Printing Three-dimensional Conducting Polymer Structures Using Scanned Nanopipettes with Submicron Resolution

INTRODUCTION: Conducting polymers (CP) are organic polymers that have a capability to conduct electrical current, while keeping the other properties of polymers such as elasticity. The unique combination of electrical and... [ view full abstract ]

INTRODUCTION: Conducting polymers (CP) are organic polymers that have a capability to conduct electrical current, while keeping the other properties of polymers such as elasticity. The unique combination of electrical and mechanical properties of CPs makes them a promising material for wide range of new applications such as printable flexible electronic circuits, biosensors or electroactive scaffolds for tissue engineering. A number of different strategies for printing of CPs or creating scaffolds containing CPs have been developed over the years, however controlled assembly of three-dimensional CP-based structures with submicron resolution remains challenging. Here we explore the use of glass nanopipettes and principles of scanning ion conductance microscopy (SICM) for printing CP structures.

METHODS: SICM is a non-contact type of scanning probe microscopy utilising tapered glass nanopipette filled with electrolyte. In this work, we used nanopipettes with tip diameter in the range of 100 - 300 nm filled with 0.1 M pyrolle dissolved in 0.1 M H₂SO₄ mounted on z-axis piezoactuator of the SICM scanner above a conductive substrate. The nanopipette position was controlled based on the current flowing between the substrate acting as a working electrode and the Ag/AgCl reference electrode immersed in the monomer solution in the nanopipete (Figure 1A).

RESULTS: We have implemented a software module for SICM scanner capable of executing complex 3D movements of the nanopipette at controlled velocity and defined nanopipette voltage. Using the velocity control of the module, we were able to control the thickness of vertically printed polypyrolle rods in the range of 500 nm – 2 µm, demonstrating the submicron resolution of the setup (Figure 1B). Lateral movement of the nanopipette created approximately 300 nm high layer of the polymer allowing printing more complex 3D structures with submicron resolution using layer-by-layer approach as illustrated in Figure 1C.

DISCUSSION: According to our knowledge, this is first successful attempt to create conductive polypyrolle structures of substantial complexity using submicron sized nanopipettes. This technological advancement opens possibilities for designing custom shaped interfaces between man-made electronics and submicron sized membrane structures such as neuronal dendrites.