Ultratrace and robust visual sensor of Cd2+ ions based on the size-dependent optical properties of Au@g-CNQDs nanoparticles in mice models

Visual inspection is expected as an ideal technique, which can directly and conveniently detect heavy metal ions by observing the color change. Insensitivity of detecting weakly colored heavy transition metal ions and low adsorptivity of metal ions on nanoparticle surface are two main factors hindering the application of visual detection in heavy metal ions detection. Herein, we demonstrated an operational colorimetric sensor based on the color dependence of nanoparticles aggregation to selective and facile detect weakly colored transition heavy metal Cd 2+ ions that have been considered as the origin of the “Itai-itai” disease. Uniform colloidal 15   nm graphite-like nitride doped carbon quantum dots-capped gold nanoparticle (Au@g-CNQDs) was successfully prepared, wherein the existence of numerous heptazine, carboxyl and hydroxyl groups on the nanoparticle's surface strengthened adsorption of the Cd 2+ ions on the surface of Au@g-CNQDs through the “cooperative effect”. As a consequence, without expensive and intricate exogenous indicators or other special additives, the Cd 2+ ions could sensitively and quickly captured to detect at ultra-low concentration within 30   s by the naked-eye. Under the optimal conditions, the Cd 2+ ions sensor possesses good analytical performances with a wide linear range of 0.01–3.0   μM and a detection limit of 10   nM (S/N = 3). Moreover, the biodistribution and aggregation of Cd 2+ ions were detected effectively in mice organ tissues suggesting its great potential use for real-word applications.