Buffer output of operational amplifier
Your resistors do nothing but make the op-amp drive a bit more current. You can either capacitively couple it, or bias the op-amp up to a few volts by putting a divider on the non-inverting input. 

Vgs(th) is 0.8 to 3V for the BS170 and your op-amp circuit has a DC gain of 1.0 from the non-inverting input. So you can try 4 volts on the non-inverting input. 

Bear in mind that the threshold will vary from part to part, though you will not see that in the simulation. For this reason, an NPN BJT emitter follower is considerably more predictable.