Fig. 7. (a) The structure of the pDA polymer. (b) The schematic of the pDA-PEG nanoparticle based NIR-II probe. (c) AFM image of the pDA-PEG probe. (d) Absorption and emission spectra of pDA-PEG; (e) white-light and NIR-II images of EGFR-positive MDA-MB-468 cells and EGFR-negative U87MG cells incubated with the pDA-PEG-Erbitux conjugate. (f) Average NIR-II fluorescence of EGFR-positive MDA-MB-468 cells and EGFR-negative U87MG cells, showing a positive/negative ratio of 5.8. (g) A time course of NIR-II fluorescence images of a mouse hindlimb immediately following intravenous injection of pDA-PEG. (h) A plot of the distance travelled by the blood flow front as a function of time. The linear fit reveals an average blood velocity of 4.36 cm s^–1 in the femoral artery. (i) A plot of instantaneous velocity (derived by dividing flow front travelled distance between two consecutive frames by the time interval of 39 ms) as a function of time, revealing periodic changes of instantaneous velocity corresponding to cardiac cycles. (j) An NIR-II fluorescence image of the same mouse hindlimb after full perfusion of pDA-PEG-containing blood into the hindlimb, upon which the fluorescence intensity in the hindlimb became unchanging. The scale bars in (g) and (j) indicate 5 mm. Reproduced from ref. 39 with permission from Springer Nature.