If you are referring to a quartz microplate, then I agree with Michael Weller that you should try washing it with SDS and rinsing it thoroughly afterwards. Alcohol might also work. If that is insufficient, you could use chromic acid, with due safety precautions. That will remove all organic residues, but is somewhat dangerous to work with.

If you are referring to a plastic plate, do not try to reuse it. The optical surface is delicate and easily damaged, after which it will not give good results.

Most 96-well plates should not be treated with solvents. Therefore, a surfactant solution would be better from my point of view. SDS is very efficient but might interfere with your assay afterward if not removed carefully. Tween 20 is a more biocompatible option. In any case, the cleaning might take a while. 12 hrs at 37 °C would be a good start. Finally, the plate should be rinsed with deionized water several times.

If you are referring to a quartz microplate, then I agree with Michael Weller that you should try washing it with SDS and rinsing it thoroughly afterwards. Alcohol might also work. If that is insufficient, you could use chromic acid, with due safety precautions. That will remove all organic residues, but is somewhat dangerous to work with.

If you are referring to a plastic plate, do not try to reuse it. The optical surface is delicate and easily damaged, after which it will not give good results.

I was referring to plastic plate... When I asked that question to people giving technical help, they said,  cleaning can be done with 25% NaOH solution but we are not 100% sure, so I couldn't be sure as well.

I have plates but in limited number... It would be good If I could efficiently re-use them..

Thank you!

I would not like to be the one to have to clean 96-well plates with 25% (about 6 M) NaOH! Extreme care would be needed to avoid splashing any of this highly caustic solution on oneself or the surroundings. Try the detergent or alcohol method first. Then you can just dump the solution out in the sink. You can dispense the cleaning solution with a standard laboratory squirt bottle, or a multichannel pipettor. If you have a plate mixer, it might be effective to mix the solution around in the wells for a while. Be very careful not to scratch the underside of the plate or the bottom surface of the wells. Wash very thoroughly with distilled water and let the plates dry completely. Good luck.

That's why I couldn't go forward... Thank you so much for your advices.