Myoglobin-loaded layer-by-layer films containing SiO(2) nanoparticles studied using electrochemistry

In the present work, a new kind of protein-loaded layer-by-layer (LbL) film based on nanoparticles was fabricated on electrodes. First, oppositely charged SiO(2) nanoparticles and poly(diallyldimethylammonium) (PDDA) were alternately adsorbed on solid surfaces, forming {PDDA/SiO(2)}(n) LbL films. In the next step, the films were immersed in myoglobin (Mb) solution at pH 5.0 to load Mb, forming {PDDA/SiO(2)}(n)-Mb films. The loading behavior of {PDDA/SiO(2)}(n) films toward Mb was investigated by monitoring the cyclic voltammetric responses of the Mb heme Fe(III)/Fe(II) redox couple, and comparing them with those of {PDDA/PSS}(n) films, where PSS stands for poly(styrenesulfonate). Scanning electron microscopy (SEM) and electroactive probe tests demonstrated that the porosity of {PDDA/SiO(2)}(n) films assembled with 'hard' and rigid SiO(2) nanoparticles was much better than that of {PDDA/PSS}(n) films fabricated with just 'soft' polyelectrolytes, which led to the better electrochemical and electrocatalytic responses for the {PDDA/SiO(2)}(n)-Mb films. A series of comparative experiments showed that the main driving force for Mb to diffuse into the films was most probably electrostatic interaction between positively charged Mb and negatively charged SiO(2) components of the films, while the major force in stabilizing Mb in the {PDDA/SiO(2)}(n)-Mb films in blank buffers was more likely hydrophobic interaction.