Seok Hyang Kim

Multi-order dynamic range DNA sensor using a gold decorated SWCNT random network

A novel electrical DNA biosensor is presented, which consists of gold (Au) nanoscale islands and a single-walled carbon nanotube (SWCNT) network on top of a concentric Au electrode array (also referred to as the CGi). The decorated Au islands on the SWCNT network provide ideal docking sites for ss-DNA probe (p-DNA) molecules. They also provide better adhesion between the SWCNT network and the chip substrate. In addition, the concentric electrode gives asymmetric current voltage characteristics in the solution and provides more flexible bias options to the electrodes. The sensor system is applied to a DNA sensor after functionalization with a 25 mer p-DNA (5-HSC(6)-C(18)-GCCATTCTCACCGGATTCAGTCGTC-3), hereafter called the [CGi+p-DNA]. The response of the DNA sensor has been measured in both real-time during hybridization with the complementary target ss-DNAs (t-DNA) and the static mode after the hybridization and washing steps. A wide dynamic range from the 100 fM to 1 μM has been achieved from the real-time mode and the static mode. Moreover, it is shown that the sensor system differentiates partially mismatched (single nucleotide polymorphism (SNP), half mismatch, noncomplementary) t-DNA, as well. The [CGi] sensor platform can be easily extended to target specific biological recognition elements such as aptamers or proteins.

Modulation of molecular hybridization and charge screening in a carbon nanotube network channel using the electrical pulse method

In this paper, we investigate the effect of electrical pulse bias on DNA hybridization events in a biosensor platform, using a Carbon Nanotube Network (CNN) and Gold Nano Particles (GNP) as an electrical channel. The scheme provides both hybridization rate enhancement of bio molecules, and electrical measurement in a transient state to avoid the charge screening effect, thereby significantly improving the sensitivity. As an example, the probe DNA molecules oscillate with pulse trains, resulting in the enhancement of DNA hybridization efficiency, and accordingly of the sensor performances in Tris-EDTA (TE) buffer solution, by as much as over three times, compared to the non-biasing conditions. More importantly, a wide dynamic range of 10(6) (target-DNA concentration from 5 pM to 5 μM) is achieved in human serum. In addition, the pulse biasing method enables one to obtain the conductance change, before the ions within the Electrical Double Layer (EDL) are redistributed, to avoid the charge screening effect, leading to an additional sensitivity enhancement.

Electrical Characteristics of the Concentric-Shape Carbon Nanotube Network Device in pH Buffer Solution

A carbon nanotube network device having concentric-shaped electrodes (source and drain) is analyzed to examine the self-gating effect of various pH buffer solutions on its electrical properties. Using the 2-D homogeneous percolation theory, current-voltage characteristics of the devices are described as the classical MOSFET formula, in which the device is modeled as the p-type transistor with positive threshold voltage and the gate is tied with the drain (at positive bias) or source (at negative bias). To determine the apparent threshold voltage change due to the corresponding pH value, the ∂VD/∂ID (VD:drain voltage; ID:drain current) curve is extracted from the measured current-voltage characteristics to find VD_SAT(= -VTH, VQS = 0). A threshold voltage shift according to the pH value is observed without an external gate electrode, showing the possibility of relaxing the requirement of the external gate electrode. By grafting protonation/deprotonation which occurs in the carboxylated single-walled carbon nanotubes, the decaying current as pH increases is explained. Better sensitivity according to the operation regime is examined by the device modeling.

Analysis of Sensing Mechanisms in a Gold-Decorated SWNT Network DNA Biosensor

We show that carbon nanotube sensors with gold particles on the single-walled carbon nanotube (SWNT) network operate as Schottky barrier transistors, in which transistor action occurs primarily by varying the resistance of Au-SWNT junction rather than the channel conductance modulation. Transistor characteristics are calculated for the statistically simplified geometries, and the sensing mechanisms are analyzed by comparing the simulation results of the MOSFET model and Schottky junction model with the experimental data. We demonstrated that the semiconductor MOSFET effect cannot explain the experimental phenomena such as the very low limit of detection (LOD) and the logarithmic dependence of sensitivity to the DNA concentration. By building an asymmetric oncentricelectrode model which consists of serially-connected segments of CNTFETs and Schottky diodes, we found that for a proper explanation of the experimental data, the work function shifts should be ~ 0.1 eV for 100 pM DNA concentration and ~ 0.4 eV for 100 μM.

