Fabrication of ZnO nanoplates for visible light-induced imaging of living cells

Visible light-sensitive ZnO nanoplates (ZnO NPls) were successfully synthesized using a hydrothermal sol-gel method and their structures were characterized by using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmitting electron microscopy (TEM), atomic force microscopy (AFM) and FT-IR analysis. From these studies it was found that the nanoplates have excellent crystallinity and a perfect nanoplate morphology with diameter ranging from 50 nm to 250 nm and a thickness of ∼10 nm. Surfaces of the ZnO NPls were further conjugated with hydrophilic amino groups such as aminopropyl triethoxysilane (APTES) to enhance the biocompatibility and cell penetrations. The resultant APTES-modified ZnO NPls showed excellent colloidal stability in various aqueous media, exhibiting stable and strong red fluorescence emission (∼650 nm) under visible light-excitation at 405 nm. They also exhibited strong red emission even after being penetrated into living cells with negligible cytotoxicity. Therefore, the APTES-modified ZnO NPls should be promising alternative nanomaterials to the traditional quantum dots as well as previously reported ZnO cellular labelling agents which exhibit green emission by UV-excitation.