A vertical molten sulfur pump assembly includes a pump motor disposed in a top portion and an impeller disposed in a bottom portion, within an impeller casing. A pump inlet is disposed at the second end below the impeller casing. The vertical molten sulfur pump assembly is configured to pump molten sulfur into the inlet and upwards through a discharge passageway by rotation of the impeller. A vibration sensor and a temperature sensor are disposed on an external surface of the bottom portion, on or proximate to the impeller casing and the pump inlet. A temperature sensor is configured to measure a temperature of the molten sulfur proximate to the pump inlet. A vibration sensor includes a substrate comprising a polymer and a resonant layer, and resonant layer includes an electrically conductive nanomaterial and is configured to produce a resonant response in response to receiving a radio frequency signal.