Dual-Emission Carbon-Dot Ratiometric Fluorescence Sensor for Morphine Recognition in Biological Samples

Abstract

Herein, a novel nitr[ogen-doped carbon dot (N-CD) fluorescence sensor with a dual emission ratio is developed using the microwave-assisted synthesis of m-phenylenediamine and spermidine. As a result of the fluorescence inner filtration effect (IFE) effect between morphine (MOR) and N-CD, the blue fluorescence of N-CDs at 350 nm was reduced in the presence of MOR, whereas the fluorescence of N-CDs at 456 nm increased substantially. The results demonstrated that the approach has a tremendous potential and that the linear range of MOR detection is 0.25-25 µg/mL, with a 71.8 ng/mL detection limit. Under UV light, the blue fluorescent system is easily visible to the naked eye. More significantly, the sensor proved successful in providing satisfactory results for the speciation measurement of MOR in a variety of biological samples.

Keywords: carbon dots; dual-emission; fluorescent sensor; morphine.

Figure 1

A schematic illustrating the synthesis and morphine detection of N-CDs.

Figure 2

The analysis of N-CDs using (A) particle size distribution and (B) TEM images at different scales; (C) FT-IR; (D) XRD.

Figure 3

(A) XPS spectra of N-CDs, high resolution (B) C 1s, (C) N 1s, and (D) O 1s peaks of N-CDs.

Figure 4

(A) UV-Vis absorption spectra of N-CDs; (B) fluorescence spectra of N-CDs.

Figure 5

Effect of (A) pH under the same conditions (system temperature: 44 °C; N-CDs: 100 µL; MOR concentration: 10 μg/mL; Ex: 310 nm; Em: 350 nm and 456 nm) and (B) system temperature under the same conditions (pH: 8.0; N-CDs: 100 µL; MOR concentration: 10 μg/mL; Ex: 310 nm; Em: 350 nm and 456 nm).

Figure 6

Effect of (A) interfering ions and (B) interfering substances under the same conditions (pH: 8.0; system temperature: 44 °C; N-CDs: 100 µL; MOR concentration: 10 μg/mL; Ex: 310 nm; Em: 350 nm and 456 nm) (n = 3); (C) fluorescence spectra of MOR and its analogues (pH: 8.0; system temperature: 44 °C; N-CDs: 100 µL; concentration of MOR and its analogues: 10 μg/mL).

Figure 7

(A) A linear plot of I₃₅₀/I₄₅₆ versus the concentration of morphine in the range of 0.25–25 μg/mL (n = 3); (B) Fitted curves of I₃₅₀/I₄₅₆ versus the morphine concentration plotted on a log scale.

Figure 8

(A) Fluorescence spectra of N-CD solution with different concentrations of morphine. (B) The fluorescence lifetime curve of N-CDs and N-CDs + morphine. (C) The fluorescence spectra of N-CDs in different apolar solvents.

Figure 8

(A) Fluorescence spectra of N-CD solution with different concentrations of morphine. (B) The fluorescence lifetime curve of N-CDs and N-CDs + morphine. (C) The fluorescence spectra of N-CDs in different apolar solvents.