectrode array (IMA) to detect and monitor SARS-CoV-2 antibodies in human serum. Conjugation chemistry was applied to functionalize and covalently immobilize the spike protein (S-protein) of SARS-CoV-2 on the surface of the IMA to serve as the recognition layer and specifically bind anti-spike antibodies. Antibodies bound to the S-proteins in the recognition layer result in an increase in capacitance and a consequent change in the impedance of the system. The impedimetric immunosensor is label-free and uses non-Faradaic impedance with low nonperturbing AC voltage for detection. The sensitivity of a capacitive immunosensor can be enhanced by simply tuning the ionic strength of the sample solution. The device exhibits an LOD of 0.4 BAU/ml, as determined from the standard curve using WHO IS for anti-SARS-CoV-2 immunoglobulins; this LOD is similar to the corresponding LODs reported for all validated and established commercial assays, which range from 0.41 to 4.81 BAU/ml. The proof-of-concept biosensor has been demonstrated to detect anti-spike antibodies in sera from patients infected with COVID-19 within 1 h.Photolithographically microfabricated interdigitated microelectrode array sensor chips & label-free impedimetric detection of COVID-19 antibody.

A label-free impedimetric immunosensor for zearalenone based on CS-CNT-Pd nanocomposite modified screen-printed disposable electrodes

A label-free electrochemical impedimetric immunosensor has been developed for the rapid and sensitive detection of zearalenone (ZEN) by immobilizing monoclonal anti-zearalenone antibodies (ZEN-MAb) onto the palladium nanoparticle embedded functionalized carbon nanotube-chitosan (SPCE/CS-CNT-Pd) modified electrode. This CS-CNT-Pd nanocomposite consists of finite Pd nanoparticles implanted onto the covalently functionalized CNTs by the chemical reduction method. The structure of the nanocomposite was studied by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The major advantages of the coexistence of Pd nanoparticles with CNTs are greatly enhanced conductive, catalytical properties of transducer surface, and better immobilization of bio-recognition antibody. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to verify the stepwise assemblage of the developed immunosensor. The immobilization of antibodies and the binding of zearalenone to the modified electrode increased the electron-transfer resistance (Rct), which was directly measured with EIS using [Fe(CN)6]3/4- as a redox probe. The developed immunosensor was quite sensitive and simple compared with various conventional methods. The immunosensor performance was tested under the optimized conditions, towards the detection of ZEN, from 0.25 to 16 ng mL−1 with a detection limit of 0.25 ng mL−1. The new biocompatible CS-CNT-Pd based immunosensor was successfully applied to assay ZEN in corn samples, and the good recovery values were gained, this holds the considerable promise for the sensor performance in the food industries.

An impedimetric immunosensor for the selective detection of CD34+ T-cells in human serum

Chimeric antigen receptor T (CAR-T) cell therapy has led to a paradigm change in cancer treatment. To allow widespread use of this therapy, it is important to reduce the costs associated with cells manufacturing whilst ensuring a high-quality production. Online biosensors can help monitor in real time the effectiveness of engineering CAR-T cells, with the possibility to be integrated on the workflow without the need to extract samples for off line analysis that require specialised personnel and expensive analytical equipment. In this context, we present an innovative label-free impedimetric immunosensor for the detection of CD34+ T-cells in human serum. The sensor is based on screen-printed gold electrodes functionalised with anti-CD34 antibody, via a mixed self-assembled monolayer of 11-mercaptoundecanoic acid and 6-mercapto-1-hexanol, which recognizes the CD34 antigen expressed onto the T-cells surfaces. The immunosensor exhibits a high selectivity and a wide working range in human serum, both in Faradaic and non-Faradaic detection conditions, being respectively of 230 – 1.4 × 103 cell mL−1 and 50 – 1 × 105 cell mL−1. This result, along with performance validation both in batch and flow-through operations, demonstrates the applicability of the developed immunosensor for clinical use.

