More details are needed to sufficiently answer your question. How large is your polymer? If relatively small, MALDI-MS, AUC, or SEC could be used. Could also try a Bradford-type assay of your polymeric materials do not interfere. If the protein is an enzyme, monitor the activity to get an estimate of the concentration. Is the protein linkage to the polymer reversible? If so, you have many many methods you can try.

first, you should know about the amount of protein concentration before get it to immobilized into polymers and after the immobilization find the amount of protein present in washed. and by subtracting washed protein concentration from the initial one, then you are able to know what amount of your protein get immobilized. 

Dear Douglas A Mitchel, size of polymeric particles is 10 microns in diameter. Polymer was activated by epoxy-groups. Thus, bounding was performed with amino-group of protein. I'm worrying, that analysis of suspension cannot be made by MS, AUC or SEC.

Ashish, Yes, you are right. It's typically, what everybody does during protein immobilization. But in my case I do not perform immobilization, so I don't know protein concetration before and after. That's the problem. 

There are some other orthogonal approaches that might be amenable to your situation without knowing any other background information.  If there's no nitrogen content in the polymer then you might consider Kjeldahl analysis.  If the protein has a specific protease site then you might clip off a fragment form the each bound protein molecule and then assay the solution by numerous methods such as HPLC, colorimetric, etc.  If there's an antibody against the protein then you might try enzyme linked immuno assays that can be very specific and sensitive as long as the epitope is available and not denatured.  If the immobilized protein can bind a labeled (fluorescentt, radioactive) ligand then that can be quantified by solid or liquid phase assays.  There are other strategies but perhaps this is a start as I may not have enough information to suggest the best compatible method.  

Our primary approach is to monitor protein concentration before and after addition to the resin. We use Bradford, UV, or SDS PAGE to do this, but most often Bradford. We do characterize our proteins activities on resin as well as cofactor binding, but have never used this to quantify the amount. 

Article Functional chromatographic technique for natural product isolation

Thank you colleagues, for suggestions!

I agree with Chapman. Bradford is probably the best options. If you expect very low protein concentrations tray Lowry method (it is more sensitive).

I use Bradford.