Trypan Blue-Based Carbon Dots for Sensing of Al3+ in Real Samples and Living Cells

Abstract

Aluminum is widely used in diverse fields of our daily life including maquillage, vaccine adjuvants, food packing, etc. Long-term aluminum exposure will lead to osteoporosis, Alzheimer's disease, and chronic renal failure. There still remains a need to develop low-cost, suitable, and rapid methods for the detection of Al³⁺. Herein, trypan blue-carbon dots (TB-CDs) were fabricated via a facile hydrothermal approach. The obtained TB-CDs were thoroughly analyzed by TEM, X-ray diffraction, FT-IR, XPS, UV-vis spectrophotometry, and fluorescence spectrophotometry. TB-CDs were spherical with a mean particle size of 2.9 nm and exhibited a high aqueous solubility with a fluorescence quantum yield of 6.37%. The obtained TB-CDs showed excellent photostability and relatively low cytotoxicity. The extent of fluorescence enhancement of TB-CDs was linearly related to the logarithmic concentration of Al³⁺. Thus, a fluorescence-on method was developed for fast and highly specific detection of Al³⁺ within the range of 0.5 to 4 μmol L^-1. The limit of detection was 0.2 μmol L^-1. Furthermore, the established sensing platform was successfully utilized for Al³⁺ determination in real samples and the intracellular imaging of Al³⁺. Owing to their convenience, low cost, and fast response, TB-CDs displayed promising potential in biochemical analysis and bioimaging fields.

1. Schematic Presentation of the Manufacturing Route of TB-CDs and Its Utilization for Al³⁺ Detection

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(a) TEM photo of the TB-CDs. Inset: HRTEM photo of TB-CDs. (b) Particle diameter distribution and Gaussian fitting curve of TB-CDs.

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(a) UV–vis absorbance and fluorescence spectra of TB-CDs. Inset: photographs of TB-CDs aqueous solution under visible light (left) and 365 nm UV light (right). (b) Fluorescence emission spectra of TB-CDs under various excitation wavelengths.

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(a) XPS wide scan spectra of TB-CDs. (b) XPS S 2p outcomes. (c) XPS C 1s outcomes. (d) XPS N 1s outcomes. (e) XPS O 1s results of the obtained TB-CDs.

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Influence of different parameters (a) NaCl concentration. (b) pH values. (c) UV light excitation time. (d) temperature range from 20 to 90 °C. (e) constant temperature of 70, 80, and 90 °C at different time intervals on the fluorescence emission intensity of TB-CDs.

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(a) Fluorescence responses of TB-CDs (10 μg mL^–1) to various concentration of Al³⁺ in Tris-HCl buffer solution (10 mmol L^–1, pH 5.0). (b) Fluorescence enhancement efficiency of TB-CDs (10 μg mL^–1) upon increasing concentration of Al³⁺ (0–8 μmol L^–1) in Tris-HCl buffer solution (10 mmol L^–1, pH 5.0). (c) Linear correlation between F/F ₀ and the logarithmic density of Al³⁺ within the scope of 0.5–4 μmol L^–1.

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(a) Fluorescence responses of TB-CDs (10 μg mL^–1) to various concentrations of metal ions in 10 mmol L^–1 Tris-HCl solution (pH 5.0). (b) Selectivity of TB-CDs (10 μg mL^–1) toward diverse metal ions in a 10 mmol L^–1 Tris-HCl solution (pH 5.0). The concentration of each metal ion was 2 μmol L^–1.

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(a) Bright-field microscopic pictures of A549 cells. (b) Incubated with 0.2 mg mL^–1 of TB-CDs for 6 h at 37 °C. (c) Further cultured with 50 μmol L^–1 Al³⁺ for additional 1 h at 37 °C. Upper panel: (a–c) bright-field microscopic pictures; lower panel: (d–f) their homologous fluorescence pictures, respectively. Scale bar: 50 μm.