  We introduce a new DNA tile self-assembly model: the Surface Flexible Tile
Assembly Model (SFTAM), where 2D tiles are placed on host 3D surfaces made of
axis-parallel unit cubes glued together by their faces, called polycubes. The
bonds are flexible, so that the assembly can bind on the edges of the polycube.
We are interested in the study of SFTAM self-assemblies on 3D surfaces which
are not always embeddable in the Euclidean plane, in order to compare their
different behaviors and to compute the topological properties of the host
surfaces.
  We focus on a family of polycubes called cuboids. Order-0 cuboids are
polycubes that have six rectangular faces, and order-1 cuboids are made from
two order-0 cuboids by substracting one from the other. Thus, order-1 cuboids
can be of genus 0 or of genus 1 (then they contain a tunnel). We are interested
in the genus of these structures, and we present a SFTAM tile assembly system
that determines the genus of a given order-1 cuboid. The SFTAM tile assembly
system which we design, contains a specific set $Y$ of tile types with the
following properties. If the assembly is made on a host order-1 cuboid $C$ of
genus 0, no tile of $Y$ appears in any producible assembly, but if $C$ has
genus 1, every terminal assembly contains at least one tile of $Y$.
  Thus, we are able to distinguish the host surfaces according to their genus,
by the tiles used in the assembly. This system is specific to order-1 cuboids
but the techniques we use should be generalizable to other families of shapes.
