Amphiphilic complexes of Ho(iii), Dy(iii), Tb(iii) and Eu(iii) for optical and high field magnetic resonance imaging

Abstract

Lanthanides, holmium(iii), dysprosium(iii), and terbium(iii), were coordinated to an amphiphilic DOTA bis-coumarin derivative and then further assembled with an amphiphilic europium(iii) DTPA bis-coumarin derivative into mono-disperse micelles. The self-assembled micelles were characterized and assessed for their potential as bimodal contrast agents for high field magnetic resonance and optical imaging applications. All micelles showed a high transverse relaxation (r) of 46, 34, and 30 s mM at 500 MHz and 37 °C for Dy(iii), Ho(iii) and Tb(iii), respectively, which is a result of the high magnetic moment of these lanthanides and the long rotational correlation time of the micelles. The quantum yield in aqueous solution ranged from 1.8% for Tb/Eu to 1.4% for Dy/Eu and 1.0% for the Ho/Eu micelles. Multi-photon excited emission spectroscopy has shown that due to the two-photon absorption of the coumarin chromophore the characteristic Eu(iii) emission could be observed upon excitation at 800 nm, demonstrating the usefulness of the system for in vivo fluorescence imaging applications. To the best of our knowledge, this is the first example reporting the potential of a holmium(iii) chelate as a negative MRI contrast agent.

High‐Field MRI Contrast Agents and their Synergy with Optical Imaging: the Evolution from Single Molecule Probes towards Nano‐architectures

“…This system was built on further to evaluate and compare Ho 3+ with Dy 3+ and Tb 3+ while using an Eu 3+ /coumarin optical probe, displaying multi photon excitation at 800 nm and NIR emission at 700 nm in a step towards any biological application (Figure and ) . Dy 3+ outperformed Ho 3+ and Tb 3+ in this series as a negative contrast agent, displaying a transverse relaxivity of 46 s −1 m m −1 (11.7 T, 310 K) most likely due to the slightly longer electronic relaxation time . Ho 3+ and Tb 3+ showed transverse relaxivities of 34 and 30 s −1 m m −1 at 11.7 T and 310 K respectively and the quantum yield of the micelles was in the range of 1 to 2 %.…”

“…Tb 3+ aggregates exhibit higher quantum yields that Dy 3+ , reaching 7.3 % and impressive transverse relaxivity, 15 s −1 m m −1 at 11.7 T . This system was built on further to evaluate and compare Ho 3+ with Dy 3+ and Tb 3+ while using an Eu 3+ /coumarin optical probe, displaying multi photon excitation at 800 nm and NIR emission at 700 nm in a step towards any biological application (Figure and ) . Dy 3+ outperformed Ho 3+ and Tb 3+ in this series as a negative contrast agent, displaying a transverse relaxivity of 46 s −1 m m −1 (11.7 T, 310 K) most likely due to the slightly longer electronic relaxation time .…”

“…[46] Dy 3 + outperformed Ho 3 + and Tb 3 + in this series as an egative contrast agent, displaying at ransverse relaxivity of 46 s À1 mm À1 (11.7 T, 310 K) most likely due to the slightly longer electronic relaxation time. [46] Ho 3 + and Tb 3 + showedt ransverse relaxivities of 34 and 30 s À1 mm À1 at 11.7 Ta nd 310 Kr espectively and the quantum yield of the micelles was in the range of 1t o2 %. Modification of this system by using Gd 3 + in place of the latter lanthanide ions allowed magnetic field dependent switching from T 1 to T 2 contrast with increasing field strength, showing efficient r 1 relaxation of 26 s À1 mm À1 at 1.5 Tand r 2 relaxation of around5 0s À1 mm À1 above 7T .…”

“…Reproduced with authors rightsf rom Ref. [46] The Royal SocietyofC hemistry. [46] plimentaryt echniques need to be carefully considered.…”

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