Chen-Pin Hsu

AlGaN/GaN high electron mobility transistors for protein–peptide binding affinity study

Abstract Antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect a short peptide consisting of 20 amino acids. One-binding-site model and two-binding-site model were used for the analysis of the electrical signals, revealing the number of binding sites on an antibody and the dissociation constants between the antibody and the short peptide. In the binding-site models, the surface coverage ratio of the short peptide on the sensor surface is relevant to the electrical signals resulted from the peptide–antibody binding on the HEMTs. Two binding sites on an antibody were observed and two dissociation constants, 4.404×10−11 M and 1.596×10−9 M, were extracted from the binding-site model through the analysis of the surface coverage ratio of the short peptide on the sensor surface. We have also shown that the conventional method to extract the dissociation constant from the linear regression of curve-fitting with Langmuir isotherm equation may lead to an incorrect information if the receptor has more than one binding site for the ligand. The limit of detection (LOD) of the sensor observed in the experimental result (∼10pM of the short peptide) is very close to the LOD (around 2.7–3.4pM) predicted from the value of the smallest dissociation constants. The sensitivity of the sensor is not only dependent on the transistors, but also highly relies on the affinity of the ligand-receptor pair. The results demonstrate that the AlGaN/GaN HEMTs cannot only be used for biosensors, but also for the biological affinity study.

Human immunodeficiency virus drug development assisted with AlGaN/GaN high electron mobility transistors and binding-site models

Human immunodeficiency virus (HIV) Reverse Transcriptase (RT)-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) and binding-site models were used to find out the dissociation constants of the HIV RT-inhibitor complex and the number of the binding sites on RT for the inhibitor, Efavirenz. One binding site on the RT for the inhibitor is predicted and the dissociation constant extracted from the binding-site model is 0.212 nM. The AlGaN/GaN HEMTs and the binding-site-models are demonstrated to be good tools to assist drug developments by elucidating the dissociation constants and the number of binding sites, which can largely reduce the cost and time for drug developments.

Risk stratification of heart failure from one drop of blood using hand-held biosensor for BNP detection

Continued risk assessment by evaluating cardiac biomarkers in healthy and unhealthy individuals can lower the mortality rate of cardiovascular diseases (CVDs). In this research, we have developed a hand-held biosensor system to rapidly screen for brain natriuretic peptide (BNP) from a single drop of whole blood. The sensor methodology is based on extended gate design of electrical double layer (EDL) field effect transistor (FET), that can directly detect BNP in whole blood, without extensive sample pre-treatments, thereby eliminating the limitations of charge screening in high ionic strength solutions. A simple sensor array chip is fabricated to integrate with the MOSFET sensor system. Sensing characteristics are elucidated using purified BNP samples in 1 × PBS (with 4% BSA), spiked BNP samples in whole blood and clinical whole blood samples. The blood cells can be gravitationally separated without the use of any external actuation. The sensor exhibits very high sensitivity over wide dynamic range of detection. The sensing characteristics are not adversely affected by the presence of background proteins or blood cells, even without gravitational blood cell separation. Thus, the biosensor system can allow users to perform rapid whole blood diagnostics with minimal user protocols, in 5 min. The features of high sensitivity, cost-effectiveness and convenience of usage empower this technology to revolutionize the mobile diagnostics and healthcare industry.

Single Drop Whole Blood Diagnostics: Portable Biomedical Sensor for Cardiac Troponin I Detection

Detection of disease biomarkers from whole blood is very important in disease prevention and management. However, new generation assays like point-of-care or mobile diagnostics face a myriad of challenges in detecting proteins from whole blood. In this research, we have designed, fabricated, and characterized a portable biomedical sensor for the detection of cardiac troponin I (cTnI) directly from whole blood, without sample pretreatments. The sensing methodology is based on an extended gate electrical double layer (EDL) gated field effect transistor (FET) biosensor that can offer very high sensitivity, a wide dynamic range, and high selectivity to target analyte. The sensing methodology is not impeded by electrostatic screening and can be applied to all types of FET sensors. A portable biomedical system is designed to carry out the diagnostic assay in a very simple and rapid manner, that allows the user to screen for target protein from a single drop of blood, in 5 min. This biomedical sensor can be used in hospitals and homes alike, for early detection of cTnI which is a clinical marker for acute myocardial infarction. This sensing methodology could potentially revolutionize the modern health care industry.

