Carboxyethylsilanetriol-Coated Magnetic Nanoparticles as an Ultrasensitive Immunoplatform for Electrochemical Magnetosensing of Cotinine.

In the present study, an innovative and simple electrochemical magneto biosensor based on carboxyethylsilanetriol-modified iron oxide (Fe3O4) magnetic nanoparticles was designed for ultrasensitive and specific analysis of cotinine, an important marker of smoking. Anticotinine antibodies were covalently immobilized on carboxylic acid-modified magnetic nanoparticles, and the cotinine-specific magnetic nanoparticles created a specific surface on the working electrode surface. The use of magnetic nanoparticles as an immobilization platform for antibodies provided a large surface area for antibody attachment and increased sensitivity. In addition, the advantages of the new immobilization platform were reusing the working electrode numerous times, recording repeatable and reproducible signals, and reducing the necessary volume of biomolecules. The specific interaction between cotinine and cotinine-specific antibody-attached magnetic nanoparticles restricted the electron transfer of the redox probe and changed the impedimetric response of the electrode correlated to the concentration of cotinine. The magneto biosensor had a wide detection range (2-300 pg/mL), a low LOD (606 fg/mL), and an acceptable recovery (97.24-105.31%) in real samples. In addition, the current biosensor's measurement results were in good agreement with those found by the standard liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA) methods. These results showed that a simple impedimetric immunosensing platform was generated for the cotinine analysis.

Label-Free Electrochemical Immunosensor Based on Conjugated Polymer Film Coated Disposable Electrode for Ultrasensitive Determination of Resistin Potential Obesity Biomarker.

A new label-free immunosensor was designed for sensitive detection of resistin obesity biomarker in human biological fluids. To construct a sensing interface, the monomer of double epoxy groups-substituted thiophene (TdiEpx) was synthesized for the fabrication of the biosensing system. A disposable indium tin oxide sheet was first modified by electrochemical polymerization of the TdiEpx monomer, and this robust and novel surface was characterized using different spectroscopic and electrochemical analyses. The double epoxy ends were linked to the amino ends of anti-resistin, and they served as binding points for the covalent binding of biomolecules. The double epoxy ends present in each TdiEpx monomer ensured an extensive surface area, which improved the quantity of attached anti-resistin. The determination of resistin antigen was based on the specific coupling of resistin with anti-resistin, and this interaction hindered the electron transfer reaction. The immunosensor introduced a wide linear range of 0.0125-15 pg/mL, a low detection limit of 4.17 fg/mL, and an excellent sensitivity of 1.38 kohm pg mL-1 cm2. In this study, a sandwich enzyme-linked immunosorbent assay spectrophotometric method was utilized as a reference technique for the quantitative analysis of resistin in human serum and saliva samples. Both measurements in clinical samples displayed correlations and high-correlation coefficients. In addition, this immunosensor had good storage stability, acceptable repeatability and reproducibility, high specificity, and good accuracy. The proposed immunosensor provided a simple and versatile impedimetric immunosensing platform and a promisingly sensitive way for clinical applications.

Ultrasensitive detection of NSE employing a novel electrochemical immunosensor based on a conjugated copolymer.

In the current study a simple and highly specific label-free impedimetric neuron specific enolase (NSE) immunosensor based on a copolymer matrix-coated disposable electrode was designed and tested. The copolymer matrix was prepared using a very conductive EDOT monomer and semi-conductive thiophene-bearing epoxy groups (ThEp), and the combination of the two monomers enhanced the conductivity and protein loading capacity of the electrode surface. The P(ThEp-co-EDOT) copolymer matrix was prepared via a drop-casting process and anti-NSE recognition biomolecules were immobilized directly on the epoxy groups of the copolymer. After the coupling of NSE molecules on the P(ThEp-co-EDOT) copolymer matrix-coated electrode surface, the charge transfer resistance (Rct) of the biosensor changed dramatically. These changes in Rct were proportional to the NSE molecule amounts captured by anti-NSE molecules. Under optimized experimental conditions, the increment in the Rct value was proportional to the NSE concentration over a range of 0.01 to 25 pg mL-1 with a detection limit (LOD) of 2.98 × 10-3 pg mL-1. This copolymer-coated electrode provided a lower LOD than the other biosensors. In addition, the suggested electrochemical immuno-platform showed good selectivity, superior reproducibility, long-term stability, and high recovery of NSE in real serum (95.64-102.20%) and saliva (95.28-105.35%) samples. These results showed that the present system had great potential for electrochemical biosensing applications.

