A microelectrode assembly for in vivo neurotransmitter monitoring according to one embodiment of the present disclosure includes: a microelectrode part formed of a single strand; and a polymer coating layer surrounding the microelectrode part, wherein a portion of the microelectrode part may protrude from the polymer coating layer, neurotransmitters in vivo may be sensed by the protruding portion of the microelectrode part, and plasmonic nanostructures may be formed on the surface of the microelectrode part.