What kind of multimeter must i use inorder to measure currents of less than 1mA?

I have designed a yeast Microbial Fuel Cell using methylene blue as a mediator and Potassium ferricyanide as the cathodic solution, I had even supplied nitrogen in the anodic chamber in order to ensure anaerobic conditions.A Nafion Proton Exchange membrane was also used.Volume of both chambers was 350 ml and carbon cloth electrodes and Cu wires were used.After connecting it to a multimeter and turning the nob to 20 mA I could not get any readings even after a long period of time.Could someone suggest possible corrections or suggest a different multimeter which may help in measuring currents less then 1 mA.