Elif Burcu Aydın

A highly sensitive immunosensor based on ITO thin films covered by a new semi-conductive conjugated polymer for the determination of TNFα in human saliva and serum samples

A novel, ultrasensitive impedimetric immunosensor was constructed for the detection of tumor necrosis factor α (TNFα) by using Poly(3-thiophene acetic acid) (P3), a conjugated polymer as an immobilization matrix. The polymer P3 contains a lot of carboxylic acid groups on its surface that provide a larger biorecognition surface. This developed immunosensor was prepared on hydroxy-bearing ITO surface via an ester bond linkage of polymer P3 to immobilize anti-TNF α antibodies. The ITO electrode modification steps and interaction between anti-TNF α antibody and TNF α antigen were monitored by cyclic voltammetry (CV) and by electrochemical impedance spectroscopy (EIS) method. After the analytical parameters optimization, a linear detection response from 0.01pg/mL to 2pg/mL, a limit of detection LOD of 3.7 fg/mL and a limit of quantification (LOQ) of 12.4 fg/mL were achieved, which provided accurate results (relative standard deviation; 4.03%). The characterization of this developed immunosensor was performed by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), SEM-energy dispersive X-ray (EDX) mapping and atomic force microscopy (AFM). The immunosensor allowed a simple and fast detection of TNF α antigen in human serum and satisfied recoveries (98.69-105.20%) were obtained by using standard addition method.

A sensitive and disposable electrochemical immunosensor for detection of SOX2, a biomarker of cancer

A novel, sensitive, disposable indium tin oxide (ITO)-based electrochemical immunosensor was developed firstly for simple, rapid determination of Sex-determining region Y-box 2 (SOX2). SOX2 is a cancer biomarker and used for detecting small cell lung cancer, lung adenocarcinoma, squamous cell carcinoma, skin cancer, prostate cancer, and breast cancer. In this study, a disposable ITO thin film based electrode was used as working electrode for biosensing the interaction between SOX2 antigen and anti-SOX2 antibody. In this study, carboxyethylsilanetriol (CTES) was also utilized for electrode modifying so as to obtain self-assembled monolayers. The formed self-assembled monolayers were activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) chemistry and they were used as a heterobifunctional crosslinker and activator, respectively. Anti-SOX2 antibody was used as a biorecognition molecule and was covalently immobilized onto the ITO thin film modified with CTES. Immobilization steps were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The optimum immobilization conditions such as antibody concentration, antibody and antigen incubation times were examined for the best sensitivity of the immunosensor. Under optimal conditions, this immunosensor had a wide linear detection range (25fg/mL-2pg/mL) with a detection limit as low as 7fg/mL SOX2. Furthermore, the developed SOX2 immunosensor had good storage stability (79.36% of initial activity after 9 weeks), repeatability (3.88% of RSD) and reproducibility (4.25% of RSD). Our developed immunosensor has an acceptable performance for detection of SOX2 antigen, exhibits low detection limit, and has selective and reproducible results in immunoreaction analysis.

A disposable immunosensor using ITO based electrode modified by a star-shaped polymer for analysis of tumor suppressor protein p53 in human serum

Label-free immunosensor based on tetra armed star-shaped poly(glycidylmethacrylate) (StarPGMA) modified disposable ITO electrode was developed for detection of p53 protein, an important colorectal cancer biomarker. This disposable biosensor was fabricated by spin-coating technique using star-shaped StarPGMA with epoxy side groups. After formation of a stable film with epoxy ends, anti-p53 antibodies were bound to these groups covalently. Stepwise modification of the electrode was followed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) studies. The electrochemical performance of the immunosensor was studied by EIS. Furthermore, the antibody and antigen coupling was monitored by single frequency impedance (SFI) technique. The immunosensor showed a low limit of detection (7 fg/mL) and a linear detection range between 0.02 pg/mL and 4 pg/mL. Additionally, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were utilized for monitoring of immunosensor surface at different stages of fabrication. The antibody coupling on the electrode surface was proved by Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. Furthermore, the proposed immunosensor had good reproducibility and repeatability.

A highly selective electrochemical immunosensor based on conductive carbon black and star PGMA polymer composite material for IL-8 biomarker detection in human serum and saliva

A new approach to enhance the electrochemical performance of biosensor was attempted by using Super P© carbon black/Star polymer composite material. In this study, we developed an electrochemical IL 8 biosensor by modification with a conductive composite including Super P, polyvinylidene fluoride (PVDF) and star polymer (SPGMA) of disposable ITO electrode surface. The Super P carbon black as carbonaceous material had a high conductivity and was used for the enhancement of electron transfer between electrode surface and electrolyte. Anti-IL 8 antibodies were utilized as biorecognition molecules and bound to epoxy groups of star polymer covalently. The chemical characterization of antibody immobilization on this composite was performed by using Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The characterizations of stepwise modification of this immunosensor were performed by electrochemical techniques such as Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and Single Frequency Impedance (SFI); and morphological techniques such as Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Several variables that affect the immunosensor performance were optimized. Under optimum conditions, a wide linear range 0.01-3 pg/mL and low detection limit 3.3 fg/mL were obtained. Super P-star polymer composite modified immunosensor was easy, sensitive, cheap and reliable analytical method for IL 8 detection. The applicability of the proposed immunosensor to determine IL 8 in saliva and serum samples were examined. The results of biosensor and Enzyme-linked Immunosorbent Assay (ELISA) kit were in compatible. Consequently, it was concluded that the electrochemical immunosensor offers a potential approach for IL 8 detection in clinical applications.

