Measurement of Interfacial Adhesion Force with a 3D-Printed Fiber-Tip Microforce Sensor

Abstract

With the current trend of device miniaturization, the measurement and control of interfacial adhesion forces are increasingly important in fields such as biomechanics and cell biology. However, conventional fiber optic force sensors with high Young’s modulus (>70 GPa) are usually unable to measure adhesion forces on the micro- or nano-Newton level on the surface of micro/nanoscale structures. Here, we demonstrate a method for interfacial adhesion force measurement in micro/nanoscale structures using a fiber-tip microforce sensor (FTMS). The FTMS, with microforce sensitivity of 1.05 nm/μN and force resolution of up to 19 nN, is fabricated using femtosecond laser two-photon polymerization nanolithography to program a clamped-beam probe on the end face of a single-mode fiber. As a typical verification test, the micronewton-level contact and noncontact adhesion forces on the surfaces of hydrogels were measured by FTMS. In addition, the noncontact adhesion of human hair was successfully measured with the sensor.

Keywords: adhesion force measurement; clamped-beam probe; femtosecond laser 3D printing; fiber-tip microforce sensor (FTMS); optical fiber sensor.

Figure 1

Schematic diagram of fiber-tip microforce sensor (FTMS).

Figure 2

Sensing schematic diagram of the proposed sensor. (a) Simulation results for the device under an applied external force, (b) FTMS fabrication process.

Figure 3

Characteristics of the FTMS. (a) SEM image of the FTMS. (b) Optical microscope image of the FTMS when pressed on the glass slide edge. (c) Reflection spectrum for the FTMS.

Figure 4

Microforce measurements. (a) Reflection spectral evolution of the FTMS while the external force increases from 0 to 1800 nN. (b) Measurement system setup. (c) Linear relationship between dip wavelength and microforce. The line is the linear fitting of measured data points and the error bar is obtained by critically repeating the experiment of force measurement three times.

Figure 5

(a) Probe of the FTMS was encapsulated by micro-protrusions of the hydrogel under the effect of the adhesion force. (b) Simulation results for adhesion of the FTMS to agarose hydrogels. (c) Evolution of the reflection spectrum under the action of the adhesion.

Figure 6

(a) Drift of the FTMS reflection spectrum under the action of the noncontact adhesion force of hydrogels. (b) Noncontact adhesion forces between the probe and the agarose hydrogels at different distances. (c) Noncontact adhesion forces measurement of human hair.