Carbon dots are an emerging class of carbon-based nanostructures produced by low-

cost raw materials which exhibit a widely-tunable photoluminescence and a high quantum yield.

The potential of these nanomaterials as a substitute of semiconductor quantum dots in

optoelectronics and biomedicine is very high, however they need a customized chemistry to be

integrated in host-guest systems or functionalized in core-shell structures. During the lecture

the recent advances of the sol-gel chemistry applied to the C-dots technology will be illustrated.

The surface modification, the fine tailoring of the chemical composition and the embedding into a complex

nanostructured material are the main targets of combining sol-gel processing with C-dots

chemistry. In addition, the synergistic effect of the sol-gel precursor combined with the C-dots

contribute to modify the intrinsic chemo-physical properties of the dots, empowering the

emission efficiency or enabling the tuning of the photoluminescence over a wide range of the

visible spectrum.

Green photonics describe any device or process that uses photonics in a sustainable way, yielding an environmentally sustainable outcome and improved public health. Distinct main areas were selected as targets towards green photonics, including solid-state lighting, photovoltaics, optical communications and sensing with the common goals of generate or conserve energy, and cut greenhouse gas emissions. Organic-inorganic hybrids lacking metal activator centers and doped with lanthanide ions (Ln3+, natural-based molecules or nanoparticles will be used as a key elements for the development of white light emitting LEDs (1), luminescent solar concentrators (2) and new luminescent QR codes multiplexed in colour with enhanced information storage capacity and the ability to sense temperature in real time (3,4).

Hybrid materials have been of interest to the materials community since the first contributions in that field. The development of hybrid sol-gel coatings during the last years turned out to be the highly demanded by the industrial sector, due to their capability to induce new properties in a wide variety of materials. The possibility of incorporating organic dopants into transparent matrices allowed the preparation of many different hybrid materials (including room temperature prepared hybrid metal oxides particles) that find application in the field of optics and other related applications. These new materials were mainly applied as thin-films coating in whose porosity the dopant molecules are allocated or attached to the hybrid network. These matrices can be tailor made to design both, the properties of the matrix itself and the properties of the pore cage, in terms of pore size and chemical environment, which will have an important effect on the performance of the developed material.

The most representative contributions of the SGG@Madrid in the field of hybrid materials for optics and electrooptics will be presented: Hybrid coatings for applications as smart windows, materials that show high photostability under UV radiation as protection coatings, coatings for optical lenses and photochromic materials, biofilms created by the bacterium Pseudomona putida mt-2 for the fabrication of a variable light-transmission device, and nanosensors for space applications.

During the last 20 years, hybrid materials for optics and photonics have reached a quite mature situation, with some products already available in the market. However, many difficulties related to the replacement of existing technologies make it difficult to fully accomplish some of the new proposed challenges and developments. There is still much work to do in terms of multidisciplinary research in the areas of chemistry and physics to exploit this technical opportunity of creating novel materials that satisfy the requirements of a variety of applications and devices in which important contributions are expected in the coming years from novel approaches for hybrid functional sol-gel materials.

Different alternatives can be considered to increase the corrosion resistance of metals being the surface modification by deposition of coatings and especially by using sol-gel process one of the most suitable. This process is one of the key technologies to prepare efficient anti-corrosive coatings with well-known advantages, including relative low processing temperatures, good covalent bonding and strong adhesion to the substrate, a wide range of compositions and properties, etc.

Inorganic sol-gel coatings have been proposed as good barrier against oxygen diffusion. Coatings prepared from TEOS demonstrated to act as good barrier improving the oxidation resistance of stainless steels and other metals and alloys. However, the protective properties of these coatings against electrochemical corrosion are low due to the presence of residual porosity or micro-cracks that enable the access of the electrolyte to the substrate. In this sense, the use of hybrid organic–inorganic sol–gel coatings with interpenetrated networks effectively improved the performance of these coatings. In this case, the organic component provides ductility and facilitates the stress relaxation in the inorganic network; thus, it allows obtaining a drastic increase in thickness without cracking of coatings. In general, the control of the synthesis parameters, the incorporation of different organic monomers and inorganic nanoparticles allows obtaining materials with the desired properties like density, hydrophilic character and coatings which act as physical barrier. However, corrosive ions still can diffuse through micro-pores and attack the metallic substrate, producing their degradation when they are exposed to aggressive medium. Thereby, a recent trend is the development of sol–gel coatings doped with environmentally friendly inhibitors. The combination of hybrid silica coatings with systems based on cerium or other rare earths, or organic inhibitors are regarded as promising candidates to combine passive and active corrosion protection and self-healing ability.

Using a sol-gel process, it is possible to prepare transparent hybrid glasses that are rigid at room temperature, but soften and flow around 110ºC.  Combinations of mono-substituted alkoxysilanes and di-substituted alkoxysilanes give a range of viscosities, glass transition temperatures and consolidation temperatures.  This softening quality gives rise to “melting gels”.  The softening and rigidifying is reversible until the “melting gels” are heated above the consolidation temperature for 1 day, after which they no longer soften.  Applications for melting gels include hermetic coatings for corrosion protection [1], hosts for plasmonic nanoparticles [2], matrices for phase change materials, self-limiting electrospray films on contoured parts [3], and imprinted surfaces for water harvesting.