Investigation of DNA Detection Mechanism with AlGaN/GaN High Electron Mobility Transistor (HEMT) Biosensor in High Ionic Strength Solution

In this research, the electrical double layer HEMT device is used to serve as the cardiovascular disease (CVD) RNA biomarkers biosensor. In this experiment, we try to use the DNA equivalent to miRNA-126 to test the ability of the novel DNA sensors. Short Debye length has been a haunted problem among all the field effect transistor (FET) biosensor for years. As the Debye length is extremely short in high ionic strength solutions, the traditional FET may not be directly detecting the biomolecule. The novel HEMT sensors using AlGaN/GaN can perform high sensitivity and great specificity in DNA sequences testing. The detection limit can be down to the 1fM and the specificity measurement can identify the signals between two DNA sequences with six-base mismatch. Furthermore, the mechanism of the sensor structure has also been studied. Since the structure of the device has the separation between source drain channel and gate electrode, the comparison with different electrode area and gap distance has been done as well. With repeating electrical measurement confirming, the reusability can also be seen after the 95℃ dehybridization process. With the Gibbs free energy ∆G of the specific sequences, we can also predict the equilibrium reaction constant and the binding ratio of probe DNA with the target DNA. The comparison between the thermal dynamics with the experiment consequence has been demonstrated too.

Elucidation of dissociation constants and binding sites of antibody-antigen complex using AlGaN/GaN high electron mobility transistors

In this study, we used antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) for detecting a short peptide, and revealing the number of binding sites of the antibody for the peptide and the dissociation constants of the antibody-peptide complex. In our case, two binding sites were found on the ferritin heavy chain (FHC) antibody and the dissociation constants of the antibody-peptide complex were 2.723×10-11M and 6.994×10-9M for the two binding sites, respectively. The estimated dissociation constants are consistent within the reasonable range of the IGg antibody-antigen complexes binding constants. It also reveals the limit of detection is not only decided by the performance of the transistors but also the dissociation constant of the detected molecules. To our knowledge, it is the first time that AlGaN/GaN HEMTs using on the study of protein-peptide binding affinity. The results show that AlGaN/GaN HEMTs can not only be used as biosensors, but also a good tool and platform for analytical chemistry with numerous advantages since they are label-free, low-cost, biocompatible, stable in high temperature, real-time detection. Compared with other methods and techniques investigating the binding and kinetics of biological molecules, we do demonstrate AlGaN/GaN HEMTs have great potential to compete with conventional or proposed methods.

Pushing or pulling droplets on ZnO nanorods with an UV light

Water droplets were either pushed or pulled with an UV light on the surface of vertically aligned and superhydrophobic ZnO nanorods (NRs). The contact angle of the droplets reduce to a lower value due to the absorption of UV by ZnO NRs and a circulating current was observed inside the droplet. The droplets were either pushed away from or pulled toward to the center of the UV light depending on the locations of the droplets to the UV light. It is obvious that in the pushing mode, the circulating current dominate the direction of the movement of the droplets, while in the pulling mode, the contact angle change dominate the direction of the droplet movement

Measurement of optical characteristics in dielectric liquid lens by Shack-Hartmann wave front sensors

Liquid lenses based on the principle of driving two dielectric fluids via controlled electric field were investigated with an experimental apparatus designed for analysis of wave front read from a Shack-Hartmann sensor. Due to small available aperture and requirements in dynamic responses, wave front measurement was selected for study of optical characteristics in dielectric lenses. With the advent of commercial electro-optics sensors in wave front measurement, the experimental apparatus was first designed and simulated with the help of ASAP program. The simulated results proved the conceptual design with handful of engineering insights so that less trial and error efforts could be relieved from building the optics system on the bench. In-house built liquid lens modules with driving circuits were then set on the apparatus for initial calibration and functional tests. Since the electric field generated for the control of liquid profile must be alternating current, various frequency and modulation schemes were put through the liquid lens module to further study the influences on dynamic responses in terms of optical characteristics. Furthermore, effects due to material impurity and ambient effects were also carefully studied for established the fundamental phenomena of liquid lenses made of dielectric fluids. More detailed observations were possible with the measured wave-front data. In conclusion, the wave-front measurement proved to be more reliable and less expensive compared to measurement based on interferometer.