In the example shown in Fig. , when n=0, the dye is yellow and provides sensitization to blue light. Dyes which sensitize in the blue are particularly important for AgCl emulsions, which lack intrinsic blue sensitivity. When n=1, the dye, a carbocyanine, is magenta and absorbs green light. For n=2, a dicarbocyanine, the dye appears cyan and sensitizes silver halide to red light. Extending the conjugation further produces dyes which absorb in the infrared, producing films useful for aerial photography and thermal analysis. Indocyanine green (ICG) is a Cy7 cyanine dye (Fig. ), negatively charged, amphiphilic, water-soluble but relatively hydrophobic, with a molecular weight of 751.4 Da, which was firstly developed by Heseltine and Brooker in Kodak Research Laboratories in 1955 and was secured by US Patent 2895955 in 1959 . But actually from 1956, with the collaboration of Dr. Fox in Mayo Clinic, this "new dye" has already been introduced for cardiac output measurement. In addition, Wheeler et al. has investigated its feasibility in hepatic function study in 1958. In 1959, ICG was approved by FDA for determining cardiac output, hepatic function and liver blood flow, and for ophthalmic angiography .