check this articles may be help you

https://www.jstage.jst.go.jp/article/bpb/32/4/32_4_578/_article/-char/ja/

Hi Chen Chien Hua ,

Yes you can do it one by one but it is a tedious job.

The best way is to use the same well-plate in which cells are growing.

What you have to do is to add just the same amount of Griess Reagent (1:1)to each well and follow the procedure for plate reading.

I hope you got your answer..........

Thanks and Good luck.....