Fig. 1. Enzyme immobilization onto the surface of the VFD reactor.

(a) First, the surface of the sample tube is coated with APTES (3-aminopropyl triethoxysilane) to generate a high concentration of surface-bound amines; a simplified depiction of this surface coating is shown here. (b) β-glucosidase is added directly to the APTES-coated sample tube for non-covalent immobilization. (c) After derivatization of the APTES layer with glutaraldehyde, β-glucosidase is attached in this simplified structure of the linker and cross-link. (d) The imineglutaraldehyde is reduced with NaBH₃CN. (e) The immobilization efficiency was tested by VFD processing in the presence of the β-glucosidase substrate, 4-nitrophenyl β-D-glucopyranoside. (f) The sample tube can be regenerated through rapid treatment with a thin film of piranha solution. Some of the reactions in this manuscript were performed in continuous flow, further information on the reactor setup has been previously reported.³⁹