Reversed weighing for non-invasive evaluation of ripeness of tomato fruits with self-powered tactile sensors

Non-invasive evaluation of the ripeness of tomato fruits could significantly improve their production, marketing and nutrition considering their huge yields. Herein a strategy of reversed weighing was developed for quantitative and non-invasive assessment of their ripeness at different stages using self-powered tactile sensors prepared with two types of (polyvinyl alcohol (PVA)/barium titanate nanoparticles (BTO) and PVA/HOCH₂(CF₂)₃CH₂OH (2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD) piezoelectric hydrogels (PEHs). PEHs were optimized based on their physical characteristics and piezoelectric responses generated from single PEHs tentacle under a static pressure of 1 N. Three PEHs tentacles with a static pressure of 1 N were applied for evaluation of tomato fruits ripeness to avoid any possible damages. Experimental results demonstrated that piezoelectric responses of PEHs gradually decreased with the increased storage days of tomato fruits, suggesting the capability of the self-powered tactile sensors for differentiation of the ripening stages. Furthermore, the piezoelectric signals of the sensors were correlated with the inside pH values and the gray values of tomato fruits at different ripening stages. The inside pH values and the gray values increased with the decreased of the piezoelectric signals when the tomato fruits transferred from immature to mature. This strategy could be potentially extended for construction of robotic hands for non-invasive and quantitative evaluation of the ripeness of fruits. This study suggested the potential applications of PEHs based self-powered tactile sensors for agricultural intelligence in precision agriculture.