Copper and nickel doped carbon dots for rapid and sensitive fluorescent turn-off detection of bilirubin

Abstract

Carbon dots doped with metals and non-metals have gained much popularity due to the enhancement in their optical and electronic properties. In this study, polyethyleneimine-functionalized transition metal (nickel or copper) doped carbon dots (CD, NiCD and CuCD) were synthesized through hydrothermal method. The carbon dots exhibited a blue fluorescence at 470 nm when excited at 350 nm. The as-synthesized carbon dots were utilised for the fluorimetric detection of bilirubin in the range 0.5 µM - 280 µM, with CuCD exhibiting the highest sensitivity of 155.38 a.u/log µM in the concentration range 0.5 to 10 µM and 84.01 a.u/ log µM in the concentration range 10 to 280 µM. CuCD also exhibited the lowest limit of detection of 0.0907 µM and the lowest limit of quantification of 0.3023 µM. All the carbon dots showed negligible interference in the presence of biomolecules and metal ions present in human serum implying the remarkable selectivity of the method to bilirubin detection. Further, the carbon dots were successfully tested for their real-time application in human serum using bilirubin-spiked serum samples.

Keywords: Bilirubin; Biosensor; Carbon dots; Copper-doped carbon dots; Fluorescence quenching; Nickel-doped carbon dots.

Fig. 1

UV-Vis absorption and PL spectra of (A) CD, (B) NiCD, and (C) CuCD at excitation wavelength 350 nm.

Fig. 2

HR-TEM images of (A) CD, (B) NiCD, and (C) CuCD and the particle size distribution histograms of (D) CD, (E) NiCD and (F) CuCD. (The insets depict the interplanar spacing (d-spacing) of the corresponding C-dots).

Fig. 3

(A) XRD and (B) FT-IR spectra of CD, NiCD and CuCD.

Fig. 4

PL emission spectra of the carbon dots (A) CD (B) NiCD and (C) CuCD with increasing concentration of bilirubin from 0.5–280 µM (λ_ex = 350 nm). Dual linear plots of log of concentration of bilirubin (µM) with PL intensity of carbon dots (D) CD (E) NiCD and (F) CuCD in the ranges 0.5–10 µM and 10–280 µM. Photographs depicting the quenching of fluorescence of carbon dots (G) CD (H) NiCD and (I) CuCD with increasing concentrations of bilirubin under UV illumination.

Fig. 5

Selectivity study of the carbon dots (A) CD (B) NiCD and (C) CuCD towards potential interference biomolecules in serum uric acid (UA), ascorbic acid (AA), creatinine (Crt), dopamine (DA), glucose (Glu), urea (Urea), glycine (Gly), L-alanine (L-Ala), L-aspartic acid (L-Asp), L-cystine (L-Cys), and vitamin B12 (Vit. B12) in comparison with bilirubin.

Fig. 6

Selectivity study of the carbon dots (A) CD (B) NiCD and (C) CuCD towards potential interference metal ions in serum Na(I), K(I), Cu(II), Zn(II, Ca(II), Mg(II), Co(II), Al(III), Fe(III), Fe(II), and Ni(II) in comparison with bilirubin.

Fig. 7

PL emission spectra of the carbon dots (A) CD (B) NiCD and (C) CuCD with increasing concentration of bilirubin spiked serum (λ_ex = 350 nm). Dual linear plots of log of concentration of bilirubin spiked serum (µM) with PL intensity of carbon dots (D) CD (E) NiCD and (F) CuCD.