Improving the Selective Efficiency of Graphene-Mediated Enhanced Raman Scattering through Molecular Imprinting

Enhancement of Raman scattering signal through graphene is an important property that could be exploited for producing innovative sensing devices with advanced properties. Because the enhancement of Raman scattering is due to only a chemical mechanism, the amplification of the signal is lower than that one produced by excitation of localized surface plasmons. The combination of a highly selective technique, which is molecular imprinting, with graphene-mediated enhanced Raman scattering, represents a new synergistic approach that we have developed in the present work. The careful material design has allowed obtaining a porous composite embedding exfoliated graphene and molecular cavities specifically designed for recognizing Rhodamine 6G. The molecularly imprinted porous samples have shown a signal enhancement that increases as a function of the number of molecular cavities, which are also accountable for the molecular recognition properties. Environmental ellipsometric porosimetry has shown no substantial difference between molecularly imprinted and not-imprinted films confirming that the signal enhancement of the imprinted samples is due to the molecular cavities. Interestingly, the most efficient sample has shown a Raman enhancement per cavity that exceeds the value of 1 × 10¹² and a remarkable molecular selectivity allowing for a Rhodamine 6G signal amplification 4.5 higher than structural analogues such as Rhodamine B and methylene blue. The robust and flexible matrix ensures a good recyclability of the samples without lack of linear response. These results prove the great potential of molecular imprinting as a general strategy to provide selectivity to GERS-active substrates for a new generation of sensing devices.

Hard X-rays for processing hybrid organic-inorganic thick films

Hard X-rays, deriving from a synchrotron light source, have been used as an effective tool for processing hybrid organic-inorganic films and thick coatings up to several micrometres. These coatings could be directly modified, in terms of composition and properties, by controlled exposure to X-rays. The physico-chemical properties of the coatings, such as hardness, refractive index and fluorescence, can be properly tuned using the interaction of hard X-rays with the sol-gel hybrid films. The changes in the microstructure have been correlated especially with the modification of the optical and the mechanical properties. A relationship between the degradation rate of the organic groups and the rise of fluorescence from the hybrid material has been observed; nanoindentation analysis of the coatings as a function of the X-ray doses has shown a not linear dependence between thickness and film hardness.

Highly flexible silica/chitosan hybrid scaffolds with oriented pores for tissue regeneration

Inorganic/organic sol-gel hybrids have nanoscale co-networks of organic and inorganic components that give them the unique potential of tailored mechanical properties and controlled biodegradation in tissue engineering applications. Here, silica/chitosan hybrid scaffolds with oriented structures were fabricated through the sol-gel method with a unidirectional freeze casting process. 3-Glycidoxypropyl trimethoxysilane (GPTMS) was used to obtain covalent inorganic/organic coupling. Process variables were investigated such as cooling rate, GPTMS and inorganic content, which can be used to tailor the mechanical properties and hybrid chemical coupling. Structural characterization and dissolution tests confirmed the covalent cross-linking of the chitosan and the silica network in hybrids. The scaffolds had a directional lamellar structure along the freezing direction and a cellular morphology perpendicular to the freezing direction. Compression testing showed that the scaffolds with 60 wt% organic were flexible and elastomeric perpendicular to the freezing direction whilst behaving in an elastic-brittle fashion parallel to the freezing direction. The compressive strengths are about one order of magnitude higher in the latter direction reaching values of the order of 160 kPa. This behaviour provides potential for clinicians to be able to squeeze the materials to fit tissue defect sites while providing some mechanical support from the other direction.