臺大光電所所訊

Characterizations of Protein-Ligand Reaction Kinetics by Transistor-Microfluidic Integrated Sensors

Professor Jian-Jang Huang’s Lab

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所黃建璋教授

Understanding the binding affinities and kinetics of protein-ligand interactions using a label-free method is crucial for identifying therapeutic candidates in clinical diagnostics and drug development. In this work, the IGZO-TFT (thin-film transistor) biosensor integrated with a tailored microfluidic chip was developed to explore binding kinetics of protein-ligand biochemical interactions in the real-time manner. The IGZO-TFT sensor extracts the binding characteristics through sensing biomolecules by their electrical charges. Using lysozyme and tri-N-acetyl-D-glucosamine (NAG₃) as an example, we established a procedure to obtain the parameters, such as the dissociation constant, K_d, and association rate constant, k_a, that are critical to biochemical reactions. The correlation between the lysozyme concentration and TFT drain current signal was first constructed. Next, solutions of lysozyme and NAG₃ of different mixing ratios were prepared. They were pre-mixed for various periods of reaction time before applying to the TFT sensor to extract signals of lysozyme molecules and the concentration remaining. With the knowledge of drain current changes at different reaction times, k_a and K_d can be obtained. The values from our experiment are comparable to other methods, which suggests the proposed approach can be employed to explore protein-ligand interaction kinetics in the massively parallel manner if the TFT array is considered.

Fig. 1. (a) Schematic diagram of the IGZO-TFT biosensor integrated with a microfluidic channel. (b) Cross sectional view of the staggered and double-gated TFT.

Fig. 2 Illustration of molecule capture process of (a) Lysozyme solution (b) lysozyme + NAG₃ solution. Note that in addition to the screening effect, with the presence of NAG₃, the drain current will be increased instead of decreased as opposed to the case of purelysozyme solution.

Flexible Complementary Oxide Thin-Film Transistor-Based Inverter with High Gain

Professor I-Chun Cheng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所陳奕君教授

Wearable bio-sensing devices are considered promising for ubiquitous heath monitoring. To accurately read out small bio-signals, the development of high-performance flexible front-end circuits is crucial. Oxide semiconductors are considered one of the most promising active channel materials for on-polymeric-foil electronics. So far, most flexible complementary TFT inverters have been based on either pseudo-CMOS or organic-inorganic hybrid-CMOS configurations. In this study, a high-gain flexible CMOS inverter with a beta ratio (width-to-length ratio between the pull-up and pull-down transistors) of 1 was demonstrated by monolithically integrating a top-gated n-type IGZO TFT and a bottom-gated p-type SnO TFT on a 5.5-μm-thick polyimide substrate, as shown in Figure 1. The IGZO TFT exhibits a field-effect mobility of 8.0 cm²V^-1s^-1, threshold voltage of 5.2 V, subthreshold swing of 0.15 V/decade, and high on/off current ratio of >10⁷. The corresponding values for the SnO TFT are 1.6 cm²V^-1s^-1, 2.8 V, 2.3 V/decade and >10³, respectively. No apparent current crowding is observed in the output characteristics, suggesting that ohmic contacts exist between the source/drain electrodes and the channel layers. The flexible inverter exhibited a high static voltage gain of 370 V/V and balanced noise margins (noise margin high of 4.8 V, noise margin low of 4.7 V) for a supply voltage of 10 V, as shown in Figure 2(a). In addition, as shown in Figure 2(b), the voltage transfer characteristics remained virtually unchanged when the device was subjected to an outward or an inward bending radius of 2.5 mm, indicating the complementary oxide-TFT-based inverter is practical for flexible electronics applications. [IEEE Trans. Electron Devices, vol. 68, No. 3, p. 1070, Mar 2021]

Fig. 1 (a) Schematic cross section of a flexible oxide-TFT-based CMOS inverter. (b) Photograph of flexible CMOS inverters fabricated on an ultrathin polyimide substrate.

Fig. 2 (a) Voltage transfer characteristics of a flexible CMOS inverter with a beta ratio of 1 at different V_DD. (b) Static voltage gain of the flexible CMOS inverter under different bending conditions.