Humidified Microcontact Printing of Proteins: Universal Patterning of Proteins on Both Low and High Energy Surfaces

Microcontact printing (mu CP) of proteins is widely used for biosensors and cell biology but is constrained to printing proteins adsorbed to a low free energy, hydrophobic surface to a high free energy, hydrophilic surface. This strongly limits mu CP as harsh chemical treatments are required to form a high energy surface. Here, we introduce humidified mu CP (H mu CP) of proteins which enables universal printing of protein on any smooth surface. We found that by flowing water in proximity to proteins adsorbed on a hydrophilized stamp, the water vapor diffusing through the stamp enables the printing of proteins on both low and high energy surfaces. Indeed, when proteins are printed using stamps with increasing spacing between water-filled microchannels, only proteins adjacent to the channels are transferred. The vapor transport through the stamp was modeled, and by comparing the humidity profiles with the protein patterns, 88% relative humidity in the stamp was identified as the threshold for H mu CP. The molecular forces occurring between PDMS, peptides, and glass during printing were modeled ab initio to confirm the critical role water plays in the transfer. Using H mu CP, we introduce straightforward protocols to pattern multiple proteins side-by-side down to nanometer resolution without the need for expensive mask aligners, but instead exploiting self-alignment effects derived from the stamp geometry. Finally, we introduce vascularized H mu CP stamps with embedded microchannels that allow printing proteins as arbitrary, large areas patterns with nanometer resolution. This work introduces the general concept of water-assisted mu CP and opens new possibilities for solvent-assisted printing of proteins and of other nanoparticles.