I like the concept and the layout, but there are some weird things going on with
pixelation and colors, I think. It seems like you have scaled up a lot of the elements, which leads to pixelation. One thing you should try to do is generate your source material in very high resolutions and then scale down to get natural anti-aliasing for a smoother look.
If you look at places like the stem of the microscope (from the base to the upper body), you can see that there are small 1 pixel derivations in your lines. These kinds of small imperfections add up throughout the piece to give it a kind of sloppy look, and would probably be reduced if you were working at a high resolution and scaling down.
In terms of the coloring, I'm not really sure what to advise, but I would suggest starting with more natural colors and maybe fewer colors. Color balancing is really not very easy to do (I consult my partner for all of my artwork, as she has a very good eye for color - UI2's colors owe a lot to her refinements). Getting different elements to blend is not easy but color is a really big part of this. It can help to look at other things you like and steal color samples from them to see how different colors mix.