Evaluation of europium-based carbon nanocomposites as bioimaging probes: Preparation, NMR relaxivities, binding effects over plasma proteins and cytotoxic aspects

Abstract

It is highly desirable to develop water-dispersible lanthanide-based luminescent probes with facile preparation, great bioavailability, and excellent photo properties for biomedical applications. Numerous carbon photoactive nanostructures (from diverse sources) have been reported for broad applications as surfactants, pollutants degradation, metal sensing and in vitro/in vivo bioimaging applications. Here, europium-based carbon nanocomposites (EuCQD) have been synthesized and well-characterized by their magneto-optical and biophysical properties. The obtained EuCQD is small in size (≅ 5 nm), highly water dispersible and composed essentially of carbon, europium and oxygen. Furthermore, the obtained nanocomposite presents Eu/CQD hybrid luminescent properties and high NMR relaxivities. The impact on biological media has been investigated based on plasma protein interactions and cytotoxicity assays. The results reveal that EuCQDs bind firmly (Ka ≈ 104–105 M−1) to studied plasma proteins (BSA and HTF) mainly by Van der Waals interaction and hydrogen bonds. Furthermore, protein CD spectra reveal that both proteins experience structural changes during EuCQD interaction, and the nanocomposite presents very low toxicity against HBMEC, A549, and HTC116 cells. All the presented results expose EuCQD as an excellent alternative to other lanthanide probes for bi-functional bioimaging applications and open the prospect of turning it accessible for industrial production and clinical translation.