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. Author manuscript; available in PMC: 2009 Oct 1.

Published in final edited form as: Nat Nanotechnol. 2009 Feb 22;4(4):255–258. doi: 10.1038/nnano.2009.11

Scheme 1 — Active protease (pepsin, blue) is absorbed into the first layer. The assay is then carried out by addition of substrate (α-casein, red). The pores of the second layer are too small to admit the protease or its substrate. However, digestion of the substrate by pepsin produces fragments (green) sufficiently small to infiltrate the 2nd layer. The entire structure is probed by optical reflectivity, allowing detection of the enzymatic reaction in real-time.

Scheme 1 — Active protease (pepsin, blue) is absorbed into the first layer. The assay is then carried out by addition of substrate (α-casein, red). The pores of the second layer are too small to admit the protease or its substrate. However, digestion of the substrate by pepsin produces fragments (green) sufficiently small to infiltrate the 2nd layer. The entire structure is probed by optical reflectivity, allowing detection of the enzymatic reaction in real-time.