Rapid and On-Site Detection of Uranyl Ions via Ratiometric

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Rapid and On-site Detection of Uranyl Ions via Ratiometric Fluorescence Signals Based on a Smartphone Platform Xinfeng Chen, Qingsong Mei, Long Yu, Hongwei Ge, Ji Yue, Kui Zhang, Tasawar Hayat, Ahmed Alsaedi, and Suhua Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b13765 • Publication Date (Web): 07 Nov 2018 Downloaded from http://pubs.acs.org on November 7, 2018

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ACS Applied Materials & Interfaces

Rapid and On-site Detection of Uranyl Ions via Ratiometric Fluorescence Signals Based on a Smartphone Platform Xinfeng Chena,||, Qingsong Meib,||, Long Yua, Hongwei Gea, Ji Yuea, Kui Zhangc,*, Tasawar Hayatd, Ahmed Alsaedid, and Suhua Wanga,* aCollege

of Environmental Science and Engineering, North China Electric Power University,

Beijing, 102206, China bSchool

of Biological and Medical Engineering, Hefei University of Technology, Hefei, Anhui,

230009, China cSchool

of Chemistry and Chemical Engineering, Anhui University of Technology, Ma’anshan,

Anhui, 243032, China dNAAM

Research Group, King Abdulaziz University, Jeddah 21589, Saudi Arabia

* Corresponding author: [email protected]; [email protected]. ||

These authors contributed equally to this work

KEYWORDS Smartphone, Uranyl ions, Ratiometric fluorescence sensor, 3D-printed, APP

ACS Paragon Plus Environment

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ABSTRACT

Fluorescent quantum dots of carbon and semiconductor have superior optical properties and show great potential in sensing applications. This paper reports a novel method for rapid detection of uranyl ions via ratiomedtric fluorescence signals by employing the two types of quantum dots as the key materials. As the most soluble and stable toxic uranium species, uranyl has been recognized as an important index for nuclear industrial wastewater. However, its onsite, rapid and sensitive determination remains challenging. This work uses the ratiometric fluorescent signal of quantum dots and combines a smartphone-based handheld device for on-site and rapid detection of uranyl. The ratiometric fluorescent probe is achieved by integrating carbon dots (C-dots) and CdTe quantum dots (MPA@CdTe QDs) through chemical hybridization. The presence of uranyl ions greatly quenches the red fluorescence of the CdTe QDs, whereas the green fluorescence keeps constant, leading to obvious color change. An App and a 3D-printed accessory have been developed on a smartphone to analyze and calculate the content of uranyl on the basis of captured fluorescence signals from a test strip with immobilized probe. This new designed mobile detection system displays good analytical performance for urnayl ions in wide concentration range from 1 μM to 150 μM, which shows great potential application in controlling the nuclear industrial pollution.

INTRODUCTION

Uranium has been widely used either in military or in civilian, such as for nuclear explosives, city power plants and etc. Especially, the low-radiation depleted uranium was commonly applied in armor or containers for transporting radioactive sources in hospital.1-3 Nevertheless, with increasing anthropogenic activity, considerable amounts of


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uranium containing wastes have been released into environment, which can enter into the human body through the skin, the respiratory tract, and digestive system. It is well known that uranium is a chemo-toxic, radiotoxic and long half-life metal ion, and it can cause acute toxicological effects in mammals and influence the normal function of brain, kidney, liver, heart and other systems.4-5 In nature, uranium in compounds has various oxidation states (+2, +3, +4, +5, and +6), and the most soluble and stable species in environment is uranyl ions (UO22+).6-7 Thus, it is in high demand to develop a sensitive, selective, and portable analytical method to measure the amount of uranyl ions in aqueous media. Conventional analytical techniques for determination of uranyl ions have been reported, including coupled plasma mass spectrometry,8-9 laser-induced kinetic phosphorimetry,10 Raman spectrometry,11 complexometric titration,12 electrochemical approaches,13 and so on. These methods have satisfactory detection limit and good selectivity to uranyl ions, but mostly need expensive instruments, tedious sample pre-treatments, and strict detection conditions.5,14-15 Nano material fluorescence-based analyses of uranyl ions have recently attracted much interest for their convenient, low-cost and real-time features. For example, Zhou et al. reported a metal-organic framework material fluorescence sensor for uranyl ions with high selectivity and wide detection range, which was further used to detect uranyl ions in different polluted sites.16 Wen et al. designed a aggregation-induced emission (AIE) organic fluorescent probe TPE-T (tetraphenylethene modified with 2-(4,5-dihydrothiazol2-yl) phenol) for the visual determination of uranyl ions in aqueous media based on the selective binding between TPE-T and uranyl ions.17 R.K. Dutta et al. had modified cadmium sulfide quantum dots (CdS) with amine groups and used it as an chemical


