Photoluminescent and superparamagnetic quantum dots

Quantum dots are semiconducting nanostructures which emit radiation over a narrow spectrum. This is caused by the restricted movement of excitons, formed when electrons are excited from the valence band into the conduction band leaving holes. When excitons relax light is emitted over a narrow spectrum due to the small crystal size, typically 2-50 nm, with the wavelength of light emitted dependent on the size.

Recent work by Biqiong Chen and Shelia MacNeil at the Polymer Centre, in collaboration with various researchers, have harnessed the narrow spectrum emission of quantum dots for the potential of medical imaging alongside drug delivery and photothermal therapy.

The GO quantum dots, composed of reduced graphene oxide-iron oxide, combined the superparamagnetic properties of iron oxide with the drug loading capabilities of graphene oxide. The quantum dots were found to be inherently photoluminescent and superparamagnetic alongside being biocompatible making the materials ideal for use as medical devices.

Photoluminescence is useful in providing detection of the materials by fluorescent imaging. Superparamagnetism allows the magnetic moment of the quantum dots to be changed on a nanoscale. Hence, drug release from quantum dots can be stimulated by applying an external magnetic field for targeted drug delivery. Superparamagnetism also allows imaging by magnetic resonance imaging (MRI) to aid the visualisation of tumours and image guided surgeries.

The GO quantum dots were loaded with the model drug lidocaine hydrochloride. The loading ratio of drug to quantum dots was 0.31:1 which was fully released in phosphate buffered saline solution over 8 hours indicating efficient drug elution.

Testing of the GO quantum dots over a range of concentrations with varying laser powers showed a maximum temperature increase of 50 °C. This large temperature increase would be useful for treating tumours by photothermal therapy, where heat is applied directly to tumours to damage the cancerous cells.

Original article: Photoluminescent and superparamagnetic reduced graphene oxide-iron oxide quantum dots for dual-modality imaging, drug delivery and photothermal therapy, R. Justin, K. Tao, S. Román, D. Chen, Y. Xu, X. Geng, I. M. Ross, R. T. Grant, A. Pearson, G. Zhou, S. MacNeil, K. Sun and B. Chen, Carbon N. Y., 2016, 97, 54–70.

Article by Jasmine Lord; a PhD Student on the EPSRC Polymers, Soft Matter and Colloids CDT programme. For more information, please contact Dr Joe Gaunt at the Polymer Centre.