To be able to overcome these issues we compiled a library of adapted sample holders which can be printed on a 3D printer.
Using the free software OpenSCAD we created the sample holders and exported them to STL files. Since we require the sample holders to be perfectly water (or liquid) proof, the cheapest and most common 3D printing method (fused deposition modeling) was not suitable for our purposes. With these extrusion methods, small gaps in the 3D printed object can remain. After some testing, we chose a high-quality stereolithography printer (Form 2, Formlabs, Somerville, USA) to print our STL files to physical objects.