 Fabrication
| Another matrix commonly used is Decyl
Methacrylate. This material is hydrophobic, which allows
the use of hydrophobic dyes and ionophores. An indirect
sensing scheme is often used with these PEBBLEs which
involves an "optically silent" ionophore,
which is very selective for its analyte, but not
fluorescent, and |
 |
| a fluorescent pH indicator. The sensing
is accomplished by an ion exchange, where the analyte
(say a sodium ion, which has a +1 charge) comes in and
binds to the ionophore. But, to keep charge neutrality,
a hydrogen ion must leave, which changes the pH inside
the PEBBLE (and thus changes the fluorescence of the pH
dye. |
To keep these PEBBLEs from sticking to each other,
polyethylene glycol (PEG) is used as a steric stabilizer
in the formulation.These SEM images show the dramatic
difference between using PEG and not!
 
Decyl Methacrylate formulations With PEG (left)
and Without PEG (right - large chunks
~ 50 microns in size). |
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