Chromium is a harmful contaminant showing mutagenicity and carcinogenicity.Therefore,detection of chromium requires the development of low-cost and high-sensitivity sensors.Herein,blue-fluorescent carbon quantum dots were synthesized by one-step hydrothermal method from alkali-soluble Poria cocos polysaccharide,which is green source,cheap and easy to obtain,and has no pharmacological ac-tivity due to low water solubility.These carbon quantum dots exhibit good fluorescence stability,water solubility,anti-interference and low cytotoxicity,and can be specifically combined with the detection of Cr(Ⅵ)to form a non-fluorescent complex that causes fluorescence quenching,so they can be used as a label-free nanosensor.High-sensitivity detection of Cr(Ⅵ)was achieved through internal filtering and static quenching effects.The fluorescence quenching degree of carbon dots fluorescent probe showed a good linear relationship with Cr(Ⅵ)concentration in the range of 1-100 μM.The linear equation was F0/F=0.9942+0.01472[Cr(Ⅵ)](R2=0.9922),and the detection limit can be as low as 0.25 μM(S/N=3),which has been successfully applied to Cr(Ⅵ)detection in actual water samples herein.

Objectives To analyze the spatial and temporal aggregation of multidrug resistant pulmonary tuberculosis (MDR-TB) incidence in Nanning at the township / street scale from 2017 to 2021, to explore the spatial and temporal characteristics of the spread of MDR-TB in Nanning, and to provide a scientific reference basis for the health administrative departments to achieve the precise implementation of MDR-TB prevention and control. Methods Based on the data of MDR-TB cases in Nanning from 2017 to 2021, the spatial-temporal scanning analysis software SaTScan v9.7 was used to retrospectively detect and analyze the areas where MDR-TB cases gathered. Results Through simple spatial scanning analysis, it was found that there were three first-class aggregation areas (the aggregation center was Fujiayuan Street, Jiangnan District, 2017, Xinyang Street, Xixiangtang District, 2019, and Zhonghe Town, Yongning District, 2020), and one second-class aggregation area (the aggregation center was Jinchai Town, Mashan County, 2020). Simple time scanning showed that the clustering occurred from May 2019 to December 2020. Temporal and spatial aggregation analysis showed that Xinyang Street in Xixiangtang District was the center of the first-class aggregation area, Zhonghe Town in Yongning District was the center of the second-class aggregation area, and Jinchai Town in Mashan County was the center of the third-class aggregation area. Conclusion The multidrug resistant pulmonary tuberculosis epidemic in Nanning is distributed in an aggregated manner, especially in Xinyang Street, Xixiangtang District, which has the highest spatial and temporal aggregation. It is necessary to focus on and take regional prevention and control measures to control the epidemic.