Carbon Nanotube-Based CMOS Gas Sensor IC: Monolithic Integration of Pd Decorated Carbon Nanotube Network on a CMOS Chip and Its Hydrogen Sensing

The integration of carbon nanotube (CNT)-based sensor and readout complementary metal-oxide-semiconductor integrated chip (CMOS IC) to detect hydrogen gas in a single chip is presented. First, we have fabricated the CMOS IC using the standard 0.35-μm CMOS process. Then, we have built 8 × 8 CNT-based sensor cells on it using a proposed tractable postprocessing strategy and judicious electrode scheme. The fabricated sensor IC can operate down to 10-ppm concentration of hydrogen in air as a hydrogen sensor. This paper is expected to have a major impact upon the integration of the CNT technology with CMOS technology and be extended to the development of CMOS IC integrated with various nanomaterials.

Electrical passivation of nonselective bio molecules in carbon nanotubes: Effect of pulse train in serum

We present an experimental and simulation study about a desorption of albumin, a representative nonselective molecules in serum, on carbon nanotube (CNT) surface as an electrical bio sensing channel under the pulse train condition. The motivation of the study on binding kinetics between CNT surface and albumin is to suppress the adsorption of nonselective proteins in blood such as albumin, thereby enhancing the selectivity of the electrical biosensor. To theoretically model the behavior of molecules and ions under the step pulse bias, the physics on the reaction rate, mass transport, and the resulting surface pH-value are considered using the Poisson and drift-diffusion equations. For the simulation model, the phosphate buffered saline is considered as the electrolyte solution and albumin is considered as a representative charged molecule for nonspecific binding in serum. Both the transient simulation and experimental result indicate that the suppression of the nonspecific binding under the pulse train is...

A time dependent signal of DNA hybridization from CMOS chip integrated with CNT network

A fully CMOS integrated carbon nanotube (CNT) sensor array platform that consists of an 8×8 array of unitary CNT elements has been designed and fabricated. For digital conversion of the analog voltage of CNT sensor elements, a correlated double sampling (CDS) type Successive Approximation Register (SAR) Analog/Digital converter has been used. The chip has been applied to sense the DNA hybridization event in the transient state, even though the chip can be applied to general molecular detection. It is shown that the fabricated fully CMOS integrated CNT sensor array platform can measure the time change of the resistance value of the sensor array cell in micro second interval by changing the clock frequency. The CMOS sensor chip presented in this research can be used various sensor applications by proper functionalization of CNT networks.

Highly selective dengue virus detection using carbon nanotubes: Effect of pulse biasing in serum

Electrical pulse biasing was used for selective and sensitive detection in serum of a target DNA sequence (dengue fever virus-specific sequence in this study) based on a carbon nanotube network decorated with gold nano particles. A significant increase in the affinity constant (as much as 1.01×109 M-1 from the Langmuir fitting) has been obtained in addition to the enhancement in selectivity against the nonselective molecules. The physical reason of the enhancement is believed to be the physical oscillation of the probe DNA molecules caused by the applied electrical pulse trains, thereby increase in the binding chance between the probe and target DNAs. With the technique, a wide dynamic range (10 pM-10 μM) detection of the target DNA molecules has been achieved in the serum condition.

“C-chip” Platform for Electrical Biomolecular Sensors

In this chapter, a new CMOS platform for the real time, multiple molecules detection of the bio molecules will be introduced. The semiconductor channel of the sensor device is composed of the carbon nanotube network (CNN) decorated with the gold nano particles (GNP) as the docking agents for the probe molecules and integrated onto the CMOS chip which receives the modulation of the channel resistance and performs the necessary signal processing. The number of the sensor devices on a chip is in the range of a few thousands and statistical analysis of the multiple sensing is possible in addition to multiple targeting by adding different probe molecules. In addition, the charge screening effects and non selectivity problem, which have been regarded as the show stoppers of the electrical sensing of the bio molecules can be widely avoided by introducing the electrical pulse technique. The architecture of the platform, salient feature of the sensor devices and the behavior of the sensor devices on the electrical pulse agitation will be reviewed.

The acid-base properties of carboxylated CNT and the design of CNT based biosensor

We observed the sign of the two responses from carboxylated carbon nanotube (CNT) based sensor in aqueous solution by means of dynamic measurements. Two types of surface groups, the hydroxyl and the carboxyl group of sensor surface are amphoteric materials depending on the pH. The protonation/deprotonation of these surface groups modulates CNT conductance. After blocking of COOH group on the CNT surface, CNT characteristics become insensitive to pH condition. This result brings benefits to reliable operation and high sensitivity of CNT based sensor.