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fluorescence sensor to monitor the uranyl ions at ultratrace levels, and the detection limit was calculated to be 0.07 μg/L.18 However, most of these fluorescence-based sensors employed single fluorescent intensity as only responsive signal, which is readily influenced by some experimental factors, including instrument deviation, solvent influence and etc. Different from the single fluorescence based methods, the ratiometric fluorescence method can minimize the above interference, realization of higher analytical accuracy by self-calibration of two fluorescence intensities. Generally, ratiometric fluorescence methods accompany with perceived color variations, enabling rapid visual identification.19-20 Herein, for the first time, a ratiometric fluorescence probe has been developed by hybridizing green-emissive C-dots and red-emissive CdTe QDs for rapid and sensitive detection of uranyl ions. Due to its relatively high stable chemical properties and high stability against various metal ions, the C-dots with green fluorescence synthesized from urea were chosen as the self-referencing signal. But the responsive unit was red fluorescent MPA@CdTe QDs, because molecule of MPA contained a carboxyl group and bidentate thiol group that can react with the uranyl ions easily and may form a charge-transfer complex. As a result, the ratios of fluorescence intensity at 525 nm and 640 nm (I525

nm/I640 nm)

of the ratiometric fluorescent probe

gradually enhanced upon the addition of uranyl ions, and the corresponding color continuously changed from red to green, which can be employed for further quantitative measurement and visual identification, respectively. Furthermore, the properties of the probe including superior spectroscopic properties, good water solubility, low photobleaching and optical blinking, made the ratiometric probe more suitable for sensitive detection of uranyl ions in various aqueous conditions.21-24


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In the past decade, a variety of applications have been developed on smartphone because of its powerful computing and high resolution camera, including some report for biological and chemical detection.25-26 It has been reported that a variety of smartphonelinked sensors based on 3D printing had been designed for collecting different types of signals including optical, impedance and electrochemical current, largely promoting the development of smartphone-based detection platforms.27-28 For instance, Qingjun Liu and et al. reported a smartphone-based sensing system for quantitative assays of 2,4,6trinitrotoluene (TNT) by using printed electrodes to receive impedance signals.29 Bixia Lin and Ying Yu reported a smartphone device to shoot and record the color changes of aptasensor fluorescence caused by streptomycin, and the corresponding digital images were then transferred to RGB data and analyzed by smartphone.30 Herein, a portable smartphone platform combined with ratiometric fluorescence probe was first designed and established for on-site and point-of-care detection of uranyl ions. The uranyl ions and the responsive ratiometric probe were first mixed with different concentrations, and each reacted solution was then fixed onto cellulose acetate test strip. The strip was placed into the smartphone accessory equipped with a light source of 365 nm output. The uranyl ion-induced the color variation of ratiometric probe on test paper was recorded by camera of the smartphone, and the corresponding digital image was then analyzed by a self-designed color identification APP “Concentration Detection”. The APP could quickly recognize the color of image and translate it into digital information. This work demonstrated a smartphone-based detection platform that could not only realize the point-of-care monitoring uranyl ions concentrations in environment, but also provide a possible way to design new sensing platforms for other environmental pollutant detection.


