Up until now scientists have needed devices the size of rooms to measure polymer units. Researchers led by Prof. Dr. Jan C. Behrends and Dr. Gerhard Baaken from the University of Freiburg have developed a chip the size of a fingertip containing biological nanopores that determine molecule size with great precision. Developing this new system, which is a combination of biological and micro-technical components, involved a great deal of technical skill. The system has the same level of sensitivity as a chromatography device, but is much easier to handle and is also cheaper than the large devices. The chip has also the potential to be used for sequencing genes and for analysing other molecule classes.
The ingredients of creams and lotions would separate if they did not contain polyethylene glycol (PEG), a compound composed of repeating ethylene glycol units; the macromolecule is used in tablets as a drug carrier and enables the continuous release of the pharmaceutical substances contained in the formulation. Every year, hundreds of tons of polymers are produced worldwide. The production of pharmaceutical substances, amongst other things, is subject to strict regulations and chain length and mass distribution of products must be precisely controlled. Up until now, liquid and gas chromatography techniques have been indispensable tools for determining the size and sequence of the individual polymer units. However, chromatography devices are expensive and tend to fill entire rooms, which is why researchers and companies around the world have been working on the development of smaller and less expensive tools. “It would be good to have methods that are easy to apply, cheap and accurate, especially for molecules that need to be tested frequently,” said Prof. Dr. Jan C. Behrends from the Institute of Physiology at the University of Freiburg. Working in cooperation with the Laboratory for Chemistry and Physics of Interfaces led by Prof. Dr. Jürgen Rühe in the Department of Microsystems Engineering (IMTEK), Behrends has brought the fields of biology and microsystems engineering together. This has resulted in the development of a chip the size of a fingertip on which the researchers arranged biological nanopores that serve as sensors for determining the size of molecules; the nanopores were then combined with a system of microelectrodes.
Biological pores are channel proteins contained within cells. Their function is to transport ions and other molecules across membranes. Bacteria contain many transmembrane proteins, which differ from each other in pore diameter and other molecular characteristics. They are an absolute treasure trove for researchers who are able to technically exploit their potential. The chip developed by Behrends and Dr. Gerhard Baaken, a scientist in Dr. Rühe’s department, consists of a glass plate with sixteen tiny cavities arranged on an area of one square millimetre. Each cavity is covered with a tiny synthetic cell membrane containing an alpha haemolysin molecule, a protein produced by staphylococci to destroy red blood cells in infected organisms. If a polymer gets into one of the channel proteins, the channel is blocked for a fraction of a second, which in turn leads to changes in the membrane’s ability to transport ions. The researchers can therefore use special microelectrodes for measuring changes in the system’s electrical conductivity. “Our measuring method is extremely sensitive and even allows us to detect the presence of a single molecule and derive the number of units of the polymer trapped in the channel,” said Baaken.
The theory behind the innovative chip sounds rather simple. However, the development of the chip has not been a trivial matter. “The work relating to the technical aspects of the chip amounted to an art in itself,” said Behrends. He has been concentrating on merging biology and technology for more than ten years and has achieved good results. While working at the University of Munich, one of his many achievements involved transferring the patch clamp method to a planar chip. When he moved to Freiburg around three years ago, he met Prof. Rühe from the IMTEK whose openness and expertise has contributed enormously to the development of the innovative chip. Meeting Prof. Rühe and starting a collaborative project with Rühe’s research group was an enormous piece of good luck for Behrends. He is full of praise for Baaken’s interdisciplinary commitment and in particular for his achievements in establishing the technology behind their joint chip project. Baaken has been intellectually as well as physically connected with Rühe’s laboratory at IMTEK and Behrends’ Institute of Physiology for around three years now. The stability of the silver electrodes in the chip matrix was one of the major challenges the researchers faced. “To ensure that electrodes do not polarize over time and become instable, the material used needs to be highly dense and have a relatively large surface,” said Baaken explaining that they had to produce a surface with nanoscopic pores as well as finding a reproducible way to do this.
Prof. Dr. med. Jan C. Behrends
Institute of Physiology
Tel.: +49 (0)761/ 2035 146
Fax: +49 (0)761/ 2035 147
Dr. Ing. Gerhard Baaken
University of Freiburg
Department of Microsystems Engineering (IMTEK)
Laboratory for Chemistry and Physics of Interfaces (CPI)
Tel.: +49 (0)761/ 203 - 5145
Fax: +49 (0)761/ 203 - 7162