Expanding the circularity of plastic and biochar materials by developing alternative low environmental footprint sensors

Flexible screen-printing technology combined with the use of a nano/material coating for improving electrode functionalities boosted the manufacturing of highly sensitive electrochemical sensors addressing the need for fast and easy-to-handle tests in different application fields. However, due to the large-scale production and disposable and single-use nature of these devices, their environmental footprint should be taken into careful consideration. Herein, the innovative reuse of post-consumer polyethene terephthalate (PET) plastics as an alternative substrate coupled with biochar as an environmentally friendly and cost-effective modifier is described as a sustainable alternative for the production of robust electrochemical sensors. The good printability of reused plastics with graphite inks despite the chemical heterogeneity, different crystallinity, and surface roughness was demonstrated using atomic force microscopy and attenuated total reflection Fourier transform infrared spectroscopy. Functionalization with brewers’ spent grain biochar enabled the fabrication of highly performing electrochemical sensors for nitrite detection in water having a limit of detection and a limit of quantification of 3.3 nM and 10.3 nM, respectively, with a linear range spanning from 0.01 to 500 μM, and good reproducibility (RSD% 8%). The innovative intervention of the biochar-multilayer system markedly enhanced the electron transfer process at the electrode interface while simultaneously serving as an absorptive material for the investigated analyte. This work lays a foundation for repurposing end-of-life plastics for the electronics industry and presents a customizable reuse strategy aimed to keep the value of plastics in the economy and reduce waste and leakage into the natural environment.