Developments of Yoctowell Cavities as a Nano and Bio-technological Tool

Abstract

Biological energy conversion and molecular recognition processes normally occur on a nanoscale level. The PRCs (photosynthetic reaction centres) is one of the best example of energy conversion, which are equipped with protein helices in combination with ATP, porphyrins, and co-enzymes; such machinery of life was developed biologically in a long-term evolutionary process on a 1-10 yoctoliter (1 yL=10 -24 L or 1 nm 3 ) scale [1]. So far, scientists have been successful with the isolation and analysis of such systems but not with reproduction of the working molecular apparatus. We have introduced a simple system of so-called "yoctowells", rigid molecular monolayers made of α,ω-diamido bolaamphiphiles around a porphyrin island of yoctoliter-sized volume, on to gold electrodes, colloidal gold particles, silica particles and magnetic silica particles (Figure 1The main motivation to work with membrane gaps, such as yoctowell systems, instead of proteins is their simplicity it would make it simpler to answer biological questions, which are very difficult to approach in complex biological systems. Designer yoctowells which may act as nano-and bio-technological tools via manipulating the interactions between guest molecules and the walls of the yoctowell gap were thought to offer an opportunity for studying intermolecular interactions [3]. The inner properties of the yoctowell can be fine-tuned by the nature of the bolaamphiphile monolayers (hydrophobic, hydrophilic and peptidic) to exploit the resulting electrostatic effects, which can be used to discriminate between substrates. The importance of these yoctowell cavities is the use of porphyrins as an optical sensor by means of absorption and emission in the host-guest event. Herein, we give a brief description of the developments of yoctowells and their usefulness in various technological applications. The stability of yoctowells can be confirmed by size exclusion fluorescence quenching experiments. Large molecules over 20 Å in diameter cannot enter into the gaps whereas molecules with size proportionate with that of the yoctowell gaps are able to enter and quench the fluorescence of the base porphyrin, whose role is both as a structural element and as a fluorescence reporter. In 2000, fluid and rigid yoctowells had been developed and used as carriers for heterodimers of porphyrins on gold platelets and colloidal gold nanoparticles [4][5][6][7][8]. However, one drawback of gold-based systems is plasmon absorption, which can cause problems (quenching the florescence of the base porphyrin) in photophysical studies.We then prepared yoctowell systems on photoinactive, amino-coated, silica particles. These particles are colorless, keeping the porphyrin fluorescence intact, and can be prepared using a variety of conditions with different coatings [9]. We have optimised these conditions and prepared particles with a perfectly smooth surface and uniform diameter of 100 nm. The rigid yoctowells were prepared in two steps via self-assembly; first, covalently attachment of activat...