Atto Rho101 NHS ester is a derivative of the well-known dye Rhodamine 101 for coupling to bio-molecules such as DNA, RNA or proteins. Characteristic features of the label are strong absorption, extraordinarily high fluorescence quantum yield, and high thermal and photo-stability. The dye is moderately hydrophilic. ATTO Rho101 is a cationic dye. After coupling to a substrate the dye carries a net electrical charge of +1.