(A) AlGaN/GaN High electron mobility transistor (HEMT)-based biosensors:

We have been developing AlGaN/GaN High electron mobility transistor (HEMT)-based sensors and the sensor models for studying ligand-receptor binding affinity and demonstrating various novel applications. And we study peptide-antibody binding affinity with the HEMT-based sensors and elucidate the number of binding-sites and the corresponding dissociation constants. The result was very encouraging as shown in Figure 1, and published in the renowned journal “Biosensors and Bioelectronics.” [Link]

 
Figure 1. (a) IgG antibody-immobilized sensor (b) Number of the binding sites and the corresponding dissociation constants are elucidated from the analysis of the signals with the the sensor model.

We have also demonstrated that the method we develop can be used for HIV drug development. The FDA approved HIV drug, efavirenz, was shown to bind only one binding-site on the HIV RT enzyme, and the dissociation constant was also resolved, using our sensor as depicted in Figure 2. This work successfully shows that the conventionally time-consuming and costly drug development can become quick, efficient, and cheap process, by using our devices and developed methods. This work was published in Applied Physics Letters. [Link] 

   
Figure 2. (left) The FDA-approved HIV drug (center) The schematic of the HIV RT enzyme-immobilized sensor (right) The sensor signals perfectly fit into the one-binding site model.

In addition to the assist drug development, we also use the HEMTs to study the binding affinity between SARS protein and dsDNA. The results are very consisten with exsiting literature. This work can facilitate the understanding of the SARS virus using the advantages of the HEMT-based sensors. This work has been published in the renowed journal “Sensors and actuators B: chemial”. [Link]

Besides studying the binding affinity with our HEMTs, we have also found an interesting phenomena that the devices can response to polar liquids which have different polarity and viscosity. This turns out that we can use HEMTs to measure the viscosity of polar liquids in a very tiny volume. The interesting work was quickly published in the renowned journal “Journal of Applied Physics”. [Link]

(B)  Conducting polymer-based biosensors:

Besides the HEMT-based sensors, we have also developed conducting polymer-based biosensors. This kind of sensor is very different from the HEMT-based sensors. The HEMT-based biosensors are affinity-type sensors, which utilize the ligand-receptor binding to detect the specific biomolecule. There is not charge transfer between the biomolecules and the transistors. However, the conducting polymer is allowed to have charge transfer with the biomolecules. This feature is quite useful because many biochemial reactions are under going oxidation or reduction. We fabricate horseredish peroxidase-immobilized conducting polymer sensor to detect trace hydrogen peroxide, as shown in Figure 3.

Figure 3 (a) The schematic of the HRP-immobilized conducting polymer-based hydrogen peroxide sensor and the enzyme/substrate reaction (b) the top-view photography of the packaged hydrogen peroxide sensor.

Hydrogen peroxide is an important signaling molecule for many biological reactions and one of the reactive oxidative species, which is often measured for oxidative stress studies. Oxidative stress is currently an important research topic and is believed to be relevant to tumors, cancers, parkinsus disease, and aging. However, the concentration of hydrogen peroxide in biological systems could be very low. For example, the intramitochondrial H2O2 concentration is estimated and reported as 4.8 nM only. While most hydrogen peroxide can only detect µM, our sensor can easily detect 0.6nM, which is in the top three in the detection limit in the world. The high sensitivity and the scientific investigation of the sensing mechanism in detail, has led our work to being quickly published in the renowed journal “Biosensors and Bioelectronics” again. [Link]

Figure 4. The conductance change of the conducting polymer for detection of cholesterol in physiological concentration range.