Understanding the adsorption of 1 NLB antibody on polyaniline nanotubes as a function of zeta potential and surface charge density for detection of hepatitis C core antigen: A label-free impedimetric immunosensor

The interaction of colloidal species is prominently governed by their surface properties. The adsorption of charged proteins at the surface of the Polyaniline nanotubes (PN) results in the electrostatic interactions which can be moulded by controlling the surrounding zeta potential. The zeta potential of PN as a function of pH, charge density and ionic strength was determined and the results are duly explained by 1-pK model and Grahame model as empirical data fits well to these models. Similarly, the surface charge and zeta potential of the 1 NLB antibodies were also determined which later on explained the adsorption of 1 NLB antibodies on PN in aqueous media. The isoelectric point (IEP) of PN showed variation as function of surface coverage by adsorbed 1 NLB antibody mass. These results were utilized to fabricate a label-free impedimetric immunosensor aimed at the detection of hepatitis C (HCV) 1 NLB monoclonal antibodies (anticore mAbs 19D9D6). The bioactive interfacial layer was attained by the immobilization of 1 NLB monoclonal antibodies at the PN which were later on spin coated on ITO substrate for fabricating impedimetric immunosensor. The impedimetric immunosensor shows linear response range of 01 ng mL −1 to 200 ng mL −1 of HCV core antigen concentration with detection limit of 0.02 ng mL −1 (3σ/S). The charge transfer resistance change (R ct ) showed an absence of the prominent change depicting the stability of the impedimetric immunosensor whereas the sensitivity of sensor was found to be 12.215 Ω mL ng −1 . • Polyanilne nanotubes (PN) based label-free impedimetric immunosensor is proposed. • Electrokinetics of PN illuminates the changing chemistry of PN surface due to coverage by adsorbed proteins. • The charge transfer resistance increases with the increase in antigen concentration (Polypeptide 13-40 residue). • Selectivity of 12.215 Ω mL ng -1 was achieved due to the specific nature of 1 NLB interaction with HCV core nucleocapsid polypeptide antigen.

Fabrication of electrochemical immunosensor based on GCN-β-CD/Au nanocomposite for the monitoring of vitamin D deficiency

Serum 25-hydroxyvitamin D (25(OH)D) has been clinically considered as a novel biomarker for vitamin D deficiency. The current standard technologies for the detection of 25(OH)D are performed in sophisticated laboratories exhibiting the practical limitations for onsite and affordable testing. Therefore, the development of a cost-effective device for Vitamin D is extremely necessary to provide an earlier diagnosis. Herein, for the first time, we propose a novel label-free impedimetric immunosensor for the detection and quantification of 25-hydroxyvitamin D3 (25(OH)D3) biomarker in serum samples based on the Au nanoparticles functionalized GCN–β-CD nanocomposite. To fabricate the sensing probe, Ab-25(OH)D3 antibodies were covalently immobilized on GCN–β-CD@Au/GCE using carbodiimide chemistry. The surface morphology and structural properties of constructed immunosensor were confirmed by different analytical techniques. Electrochemical impedance spectroscopy technique (EIS) has been selected as the main detection method to measure the Antibody (Ab) and Antigen (Ag) interaction at the immunosensor surface because it is label-free, less destructive to the activities of the biomolecule, and highly sensitive. The as-prepared immunosensor exhibited an excellent concentration range from 0.1 ng/ml to 500 ng/ml with the lowest limit of detection of 0.01 ng/ml. Furthermore, the sensing probe was validated in serum samples and obtained results were compared with the standard CLIA technique. The results have revealed that the sensing probe could be used for clinical diagnosis of Vitamin D deficiency in the clinical laboratories.

Electrochemical and morphological layer-by-layer characterization of electrode interfaces during a label-free impedimetric immunosensor build-up: The case of ochratoxin A

