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Abstract
The use of luminescent probes with proper optical and morphological properties, high serum stability, low cytotoxicity, and good biocompatibility is a cost‐effective method for bioimaging. In this work, a route is developed to produce a novel bioimaging probe framework. A C3N4 material (UCN‐H) is produced by thermal condensation of urea under humidified air treatment. Chemical characterizations reveal that the UCN‐H contains C3N4 networks with smaller grain sizes and more amine‐based functionalities at the edges than UCN, which is separately produced without the humidified air treatment. Highly stable aqueous dispersions including fluorescent C3N4 nanoplatelets are generated by sonication of the UCN‐H powder. The photoluminescence (PL), time resolved‐PL, and 2D excitation‐emission spectra of the dispersions show that the UCN‐H has less‐intra bandgap traps and longer PL lifetime than UCN. In confocal microscopic study using the nanoplatelets, clear fluorescent cell images are obtained without any cytosolic aggregation. In in vivo imaging studies with MDA‐MB‐231 tumor‐bearing mice models, persistently strong fluorescence signals are successfully observed on tumor lesions without any interference of autofluorescence from live tissues after their accumulation by passive tumor targeting. Ex vivo biodistribution and histology results are well‐matched with in vivo fluorescence imaging results.

Dawoon Jang, Heesu Ahn, Junghoon Oh, Donggyu Lim, Chul Hee Kim, Seungjoo Choi, Young‐Hoon Kim, Jinwoo Park, Kyeong Yeon Jang, Ran Ji Yoo, Tae‐Woo Lee, Jeongho Kim, Yong Jin Lee, Dong Wook Kim, Sungjin Park