Joonhyung Lee

Two-dimensional Layered MoS2 Biosensors Enable Highly Sensitive Detection of Biomolecules

We present a MoS2 biosensor to electrically detect prostate specific antigen (PSA) in a highly sensitive and label-free manner. Unlike previous MoS2-FET-based biosensors, the device configuration of our biosensors does not require a dielectric layer such as HfO2 due to the hydrophobicity of MoS2. Such an oxide-free operation improves sensitivity and simplifies sensor design. For a quantitative and selective detection of PSA antigen, anti-PSA antibody was immobilized on the sensor surface. Then, introduction of PSA antigen, into the anti-PSA immobilized sensor surface resulted in a lable-free immunoassary format. Measured off-state current of the device showed a significant decrease as the applied PSA concentration was increased. The minimum detectable concentration of PSA is 1 pg/mL, which is several orders of magnitude below the clinical cut-off level of ~4 ng/mL. In addition, we also provide a systematic theoretical analysis of the sensor platform – including the charge state of protein at the specific pH level, and self-consistent channel transport. Taken together, the experimental demonstration and the theoretical framework provide a comprehensive description of the performance potential of dielectric-free MoS2-based biosensor technology.

Enhanced Moisture-Reactive Hydrophilic-PTFE-Based Flexible Humidity Sensor for Real-Time Monitoring

Flexible sensors connected to cell phones are a promising technology that can aid in continuously monitoring signals in our daily lives, such as an individual’s health status and information from buildings, farms, and industry. Among such signals, real-time humidity monitoring is crucial to a comfortable life, as human bodies, plants, and industrial environments require appropriate humidity to be maintained. We propose a hydrophilic polytetrafluoroethylene (H-PTFE)-based flexible humidity sensor integrated with readout circuitry, wireless communication, and a mobile battery. To enhance its sensitivity, linearity, and reliability, treatment with sodium hydroxide implements additional hydroxyl (OH) groups, which further enhance the sensitivity, create a strong linearity with respect to variations in relative humidity, and produce a relatively free hysteresis. Furthermore, to create robust mechanical stability, cyclic upward bending was performed for up to 3000 cycles. The overall electrical and mechanical results demonstrate that the flexible real-time H-PTFE humidity sensor system is suitable for applications such as wearable smart devices.

Label-Free and Recalibrated Multilayer MoS2 Biosensor for Point-of-Care Diagnostics

Molybdenum disulfide (MoS2) field-effect transistor (FET)-based biosensors have attracted significant attention as promising candidates for highly sensitive, label-free biomolecule detection devices. In this paper, toward practical applications of biosensors, we demonstrate reliable and quantitative detection of a prostate cancer biomarker using the MoS2 FET biosensor in a nonaqueous environment by reducing nonspecific molecular binding events and realizing uniform chemisorption of anti-PSA onto the MoS2 surface. A systematic and statistical study on the capability of the proposed device is presented, and the biological binding events are directly confirmed and characterized through intensive structural and electrical analysis. Our proposed biosensor can reliably detect various PSA concentrations with a limit of 100 fg/mL. Moreover, rigorous theoretical simulations provide a comprehensive understanding of the operating mechanism of the MoS2 FET biosensors, and further suggests the enhancement of the sensitivity through engineering device design parameters.

Increase in detection sensitivity of surface acoustic wave biosensor using triple transit echo wave

Here, we present a surface acoustic wave (SAW) biosensor for the highly sensitive detection of cardiac troponin I, a gold standard biomarker for the diagnosis of myocardial infarction, using a triple transit echo (TTE) wave of a SAW rather than a conventional main wave. Compared with the main wave, the TTE wave is caused by reflections from output and input interdigitized transducers (IDTs) after traversing the propagation path three times between input and output IDTs. The SAW biosensor using a TTE wave signal showed enhanced sensitivity for measuring the viscosity of glycerol solution and the mass loading effect of immunoassay reaction due to much bigger modulation induced in the amplitude, phase, frequency, and time-delay of the TTE wave. Our results showed that the proposed SAW biosensor could quantitatively analyze cardiac troponin I. Detection limit values using the main wave and the TTE wave were 766 pg/ml and 24.3 pg/ml, respectively. Therefore, one can say that the sensitivity of the SAW biosensor substantially improved when the TTE wave is used.Here, we present a surface acoustic wave (SAW) biosensor for the highly sensitive detection of cardiac troponin I, a gold standard biomarker for the diagnosis of myocardial infarction, using a triple transit echo (TTE) wave of a SAW rather than a conventional main wave. Compared with the main wave, the TTE wave is caused by reflections from output and input interdigitized transducers (IDTs) after traversing the propagation path three times between input and output IDTs. The SAW biosensor using a TTE wave signal showed enhanced sensitivity for measuring the viscosity of glycerol solution and the mass loading effect of immunoassay reaction due to much bigger modulation induced in the amplitude, phase, frequency, and time-delay of the TTE wave. Our results showed that the proposed SAW biosensor could quantitatively analyze cardiac troponin I. Detection limit values using the main wave and the TTE wave were 766 pg/ml and 24.3 pg/ml, respectively. Therefore, one can say that the sensitivity of the SAW biosenso...