In this paper, we provide an in-depth electrochemical characterization of a label-free impedimetric immunosensor for rapid detection of ochratoxin A. The sensor was based on a carbodiimide-mediated amide coupling reaction to immobilize a specific ochratoxin A antibody onto 4-mercaptobenzoic acid-modified commercial screen-printed gold electrode. Different variables affecting the performance of the developed sensor were optimized. Cyclic voltammetry and electrochemical impedance spectroscopy were used to analyse modifications of the interfacial properties occurring at each step of the biosensor assembly. The free electrode surface area, the diffusion coefficient, the peak-to-peak separation, the heterogeneous electron transfer constant, and charge transfer resistance have been calculated and compared. The decrease of charge transfer resistance values was linearly proportional to the ochratoxin A concentration in the range of 0.37– 2.86 ng/mL, with a detection limit of 0.19 ng/mL, a limit of quantification of 0.40 ng/mL, very good selectivity, reproducibility, and storage stability in the absence of antifouling agents. Surface morphology and topographic data at each step of the immunosensor assembly were studied by Atomic Force Microscopy, which also provided information on the specific binding of ochratoxin A. Finally, contact angle measurements revealed the hydrophilicity evolution of the surface during sensor assembly enabling OTA binding.

A novel label-free impedimetric immunosensor for sensitive detection of prostate specific antigen using Au nanoparticles/MWCNTs- graphene quantum dots nanocomposite

In this study, a novel impedimetric immunosensor based on Au nanoparticles@ multiwall carbon nanotubes-graphene quantum dots (AuNPs@MWCNTs-GQDs) was designed for the detection of prostate cancer biomarker with high sensitivity and selectivity in human serum. This label-free immunosensor was constructed by glassy carbon electrode surface coating with AuNPs@MWCNTs-GQDs as a signal amplifier and then an antibody against ،Prostate specific antigen)PSA(was immobilized on the modified electrode. The constructed immunosensor was characterized using transmission electron microscopy (TEM), Energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques. EIS measurements were applied to investigate the specific immuno-interactions at the immunosensor surface utilizing redox probe [Fe (CN)6]3−/4− to detect prostate specific antigen (PSA). The label-free immunosensor was successfully used to improve the analytical performance significantly and the impedance increment was linearly related to the PSA concentration in a wide linear range of 1–10,000 pg/mL and a low detection limit of 0.48 pg/mL. The responses of the proposed immunosensor in the real samples were compared with the commercial enzyme-linked immunosorbent assay (ELISA) method. The obtained were in good agreement with those obtained by the reference ELISA method. Therefore, this sensor with high sensitivity, selectivity and repeatability, could be utilized for early clinical diagnosis of prostate cancer in the clinical laboratories.

Label free Impedimetric Immunosensor for effective bladder Cancer detection in clinical urine samples.

Galectin-1 protein has been recently recognized as a valuable urinary biomarker for the diagnosis and prognosis of bladder cancer. Herein, we present a sensitive and specific impedimetric immunosensor for the quantitative and label free detection of Galectin-1 protein in clinical urine samples. The immunosensor consists of nine gold interdigitated microelectrodes (3 × 3 array), which can simultaneously monitor multiple immunoreactions by analyzing the normalized impedance variations at each microelectrode during immunosensing. To obtain enhanced sensitivities, we have utilized Galectin-1/Al2O3 nanoprobes (Galectin-1 antibody conjugated to alumina nanoparticles) that can be selectively trapped on the microelectrode surface using positive dielectrophoresis (p-DEP). Preliminary studies highlight the feasibility of the proposed immunosensor for Gal -1 detection in T24 cell lysate spiked phosphate buffer saline and artificial urine samples with a limit of detection that is estimated to be in the pg/ml range. To verify its practical feasibility, we have tested the immunosensor for Galectin-1 detection in clinical urine samples obtained from normal patients and those diagnosed with bladder cancer. Analysis of the clinical tests shows that the median normalized impedance variation during immunosensing for 22 cancer patients and 26 normal patients is 27% and 10%, respectively, with an identified cutoff point of 19.5% above which the sensitivity and specificity of bladder cancer detection was 82.1% and 80.8%, respectively. Based on these results, the proposed immunosensor shows promise for bladder cancer diagnosis and prognosis in a point of care format, thus enabling improved public health monitoring.

