Novel form of photonic crystals for bioimaging contrast enhancement

We report here a diatom frustule-based photonic structure acting as an efficient near infrared contrast agent. The frustule of diatom Pinnularia sp. consists of two valves with same exquisite fine 2D periodicity at the submicron scale, similar to a 2D photonic crystal. Decoration of diatom frustules with higher refractive index materials leads to a refractive indices contrast increase between the array of pores and the frame. Our calculation and measurements show that magnetite nanoparticle-decorated diatom frustules have a wide pseudo photonic band gap in near infrared range, resulting in a strong near infrared reflection. It allows the magnetite nanoparticle-decorated diatom frustules to be imaged with a high optical coherence tomography contrast.