Microfluidic active sorting of DNA molecules labeled with single quantum dots using flow switching by a hydrogel sol–gel transition

The fluorescence-activated cell sorter instrument has contributed significantly to life sciences. However, this instrument has limitations including the inability to detect and hence sort nanometer-sized particles such as quantum dots (Qdots) and virus particles. Here, a microfluidic device for analyzing and sorting nanometer-sized particles has been developed. To achieve sensitive detection, the sample flow was hydrodynamically sheathed and effectively excited with a focused laser beam. Flow control was performed by a sol–gel transition of a thermoreversible gelation polymer. This flow control approach enabled us to restrict the lateral diffusion of nanometer-sized particles and to sort the particles in ∼10 μm channels. Single Qdots with diameters of ∼10 nm were detected at a linear flow velocity of about 4 mm/s, and the Qdots were successfully sorted with the sorting system. Using the developed sorter in an application, Qdot-labeled actin DNA was separated from unwanted glyceraldehyde-3-phosphate dehydrogenase DNA, and the purity of Qdot-labeled actin DNA increased following the sorting. This study represents the first example of active separation of biomolecules labeled with single 10 nm-sized particles of Qdots.