ABSTRACTPeptoids, N‐substituted glycine oligomers, can adopt stable three‐dimensional structures and have found diverse application as peptide surrogates and as nanomaterials. In this report, we have expanded peptoid function to include pH sensing by coupling pH‐induced peptoid conformational changes with fluorescence intensity changes. We report two new peptoids (2 and 3) that comprise carboxylic‐acid functionalized side chains and undergo conformational rearrangement in response to pH. Peptoids 2 and 3 are also labeled at one side‐chain with an environmentally sensitive fluorophore, 4‐N,N‐dimethylamino‐1,8‐naphthalimide (4DMN). The fluorescence intensity of 2 varies 24‐fold over the pH range studied. These spectroscopic properties make 2 a sensitive, biocompatible pH sensor. © 2013 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 380–386, 2013.