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La plataforma permanente Atomium Culture reúne a las universidades, periódicos y empresas más prestigiosos de Europa para promover el flujo del conocimiento más allá de fronteras, entre sectores y hacia el público en general.

Molecular Polymer Brushes as Smart Nanovalves

Por: | 12 de septiembre de 2013

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By Szczepan Zapotoczny, Jagiellonian University in Krakow

Corporations and individual consumers focus on the tremendous benefits of making computers and cell phones ever smaller and more efficient. Less public attention has been paid to the advantages of ‘miniaturising’ sophisticated biomedical apparatuses and sensors. Full blood analysis from just a single drop; detection of traces of dangerous explosives or toxic substance in the environment; and non-invasive and controlled delivery of therapeutic substances are just a few examples of such benefits of miniaturisation.

The studies conducted by Professor Szczepan Zapotoczny’s group, from the Jagiellonian University in Krakow, follow the miniaturisation trend and focus on molecular-sized brushes that can be used for a variety of purposes on very small scales. Similar in form to conventional toothbrushes, these small brushes have bristles with lengths on the level of nanometres (one millionth of a millimetre). Thanks to unique properties of the brush architecture, these dense assemblies of molecular chains, tethered by one end to a surface, serve as vital components of miniature instruments, also known as micro- or nano-devices. This micro-brush technology is very versatile and may be applied, for example, to lubrication of joint implants or controlling adhesion of bacteria and cells to various surfaces. This is particularly important for the fabrication of miniaturised biosensors capable of detection of, for example, dangerous pathogens in very small amounts of biological material. 

What about the micro-brush architecture allows for such a wide assortment of applications? Polymer brushes composed of thermoresponsive chains may collapse and stretch in response to even small changes of temperature around a certain critical value. By tethering such brushes to the very narrow (a few tens of nanometres) opening of a microcontainer, one can, for instance, open and close the container’s ‘mouth’ by simply varying the temperature. This smart ‘hairy valve’, as it is known, with its opening mechanism, is very convenient at small dimensions, where application of caps or mechanical valves is very difficult. Such designed systems enable researchers and medical practitioners to deliver very small amounts of active (bio)molecules, in precisely controlled, spatially confined conditions.

What’s more, the brush nanovalves may be easily applied to an array of microcontainers that can be individually addressed (heated and cooled), similar to small diodes in LED flat panels that can be selectively switched on and off producing an image. The appropriate matrices may be formed on a large scale using electrochemically modified surfaces of aluminium, which creates densely packed microcontainers with openings as narrow as 30 nanometres. On such a surface, the thermoresponsive brushes are grown, covering the pores’ outlets and forming smart nanovalves. Once the temperature is increased above 32°C, the containers may be loaded with selected molecules (see Figure 1 below, showing the valves open) and subsequently sealed by lowering the temperature (valves closed). Such a loaded matrix does not leak, and the substance is released only on demand, upon little heating. The behaviour can be fully reversed and the matrix easily reloaded if necessary.

Such two-dimensional delivery systems may find applications in the fabrication of miniaturised biosensors. Those miniaturised devices can lower the limit of detection (the lowest possible measurable amount of a substance) and speed up various biomedical analyses; significantly improve the screening of molecules for new drugs or in forensic investigations; and be useful in many other applications in chemical syntheses and sensing.

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Figure 1. Side view of the array of microcontainers equipped with thermoresponsive polymer brush nanovalves. (A, B) Molecules (green circles) are loaded into the containers by increasing the temperature above 32°C; (C) nanovalves are closed by lowering the temperature below 32°C; (D) molecules are released when temperature is increased.

Smaller very often means better, especially where the weight of our portable electronic devices is concerned. The ongoing studies on nanometre-sized molecular brushes may also contribute to a higher quality of life in the near future, by improving medical diagnostics or detection of hazardous substances in the environment.

 

Szczepan Zapotoczny
Jagiellonian
University in Krakow
www.atomiumculture.eu

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