Abstract
The drive toward
miniaturization of enzyme-based bioelectronics
established a need for three-dimensional (3D) microstructured electrodes,
which are difficult to implement using conventional manufacturing
processes. Additive manufacturing coupled with electroless metal plating
enables the production of 3D conductive microarchitectures with high
surface area for potential applications in such devices. However,
interfacial delamination between the metal layer and the polymer structure
is a major reliability concern, which leads to device performance
degradation and eventually device failure. This work demonstrates
a method to produce a highly conductive and robust metal layer on
a 3D printed polymer microstructure with strong adhesion by introducing
an interfacial adhesion layer. Prior to 3D printing, multifunctional
acrylate monomers with alkoxysilane (−Si–(OCH
3
)
3
) were synthesized via the thiol–Michael addition
reaction between pentaerythritol tetraacrylate (PETA) and 3-mercaptopropyltrimethoxysilane
(MPTMS) with a 1:1 stoichiometric ratio. Alkoxysilane functionality
remains intact during photopolymerization in a projection micro-stereolithography
(PμSLA) system and is utilized for the sol–gel reaction
with MPTMS during postfunctionalization of the 3D printed microstructure
to build an interfacial adhesion layer. This leads to the implementation
of abundant thiol functional groups on the surface of the 3D printed
microstructure, which can act as a strong binding site for gold during
electroless plating to improve interfacial adhesion. The 3D conductive
microelectrode prepared by this technique exhibited excellent conductivity
of 2.2 × 10
7
S/m (53% of bulk gold) with strong adhesion
between a gold layer and a polymer structure even after harsh sonication
and an adhesion tape test. As a proof-of-concept, we examined the
3D gold diamond lattice microelectrode modified with glucose oxidase
as a bioanode for a single enzymatic biofuel cell. The lattice-structured
enzymatic electrode with high catalytic surface area was able to generate
a current density of 2.5 μA/cm
2
at 0.35 V, which
is an about 10 times increase in current output compared to a cube-shaped
microelectrode.