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One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels

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ABSTRACT

We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core–shell QDs) was used for passivating the defect emission (650 nm) and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530–600 nm). Moreover, the PL emission peak of CdSe/CdS core–shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core–shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol)-2-diphenyltertrazolium bromide (MTT) assay. The results showed the satisfactory (>80%) biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 μg/ml.

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a XRD patterns of plain CdSe and CdSe/CdS core/shell nanocrystals. b EDX spectrum of the CdSe/CdS core/shell nanocrystals prepared on a copper grid.
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Figure 2: a XRD patterns of plain CdSe and CdSe/CdS core/shell nanocrystals. b EDX spectrum of the CdSe/CdS core/shell nanocrystals prepared on a copper grid.

Mentions: In the present study, Cd(Ac)2 and Se powder are selected as source. Triethylene glycol (TREG) is used as the solvent due to its good hydrophilic feature and high boiling point (288°C). A water-soluble and biocompatible polymer with carboxylic functional groups, PAA, is selected as a capping ligand for controlling the crystal quality of QDs such as size, size distribution, and crystallinity by the formation of the chelated cadmium precursors. Moreover, since PAA is considered as a biocompatible polymer [8], we believe that the PAA could absorb on the surface of the QDs through the synthetic process, which may be advantageous for improving the hydrophilicity and biocompatibility as fluorescent biological labels. Due to the low solubility of selenium powder in TREG, no reaction had been observed at low temperature. When the temperature rose around the melting point of selenium powder (221°C), it was quickly reduced in the polyol system with reductive hydroxide groups and reacted with the carboxylate precursors forming numerous of nuclei. The explosive nucleation brings a narrow size distribution and also reduces the tendency of Ostwald ripening [17]. The nanocrystals grow larger as the extension of reaction time, causing the redshift of both absorption and emission spectra. Figure 1a shows the ultraviolet–visible (UV–vis) absorption and photoluminescence (PL) emission spectra of the PAA-capped CdSe QDs as a function of reaction time. With the extension of the reaction time, the CdSe QDs gradually grow up, and their PL emission peak can be tuned from 520 to 586 nm. The full width at half maximum (FWHM) of the PL spectra is around 50 nm. Figure 1b shows the typical TEM image of the as-synthesized PAA-capped CdSe QDs with the absorption peak around 540 nm. The average core size of as-prepared CdSe QDs calculated from the statistical results was about 2.8 nm. The HRTEM image (Figure 1c) and SAED pattern (Figure 1d) confirm the formation of the cubic CdSe QDs by PAA-assisted polyol approach. The XRD pattern of as-synthesized CdSe QDs shown in Figure 2a also shares same crystal structure with zinc-blende CdSe (JCPDS file No. 19-0191).


One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels
a XRD patterns of plain CdSe and CdSe/CdS core/shell nanocrystals. b EDX spectrum of the CdSe/CdS core/shell nanocrystals prepared on a copper grid.
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Related In: Results  -  Collection

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Figure 2: a XRD patterns of plain CdSe and CdSe/CdS core/shell nanocrystals. b EDX spectrum of the CdSe/CdS core/shell nanocrystals prepared on a copper grid.
Mentions: In the present study, Cd(Ac)2 and Se powder are selected as source. Triethylene glycol (TREG) is used as the solvent due to its good hydrophilic feature and high boiling point (288°C). A water-soluble and biocompatible polymer with carboxylic functional groups, PAA, is selected as a capping ligand for controlling the crystal quality of QDs such as size, size distribution, and crystallinity by the formation of the chelated cadmium precursors. Moreover, since PAA is considered as a biocompatible polymer [8], we believe that the PAA could absorb on the surface of the QDs through the synthetic process, which may be advantageous for improving the hydrophilicity and biocompatibility as fluorescent biological labels. Due to the low solubility of selenium powder in TREG, no reaction had been observed at low temperature. When the temperature rose around the melting point of selenium powder (221°C), it was quickly reduced in the polyol system with reductive hydroxide groups and reacted with the carboxylate precursors forming numerous of nuclei. The explosive nucleation brings a narrow size distribution and also reduces the tendency of Ostwald ripening [17]. The nanocrystals grow larger as the extension of reaction time, causing the redshift of both absorption and emission spectra. Figure 1a shows the ultraviolet–visible (UV–vis) absorption and photoluminescence (PL) emission spectra of the PAA-capped CdSe QDs as a function of reaction time. With the extension of the reaction time, the CdSe QDs gradually grow up, and their PL emission peak can be tuned from 520 to 586 nm. The full width at half maximum (FWHM) of the PL spectra is around 50 nm. Figure 1b shows the typical TEM image of the as-synthesized PAA-capped CdSe QDs with the absorption peak around 540 nm. The average core size of as-prepared CdSe QDs calculated from the statistical results was about 2.8 nm. The HRTEM image (Figure 1c) and SAED pattern (Figure 1d) confirm the formation of the cubic CdSe QDs by PAA-assisted polyol approach. The XRD pattern of as-synthesized CdSe QDs shown in Figure 2a also shares same crystal structure with zinc-blende CdSe (JCPDS file No. 19-0191).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core–shell QDs) was used for passivating the defect emission (650 nm) and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530–600 nm). Moreover, the PL emission peak of CdSe/CdS core–shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core–shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol)-2-diphenyltertrazolium bromide (MTT) assay. The results showed the satisfactory (>80%) biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 μg/ml.

No MeSH data available.