A new immunosensing platform based on conjugated Poly(ThidEp-co-EDOT) copolymer for resistin detection, a new obesity biomarker.

The design of a novel electrochemical impedimetric biosensor for label-free analysis of resistin, a biomarker for obesity, is reported. For the fabrication of the immunosensor, a novel approach composed of electrochemical copolymerization of double epoxy groups-substituted thiophene (ThidEp) and 3,4-Ethylenedioxythiophene (EDOT) monomers was utilized. Anti-resistin antibodies were covalently attached to the copolymer-coated electrode. The capture of resistin antigens by anti-resistin antibodies caused significant variations in charge transfer resistance (Rct) because of the immunoreactions between these proteins. Under optimum experimental variables, the changes in impedance signals were employed for the determination of resistin antigen concentration, and the prepared immunosensor based on conjugated copolymer illustrated a wide linear range between 0.0125 and 22.5 pg/mL, a low detection limit (LOD) of 3.71 fg/mL, and a good sensitivity of 1.22 kΩ pg-1mL cm2. The excellent analytical performance of the resistin immunosensor in terms of selectivity, sensitivity, repeatability, reproducibility, storage stability, and low detection limit might be attributed to the conductive copolymer film layer generation on the disposable indium tin oxide (ITO) platform. The capability of this system for the determination of resistin in human serum and saliva samples was also tested. The immunosensor results were in accordance with the enzyme-linked immunosorbent assay (ELISA) results. The matrix effects of human serum and saliva were also investigated, and the proposed immunosensor displayed good recovery ranging from 95.91 to 106.25%. The engineered immunosensor could open new avenues for obesity monitoring.

A novel electrochemical impedance immunosensor for the quantification of CYFRA 21-1 in human serum.

A sensitive, simple, and reliable immunosensor was constructed to detect the lowest alteration of a fragment of cytokeratin subunit 19 (CYFRA 21-1), a protein lung carcinoma biomarker. The proposed immunosensor was manufactured with a carbon black C45/polythiophene polymer-containing amino terminal groups (C45-PTNH2) conductive nanocomposite, resulting in an excellent, biocompatible, low-cost, and electrically conductive electrode surface. Anti-CYFRA 21-1 biorecognition molecules were attached to the electrode thanks to the amino terminal groups of the used PTNH2 polymer with a relatively simple procedure. All electrode surfaces after modifications were characterized by electrochemical, chemical, and microscopic techniques. Electrochemical impedance spectroscopy (EIS) was also utilized for the evaluation of the analytical feature of the immunosensor. The charge transfer resistance of the immunosensor signal was correlated with the CYFRA 21-1 concentration in the concentration range 0.03 to 90 pg/mL. The limit of detection (LOD) and the limit of quantification (LOQ) of the suggested system were 4.7 fg/mL and 14.1 fg/mL, respectively. The proposed biosensor had favorable repeatability and reproducibility, long storage stability, excellent selectivity, and low cost. Furthermore, it was applied to determine CYFRA 21-1 in commercial serum samples, and satisfactory recovery results (98.63-106.18%) were obtained. Thus, this immunosensor can be offered for clinical purposes as a rapid, stable, low-cost, selective, reproducible, and reusable tool.

Biosensors for saliva biomarkers.

