市售烟叶经烘干、剪碎后，分取1 g置于100 mL反应釜中，加入60 mL水，于180℃保温8 h。过滤，将滤液酸度调至中性，离心15 min，依次过0.45，0.22 μm水系滤膜，滤液用水稀释至100 mL，即得烟叶碳量子点（CQDs），用透射电子显微镜、紫外-可见分光光度计、荧光分光光度计等对其进行表征。渭河水样经静置过夜后，离心10 min，分取2 mL上清液置于比色管中，加入100 μL烟叶CQDs和3 mL伯瑞坦-罗宾森（B-R）缓冲溶液（pH 1.81），用水稀释至10 mL，静置4 h，置于荧光分光光度计中，在激发、发射波长分别为440，510 nm处检测。结果显示：烟叶CQDs呈规则球形，且分布均匀、尺寸均一，在260，280 nm处具有明显的紫外吸收峰，量子产率为4.88%，其荧光能够被亚硝酸盐猝灭；亚硝酸盐的浓度在2.00×10^-4~2.50×10^-1μmol·L^-1内与其对应的荧光强度猝灭值呈线性关系，检出限（3s）为0.66×10^-4μmol·L^-1；对渭河水样进行加标回收试验，回收率为97.5%~108%，测定值的相对标准偏差（n=5）为1.6%~3.3%。

Commercially available tobacco leaves were dried and cut, and then an aliquot (1 g) was placed into a 100 mL-reaction kettle. After 60 mL of water was added, the mixture was heated at 180℃ for 8 h, and filtrated, and the acidity of the filtrate was adjusted to neutral. The solution was centrifuged for 15 min, and passed through 0.45, 0.22 μm aqueous filtrate membranes in turn. The filtrate was diluted to 100 mL with water, and tobacco leaf CQDs were obtained, which were characterized by transmission electron microscopy, ultraviolet-visible (UV-Vis) spectrophotometer and fluorescence spectrometer. The Weihe water sample was centrifuged for 10 min after settling overnight, and 2 mL of the supernatant was placed into a colorimetric tube, in which 100 μL of tobacco leaf CQDs and 3 mL of B-R buffer solution (pH 1.81) were added. The mixed solution was diluted to 10 mL with water, settled for 4 h, placed in the fluorescence spectrophotometer and detected at excitation wavelength of 440 nm and emission wavelength of 510 nm, respectively. It was shown that the tobacco leaf CQDs were regular spherical in shape, uniform in distribution and size, with UV obvious absorption peaks at 260, 280 nm and quantum yield of 4.88%, and the fluorescence could be quenched by nitrite. Linear relationship between the concentrations of nitrite and quenching values of fluorescence intensity was kept in the range of 2.00×10^-4-2.50×10^-1μmol·L^-1, and the detection limit (3s) was 0.66×10^-4μmol·L^-1. The recoveries obtained by the spiked recovery test on the Weihe river water ranged from 97.5% to 108%, with RSDs (n=5) of the determined values in the range of 1.6%-3.3%.