A new hybrid organic–inorganic material for sensing spermine (Spm) and spermidine (Spd) has been prepared and characterized. The material is based on MCM-41 particles functionalized with an N-hydroxysuccinimide derivative and loaded with Rhodamine 6G. The cargo is kept inside the porous material due to the formation of a double layer of organic matter. The inner layer is covalently bound to the silica particles, while the external layer is formed through hydrogen and hydrophobic interactions. The limits of detection determined by fluorimetric titration are 27 µM and 45 µM for Spm and Spd, respectively. The sensor remains silent in the presence of other biologically important amines and is able to detect Spm and Spd in both aqueous solution and cells.

A new approach to describe the composition of Maya blue (MB), an ancient organic− inorganic hybrid material, is presented. It is based on the analysis of attenuated total reflection-Fourier transform infrared (ATR-FTIR), Raman spectroscopy, UV−visible (vis) spectroscopic, and electrochemical data for indigo and dehydroindigo plus palygorskite hybrids, including a novel methodology using electrocatalytic effects on the oxygen reduction reaction. As a result, it is concluded that MB results from the tautomerization of indigo-to-indigo hemienol and the subsequent oxidation of these isomeric forms to dehydroindigo, all associated with the palygorskite clay framework, at temperatures above 100 °C. This model is also consistent with 13 C NMR data on indigo plus sepiolite hybrids. A consistent set of thermochemical parameters is obtained from ATR-FTIR, solid-state electrochemistry, and UV−vis diffuse reflectance spectra for the successive isomerization and redox tuning processes experienced by palygorskiteassociated indigo.