Rapid microwave-assisted synthesis of nitrogen-doped carbon quantum dots as fluorescent nanosensors for the spectrofluorimetric determination of palbociclib: application for cellular imaging and selective probing in living cancer cells

Abstract

The current study introduces a spectrofluorimetric methodology for the assessment of palbociclib without the need for any pre-derivatization steps for the first time. This approach relied on the palbociclib quenching effect on the native fluorescence of newly synthesized nitrogen-doped carbon quantum dots (N-CQDs). An innovative, facile, and rapid microwave-assisted pyrolysis procedure was applied for the synthesis of N-CQDs using available and economic starting materials (the carbon source is orange juice and the nitrogen source is urea) in less than 10 minutes. Full characterization of the prepared QDs was carried out using various techniques. The prepared N-CQDs exhibited good fluorescence emission at 417 nm after excitation at 325 nm with stable fluorescence intensity and good quantum yield (29.3%). They showed spherical shapes and narrow size distribution with a particle size of around 2-5 nm. Different experimental variables influencing fluorescence quenching were examined and optimized. A good linear correlation was exhibited alongside the range of 1.0 to 20.0 μg mL^-1 with a correlation coefficient of 0.9997 and a detection limit of 0.021 μg mL^-1. The proposed methodology showed good selectivity allowing its efficient application in tablets with high percentage recoveries and low percentage RSD values. The mechanism of quenching was proved to be static by applying the Stern-Volmer equation at four different temperatures. The method was validated in accordance with ICHQ2 (R1) recommendations. Intriguingly, N-CQDs demonstrated good biocompatibility and low cytotoxicity, which permitted cellular imaging and palbociclib detection in living cancer cells. Therefore, the proposed method may have potential applications in cancer therapy and related mechanism research.

Fig. 1. Chemical formula of PLB.

Scheme 1. Synthesis of N-CQDs and application for determination of PLB.

Fig. 2. (A) Fluorescence spectra of N-CQDs; (a) excitation and (b) emission spectra (inset: photographs of N-CQDs under visible light and UV light), (B) Fluorescence spectra of N-CQDs at varied excitation wavelengths (310–380 nm).

Fig. 3. (A) UV absorption spectrum of N-CQDs, (B) FTIR spectrum presenting the surface functionality of N-CQDs.

Fig. 4. HRTEM images of N-CQDs; (a) 50 nm, (b) 100 nm, (c) 200 nm.

Fig. 5. (A) Fluorescence emission spectra of N-CQDs after addition of different PLB concentrations (from top to bottom: 0, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 18.0, 20.0 μg mL⁻¹), (B) The linearity plot of fluorescence quenching against PLB concentration.

Fig. 6. Stern–Volmer plots for the quenching of N-CQDs fluorescence by PLB at four different temperature settings (298, 303, 313, and 323 K).

Fig. 7. Effect of addition of PLB on the UV absorption spectrum of N-CQDs.

Fig. 8. Effect of pH (a), buffer volume (b), and incubation time (c) on the quenching of the fluorescence spectrum of N-CQDs by PLB (6.0 μg mL⁻¹).

Fig. 9. Viability of HepG2 cells after incubation for 48 hours with various concentrations of N-CQDs and doxorubicin as a control in the MTT assay.

Fig. 10. Confocal microscopy images of HepG2 cells incubated with 0.015% of N-CQDs for 6 hours. (a) Bright field images, (b) after excitation at 360 nm, and (c) after addition of 10 nM of PLB.