Time-correlated single photon counting measurements. (a) Zeta potential measurements for AlPcS-QDs and QDs. (b) Emission spectra of the QDs (0.05 μM), AlPcSs (5 μM) and AlPcS-QDs (0.05 μM) in aqueous solutions. Excitation, 405 nm. (c) Fluorescence comparison of free AlPcS and AlPcS-QDs in aqueous solutions under the excitation at 532 nm. (d) PL lifetime curves of the conjugated QDs and free QDs in aqueous solutions excited by a 405-nm ps laser and measured by TCSPC with a 585- to 640-nm band-pass filter.