All-Oxide Raman-Active Traps for Light and Matter: Probing Redox Homeostasis Model Reactions in Aqueous EnvironmentAll-Oxide Raman-Active Traps for Light and Matter: Probing Redox Homeostasis Model Reactions in Aqueous Environment

摘要

Developing new tools to investigate chemical reactions under real working conditions is a hot topic in many research fields~([1]) Vibrational spectroscopy (infrared and Raman) can provide insightful information about intra- and interatomic bonds and physico-chemical processes dynamics (redox and acid-base reactions, conformational changes, etc.). This capability offers several advantages over other ultra-sensitive techniques like fluorescent tags or mass-based sensors,for example in terms of chemical specificity and low invasiveness. However, in the case of reactions taking place in aqueous environment, like biological or biomimetic processes, the usefulness of infrared spectroscopy is severely limited by the strong contribution of water vibrational modes, that can overwhelm the analyte signals. In particular, the -OH stretching and bending modes can mask most of the spectral information about proteins or small biomolecules. Due to its relative insensitivity to water, Raman can be a valid alternative to IR, yet the very low Raman cross-sections of many analytes restrict the range of application of this technique to few cases involving resonant chromophores or labelling Raman reporters. Surface enhanced Raman scattering (SERS) takes advantage of surface plasmon-polaritons to increase the Raman cross-section of analytes that are either physisorbed or covalently linked to metal nanop articles. ~([2]) This coupling is the key factor to achieve ultrasensitive detection of the analytes and real-time monitoring of their concentration, but in most of the cases inherently introduces a strong perturbation to the system under analysis. The intense electromagnetic fields generated and dissipated through radiative~([3]) and non-radiative (heat)~([4]) channels in a typical SERS experiment can significantly alter both structure and reactivity of biological analytes (e.g. by promoting protein denaturation and/or interfering with chemical reactions involving charge transfer or, in general, any complex pathways).~([5]) Analogous effects can also originate from the chemical conjugation of the analyte with colloidal nanoparticles used as SERS-active substrates, which can be directed or mediated by means of linker and spacers.~([6]) In both the cases, denaturation of the analytes and/or passivation of some of their reactive moieties are unavoidable shortcomings.