Peptide modified C-dots for bioimaging applications

Abstract

The aims of this project included, synthesis and characterisation of Carbon dots (C-dots), surface modification of the C-dots to secure cell penetration and enhance Photoluminescence (PL) properties and the development of peptide C-dot conjugation to improve cell selectivity.
Fluorescent C-dots were prepared by the pyrolysis treatment of citric acid monohydrate and ethanolamine at 300ºC. PL studies reveal that C-dots display excitation-dependent behaviour, show a high level of conjugation on the surface and can disperse well in water. A cell penetrating peptide (K7) made up of seven-lysine amino acids was synthesized using a semi-automated peptide synthesizer and purified using HPLC analysis. Based on the as-prepared C-dots, the K7 peptide was attached onto the surface of the C-dot via two methods to form two conjugated systems, C-dotK7A and C-dotK7B, respectively. Method A relies on the covalent attachment of C-dot at the end of the uncleaved peptide as grown in the synthesizer, whereas in method B the cleaved peptide is used for the conjugation. Both conjugated systems demonstrate very low levels of haemolytic activity. A synergistic effect noticed for both C-dotK7A and C-dotK7B materials when tested against E.coli and Staphylococcus bacteria. At very low concentrations (0.01 mg ml-1 both materials effectively suppress bacteria colonies. The C-dotK7A material killed 43% of E. coli and Staphylococcus colonies and the C-dotK7B material killed 63% of E.coli colonies and 43% Staphylococcus colonies. Their unique photoluminescent behaviour, their antimicrobial properties and their supreme optical properties, makes C-dotK7 promising materials for bioimaging applications