Low power way to switch on MOSFET with ~100mV input singal?
Consider this circuit







simulate this circuit &ndash; Schematic created using CircuitLab

You can drop the +9 volts to +6v or maybe +4 or +3v.

The slewing of Q11 collector, from fully one direction to the other, may set the propagation delay. 

Headroom on Q2 and Q3 is marginal; you may need triple Darlingtons to create more headroom, to drive the NPN diode loads.