Manganese(ii) enhanced fluorescent nitrogen-doped graphene quantum dots: a facile and efficient synthesis and their applications for bioimaging and detection of Hg2+ ions

Abstract

Manganese ion (Mn²⁺) bonded nitrogen-doped graphene quantum dots (Mn(II)-NGQDs) with water solubility have been successfully synthesized by a simple, one-pot hydrothermal carbonization, using sodium citrate, glycine and manganese chloride as raw materials. The photoluminescence (PL) characteristics of Mn(II)-NGQDs were studied in detail. The resulting Mn(II)-NGQDs show a remarkably enhanced PL intensity and quantum yield (QY = 42.16%) compared with the product without Mn(II)-doped (named as NG, QY = 27.06%) and the product doped with other metal ions. The Mn(II)-NGQDs not only display low toxicity and high cellular uptake efficiency for fluorescence live cell imaging in biological evaluations but also exhibit a fast, highly selective and sensitive fluorescence quenching effect toward Hg²⁺ ions, with a detection limit of 3.4 × 10⁻⁸ mol L⁻¹.