Porphyrin-decorated ZnO nanowires as nanoscopic injectors for phototheragnosis of cancer cells

Abstract

Visible light-responsive ZnO nanowires (NWs) had been previously fabricated in our lab as an optical diagnostic probe for the subcellular specific targeting of biomolecules. Herein the ZnO NWs were further modified by binding protoporphyrin IX (PpIX) to prepare new optoelectronic ZnO NW hybrids. Structural characteristics of the as-prepared nanohybrids were analysed by scanning electron microscopy (SEM), tunnelling electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photoluminescence (PL) spectra of PpIX-bound ZnO NWs exhibited red emission (580–630 nm) from the porphyrin and green emission (464 nm) from the ZnO NWs upon excitation at 405 nm. The red emission was observed to be quenched as compared to that of free PpIX, while the ZnO NW green emission was unaffected. Both the nanoscopic PL image and spectrum of a single PpIX-bound ZnO NW hybrid demonstrated the preserved waveguide behaviour of the ZnO NWs. The quenched emission of PpIX and its decay times supported efficient intersystem crossing from the excited singlet to triplet state, which consecutively generated ¹O₂. Accordingly, the PpIX-bound ZnO nanowire hybrids were injected into HeLa cancer cells, which were killed by ¹O₂ upon red light (633 nm) irradiation with a He–Ne Laser. Thus, the PpIX-bound ZnO nanowire hybrids could be new nanoscopic injectors for photo-theragnosis of cancer cells, predicated on their optical waveguided and photodynamic properties.