lm741 operational amplifier
There is no such a thing like "minimum input voltage". Opamps are linear devices and will amplify any input voltage.
However, because of temperature drifts, bla, bla ,bla .. with opamps like 741 one should avoid using them with voltages below "certain" level. I wouldn't use 741 for amplifying signals below,say, 1mV. Try to employ more contemporary common opamp and (LM)358 (bipolar) wouldn't be wrong choice as it can operate of single supply starting from 0V at the input..
Other option would be CA3140(FET), also working very well with single supply and behaving good at 0V input..