IRDye Labeling Kits come in 3 forms: HMW : The IRDye infrared dye bears an NHS ester reactive group that will couple to free amino groups and form a stable conjugate with high molecular weight proteins (45 - 200 kDa). LMW : The IRDye infrared dye bears an NHS ester reactive group that will couple to free amino groups and form a stable conjugate with low molecular weight proteins (15 - 45 kDa). Microscale : The IRDye infrared dye bears an NHS ester reactive group that will couple to free amino groups and form a stable conjugate with 100 µg of protein with molecular weight 14 - 200 kDa.