Nanowire Array Breath Acetone Sensor for Diabetes Monitoring

Abstract

Diabetic ketoacidosis (DKA) is a life-threatening acute complication of diabetes characterized by the accumulation of ketone bodies in the blood. Breath acetone, a ketone, directly correlates with blood ketones. Therefore, monitoring breath acetone can significantly enhance the safety and efficacy of diabetes care. In this work, the design and fabrication of an InP/Pt/chitosan nanowire array-based chemiresistive acetone sensor is reported. By incorporation of chitosan as a surface-functional layer and a Pt Schottky contact for efficient charge transfer processes and photovoltaic effect, self-powered, highly selective acetone sensing is achieved. The sensor has exhibited an ultra-wide acetone detection range from sub-ppb to >100 000 ppm level at room temperature, covering those in the exhaled breath from healthy individuals (300-800 ppb) to people at high risk of DKA (>75 ppm). The nanowire sensor has also been successfully integrated into a handheld breath testing prototype, the Ketowhistle, which can successfully detect different ranges of acetone concentrations in simulated breath samples. The Ketowhistle demonstrates the immediate potential for non-invasive ketone monitoring for people living with diabetes, in particular for DKA prevention.

Keywords: Diabetic ketoacidosis; InP nanowires; acetone sensor; breath test prototype; chitosan.

Figure 1

The fabrication process of the InP/Pt/chitosan NW array acetone sensor. Scanning electron microscope (SEM) images in the top panel with the corresponding schematics in the bottom panel represent the sensor device fabrication processes, including a) the as‐grown NWs; b) SU8 planarization and etching to expose the top portion of the NWs; c) tilt‐angle deposition of Pt electrode, causing a slight NW bending due to the small NW diameter; d) drop‐casting of chitosan for surface functionalization in 45° tilt‐angle imaging; and e, the Ti/Au bottom contact fabrication next to the NW array for electrical connection.

Figure 2

Acetone sensing performance of the b‐InP/Pt/chitosan NW sensor. a) Schematic of the laboratory gas sensing setup for acetone sensing measurement. b) I–V curves measured from the sensor device under dark/light conditions. Inset: zoom‐in plot of the I–V curve for displaying I _SC and V _OC. c) Time‐dependent sensing response measured from short‐circuit current under light illumination for different ranges of acetone concentration: c) 2–10 ppm, d) 100–1000 ppb, e) 1–10 ppb, and f) 0.4–1 ppb. The yellow strips indicate acetone exposure. g) Concentration versus response curve for the acetone concentration range of 100–1000 and 0.4–10 ppb (inset), respectively.

Figure 3

Selectivity and humidity test of the b‐InP/Pt/chitosan NW sensor. a) Selectivity measurements performed for different gases, including acetone, 2‐butanone, ethyl benzene, ethanol, propane, and NO₂ under a concentration of 1 ppm, and CO₂ of 1%, with the standard deviation shown as error bars derived following 10 cycles of sensing measurements. b) Time‐dependent sensing response of acetone and 2‐butanone with concentrations ranging from 0.57% (5,700 ppm) to 16.05% (160,500 ppm). c,d) Sensing response to the acetone concentration of 1–5 ppm under the RH levels of 0%, 30%, 50%, and 65%. e) Gas sensing selectivity measurement to 1 ppm acetone, ethanol, and 1% CO₂ under different RH conditions.

Figure 4

Acetone sensing mechanism investigation. a) Temporal short‐circuit current (I _SC) response of the Pt/InP NW device with and without chitosan under light illumination. b) Time‐dependent acetone sensing response of the sensor with and without chitosan (under low oxygen conditions and in simulated air). c) Schematic of an InP NW with Pt contact used for the simulation study. d) Energy band diagram of the structure with the simulated electron concentration, corresponding to the various critical condition/steps of acetone sensing process. E_c, E_v, and E_fn represent the conduction band, valence band, and electron quasi‐Femi level, respectively.

Figure 5

The Ketowhistle for simulated breath testing. a) Pictures of the portable Ketowhistle breath testing prototype using Tedlar bags for the collection of simulated breath samples. b) Breath acetone spectrum showing the ranges of breath acetone concentration corresponding to various physiological states and ketosis ranges.^{[ 39c ]} c) Ketowhistle calibration for acetone concentration ranging from 0.1–1000 ppm to cover the entire breath acetone spectrum d) OLED screen displaying the response of an exhaled breath sample of a non‐diabetic (left) and a simulated diabetic breath sample (right). e) PCA for Non‐diabetic breath samples and simulated diabetic breath samples.