Directly writing flexible temperature sensor with graphene nanoribbons for disposable healthcare devices

Abstract

Disposable temperature sensors have great advantages in public health security and infectious disease control. However, complicated fabrication processes and poor performances persistently restrict their practical applications. In this paper, a flexible temperature sensor is firstly developed by directly writing or mask spraying commonly-used paper with a highly thermo-sensitive graphene nanoribbon (GNR) ink. The inexpensive, green materials and process endow the GNR sensors with the properties of being low cost, degradable and pollution free. The band gap and the local traps of GNRs, caused by the nanoscale effect and oxygen doping, make the sensor highly thermo-sensitive. The sensor also shows fast response, precise resolution and good bendable properties. As demonstrated, the sensor achieves monitoring of respiratory rate, measurement of body temperature, identification of human touch and constituting a 5 × 5 array for temperature mapping. These results demonstrate that the GNRs sensor is highly promising as an economical disposable device for personal healthcare and disease monitoring.

Fig. 1. (a) Schematic diagrams showing fabrication process of the paper-based GNRs sensors. (b) Demonstration photographs of the GNRs sensors adhering to human body and an artificial finger.

Fig. 2. SEM images of (a) MWCNTs and (e) GNRs. High resolution TEM images of (b) MWCNTs and (f) GNRs. X-ray diffraction patterns of (c) MWCNTs and (g) GNRs. Raman spectra of (d) MWCNTs and (h) GNRs.

Fig. 3. XPS spectra of MWCNTs and GNRs: (a) full spectra, (b) fine spectra of carbon. (c) Plots of (αhν)^1/2 against the photon energy in UV-vis absorption spectrum of GNRs. (d) Mechanism schematic diagram demonstrating thermal response of GNRs.

Fig. 4. (a) Step-like curve with the variation of temperature of the GNRs sensor. The right y-coordinate is corresponding temperature of normalized current change. (b) I–V curves of the sensor from 30–80 °C. (c) Plot of normalized current change versus temperature. (d) showing linear relationship between ln(I) and 1000/T.

Fig. 5. (a) Response and recovery time of the GNRs sensor. (b) Step-like curve showing precise temperature resolution and high signal-to-noise ratio of the GNRs sensor. (c) Cyclic curves of the GNRs sensor in temperature range of 30–60 °C showing its operational stability. (d) Sensing performance of the GNRs sensor after manifold bending cycles at curvature radius of 1 cm.

Fig. 6. (a) GNRs sensor was attached below the nose to monitor human respiratory rate in calm state through sensing temperature difference of breathing gas. (b) Measurement of human body temperature by the GNRs sensor adhered to the forehead. The GNRs sensor directly attached on the artificial hand for (c) sensing waters with different temperatures and (d) identifying human touch. (e) Photo of the GNRs sensor array covered a part by a hot plate. (f) Temperature distributions measured by the GNRs sensor array.