Peptide functionalized Dynabeads for the magnetic carrier separation of rare-earth fluorescent lamp phosphors

Novel separation processes for end of life fluorescent lamp phosphors could greatly contribute towards a more sustainable rare-earth element market. Furthermore, surface-binding peptides bound to magnetic carriers are a promising biotechnological tool for selective particle separation processes. In this work, we investigate the magnetic carrier separation of the three most common rare-earth fluorescent lamp phosphors, facilitated by Dynabeads functionalized with previously identified selectively surface-binding peptides. We present an active ester-mediated coupling to chemically immobilize the peptides on amine and carboxylic acid coated beads. We report on the impact of the peptide functionalization on the surface properties of the beads, based on zeta potential investigations of variously functionalized beads and a Raman spectroscopic structural study of the investigated peptides. Fluorometrically, we show that the phosphor removal strongly depends on the medium and the surface coating of the beads. Furthermore, the Raman spectroscopic evidence of various simultaneously present disulfide bond conformations indicates an equilibrium of multiple peptide conformations and/or the presence of intermolecular disulfide bonds. Moreover, we found that carboxylic acid coated Dynabeads have a high affinity for the red phosphor Y2O3:Eu3+ and based on the determined isoelectric points we hypothesize that this is driven by electrostatic surface interactions. This work can contribute towards novel rare-earth phosphor separation processes and towards a better understanding of magnetic carrier separation processes facilitated by surface-binding peptides.