Improved performance and stability of field-effect transistors with polymeric residue-free graphene channel transferred by gold layer.

One of the most significant issues that occurs when applying chemical-vapor deposited (CVD) graphene (Gr) to various high-performance device applications is the result of polymeric residues. Polymeric residues remain on the Gr surface during Gr polymer support transfer to an arbitrary substrate, and these residues degrade CVD Gr electrical properties. In this paper, we propose that a thin layer of gold be used as a CVD Gr transfer layer, instead of a polymer support layer, to enable a polymer residue-free transfer. Comparative investigation of the surface morphological and qualitative analysis of residues on Gr surfaces and Gr field-effect transistors (GFETs) using two transfer methods demonstrates that gold-transferred Gr, with uniform, smooth, and clean surfaces, enable GFETs to perform better than Gr transferred by the polymer, polymethylmethacrylate (PMMA). In GFETs fabricated by the gold transfer method, field-effect carrier mobility was greatly enhanced and the position of the Dirac point was significantly reduced compared to GFETs fabricated by the PMMA transfer method. In addition, compared to the PMMA-transferred GFETs, the gold-transferred GFETs showed greatly increased stability with smaller hysteresis and higher resistance to gate bias stress effects. These results suggest that the gold transfer method for Gr provides significant improvements in GFET performance and reliability by minimizing the polymeric residues and defects on Gr.

Electrical graphene aptasensor for ultra-sensitive detection of anthrax toxin with amplified signal transduction.

Detection of the anthrax toxin, the protective antigen (PA), at the attomolar (aM) level is demonstrated by an electrical aptamer sensor based on a chemically derived graphene field-effect transistor (FET) platform. Higher affinity of the aptamer probes to PA in the aptamer-immobilized FET enables significant improvements in the limit of detection (LOD), dynamic range, and sensitivity compared to the antibody-immobilized FET. Transduction signal enhancement in the aptamer FET due to an increase in captured PA molecules results in a larger 30 mV/decade shift in the charge neutrality point (Vg,min ) as a sensitivity parameter, with the dynamic range of the PA concentration between 12 aM (LOD) and 120 fM. An additional signal enhancement is obtained by the secondary aptamer-conjugated gold nanoparticles (AuNPs-aptamer), which have a sandwich structure of aptamer/PA/aptamer-AuNPs, induce an increase in charge-doping in the graphene channel, resulting in a reduction of the LOD to 1.2 aM with a three-fold increase in the Vg,min shift.

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.

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.