Hajime Fujita1,Kento Yamagishi2,Wenshen Zhou2,Yu Tahara3,Shaoying Huang2,Michinao Hashimoto2,Toshinori Fujie1
Tokyo Institute of Technology1,Singapore University of Technology and Design2,Waseda University3
Hajime Fujita1,Kento Yamagishi2,Wenshen Zhou2,Yu Tahara3,Shaoying Huang2,Michinao Hashimoto2,Toshinori Fujie1
Tokyo Institute of Technology1,Singapore University of Technology and Design2,Waseda University3
A battery-free glucose sensor based on phenylboronic acid hydrogel and the flexible interdigitated capacitor was fabricated for rapid detection of postprandial hyperglycemia (PPHG). Excessive elevation of the postprandial glucose level is a general risk factor for type 2 diabetes, obesity, hypertension, and severe organ diseases. The postprandial glucose level reaches its peak at 30 to 60 minutes after food intake, and PPHG should be detected within 30 minutes. Battery-free flexible glucose sensors are a promising tool for the detection of PPHG and continuous monitoring with a relatively low impact on biological tissues and living bodies because they are lighter and more flexible than conventional battery-driven glucose sensors. Existing battery-free glucose sensors, however, are inadequate for the practical diagnosis of PPHG due to their long reaction time (> 1 h) and response variability. To bridge this gap, we developed a battery-free glucose sensor with a response time sufficient for detecting PPHG. A previous study demonstrated the detection of an elevated glucose level using a sensor that forms a layer of glucose-responsive phenylboronic acid hydrogel on a field-effect transistor (FET). However, this sensor requires a battery attached to the sensor and is thus not wearable. We overcame this limitation by using PBA hydrogel embedded on a flexible, interdigitated capacitor (IDC) instead of a battery-driven FET without compromising the speed of signal transduction (<i>i.e.,</i> < 5 minutes). Here, we present a battery-free flexible glucose sensor that combines phenylboronic acid hydrogel with an inkjet-printed IDC. We achieved a 5-minute response to an increased glucose level (from 0 mg/dL to 216 mg/dL) by using the IDC to detect the dielectric transition inside a 200-µm-thick layer of phenylboronic acid hydrogel. To demonstrate battery-free sensing, the sensing data are transferred to a vector network analyzer using inductive coupling. When the glucose level increases, the peak of the transferred signal, namely the resonant frequency, shifts lower by about 3% under an in-vitro setting and about 60% lower under an ex-vivo setting within 5 minutes. The proposed design experimentally shows an increase in the response speed for battery-free glucose sensing and has great potential to extend the range of target biomarkers by replacing glucose-responsive hydrogel with other types of the stimuli-responsive hydrogel. It can extend the lifetime of wearable glucose sensors over 2 weeks, resulting in a significant benefit to health monitoring for the longer term and early prediction of risk factors associated with diabetes.