A Fully Integrated Paper-Based Readout System, Sensor and Battery

Abstract

Chemical analysis of paper-based electronic sensors is frequently interpreted using complex software and electronic displays which compromises the advantages of using paper. The ultimate aim of this PhD project is to develop simple and versatile paper-based readout systems that could directly convert the electrical signal into colour visualisation and later progress towards an integrated sensing device combining a readout system, a sensor and battery. The research starts with developing two semi-quantitative paper-based readout systems that can visually measure a change in resistance of a resistive-based sensor. The readout system exploits the electrochromic concept and also the effect of voltage gradient generation along a low-resistive gold nanoparticle film upon application of voltage. Due to this phenomenon, the electrochromic material changes colour along the gold nanoparticle film where the voltage is at the redox potential of the electrochromic materials. Hence, the resistance of the sensor can be semi-quantified by measuring the length of the transparent film (analog readout) or by counting the number of transparent gold segments (digital readout). The concept of displaying an electrical signal colorimetrically is validated by integrating an improved type of digital readout system, a piezoresistive pressure sensor and battery for developing a lightweight device for measuring bandage compression. A new type of piezoresistive pressure sensor is fabricated using an optimised mixture of irregular-shaped copper particles, polydimethylsiloxane and carbon paste. Through this integration, the pressure applied to the sensor can be visualised by counting the number of transparent gold nanoparticle segments in the readout system. The integration of a piezoresistive pressure sensor and readout system is extended for developing “balance-in-a-box” to determine the weight of a newborn baby. A new concept of tuning the resistive properties of the readout is introduced to change the critical weight value in which the gold segment changes colour. The significance of this work is that various desired reading ranges can be obtained while using the same type of pressure sensor. The last part of the study addresses the adaptability of the readout system for a chemical sensor, in particular a pH potentiometric paper-based sensor. Overall, these integrated sensing devices have paved the way for use in situations where weight is a premium or a simple colour reading will suffice.