Controlling pH in microfluidics could allow the activity of single enzymes to be measured, say Dutch scientists.

The abiltiy to vary pH in fluidic systems is useful for studying single cells in bioassays or cell-based research, but current methods are slow or produce unwanted side-products. Jan Eijkel and colleagues at the University of Twente, Enschede, The Netherlands, have used an external electrode to adjust the number of positive ions in the solution. 

One plate is the conducting solution and the other is a metal plate and they are separated by a silicon nitride layer, explains Eijkel. Applying a negative voltage to the metal plate attracts positive ions to the nitride surface - removing them from the solution and making it more basic. Reversing the charge has the opposite effect - making a more acidic solution. 

 

An external electrode is used to move positive ions in and out of the solution

Eijkel says that their method would be useful for cell-based research as it does not need electrochemical reactions that can often change the cellular environment in an unpredictable way. It has the potential to 'measure the activity of a single enzyme as a function of pH, if scaled down further,' suggests Eijkel.

 

Piotr Garstecki, an expert in microfluidics at the Polish Academy of Sciences, Warsaw, is impressed: '[the work] takes true advantage of the geometrical confinement of the channel in a surprising way, which seems quite a natural idea after the fact.'

 

The team are now working on improving the quality of the system to enable higher applied fields and control of larger numbers of protons, says Eijkel.

 

Christina Hodkinson

 

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