Absorption and fluorescence spectra of tetraphenylporphyrin-doped PFBT dots with different density of side-chain carboxylic acid functional groups. The left panels show the absorption spectra of PFBT-C2 (black), PFBT-C14 (red), and PFBT-C50 (blue) aqueous solution of Pdots before (a) and after (b) centrifugal filtration; (c) shows the absorption spectra of the filtrate for the three types of Pdots. The right panels show the fluorescence spectra of PFBT-C2 (black), PFBT-C14 (red), and PFBT-C50 (blue) aqueous solutions before (d) and after (e) centrifugal filtration; (f) shows the fluorescence spectra of the filtrate for the three types of Pdots. The insert in (f) shows the fluorescence spectra obtained under the excitation wavelength of 450 nm for the filtrate of PFBT-C2, PFBT-C14, and PFBT-C50 aqueous solutions.