The analysis of salivary biomarkers has gained interest and is advantageous for simple, safe, and non-invasive testing in diagnosis as well as treatment. This chapter explores the importance of saliva biomarkers and summarizes recent advances in biosensor fabrication. The identification of diagnostic, prognostic and therapeutic markers in this matrix enables more rapid and frequent testing when combined with the use of biosensor technology. Challenges and future goals are highlighted and examined.

A Simple and Low-Cost Electrochemical Immunosensor for Ultrasensitive Determination of Calreticulin Biomarker in Human Serum.

An early on time detection of breast cancer significantly affects the treatment process and outcome. Herein, a new label-free impedimetric biosensor is developed to determine the lowest change in the level of calreticulin (CALR), which is a new biomarker of breast carcinoma. The proposed immunosensor is fabricated by using reduced graphene oxide/amino substituted polypyrrole polymer (rGO-PPyNH2 ) nanocomposite modified disposable electrode. The anti-CALR antibodies are first attached on the rGO-PPyNH2 nanocomposite coated electrode through glutaraldehyde crosslinking; the CALR antigens are then immobilized with the addition of CALR antigens to form an immunocomplex on the sensing surface. This immunocomplex induces considerably larger interfacial electron transport resistance (Rct ). The variation in the Rct has a linear relationship with CALR level in the detection range of 0.025 to 75 pg mL-1 , with a detection limit of 10.4 fg mL-1 . The suggested biosensor shows high selectivity to CALR, good storage stability (at least 5 weeks) and suitable reproducibility results as shown in quality control chart. The designed immunosensor is utilized to analyze CALR levels in human sera with satisfying results. This immunosensor provides a novel way for the clinical determination of CALR and other cancer biological markers.

Impedimetric Detection of Calreticulin by a Disposable Immunosensor Modified with a Single-Walled Carbon Nanotube-Conducting Polymer Nanocomposite.

A label-free impedimetric immunosensing system was constructed for ultrasensitive determination of the calreticulin (CALR) biological marker in human serum samples utilizing an electrochemical impedance spectroscopy analysis technique for the first time. The new biosensor fabrication procedure consisted of electrodeposition of single-walled carbon nanotubes (SWCNTs) incorporating polymerization of an oxiran-2-yl methyl 3-(1H-pyrrol-1-yl) propanoate monomer (Pepx) onto a low-cost and disposable indium tin oxide (ITO) electrode. The SWCNTs-PPepx nanocomposite layer was prepared onto the ITO after the one-step fabrication procedure. The fabrication procedure of the immunosensor and the characteristic biomolecular interactions between the anti-CALR and CALR were characterized by electrochemical analysis and morphological monitoring techniques. Under optimum conditions, the proposed biosensor was responsive to CALR concentrations over the detection ranges of 0.015-60 pg/mL linearly, and it had a very low detection limit (4.6 fg/mL) and a favorable sensitivity (0.43 kΩ pg-1 mL cm-2). The reliability of the biosensor system in clinical analysis was investigated by successful quantification of CALR levels in human serum. Moreover, the repeatability and reproducibility results of the biosensor were evaluated by using Dixon, Grubbs, T-test, and F-tests. Consequently, the proposed biosensor was a promising method for scientific, rapid, and successful analysis of CALR in human serum samples.

Ultrasensitive and Selective Impedimetric Determination of Prostate Specific Membrane Antigen Based on Di-Succinimide Functionalized Polythiophene Covered Cost-Effective Indium Tin Oxide.

