This image shows live cells incubated with the polymer nanoparticles. The green color is the fluorescence coming from the molecules trapped within the nanoparticles. Credit: Francisco Raymo / University of Miami

University
of Miami scientists have developed a way to switch fluorescent
molecules on and off within aqueous environments, by strategically
trapping the molecules inside water-soluble particles and controlling
them with ultraviolet light. The new system can be used to develop
better fluorescent probes for biomedical research.

Previous
studies have used water-soluble particles to bring organic molecules
into water. What is novel about this system is the use of a
photoswitching mechanism in combination with these particles.

The
findings published online by Chemistry-A European Journal, describe the
creation of a fluorescent photoswitchable system that is more efficient
than current technologies, says Francisco Raymo, professor of chemistry
at the UM College of Arts and Sciences and principal investigator of
this study.

“Finding
a way to switch fluorescence inside cells is one of the main challenges
in the development of fluorescent probes for bioimaging applications,”
Raymo says. “Our fluorescent switches can be operated in water
efficiently, offering the opportunity to image biological samples with
resolution at the nanometer level.”

Fluorescent
molecules are not water soluble; therefore Raymo and his team created
their system by embedding fluorescent molecules in synthetic
water-soluble nanoparticles called polymers that serve as transport
vehicles into living cells. Once inside the cell, the fluorescence of
the molecules trapped within the nanoparticles can be turned on and off
under optical control.

“The
polymers can preserve the properties of the fluorescent molecules and
at the same time assist the transfer of the molecules into water,” Raymo
says. “It’s a bit like having a fish in a bowl, so the fish can carry
on with its activities in the bowl and the whole bowl can be transferred
into a different environment.”

The
new system is faster and more stable than current methods. The
fluorescent molecules glow when exposed simultaneously to ultraviolet
and visible light and revert back to their original non-luminous state
in less than 10 microseconds after the ultraviolet light is removed.

By
using engineered synthetic molecules, the new system is able to
overcome the natural wear down process that organic molecules are
subject to when exposed to ultraviolet light.

“The
system can be switched back and forth between the fluorescent and
non-fluorescent states for hundreds of cycles, without sign of
degradation,” Raymo says.

The
surface of the system can be customize to help it attach to specific
molecules of interests, thus allowing researchers to visualize
structures and activity within cells, in real time, with a resolution
that would otherwise be impossible to achieve.

Raymo and his team will continue improving the properties of the molecules for future biomedical applications.

Fast Fluorescence Switching within Hydrophilic Supramolecular Assemblies

Source: University of Miami