Silicon nanoparticles-based ratiometric fluorescence platform: Real-time visual sensing to ciprofloxacin and Cu2+

https://doi.org/10.1016/j.saa.2021.119599Get rights and content

Highlights

  • The Si NPs-Eu3+ ratiometric sensing platform for CIP and Cu2+ was developed.

  • The strategy was convenient to construct and rapid in response.

  • The dramatic fluorescent color change displayed the high sensitivity of this probe.

  • Paper-based visual sensor was successfully applied to the assay of CIP in food samples.

Abstract

In this work, a silicon nanoparticles (Si NPs)-based ratiometric fluorescence sensing platform was conveniently fabricated by simply mixing fluorescent Si NPs as co-ligands and reference signal with lanthanide metal ion Eu3+ as response signal. The introduction of ciprofloxacin (CIP) remarkably turned on the characteristic fluorescence of Eu3+ at 590 nm and 619 nm through the “antenna effect”. At the same time, the blue emission of Si NPs at 445 nm kept comparatively stable. A good linear relationship between the ratio fluorescence intensity and CIP concentration in the range of 0.211–132.4 μM with a limit of detection (LOD) of 89 nM was obtained. In the presence of Cu2+, the fluorescence emission of Eu3+ was sharply turned off because of the stronger coordination ability of Cu2+ with CIP, which guaranteed the sequential detection of Cu2+. Meanwhile, the distinct fluorescent color change from bright blue to red, then back to blue, enabled naked-eye visual detection of CIP and Cu2+ in the solution phase and on paper-based test strip, and was successfully applied to determine the levels of CIP in complicated food samples with high sensitivity.

Graphical abstract

In this work, a silicon nanoparticles (Si NPs)-based ratiometric fluorescence sensing platform was conveniently fabricated by simply mixing fluorescent Si NPs as co-ligands and reference signal with lanthanide metal ion Eu3+ as response signal. The introduction of ciprofloxacin (CIP) remarkably turned on the characteristic fluorescence of Eu3+ at 590 nm and 619 nm through the “antenna effect”. At the same time, the blue emission of Si NPs at 445 nm kept comparatively stable. In the presence of Cu2+, the fluorescence emission of Eu3+ was sharply turned off because of the stronger coordination ability of Cu2+ with CIP. Meanwhile, the distinct fluorescent color change from bright blue to red, then back to blue, enabled naked-eye visual detection of CIP and Cu2+ in the solution phase and on paper-based test strip.

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Introduction

Silicon nanoparticles (Si NPs), a novel type of photoluminescence nanoparticles, have attracted considerable attention in the chemical and biological fields due to their superior merits, including good optical properties, facile synthetic routes, low cost, storage stability, surface tailorability, excellent biocompatibility and low cytotoxicity [1], [2]. These advantages make Si NPs superior to classic fluorescent molecules and toxic heavy metal-containing quantum dots such as CdTe QDs [3]. In the past few years, the researches of fluorescent nanoprobes based on Si NPs were mainly focused on fluorescence detection and imaging [4], [5], [6]. Li et al. reported a water-soluble Si QDs for selective Zn2+ sensing [7]. Chen and coworkers proposed a Si NPs-based dual-responsive ratiometric probe for selective hypochlorite sensing and cell imaging [8]. Recently, we have also developed Si NPs-based fluorescent sensing assay for the simultaneous discrimination and detection of catechol and hydroquinone [9]. Therefore, Si NPs can be highly exploitable in the development of novel optical sensors.

Nowadays, lanthanide-based fluorescent probes have been concerned in many research fields because of their unique optical properties, including long fluorescence lifetime, high luminescence quantum yield, large Stokes and/or anti-Stokes shifts and sharp line-like emission bands. The research of fluorescence sensing platforms based on lanthanide coordination nanoparticles has been designed for a series of targets detection [10], [11], diagnosis [12], [13] and bioimaging [14], [15]. In particular, Eu3+-based coordination nanoprobes have the excellent red fluorescence emission characteristic, which is helpful to distinguish from background fluorescence and reduce the interference of autofluorescence in biological samples. These advantages make the Eu3+-based fluorescence probes particularly suitable for visual detection in practical applications. Rong et al. have presented europium-doped carbon dots synthesized by citric acid and europium nitrate as fluorescent probe to detect DPA on a test stripe. This method effectively utilized the red characteristic fluorescence of Eu3+ and realized the visual and sensitive detection of DPA [16]. Chen’s group have synthesized Eu-doped silicon nanoparticles via stirring APTES, AA and EuCl3·6H2O mixture for 10 h to monitor anthrax spore biomarker-dipicolinic acid [17]. In spite of the satisfactory detecting results, the obvious disadvantage of tedious preparation process in this method can’t be neglected. Chu and coworkers have realized the long-term and real-time measurement of pH in live cells by using europium-doped silicon nanorods (Eu@SiNRs) as ratiometric fluorescent probe. In this sensing system, the emission peak of SiNRs at 470 nm was pH sensitive, and that of Eu3+ at 620 nm was pH insensitive [18].

