Schematic representation of a multifunctional NP for diagnostics and drug delivery. Polyethylene glycol (PEG) copolymers are one of the most popular vehicles for drug delivery. The NPs can be functionalized with suitable fluorescent markers, antibodies against tumoural marker, gene delivery agents and drug molecules coated with a form of PEG. The antibody is using a long linking molecule that allows the antibody to stick to PEG coatings. In contrast, cell penetrating peptides (CPP), employed to trigger rapid cell uptake, are attached using short linkers.