Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing

Alejandro Lapresta-Fernández, Tristan Doussineau, Silvio Dutz, Frank Steiniger, Artur J. Moro, Gerhard J. Mohr

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (∼10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (∼3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.

Original languageEnglish
Article number415501
JournalNanotechnology
Volume22
Issue number41
DOIs
Publication statusPublished - 14 Oct 2011

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Nanoparticles
Coloring Agents
Dyes
Silicon Dioxide
Silica
Fluorescence
Magnetic cores
Fluorophores
Water
Microemulsions
Dynamic light scattering
Coprecipitation
Fluorescein
Iron oxides
Fourier transform infrared spectroscopy
Condensation
Hydrolysis
Buffers
Oils
Salts

Cite this

Lapresta-Fernández, A., Doussineau, T., Dutz, S., Steiniger, F., Moro, A. J., & Mohr, G. J. (2011). Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing. Nanotechnology, 22(41), [415501]. https://doi.org/10.1088/0957-4484/22/41/415501
Lapresta-Fernández, Alejandro ; Doussineau, Tristan ; Dutz, Silvio ; Steiniger, Frank ; Moro, Artur J. ; Mohr, Gerhard J. / Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing. In: Nanotechnology. 2011 ; Vol. 22, No. 41.
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abstract = "This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (∼10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (∼3.0{\%}) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2{\%} of horse serum, indicating that there are no significant statistical differences at a 95{\%} confidence level.",
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note = "We gratefully acknowledge the financial support from the EU projects 'Sensor nanoparticles for ions and biomolecules' (MTKD-CT-2005-029554) and 'Development of robust and quantitative biosensors based on near-infrared two-dyed silicate nanoparticles' (PIEF-GA-2008-220775) as well as from the projects MO 1062/6-1 and MO 1062/5-2 of Deutsche Forschungsgemeinschaft. This work was also supported by the Bayerische Staatsministerium fur Wirtschaft, Infrastruktur, Verkehr und Technologie within project AZ-Nr.: 20.10-3410-2 (Projekt Sensormaterialien).",
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Lapresta-Fernández, A, Doussineau, T, Dutz, S, Steiniger, F, Moro, AJ & Mohr, GJ 2011, 'Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing', Nanotechnology, vol. 22, no. 41, 415501. https://doi.org/10.1088/0957-4484/22/41/415501

Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing. / Lapresta-Fernández, Alejandro; Doussineau, Tristan; Dutz, Silvio; Steiniger, Frank; Moro, Artur J.; Mohr, Gerhard J.

In: Nanotechnology, Vol. 22, No. 41, 415501, 14.10.2011.

Research output: Contribution to journalArticle

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AU - Lapresta-Fernández, Alejandro

AU - Doussineau, Tristan

AU - Dutz, Silvio

AU - Steiniger, Frank

AU - Moro, Artur J.

AU - Mohr, Gerhard J.

N1 - We gratefully acknowledge the financial support from the EU projects 'Sensor nanoparticles for ions and biomolecules' (MTKD-CT-2005-029554) and 'Development of robust and quantitative biosensors based on near-infrared two-dyed silicate nanoparticles' (PIEF-GA-2008-220775) as well as from the projects MO 1062/6-1 and MO 1062/5-2 of Deutsche Forschungsgemeinschaft. This work was also supported by the Bayerische Staatsministerium fur Wirtschaft, Infrastruktur, Verkehr und Technologie within project AZ-Nr.: 20.10-3410-2 (Projekt Sensormaterialien).

PY - 2011/10/14

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N2 - This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (∼10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (∼3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.

AB - This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (∼10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (∼3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.

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Lapresta-Fernández A, Doussineau T, Dutz S, Steiniger F, Moro AJ, Mohr GJ. Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing. Nanotechnology. 2011 Oct 14;22(41). 415501. https://doi.org/10.1088/0957-4484/22/41/415501