Ciprofloxacin (CIP), as one of the most important fluoroquinolone antibiotics, has been widely applied as veterinary and human medicines to fight against bacterial infections, playing an important role in human health and many other fields due to the advantages of powerful therapeutic effect, good oral absorption, relatively low toxicity and cheap price [19]. However, the irrational abusing of CIP will lead to residue spread through the food chain, and finally accumulate in the human body, resulting in immediate adverse effects on human beings such as gastrointestinal complaints and central nervous system disorders [20]. Additionally, CIP can cause joint injury in the development stage, which is not suitable for pregnant women or children [21]. Thus, the determination of CIP has attracted much attention, especially in blood serum [22], urine [23] and environmental water [24]. However, the researches on the detection of CIP residues in food are rarely reported, especially in our daily food, such as fish, beef, chicken, pork, eggs and honey et al. Consequently, it is still highly desirable to construct a convenient, practical and reliable strategy for the detection of CIP in food samples, which is of great significance for guaranteeing environmental and food safety, as well as human health.

To date, various methods have been developed for the detection of CIP, including high-performance liquid chromatography (HPLC) [25], capillary electrophoresis [26], chemiluminescence [27], colorimetry [28], electrochemical techniques [29] and fluorescence [22]. Compared with other methods, fluorescence method has obvious advantages due to their simplicity, high-speed, high sensitivity, low-cost and non-destruction. Moreover, based on determining the intensities of two different emission wavelengths at the same time under same excitation wavelength to obtain the intensity ratio, ratiometric fluorescence assays can efficiently reduce fluorescence background interference from instrumental or environmental factors, which provides more accurate measurement in analytical applications, especially for complex samples [30], [31], [32].

Copper is one of the trace elements essential for human health. However, exposure to high concentrations of copper can lead to the disturbance of the cellular homeostasis, which will cause serious diseases. Therefore, the US Environmental Protection Agency (EPA) has set the maximum allowable limit of copper in drinking water to 1.3 ppm (~20 μM) [33]. Nevertheless, due to the wide use of Cu2+ in agriculture and industry, copper contamination and the detection continue to be challenging problems. In recent years, the methods that have been reported to detect copper are usually complicated, time-consuming and expensive [34], [35]. Accordingly, it is of great significance to develop a simple and rapid fluorescent probe for Cu2+ determination.

In consideration of these above factors, herein, we developed a novel strategy to propose a dual-emitting ratiometric fluorescent probe based on Eu3+ functionalized Si NPs for selective and sequential detection of CIP and Cu2+. Si NPs were easily synthesized by one-step hydrothermal method. Without any further synthesize and post-treatment process, only by simply mixing the obtained blue fluorescence Si NPs with Eu3+, the fluorescence ratiometric sensing platform was then developed. When CIP was added to the system, the red fluorescence of Eu3+ was turned on significantly (Scheme 1), and the good linear relationship between the ratio fluorescent intensity and CIP concentration insured the sensitive analysis of CIP in food samples. In the presence of Cu2+, the fluorescence of Eu3+ was sharply turned off because of the stronger coordination ability of CIP with Cu2+ than that with Eu3+. Therefore, the Si NPs-Eu3+-CIP platform has also been successfully applied to the recognition of Cu2+. With the addition of different concentrations of CIP and Cu2+, the distinct fluorescence color changing of the system from blue to red, then back to blue, can be easily recognized by the naked eye, which laid the foundation of visual detection strategy for CIP and Cu2+ by means of a paper-based test strip.

Section snippets

Chemicals.

Ciprofloxacin (CIP), tetracycline (TC), fleroxacin (FLE), norfloxacin (NOR), enoxacin (ENO), erythromycin (TRY), penicillin (PEN), chloramphenicol (CHL), streptomycin sulfate (STR) and europium nitrate were obtained from Dalian Meilun Biotechnology Co., Ltd. Trimethoprim (TRI) was bought from Yuanye Biological Technology Co., Ltd. (Shanghai, China). Disodium ethylenediamine tetraacetate (EDTA) was purchased from Chengdu Chemical Reagent Factory. 3-Aminopropyl trimethoxysilane (APTMS) was

Characterization of the fluorescent Si NPs and Si NPs-Eu3+

The maximum fluorescence emission intensity of the as-prepared Si NPs at 455 nm can be obtained with an excitation wavelength at 360 nm (Fig. 1A). Meanwhile, the water solution of Si NPs exhibitted bright blue fluorescence under excitation of 365 nm UV light (inset of Fig. 1A). The emission quantum yield of Si NPs was calculated to be 21.86% by using quinine sulfate (ΦR = 0.54) solution as a reference (Fig. S1). After mixed with Eu3+, neither the fluorescence emission wavelength nor the

Conclusions

In summary, by simply mixing Si NPs and Eu3+, a simple, fast, and sensitive ratiometric fluorescence sensing platform for CIP and Cu2+ was conveniently developed and validated. With its high selectivity and sensitivity, the proposed Si NPs-Eu3+ nanosystem was applied to detect CIP in different food samples with satisfactory recoveries. In addition, the fabrication of fluorescence test strips based on Si NPs-Eu3+ provided a new strategy in quantitatively determining CIP. Hence, this Si NPs-Eu3+

CRediT authorship contribution statement

Xiaoying Yuan: Formal analysis, Methodology, Visualization, Writing - original draft. Wendi Lv: Data curation. Bing Wang: Investigation. Chenglu Yan: Validation. Qiuting Ma: Software. Baozhan Zheng: Project administration. Juan Du: Conceptualization, Funding acquisition, Supervision. Dan Xiao: Resources.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (No.21876117, U1833124 and U1833202). We also appreciate Analytical & Testing Centre of Sichuan University for the characterizations.

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