Magnetically Driven Micromachines Created by Two-Photon Microfabrication and Selective Electroless Magnetite Plating for Lab-on-a-Chip Applications

Abstract

We propose a novel method to fabricate three-dimensional magnetic microparts, which can be integrated in functional microfluidic networks and lab-on-a-chip devices, by the combination of two-photon microfabrication and selective electroless plating. In our experiments, magnetic microparts could be successfully fabricated by optimizing various experimental conditions of electroless plating. In addition, energy dispersive X-ray spectrometry (EDS) clarified that iron oxide nanoparticles were deposited onto the polymeric microstructure site-selectively. We also fabricated magnetic microrotors which could smoothly rotate using common laboratory equipment. Since such magnetic microparts can be remotely driven with an external magnetic field, our fabrication process can be applied to functional lab-on-a-chip devices for analytical and biological applications.

Functional Materials for Two‐Photon Polymerization in Microfabrication

“…In this way it is possible to pattern with different metals the amine‐modified surfaces, taking advantage of the amine ability to coordinate and reduce metal salts in solution . Similar methods can be used to also functionalize cationic photoresists (e.g., US‐8) and to prepare different kind of metamaterials, MEMS capable of magnetic actuation, and propulsion . Multistep polymerizations, despite being practical in achieving differentiated surfaces, are often time consuming as they involve the replacement of the photoresist which can damage the structures and induce misalignment.…”

Acoustic Vibration‐Induced Actuation of Multiple Microrotors in Microfluidics

“…1) For other microrotor fabricated with two‐photon polymerization, Guan et al [ 26 ] have realized the maximum rotational speed of single microrotor at 75 RPM with hydrodynamic liquid flow rate of ≈170 µm s −1 . Zandrini et al [ 20 ] have utilized the magnetic field to manipulate multiple microrotors (coated successively with amine, Pd and magnetite) with the maximum speed of 600 RPM; Köhler et al [ 23 ] have demonstrated single microrotor assembly with holographic optical tweezer, and a rotation speed of ≈25 RPM was achieved. 2) For microrotor fabricated with UV polymerization, Kaynak et al [ 14 ] have achieved ≈1200 RPM with acoustic actuation of single microrotor at peak‐to‐peak voltage of 160 V and frequency of 4.3 kHz; Moon et al [ 27 ] have adopted the hydrodynamic method to manipulate multiple microrotors and achieved 650 RPM with flow rate of 130 µL min −1 ; Yue et al [ 60 ] have utilized optical laser stimuli to control single microrotor with 60 RPM at a laser power of 2 W. 3) For microrotor fabricated with direct cutting, Loget et al [ 19 ] have adopted the electric field at 0.5 kV m −1 in 50 × 10 −3 m HCl to achieve the single microrotor rotation at the speed of 1 RPM; Jang et al [ 15 ] have combined the teflon tubes together with the laser cutting bodies to generate microrotor, then actuated it with injected bubble acoustic oscillating to achieve a maximum rotation speed of 154 RPM at 2.15 kHz frequency.…”

“…To produce the mechanical motion of microrotors, it can be generally classified into two categories according to the source of energy: One is driven by an external actuation, such as through acoustic, [ 14–17 ] electric, [ 18,19 ] magnetic, [ 11,20,21 ] optical [ 22–25 ] field, and external forces like hydrodynamic force [ 26,27 ] and bacterial movement. [ 28–30 ] The other type of actuation is relying on the chemical energy [ 19,31 ] conversion within the microfluidic system, which can obtain self‐sustaining energy from the surrounding environment and exhibit microrotor self‐propulsion [ 32,33 ] capability.…”

“…Loget et al [ 19 ] have adopted the electric field to induce the redox chemistry reaction inside microrotor system, which could generate the asymmetric gas bubbles thus achieved the speed and direction control of microrotor. Zandrini et al [ 20 ] have utilized the two‐photon polymerization method to fabricate the microrotor, then site‐selectively deposited the magnetic nanoparticles onto rotor part and manipulated the rotation with magnetic field. Būtaitė et al [ 22 ] have demonstrated optical actuation of microrotors triggered by highly localized flow‐fields in a closed‐loop control, thus extending the optical tweezer application.…”

Microstructures Fabricated by Two‐Photon Polymerization and Their Remote Manipulation Techniques: Toward 3D Printing of Micromachines

“…It is found that the rotation speed reached 400 rpm under a rotating magnetic field . Zandrini et al also proposed a magnetic microrotor recently . In this study, Pd catalyst absorption and Fe 3 O 4 deposition were utilized to treat acrylic‐based structures.…”