Marcel Suter

Superparamagnetic photocurable nanocomposite for the fabrication of microcantilevers

We present a photocurable polymer composite with superparamagnetic characteristics for the fabrication of microcantilevers. Uniform distribution and low particle agglomeration (<50 nm) in the photocurable polymer matrix SU-8 are achieved by using superparamagnetic nanoparticles with a surfactant. Particles and composite are characterized by a transmission electron microscope, UV-VIS spectrometer and magnetic measurements. The composite contains 5 vol.% (18 wt.%) of Fe3O4 nanoparticles with diameters of 12.1 ± 3.5 nm. The composite exhibits a magnetization saturation of 13.2 kA m −1 . Superparamagnetic composite microcantilevers with typical dimension of 2 μm × 14 μm × 80‐300 μm are successfully fabricated by two conventional photolithography steps and a sacrificial layer etch. Exposure doses of 10000 mJ cm −2 must be applied for microcantilever thicknesses of 1.8 μm due to the high UV absorption of the particles in the composite. The magnetic polymer cantilevers are successfully actuated in resonance in air with an amplitude of 29 nm. An off-chip coil is used to generate a magnetic field to actuate the cantilevers. (Some figures in this article are in colour only in the electronic version)

Superparamagnetic photosensitive polymer nanocomposite for microactuators

We present a photosensitive polymer composite with superparamagnetic characteristics for the fabrication of microactuators. A uniform distribution of particles in the photosensitive polymer matrix SU-8 is achieved by applying superparamagnetic nanoparticles with the aid of a surfactant. The composite contains Fe3O4 nanoparticles up to 3 vol.% (12 wt.%) with diameters of around 13 nm. Superparamagnetic composite microcantilevers are successfully fabricated and actuated in resonance by the magnetic field of an external coil.

Bacteria-inspired magnetic polymer composite microrobots

Remote-controlled swimming microrobots are promising tools for future biomedical applications. Magnetically actuated helical microrobots that mimic the propulsion mechanism of E. coli bacteria are one example, and presented here is a novel method to fabricate such microrobots. They consist of a polymer-nanoparticle composite, which is patterned using a direct laser writing tool. The iron-oxide nanoparticles respond to the externally applied low-strength rotating magnetic field, which is used for the actuation of the microrobots. It is shown that a helical filament can be rotated around its axis without the addition of a body part and without structuring the magnetization direction of the composite. The influence of the helicity angle on the swim behavior of the microrobots is examined and experimental results show that a small helicity angle of 20 degrees is preferred for weakly magnetized microstructures.

Cobalt-nickel microcantilevers for biosensing

We present microcantilevers that utilize magnetic actuation for use as mass sensors for bioapplications. The microcantilevers are made of electroplated cobalt–nickel that has low coercivity and high saturation magnetization. The microcantilevers are actuated by applying magnetic fields, and the deflection is measured using a laser Doppler vibrometer. The microfabrication of the microcantilevers is based on two lithography steps, an electroplating step and a sacrificial layer etching step. The magnetic actuation and optical readout using the fabricated cobalt–nickel microcantilever were successfully demonstrated in air under atmospheric pressure and in deionized water. A feedback circuit is used to enhance the quality factor of the microcantilever. The quality factor increased from approximately 550 to 1600 in air and from 7.3 to 10.6 in deionized water. The microcantilevers can be readily functionalized with selective binding molecules and used as a biomass sensor.

Low-cost fabrication of PMMA and PMMA based magnetic composite cantilevers

We present a simple and low-cost fabrication process for microcantilevers from both pure Polymethylmethacrylate (PMMA) and magnetic PMMA composites with maghemite nanoparticle concentrations up to 3 vol.% (12 wt.%). The fabricated cantilevers have lengths of 30 – 300 µm, widths of 14 µm and a thickness of 3 µm. The presented fabrication process consists of structural layer patterning by hot embossing, removal of the residual layer by a deep ultraviolet (DUV) exposure step through a partially transparent mold and a sacrificial layer etch to release the suspended microstructures. Process parameters including hot embossing temperature and pressure have been studied. The optimized parameters for pure PMMA are 180° C and 2370 N/cm2 and for magnetic composite with 3 vol.% nanoparticle concentration 195° C and 2660 N/cm2. The molded cantilevers show a well transferred pattern and a sharp side wall profile.

Characterization and actuation of a magnetic photosensitive polymer cantilever

Magnetic polymer microactuators made of SU-8 and superparamagnetic nanoparticles are reported. Homogenous distribution of nanoparticles in the composite was obtained using superparamagnetic nanoparticles and a surfactant. The magnetic polymer composite (MPC) was micromachined into cantilevers using photolithography. The magnetic characterization of the MPC was performed by a superconducting quantum interference device (SQUID). An electromagnet applied magnetic forces to this composite. The force per volume of composite was determined experimentally by measuring the force on a film of MPC using a micro-force sensor. The cantilevers were excited with an AC electromagnet at different frequencies, and their resonance modes were captured by a laser-Doppler vibrometer. Deflections were increased about 10 times by the addition of a DC field. The tip deflection amplitude of a cantilever (160 µm x 1.65 µm) in resonance was found to be 63 nm at 15.78kHz.

An in-plane cobalt-nickel microresonator sensor with magnetic actuation and readout

We present magnetic microresonators that utilize magnetic actuation and readout for use as mass sensors. A magnetic readout method was developed for the detection of microresonator vibration. Together with wireless actuation, the wireless magnetic readout results in completely passive microresonators. The magnetic readout is based on the induced voltage on a pair of differential pick-up coils, which is generated by the movement of the magnetized microresonator. The successful operation of the readout was demonstrated with CoNi microresonators under atmospheric pressure and in water. The microresonator can be readily functionalized and used as a mass sensor for bio applications.