Electrochemical immunosensor based on chitosan/conductive carbon black composite modified disposable ITO electrode: An analytical platform for p53 detection

In this study, we fabricated a label-free electrochemical immunosensor for sensitive and selective detection of tumor marker p53. This immunosensor was based on chitosan/carbon black composite (Chitosan-CB) layer coated ITO electrode. This composite was utilized for enhancement of the conductivity of the immunosensor. Anti-p53 antibodies were captured on the modified ITO electrode through the cross-linking of chitosan and glutaraldehyde. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques were utilized for electrochemical characterization of the proposed immunosensor. Moreover, the biosensor construction steps were monitored by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The immobilization of anti-p53 antibodies on the electrode surface was investigated by using Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The change in impedance which formed during the specific interaction between anti-p53 antibody and p53 antigen was used to detect p53. Under optimized experimental conditions, the fabricated immunosensor had a wide linear range of 0.01-2 pg/mL and low detection limit of 3 fg/mL. The fabricated immunosensor had good sensitivity, stability and repeatability. Furthermore, it was successfully applied to analyze p53 in human serum.

An impedimetric immunosensor for highly sensitive detection of IL-8 in human serum and saliva samples: A new surface modification method by 6-phosphonohexanoic acid for biosensing applications

In this study, we fabricated a sensitive and label-free impedimetric immunosensor based on 6-phosphonohexanoic acid (PHA) modified ITO electrode for detection of interleukin-8 (IL-8) in human serum and saliva. PHA was first employed to cancer biomarker sensing platform. Anti-IL-8 antibody was used as a biorecognition element and the detection principle of this immunosensor was based on monitoring specific interaction between anti-IL-8 antibody and IL-8 antigen. The morphological characterization of each electrode modification step was analyzed by scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) while electrochemical characterization was performed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and single frequency impedance (SFI) techniques. Moreover, the antibody immobilization on the electrode surface was proved Fourier-transform infrared spectroscopy (FTIR) and Raman Spectroscopy. This proposed impedimetric immunosensor exhibited good performances with a wide linear in the range from 0.02 pg/mL to 3 pg/mL as well as a relative low detection limit of 6 fg/mL. The impedimetric immunosensor had a good specificity, stability and reproducibility. This study proved that PHA was a suitable interface material to fabricate an electrochemical biosensor.

A disposable and ultrasensitive ITO based biosensor modified by 6-phosphonohexanoic acid for electrochemical sensing of IL-1β in human serum and saliva

In this study, we constructed a new and sensitive ITO based electrochemical immunosensor for detection of interleukin 1β (IL-1β), a cancer biomarker found in serum and saliva. 6-phosphonohexanoic acid (PHA) was used as a biomolecule immobilization matrix for the first time. Anti-IL-1β antibody was utilized as a biorecognition molecule that immobilized onto carboxyl groups of 6-phosphohexanoic acid (PHA) via amide bond. Selective interaction between anti- IL-1β antibodies and IL-1β antigens was investigated by Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and Single Frequency Impedance (SFI) methods. The surface characterization of the immunosensor was performed by fourier transform infrared spectroscopy (FTIR), raman spectroscopy, scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) in order to illustrate individual steps of biosensor construction. Under the optimized experimental conditions, the change in impedance was proportional to IL-1β concentrations in the range of 0.025-3 pg/mL (R2 = 0.99) with detection limit of 7.5 fg/mL. The reproducibility, repeatability, stability, and specificity of the developed immunosensor were analyzed. In addition, the developed immunosensor was successfully utilized for the determination of IL-1β in serum and saliva samples by using the standard addition method with recoveries of 96.7-105.4%. This immunosensor was applicable for the requirements of routine analysis with respect to performance, functionality and cost.

A label-free electrochemical biosensor for direct detection of RACK 1 by using disposable, low-cost and reproducible ITO based electrode

In this study we designed an ultrasensitive electrochemical immunosensor for RACK 1 detection using 11-cyanoundecyltrimethoxysilane (11-CUTMS) as a immobilization matrix to immobilize biorecognition element. The used silane agent (11-CUTMS) provides a favorable platform for efficient loading of anti-RACK 1 antibody. The effective loading of the biorecognition element on the 11-CUTMS matrix was monitored by scanning electron microscopy (SEM), atomic force microscopy (AFM) images and fourier transform infrared spectroscopy (FTIR) spectra. The electrochemical characterization of the immunosensor was performed by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Moreover, biorecognition interaction between anti-RACK1 antibodies and RACK1 antigens was monitored by using single frequency technique (SFI). The operating conditions, calibration curves obtained during optimization of experiments and reproducibility of the proposed impedimetric RACK1 biosensor are also investigated and discussed. The electrochemical immunosensor illustrated a sensitive response to RACK 1 antigen with detection limit of 10.8 fg/mL and in the linear range of 0.036-2.278 pg/mL (R2 = 0.999). Owing to high specificity, good reproducibility, long stability and reusability, the fabricated immunosensor will provide a sensitive, selective approach to RACK 1 detection. Furthermore, the practical applicability in human serum samples were investigated with a satisfactory result.