Fig. 1. Illustration of the on-chip sample preparation approach. (a) Perspective view of a simple glass chip with two chambers. Each chamber (some tens of μm high) has two openings to enable capillary flow. Purple shading indicates reagent concentration. (Left) In a (hypothetical) chamber with reagents deposited without matrix, reagents would be washed off toward the end of the chamber during inflow. (Right) In a chamber with reagents embedded in a matrix, reagents are homogeneously distributed, as their release is delayed during inflow. (b) (Side view) (Left) The chamber without matrix shows strong reagent wash-off. (Right) The chamber with matrix shows uniform reagent distribution. Purple shading indicates reagent concentration.