This paper describes the introduction of a planar defect layer within inverse opal hydrogels for the elaboration of tunable photonic crystal pH sensors with enhanced optical properties. We demonstrate a mechanically robust, highly sensitive and fast response photonic crystal fabricated by a stepwise strategy combining the Langmuir-Blodgett technique and the photonic crystal template method. The resulting material consists of a three-dimensional, highly-ordered and interconnected macroporous array of poly(methacrylic acid), which is a hydrogel sensitive to pH. The optical properties of these inverse opals were investigated using reflection spectroscopy. The defect layer was shown to enhance both the sensitivity and the response time of the photonic crystal sensing materials.