pH-sensitive holograms for continuous monitoring in plasma

Conventional electrochemical methods of determining the pH of body fluids have drawbacks. Newer optical methods offer the promise of miniaturisation and continuous in vivo measurements without drift. This report examines the ability of a holographic sensor based on a thin-film, biocompatible hydrogel (approximately 10 μm) of poly(2-hydroxyethyl methacrylate) and ionisable 2-(dimethylaminoethyl) methacrylate to accurately measure the pH of blood plasma ex vivo. It is found that the sensors behave in a fully reversible manner. After an initial calibration with buffers, they can measure pH over extended periods (more than 40 h). Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.