Complex I is composed of over 45 different proteins. If you don't mind having all the proteins in the assay, you might be ok with the Abcam assay kit. It is colorimetric though. Here's the link to the assay:

http://www.abcam.com/complex-i-enzyme-activity-microplate-assay-kit-ab109721.html

Respected Madam,

Thanks alot for your valuable suggestion. I think it will help me to design my research work.

With regards,

Amarendranath.

Hi Amarendranath,

If you would like to check overall Complex I activity, you might consider doing it with respirometric analysis, either in your lysates or isolated mitochondria. Main idea is adding substrates which supply electrons to Complex I and compare the oxygen consumption between your samples.

We used respiration rates to assess Complex I and II activities.

This paper might be helpful for you:

http://www.sciencedirect.com/science/article/pii/S0531556505002305#

Regards