Product Description: Cy5-PEG2-TCO4 is a dye derivative of Cyanine 5 (Cy5) (HY-D0821) containing 2 PEG units. Cy5-PEG2-TCO4 utilizes its own TCO group to undergo an inverse electron demand Diels-Alder reaction (iEDDA) with molecules bearing Tetrazine groups.