Three-Dimensional-Printing Micro-Spring Probe With the Function of Displacement Self-Detection for Micro-Force Measurement

Accurate micro-force detection is essential for micro-operation and biomedical applications. However, conventional techniques, such as atomic force microscopy (AFM), are bulky and spatially demanding. In this study, we presented micro-spring probes fabricated by femtosecond-laser two-photon polymerization for flexible and precise mechanical sensing. The mechanical stiffness of the probes was tuned by adjusting the spring-wire diameter, with diameters of 2 µm, 2.5 µm, and 3 µm, exhibiting the corresponding micro-force sensitivity of −0.28 nm/µN, −0.09 nm/µN, and −0.07 nm/µN, respectively. The probes enabled accurate measurement of Young’s modulus of the polydimethylsiloxane (PDMS), exhibiting excellent consistency with AFM results. We further proposed a fiber-based self-referenced displacement detection scheme that integrated sensing and reference springs, allowing Young’s modulus characterization without the need for a piezoelectric stage. With the growing development of the “lab-on-fiber” paradigm, the proposed micro-spring probe provides a promising platform for high-accuracy and compact micro-force sensing.