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Integrating Fluorescent Carbon Nanodot Synthesis and Optical Detection of Methylmercury

In the last years there has been a great interest towards the development of optical nanosensors. To this end, fluorescent nanomaterials have been implemented in analytical systems for the detection of toxic metal species. Recently, fluorescent carbon dots (CDs) have received much attention due to their attractive properties such as strong fluorescence, tunable color emission and high photostability.
Mercury and its compounds are well-known environmental pollutants. Among mercury species, methylmercury is the most toxic to living systems due to its ability to cross biological membranes resulting in accumulation and bioamplification through the food chain. Since the main human exposure to this toxic is linked to fish consumption, the control of methylmercury levels has become of paramount importance. Conventional methods for detecting methylmercury are typically based on the use of complex hybrid techniques involving a chromatographic separation coupled to a specific detector. Further efforts should be focused on development of simple and fast assays with the possibility of on-site analysis.
In this work, a novel assay that integrates the synthesis of fluorescent CDs and sensing within a single step for methylmercury detection is presented. To this end, high-intensity sonication of carbohydrates is used for the synthesis of CDs in the presence of the target analyte. It has been observed that ultrasound facilitates the permeation of methylmercury through the passivation coating of CDs made of PEG, which causes the fluorescence quenching as a result of a non-radiative electron/hole recombination. This novel assay allows detecting methylmercury at nM level in only 1 min using very low amounts of organic precursors and a portable micro-fluorospectrometer.

Acknowledgements: Financial support from the Spanish Ministry of Economy and Competitiveness and the European Commission (FEDER) (Project CTQ2012-32788) is gratefully acknowledged.