Nature Materials 10, 389–397 (2011); published online 17 April 2011; corrected online 10 May 2011.

In the version of this Letter originally published, in Fig. 1 a double bond in the maleimide cycle of the crosslinker molecular structure was missing; the definition of the SP94 peptide in the text should have read H2N-SFSIIHTPILPLGGC-COOH; and in Fig. 6a the lowest value of the right-hand y axis should have read 106. These errors have now been corrected in the HTML and PDF versions.