Optothermal sample preconcentration and manipulation with temperature gradient focusing

In this article, we present an optothermal analyte preconcentration method based on temperature gradient focusing. This approach offers a flexible, noninvasive technique for focusing and transporting charged analytes in microfluidics using light energy. The method uses the optical field control provided by a digital projector as established for particle manipulation, to achieve analogous functionality for molecular analytes for the first time. The optothermal heating system is characterized and the ability to control of the heated zone location, size, and power is demonstrated. The method is applied to concentrate a sample model analyte, along a microcapillary, resulting in almost 500-fold local concentration increase in 15 min. Optically controlled upstream and downstream transport of a focused analyte band is demonstrated with a heater velocity of *170 lm/min.