A new and ultrasensitive impedimetric biosensor fabricated by using conjugated di-succinimide substituted polythiophene (P(ThidiSuc)) polymer modified indium tin oxide electrode is developed for the first time to detect the prostate specific membrane antigen (PSMA). The polymer P(Thi-diSuc) is synthesized by using a simple way and used in the fabrication of the proposed biosensor. The synthesized polymer contains di-succinimide groups, which offers covalent immobilization of PSMA specific antibodies. The developed strategy shortens the biosensor fabrication steps, because these active groups bind covalently to the amino ends of PSMA specific antibodies and this reaction does not require any crosslinking agent. Various characterization studies like impedimetric and voltammetric measurements, and morphological analyses are utilized to confirm the successful development of the biosensor. Under optimum conditions, the biosensing ability of the PSMA determination has a wide linear determination range from 0.015 to 14.4 pg mL-1 , as well as a low limit of detection of 6.4 fg mL-1 and a high sensitivity of 1.36 kohm pg-1 mL cm-2 . Furthermore, the proposed biosensor is able to measure the PSMA antigen in real human serums, which offers that it is a simple, low-cost, and sensitive tool with excellent potential for application in the quantification of PSMA.

New Impedimetric Sandwich Immunosensor for Ultrasensitive and Highly Specific Detection of Spike Receptor Binding Domain Protein of SARS-CoV-2.

An impedance sensing platform-combined conducting nanocomposite layer was fabricated to develop an effective and rapid method for detection of coronavirus infection (COVID-19) specific spike receptor binding domain (RBD) protein, a precious antigen marker of COVID-19 disease. Coronavirus infection has spread globally and swiftly with major impacts on health, economy, and quality of life of communities. Fast and reliable detection of COVID-19 is a very significant issue for the effective treatment of this bad illness. For this aim, first, an Epoxy functional group-substituted thiophene monomer was synthesized and electrodeposited on a single-use indium tin oxide (ITO) platform in the presence of acetylene black by employing a cyclic voltammetry technique; thus, a conducting nanocomposite (C-NC) layer with high conductivity was obtained. This composite was electrodeposited for the first time on the ITO surface to generate a facile and cost-effective impedimetric biosensor. In addition, this composite provided proper attachment points for antibody binding and also supported the biosensor construction. The immuno-specific biointeractions between anti-RBD and RBD proteins hampered the electron transfer between the ITO substrate surface and electrolyte, and this reaction caused variations in impedance signals, and these signals were proportional to the immobilized RBD antigen amounts. The as-prepared immunosensor showed a wide linear dynamic range (0.0012-120 pg/mL), an ultra-low detection limit of 0.58 fg/mL with added superiorities of great selectivity, suitable repeatability, multiple reusability, and excellent reproducibility.

Highly selective and sensitive sandwich immunosensor platform modified with MUA-capped GNPs for detection of spike Receptor Binding Domain protein: A precious marker of COVID 19 infection.

A label-free electrochemical biosensing system as a suitable analysis technique for COVID 19 specific spike receptor-binding domain protein (RBD) was developed with an aim to facilitate the diagnosis of coronavirus. A novel production procedure for the fabrication of gold nanoparticles (GNPs)-capped 11-mercaptoundecanoic acid (MUA) modified bioelectrode was presented and its application potential for RBD biosensing was examined. The bioelectrode fabrication protocol was based on covalent ester linking formation between hydroxylated ITO electrode and GNPs-capped MUA (GNPs@MUA) with carboxyl ends. For this aim, spherical GNPs were prepared and characterized with scanning-transmission electron microscopy (S-TEM), UV-vis, and Raman spectroscopy. The synthesized GNPs were functionalized with MUA yielding Au-S bonds. Then, covalent immobilization of anti-RBD antibodies on the GNPs@MUA was performed with the help of carbodiimide coupling chemistry. The assembly processes of GNPs@MUA, anti-RBD antibodies and RBD antigens were characterized electrochemical, chemical and morphological techniques. GNPs@MUA was used as immobilization environment and provided the most effective surface design for target immunosensor. The resulting immunosensor is further applied to the impedimetric detection of RBD and it displayed a linear response to RBD antigen in the linear range of 0.002-100 pg mL-1 with a limit of detection of 0.577 fg mL-1 and sensitivity of 0.238 kohmpgmL-1 cm-2. The fabricated immunosensor had a good repeatability, long storage, stability and a reusable property after simple regeneration process. Furthermore, it was successfully employed for selective determination of RBD in artificial nasal secretion samples.

