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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]

Glutathione (GSH) plays vital roles in a variety of biological processes, and the development of simple and effective GSH detection method is an important research topic. Herein, a multifunctional probe based on Ag&Mn:ZnInS quantum dots (QDs) was developed for bimodal imaging of GSH. MnO 2 , as an efficient fluorescence quencher, was in-situ grown on the surface of QDs, and then modified with hyaluronic acid (HA) to improve the stability and targeted recognition capability of the probe due to the binding between HA and CD44 receptors. After MnO 2 was deconstructed by GSH, the fluorescence of the probe was recovered and the generated Mn2+ could serve as good magnetic resonance imaging (MRI) contrast agent. Moreover, the near-infrared emission probe was successfully employed in living cell and zebrafish imaging due to its low toxicity and high anti-biological interference performance. This strategy provides a simple dual-mode fluorescence/MRI imaging of GSH, which may have a broad application in biological detection. [Display omitted] • We developed a GSH-responsive Ag&Mn:ZnInS QDs@SiO 2 –MnO 2 -HA probe for dual-mode fluorescence and magnetic resonance imaging. • In the presence of GSH, MnO 2 was reduced to Mn2+, causing the dual-modal property of the probe to turn on. • The near-infrared emission probe was successfully employed in imaging of GSH in living cells and zebrafish due to its low toxicity and high anti-biological interference performance. [ABSTRACT FROM AUTHOR]

Carbon dots without heteroatoms-doping and surface modifications were designed to be a novel chemosensing strategy on the quantitative detection of uric acid (UA) with the aid of uricase-induced enzymatic reaction and Fenton reaction. In this work, ascorbic acid (AA)-derived carbon dots (A-CDs) were prepared in the mixture of ethanol and water via one-step hydrothermal synthesis at a relatively low temperature (120 °C) for 10 h. The resultant A-CDs were proved to be excitation-independent. When excited at the wavelength of 420 nm, the nanodots displayed green fluorescence (535 nm) which was then linearly quenched as UA concentration increased in the range of 0–56 μM, according to which the detection limit was calculated to be 0.49 μM. With regards to the excellent sensitivity and selectivity to UA, real sample assay was performed on the A-CDs detection system, which provided relatively reliable recoveries of UA contained in human serum/urine. Besides, in view of the high quantum yield, the A-CDs were applied to live-cell imaging assay and were considered to become an alternative tracer tool in biomedical imaging. [Display omitted] • Carbon dots are prepared at a relatively low temperature without heteroatoms doping and surface modification. • The sensing system based on the carbon dots has a low detection limit to uric acid. • The system not only allows for quantifying uric acid and H 2 O 2 , but also possesses the imaging ability to living cells. [ABSTRACT FROM AUTHOR]