FluidFM is a force-controlled nanopipette [1], combining AFM technology and microfluidics. A fluidic channel is incorporated directly in a hollow AFM cantilever. This channel ends in a nanosized aperture at the apex of the AFM pyramidal tip, allowing for local dispensing of soluble molecules in air and in liquid, while retaining the inherent imaging capabilities and force feedback of an AFM system.

Recently, we have achieved 2D electrochemical patterning with sub-micron precision by reduction of copper as well as diazonium salts filled in the microchannel with subsequent in-situ AFM imaging [2]. Furthermore, we recognized that this method offered an access to the 3^rd dimension.

Micro- and nanometer-scale patterning of functional materials is of great interest in various fields such as microelectronics or micro-electromechanical systems (MEMS) design [3], but also for biosensing and biomedical applications, where manipulation techniques often have to be suitable for use in a liquid environment. In this context, we currently explore the use of FluidFM as a tool for both fabrication and subsequent imaging of microstructures in liquid using the same probe.

Indeed, we succeeded in using the system in the same configuration for 3D additive manufacturing of copper on the micrometer scale [4]. In the proposed protocol, we take advantage of the FluidFM probes as a local source of Cu²⁺ in a macro electrochemical cell. The nanopipette is approached to the working electrode and metal ions are provided by inducing a liquid flow. Thus, metal can be reduced locally under the FluidFM probe. Conveniently, the inherent force sensing capability of the cantilever provides a means to automate this process: Whenever the growing metal deposit touches the cantilever, the cantilever bends, and its deflection is registered so that the probe may be positioned to the next place, where the process continues. Therefore, our protocol enables true voxel-by-voxel (i.e. layer-by-layer) printing with consequent almost complete geometry freedom (see the three interwined helixes).

Upon introducing the microprinting protocol with copper, we discuss our current efforts to adapt it to other metals.

[1] A. Meister et al. (T. Zambelli), Nano Lett. 2009 9:2501

[2] L. Hirt et al. (T. Zambelli), RSC Adv. 2015 5:84517

[3] L. Hirt et al. (T. Zambelli), Adv. Mater. 2016 DOI: 10.1002/adma201604211

[4] L. Hirt et al. (T. Zambelli), Adv. Mater. 2016 28:2311