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Natural nanoscale surface potential of clinochlore and its ability to align nucleotides and drive DNA conformational change

Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, P. Porta San Donato 1, 40126 Bologna, Italy, e-mail: giovanni.valdre{at}unibo.it

The knowledge of the surface properties of minerals is of great importance in understanding both basic and applied technological issues, such as for example liquid/surface interactions, microfluidity, friction or tribology and biomolecule self-assembly and adhesion.

Recent developments of scanning probe microscopy (SPM) have widened the spectrum of possible investigations that can be performed at a nanometric level on the surface of minerals. They range from physical properties such as electric field topological determination to chemical and spectroscopic analysis in a variety of environments (air, liquid, gas and vacuum).

Here we show that the surface potential characteristics of chlorite can be assessed by working in electric force microscopy (static and dynamic EFM) and in Kelvin probe modes of operation. In particular, this work reports electrostatic force simulations through finite element analysis and electric force microscopy observations of cleaved surfaces of chlorite before and after nucleotide and DNA deposition. As expected, chlorite presents a surface potential anisotropy at the nanoscale related to its peculiar crystal chemistry. A freshly cleaved surface is usually made up of positively and negatively charged layers with a lateral extent of a few nm. After nucleotide deposition at room temperature (25 °C) and atmospheric pressure, spontaneous formation of ordered structures and micrometre long aligned segments of nucleotides occur because of topologically driven electrostatic interaction. The surface potential anisotropy is also able to order and stretch larger molecules such as DNA filaments thus inducing a natural change in its conformation.

The relevance of these results has to be considered in the context of the possible role played by the surface of mixed-oxide minerals, such as chlorite which is rich in Brønsted and Lewis sites, in the prebiotic synthesis and polymerization of biomolecules with important implications for earth and life sciences. The ability to control the binding of biomolecules onto non-conductive solid substrates with atomically flat boundaries has also important and promising applications in nano-biotechnology such as in microelectronics, microarrays and sensors.

Key-words: clinochlore, AFM, Kelvin probe, DNA, nucleotides.