Integrated Nanoscale Silicon Membranes for Separation, Collection, and Preconcentration of Biomolecules Thomas R. Gaborski Jessica Snyder James L. McGrath University of Rochester, Rochester, NY, USA Funding Support Johnson & Johnson/URMC Discovery Fund Electrical and Computer Engineering Biomedical Engineering Christopher C. Striemer David Z. Fang Philippe M. Fauchet

Pnc-Si Membranes Ultrathin: 3 nm - 25 nm thickness Porous nanocrystalline Si: thickness = 15 nm minimal surface area – low loss Nanopores: <5 nm to 50 nm diameter Low complexity fabrication: Si integration Stable: temperature / pressure Known/controllable pore size distribution 1 thickness transport rate 

Membrane fabrication – part I

Pore formation Form spontaneously during crystallization phase change volume contraction dynamic strain during anneal Critical process variables anneal temperature film thickness deposition conditions Novel result – not previously reported

Pore size control Pore morphology - strong function of RTP temperature. Increasing temperature: larger pores higher porosity cutoff

Membrane fabrication – part II

Anisotropic EDP etching (111) planes form etch-stops – well defined edges/corners Very slow SiO 2 etch rate – enables membrane formation (111)

Pnc-Si membranes Buffered oxide etch – complementary high-contrast etch pnc-Si/SiO 2 sandwich 7 nm pnc-Si

Membrane stability 15 PSI 9 PSI 6 PSI 3 PSI 0 PSI 12 PSI Elastic deformation without rupture 200  m 15 nm thickness

Molecular separations

Molecular separation demo Pnc-Si membranes are highly effective in separating small molecules from proteins Time lapse movie – 6.5 minutes

Dye transport rate comparison The diffusion rate of dye through pnc-Si is > 9X that of a commercial dialysis membrane with 50 kDa cutoff porosity = 0.2%

Transport rate comparison Pnc-Si membranes differing by nearly 40X in porosity have dye rates within 10%. Bulk diffusion is rate-limiting. porosity = 0.2% porosity = 7.8%

Summary Ultrathin porous nanocrystalline silicon membranes are a newly discovered material with interesting properties. Pnc-Si membranes are robust and practical for laboratory applications. For dialysis applications, pnc-Si exhibits a 9X increase in molecular transport rate relative to commercial membranes. Contact: Christopher Striemer