Photothermomechanical Nanopump: A Flow- Through Plasmonic Sensor at the Fiber Tip

Optical fibers equipped with plasmonic flow sensors at their tips are fabricated and investigated as photothermomechanical nanopumps for the active transport of target analytes to the sensor surface. The nanopumps are prepared using a bottom-up strategy: i.e., by sequentially stacking a monolayer of a thermoresponsive polymer and a plasmonic nanohole array on an optical fiber tip. The temperature-dependent collapse and swelling of the polymer is used to create a flow-through pumping mechanism. The heat required for pumping is generated by exploiting the photo thermal effect in the plasmonic nanohole array upon irradiation with laser light (405 nm). Simultaneous detection of analytes by the plasmonic sensor is achieved by monitoring changes in its optical response at longer wavelengths (similar to 500-800 nm). Active mass transport by pumping through the holes of the plasmonic nanohole array is visualized by particle imaging velocimetry. Finally, the performance of the photothermomechanical nanopumps is investigated for two types of analytes, namely nanoscale objects (gold nanoparticles) and molecules (11-mercaptoundecanoic acid). In the presence of the pumping mechanism, a 4-fold increase in sensitivity was observed compared to the purely photothermal effect, demonstrating the potential of the presented photothermomechanical nanopumps for sensing applications.

Automated summary

In this research, optical fibers equipped with plasmonic flow sensors were fabricated as photothermomechanical nanopumps for active transport of target analytes. The nanopumps were prepared by stacking a thermoresponsive polymer monolayer and a plasmonic nanohole array on an optical fiber tip. The pump mechanism relied on the temperature-dependent collapse and swelling of the polymer, while the required heat was generated by the photo thermal effect in the plasmonic nanohole array. Simultaneous detection of analytes was achieved by monitoring changes in the plasmonic sensor's optical response. The active mass transport through the nanohole array was visualized using particle imaging velocimetry. The presence of the pump mechanism led to a 4-fold increase in sensitivity compared to the purely photothermal effect, demonstrating the potential of these photothermomechanical nanopumps for sensing applications.