Hi Heba,

from 'googleing' I have learned  that you will image the distribution of proteins on a membrane substrate. I assume that the additional mass coverage of the proteins is far small relative to the areal mass of your membrane. Doing this imaging by x-ray is a very bold task.

Furthermore your membrane molecules as well as your proteins  preferably consist of low atomic number atoms; so their x-ray attenuation is very small.

You have seen that even a five minutes exposure does not really help.

In order to increase attenuation sensitivity of the x-rays and therefore increase the image contrast  with respect to your sample system, you have to go the very small voltage values of your x-ray tube. On the other hand the maximum  mA setting (tube current) of the tube will also go down, when decreasing the voltage (this is a property of the electron optics in the tube). So you have to increase the exposure time further on.

Good luck.

By the way, is there a way to couple high atomic number atoms to your proteins? (like 'staining' of special cells). So you will significantly improve the x-ray attenuation associated with your proteins and with that increase the protein contrast relative to the membrane.

A further tip1: please remove all filters at the exit window of your x-ray tube. They preferably kill the low energy x-ray photons which you urgently need.

Further tip 2: please expose only your net menbrane (keep the exposed field of view as small as possible) in order to avoid any unneccessary multiple x-ray scatter contribution on to your x-ray image. X-ray scatter will decrease your image contrast .