A wireless monitoring sub-nA resolution test platform for nanostructure sensors.

We have constructed a wireless monitoring test platform with a sub-nA resolution signal amplification/processing circuit (SAPC) and a wireless communication network to test the real-time remote monitoring of the signals from carbon nanotube (CNT) sensors. The operation characteristics of the CNT sensors can also be measured by the ISD-VSD curve with the SAPC. The SAPC signals are transmitted to a personal computer by Bluetooth communication and the signals from the computer are transmitted to smart phones by Wi-Fi communication, in such a way that the signals from the sensors can be remotely monitored through a web browser. Successful remote monitoring of signals from a CNT sensor was achieved with the wireless monitoring test platform for detection of 0.15% methanol vapor with 0.5 nA resolution and 7 Hz sampling rate.

Detection of 10 nM ammonium ions in 35 per thousand NaCl solution by carbon nanotube based sensors.

We fabricated carbon nanotube (CNT) based chemical sensors for marine applications by photolithography process, where the electrodes were insulated by photoresist exposing only the carbon nanotube sensing section (2 microm gap width) for detection of ammonium ions (NH4+) in 35 per thousand NaCI solution used as artificial seawater environment. The I-V curve of the CNT sensor was measured by sweeping the source-drain voltage from -3 to 3 V and the on/off ratio of the CNT sensor was measured to be 20 when the gate voltage was swept from -5 to 5 V and from these results the CNTs were found to appear as a p-type semiconductor. All of the cocktail solutions prepared for experiment were measured to have -pH 6 which implied 99.9% of NH4+ remained ionized. We successfully detected 10, 100, 1000 nM (0.18, 1.8, 18 ppb) concentration of NH4+ in 35 per thousand NaCI solutions by using the CNT sensor.

Processing technique for single-walled carbon nanotube-based sensor arrays.

We investigated a selective assembly method of fabricating single-walled carbon nanotubes (SWCNTs) on a silicon-dioxide (SiO2) surface by using only a photolithographic process; then, we fabricated 8 x 8 field-emission transistor (FET) arrays for sensor applications. Photoresist (PR) patterns were made on a SiO2-grown Si substrate by using the photolithographic process. This PR-patterned substrate was dipped into a SWCNT solution dispersed in dichlorobenzene (DCB). The PR patterns were removed by using acetone. As a result, selectively-assembled SWCNT channels in 8 x 8 FET arrays could be fabricated between source and drain electrodes without complicated chemical steps using octadecyltrichlorosilane (OTS). Finally, we successfully fabricated 8 x 8 SWCNT-based multi-channel FET arrays by using our novel self-assembly method.