Advances in immunosensor technology.

In recent years, advances in immunosensor device fabrication have significantly expanded the use of this technology in a broad range of applications including clinical diagnosis, food analysis, quality control, environmental studies and industrial monitoring. The most important aspect in fabrication is to obtain a design that provides a low detection limit. The utilization of nanomaterials as a label, catalyst and biosensing transducer is, perhaps, the most popular approach in ultrasensitive devices. This chapter reviews recent advances in immunosensor fabrication and summarizes the most recent studies. Strategies employed to significantly improve sensitivity and specificity of immunosensor technology and the advantages and limitations thereof are explored.

Detection of Kallikrein-Related Peptidase 4 with a Label-free Electrochemical Impedance Biosensor Based on a Zinc(II) Phthalocyanine Tetracarboxylic Acid-Functionalized Disposable Indium Tin Oxide Electrode.

A new impedimetric biosensing system based on kallikrein-related peptidase 4 (KLK 4) antigen-specific antibodies and a zinc(II) phthalocyanine tetracarboxylic acid (Zn-PcTCa) matrix material was developed for the first time in this study. First, a Zn-PcTCa-coated indium tin oxide surface was used as an interface matrix material for the immobilization of anti-KLK 4 antibodies, and they bound to the platform via amide bonds. In the presence of KLK 4 antigens, the anti-KLK 4 antibodies specifically captured these antigens and caused changes in the electrochemical properties of the system. Randles equivalent circuit was utilized to evaluate the impedimetric signal, which was measured with the help of an electrochemical impedance spectroscopy method. After the specific interaction, the electron transfer resistance (Rct) was remarkably increased and displayed a linear relationship with the level of the KLK 4 antigen in the range of 0.02-15 pg/mL, with a a detection limit of 6.8 fg/mL. The designed biosensor was able to detect a KLK 4 antigen with good sensitivity, excellent specificity, and high stability. In addition, because of having a low-cost and robust procedure for fabrication, it could be repeatedly used in several areas including clinical diagnosis.

Electrochemical Immunosensor for Detection of CCR4 Cancer Biomarker in Human Serum: An Alternative Strategy for Modification of Disposable ITO Electrode.

Herein, a new strategy for the fabrication of a sensitive immunosensor capable of determination of CC Chemokine receptor 4 (CCR4) in complex serum samples is developed through the polymer modification on the disposable indium tin oxide electrode. Anti-CCR4 antibodies, which are utilized as sensing biomolecules, are covalently attached on the succinimide groups of polypyrrole polymer (PPyr-CSsg). The constructed immunosensor illustrates promising performances for the quantification of CCR4 antigen, with a linear detection range of 0.024-12 pg mL-1 and a low detection limit of 7.3 fg mL-1 , calculated at a signal-to-noise ratio of 3. In addition, the impedimetric immunosensor displays a very successful analytical performance in terms of sensitivity, selectivity, repeatability, reproducibility, and long-term stability as well as successful applicability for the accurate quantification of CCR4 in human serum samples. The constructed immunosensor is successfully used for quantification of CCR4 antigen in human serums. In addition, the immunosensor displays only 27.54% loss in its initial signal after nine weeks storage at 4 °C. Moreover, the fabricated immunosensor is economical, highly sensitive, and selective for CCR4 antigen detection, and suitable for potential application in clinical diagnosis.

Fabrication of electrochemical immunosensor based on acid-substituted poly(pyrrole) polymer modified disposable ITO electrode for sensitive detection of CCR4 cancer biomarker in human serum.

