How do individual cells or proteins react to changing pH levels?
Researchers at the MESA+ Institute for Nanotechnology at the
University of Twente have developed a technique for 'gently'
adjusting pH: in other words, without damaging biomolecules. This
should soon allow them to measure the activity of a single enzyme
as a function of pH. The researchers will publish their findings in
the journal Lab on a Chip, which will devote a cover story to their
research in the December 21st issue.
Current methods for adjusting pH often have unpredictable
effects on the immediate environment of a cell or biomolecule.
Electrochemical reactions may occur that affect measurements, or pH
levels may not change rapidly enough. It is then difficult to
determine exactly what happens when the pH changes, or the
measurement itself may even produce unwanted side effects.
Researcher Rogier Veenhuis and his colleagues have developed a
technique which resembles traditional titration, but which is
controlled electrically and takes place using extremely small
volumes of solution. The greatest benefit of this technique is that
there are no undesirable side effects: it is a 'gentle'
approach.
Light intensity indicates pH
The researchers achieve this effect by using silicon nitride for
the base of the micro and nano fluid channel, under which an
electrode is attached. The electrode is given a negative charge
which results in protons being attracted to the nitride surface.
This causes the solution to become more basic and the pH rises. A
positive charge results in the opposite effect: protons are
released from the surface, the solution becomes more acidic and the
pH decreases. There is no reaction on the electrode as there would
be during electrolysis because the silicon nitride acts as an
insulator: this arrangement creates a kind of capacitor. Acidity
can be adjusted by 'fiddling with the knob' to change the
electrical current. The changes can be made visible by introducing
a fluorescent pH indicator to the solution: light intensity
reflects changes in pH.
This new method of titration takes place in extremely small
quantities of fluid; substances can be titrated in the attomol
range (10-18 mol). This should soon allow the
researchers to measure the activity of a single enzyme as a
function of pH.
The research was conducted by the BIOS Lab-on-a-Chip research
group of Prof. Albert van den Berg, who recently won one of the
three 2009 Spinoza Prizes. The research group is part of the MESA+
Institute for Nanotechnology of the University of Twente.
The article 'Field-effect based attomole titrations in
nanoconfinement' by Rogier Veenhuis, Egbert van der
Wouden, Jan van Nieuwkasteele, Albert van den Berg and Jan Eijkel
is available online and will be published as an 'inside cover'
story in the December 21st edition of the journal Lab on a
Chip.
