Carboxyrhodamine 110-PEG4-DBCO is a PEG derivative containing a DBCO group and a rhodamine dye. DBCO enables copper free Click Chemistry and will react with azide-bearing compounds or biomolecules to form a stable triazole linkage. This reagent will be an ideal alternative to copper intolerant applications and can be used to label cells, tissues, biomarkers or nanoparticles.