hi everybody , i am working on my graduation project that measures the electrical coductivity of liquids in small scales ( like nanosiemens/cm ) by using arduino . i searched for a specific probes that can be used in this project but i didn't find any . so any one can help me please ..... and thanks in advance 
What are you looking for ? Just the probes ?
Do you want to connect the probes to an Arduino ? How ?
What kind of probes ?
Normally resistivity of liquids is measured with low voltage ac to reduce the effects of polarisation,
and when the currents are small you will have to worry about stray capacitance which will also allow
small currents to flow with ac. So low frequency ac is best
The simplest way I know to get a rough guide to current flow over a wide
dynamic range is to put the current through a diode and measure/amplify the diode voltage
using a high input impedance op-amp. The voltage is logarithmically related to the current.
The voltage depends also on diode temperature though, and although you can compensate its still
only a rough guide - good enough to select a range for more detailed measurement.