Carbon-based nanopigments derived from açaí seed residues with tunable optical properties and biofunctional performance

Bio-based carbon nanomaterials have attracted increasing interest as sustainable alternatives to conventional dyes and pigments due to their tunable optical properties and multifunctionality. In this work, carbon-based nanopigments were synthesized from agro-industrial residues of açaí palm ( Euterpe oleracea ) seeds via a hydrothermal process. The resulting nanomaterials were structurally and optically characterized and evaluated for their functional performance in aqueous media and biological systems. Spectroscopic analyses revealed broad and intense absorption in the ultraviolet–visible region, associated with π–π* and n–π* electronic transitions typical of carbonaceous chromophores, along with excitation-dependent photoluminescence behaviour. Structural characterization indicated nanoscale particles with surface functional groups rich in oxygen- and nitrogen-containing moieties, which contribute to their dispersibility, optical response, and interaction with surrounding media. The nanopigments exhibited high colloidal stability and preserved their optical properties at low concentrations, demonstrating suitability for applications requiring efficient light–matter interaction. In agro-related applications, foliar treatment with the nanopigments at low concentrations (10 mg L -1 ) promoted marked improvements in early plant development, increasing relative growth rate by 24.4% in maize and 164.6% in sorghum, while root volume increased by 23.1 and 59.9%, respectively, compared to untreated controls. These results demonstrate that the optical activity and surface functionality of the carbon nanopigments can be effectively translated into measurable biological responses, highlighting their multifunctional potential across both optically active materials and emerging agricultural technologies. • Carbon nanopigments synthesized from açaí seed residues via a hydrothermal route • Multifunctional nanopigments combine optical properties with biofunctional activity • Relative growth rate increased by up to 165% without phytotoxic effects • Sustainable approach links residue valorization to agronomic performance