A bimetallic CoNi-based metal−organic framework as efficient platform for label-free impedimetric sensing toward hazardous substances

A novel bimetallic CoNi-based metal−organic framework (CoNi-MOF) has been synthesized using the mixed organic linkers of 4-(1H-tetrazol-5-yl)benzoic acid (H2TZB) and 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT), which can be employed as a platform for the feasible construction of label-free impedimetric immunosensor to efficiently detect the trace hazardous substances of deoxynivalenol (DON) and salbutamol (SAL). As compared with the individual Co-MOF and Ni-MOF, the bimetallic CoNi-MOF exhibits much smaller particle sizes and superior electrochemical activity. Owing to the carboxyl groups of H2TZB that can generate electrostatic interaction with the amino groups of antibodies to realize the high immobilization amounts of antibodies, as well as the π−π* stacking and multivalent affinity interactions between CoNi-MOF and antibodies, the as-prepared CoNi-MOF shows excellent biosensing ability toward analytes determined by electrochemical techniques. The developed CoNi-MOF-based electrochemical immunosensor demonstrates high sensitivity with low detection limits of 0.05 and 0.30 pg·mL−1 toward DON and SAL, respectively, in the concentration range of 0.001 to 0.5 ng·mL−1, which also shows good selectivity in the presence of other interferences. Therefore, with the advantages of high sensitivity, good selectivity, and simple operation, this new strategy is believed to exhibit great potential for convenient detection of poisonous and harmful residues in foods.

A label-free impedimetric immunosensor based on covalent immobilization of anti-E. Coli antibody via a copper-catalyzed azide-alkyne cycloaddition reaction.

In this article, an original method is proposed for address and covalent immobilization of anti-E. coli antibodies on a screen-printed electrode (SPE). The method is based on a copper-catalyzed "click" reaction between a polyvinylbenzylazide (PVBA) film electrochemically deposited on the electrode surface and acetylene fragments of propargyl-N-hydroxysuccinimide ester. The products of electrochemical oxidation of copper particles incorporated in the polymer film on the electrode were first used for catalysis of the click reaction. This approach allowed us to reduce the immobilization time from a few hours for conventional methods to just 30min, and to prevent denaturation of the immunoreceptor. The modified electrodes were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Based on the results obtained, a label-free impedimetric immunosensor for E. coli detection was developed. The detection limit of the immunosensor was estimated as 6.3CFU/ml, with a linear range of 103-106CFU/ml. The immunosensor demonstrated good stability during 30days of storage in phosphate buffer solution (PBS, pH7) and selectivity toward excess Staphylococcus aureus bacteria.

A label-free and sensitive impedimetric immunosensor for TNF α biomarker detection based on epoxysilane-modified disposable ITO-PET electrode

ABSTRACTThe present study constructed a simple and cost-effective electrochemical immunosensor based on 3-glycidoxypropyltriethoxysilane (GPTES) monolayer coated indium tin oxide-polyethylene terephthalate (ITO-PET) electrode for selective and sensitive determination of Tumour necrosis factor α (TNF α) cancer biomarker. GPTES was a well-known surface coupling silane agent which had epoxy groups to bind antibodies. Anti-TNF α antibodies were chosen as biorecognition elements and they attached covalently on the GPTES modified ITO-PET electrode. Electrochemical determination of immunoreaction between anti-TNF α antibodies and TNF α antigens was the basic principle of the proposed immunosensor. The electrochemical characterisation of the designed biosensor was tested with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. In addition, the surface morphological characteristics of the ITO-PET electrodes after several modification stages were monitored by scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging. The analytical success of the proposed immunosensor was tested with respect to linear detection range, detection limit, repeatability, reproducibility, reusability, regeneration and long-term stability. The present biosensor had a wide linear range from 0.01 to 1.5 pg/mL and a low detection limit of 3.1 fg/mL. Finally, the biosensor successfully detected TNF α cancer biomarker in human serum samples with high recovery ranges.