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EXPERIMENTAL SECTIONS

Regents

Cadmium

chloride

hydrate

(CdCl2•2.5H2O),

tellurium

powder,

3-

mercaptopropionic acid (MPA), uranium nitrate (UO2(NO3)2•6H2O), urea, citric acid, sodium borohydride (NaBH4), sulfuric acid (H2SO4), sodium hydroxide (NaOH), copper chloride dihydrate (CuCl2•2H2O), and mercury nitrate (Hg(NO3)2) were obtained from Aladdin Biochemical Technology Co. Ltd. All chemicals were of analytical grade and used directly. All aqueous solutions were directly prepared using ultrapure water (18.2 MΩ•cm) before use. Instrumentation The fluorescence intensities were measured in a 1 cm quartz cuvette on a Perkin-Elmer LS-55 luminescence spectrometer. The high resolution transmission electron microscope (HRTEM) images were performed on a JEOL 2010 transmission electron microscope. The smartphone-linked device was produced by 3D printer Replicator 2X. The photographs were taken with a brand smartphone and a Canon 600D digital camera. The smartphone were also employed for the real sample detection. Synthesis of the urea C-dots and MPA@CdTe QDs The green-emissive C-dots were synthesized by following a one-pot hydrothermal method.31-32 The citric acid and urea mass ratio was 1:3. Specifically, citric acid (1g) and urea (3 g) were dissolved into 10 mL of deionized water in a beaker to form clear solution. The solution was heated and kept at 200 °C for 2 hours at ambient conditions, and a dark-brown clustered solid produed. The separated solid was re-dissolved in pure water and the agglomerated particles were removed by centrifugation (10000 rpm, 10 min). Finally, the solution of blue-emitting Cdots was stored in dark at 4 °C. The red-emitting quantum dots of MPA@CdTe were synthesized using our previous method in aqueous solution.33-34


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Synthesis of the ratiometric fluorescent probe For different purposes, the dual emission probe were constructed in two strategies. To perform the spectral measurement, 2 μL of green fluorescent C-dots solution and 3 μL of red-emitting MPA@CdTe QDs were thoroughly mixed in a cuvette with 2 mL of ultrapure. To perform the smartphone application, the mixture of MPA@CdTe QDs and C-dots were stirred in different mass ratio (1:1, 1:2, 1:3, respectively, and diluted with one fold pure water). Fluorescence response of the ratiometric fluorescent probe to uranyl ions The detection media were optimized by fluorescence intensity, reproducibility and sensitivity to uranyl ions in different solvents and pH values, and the result demonstrated that the ultrapure water was the most suitable media for uranyl ions detection. A solution of uranyl (1 mM) was prepared by directly dissolving 0.197 g of UO2(NO3)2·6H2O in 500 mL of ultrapure water and the pH value was 4.0. The working uranyl solution with lower concentration was prepared by diluting the stock solution and pH value increased to 5.78 due to the hydrolyzation of uranyl. To estimate the sensitivity of ratiometric probe, 2, 2, 3, 3, 4, 6, 8, 10 and 12 μL of uranyl solution (10 μM) was added into 2 mL of as-prepared probe solutions in quartz cuvettes to measure the fluorescence spectra after 30 s. The fluorescence spectra were recorded by a 365 nm excitation at ambient conditions, and all the fluorescence intensities were an average of three independent measurements. As a control experiment, the same processes were carried out for the possible interfering metal ions. Selectivity and Interference Study The stock solution of each tested metal ion was prepared directly by dissolving the corresponding salt in ultrapure water. And the solution of mercuric nitrate was prepared in 0.1 M HNO3 to avoid hydrolysis. For the detection experiments, 2 mL of as-prepared probe solution and 4 μL of each metal ion solution (0.1


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mM for Fe3+, Al3+, Hg2+, and Cu2+, 1 mM for Na+, K+, Ni+, Ca2+, Mg2+, In3+, Co2+, Mn2+, Al3+, Ag+, Zn2+, Ba2+, Pb2+, Co2+, and Cd2+) were thoroughly mixed in quartz cuvette, respectively, followed by recording the fluorescence spectra. For the detection in the presence of Cu2+ and Ag+, 4 μL of extra solution of Na2S was added into the mixed solution to precipitate the interfering metal ions, and the spectra were measured for comparison. For the interference study, 2 μL of 0.1 mM uranyl ions was subsequently introduced into the above mixture of each metal ion solution, and the spectral response were then collected.

