Monitoring the size and the stability of zinc oxide quantum dots in biological media: a soft ionization mass spectrometr
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Monitoring the size and the stability of zinc oxide quantum dots in biological media: a soft ionization mass spectrometry technique (MALDI-TOF-MS)
Jean-Jacques Gaumet1, Gabriel Gaiffe1, Clément Dezanet2, Stéphane Dalmasso1, Pierre Magri1, Lavinia Balan3 and Raphaël Schneider2. 1
Université de Lorraine, LCP-A2MC, Jean Barriol Institute, 1 bd Arago, 57078 Metz Cedex 03, France.
2
Université de Lorraine, LRGP, CNRS, UMR 7274, 1 rue Grandville, 54001 Nancy, France
3
IS2M, UHA, 15 rue Jean Starcky, BP 2488, 68057 Mulhouse Cedex, France
ABSTRACT We present herein a joint physical/physico-chemical study and, more specifically, the first application of Matrix Assisted Laser Desorption Ionization coupled with Time of Flight Mass Spectrometry (MALDI-TOF-MS) to analyze small-sized ZnO quantum dots (QDs) (2.8-3.1 nm diameter range) synthesized by sol-gel chemistry and stabilized through an aminosilane coating. A careful investigation of the stability of ZnO QDs was initiated once these dots were dispersed in different media (water, biological buffer) for a period up to 3 weeks. Positive ion mode mass spectra MALDI-TOF-MS combined with optical spectrometry was used to monitor the stability of ZnO QDs when aging. Such a unique combination of MALDI-TOF-MS and physico-chemical techniques is likely to bring new insights into the structure analysis, the stability and consequently the potential toxicity of QDs. INTRODUCTION With the developments in material sciences, the characterization of nanomaterials has become a key consideration issue in managing their fascinating size-dependent physical and chemical properties. Controlling these properties from synthesis to the application phase, and consequently to their fate as a worldwide environmental and societal concern is becoming more and more critical [1-3]. The potential toxicity of nanoparticles thus needs to be evaluated when responsibly developing applications. Zinc oxide (ZnO) nanoparticles are largely found as powders and dispersions with antibacterial, anti-corrosive, antifungal and UV filtering properties. ZnO nanoparticles can also be used for various applications ranging from food and cosmetics up to coating agents and in the manufacturing of concrete. Research is actively being conducted towards in their use in solar cells, photocatalysis, optical devices and sensors. This has already started to show economic potential worldwide. The principal techniques currently used to achieve the characterization of nanoparticles are physical and physico-chemical methods, such as Transmission Electron Microscopy (TEM), X-
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ray diffraction, and photoluminescence (PL). All these analytical tools are excellent for global analyses of clusters and nanomaterials. Soft ionization mass spectrometry (MS) methods such as Nanospray MS for very small QDs (up to 1.5 nm) [4], Matrix Assisted Laser Desorption Ionization coupled with Time of Flight MS (MALDI-TOFMS) have already proven their potential as tools in the nanometrology of small-sized II-VI quantum dots (QDs) such as CdS, CdSe, ZnS
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