Bright Near-Infrared p-Conjugated Oligomer Nanoparticles for Deep-Brain Three-Photon Microscopy Excited at the 1700 nm Window in Vivo

The development of three-photon fluorophores with 1700 nm excitation is pressingly desirable for in vivo imaging of tissue resided deep inside the brain. Herein, we report a designed and synthesized fluorescent molecule (OFET) for in vivo mouse brain imaging with three-photon microscopy at a record imaging depth. The OFET molecule has a relatively high fluorescence brightness and has a near-infrared (NIR) maximum emission at 820 nm after integrating as water dispersible nanoparticles (OEFT NPs). Under 1720 nm excitation, OFET NPs show a large three-photon action crosssection of 1.06 x 10(-82) cm(6) s(2)/photon(2), which is more than twice that of the commonly used sulforhodamine 101 (SR101) dye. Benefiting from the high tissue penetration depths for both the long excitation in the second NIR window of 1720 nm and the emission wavelength in the first NIR window of 820 nm, a high brightness, and a large action cross-section of three-photon, OFET NPs have good deep-brain imaging performance. Brain vasculatures of a mouse located at a depth of 1696 mu m can be clearly resolved in vivo. With no observable cytotoxicity even in a high concentration, the present OFET NPs suggest that fluorescent it-conjugated oligomers are of great potential in high-resolution 3PM imaging of in vivo deep-tissue.

Automated summary

Researchers have developed a designed and synthesized fluorescent molecule (OFET) for in vivo mouse brain imaging using three-photon microscopy. The OFET molecule, integrated as water dispersible nanoparticles (OFET NPs), has high fluorescence brightness and maximum emission at 820 nm. Under 1720 nm excitation, OFET NPs exhibit a large three-photon action crosssection, more than twice that of commonly used SR101 dye. With the advantages of long excitation and emission wavelength, and high tissue penetration depth, OFET NPs show good deep-brain imaging performance.