# Nano- and Micropatterning on Optical Fibers by Bottom-Up Approach: The Importance of Being Ordered
## 5 Conclusions  
Self-assembly processes represent a cost-effective option for the mass production of technologically advanced platforms based on OFs. The nanofabrication of highly ordered structures on a non-conventional substrate like the OF is challenging, whilst coupling the OF with ordered nanopatterns is required for the development of several advanced sensing and biosensing technological platforms. Bottom-up approaches are capable of building nanostructures, hierarchically ordered structures and sophisticated micro- and nanopatterns on the OFs with a high degree of order and a wide geometrical parameters control, according to the characteristics summarized in Table 1. At the same time, they have the advantage of high throughput and low-cost processing, two key elements suitable to accelerate the real market exploitation of lab-on-fiber probes. Withstanding this, a few limitations characteristic of these self-assembling approaches still hinder the establishment of these technologies as the springboard for the transition from valuable lab-on-fiber proofs of concept toward the market. One of the main constraints relies on the limited number of implementable geometries. The self-organization process at the basis of the pattern formation typically consists of creating the controlled conditions suitable to push the \"disassembled\" system toward an equilibrium state corresponding to the self-packing of nanostructures in a compact fashion. When operating with nanospheres the natural achievement of this minimum energy equilibrium state corresponds to hexagonal packing in a 2D planar pattern as well as fcc symmetry in 3D structures. Most of the reported structures feature indeed similar patterns directly or indirectly obtained by such basic geometries. Currently, remarkable attempts to enlarge the set of attainable geometries are only associated with the DSA method, a combination of top-down and bottom-up approaches, which using substrates patterned with linear, hexagonal and circular structures, demonstrated the formation of unusual patterns. Nonetheless, nature already demonstrated that different geometries are surely possible in full self-assembly approaches. Self-assembling of aperiodically ordered structures is present in nature too but controlled methods to artificially build photonic quasicrystals by auto-organization are still not demonstrated. The enlargement of the attainable structures is important for conferring versatility to the nanofabrication process. Overall, hierarchical structures, DSA and post-processing treatments can open new routes to self-assembling nanostructures. Nanofabrication techniques based on self-assembly processes have already proved their usefulness in the creation of OF sensors and biosensors, but many self-assembly processes are still unexplored with OFs [4]. So far, the assembly of colloidal crystals has surely given the most consistent contribution, especially because it can count on a consolidated assembly process and on the post-assembly modification processes provided by NSL. Hierarchical structures based on nanospheres with different diameters [106; 107; 108; 109], as well as on the assembly of anisotropic particles [110], could offer new degrees of freedom in pattern design and open new opportunities related to the NSL development, as shown by the examples reported in Figure 7.  
A less exploited and therefore potentially capable of opening new scenarios is also the breath figure patterning. Great potentiality is promised by the DSA paradigm, which combines BCP self-assembly with patterns obtained by classical lithographic techniques, which surprisingly has only been marginally explored on OFs so far. Another key limitation in self-assembly approaches relies on defect formation, which seems inevitable for all proposed techniques at least in the \"long-range\" scale.