An ultrasmall chitosan nanosphere encapsulating carbon dots and rhodamine B as a ratiometric probe for the determination
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ORIGINAL PAPER
An ultrasmall chitosan nanosphere encapsulating carbon dots and rhodamine B as a ratiometric probe for the determination of Hg2+ Xiaoyu Wang 1 & Xiaobo Sun 1 & Zhigang Xu 1 & Wei Pan 1 & Guifeng Yu 1 & Jinping Wang 1 Received: 24 June 2020 / Accepted: 28 October 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Hg2+-sensitive carbon dots (CDs) were synthesized by microwave-assisted pyrolysis of citric acid, sodium fluoride, and urea. The CDs as a signal report unit and rhodamine B (RhB) as a reference were then encapsulated in a nanosphere of chitosan assembled by a nonsolvent-induced chitosan colloidal formation and in situ cross-linking to construct a ratiometric probe for Hg2+ (chitosan-CDs-RhB). Interestingly, without any assistance from acids to improve the solubility of chitosan, the nanosphere containing CDs and RhB had an ultrasmall size of 9.7 nm with only approximately 1.1-nm-thick layers of chitosan enclosing one dot. In order to keep the residual functional groups on the nanosphere from compromising the fluorescence response of CDs to Hg2+, Co2+ was used as a fluorescently intact metal ion to saturate the functional groups. The saturated chitosan-CDs-RhB was thus potentially developed for determining Hg2+ in the fruit bodies and mycelia of edible and medicinal fungi. Limits of detection (LODs) of 2.24, 5.29, and 2.03 μM and recoveries in the ranges 98.3 to 101.8%, 99.5 to 104.6%, and 97.4 to 100.9% were estimated for the determination of Hg2+ in the fruit bodies of Pleurotus ostreatus, Lentinus edodes, and Hypsizygus marmoreus, respectively. Chitosan-CDs-RhB was further developed as a fluorescent ratiometric probe for quantitatively determining intracellular Hg2+ in fungal mycelia with a linear calibration curve of RIgreen/Ired = − 0.145c + 1.69 within the range 0.013 to 0.356 μg g−1. Keywords Chitosan, Colloidal formation . In situ cross-linking . Intracellular determination . Edible and medicinal fungi . Ratiometric probe . Fluorescence . Carbon nanomaterials
Introduction Hg2+ can be toxic to humans, and long-term uptakes of food and water contaminated by Hg2+ can cause chronic mercury poisoning and possible death [1–3]. Therefore, highly selective and sensitive approaches to determining Hg2+ in foods should be available to improve food safety. Edible and medicinal fungi are of recognized functional foods; they may absorb a large amount of Hg2+ from the air, water, and medium in their growth process [4]. For food safety, highly selective and
Xiaobo Sun is a co-first author. * Jinping Wang [email protected] 1
College of Chemical and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, People’s Republic of China
sensitive determination of Hg2+ in the fruit bodies of edible and medicinal fungi has been generally focused on by scientists. However, determining intracellular Hg2+ with nontoxic and biocompatible probes to understand its transport and distribution in fungal cells would also be beneficial to Hg2+ contamination control [5, 6]. A
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