Search for Magneto-Sensing Fluorophores

Abstract

Magnetic nanoparticles have shown its potential contributions in the area of medical application such as MRI contrast agent, for cancer therapy and for targeted drug delivery system. Hypothetical studies have also shown the existence of magnetite nanoparticles and their utilization among animal. Magnetic field imaging for micro and nano size particles and structures has been needed. Among various magnetic field imaging methods, fluorescence microscopy has been employed to measure the magnetic field strength with a magneto-sensing fluorophore as an indicator. One-photon fluorescence microscopy provided a two-dimensional wide-field image of magnetic field and two photon-induced fluorescence microscopy provided three-dimensional imaging for peripheral magnetic field of iron structure. In earlier works, phen-12-O-2-DMA which is the magneto-sensing fluorophore for magnetic field imaging showed large magnetic field effect but it was photolabile. New magneto-sensing fluorophores which are bright and photostable were demanded. In my work, m-MTDATA:t-Bu-PBD mixture in N,N-dimethylformamide and carbazole:diphenyloxadiazole (DPOz) mixture in dichloromethane and in toluene were tested as new candidates of magneto-sensing fluorophore. These two mixtures did not show their exciplex emission so I proposed using other solvents to change solvent polarity for observing their exciplex emission. In case of phen-12-O-2-DMA, I expected to take advantage of excitation wavelength for magnetic field effect by using three photon-induced fluorescence. In this work, three photon-induced fluorescence of phen-12-O-2-DMA showed that exciplex emission intensity was small. I think that small exciplex emission intensity occurred by a small absorption cross section of three photon-induced fluorescence. Considering that two photon absorption cross section is bigger than three photon absorption cross section and the wavelength range of available laser source is 680-1080 nm, I propose molecules which change electron acceptor to other polyaromatic group to absorb within 340-540 nm wavelength range. I have found that anthracene, tetracene, benzopyrene and perylene could be the new electron acceptor of the two photon-induced magneto-sensing fluorophores.