A flexible multifunctional sensor based on in situ reduction of Ag nanoparticles by yam polysaccharides

Developing flexible multifunctional sensors that combine humidity, temperature, and strain sensing properties is a challenge. In this paper, PVA/YPs/H₃PO₄/AgNPs (PYHA) flexible composite films loaded with Ag nanoparticles (AgNPs) were synthesized through in situ reduction and solution casting using polyvinyl alcohol (PVA), yam polysaccharide (YPs), phosphoric acid (H₃PO₄), and silver nitrate (AgNO₃) as raw materials, which exhibited sensitivity to humidity, temperature, and strain. The prepared PYHA humidity sensor was capable of generating stable electrical signals through adsorption and desorption over the relative humidity (RH) range of 35-95 %. Furthermore, the humidity sensor displayed minimal hysteresis (2.17 % RH) and excellent linearity (R² = 0.973) during respiratory rate monitoring in different body states. As a temperature sensor, the PYHA sensor was capable of sensing human body temperature, exhibiting strong temperature sensitivity (TCR = -1.058 % °C^-1) and maintaining excellent linearity (R² = 0.994) ranging from 35 to 95 °C in temperature. Moreover, the PYHA flexible strain sensor boasted an extensive strain detection range (1-320 %) and swift response/reply time (0.8/1.1 s), and detected physiological signals due to large movements of body joints and weak changes in facial expressions. Therefore, the designed PYHA multifunctional sensor has a promising use in flexible wearable.