Reusable Xerogel Containing Quantum Dots with High Fluorescence Retention

Abstract

Although various analytical methods have been established based on quantum dots (QDs), most were conducted in solution, which is inadequate for storage/transportation and rapid analysis. Moreover, the potential environmental problems caused by abandoned QDs cannot be ignored. In this paper, a reusable xerogel containing CdTe with strong emission is established by introducing host⁻guest interactions between QDs and polymer matrix. This xerogel shows high QDs loading capacity without decrease or redshift in fluorescence (the maximum of loading is 50 wt % of the final xerogel), which benefits from the steric hindrance of β-cyclodextrin (βCD) molecules. Host⁻guest interactions immobilize QDs firmly, resulting in the excellent fluorescence retention of the xerogel. The good detecting performance and reusability mean this xerogel could be employed as a versatile analysis platform (for quantitative and qualitative analyses). In addition, the xerogel can be self-healed by the aid of water.

Keywords: host–guest interactions; quantum dots; xerogel.

Scheme 1

The fabrication process of HEMA-Ad@βCD-CdTe/PHMAAm xerogel.

Figure 1

(a) Fluorescence spectra of βCD-CdTe at different reflux time (λ_ex = 380 nm). Insert is the photograph of the corresponding βCD-CdTe solutions (a small amount of the reaction solution is taken out at specific times during the reflux process) under ultraviolet lamp (λ_ex = 365 nm). From left to right: 30, 50, 70, 120 min. (b) Relative fluorescence intensity of βCD-CdTe under different pH conditions (PBS, 50 mM, βCD-CdTe: 5 mg/mL). The fluorescence intensity of βCD-CdTe at pH = 7.97 is set as 100%. (c) TEM (scale bar: 20 nm); and (d) high-resolution TEM (HRTEM, scale bar: 5 nm) images of βCD-CdTe dispersed in ultrapure water. One of the βCD-CdTe nanocrystals is marked by a red circle in the HRTEM image.

Figure 2

The relationship between fluorescence property and its concentration of HEMA-Ad/βCD-CdTe. (a) Photograph of HEMA-Ad@βCD-CdTe under ultraviolet light (λ_ex = 365 nm) with different concentrations (from left to right: 1/2/5/10/20/40/75/100/200 mg/mL); (b) fluorescence spectra of HEMA-Ad@βCD-CdTe with different concentrations (λ_ex = 380 nm); and (c) MFI scatterplot of HEMA-Ad@βCD-CdTe with different concentrations.

Figure 3

The fluorescence property of the xerogels. (a) photographs of βCD-CdTe (1, 20 mg/mL), HEMA-Ad@βCD-CdTe (2, 20 mg/mL) and the corresponding xerogel (3) under ultraviolet light (λ_ex = 365 nm); (b) the relative fluorescence intensity of 1, 2 and 3, in which the fluorescence intensity of 1 is set as 100%; (c) fluorescence spectra of 1, 2 and 3; and (d) fluorescence spectra of CdTe (20 mg/mL) and the corresponding xerogel (CdTe-xerogel). For all the fluorescence spectra, the excitation wavelength is 380 nm.

Figure 4

The detecting performance and reusable property of the xerogel. (a) Fluorescence spectra of the xerogel with different concentration Van (λ_ex = 380 nm). At the left is the corresponding photographs under ultraviolet light (λ_ex = 365 nm); (b) Calibration plot between I₀/I and the concentration of Van (c, mg/L); (c) Schematic illustration of the reclamation process; (d) The relative fluorescence intensity between the original xerogel and the recycled ones. The fluorescence intensity of the original xerogel is set as 100%. Below this are photographs of the corresponding xerogels under ultraviolet light (λ_ex = 365 nm). For the above test samples, Van is dissolved in PBS (pH = 8.01, 50 mM).

Figure 5

The interactions between the xerogel and various aromatic molecules. (a) The fluorescence spectra (λ_ex = 380 nm) of the xerogel after interacting with PBS (1, blank control, pH = 8.00), Van (2), PCA (3), HQ (4), p-NP (5) and o-NP (6); (b) The calculated quenching efficiency and (c) chemical structures of the detected aromatic molecules.