Bio-Adsorptive Recovery of Silica Nanoparticles Using Supercharged Green Fluorescent Proteins

Silica nanoparticles (SiNPs) produced during semiconductor manufacturing possess dimensions in the nanometer range with a high net negative surface charge, imparting them with exceptional colloidal stability. These, when released into the environment, persist for extended periods, leading to ecological and health risks. Although conventional treatment strategies such as coagulation-flocculation and membrane-based separations are effective, they depend on nonbenign chemical additives and are prone to fouling, respectively. Motivated by this, we introduce a bioadsorptive recovery strategy that exploits recombinantly expressed supercharged green fluorescent proteins (scGFPs), which act as an adsorbent to selectively capture SiNPs (adsorbate) through tunable electrostatic interactions under aqueous conditions. A panel of scGFP was systematically evaluated to validate electrostatics-driven adsorption onto silica nanoparticles. The highly charged protein variants act as multivalent linkers, simultaneously binding multiple silica nanoparticles and thereby inducing nanoparticle-nanoparticle bridging and aggregation. This was monitored through the intrinsic fluorescence of scGFP and a complementary colorimetric silicate ion assay. The critical role of electrostatics was highlighted through molecular dynamics and metadynamics simulations. The applicability of these proteins was demonstrated through single-batch adsorption with a reuse capacity of up to three times. Additionally, to translate this interaction into a solid-phase recovery system, silica microparticles were sequentially coated with scGFP and assessed for their ability to adsorb SiNPs in a simple single-pass column adsorption. Together, these findings establish a tunable, charge-driven, and fully aqueous protein-based platform for SiNP recovery, offering a promising alternative to conventional separation methods used in semiconductor wastewater treatment.