In Situ Direct Laser Writing of 3D Graphene‐Laden Microstructures

Abstract

A wide range of applications rely on the ability to integrate electrically conductive microstructures with microfluidic channels. To bypass the planar geometric restrictions of conventional microfabrication processes, researchers have recently explored the use of “Direct Laser Writing (DLW)”—a submicron‐scale additive manufacturing (or “3D printing”) technology—for creating conductive microfeatures with fully 3D configurations. Despite considerable progress in the development of DLW‐compatible photomaterials, thermal post‐processing requirements to support electrical conductivity remain a critical barrier to microfluidics integration. In this work, novel graphene‐laden photocomposites are investigated to enable DLW‐based printing of true 3D conductive microstructures directly inside of enclosed microchannels (i.e., in situ). Photoreactive composite materials comprising reduced graphene oxide (rGO) particle concentrations of up to 10 wt% exhibited high compatibility with DLW, with minimal optical interference at critical wavelengths. Developed rGO‐photocomposites revealed an ultimate DC conductivity of 9.85 ± 0.48 × 10−5 S m−1. Experimental results for DLW of 3D microcoils (1 wt% rGO; wire diameter = 10 µm; coil diameter = 40 µm) revealed an impedance of 2.71 ± 0.12 MΩ at 2 MHz. In addition, results for in situ DLW of geometrically sophisticated rGO‐laden microstructures suggest utility of the presented approach for potential 3D microelectronics‐based microfluidic applications.

Towards Repeatable, Scalable Graphene Integrated Micro-Nano Electromechanical Systems (MEMS/NEMS)

“…As a consequence, Q-factor and resonance frequency of suspended rGO resonators are lower than that of graphene. In addition, liquid phase reduced graphene oxide can be printed on the targeted location and polymerized by two-photon polymerization by direct laser writing [220]. This enables production of interesting features of coils in micron sizes.…”

3D‐Printed Microinjection Needle Arrays via a Hybrid DLP‐Direct Laser Writing Strategy

“…DLW entails scanning a femtosecond pulsed IR laser in a point-by-point, layer-by-layer manner to selectively crosslink a photocurable material in target locations via two-photon (or multiphoton) polymerization to ultimately produce 3D objects comprising cured photomaterial with feature resolutions down to the 100 nm range. [43][44][45][46] Previously, researchers have demonstrated the utility of using DLW to print MNA master molds, which can then be used to replicate solid MNAs with drug coatings [47][48][49][50] or solid MNAs that are fully dissolvable. [51,52] Additionally, Rad et al reported the use of DLW to print molds and MNAs directly that include open (i.e., unenclosed) side channels.…”

Multiphoton Lithography of Organic Semiconductor Devices for 3D Printing of Flexible Electronic Circuits, Biosensors, and Bioelectronics

“…Although relatively high specific electrical conductivities up to ≈10 6 S m −1 wt% −1 (conductivity per concentration of metallic nanoparticles) can be achieved, metal‐nanoparticle‐loaded resins produce planar structures. [ 17 ] On the other hand, MPL‐compatible composite resins containing carbon nanotubes (CNTs) [ 23–25 ] and graphene [ 26,27 ] exhibit 3D microstructures. However, these nanomaterials demonstrate low specific electrical conductivities up to only ≈200 S m −1 wt% −1 .…”

“…Development of innovative 3D micro and nanoscale technologies in nanoelectronics, [1] micro/nanoelectromechanical systems, [2] nanophotonics, [3] micro/nanofluidics, [4] and nanobiosciences [5] requires advancements in existing light inducedadditive manufacturing techniques including electron beam lithography, [6] Digital Light Processing, [7] dip pen lithography, [8] concentration of metallic nanoparticles) can be achieved, metalnanoparticle-loaded resins produce planar structures. [17] On the other hand, MPL-compatible composite resins containing carbon nanotubes (CNTs) [23][24][25] and graphene [26,27] exhibit 3D microstructures. However, these nanomaterials demonstrate low specific electrical conductivities up to only ≈200 S m −1 wt% −1 .…”