Highly fluorescent nitrogen-doped carbon dot (NCD) threads were synthesized via simple pyrolysis of citric acid, p-hydroxybenzoic acid, and ammonia. The NCDs show excitation-independent behavior with maximum excitation and emission wavelengths of 350 nm and 435 nm, respectively. The developed probe was used as a turn-off fluorescent sensor for the selective and sensitive determination of permanganate ions in aqueous media. The probe's hydrogel hybrid displayed a beautiful purple color demonstrating its potential as a naked eye sensor for gold detection. The ratiometric sensor exhibited excellent selectivity towards permanganate ions over 27 other ions with a linear range of 510 nM to 2 μM, a detection limit of 170 nM, and a linear regression value (R2) of 0.9944. Similarly, the linear range and limit of detection for gold ions was 3.89-20 μM and 1.285 μM, respectively. The synthesized NCDs were also used as a fluorescent ink as well as a naked eye marker in association with a gold solution demonstrating its potential forensic and anti-counterfeiting applications. Graphical abstract.

中文翻译：

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氮掺杂碳点可作为高锰酸根离子的“关闭”荧光探针，而其水凝胶混合物可作为金（III）离子的肉眼传感器。

通过柠檬酸，对羟基苯甲酸和氨的简单热解合成了高度荧光的氮掺杂碳点（NCD）线。NCD显示出与激发无关的行为，最大激发和发射波长分别为350 nm和435 nm。所开发的探针用作关闭荧光传感器，用于选择性和灵敏地测定水性介质中的高锰酸根离子。该探针的水凝胶杂化体显示出美丽的紫色，证明了其作为裸眼传感器进行金检测的潜力。比例传感器对其他27种离子具有高锰酸根离子选择性，线性范围为510 nM至2μM，检测极限为170 nM，线性回归值（R2）为0.9944。同样，金离子的线性范围和检测极限是3。分别为89-20μM和1.285μM。合成的NCD还用作荧光墨水以及与金溶液结合使用的裸眼标记物，证明了其潜在的法医学和防伪应用。图形概要。