Recently, we described a series of novel porphyrin-impregnated hydrogels capable of producing microbicidal singlet oxygen (O-1(2)) on photoactivation. Indirect assessment of the efficacy of O-1(2) production from such hydrogels has been previously described using microbiological techniques, but here we report a novel, direct method of quantification. Anthracene-9,10-dipropionic acid (ADPA) is known to irreversibly form an endoperoxide on reaction with O-1(2), causing photobleaching of its absorbance band at approximately 378 nm. Here, the reaction of this probe is exploited in a novel way to provide a simple, inexpensive, and convenient measurement of O-1(2) generation from the surface of porphyrin-incorporated photosensitising hydrogels, with the ability to account for effects due to hydrogel porosity. Ingress of the probe into the materials was observed, with rates of up to 3.83 x 10(3) s(-1). This varied by up to 200-fold with material composition and surface modification. Rates of O-1(2) generation in these porphyrin-incorporated hydrogels, after compensating for ADPA ingress, ranged from 1.86 x 10(3) to 5.86 x 10(3) s(-1). This work demonstrates a simple and straightforward method for direct O-1(2) quantification from porous materials, with general utility. (C) 2014 Elsevier B.V. All rights reserved.