A two-photon fluorescent probe for viscosity imaging in vivo

Area of Science:

• Biomedical Engineering
• Chemical Biology
• Molecular Imaging

Background:

• Viscosity is a critical biophysical parameter influencing cellular functions.
• Developing sensitive probes for intracellular viscosity measurement remains a challenge.
• Two-photon microscopy offers deep tissue penetration and reduced phototoxicity.

Purpose of the Study:

• To develop and characterize a novel two-photon fluorescent probe (MCN) for viscosity imaging.
• To evaluate the probe's performance in various biological systems, including cells and tissues.
• To demonstrate the application of MCN for real-time monitoring of cellular events and deep tissue imaging.

Main Methods:

• Synthesis and characterization of the MCN fluorescent probe based on a 6-substituted quinoline framework.
• Testing the probe's fluorescence response in a glycerol-water viscosity system.
• Performing two-photon fluorescence lifetime imaging (FLIM) in living HeLa cells and zebrafish.
• Evaluating probe performance in living tissue slices for deep tissue imaging.

Main Results:

• MCN exhibited an excellent "off-on" fluorescence response with a ~90-fold enhancement upon increasing viscosity.
• The probe demonstrated high sensitivity to viscosity (R² = 0.98) and low cytotoxicity.
• Intracellular viscosity in HeLa cell cytosol was measured at 73.45 ± 21.55 cP using FLIM.
• MCN enabled deep tissue imaging (∼130 μM) and in vivo imaging in zebrafish.

Conclusions:

• MCN is a highly sensitive and effective two-photon fluorescent probe for viscosity imaging.
• The probe facilitates real-time monitoring of micro-viscosity changes in living cells, including during apoptosis.
• MCN shows significant potential for deep tissue and in vivo viscosity imaging applications.