Construction of a ratiometric fluorescent probe for visual detection of urea in human urine based on carbon dots prepared from Toona sinensis leaves and 5-carboxyfluorescein.

In this work, pH-sensitive blue fluorescent carbon dots (CDs) with high fluorescence quantum yield (17.24%) were synthesized by hydrothermal method using Toona sinensis leaves and ethylenediamine (EDA) as raw materials. The CDs can detect urea with a limit of detection (LOD) of 6.700 mmol L-1. For more sensitive detection of urea, we constructed a ratiometric fluorescent probe (CDs@5-FAM) using CDs and 5-carboxyfluorescein (5-FAM). The CDs@5-FAM probe can rapidly and sensitively detect urea according to the changes of I514/I405, with LOD as low as 0.014 mmol L-1. Furthermore, with the help of a smartphone and RGB analysis software, urea's visual intelligent detection was realized using a CDs@5-FAM probe. The method proposed in this paper is consistent with the standard method, which indicates that the pH-sensitive ratiometric fluorescent probe CDs@5-FAM is accurate and reliable for practical application. It provides a new way for rapid and visual detection of urea.

H2O2-assisted detection of melamine using fluorescent probe based on corn cob carbon dots-Ionic Liquid-Silver nanoparticles.

In this work, a new sustainable melamine detection method was developed. Biomass-derived carbon dots (CDs) were successfully prepared by ionic liquid (1-Allyl-3-methylimidazolium chloride, IL) hydrothermal method using agricultural waste corn cob as the carbon source, and combined with silver nanoparticles (AgNPs) to construct fluorescent probe CDs@IL-AgNPs. The probe was characterized and the formation mechanism of the probe was discussed. The direct detection of H2O2 and the indirect sensitive detection of melamine were realized. The detection limit of melamine was 0.94 µmol/L, which is far lower than the minimum allowable amount of melamine in milk powder (7.95 µmol/L). The high sensitivity and selectivity probe was used to detect melamine in commercial dairy products, and the recovery rate of standard addition was between 94 % and 110 %. This study provides valuable new application ideas for the detection of melamine in dairy products and the low-carbon and environmentally friendly treatment of agricultural waste.

Imaging of water soluble CdTe/CdS core-shell quantum dots in inhibiting multidrug resistance of cancer cells.

Two different colors of water-soluble core-shell quantum dots CdTe/CdS (green and orange red) have been synthesized and characterized in this paper. The formation of core-shell quantum dots not only improves the fluorescence quantum yield, but also reduces the biological toxicity of quantum dots, and improves the fluorescence lifetime. Two novel fluorescent bioprobes, CdTe/CdS (λem = 545 nm)-5-Fu and Bio-CdTe/CdS (λem = 600 nm)-TAM, have been synthesized via the interaction of these two core-shell quantum dots with anticancer drugs (5-Fu) and P-gp inhibitors (TAM), respectively. These two fluorescent probes have been simultaneously used in fluorescence imaging of human breast cancer cells MDA-MB-231/MDR. It can be observed that under the action of P-gp inhibitors distributed on the cell membrane, anticancer drugs can be retained in cancer cells. According to the color of quantum dots on the probe, the visualization results of the action of anticancer drugs and P-gp inhibitors can be obtained. This study shows that to prepare functional bioprobes using core-shell quantum dots CdTe/CdS has great potential in the field of biomedical research such as anticancer drugs.