Activatable Dendritic 19F Probes for Enzyme Detection

Abstract

We describe a novel activatable probe for fluorine-19 NMR based on self-assembling amphiphilic dendrons. The dendron probe has been designed to be spectroscopically silent due to the formation of large aggregates. Upon exposure to the specific target enzyme, the aggregates disassemble to give rise to a sharp ¹⁹F NMR signal. The probe is capable of detecting enzyme concentrations in the low nanomolar range. Response time of the probe was found to be affected by the hydrophilic-lipophilic balance of dendrons. Understanding the structural factors that underlie this design principle provides the pathway for using this strategy for a broad range of enzyme-based imaging.

Figure 1

Schematic representation of assemblies formed from enzyme-cleavable dendrons and the release of the ¹⁹F reporter upon enzyme exposure.

Figure 2

(a) Chemical structure of enzyme-cleavable dendron 1. (b) ¹⁹F NMR spectra of 1 (25 μM) in the presence or absence of PLE (1 μM) (TFA as an internal standard for chemical shift). (c) Size evolution of 1 (25 μM) in the presence of PLE (1 μM) using DLS.

Chart 1. Structures of ¹⁹F-Containing Amphiphilic Dendrons

Figure 3

(a) Temporal evolution of ¹⁹F NMR intensity (−63.7 ppm) of G1 dendrons (25 μM) treated with PLE (1 μM) over the first 8 h. (b) Dependence of the ¹⁹F NMR intensity (−63.7 ppm) on PLE concentration for dendron 1 (25 μM) (measurements taken after 24 h PLE incubation). All experiments were performed in 25 mM Tris buffer (pH 7.4, 0.2 mM TFA as an internal standard for peak intensity and chemical shift, 10% D₂O (v/v)) at 25 °C.