Duck-Jin Kim

Reduced graphene oxide field-effect transistor for label-free femtomolar protein detection.

We report reduced graphene oxide field effect transistor (R-GO FET) biosensor for label-free ultrasensitive detection of a prostate cancer biomarker, prostate specific antigen/α1-antichymotrypsin (PSA-ACT) complex. The R-GO channel in the device was formed by reduction of graphene oxide nanosheets networked by a self-assembly process. Immunoreaction of PSA-ACT complexes with PSA monoclonal antibodies on the R-GO channel surface caused a linear response in the shift of the gate voltage, V(g,min), where the minimum conductivity occurs. The R-GO FET can detect protein-protein interactions down to femtomolar level with a dynamic range over 6-orders of magnitude in the V(g,min) shift as a sensitivity parameter. High association constants of 3.2 nM(-1) and 4.2 nM(-1) were obtained for the pH 6.2 and pH 7.4 analyte solutions, respectively. The R-GO FET biosensor showed a high specificity to other cancer biomarker in the phosphate buffered saline solutions as well as in the human serum.

Organic electrochemical transistor based immunosensor for prostate specific antigen (PSA) detection using gold nanoparticles for signal amplification

We demonstrated a highly sensitive organic electrochemical transistor (OECT) based immunosensor with a low detection limit for prostate specific antigen/alpha1-antichymotrypsin (PSA-ACT) complex. The poly(styrenesulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) based OECT with secondary antibody conjugated gold nanoparticles (AuNPs) provided a detection limit of the PSA-ACT complex as low as 1pg/ml, as well as improved sensitivity and a dynamic range, due to the role of AuNPs in the signal amplification. The sensor performances were particularly improved in the lower concentration range where the detection is clinically important for the preoperative diagnosis and screening of prostate cancer. This result shows that the OECT-based immunosensor can be used as a transducer platform acceptable to the point-of-care (POC) diagnostic systems and demonstrates adaptability of organic electronics to clinical applications.

pH sensing characteristics and biosensing application of solution-gated reduced graphene oxide field-effect transistors

Solution-gated reduced graphene oxide field-effect transistors (R-GO FETs) were investigated for pH sensing and biochemical sensing applications. A channel of a networked R-GO film formed by self-assembly was incorporated as a sensing layer into a solution-gated FET structure for pH sensing and the detection of acetylcholine (Ach), which is a neurotransmitter in the nerve system, through enzymatic reactions. The fabricated R-GO FET was sensitive to protons (H(+)) with a pH sensitivity of 29 mV/pH in terms of the shift of the charge neutrality point (CNP), which is attributed to changes in the surface potential caused by the interaction of protons with OH surface functional groups present on the R-GO surface. The R-GO FET immobilized with acetylcholinesterase (AchE) was used to detect Ach in the concentration range of 0.1-10mM by sensing protons generated during the enzymatic reactions. The results indicate that R-GO FETs provide the capability to detect protons, demonstrating their applicability as a biosensing device for enzymatic reactions.

Effect of Heat Treatment on Electrical Properties of Amorphous Oxide Semiconductor In–Ga–Zn–O Film as a Function of Oxygen Flow Rate

The effect of heat treatment on the electrical properties of an amorphous In–Ga–Zn–O (a-IGZO) film deposited by radio frequency (rf) magnetron sputtering at room temperature (RT) was investigated as a function of the oxygen flow rate. All of the films deposited with increasing O2 concentration in the Ar and Ar + O2 atmospheres exhibited insulating behavior in terms of their electrical properties, but their carrier concentration and resistivity were markedly affected after annealing at 400 °C in either a vacuum furnace or an rapid thermal annealing (RTA) system. However, the carrier concentration and resistivity of the films annealed in a normal furnace were not changed, compared with those of the as-deposited films annealed in the vacuum furnace. The difference in the electrical properties as a function of the annealing conditions was attributed to the number of oxygen vacancies. From X-ray photoemission spectroscopy (XPS), we confirmed that the formation of an O-rich surface was reduced by heat treatment under vacuum conditions. The output and transfer characteristics of the thin-film transistors (TFTs) exhibited excellent performance as depletion-mode n-channel field-effect TFTs after being annealed irrespective of the annealing system.