Yasar Gurbuz

Comparison and analysis of Pd‐ and Pt‐GaAs Schottky diodes for hydrogen detection

Hydrogen‐sensing behaviors of Pd‐ and Pt‐GaAs Schottky diodes, fabricated on the same GaAs substrate, have been systematically compared and analyzed as a function of hydrogen partial pressure and temperature by I‐V and ΔI‐t methods under steady‐state and transient conditions. The effects of hydrogen adsorption on the device parameters such as the barrier height and the ideality factor are investigated. The significant differences in their hydrogen sensing characteristics have been examined in terms of sensitivity limit, linearity of response, response rate, and response time. Adsorption activation energy of hydrogen and the heat of adsorption per hydrogen molecule on the surface of Pd and Pt are investigated and compared in both devices in a low‐temperature range (27–100 °C). For the temperature range investigated, Pd‐GaAs shows better performance for H2 detection than Pt‐GaAs under the same testing conditions. The physical and chemical mechanisms responsible for hydrogen detection are discussed. Analysis...

Label-free capacitive biosensor for sensitive detection of multiple biomarkers using gold interdigitated capacitor arrays

In this study, a highly sensitive and label-free multianalyte capacitive immunosensor was developed based on gold interdigitated electrodes (GID) capacitor arrays to detect a panel of disease biomarkers. C-reactive protein (CRP), TNFalpha, and IL6 have strong and consistent relationships between markers of inflammation and future cardiovascular risk (CVR) events. Early detection of a panel of biomarkers for a disease could enable accurate prediction of a disease risk. The detection of protein biomarkers was based on relative change in capacitive/dielectric properties. Two different lab-on-a-chip formats were employed for multiple biomarker detection on GID-capacitors. In format I, capacitor arrays were immobilized with pure forms of anti-CRP, -TNFalpha, and -IL6 antibodies in which each capacitor array contained a different immobilized antibody. Here, the CRP and IL6 were detected in the range 25 pg/ml to 25 ng/ml and 25 pg/ml to 1 ng/ml for TNFalpha in format I. Sensitive detection was achieved with chips co-immobilized (diluted) with equimolar mixtures of anti-CRP, -IL6, and -TNFalpha antibodies (format II) in which all capacitors in an array were identical and tested for biomarkers with sequential incubation. The resulting response to CRP, IL6, and TNFalpha in format II for all biomarkers was found to be within 25 pg/ml to 25 ng/ml range. The capacitive biosensor for panels of inflammation and CVR markers show significant clinical value and provide great potential for detection of biomarker panel in suspected subjects for early diagnosis.

Surface plasmon resonance based immunosensor for the detection of the cancer biomarker carcinoembryonic antigen

An immunoassay in optimised conditions with a highly sensitive surface plasmon resonance (SPR) based biosensor was developed for the detection of the cancer biomarker carcinoembryonic antigen (CEA). Different formats of the immunoassay were initially investigated on the surface of the gold sensor chip. A self-assembled monolayer (SAM) was formed on the gold chip using 11-mercaptoundecanoic acid (MUDA), before the immobilisation of the antibodies was conducted. The assay was then formed in a direct capture and a sandwich assay. In order to increase the sensor signal the CEA antigen was incubated with the detection/capture antibody before it was injected to the sensor chip surface and the results were recorded in real-time using the Biacore 3000 instrument. A detection limit of 3 ng ml(-1) CEA was obtained with a dynamic detection range from 3 ng ml(-1) to 400 ng ml(-1) with correlation coefficients of 1.00 and 0.99 for the sandwich and rabbit anti-mouse (RAM) capture assay. Kinetic data analysis was performed for the standard capture test and subsequently for the developed assays and R(max) showed an increase from 215 RU for the standard capture test to 428 RU for the RAM-capture assay and 734 RU for the sandwich assay, respectively. The developed SPR immunosensor using the sandwich assay format showed high sensitivity and reproducibility for CEA detection which makes it a promising procedure for cancer biomarker analysis.

Development of surface chemistry for surface plasmon resonance based sensors for the detection of proteins and DNA molecules

The immobilisation of biological recognition elements onto a sensor chip surface is a crucial step for the construction of biosensors. While some of the optical biosensors utilise silicon dioxide as the sensor surface, most of the biosensor surfaces are coated with metals for transduction of the signal. Biological recognition elements such as proteins can be adsorbed spontaneously on metal or silicon dioxide substrates but this may denature the molecule and can result in either activity reduction or loss. Self assembled monolayers (SAMs) provide an effective method to protect the biological recognition elements from the sensor surface, thereby providing ligand immobilisation that enables the repeated binding and regeneration cycles to be performed without losing the immobilised ligand, as well as additionally helping to minimise non-specific adsorption. Therefore, in this study different surface chemistries were constructed on SPR sensor chips to investigate protein and DNA immobilisation on Au surfaces. A cysteamine surface and 1%, 10% and 100% mercaptoundecanoic acid (MUDA) coatings with or without dendrimer modification were utilised to construct the various sensor surfaces used in this investigation. A higher response was obtained for NeutrAvidin immobilisation on dendrimer modified surfaces compared to MUDA and cysteamine layers, however, protein or DNA capture responses on the immobilised NeutrAvidin did not show a similar higher response when dendrimer modified surfaces were used.

