Single molecule and single quantum dot photodynamics by polarization-rotating modulation microscopy

We present our recent study of polarization modulating fluorescence imaging microscopy on single CdSe colloidal quantum dots (QDs) and quantum rods (QRs) adsorbed on silica glass substrates at room temperatures. Simple optical setup is introduced to provide detection of emission profiles projected on to the sample plane as well as detection of rotating excitation polarization effect. While most studies so far in structural changes in biological or amorphous systems rely on extrinsic fluorophores with linear transition dipoles, those with twofold degenerate dipoles are noteworthy due to the intrinsic advantage for 3D orientation information. Performance of modulations is also evaluated in combination with tetramethylrodamine moieties as typical linear emitters. CdSe QDs with aspect ratio of 1.3 actually reveal plane-polarized emission at room temperature and, based on maximum-likelihood analysis, are exceptionally highly oriented on silica glass substrates.