A quantum dot conjugated sugar ball and its cellular uptake. On the size effects of endocytosis in the subviral region

The lipophilic CdSe quantum dot (QD) coated with trioctylphosphine oxide (^TOPOQD) can be extracted from chloroform into water upon interaction with macrocyclic glycocluster amphiphile 1. The QD-conjugated and highly fluorescent sugar ball of a size of 15 nm (^TOPOQD¹) thus solubilized in water readily invades Hela cells via endocytosis. The endocytic activity of ^TOPOQD¹ (15 nm), in light of those of the micellar homoaggregate of 1 (5 nm) and the virus-like 1-DNA conjugate (50 nm) as references, reveals a dramatic size effect (50 ≫15 ≫5) in the subviral size region. The optimal size at ∼50 nm indicates that size complementarity which governs molecular recognition in small host-guest systems also plays key roles in the encapsulation of nanometric guest particles by the endocytic vesicles (≤100 nm) as a macrobiomolecular host. The work thus suggests an utmost importance of size control at the viral size when designing molecular (gene, drug, probe, etc.) delivery machines.