pH-responsive polyaniline/polyethylene glycol composite arrays for colorimetric sensor application

Polyanilines are conjugated polymers that exhibit dynamic optical and electrical properties upon pH change. In this study, we constructed two different types of polyaniline/polyethylene glycol (PANI/PEG) composite arrays via simple PEG photolithography: (1) positional PANI/PEG array films and (2) non-positional PANI/PEG suspension arrays. The patterning process based on PEG photolithography allows the precise control of shapes and sizes in PANI/PEG composite arrays. Both positional/non-positional PANI/PEG composite arrays demonstrated reversible optical property changes accompanied by excellent colorimetric changes from deep blue to blue, cyan, and green in response to pH changes. Specifically, we used PANI/PEG composite arrays as a pH sensitive indicator to detect bacterial growth because of their colorimetric responses to pH changes. The PANI/PEG composite arrays exhibited distinct changes in the two absorption bands at 420 and 600 nm with a color change when exposed directly to Escherichia coli (E. coli) growth medium. We envision that the novel approach described here could provide a new insight into the design and construction of versatile optical, electrochemical, electronic sensors based on functional conjugated polymer/hydrogel composite materials.