measuring microampere current without noise
Take a look at the MAX4239...

http://www.maximintegrated.com/en/products/analog/amplifiers/MAX4239.html

It is an "auto-zero" type amplifier that is perfectly suited to measuring tiny voltage differentials (and hence tiny currents across a shunt resistor) very accurately with amazingly low noise. 

For bench-top use, you can buy the uCurrent...

https://www.adafruit.com/product/882

...which is the above part made into a product. It has a MAX4239, battery, and shunt resistors all on a well designed board with nice connectors. It lets you easily see nanoamps on your scope. 

I know StackExchange frowns on product recommendations, but I consider the uCurrent to be a tool class like an "oscilloscope" or "voltmeter" rather than a specific product. If you ever need to accurately measure 1mA or less, buy or build one.