Jeo-young Shim

Label-Free CMOS DNA Quantification with On-Chip Noise Reduction Schemes

We present a label-free CMOS DNA sensor with a new sensing-pixel architecture and background noise reduction scheme. The proposed sensor generates a differential signal between bio-samples and reference buffer solution with significant reduction in offset and gain fixed pattern noise by employing on-chip correlated double sampling circuits. Non-surface-binding detection technique allows to quantify DNA molecules continuously and sequentially and to reuse the sensor by simple washing protocol. By directly reading the negative charges of DNA molecules, DNA concentrations from 1 muM to 10 muM have been successfully discriminated.

Pulsed I –V measurement method to obtain hysteresis-free characteristics of graphene FETs

Current-voltage (I–V) characteristics of the graphene field effect transistors (GFETs) are measured by the dc, fast I–V (FIV), and pulsed I–V (PIV) methods and analyzed. The hysteresis and conductance in the dc measurement are affected by the sweeping bias range and direction. The I–V curves measured by the FIV method show reduced hysteresis and enhanced conductance at a faster sweeping rate, but are still affected by the sweeping bias range. By applying the PIV method, the hysteresis can be suppressed significantly while the conductance is improved by controlling turn-on, turn-off times (t on and t off) and the gate bias during t off (V base) regardless of the sweeping bias range. With short t on, long t off, and V base of 0 V, the hysteresis-free characteristics of GFETs are obtained.

Real-time label-free quantitative monitoring of biomolecules without surface binding by floating-gate complementary metal-oxide semiconductor sensor array integrated with readout circuitry

We report a label-free field-effect sensing array integrated with complementary metal-oxide semiconductor (CMOS) readout circuitry to detect the surface potential determined by the negative charge in DNA molecules. For real-time DNA quantification, we have demonstrated the measurements of DNA molecules without immobilizing them on the sensing surface which is composed of an array of floating-gate CMOS transistors. This nonimmobilizing technique allows the continuous monitoring of the amount of charged molecules by injecting DNA solutions sequentially. We have carried out the real-time quantitative measurement of 19bp oligonucleotides and analyzed its sensitivity as a function of pH in buffer solutions.

Analysis and suppression of drain current drift in graphene FETs

The cause of drain current (ID) drift in graphene field-effect transistors is analyzed and a method to suppress the drift is proposed. By analyzing ID-time characteristics, a condition of reasonable gate, drain and source biases (VG, VD, and VS) is proposed to suppress ID drift. Based on this result, we find a condition for VG during off-time (Vbase), VD, and VS in pulsed I-V measurement to obtain the intrinsic ID-VG curves, and analyze the effect of Vbase on the Dirac point shift. Through an analysis of ID-time characteristics depending on VG, ID drift according to the range of VG is explained.

Bandwidth limitation of the electrolytes for DNA sequencing using nanopore sensors

DNA sequencing using nanopore-based sensors attracts considerable interests because of the possibility of ultimate sensitivity of single-molecule resolution. Due to the fast DNA translocation speed on the order of microsecond, the sensor requires a wide bandwidth exceeding a megahertz. Such a high frequency signal transmits through the electrolyte and the sensor measures ionic current changes. The electrolyte is essential to dissolve DNA sample into the sensor. However, the bandwidth of the electrolyte has not been considered yet. This study presents the bandwidth limitation of the electrolyte and we believe it should be considered when using DNA sequencing method via high frequency signal detection through the electrolyte.