Fig. 4From: Sulfuric Acid Assisted Preparation of Red-Emitting Carbonized Polymer Dots and the Application of Bio-ImagingTwo-photon photoluminescence spectra of SA-CPDs (a) and confocal fluorescence microscopy images of HeLa cells treated with SA-CPDs excited by 850 nm, 30 mW femtosecond pulse laser (b–e)Back to article page