Three-photon imaging using defect-induced photoluminescence in biocompatible ZnO nanoparticles

Abstract

BackgroundAlthough optical spectroscopy promises improved lateral resolution for cancer imaging, its clinical use is seriously impeded by background fluorescence and photon attenuation even in the so-called two-photon absorption (2PA) imaging modality. An efficient strategy to meet the clinical cancer imaging needs, beyond what two-photon absorption (2PA) offers, is to use longer excitation wavelengths through three-photon absorption (3PA). A variety of fluorescent dyes and nanoparticles (NPs) have been used in 3PA imaging. However, their nonlinear 3PA coefficient is often low necessitating high excitation powers, which cause overheating, photodamage, and photo-induced toxicity. Doped wide band gap semiconductors such as Mn:ZnS NPs have previously been used for 3PA but suffer from poor 3PA coefficients.MethodsHere, we prepared ZnO NPs with intrinsic defects with high 3PA coefficients using a polyol method. We functionalized them with peptides for selective uptake by glioblastoma U87MG cells and used breast cancer MCF-7 cells as control for 3PA studies. Uptake was measured using inductively coupled plasma-mass spectrometry. Biocompatibility studies were performed using reactive oxygen species and cell viability assays.ResultsWe demonstrate that ZnO NPs, which have a band gap of 3.37 eV with an order of magnitude higher 3PA coefficients, can facilitate the use of longer excitation wavelengths 950–1,100 nm for bioimaging. We used the presence intrinsic defects (such as O interstitials and Zn vacancies) in ZnO NPs to induce electronic states within the band gap that can support strong visible luminescence 550–620 nm without the need for extrinsic doping. The peptide functionalization of ZnO NPs showed selective uptake by U87MG cells unlike MCF-7 cells without the integrin receptors. Furthermore, all ZnO NPs were found to be biocompatible for 3PA imaging.ConclusionWe show that defect-induced luminescence 550–620 nm in ZnO NPs (20 nm) due to 3PA at longer excitation (975 nm) can be used for 3PA imaging of U87MG glioblastoma cells with lower background noise.

Doped Plasmonic Zinc Oxide Nanoparticles with Near-Infrared Absorption for Antitumor Activity

“…Figure shows the diffractograms of doped ZnO NPs at 5% with the different metals and nondoped ZnO NPs. The XRD peaks correspond to the diffraction planes from (100), (101), (102), (110), (103), and (200) of the ZnO NPs lattice, which is typical of the wurtzite phase . The XRD peaks of nondoped ZnO NPs showed a strong orientation at (002), indicating that the growth pattern, in this case, is along the direction of the c axis, which represents the formation of ZnO nanorods .…”

“…Fluorescent ZnO quantum dots (QDs) have been used in the diagnostics of cancer cells upon imaging fluorescence using a continuous-wave laser . In vivo studies have shown an excellent ability of the ZnO QDs to deliver doxorubicin and 5-fluorouracil in the tumor microenvironment of neoplasms. , In fact, ZnO nanocarriers increase the chemotherapeutics efficiency and cell death in cervical, breast, and lung cancer, with low cytotoxic effects in healthy cells. − …”

Multifunctional ZnO nanostructures: a next generation nanomedicine for cancer therapy, targeted drug delivery, bioimaging, and tissue regeneration

“…Despite these improvements, several other problems such as the bandgap in the UV region, insolubility, instability in in vivo, and blue emission as well as overlapping of fluorescence with the biological autofluorescence are the biggest challenges of using ZnO for bioimaging. Therefore, two-photon imaging or multiphoton imaging, or fluorescence lifetime imaging could be the potential solutions to the above problems [149].…”

Biodistribution, Excretion, and Toxicity of Inorganic Nanoparticles

“…nanodiamonds 34 ), two-, three-or multiphoton microscopy (e.g. UCNPs 35 , ZnO NPs 36 and other non-linear optical techniques 37 ). Being electron-dense materials, inherently photoluminecent inorganic NPs may further be suitable for correlative light and electron microscopy (CLEM) 38 , rendering them suitable as intracellular dual-contrast markers for studying intracellular processes and trafficking of biomolecules.…”