Highly Sensitive Metal Ion Detection Using Tetraphenylporphyrin-Functionalized Graphene Field-Effect Transistors

Owing to the rapid advancements in smart agriculture, the importance of developing sensors for agricultural digitization is increasing. Heavy metal ions, as detrimental variables, pose a major hurdle in agricultural development, food safety, and human health. Herein, electrolyte-gated tetraphenylporphyrin (TPP)-functionalized graphene field-effect transistors (GFETs), i.e., G-TPP FETs, were developed for the sensitive and reliable 25 °C detection of heavy metal ions at the solid–liquid interface of the G-TPP FETs. The central nitrogen atoms of the porphyrin skeleton act as ideal pockets for metal ion incorporation, endowing the G-TPP FETs with high sensitivity toward Cd2+, Cu2+, Fe3+, Mn2+, and Ni2+. The G-TPP FET sensitivity toward Fe3+ is more than double that of nonfunctionalized GFETs. Furthermore, the G-TPP FETs exhibit better reproducibility (relative standard deviation = 8.5) and a wide sensing range (1 nM–1 mM) for Cd2+. The sensitivity of the G-TPP FETs to the changes in the gate potential at the Dirac point in various heavy metal ionic solutions was systematically investigated. Moreover, the charge transfer between graphene and TPP or metalated-TPP was validated based on density functional theory simulations. Thus, this study provides a foundation for the development of next-generation agricultural sensors toward enhanced tracing systems of agricultural products to ensure better health and safety.