Green synthesized nitrogen-doped carbon quantum dots for fluorescence sensing, information encryption and smartphone-assisted visual detection

The synthesis of carbon quantum dots (CQDs) with high added value from a wide range of renewable biowaste sources holds utmost significance in addressing environmental and economic concerns. Herein, we present a simple and environmentally friendly method for synthesizing high-quality fluorescent nitrogen-doped CQDs (N-CQDs) using orange peel. The obtained N-CQDs were employed as an efficient on-off-on fluorescent sensor for sequential ferric ions (Fe 3+ ) and ascorbic acid (AA) detection. The linear range for the determination of Fe 3+ was observed to be 2–150 μM, with a limit of detection (LOD) of 0.253 μM. Additionally, within the concentration range of 30–130 μM, the recovery fluorescence exhibited a favorable linearity with the concentration of AA. The calculated LOD for this range was found to be 1.57 μM. In addition, the prepared N-CQDs have been readily applied as information encryption. Besides, the paper based N-CQDs sensor, combined with the RGB/HSV analysis software, provides a cost-effective and portable solution for on-site fluorescence detection. To our knowledge, it is the first time that the CQDs derived from orange peel have been utilized in the domains of anti-counterfeiting and smartphone-assisted portable detection. These findings highlight the significant and diverse applications of biomass-derived CQDs.