As shown in the figure, isolated mSbsC-eGFP forms fluorescent tubular assemblies. Electroless metal plating with 150 mM Pt salt solution resulted in the formation of S-layer assemblies decorated with Pt nanoparticles (Ø > 3 nm) that were closely packed and aggregated into metal clusters. Metallized nanotubes were monitored with a high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). The contact potential differences (CPD) of metallized and unmetallized samples with respect to the silicon surface were determined by Kelvin probe force microscopy (KPFM) measurements.

Metallized and unmetallized S-layer tubes differ in their surface potential, indicating that Pt deposition changes the electrostatic surface characteristics of the protein assemblies. Finally, in situ conductivity measurements were performed with a scanning tunnelling microscopy (STM) holder in a TEM (upper image). While unmetallized S-layer assemblies were not conductive, metallized samples showed linear I–V dependence between –1 and +1 V with a conductivity of ~103 S/m.

Conductive S-layer tubes may be applied in nanobiotechnology. For example, to scale down electronic devices.

The researchers presented their work in the journal Nanotechnology.