Utilising Glycobiology for Fluorescent Nanodiamond Uptake and Imaging in the Central Nervous System

Nanodiamonds are a carbon based class of nanoparticle quickly gaining popularity due to their low toxicity and versatile applications in biology and nanomedicine Their cheap and large scale synthesis, extensive optical characterisation and ease of bio-functionalisation also makes nanodiamonds an attractive material for use in bio-targeting studies Although central nervous system (CNS) cells are well known to functionally communicate via electrical and chemical signals, cell-surface glycans mediate the initial contact between cells and exogenous proteins. Glycosylation, the enzymatic process by which glycans are attached to proteins and lipids, is the most abundant and functionally important type of post-translational modification associated with brain development, neurodegenerative disorders, psychopathologies and brain cancers. The glycan structures on glycoproteins and glycolipids expressed in brain cells play key functional roles in neural development, biological processes and CNS maintenance such as cell adhesion, signal transduction, molecular trafficking and differentiation. Using EDC/NHS chemistry, we have coated fluorescent nanodiamonds with lectin proteins, which can recognise specific glycan receptor structures expressed on the cellular membrane of CNS cells There is substantial value in developing nanoparticle/lectin complexes for targeted nanoparticle based drug delivery in the CNS as their interaction with cell surface glycan receptors readily triggers endocytosis and subsequent trafficking to intracellular organelles such as endosomes and long term storage in the endoplasmic reticulum. We have engineered lectin coated fluorescent nanodiamonds and tested their ability to recognise specific CNS cell types in 2D and 3D models of brain cells in vitro and also applied them in vivo to rat brains Lectin coated nanodiamonds were successfully endocy-tosed by neurons, microglia and astrocytes in vitro and/or in vivo and remained in these cells for at least 48 hours with minimal stress to the host cells.