Rationally Designed Blue-to-Green Carbon Dot Nanoplatform for Self-Calibrated Ratiometric Fluorescence Sensing of Vitamin B2

Abstract Nanomaterial-based fluorescent probes have attracted considerable attention for sensitive biomolecule detection owing to their unique optical properties, high surface-to-volume ratio and excellent surface functionality. Herein, we report rationally designed blue-to-green carbon dots (BG-CDs) as a multifunctional carbon nanomaterial platform for self-calibrated ratiometric fluorescence sensing of vitamin B2 (VB2) through analyte-induced blue-to-green fluorescence modulation. The synthesized BG-CDs were comprehensively characterized using UV−vis and fluorescence spectroscopy, high-resolution transmission electron microscopy (HR-TEM), zeta potential analysis and FT-IR spectroscopy. The BG-CDs exhibited excitation-independent emission, pronounced pH sensitivity under acidic conditions, excellent photostability and a high quantum yield of 36.7%. The ratiometric fluorescence response was attributed to the inner filter effect (IFE), together with a possible Förster resonance energy transfer (FRET)-mediated excited-state quenching pathway between BG-CDs (donor) and VB2 (acceptor). The fluorescence intensity ratio (I535/I441) increased progressively with VB2 concentration (1−20 μM), showing a linear response over 1−10 μM with a low detection limit of 11.8 nM. The sensing platform exhibited high sensitivity and selectivity towards VB2 in the presence of potential interfering species. Furthermore, antioxidant, antibacterial and in vitro cytotoxicity studies demonstrated the multifunctional biological activities of BG-CDs. Cool white light-emitting diodes were also fabricated by embedding pristine BG-CDs and BG-CDs + VB2 in a polyvinyl alcohol (PVA) matrix, demonstrating their solid-state optoelectronic applicability. Overall, BG-CDs provide a multifunctional nano-enabled platform for ratiometric VB2 sensing, biological applications and solid-state optoelectronics.