A Mayan-inspired DAPI fluorophore stabilized and enhanced through sorption on palygorskite

Abstract

DAPI (4′,6-diamidino-2-phenylindole, di-hydrochloride) is a photoactive dye used as a fluorescent marker for nucleic acids, due to its high affinity for the major groove in the DNA double helix. By following a Mayan-inspired recipe (namely grinding, heating and washing in H2O), the DAPI molecule was fastened to the microporous framework of palygorskite – a clay mineral used to produce the famed Maya Blue pigment, whose fibrous crystals are carved by surface grooves similar in size to those of DNA – in order to obtain a newly designed fluorescent material. This hybrid composite was investigated with a multi-analytical approach, which includes FE-SEM-EDS, BET-specific surface area (SSA)/micropore volume measurements, thermogravimetry, UV–vis, fluorescence and FT-IR spectroscopies. Supramolecular interactions form between the clay and the dye already after grinding, apparently involving a two-step binding process. Evidence is found of an incipient, electrostatic interaction between cationic DAPI and the negatively charged surface of the palygorskite fibrils, which then evolves in H-bonding interaction between the dye amine groups and the zeolitic and/or structural water in the clay surface grooves. Heating and washing in H2O seemingly deteriorate the composite morphology and stability, jeopardizing – rather than strengthening – the previously formed host/guest interactions. This hybrid composite, with remarkable stability and appreciable quantum yield, is potentially fit to be used as a low-cost, fluorescent material for applications such as spectrum manipulation technologies, sensors, optical devices, imaging and design-targeted drug-delivery systems.