Real-time detection of single quantum dots inside living cells

Quantum dots have opened up a plethora of possibilities in biological detection and imaging. Their small size, stable luminescence and resistance to photobleaching make them ideal for intracellular imaging and detection. It is highly desirable to develop tools that will allow detection and imaging of biological processes without disrupting native cellular processes. A significant barrier to use of quantum dots in living cells is ability to deliver and detect single quantum dots inside living cells. In this article we describe a bacterial toxin dependent method that allows delivery of single quantum dots. We also demonstrate use of a single molecule detection system to detect both single and aggregated quantum dots in living cells in real time. We compare results of quantum dot delivery from receptor mediated endocytosis and HIV-TAT peptide mediated delivery methods with the bacterial toxin Streptolysin O. Our results show that Streptolysin O is able to deliver single quantum dots to living cells. Our results also indicate that the mechanism of cargo delivery by HIV-TAT peptide might be endocytosis dependent. Ongoing work in this direction involves showing that single, functional quantum dot probes can also be delivered using the bacterial toxin.