Insight into the Modulation of Carbon-Dot Optical Sensing Attributes through a Reduction Pathway

Oxidized/reduced carbon dots (CDs) with tunable optical features have emerged as a new class of CDs having a common "molecular origin" but different fluorescence (FL) behaviors. In the present work, using "banana peel" as a sole carbon source followed by doping with fluorine (F), boron (B), and nitrogen (N) over CDs, banana peel-derived carbon dots (BP-CDs) were synthesized using a well-known hydrothermal synthesis method. Moreover, as-synthesized BP-CDs were further reduced to "rBP-CDs" by NaBH₄. At post reduction, the FL performance (i.e., quantum yield) of rBP-CDs were found to be enhanced compared with the BP-CDs, along with variations in excitation and emission wavelengths. Interestingly, the optical sensing attributes of BP-CDs and rBP-CDs were varied, that is, BP-CDs selectively sense "Co²⁺ with a limit of detection (LOD) value of 180 nM", whereas rBP-CDs detected Co²⁺ (with an LOD value of 242 nM) as well as Hg²⁺ (with an LOD value of 190 nM). To the best of our knowledge, this work presents the very first report on the modulation of CDs' sensing behavior after reduction. The modulation in the sensing behavior with the common carbon precursor and reduction paves a new possibility for exploring CDs for different commercial applications.