Four-Dimensional Printing of a Fiber-Tip Multimaterial Microcantilever as a Magnetic Field Sensor

"Lab on Fiber" technology integrates different micro- and nanoscale structures or materials onto optical fibers to create additional functionality. With the advanced femtosecond (Fs) laser-induced two-photon polymerization (TPP) technology, polymer microstructures printed on a fiber tip have great potential as micro-optical sensors. However, additional functionalization is usually required, which is costly and complex. Based on the advanced four-dimensional (4D) printing theory, for the first time, a successive multimaterial on-fiber TPP strategy is proposed here, and a fiber-tip polymer microcantilever-based magnetic sensor is prepared in one step. First, the cantilever and the supporting base on the fiber tip are printed by TPP, and then the magnetically responsive cube on the cantilever tip is printed with a self-made magnetic fluid photoresist. The whole process is completed in one step without additional treatment. The prepared sensor shows a minuscule size and a high magnetic sensitivity of 119 pm mT–1 in the range of 0–90 mT, suitable for weak or microspace magnetic field measurement at high spatial resolution. Especially, the proposed 4D successive on-fiber TPP strategy can be extended to other stimulus-responsive materials, providing new guidance for manufacturing various stimulus-responsive microsensors and microactuators on the fiber tip.