Abstract
Quantitative and accurate determination of iron ions play a vital role in maintaining environment and human health, but very few polymeric chemosensors were available for the detection of Fe3+ in aqueous solutions. Herein, a water-soluble rhodamine-poly (ethylene glycol) conjugate (DRF-PEG), as a dual responsive colorimetric and fluorescent polymeric sensor for Fe3+ detection with high biocompatibility, was first synthesized through Schiff base reaction between rhodamine 6G hydrazide and benzaldehyde-functionalized polyethylene glycol. As expected, the introduction of PEG segment in DRF-PEG significantly improved the water solubility of rhodamine derivatives and resulted in a good biosensing performance. The detection limit of DRF-PEG for Fe3+ in pure water is 1.00 μM as a fluorescent sensor and 3.16 μM as a colorimetric sensor at pH 6.5. The specific sensing mechanism of DRF-PEG toward Fe3+ is proposed based on the intramolecular charge transfer (ICT) mechanism, in which the O and N atoms in rhodamine moiety, together with the benzene groups from benzaldehyde-modified PEG segment, participate in coordination with Fe3+. Furthermore, DRF-PEG was applied for the ratiometric imaging of Fe3+ in HeLa cells and showed the potential for quantitative determination of Fe3+ in fetal bovine serum samples. This work provides insights for the design of water-soluble chemosensors, which can be implemented in iron-related biological sensing and clinical diagnosis.
Highlights
Iron ion is one of the most abundant transition metal ions in the human body and plays a vital role in biological metabolism (Guo et al, 2015; Liu et al, 2017; Fan et al, 2019)
Water-Soluble Fluorescent Polymeric Chemosensor natural water or human body fluid is of great importance to human health and biological environment
A few water-soluble polymeric sensors obtained by combining PEG segment and rhodamine moiety have been designed for the detection of Cu2+, Hg2+, and Al3+ (Li et al, 2016; Geng et al, 2017; Li et al, 2018)
Summary
Iron ion is one of the most abundant transition metal ions in the human body and plays a vital role in biological metabolism (Guo et al, 2015; Liu et al, 2017; Fan et al, 2019). A few water-soluble polymeric sensors obtained by combining PEG segment and rhodamine moiety have been designed for the detection of Cu2+, Hg2+, and Al3+ (Li et al, 2016; Geng et al, 2017; Li et al, 2018). This work provides a facial and typical model for designing polymeric sensors with high biocompatibility and water solubility, which can be applied in living cell imaging or metal ion detection in biological systems. For the absorption and fluorescence selectivity experiment, DRF-PEG solution (0.1 mg/ml) was mixed with different metal ions (10–4 M). The cytotoxicity of DRF-PEG was evaluated by a standard MTT assay on HeLa cells (human cervical carcinoma cells) obtained from Shanghai EK-Bioscience Biotechnology Co., Ltd. HeLa cells were seeded at a density of 1 × 104 cells/well and cultured in DMEM medium with 1% antibiotic and 10% FBS (fetal bovine serum). After adding different concentrations of Fe3+ (100–1,000 μM), the fluorescent emission signals of serum samples were recorded
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