accurate quantification of protein content and composition 
 has been achieved using isotope - edited surface enhanced resonance 
 raman spectroscopy . 
 synthesis of isotopomeric rhodamine dye - linked 
 bioconjugation reagents enabled direct labeling of surface lysines 
 on a variety of proteins . when separated in polyacrylamide gels and 
 stained with silver nanoparticles . 
 the spectral signatures reflect 
 the expected statistical distribution of isotopomeric labels on the 
 labeled proteins in the gel matrix format without interference from 
 protein features .