Temperature and pH sensor based on functionalized magnetic nanofluid

Abstract

Here we report a new simple colorimetric sensing platform based on magnetic nanofluid for rapid detection of temperature and pH. The new sensing platform relies on changes in the conformation of the adsorbed macromolecular functional groups and the consequent changes in the optical properties of magnetically polarizable nanoemulsion. By biasing the sensor with a weak magnetic field, nanoemulsion self assembled to form one dimensional grating with a fixed interdroplet spacing, which is sensitive to temperature or pH, depending on the functional groups attached. The sensing action is based on the subtle changes in the interdroplet spacing that is manifested from the reflected Bragg peak shift in the visible wavelength regime. Owing to temperature and pH response of poly(vinyl alcohol – vinyl acetate) (PVA-vac) and polyacrylic acid (PAA) respectively, they are used as functional moieties. The sensor showed a linear temperature and pH response between 5 and 90 °C and 3–11.5, respectively. These results suggest that a simple coupling of magnetic nanoemulsion with suitable adsorbed moieties offers a rapid sensing platform for temperature and pH. Further, by suitably changing the functional moieties, this approach can be extended to a variety of sensing applications, including visual detection.