Enzymatic activity of individual bioelectrocatalytic viral nanoparticles: dependence of catalysis on the viral scaffold and its length†
The enzymatic activity of tobacco mosaic virus (TMV) nanorod particles decorated with an integrated electro-catalytic system, comprising the quinoprotein glucose-dehydrogenase (PQQ-GDH) enzyme and ferrocenylated PEG chains as redox mediators, is probed at the individual virion scale by atomic force microscopy-scanning electrochemical atomic force microscopy (AFM-SECM). A marked dependence of the catalytic activity on the particle length is observed. This finding can be explained by electron propagation along the viral backbone, resulting from electron exchange between ferrocene moieties, coupled with enzymatic catalysis. Thus, the use of a simple 1D diffusion/reaction model allows the determination of the kinetic parameters of the virus-supported enzyme. Comparative analysis of the catalytic behavior of the Fc-PEG/PQQ-GDH system assembled on two differing viral scaffolds, TMV (this work) and bacteriophage-fd (previous work), reveals two distinct kinetic effects of scaffolding: An enhancement of catalysis that does not depend on the virus type and a modulation of substrate inhibition that depends on the virus type. AFM-SECM detection of the enzymatic activity of a few tens of PQQ-GDH molecules, decorating a 40 nm-long viral domain, is also demonstrated, a record in terms of the lowest number of enzyme molecules interrogated by an electrochemical imaging technique.