Integrating electrochemical sensors in circular economy: biochar-film sensors based on paper industry waste for agri-food by-product valorization
Selene Fiori, Annalisa Scroccarello, Flavio Della Pelle, Michele Del Carlo, Enrico Cozzoni, Darío Compagnone
Abstract
Sustainable nanostructured paper sensors (PS) have been developed to detect bioactive compounds in plant-derived agri-food by-products. These sensors comprise 100% recycled fibers-paper and pulp industry-derived biochar and are produced using accessible, cost-effective technologies. In detail, black liquor-derived biochar (BH) was nano-dispersed in water using an ultrasound-assisted liquid phase exfoliation-like approach, avoiding solvents. Self-standing BH-sensing nanofilms were formed directly on cellulosic membranes and integrated into stencil-printed complete electrochemical sensors manufactured on recycled paper. The biochar-based paper sensors (BH-PS) were optimized, characterized, and then employed to analyze bioactive phenols present in agri-food waste and derivatives, including cocoa and coffee husks, exhausted coffee powder, and olive leaves and artichoke production waste-based supplements. BH-PS demonstrated robust performance, yielding dose-response curves for representative bio-compounds such as caffeic acid, catechin, chlorogenic acid, and oleuropein. These showed excellent linearities (R² ≥ 0.9946) and detection limits ranging from 0.03 to 0.6 µM. The sensors were successfully used to quantify biomolecules in agri-food wastes and derivatives, with results comparable to conventional photometric assays (r ≥ 0.99; relative error vs. AuNPs assay: -3% to +14%). The method produced quantitative and reproducible recoveries for all samples (97–114%; RSD ≤ 13%, n=3). Finally, the superior sustainability of the BH-PS was validated using the White Analytical Chemistry framework, achieving a significantly higher score (94%) compared to traditional colorimetric and chromatographic methods (60–80%). This work demonstrates a circular economy model, utilizing plant-derived waste exclusively to fabricate integrated paper sensors, that were then applied to determine high-value bioactive compounds in plant-derived agri-food by-products.