rhizosphere microelectrodes

[Marion Schoettelndreier]

I need some help to find the right microelectrode. 
I would like to measure pH in the rhizosphere of roots. 
The pH will be measured in a agar sheet which is applied on a 
root-soil surface. Does someone know where to get microelectrode 
with a diameter of max. 1mm?

Thanks for your help!

-- 
Marion Schoettelndreier
Plant Ecology
Lund University, SWEDEN
Marion.Schottelndreier at planteco.lu.se
http://www.planteco.lu.se/pi/marion.htm