How do you measure nano volt order signals?
Getting less than 100-200nV in a frequency range from, say, 0.001Hz to 80Hz requires the use of synchronous demodulation techniques. The best monolithic op-amps (eg. LT1028) are around 0.9nV sqrt(Hz) voltage noise alone above their corner frequency so about 8nV for 80Hz BW, but their typical noise corner frequency is several Hz, so the 1/f noise will dominate unless your actual requirement is more like 20-80Hz. The current noise in the white noise range is around 5pA/sqrt(Hz) so it will cause equal contribution at 180 ohms source impedance (and the 1/f corner of current noise is actually well above 80Hz typically so the total noise will be much higher). There is also Johnson-Nyquist noise in the source resistance which can contribute significant amounts of white noise - at room temperature a 1000 ohm resistor has about 137nV RMS  noise in your 80Hz BW. 

An LT1028 has only 35nVp-p typical (90nV maximum) noise from 0.1Hz to 10Hz, so it's a possibility if you can relax the low frequency bandwidth requirement- it will be about double that from 0.1Hz-80Hz. That's p-p not RMS. 

If you can't relax the low frequency requirement, most of what you're concerned with will be called 'drift' since it's below the 1/f corner frequency corners of voltage and current noise of the amplifier. So called zero drift monolithic amplifiers are made with CMOS techniques and tend to  have relatively high noise at higher frequencies, typically over 1uV over the 80Hz BW, but little or no 1/f noise. So 100-200nV is not so easy without lots of 1/f noise! 

For such requirements, one approach is to try to modulate the source and use synchronous demodulation techniques (amplify, filter over a narrow band, use a phase sensitive detector, and low-pass filter) on the entire signal chain. In a lab the instrument that does this is called a "lock-in amplifier" - a rack mount instrument. The idea is to shift the signal bandwidth up out of the 1/f domain into the white noise region so that the noise over your 80Hz bandwidth will be minimized. 

A skilled designer can do significantly better than the monolithic parts (usually at a high cost in power, cost, input impedance, complexity and so on), but even so there are limits. For example, if the source impedance is low enough we can parallel 100 transistors at the input and get an order of magnitude improvement, in theory. There are other less brute-force methods such as running the transistors at higher current. 

For the most extreme requirements, cost and convenience no object, I would recommend using a low Tc (4.2K - that's Kelvin, not K ohms) SQUID. It's possible to get measurements with noise in the sub nV range, with extreme care. The resistance of the wires coming out of the cryostat will probably dominate the noise.