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Graphene quantum dots sensor for the determination of graphene oxide in environmental water samples Sandra Benítez-Martínez, Angela Inmaculada López-Lorente, and Miguel Valcarcel Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/ac5035083 • Publication Date (Web): 19 Nov 2014 Downloaded from http://pubs.acs.org on November 21, 2014
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Analytical Chemistry
Graphene quantum dots sensor for the determination of graphene oxide in environmental water samples
Sandra Benítez-Martínez, Ángela Inmaculada López-Lorente, Miguel Valcárcel* Department of Analytical Chemistry, University of Córdoba, E-14071 Córdoba, Spain Phone/Fax +34 957 218616; E-mail:
[email protected] *Corresponding author. Tel./Fax: +34 957 218616; E-mail:
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Analytical Chemistry
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Abstract The paper proposes a simple and sensitive approach for the preconcentration and determination of graphene oxide (GO) in environmental samples by using fluorescent graphene quantum dots (GQDs). The method is based on the preconcentration of GO on a cellulose membrane and their subsequent elution prior fluorescence analysis of the quenching effect produced on the GQD solution due to the hydrophobic interactions between GO and GQDs. The limit of detection was 35 µg·L-1. The precision, for a 200 µg·L-1 concentration of GO is 5.16%. The optimized procedure has been successively applied to the determination of traces of GO in river water samples.
Keywords: graphene quantum dots, graphene oxide, fluorescence, quenching.
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Analytical Chemistry
Introduction The increasing use of nanomaterials in industrial applications as well as the commercialization of nanomaterial based products such as cosmetics, foods, drugs and electronic devices, will increase the human and environmental exposure to such nanomaterials. Carbon nanoparticles such as fullerenes, carbon nanotubes and most recently, graphene -a two dimensional single sheet of carbon atoms arranged in an aromatic network with sp2 hybridization- have attracted great interest in the last decades due to their exceptional properties1. The unusual and extraordinary mechanical, optical, thermal and electronic properties2 of graphene have encouraged their use in several fields such a electronics, energy sector, catalysis, (bio)medicine and materials science, as well as in the analytical chemistry field 3, 4. Due to the growing production (predicted to reach 573 tons in 2017)5 and use of graphene and graphene-family nanomaterials it is necessary to evaluate their possible effects in the environment and, subsequently, on the ecosystem health, including humans. GO nanoparticles could reach the environment through atmospheric emissions and waste stream in production and research facilities. Nanoparticles in the environment would contaminate soil, surface and underground water and interact with organism6. However, nowadays there are still few analytical methodologies available for the detection and quantification of engineered nanomaterials, although some approaches have been developed in the case of carbon nanotubes7–9 or metallic nanoparticles10, 11. Recently, the stability and transport of GO has been investigated in both artificial ground– and surface waters12. Graphene oxide (GO) possesses an unique structure composed of sp2 carbons surrounded by sp3 carbons and oxygen containing functional groups13 which confer it an excellent aqueous solubility -hence their potential presence as contaminant of environmental waters-, surface functionalizability and fluorescence quenching ability14. GO has been used as a sensor for the detection of DNA15, proteins16 and metal ions17; as sorbent for solid–phase extraction18 and
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Analytical Chemistry
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microextraction19. Recently it has been employed as adsorbent of heavy metals and organic compounds in the wastewater treatment20 as well as novel carrier for drug delivery21. The toxicological effects of GO have been evaluated. It has been demonstrated that GO is able to penetrate through the plasma membrane, altering cell morphology, inducing membrane damage and oxidative stress in adenocarcinomic human cells22. Moreover, GO toxicity, genotoxicity and cytotoxicity have been reported in human23 and animal cells24, immune cells25 and blood components26. In vivo studies in mice showed that GO can be accumulated in lungs, liver and spleen27. Graphene quantum dots (GQDs) are zero–dimensional luminescent carbon-based nanomaterials that consist on very small graphene sheets with lateral size less than 100 nm in single, double or multiple layers, which exhibit exciton confinement and quantum size effect. Their diameter ranges from 3 to 20 nm, approximately 28. The GQDs band gap is different from zero and can be tuned varying the size and the surface chemistry of GQDs29. These small graphene sheets possess special and different properties from graphene; it should be noted their high fluorescence activity, low toxicity, high biocompatibility, excellent photostability and robust chemical inertness30. These properties made GQDs a useful tool in the development of photovoltaic devices31, bioimaging32, sensors4 and biosensors33. In this paper, GQDs have been employed to develop a simple, fast and sensitive fluorescencebased sensor for the determination of GO in natural river water samples. The interaction of GO with GQDs through hydrophobic π-π interactions leads to a decrease in the fluorescence intensity –quenching- of GQDs, which has been used as analytical signal for the quantification of the presence of GO after preconcentration and subsequent elution on an acetate of cellulose membrane. As far as we are concerned, this is the first approach to the determination of graphene oxide from environmental waters.
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Analytical Chemistry
Experimental section Materials and reagents All chemical reagents were analytical-grade and were used without additional purification. Graphene (avangraphene-2,
