Green transformation of biomass-derived Indian gooseberry into fluorescent intrinsic nitrogen-functionalized carbon quantum dots for real-time detection of vitamin B2 in the nanomolar range

Abstract

Riboflavin (RF) detection is essential for controlling nutritional health due to its increasing significance in the food and pharmaceutical industries. Regular daily intake of RF (vitamin B₂) is important because it is not synthesized and stored in the human body in appreciable amounts. Therefore, an efficient and biocompatible nanosensor with good selectivity and sensitivity for RF detection is required. Carbon quantum dots (CQDs) derived from biomass have recently attracted interest in environmental science due to their simple, cost-effective methods of synthesis, as well as their sustainability advantages and practical implications. Herein, we demonstrate the utility of a ratiometric fluorescence-based CQD nanosensor for the detection of RF in its isolated, pure form as well as in pharmaceutical tablets. We report the synthesis, characterization, and sensing potential of intrinsic nitrogen-functionalized carbon quantum dots (N-CQDs) from Indian gooseberry (a renewable biomass precursor) using a microwave-assisted pyrolysis method that involves a green methodology and occurs rapidly. High-resolution transmission electron microscopy (HRTEM) indicated that N-CQDs are monodisperse with an average diameter of ∼8.1 nm. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) validated intrinsic nitrogen functionalization and the presence of amino, hydroxyl, and carboxyl groups on the surface of N-CQDs. Further, X-ray diffraction (XRD), UV-visible and fluorescence spectroscopy, and time-correlated single photon counting (TCSPC) measurements were also employed for the characterization of N-CQDs. The as-prepared nanoprobe exhibits bright green emission with a remarkable fluorescence quantum yield of 48%. Moreover, N-CQDs are highly water-soluble and are extremely stable across a range of pH, ionic strength, and light. Additionally, N-CQDs selectively and specifically detect RF (vitamin B₂) in aqueous media w.r.t various bio-analytes with a limit of detection (LOD) ∼35 nM. Our nanosensor can also detect vitamin B₂ present in commercially available pharmaceutical tablets with an LOD of ∼61 nM. Mechanistic studies confirmed that sensing involves fluorescence resonance energy transfer (FRET) between RF and N-CQD interfaces. Overall, the present work provides a new vision for the development of an innovative and sensitive approach of a green fluorescent nanosensor for the detection of RF which may find potential applications in the pharmaceutical and food industries.