Any ideas how? Ideally would like to see the brightness of the LED increase as the current goes up. I can settle for the LED lighting up when the slightest ua current is detected.

Thanks.

 

How about a bar of 10 LEDs lighting up? They make ICs that can drive such LED bars. I'm too pooped to do any looking for you though (I was out digging a sprinkler line in 100 deg F weather).

 

You'll need to look at where that 100ua meter is in your circuit and whether it's a true ammeter or one masquerading as a voltmeter.
If one side of the meter is at ground potential, this should be pretty easy. If the meter is floating, you'll need a current sensing amplifier.
The 10 LED chip Someonesdad referred to is the LM3915, available everywhere.
If you want LED intensity to vary with current, then you'll want to PWM the LED.

 

The LM3915 has a log output.
The LM3914 has a linear output. This is the one you want to use.
The LM3916 was designed for VU meters.

The LM3914N has been replaced with the LM3914N-1.
It works the same; but it is RoHS compliant, where the non-dash model was not.
Product info page: http://www.national.com/mpf/LM/LM3914.html
Datasheet: http://www.national.com/ds/LM/LM3914.pdf

 

I'll get my hands on a lm3914.

 

To get your 100uA signal translated to a voltage, you could run it across a 10k resistor; 100uA * 10000 Ohms = 1 volt. You would need a high impedance buffer for that signal, like an opamp set up as a voltage follower.

 

The LM3915 has a log output.
The LM3914 has a linear output. This is the one you want to use.
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Aw c'mon, I was only off by 1 that's only 0.026%