320-fold luminescence enhancement of [Ru(dpp)3]Cl2 dispersed on PMMA opal photonic crystals and highly improved oxygen sensing performance

Abstract

Ru complexes ([Ru(dpp)3]Cl2) were spin coated on poly(methyl methacrylate) (PMMA) opal photonic crystals (PhCs), and a ∼320-fold luminescence enhancement was observed compared to that on glass, which is the largest luminescence enhancement of dye molecules by the modulation of three-dimensional (3D) PhCs reported until now. The enhancement mechanism was carefully examined and it was shown that the luminescence of [Ru(dpp)3]Cl2 depended on the molecule concentration and temperature. It can be concluded that the suppressed non-radiative relaxation among the molecules and the field enhancement both contribute significantly to the luminescence enhancement. The PMMA PhC/Ru complex composites were then tested for their intracellular oxygen sensing and cell imaging properties; these composites effectively improved the limit of detection (LOD) and the brightness of the cell images. The performance of an optical oxygen sensor using a luminescent dye is dramatically improved by employing a textured polymer substrate. Pingwei Zhou and co-workers from Jilin University in China spin coated an ethanol solution containing the dye Ru(dpp)3Cl2 onto two different substrates: plain glass and a photonic crystal made from an array of tiny polymer spheres. They found that, on optical excitation, the dye on the polymer substrate exhibited up to 320 times stronger light emission than the dye on the glass substrate. They attributed this enhanced emission to suppression of non-radiative relaxation and field-enhancement effects from the polymer photonic crystal. The brighter emission results in an enhanced detection limit for intracellular oxygen sensing when using the dye as an oxygen probe.