This work involves the development of a novel waste-derived carbon dots (CDs) conjugated with silver (Ag) nanohybrid system-based Fluorescence Resonance Energy Transfer (FRET) sensor for the detection of melamine. CDs and Ag nanoparticles served as energy donors and energy acceptors, respectively. CDs were synthesized from orange peel waste through a combined hydrothermal and ultra-sonication route. The synthesized CDs had hydroxyl, amino, and carboxyl groups on their surface, explaining that waste-derived CDs can act as reducing and stabilizing agents and showed strong absorption and fluorescence emission at 305 and 460 nm, respectively. The bandgap, linear refractive index, conduction band, and valance band potential of CDs were observed to be 2.86, 1.849, 1.14, and 4.002 eV, respectively. No significant difference was observed in the fluorescence properties at different pH (acid and alkaline) and ionic concentrations. Given their fluorescent nature, the synthesized CDs were used for the detection of melamine. The fluorescence of CDs was found to be quenched by Ag⁺ due to the FRET energy transfer between CDs to Ag. Notably, the zeta potential of Ag@CDs was changed from − 28.7 mV to − 30.6 mV after the incorporation of Ag⁺. Ag@CDs showed excellent selectivity and sensitivity toward the sensing of melamine in the aqueous solutions with the limit of detection ~ 0.85 µM. Increasing the melamine level also raises the FL intensity of Ag@CDs. The substrate was effectively used in the detection of melamine in milk as a real application and the recovery percentage was found to be 98.03%. Moreover, other adulterants such as urea and formaldehyde can be detected selectively by Ag@CDs. Overall, the synthesized Ag@CDs can be used as an efficient material for sensing applications involving such food adulterants.

Graphical abstract

中文翻译：

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基于荧光共振能量转移的传感器，具有银共轭橙皮废物衍生碳点，用于三聚氰胺检测

这项工作涉及开发一种新型废物衍生碳点（CD），与基于银（Ag）纳米混合系统的荧光共振能量转移（FRET）传感器结合，用于检测三聚氰胺。CD 和 Ag 纳米颗粒分别充当能量供体和能量受体。CDs是通过水热和超声相结合的途径从橙皮废料中合成的。合成的CD表面具有羟基、氨基和羧基，这说明废物衍生的CD可以充当还原剂和稳定剂，并分别在305和460 nm处表现出强吸收和荧光发射。观察到CD的带隙、线性折射率、导带和价带电势分别为2.86、1.849、1.14和4.002 eV。在不同pH（酸和碱）和离子浓度下，荧光特性没有观察到显着差异。鉴于其荧光性质，合成的 CD 用于检测三聚氰胺。发现 CD 的荧光被 Ag 猝灭⁺由于 CD 与 Ag 之间的 FRET 能量转移。^{值得注意的是，掺入 Ag +}后，Ag@CDs 的 zeta 电位从 - 28.7 mV 变为 - 30.6 mV 。Ag@CDs 对水溶液中三聚氰胺的检测表现出优异的选择性和灵敏度，检测限约为 0.85 µM。增加三聚氰胺含量也会提高 Ag@CD 的 FL 强度。该底物经实际应用有效地用于牛奶中三聚氰胺的检测，回收率为98.03%。此外，Ag@CDs 可以选择性地检测其他掺杂物，例如尿素和甲醛。总体而言，合成的Ag@CD可作为涉及此类食品掺假物的传感应用的有效材料。

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