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Since inorganic phosphate ion (PO 4 3−) plays very important roles in environment or living organisms, developing a selective and sensitive detection method for PO 4 3− is highly desired. Owing to the superior optical properties, graphene quantum dots (GQDs) have been developed as a promising emitting material in fluorescence analysis. Herein, we reported the first example of negatively charged molybdate-mediated nitrogen doped graphene quantum dots (Mo 7 O 24 6--mediated N-GQDs) as a fluorescence "off-on" probe for PO 4 3− via "anion ion-mediated" strategy. The N-GQDs was firstly modified with Mo 7 O 24 6− through a complex bonding system containing ionic and hydrogen bonds. The formation of N-GQDs/Mo 7 O 24 6− complex leaded to photoluminescence (PL) quenching of N-GQDs. In the presence of PO 4 3−, strong affinity between PO 4 3− and Mo 7 O 24 6− produced ammonium phosphomolybdate, which destroyed the pre-formed N-GQDs/Mo 7 O 24 6− structure and detached Mo 7 O 24 6− from N-GQDs surface. Thus, the PL of N-GQDS was in turn switched on. Under optimal conditions, this probe exhibited a good linear relationship between PL response and PO 4 3− concentration in the range from 7.0 to 30.0 μM with a limit of detection of 50 nM. Also this probe with high selectivity and sensitivity has been successfully used to sense PO 4 3− in natural water, biological fluid, and living cells. A negatively charged molybdate mediated nitrogen-doped graphene quantum dots (Mo 7 O 24 6--mediated N-GQDs) as a fluorescent off-on probe for PO 4 3− has been developed and successfully utilized in real samples and live cells imaging. Image 1 • A fluorescence "turn on" N-doped graphene quantum dots nanocomposite for inorganic phosphate ion. • The nanocomposite working in "anion ion-mediated" principle. • The probe exhibiting the excellent PO 4 3− detection performance in biological fluids and living cells. • Presenting the possible detection mechanism. [ABSTRACT FROM AUTHOR]

An I 2 -mediated N-GQDs was developed to fluorescent probes for S 2 O 3 2− and oxidative compounds such as H 2 O 2 via iodimetry reaction oriented strategy. This nanoprobe with the excellent selectivity and sensitivity (93 pM) has been successfully applied in biological fluids and living cells for S 2 O 3 2−. [Display omitted] • a I 2 -mediated N-GQDs nanocomposite as a fluorescence probe for S 2 O 3 2− and oxidative compounds. • S 2 O 3 2− detection by I 2 -mediated N-GQDs via "iodimetry reaction oriented" strategy. • I 2 -mediated N-GQDs exhibiting the high selectivity and the super low LOD of 93 pM towards S 2 O 3 2−. • successful detection of S 2 O 3 2− in real water samples, biological fluids, and living cells. Owing to the huge threat to human health and environment from thiosulfate anion (S 2 O 3 2−) widely used in various fields, the development of an effective detection method for S 2 O 3 2− is urgently desired. Herein, we developed an iodine (I 2) mediated nitrogen-doped graphene quantum dots (I 2 -mediated N-GQDs) as a fluorescence "off-on" probe for S 2 O 3 2− by iodimetry reaction oriented strategy. Firstly, I 2 interacted with N-GQDs to form non-fluorescent N-GQDs/I 2 complex due to the inner filter effect (IFE). In the presence of S 2 O 3 2−, the iodimetry reaction between I 2 and S 2 O 3 2− disintegrated N-GQDs/I 2 complex and re-switched on the quenched photoluminscence of N-GQDs. The I 2 -mediated N-GQDs nanoprobe with a limit of detection down to 93 pM has been successfully used to sense S 2 O 3 2- in biological fluids and living cells. Moreover, the I 2 -mediated N-GQDs/S 2 O 3 2− nanoplatform could further detect oxidative compounds such as hydrogen dioxide, dichromate, permanganate, iron ion (III), copper ion (II), and cerium ion (IV). [ABSTRACT FROM AUTHOR]