Developing 3D brain models for cell surface sugar targeting with bio-conjugated nanodiamonds

Glycosylation is a post-translational modification that attaches sugar receptor chains to cell surface proteins and lipids. Abnormal glycosylation is evident during multiple chronic brain pathophysiologies such as Alzheimer's, Parkinson's and Huntington's diseases and brain cancer, making sugars excellent biomarkers for selective targeting of affected cells by sugar receptors such as lectins that bind to different cell surface glycan residues. We utilised 120nm fluorescent nanodiamonds with nitrogen vacancy centres that were bio-conjugated with lectins to target sugar structures on the surface of three types of cultured central nervous system cells: astrocytes, neurons and microglia. Functionalised nanodiamonds were thus used to investigate the in vitro expression of sialic acid and N-acetylglucosamine (using wheat germ agglutinin), fucose (Aleuria aurantia lectin), and high mannose and N-acetylglucosamine (using tomato lectin) on these brain cell types. The binding of nanodiamonds to these sugars to each cell type grown in standard 2D cultures and in newly developed natural 3D brain scaffold cell growth constructs was evaluated. As glycans are a major component of the cell surface as well as of the extracellular matrix and are highly important in cell-cell interactions, our new 3D models were developed to more closely represent in vivo central nervous system conditions for assessing sugar expression and nanodiamond binding and uptake in neurons, astrocytes and microglia.