This study described the first impedimetric immunosensor reported for the determination of CCR4, a new prostate cancer biomarker. This impedimetric immunosensor was constructed through the modification of disposable indium tin oxide (ITO) sheet with a conjugated pyrrole polymer P(Pyr-Pac) and subsequent immobilization of anti-CC chemokine receptor 4 (CCR4) antibodies. Acid-substituted poly(pyrrole) P(Pyr-Pac) polymer contained a lot of carboxyl groups on its end site, which were suitable for attachment of anti-CCR4 antibodies. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were chosen to investigate electrode preparation stages and, EIS was chosen to detect the CCR4 concentration. Anti-CCR4 antibody attached biosensing surface was highly selective to CCR4 antigen, the specific interaction resulted changes in electrochemical signal. Optimization studies containing polymer amount, anti-CCR4 antibody concentration, anti-CCR4 antibody immobilization time and anti-CCR4 antibody-CCR4 antigen interaction time were studied. The developed immunosensor displayed a linear increase with concentrations of CCR4 antigen (0.02-8 pg/mL) and a low detection limit of 6.4 fg/mL. In addition, this biosensor had great reproducibility and repeatability. Moreover, the designed biosensor was successfully used for the quantification of CCR4 antigen in serum samples. The recovery for the spiked serum samples was between 98.25% and 103.99%. The suggested immunosensor illustrated a good selectivity towards some interferents including different biomarkers. This study could establish a new approach for future cancer biomarker detection.

A novel electrochemical immunosensor based on acetylene black/epoxy-substituted-polypyrrole polymer composite for the highly sensitive and selective detection of interleukin 6.

An ultrasensitive immunosensor based on acetylene black (AB)/epoxy-substituted-poly(pyrrole) polymer (EpxS-PPyr) composite coated disposable indium tin oxide (ITO) electrode was fabricated for interleukin 6 (IL 6) detection. The EpxS-PPyr polymer was a promising matrix material to increase the loading capacity of immunosensor owing to its large surface area and abundance of epoxy groups. EpxS-PPyr polymer was synthesized by an esterification reaction and used to attach IL 6 receptor owing to its excellent biocompatibility and good conductivity. The electrochemical signals of the electrodes during the immunosensor fabrication were performed with electrochemical impedance spectroscopy and cyclic voltammetry techniques. Additionally, the changes formed on ITO electrode surfaces were followed by scanning electron microscopy and atomic force microscopy analyses. Under optimized conditions, the designed biosensor illustrated an ultra-sensitive signal towards IL 6 antigen at a broad concentration range from 0.01 pg/mL to 50 pg/mL. The detection limit and sensitivity were found as 3.2 fg/mL and 0.29 pg-1mLkΩ cm-2, respectively. Acceptable reproducibility, good storage-stability and excellent selectivity were found for IL 6 determination. Moreover, the proposed biosensor was applied to human serums and the recovery rates were ranged from 99.5 to 100.5 indicating acceptable accuracy. The results illustrated that this immunosensor were suitable for detection of IL 6 in clinical samples.

Ultrasensitive detection of interleukin 1α using 3-phosphonopropionic acid modified FTO surface as an effective platform for disposable biosensor fabrication.

In this study, we utilized a carboxyalkylphosphonic acid covered fluorine doped tin oxide (FTO) as an electrode material for fabrication of Interleukin 1α (IL-1α) immunosensor. For this aim, anti-IL-1α antibodies were attached on the 3-phosphonopropionic acid (PHP) modified FTO surface covalently. Electrochemical (electrochemical impedance spectroscopy and cyclic voltammetry) and morphological (scanning electron microscopy and atomic force microscopy) characterizations were performed to monitor the successful fabrication of immunoelectrodes. After incubation of anti-IL-1α antibody immobilized FTO electrodes in IL-1α antigen solutions, increases were seen in impedimetric responses. IL-1α antigen was determined in a linear detection range from 0.02 to 2 pg/mL by EIS. The detection limit of the suggested immunosensor was 6 fg/mL. The applicability of the designed biosensor was tested by using human serum and saliva samples and acceptable results were obtained. In addition, high sensitivity, good specificity, low detection limit made the proposed immunosensor a potential technique for IL-1α antigen determination in routine clinical analysis.

