Prostate cancer (PCa) is a major mortality cause for men around the world and therefore there is a high demand for reliable diagnostic solutions. Prostate-specific antigen (PSA) is currently the representative biomarker for pre-screening of PCa, necessarily followed by biopsy examinations for confirmatory diagnosis. In the biomedical market, equipment to detect PSA in its relevant clinical concentration is already commercialized. These devices are accurate, but the bench-top systems are bulky, expensive, have a long response time, and rely on optical labels. To eliminate these drawbacks, point-of-care (POC) devices are under development, aiming at cost-effective, precise, portable, disposable and environmentally friendly designs with a fast response time. Most of the devices are utilizing conventional biosensing principles. However, the miniaturization of these approaches directly induces performance variations and a drastic decrease of the sensing accuracy. It is noteworthy that no biomarker is ideal, and no definite diagnostic decision can be based on a single biomarker. Thus, the detection of a combination of various biomarkers is recommended to provide multi-variable information for accurate diagnosis in the early stage of cancer development. Some biomarkers are more specific for PCa than others, but of a relatively low concentration in the clinical samples.Therefore, new biosensing concepts with multiplexing capability are under intensive investigation.Graphene, as an atomic carbon lattice, possesses superior electronic, optical and plasmonic properties, which trigger a revolution in the microelectronics field. Graphene is of atomic thickness but mechanically ultra-strong, and the carrier transport is ballistic in the condition of high charge carrier concentrations. In addition, this material is highly heat resistant, cheap, environmentally friendly and biocompatible.The aim of this thesis is to utilize graphene-based material for novel biosensors towards PSA detection. Graphene oxide (GO) and reduced graphene oxide (rGO), as derivatives of graphene, partially possess the promising properties of graphene. In addition, they provide diverse functionalization possibilities for immobilization of biomolecules and a wafer-scale preparation capability on arbitrary substrates. In the framework of this thesis, GO flakes were chemically exfoliated by a newly developed low-temperature exfoliation and desalination (LTEDS) method. The high-quality GO flakes were characterized intensively using scanning electron microscopy (SEM), transmission electron microscope (TEM), ultraviolet-visible (UV-VIS) spectroscopy, X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy. The graphene oxide and reduced graphene oxide ((r)GO) thin films were prepared in wafer-scale using the techniques of gas-phase silanization, spin-coating, followed with patterning by photolithography and reactive ion etching. After a thermal reduction, electronic characterizations of rGO thin films were carried out using cyclic-voltammetry, current-voltage (I-V) characterizations and lectrolyte-sensitive field-effect transistor (ESFET) measurements. These combined electronic and electrochemical characterizations aimed at analyzing the wafer-scale topographical completeness, uniformity, and field-effect mobility of the rGO thin films.The rGO thin films were utilized as functional layers in different biosensor device configurations of surface plasmon resonance (SPR) spectroscopy, electrochemical impedance spectroscopy (EIS) and ESFET. The biosensing performances and the corresponding sensing mechanisms were analyzed and evaluated in detail. The bipolar property of the rGO thin films allowed a tuning effect of the SPR intensity. Concanavalin A (ConA) was detected using the rGO based SPR principle and a limit of detection (LOD) as low as 0.01 µg/ml was achieved. Such a LOD was not attainable by the standard gold SPR chips. Besides, the electronic biosensing experiments were all carried out in a buffer solution with an ionic strength of 162 mM and a corresponding short Debye-screening length (0.76 nm), which were similar to physiological solutions (150 mM and 0.78 nm). The rGO based EIS and ESFET sensors exhibited the outstanding biosensing capability to detect PSA in its relevant clinical concentration range (4-10 ng/ml).The rGO based biosensors as developed and optimized in this thesis work showed a highly sensitive PSA detection beyond the Debye-screening limitation and demonstrated a great potential towards real biosensor applications for future healthcare.
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