Imaging of luminescent nanoparticles in flows: development of surface active luminescent lanthanide complexes

Abstract

We have developed a new ligand (H\(_3\)L\(^2\)) based on a DTPA bis-amide backbone which improves upon previous work within the group. The quantum yields of the europium and samarium complexes of H\(_3\)L\(^2\) are greatly enhanced over that of H\(_3\)L\(^1\). The previously observed nanoparticle-based quenching of the lanthanide luminescence lifetime of EuL\(^1\) is suppressed in EuL\(^2\). We have demonstrated the functionalisation of gold and platinum nanoparticles of various sizes with the surface active lanthanide complexes of H\(_3\)L\(^1\) and H\(_3\)L\(^2\). As a proof of principle, we have imaged, tracked and measured velocities of individual EuL\(^2\) functionalised nanoparticles in an aqueous flow, providing flow-rates accurate to micrometer resolution of fluids through a 2 mm diameter tube. We have also observed the microscale mixing of a nanoparticle labelled solution with water on time-scales of milliseconds to seconds. We can study the development and measure the dimensions of features present during mixing and therefore assess the efficiency of that mixing. We have also visualised a turn-on event at the boundary of aqueous solutions of Eu(III) ions and H\(_3\)L\(^2\)-functionalised nanoparticles during mixing, demonstrating a novel optical method for ascertaining the degree of mixing between two solutions and the position and area of that mixing.