Germanium as a scalable sacrificial layer for nanoscale protein patterning.

We demonstrate the use of germanium (Ge) films as water-soluble features that allow the patterning of proteins onto surfaces with commonly used organic solvents. This technique is scalable for manufacturing and is compatible with nano- and microfabrication processes, including standard lithography. We use Ge as a sacrificial layer to mask and protect areas of the substrate during surface functionalization. Since Ge dissolves in 0.35% hydrogen peroxide (H2O2) in water but not in organic solvents, Ge can be removed after patterning without significantly affecting protein activities. In this paper, we present examples of protein patterning with two different techniques. We show that 50 nm thick Ge layers can be completely removed in 10 min without residues and, importantly, nanoscale resolution and misalignment can be achieved with conventional photolithography equipment. Both biotin and streptavidin maintain ~80% and >50% activity after 10 min and 360 min incubation in 0.35% H2O2, respectively. Lastly, the process can be used to functionalize sidewalls with proteins, a capability of recent interest for cell-cell adhesion studies.