A micro-analyzer is described. This micro-analyzer includes an outer surface region on a sampler surface that receives liquid droplets, and aggregates and moves the droplets radially toward an inner surface region on the sampler surface that receives the droplets. For example, the outer surface region may include a set of micro-patterned concentric rings, each of which includes a set of radially oriented wall-groove pairs. Moreover, the sampler surface may be increasingly less hydrophobic along a radial direction toward the center of the sampler surface, thereby creating an axisymmetric wettability gradient. After the droplets are aggregated, an analysis mechanism in an area within the inner surface region performs analysis on the aggregated droplets.