New method for creating biological sensors on silicon chips

30 October 2014

Scientists from Chile and Germany  have developed a novel process to layer two readily available chemicals on a silicon substrate to mimic a cell membrane and give the ability to link biological processes to electronics.

Artificial membranes mimicking those found in living organisms have many potential applications because they offer the possibility of containing membrane proteins, which could be used for detecting toxins, diseases and many other biosensing applications. 

The importance of this type of dual-layer membrane to life is hard to overstate. It is a principal component of all living cells, separating distinct spaces within cells and defining the 'walls' around cells. It serves many physiological processes, protecting genetic material, regulating what comes in and out of cells, and maintaining the function of separate organs.

Described in The Journal of Chemical Physics, this is the first time anyone has ever made an artificial membrane without mixing liquid solvents together. And because the new process creates membranes on silicon surfaces, it is a significant step toward creating bio-silicon interfaces, where biological "sensor" molecules can be printed onto cheap silicon chips holding integrated electronic circuits.

"Our idea is to create a biosensor that can transmit electrical signals through the membrane," said María José Retamal, a PhD student at Pontificia Universidad Católica de Chile and first author of the paper.

Retamal and her colleagues chose silicon because of its low cost, wide availability and because its 'hydrophobicity' (how much it repels water) can be controlled chemically, allowing them to build membranes on top.

They evaporated the chemical chitosan onto the silicon. Chitosan is derived from chitin, a sugar found in the shells of certain crustaceans, such as lobsters or shrimp. They chose this ingredient for its ability to form a moisturizing matrix. It is insoluble in water, but is porous, so it is capable of retaining water. Next they evaporated a phospholipid known as dipalmitoylphosphatidylcholine (DPPC) onto the chitosan-covered silicon substrate.

 
Layers of chitosan and DPPC deposited on silicon mimic cell membranes and add the ability to interface with computer chips. Credit: S.E.Gutierrez-Maldonado/FCV

The researchers then showed that these chemicals formed a stable bilayer, the classic form of a membrane. Spectroscopy showed that these artificial membranes were stable over a wide range of temperatures.

More work is needed to standardize the process by which proteins are inserted in the membranes, to define the mechanism by which an electrical signal would be transmitted when a protein binds its target and to calibrate how that signal is detected by the underlying circuitry, Retamal said.

Reference

MJ Retamal, et al. Towards bio-silicon interfaces: Formation of an ultra-thin self-hydrated artificial membrane composed of dipalmitoylphosphatidylcholine (DPPC) and Chitosan deposited in high vacuum from the gas-phase. The Journal of Chemical Physics DOI: 10.1063/1.4894224.