ORDERED PARTICLE ASSEMBLIES AND HYBRID THIN FILMS FOR PLASMONIC (BIO)SENSING, OPTICAL WINDOWS AND ELECTRODES
The application of plasmonic metal NPs for detection through the exploitation of their optical properties has become extremely popular, either based on plasmon shifts due to refractive index changes when a biomolecular recognition process takes place near the NP surface (LPSR-based sensors), or on the direct identification of the analyte through its Raman scattering fingerprint when adsorbed onto it (surface-enhanced Raman scattering, SERS, sensors). Most of these new biosensors require the ordered assembly of NPs onto substrates in order to ensure high detection limits, safety and reproducibility in multiple tests. Thus, it is interesting to develop flexible methods that allow nanostructured assembled metallic substrates to be obtained with the possibility of tuning the fabrication conditions to achieve the requirements of any type of plasmonic sensor. In
this regard, self-assembly techniques compared to nanopatterning methods are attractive since the spontaneous organization of nanoscale building blocks allows for the large-scale, parallel production of periodic nanostructures at low costs. We focus our main attention on the development of ordered NP arrays and hybrid thin films of metal nanostructures with plasmonic response derived from block copolymer self-assembly/lithography techniques (BCL) by exploitation of the periodically ordered nanometric features of block copolymers (with typical dimensions of 5-50 nm) acting as templates. The size and shape of the copolymer microdomains and, thus, the resulting nanostructure can be controlled by manipulating the polymer chain lengths and composition, the volume fraction of each block, the temperature and the composition of the surrounding atmosphere. Their orientation and lateral ordering can be improved by different methods, such as graphoepitaxy, chemical patterning, applied electrical and shear fields, temperature or solvent annealing. Different strategies are used for controlling the location and distribution of nanoparticles following the nanostructured domain (in situ, ex-situ). In addition, the assembly of metal nanoparticles into ordered supercrystals is also exploited to achieve interesting collective plasmonic properties. These oriented assemblies can be obtained by slow solvent evaporation within micron sized cavities, so that the obtained supercrystals retain the shape of the templating cavities. The resulting nanostructured assemblies and thin films for sensing are devoted to the plasmonic detection of (bio)analytes such as proteins, enzymes, drugs or antibodies in complex fluids; pollutants in waste waters, and/or allergenic compounds in foods.