Fabrication of a κ-carrageenan-based electroactive cytochrome c multilayer thin film by an electrostatic layer-by-layer assembly.

The aim of this study was to demonstrate the usability of κ-carrageenan in the accumulation of a layer by layer protein film on a gold electrode. It is known that in terms of bioelectronics there are significant advantages to functional biofilms which are formed as a result of the interaction between different layer biomolecules. In this study, κ-carrageenan (κ-CG) was employed as the polyanion for the construction of the electroactive multilayer protein thin films. The protein layers were built up by successive adsorption of κ-CG and cytochrome c (cyt c) based on the opposite charge on a modified gold electrode with a cyt c monolayer. Electron transport between the cyt c layers was established without the hindrance of κ-CG. The highest electron transfer capability was achieved when the pH value of the solutions was 5, and the κ-CG concentration was a 0.25 mg mL-1. Whilst the amount of cyt c on the electrode surface was 10.87 pmol cm-2 in the monolayer structure, the amount was calculated to be 158.01 pmol cm-2 with the formation of 8-bilayer [κ-CG/cyt c] structures over the cyt c monolayer. The multilayer protein film was also characterized using electrochemical impedance spectroscopy, ellipsometry, and UV-visible absorption spectroscopy. This novel biofilm allows a high amount of electron transfer and can be used as an immobilization platform for biosensor applications.