Jung A Lee

Carbon nanotube film piezoresistors embedded in polymer membranes

We present carbon nanotube film (CNF) piezoresistors embedded in polymer membranes. CNFs by vacuum filtration are patterned on an Au-deposited Si-wafer and transferred onto the poly-dimethylsiloxane (PDMS) using the weak adhesion property between Au-layer and Si-wafer. Transmittance and I-V characteristic are measured to confirm transferred CNFs as transparent electrodes. The pressure sensor consists of CNF piezoresistors embedded in 130 μm thick circular PDMS membranes. The gauge factor of CNFs at different thickness is obtained around 10–20 when the resistance increases from 2.7 to 5.6 kΩ with applied pressure, which shows that CNFs can be used as transparent piezoresistors in polymer-based microelectromechanical systems.

Fabrication and characterization of freestanding 3D carbon microstructures using multi-exposures and resist pyrolysis

We present a fabrication method for freestanding complex 3D carbon microstructures utilizing a lithogaphy step and a heating step. We developed two fabrication methods for multi-level 3D SU-8 microstructures, which were used as polymer precursors in a carbonization process. In one method, multiple SU-8 layers were successively coated and cross-linked. In the other method, aligned partial exposures were used to control the thickness of the freestanding SU-8 layer. Freestyle, freestanding carbon microstructures were fabricated by heating 3D SU-8 microstructures below 1000 °C in a nitrogen atmosphere. Characterization of the pyrolysis process, through measurements such as dimensional changes, roughness, hardness, elastic modulus and resistivity, was performed for positive resists AZ5214 and AZ9260 as well as SU-8. 3D carbon microstructures fabricated using our methods can be utilized for various applications such as low cost resonating microsensors and microfluidics.

Biosensor utilizing resist-derived carbon nanostructures

The authors present a biosensor using pyrolyzed electron beam resist nanostructures as an active conducting channel. Versatile, arbitrarily shaped nanostructures such as nanowires, nanodots, and suspended nanobridges are fabricated by a facile electron beam resist thermal decomposition method. The nanostructures typically show 15–21nm thickness, 100–200nm width, 0.6nm roughness, and p-type majority conduction with tailored resistivity of 5.2–0.75Ωcm. Streptavidin-biotin binding and pH dependent conductance modulation are demonstrated using pyrolyzed resist based devices.

Pyrolyzed carbon biosenosor for aptamer-protein interactions using electrochemical impedance spectroscopy

We present an electrochemical biosensor utilizing pyrolyzed carbon as a working electrode for the aptamer-based thrombin detection. The pyrolyzed carbon is fabricated by photolithography and thermal decomposition of photoresist in an N2 atmosphere. Physical and electrical properties of carbon thin film pyrolyzed with a positive photoresist, AZ9260, were studied for the biosensor application. Electron transfer resistance changes due to thrombin binding onto the carbon surface modified with thrombin aptamer were measured using electrochemical impedance spectroscopy techniques. Thrombin concentrations between 0.5 nM and 500 nM were detected by the electrochemical measurements.

A Novel Microcantilever Device with Nano-Interdigitated Electrodes (Nano-IDEs) for Biosensing Applications

We present a novel microcantilever device with nano-interdigitated electrodes (nano-IDEs) and selective functionalization of nano-IDEs for biosensing applications. The nano-IDEs play a role in precisely addressing capture molecules to a specific region on a microcantilever. This leads to a detectable surface stress due to the binding of target molecules. 70~500 nm-wide gold (Au) nano- IDEs are fabricated on a low-stress SiNx microcantilever with dimensions of 100~600 μm in length, and 15~60 μm in width, with a 0.5 μm thickness using electron beam lithography and bulk micromachining. 32~96 nm-thick streptavidin is selectively deposited on one side of nano-IDEs using cyclic voltammetry at a scan rate of 0.1 V/s with a range of -0.2~0.7 V during 1~5 cycles. The selective deposition of streptavidin is confirmed by fluorescence microscopy and atomic force microscopy (AFM).

Fabrication and Characterization of Transparent Piezoresistors Using Carbon Nanotube Film

We present the fabrication and characterization of transparent carbon nanotube film (CNF) piezoresistors. CNFs were fabricated by vacuum filtration methods with 65?92% transmittance and patterned on Au-deposited silicon wafer by photolithography and dry etching. The patterned CNFs were transferred onto poly-dimethysiloxane (PDMS) using the weak adhesion property between the silicon wafer and the Au layer. The transferred CNFs were confirmed to be piezoresistors using the equation of concentrated-force-derived resistance change. The gauge factor of the CNFs was measured to range from 10 to 20 as the resistance of the CNFs increased with applied pressure. In polymer microelectromechanical systems, CNF piezoresistors are the promising materials because of their high sensitivity and low-temperature process.

DNA Selective Immobilization on a Microcantilever with Nano-Interdigitated Electrodes (Nano-IDEs) Using Cyclic Voltammetry

Abstract We present a novel microcantilever device with nano-interdigitated electrodes (nano-IDEs) and DNA selective immobilization on the nano-IDEs for biosensing applications. Using the nano-IDEs and cyclic voltammetric methods, we have achieved selective immobilization of DNA with submicrometer spatial resolution on a freestanding microcantilever. 70~500 nm-wide gold (Au) nano-IDEs are fabricated on a low-stress SiNx microcantilever with dimensions of 100~600 µm in length, and 15~60 µm in width, with a 0.5 µm thickness using electron beam lithography and bulk micromachining. Streptavidin is selectively deposited on one side of the nano-IDEs using cyclic voltammetry at a scan rate of 0.1 V/s with a range of -0.2~0.7 V during 1~5 cycles. The selective deposition of dsDNA is confirmed by fluorescence microscopy after labeling with YOYO-1 dye. 1. 서 론 공진주파수 마이크로 캔틸레버는 표면 분석 또는 정보 저장을 위한 SPM 탐침, 질량 센서, 가스 센서, DNA센서, 단백질 센서와 같은 다양한 물리량, 화학량, 생화학량 계측용 센서로 널리 연구되고 있다. DNA, 단백질과 같은 생체분자들이 마이크로 캔틸레버의 표면에 결합하였을 때 발생하는 및변위변화를이용한바이오센서는 기존 형광표지를 이용한 DNA , 칩단백질 칩에 비하여 표지를 하지 않고 고속 실시간 분석을 (1~6)구현할 수 있는 장점을 가지고 있다.마이크로 캔틸레버의 한쪽 표면에 외가닥 DNA 혹은 항원과 같은 생체감지물질을 형성한 후 외가닥 DNA에 상보 DNA 혹은 항체 등을 반응시키면 마이크로 캔틸레버 표면위에 형성된 생체분자사이의 정전력이 변화하게 된다. 변화된 정전력으로 인하여 마이크로 캔틸레버에 비대칭 응력이 발생하게 되며 이로 인하여 마이크로 캔틸레버의 변위변화가 발생하게 된다. 이러한 마이크로 캔틸레버의 변위차이를 측정함으로써 단

Real-time Detection of Protein Interactions Using Pyrolyzed Carbon

We present label-free, real-time detection of streptavidin binding using the pyrolyzed carbon with a p-type conduction behavior in aqueous solution, which is functionalized with amine-conjugated biotin. Pyrolyzed carbon derived from AZ 5214E are fabricated by photolithography and photoresist thermal decomposition in a N2 atmosphere. The streptavidin-biotin interactions on the pyrolyzed carbon are detected successfully by current change after streptavidin binding.