Butian Zhang

Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive protocols are urgently needed to be developed and employed for fully assessing and understanding the origins of the toxicity arising from different QD formulations.

Revisiting the principles of preparing aqueous quantum dots for biological applications: the effects of surface ligands on the physicochemical properties of quantum dots

Surface functionalization of quantum dots (QDs) is one of the most important aspects for the design and preparation of the desired QDs for specific biomedical applications. The surface ligands not only render the QDs water-dispersible, but also endow them with different functional groups for bioconjugation. More importantly, as the surface ligand layer on the QD surface is responsible for interacting with the biological environments, the type of surface ligand will greatly affect the response from the cells, such as the cellular uptake and cytotoxicity. In this paper, we investigate the effects of the surface ligand on the physicochemical properties of QDs and examine different QD formulations for possible biomedical applications. Seven types of QD formulations were prepared by anchoring the CdSe/CdS/ZnS QDs surface with either short-chain mercapto ligands (MPA, MSA, cysteine, AET) or PEG derivative ligands (mPEG-SH, CM-PEG-SH, NH2-PEG-SH). We then conducted a systematic study to evaluate the colloidal stability, photostability, cellular uptake and in vitro toxicity of the formulations. The colloidal stability was evaluated by the particle size change in water, acidic/neutral/alkaline buffer solutions and cell culture medium. Our results show that the carboxyl-terminated QDs have the best colloidal stability in water and alkaline solutions. PEG-capped QDs are more stable than short-chain ligand modified QDs in cell culture medium. For the photostability of different QD formulations under UV irradiation, we observed that the MPA-, MSA- and Cys-QDs had better photostability than that of the PEG modified QDs, whereas the AET-QD is the least stable one. Cellular uptake of QDs was evaluated using cell imaging and quantified by flow cytometry. The PEG chains and surface charge of QDs were found to play critical roles in the cellular uptake. Using RAW246.7 macrophage cells as the cellular uptake model, we discovered that the anionic QDs had a much higher uptake compared to the cationic QD formulations. In general, each set of prepared QD formulation with a specific type of surface ligand display certain strengths and limitations in different aspects of their physicochemical properties. Therefore, one should carefully consider and choose the type of QD formulation in the experiments thereby minimizing its impacts arising from their limitations.

Folic acid-conjugated organically modified silica nanoparticles for enhanced targeted delivery in cancer cells and tumor in vivo

In this work, we report the synthesis of dye-loaded and folic acid (FA)-conjugated organically modified silica (ORMOSIL) nanoparticles as targeted optical nanoprobes for in vitro and in vivo imaging. The dye-loaded ORMOSIL (ORMD) nanoparticles are synthesized by a facile aqueous phase (oil-in-water microemulsion) approach and they have an average size of 30 nm. We observed that the functionalization of FA onto the particle surface led to a strong cellular uptake of FA-conjugated ORMD nanoparticles for pancreatic cancer Miapaca-2 cells and hepatoma SMMC7721 cells with FA receptor overexpression. Such a trend is not observed for 293T cells and breast cancer MCF7 cells as these cells possess low-expression of the FA receptor. The in vivo imaging studies demonstrate that FA-ORMD nanoparticles are preferentially accumulated in tumor sites. Histological studies reveal that no-ill effects are observed in the major organs of treated mice when compared to the untreated ones. Because of the facile synthesis process, high specificity for tumor targeting and low toxicity of FA-ORMD nanoparticles, significant potential for early-cancer detection application is expected.

Arsenic incorporation into InGaAsP grown by low-pressure metalorganic vapor phase epitaxy using tertiarybutylarsine and tertiarybutylphosphine in N2 ambient

InxGa1−xAsyP1−y epilayers have been grown by low-pressure metalorganic vapor phase epitaxy (LPMOVPE) using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) as group V precursors and nitrogen as the carrier gas. Arsenic incorporation into InxGa1−xAsyP1−y films grown by LPMOVPE as a function of the gas phase composition ratio and V/III ratio has been systematically studied. With optimized growth conditions, the arsenic composition of the epilayers does not change linearly with the TBA source flow. It is observed that the arsenic incorporation becomes saturated when the gas phase composition TBA/(TBA+TBP) increases to 0.4. The incorporation kinetics in MOVPE growth of InxGa1−xAsyP1−y alloy has been analyzed by using an adsorption-trapping model. The As composition (y) of the InxGa1−xAsyP1−y films varies with the TBA gas phase composition ξ=TBA/(TBA+TBP) according to the expression y=2Ns*/aN0(1−e−θβξ). It is demonstrated that with the optimized growth conditions, TBA has a higher incorporation effic...

Engineering Quantum Dots with Different Emission Wavelengths and Specific Fluorescence Lifetimes for Spectrally and Temporally Multiplexed Imaging of Cells

In this work, a proof-of-concept study was performed to examine the potential of spectrally and temporally multiplexed imaging of cells by using quantum dots (QDs). The CdSe and ZAIS QDs with different emission wavelengths and well-separated fluorescence lifetimes were prepared to provide 2-dimensional information. After incubation with cells, the same type of QDs with different emission wavelengths were distinguishable in spectral imaging while different types of QDs with similar emission wavelengths but well-separated fluorescence lifetimes were resolvable in fluorescence lifetime imaging. For cells co-stained with dye and different types of QDs, the fluorescence lifetime imaging microscopy (FLIM) images showed spatially separated patterns that can be split into channel images by using the software-based time gates. Overall, the results demonstrate the feasibility of combining the 2-dimensional encoded QDs for spectrally and temporally multiplexed imaging. This method can be extended to other QDs and organic dyes to maximize the number of measurable species in multiplexed imaging and sensing applications.