A label-free immunosensor for sensitive detection of RACK 1 cancer biomarker based on conjugated polymer modified ITO electrode.

A new flexible biosensor based on conjugated polymer functionalized indium tin oxide (ITO) sheet was fabricated for Receptor for Activated C Kinase 1 (RACK 1) determination. Poly(3-thiophene acetic acid) (P(Thi-Ac)) was used as an immobilization matrix for construction of RACK 1 immunosensor. This polymer had a great number of carboxyl groups on its end site and these carboxyl ends provided anchoring points to the anti-RACK 1 antibodies. Anti-RACK 1 antibodies were covalently attached on the ITO electrode and recognized the RACK 1 antigens. Electrochemical characterizations were made by employing electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Additionally, single frequency impedance method (SFI) was applied to follow the specific biointeraction between antibody and antigen. As a result of specific biointeraction, the designed immunosensor exhibited a wide linear detection range between 0.01 pg/mL and 2 pg/mL RACK 1 with a detection limit of 3.1 fg/mL. Scanning electron microscopy and atomic force microscopy analyses were employed for electrode surface morphology investigation. The designed RACK 1 biosensor had good repeatability (5.73 %, RSD), excellent reproducibility (2.5 %, RSD), long storage-stability and reusable property. In addition, the fabricated RACK 1 biosensor was applied to determine RACK 1 concentration in human serums and the recovery was ranging from 98.79%-100.22%. This work illustrated a new tool to construct a sensitive and low-cost disposable biosensor for applications in clinical monitoring.

Highly sensitive impedimetric immunosensor for determination of interleukin 6 as a cancer biomarker by using conjugated polymer containing epoxy side groups modified disposable ITO electrode.

A novel impedimetric immunosensor based on a conjugated polypyrrole polymer containing epoxy active side groups (PPCE) modified indium tin oxide (ITO) electrode was developed for detection of interleukin 6 (IL 6), a prostate cancer biomarker. IL 6 receptor was used as a biorecognition molecule and successfully immobilized by covalent linkage on the modified ITO electrode. Pyrrole monomer containing epoxy active side group was electropolymerized on the disposable ITO electrode for the first time and used as an immobilization matrix for IL 6 receptor. The designed biosensor fabrication stages were analyzed by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. For the quantification of IL 6 biomarker, EIS technique was utilized. In addition, the specific immuno-interaction between IL 6 receptor and IL 6 antigen was followed by single frequency impedance (SFI) technique. The resulting biosensor exhibited a linear calibration curve over the 0.02-16 pg/mL IL 6 concentration range, a limit of detection (LOD) of 6.0 fg/mL and a good selectivity against other interference biomarkers. Additionally, an excellent reproducibility, a long storage stability and an acceptable repeatability were found. The proposed impedimetric immunosensor was applied successfully to quantify for the IL 6 biomarker in human serum and it displayed a remarkable response in the real sample analysis with serum samples. In comparison with the commercial ELISA kit, the immunosensor provided a lower LOD and a lower analysis cost. In conclusion, the proposed impedimetric immunosensor could be clinically useful in the early diagnosis of the prostate cancer by detection of the serum samples after only simple dilution with phosphate buffer.

Advances in electrochemical immunosensors.

Immunosensors are compact tools on which antibody and antigen interactions are formed. The specific interaction between antibody and antigen is detected by using a transducer and an electrical signal is measured. This specific interaction between these molecules makes immunosensor very attractive for several applications in different fields. Electrochemical immunosensors are successful devices in selective and sensitive detection of several analytes. Electrochemical transducing methods such as voltammetric, potentiometric, conductometric or impedimetric have been utilized in different applications due to their excellent properties such as being low-cost, sensitivity and simplicity. In this chapter, the fundamentals of electrochemical immunosensors are summarized and different applications in food, environmental and clinical analyses are investigated and discussed.