A Fluorescent Nanosensor for Silver (Ag+) and Mercury (Hg2+) Ions Using Eu (III)-Doped Carbon Dots.

Cátia Correia,José Martinho,Ermelinda Maçôas

doi:10.3390/nano12030385

Abstract

Carbon dots doped with Eu3+ ions (Eu-Cdots) were prepared by a hydrothermal treatment, using citric acid and urea as precursors and Eu (NO3)3 as a europium source. The Eu3+ ions are strongly coordinated with the carboxylate groups at the surface of the Cdots and incorporated within the nanographene network in the carbon core. Vibrational spectroscopy provides evidence of such interaction with identification of bands assigned to the stretching of the Eu-O bond. Eu3+ doped Cdots have larger diameters then undoped Cdots, but they are divided into smaller domains of sp2 carbon. The UV-vis excitation spectrum provides evidence of energy transfer from the Cdots to the Eu3+. The luminescence spectrum shows the characteristic sharp peaks of Eu3+ in the red part of the visible spectrum and a broad emission of Cdots centered at 450 nm. The luminescence of the Cdots is strongly quenched by Hg2+ and Ag+, but not by other cations. The quenching mechanism differs significantly depending on the nature of the ion. Both the blue emission of Cdots and the red emission of Eu3+ are quenched in the presence of Hg2+ while only the emission of the Cdots is affected by the presence of Ag+. A ratiometric sensor can be built using the ratio of luminescence intensities of the Cdots to the Eu3+ peaks.

Highlights

Carbon dots (Cdots) are a new class of carbon nanomaterials with interesting optical properties, such as high emission yields, excitation wavelength dependent emission, and high photostability
Europium doped Cdots where prepared by a hydrothermal process at 160 ◦ C for together with the 12 h using citric acid, urea and Eu
Undoped Cdots were prepared following the same procedure in the absence of europium salt

Summary

Introduction

Carbon dots (Cdots) are a new class of carbon nanomaterials with interesting optical properties, such as high emission yields, excitation wavelength dependent emission, and high photostability. Cdots can be prepared by top–down and bottom–up approaches using low-cost and environmentally-friendly materials. Their physicochemical properties can be controlled and tuned by doping, surface passivation and functionalization. The carbon dots need to be doped or appropriately functionalized to probe selectively the specific analyte. In many cases the analyte induces the quenching of the fluorescence (turn-off), while in others the fluorescence can be enhanced (turn-on) by suppressing the quenching or by generating new fluorescent species.

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Conclusion