An insight into impedimetric immunosensor and its electrical equivalent circuit

We report the effect of multi-component film, formed during fabrication of nanoparticles modified label-free impedimetric immunosensor, on its physico-chemical properties and the electrical equivalent circuit designing. As a model system, we fabricated an immunosensor by modifying the screen printed electrode with gold nanoparticles followed by anti-TSH antibody immobilization and blocking the electrode surface with BSA. Randles equivalent circuit fails to mimic the impedimetric response of the immunosensor, with error as high as 6%. We have proposed an open finite diffusion element to incorporate the diffusive behaviour within the Nernst Layer formed by complex nanoparticle-antibody-blocking agent layer, in addition to the Cole-Cole element for addressing the suppressed impedimetric curves with lesser curvature exhibited by immunosensor. This equivalent circuit reduces the error to 1.5–2%, making it suitable for usage in EIS based diagnostic device development.

Graphene Quantum Dots Decorated Gold-Polyaniline Nanowire for Impedimetric Detection of Carcinoembryonic Antigen

A label-free impedimetric immunosensor based on N, S-graphene quantum dots@Au-polyaniline (N, S-GQDs@Au-PANI) nanowires was fabricated for the quantitative detection of carcinoembryonic antigen (CEA). The N, S-GQDs and Au-PANI were synthesized by a simple hydrothermal pyrolysis and interfacial polymerization, respectively. Subsequently, 2–9 nm N, S-GQDs are successfully decorated onto 30–50 nm Au-PANI nanowires by Au-thiol linkage to serve as the bifunctional probe for amplifying the electrochemical activity as well as anchoring anti-CEA. The N, S-GQDs@Au-PANI nanowires are excellent conducting materials to accelerate the electron transfer, while the formation of CEA antibody-antigen bioconjugates after the addition of CEA significantly increase the charge transfer resistance, and subsequently provides a highly stable and label-free immunoassay platform for the impedimetric detection of CEA. The label-free immunosensor exhibits a wide linear range from 0.5 to 1000 ng mL−1 with a low detection limit of 0.01 ng mL−1. The N, S-GQDs@Au-PANI based immunosensor also shows high selectivity and stability over other cancer makers and amino acids. Moreover, this promising platform is successfully applied to the detection of CEA in human serum samples with excellent recovery of (96.0 ± 2.6)–(103 ± 3.8)%. These results clearly demonstrate a newly developed highly efficient and label-free impedimetric immunosensor for the detection of CEA using N, S-GQDs@Au-PANI nanowires as the biosensing probe, which can pave the gateway for the fabrication of high performance and robust impedimetric immunosensor to detect cancer makers in early stage of cancer diagnosis and therapy.

Label-free impedimetric immunosensor based on arginine-functionalized gold nanoparticles for detection of DHEAS, a biomarker of pediatric adrenocortical carcinoma

Pediatric adrenocortical carcinoma (pACC) is a rare and aggressive malignancy of high occurrence in Southern Brazil. pACC is characterized by the usual overproduction of dehydroepiandrosterone sulfate (DHEAS), whose detection in serum or plasma can be effective to the early diagnosis of the disease. Therefore, the present paper reports, for the first time, the construction and application of a label-free impedimetric immunosensor to detect DHEAS, which was based on the modification of an oxidized glassy carbon electrode with arginine-functionalized gold nanoparticles (AuNPs-ARG) and anti-DHEA IgM antibodies (ox-GCE/AuNPs-ARG/IgM). AuNPs-ARG was synthesized by a green route, and characterized by UV–VIS spectroscopy, FTIR, TEM, DLS, and XRD. The construction of ox-GCE/AuNPs-ARG/IgM was optimized through factorial design and response surface methodology. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were employed to characterize the optimized immunosensor. The DHEAS detection principle was based on the variation of charge transfer resistance (∆Rct) relative to the Fe(CN)64−/3− electrochemical probe after immunoassays in the presence of the biomarker. A linear relationship between ∆Rct and DHEAS concentration was verified in the range from 10.0 to 110.0 µg dL−1, with a LOD of 7.4 µg dL−1. Besides the good sensitivity, the immunosensor displayed accuracy, stability, and specificity to detect DHEAS. The promising analytical performance of ox-GCE/AuNPs-ARG/IgM was confirmed by quantifying DHEAS in real patient plasma samples, with results that were comparable to the reference chemiluminescence assay. Our results suggest that the presented immunosensor can find clinical applications in the early diagnosis of pACC and to monitor DHEAS levels in other adrenal pathologies.