# Biodegradable Temperature Sensors with Enhanced Sensitivity Using Bioderived Ionic Liquid with Sodium Ions

## TL;DR

This paper introduces a biodegradable temperature sensor using a sodium-doped ionic liquid to improve sensitivity for healthcare and environmental monitoring.

## Contribution

The novel use of sodium-doped choline lactate ionic liquid significantly enhances the temperature coefficient of resistance in biodegradable sensors.

## Key findings

- The Na-doped ionic gel achieved a thermal index of 7563 K and a TCR of 8.4%/K.
- The sensor degraded in phosphate-buffered solution over 48 days, leaving only the encapsulation layer.
- Enhanced intermolecular interactions from Na doping improve sensor sensitivity.

## Abstract

Gels promise the
development of flexible sensors for electronic
and ionic skins owing to their high affinity for human skin, making
them ideal for biomedical monitoring. Bioderived ionic liquids and
their gels possess favorable physical and electrochemical characteristics,
including extremely low vapor pressure, high ionic conductivity, and
biodegradability, which suit applications of transient electronics
requiring the autonomous decomposition of materials. However, their
low temperature coefficient of resistance (TCR) may hinder the use
of bioderived ionic liquids in wearable devices, implants, and environmental
sensing. To address this issue, we doped sodium (Na) ions into the
bioderived ionic liquid choline lactate to enhance its TCR for biodegradable
temperature sensors. The Na ions improve the coupling of choline and
lactate, resulting in a Na-doped ionic liquid with a high TCR, which
is attributed to enhanced intermolecular interactions. The ionic gel,
composed of the Na-doped ionic liquid and poly­(vinyl alcohol), demonstrated
a high thermal index of 7563 K, an activation energy of 1303 meV,
and a TCR of 8.4%/K. The temperature sensor degraded in phosphate-buffered
solution over 48 days, leaving the encapsulation layer. This study
provides insight into enhancing the sensitivity of temperature sensors
with ionic liquids for healthcare, wearable, and environmental applications.