Temperature dependence and effect of series resistance on the electrical characteristics of a polycrystalline diamond metal‐insulator‐ semiconductor diode

Temperature dependency and the series resistance effect on the electrical characteristics of a polycrystalline diamond‐based (Au/Ti)/undoped‐diamond/doped‐diamond metal‐insulator‐ semiconductor Schottky diode were investigated in a temperature range 25–300 °C. The current‐voltage (I‐V) characteristics of the device show rectifying behavior with the forward bias conduction limited by series resistance. Over the temperature range investigated, the I‐V data confirmed that the conduction mechanism of the diode is controlled by thermionic field emission. Modifying the thermionic field emission equation to include the series resistance model allows the ideality factor and barrier height of the Schottky diode to be calculated. Temperature dependence of the ideality factor and apparent barrier height was determined. By extrapolating the forward saturation current data, the evaluated ideality factor was observed to decrease from 2.4 to 1.1 while the apparent barrier increased linearly from 0.68 to 1.02 eV in the t...

A novel interdigitated capacitor based biosensor for detection of cardiovascular risk marker.

C-reactive protein (CRP) is a potential biomarker whose elevated levels in humans determine cardiovascular disease risk and inflammation. In this study, we have developed a novel capacitive biosensor for detection of CRP-antigen using capacitor with interdigitated gold (GID) electrodes on nanocrystalline diamond (NCD) surface. The NCD surface served as a dielectric layer between the gold electrodes. GID-surface was functionalized by antibodies and the immobilization was confirmed by Fourier transform spectroscopy (FT-IR) and contact angle measurements. The CRP-antigen detection was performed by capacitive/dielectric-constant measurements. The relaxation time and polarizability constants were estimated using Cole-Cole model. Our results showed that the relaxation time constant (tau) of only CRP-antibody was within 10(-16)-10(-13)s, which was increased to 10(-11)s after the incubation with CRP-antigen, suggesting that the CRP-antigen was captured by the antibodies on GID-surface. In addition, polarizability constant (m) of CRP was also increased upon incubation with increasing concentration of CRP-antigen. Our results showed that the response of GID-NCD-based capacitive biosensor for CRP-antigen was dependent on both concentration (25-800ng/ml) as well as frequency (50-350MHz). Furthermore, using optimized conditions, the GID-NCD based capacitive biosensor developed in this study can potentially be used for detection of elevated levels of protein risk markers in suspected subjects for early diagnosis of disease.

A new hydrogen sensor using a polycrystalline diamond-based Schottky diode

A new hydrogen sensor utilizing plasma-enhanced chemical vapor deposited diamond in conjunction with palladium (Pd) metal has been developed. The device is fabricated in a layered Pd/Undoped diamond/p-doped diamond Schottky diode configuration. Hydrogen sensing characteristics of the device have been examined in terms of sensitivity, linearity, response rate, and response time as a function of temperature and hydrogen partial pressure. Hydrogen adsorption activation energy is investigated in the temperature range from 27 to 85 C. Analysis of the steady-state reaction kinetics using the I-V method confirm that the hydrogen adsorption process is responsible for the barrier height change in the diamond Schottky diode. The ability to fabricate diamond-based hydrogen sensor on a variety of substrates makes the device very versatile for gas sensing.

Gold nanoparticle modified capacitive sensor platform for multiple marker detection.

The detection and quantification of cancer biomarkers in human blood is crucial to diagnose patients in the early stage of a disease. The recent advances in biosensor technology can improve detection by reducing the application time and cost without an invasive approach. In this study, a highly sensitive, novel nanoparticle-modified capacitive sensor was developed for the detection of cancer markers. The current work mainly focused on developing a surface modification protocol for achieving higher sensitivity using Au-NPs. An interdigitated electrode (IDE) transducer was modified using gold nanoparticles (Au-NPs) for signal enhancement, the platform was initially optimized with a small size IL-6 protein and the methodology was then applied for multiple marker detection with the aim of precise disease diagnostics. Carcinoembryonic antigen (CEA) and epidermal growth factor receptor (hEGFR) could be successfully detected in the concentration range of 20-1000 pg mL(-1) while cancer antigen 15-3 (CA15-3) was detected in the range of 10-200 U mL(-1). These results show an increase of sensitivity by five-fold with respect to those not modified, demonstrating a highly sensitive and specific capacitive immunoassay that has a great potential for the use of early diagnosis of cancer disease.

BEOL embedded RF-MEMS switch for mm-wave applications

We demonstrate for the first time the embedded integration of a Radio Frequency Microelectromechanical Systems (RF-MEMS) capacitive switch for mm-wave integrated circuits in a BiCMOS Back-end-of-line (BEOL). The switch shows state-of-the-art performance parameters. The ¿off¿ to ¿on¿ capacitance ratio is 1:10 providing excellent isolation in the mm-wave frequency range. Insertion loss and isolation are found to fall below 1.65 dB and to exceed 15 dB, respectively, in the frequency range of 60 GHz to 110 GHz. Feasibility of switch integration into single chip RF designs is demonstrated for a dual-band voltage controlled oscillator (VCO). No performance degradation was observed after ten billion hot-switching cycles.

Diamond microelectronic gas sensors

Abstract Diamond-based microelectronic gas sensors using plasma enhanced chemical vapor deposition (PECVD) technology have been explored in our laboratory. This paper presents a new gas sensor using Pd/i-diamond structure for hydrogen detection. Hydrogen sensitivity of the device has been characterized and analyzed as a function of hydrogen partial pressure and temperature by using current-voltage (I–V) and capacitance-voltage-frequency (C-V-F) methods. The hydrogen sensitivity is high, reproducible, and repeatable over a wide temperature range including room temperature.