Single-molecule optical detections of carboxytetramethylrhodamine connected by alkyl chains on silica glass substrates

To optimize far-field detection optics as well as to extend fundamental skills related to molecular manipulation, samples for single molecule fluorescence detection are fabricated by chemically immobilizing rhodamine-6G derivative molecules on a silica glass surface. While the dye molecules are bleached out within several 10s to 100s of seconds in air as usual, the sample as well as far-field detection system works efficiently. The histogram of the integrated counts of the individual fluorescent spots in the observed images indicates that most of the spots observed involve single chromophores for each spot. The histogram also indicates that there exist two kinds of distinctive molecular sites in the immobilized samples, whereas only single site is detected in the rhodamine-6G spin-coated samples. We consider so far that the existence of the two sites may correspond to the local molecular configurations caused by the mixture of two types of isomers in the cross-linked chromophores. Observation of blinking profiles is also described.