Perhaps you have to store energy in some capacitor and flash the LED at low duty cycle using e.g. low leakage buck (voltage step-down converter ) or maybe simply pulsed transformer.

Thank you Mr. Nikolay Pavlov

increase surface roughness, increase the force, use good ammeter to measure the current. light up low current LED, use capacitor, dim the room light to see the glow etc.

refer Article Significant role of CNT-ZnO core shell nanostructures in dev...