Metal nanoparticles display very interesting optical properties, related to localized surface plasmon resonances (LSPR), which give rise to well-defined absorption and scattering peaks in the visible and near-IR spectral range. Such resonances can be tuned through the size and shape of the nanoparticles, but are also extremely sensitive towards dielectric changes in the near proximity of the particles surface. Therefore, metal nanoparticles have been proposed as ideal candidates for biosensing applications. Additionally, surface plasmon resonances are characterized by large electric fields at the surface, which are responsible for the so-called surface enhanced Raman scattering (SERS) effect, which has rendered Raman spectroscopy a powerful analytical technique that allows ultrasensitive chemical or biochemical analysis, since the Raman scattering cross sections can be enhanced up to 10 orders of magnitude, so that very small amounts of analyte can be detected.

In this communication, we present several examples of novel strategies to employ nanostructured materials comprising gold nanoparticles embedded in porous oxides or polymers, as substrates for ultrasensitive detection of various analytes, including biorelevant molecules such as bacterial quorum sensing markers, which require the design of novel techniques for trapping them close to the metal nanostructures or to avoid signal contamination by larger biomolecules. Hybrid colloidal nanomaterials will also be introduced as SERS-encoded tags for cell identification and bioimaging.

Keywords: Plasmonics, SERS, Biosensing, Bioimaging

References

M.N. Sanz-Ortiz, K. Sentosun, S. Bals, L.M. Liz-Marzán, ACS Nano 2015, 9, 10489-10497.

G. Bodelón, V. Montes-García, V. López-Puente, E.H. Hill, C. Hamon, M.N. Sanz-Ortiz, S. Rodal-Cedeira, C. Costas, S. Celiksoy, I. Pérez-Juste, L. Scarabelli, A. La Porta, J. Pérez-Juste, I. Pastoriza-Santos, L.M. Liz-Marzán, Nature Materials 2016, 15, 1203-1211

In the quest for a more circular economy cellulose is expected to play a strategic role in replacing petroleum-based polymers. Increasing demand for cost-effective sustainable and high-performance materials makes nanocelluloses, which combine the properties of cellulose with the high surface area of nanomaterials, attractive for applications in sectors such as photonics, food packaging, flexible electronics or biomaterials. In particular, bacterial nanocellulose (BC) produced by microbial fermentation with the same molecular formula as plant-derived cellulose but with a higher degree of polymerization, purity and crystallinity has captured the interest of material scientists. 

We exploit BC exceptional features to create advanced materials. First, I will describe  an original route to attain a multi-nanoparticle millefeuille for a BC-layered construct (Figure 1) [1] and then I will present some BC potential applications in energy (thermoelectrics [2] and photovoltaics [3]) and health [4] (corneal bandage [5] and as cell culture supports [6])

Figure 1. Bacterial cellulose films with multiple functional nanoparticles in confined spatial distribution

References

[1] S. Roig-Sanchez, E. Jungstedt, I. Anton-Sales, D. C. Malaspina, J. Faraudo, L. Berglund, A. Laromaine, A. Roig, Nanoscale Horizons, 4, 3 (2019) 634.

[3] D. A.-Fatouh., B. Dörling, O. Zapata-Arteaga, X. Rodríguez-Martínez, A. Gómez, J. S. Reparaz, A. Laromaine, A. Roig, M. Campoy-Quiles, Energy & Environmental Science, 12 (2019) 716.

[4] J.P. Jurado, B. Dörling, O. Zapata-Arteaga, A. Roig, A. Mihi, M. Campoy-Quiles, Adv. Energy Mater. (2019) 1902385

[5] I. Anton-Sales, U. Beekmann, A. Laromaine, A. Roig, D. Kralisch, Current Drug Targets 20(8) (2019)808

[6] I. Anton-Sales, J. Christopher D’Antin, J. Fernández-Engroba, V. Charoenrook, A. Laromaine, A. Roig, R. Michael, Biomaterials Science 8 (2020) 2921

[7] T. Tronser, A. Laromaine, A. Roig, P.A. Levkin, ACS Appl. Mater. Interfaces 10 (2018) (19) 16260.

Monolithic materials are 3D architectures that can be prepared from inorganic, hybrid or composite systems. Applications are for instance in the fields of optics, sensing, insulation, energy. The lecture will be devoted to an introduction to the different strategies that can be used to obtain such material, from sol-gel molecular aproaches operating through alkoxide hydrolysis-condensation followed by solvent removal (drying, supercritical drying) to 3D controlled assemblyes of nanobuilding blocks reacting together and further thermal treatment. Control of the final microstructure and porosity will be discussed. Optical properties confered by the confinement of molecular dyes or nanoparticles in the monoliths will also be presented. Advantages and drawbacks of the different methods will be adressed.