Aluminum gallium nitride (GaN)/GaN high electron mobility transistor-based sensors for glucose detection in exhaled breath condensate

Abstract

Background: Immobilized aluminum gallium nitride (AlGaN)/GaN high electron mobility transistors (HEMTs) have shown great potential in the areas of pH, chloride ion, and glucose detection in exhaled breath condensate (EBC). HEMT sensors can be integrated into a wireless data transmission system that allows for remote monitoring. This technology offers the possibility of using AlGaN/GaN HEMTs for extended investigations of airway pathology of detecting glucose in EBC without the need for clinical visits.

Methods: HEMT structures, consisting of a 3-microm-thick undoped GaN buffer, 30-A-thick Al(0.3)Ga(0.7)N spacer, and 220-A-thick silicon-doped Al(0.3)Ga(0.7)N cap layer, were used for fabricating the HEMT sensors. The gate area of the pH, chloride ion, and glucose detection was immobilized with scandium oxide (Sc(2)O(3)), silver chloride (AgCl) thin film, and zinc oxide (ZnO) nanorods, respectively.

Results: The Sc(2)O(3)-gated sensor could detect the pH of solutions ranging from 3 to 10 with a resolution of approximately 0.1 pH. A chloride ion detection limit of 10(-8) M was achieved with a HEMT sensor immobilized with the AgCl thin film. The drain-source current of the ZnO nanorod-gated AlGaN/GaN HEMT sensor immobilized with glucose oxidase showed a rapid response of less than 5 seconds when the sensor was exposed to the target glucose in a buffer with a pH value of 7.4. The sensor could detect a wide range of concentrations from 0.5 nM to 125 microM.

Conclusion: There is great promise for using HEMT-based sensors to enhance the detection sensitivity for glucose detection in EBC. Depending on the immobilized material, HEMT-based sensors can be used for sensing different materials. These electronic detection approaches with rapid response and good repeatability show potential for the investigation of airway pathology. The devices can also be integrated into a wireless data transmission system for remote monitoring applications. This sensor technology could use the exhaled breath condensate to measure the glucose concentration for diabetic applications.

Figure 1. (A)

The layout and (B) microscope image of the multifunctional sensor chip, as well as (C) a zoom-in view of sensor active areas. The inner sensor chip is the chloride ion sensor, which has an extra electrode connecting to the gate for anodizing the Ag into AgCl. The middle sensor is the pH sensor, and the outer sensor is the glucose sensor.

Figure 2. (A)

A schematic device cross-sectional view of the Sc₂O₃-gated HEMT pH sensor. (B) A schematic device cross-sectional view of the Ag/AgCl-gated HEMT chloride ion sensor. (C) A schematic device cross-sectional view of the ZnO nanorod-gated HEMT chloride ion sensor.

Figure 3. (A)

A schematic thermal electric module. (B) An AlGaN/GaN HEMT sensor chip mounted on top of a Peltier unit (TB-8-0.45-1.3 HT 232, Kryotherm).

Figure 4.

A highly dense array of 20- to 30-nm diameter and 2-μm-tall ZnO nanorods grown on the 10 × 50-μm gate area of a HEMT sensor.

Figure 5.

(A) Real-time glucose detection using drain current (I) change in the HEMT sensor with a constant bias of 250 mV. (B) Amount of drain current change in different concentrations of glucose dissolved in a PBS buffer solution.

Figure 6.

Time-dependent source–drain current signals with a constant drain bias of 500 mV for glucose detection in DI water and PBS buffer solution.

Figure 7. (A)

Drain current (IDS) of a Sc₂O₃ immobilized as a function of time.

Figure 8.

Drain current of an AgCl thin film-immobilized HEMT sensor as a function of time when exposed to different chloride ion concentrations.