Graphene Oxide Membrane Immobilized Aptamer as a Highly Selective Hormone Removal

Abstract

Three-dimensional (3D) reduced graphene oxide (rGO) modified by polyethyleneimine (PEI) was prepared and functionalized by fluorophore-labeled dexamethasone-aptamer (Flu-DEX-apt) via π-π stacking interaction. The rGO/PEI/Flu-DEX-apt was used as a selective membrane for dexamethasone hormone removal from water. The prepared rGO/PEI/Flu-DEX-apt membranes were stable, insoluble, and easily removable from liquid media. The membrane was characterized by Raman spectroscopy, scanning electron spectroscopy, and FTIR spectroscopy. The rGO/PEI/Flu-DEX-apt membrane showed high sensitivity and specificity toward the dexamethasone hormone in the presence of other steroid hormone analogs, such as progesterone, estrone, estradiol, and 19-norethindrone. The fluorescence and UV-visible spectroscopy were used to confirm the membranes performance and the quantification of hormones removal. The resulting data clearly show that the graphene oxide concentration influence the aptamers and analytes interaction (π-π stacking interaction). It was found that by varying the graphene oxide concentration yields to different porosities of rGO/PEI/Flu-DEX-apt membranes affects the adsorption recovery rate, as well as the specificity and selectivity toward the dexamethasone hormone.

Keywords: aptamer; dexamethasone; graphene membrane; graphene oxide; polyethyleneimine.

Figure 1

Fluorescence intensity dependence on graphene oxide concentration: (a) photographs of graphene oxide solutions with different concentrations (C), i.e., C₁ = 0.500 g/L, C₂ = 0.858 g/L, C₃ = 1.358 g/L and C₄ = 3.716 g/L, the color changes from nearly clear (low concentration) to dark (high concentration); (b) 280 nm was used as wavelength excitation to generate the fluorescence emission spectrum of different graphene oxide (GO) concentrations; the emission maximum is seen at 565 nm (the insert fluorescence intensity vs. the graphene oxide concentration).

Figure 2

FTIR analysis spectra: (a1) spectrum of graphene oxide; (a2) spectrum of polyethyleneimine (PEI). (a3) spectrum of the combined product reduced graphene oxide (rGO)–PEI; (b) Raman spectra of the different rGO/PEI concentrations: i.e., C₁ = 0.500 g/L, C₂ = 0.858 g/L, C₃ = 1.358 g/L and C₄ = 3.716 g/L and the insert in Figure 2b shows the intensity ratio distribution plot of D and G peaks; and (c) the UV–visible spectra of GO and rGO/PEI.

Figure 3

(a) Optical images of the reduced graphene oxide membrane and high magnification SEM image showing the 3D porous architecture membrane. The SEM images of 3D membrane graphene oxide–PEI foam made from different concentrations (C) of GO; (b) C₁ = 0.500; (c) C₂ = 0.858; (d) C₃ = 1.358; and (e) C₄ = 3.716 g/L (200 mm scale bar).

Figure 4

(a) Comparison of fluorescence intensity quenching efficiency between reduced graphene oxide–analyte/reduced graphene oxide–aptamer–analyte complex excited at λ_max = 280 nm; (b) percentage of the absorption intensity for rGO/PEI/fluorophore-labeled dexamethasone-aptamer (Flu-DEX-apt) and the rGO/PEI-Dex for different graphene oxide concentrations.

Figure 5

Specificity and selectivity for dexamethasone: different hormone analogs of dexamethasone interaction with rGO/PEI/Flu-DEX-apt under the same experimental conditions (1- dexamethasone; 2-estrone; 3- 19-norethindrone; 4- estradiol; 5-progesterone; 6- mixed hormones); the fluorescence peaks measured from different hormones at 15 ppm.