A) FPLC chromatograms of size-variable PN’s (constant IR-783 fluorochrome, variable PEG’s) are shown. Diameters are given in Table 1. B,C) Tuning PN size with different fluorochromes. The 5 kDa PEG yielded the magenta coded chromatograms with diameters of 4.3 nm regardless of the fluorochrome used. They are PN(783)4.3 (2A), PN(545)4.3 (2B), and PN(497)4.3 (2C). The 30 kDa PEG yielded the blue coded PN’s of 10 nm. Therefore PN dimensions are determined by PEG and independent of the fluorochrome selected. (D,E,F) FPLC chromatograms of PN’s are shown before (pre) and from the sera of injected mice. PN’s were PN(783)10.0 (2D), PN(783) 6.1 (2E), and PN(783)4.3 (2F). After injection, PN’s circulate at their PEG-determined and variable pre-injection sizes. (G) Since PN’s circulate at PEG-determined, pre-injection sizes, they cross capillaries at those sizes. ICG binds albumin and can cross capillaries in two forms. “FL” is the fluorescein fluorochrome.