Conjugated Polymer Dots for Multiphoton Fluorescence Imaging

摘要

Multiphoton fluorescence microcopy has recently emerged as a powerful technique for three-dimensional imaging in biological systems. The nonlinear dependence of excitation probability on light intensity results in a highly localized excitation and improved spatial resolution. The small effective excitation volume also reduces background signal due to autofluorescence and the fluorescence of dye molecules outside of the laser focal volume, while the ability to employ near-IR wavelengths for excitation can reduce photo-damage to the sample as well as facilitate imaging of biological specimens due to the near-transparency of many tissues in this spectral range. The widespread adoption of multiphoton fluorescence imaging and microscopy has been hindered by the bulky and expensive pulsed laser sources typically required for excitation due to the relatively low multiphoton excitation cross sections of available dyes. Interest in the development of brighter probes has led to the design and synthesis of dyes with two-photon action cross sections larger than 1000 Goppert-Mayer units (GM). Gold nanorods have also been demonstrated as contrast agent for in vitro and in vivo two-photon luminescence imaging, and the two-photon action cross sections were determined to be ～2000 GM. Colloidal CdSe quantum dots appear to be very promising probes for two-photon microscopy due to their excellent photostability and large two-photon action cross sections (from 2000 to 47 000 GM), although single particle blinking and a significant fraction of "dark" nanoparticles are drawbacks for some applications.