On-demand concentration of an analyte on laser-printed polytetrafluoroethylene†
Controllable targeted deposition of an analyte dissolved in a liquid drop evaporating on a superhydrophobic surface has recently emerged as a promising concentrator approach with various applications ranging from ultrasensitive bioidentification to DNA molecule sorting. Here, we demonstrate that surface textures with non-uniform wettability fabricated using direct easy-to-implement femtosecond-pulse filament-assisted ablation of polytetrafluoroethylene substrates can be used to concentrate and deposit an analyte at a designated location out of a water droplet. The proposed surface textures contain a central superhydrophilic trap surrounded by superhydrophobic periodically arranged pillars with a hierarchical roughness. By optimizing the arrangement and geometry of the central trap and the surrounding superhydrophobic textures, the analyte dissolved in a 5 μL water drop was fixed onto a 90 × 90 μm2 target. The proposed textures provide a concentration factor of 103, an order of magnitude higher than those for the previously reported surface textures. This promising ultrasensitive versatile platform allows the detection of fingerprints of the deposited analyte via surface-enhanced spectroscopy techniques (Raman scattering or photoluminescence) at an estimated detection threshold better than 10−15 mol L−1.