RESULTS AND DISCUSSION

Characterization of the ratiometric fluorescent probe Firstly, HRTEM was used to characterize the morphologies and size of two components of probe. As shown in Figure 1a and 1b, the average size of the MPA@CdTe QDs and C-dots was estimated to be about 4 nm and 4.5 nm in diameter, respectively. The spectroscopic properties of MPA@CdTe QDs and C-dots were shown in Fig. S1. The emission center of MPA@CdTe QDs was located at 640 nm, displaying a strong red fluorescence, and the maximum emission center of C-dots was at 525 nm, exhibiting a dark green fluorescence. The quantum yields of the C-dots and MPA@CdTe QDs were carefully measured to be 21.6% and 42.2%, respectively, using quinine sulfate in 0.1 M sulfuric acid and rhodamine 6G in ethanol solution as references (Fig. S2). The ratiometric fluorescent probe displaying pink fluorescence under 365 nm UV light was obtained by completely mixing the MPA@CdTe QDs and C-dots. More characterization including Uv-vis, FT-IR, XPS, and XRD was carefully performed and analyzed for C-dots and MPA@CdTe (Fig. S3-S7). The results clearly confirmed the average sizes, chemical structure,


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surface functional, crystal structure and, and oxidation states of C-dots and MPA@CdTe. The fluorescence of C-dots was very stable against metal ions and the control experiments showed that many metal ions had no any effect on the fluorescence intensity of the C-dots (Fig. S8), demonstrating that such metal ions do not affect the sensitivity of uranyl detection. The C-dots in this work were synthesized in air and at temperature of 200 C, which decreased the surface reactivity to metal ions due to oxidation. Therefore, the C-dots prepared herein showed different chemical and spectroscopic properties from those previously reported,35-38 which were synthesized under different conditions and from materials (Table S1). The pH change in acidic range can degrade the fluorescence of MPA@CdTe quantum dots, but pH higher than 6 have no effect on the MPA@CdTe QDs (Fig. S9). The pH values of the probe solution were measured to be 6.85, at which the fluorescence of the CdTe was stable. For the measurement, only a small volume (2 ~ 40 μL) of the uranyl working solution was mixed with 2 mL of probe solution, and the pH of the final solution were measured to be from 6.85 to 6.78. Such a little variation of pH had no effect on the red fluorescence of MPA@CdTe QDs (Fig. S9), which ensured that uranyl ions were the main factor to quench the fluorescence. Actually, the probe has similar responses to uranyl ions in the pH range from 4 to 9 (Fig. S10), in which the uranyl ions take main different forms of UO22+, UO2OH+, (UO2)3(OH)5+, and etc. (Fig. S11). The results suggest that it should be the oxidation state of U(VI) that alter the fluorescence of the probe, which is independent on the actual species of uranyl ions. In this work, the measurement was carried out at pH 6.85, and the uranyl ions hydrolyzed to take the form of (UO2)3(OH)5+, which shows no obvious effect on the sensitivity and selectivity of the method. The ratiometric fluorescent intensity changes were monitored by spectrometer in two hours under consecutive illumination of ultraviolet light. As showed in the Fig. S12, the


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ratio (I525/I640) of the fluorescence intensity of the fluorescence probe had no evident change, implying the probe’s excellent stability and anti-photobleaching in aqueous solutions. To optimize the condition for visual detection of uranyl ions in solution, different fluorescence intensity ratios of ratiometric probe response to equal amount of uranyl ions were carefully studied. The results show that the intensity ratio (I525/I640) value of 1:2 is the best for uranyl detection, as showed in Fig. S13. Clearly, the variation of fluorescence color upon uranyl ions was in a wider range. For other intensity ratio such as 1:1 and 1:3, the color changes were not obvious after the addition of uranyl ions. Therefore, the 1:2 ratio (I525/I640) of fluorescence intensity was selected to fabricate the ratiometeric probe and used for subsequent analysis. The dose response of the probe to uranyl ions had been studied carefully. Without uranyl ion addition, there are two emission peaks at 525 nm and 640 nm under excitation of 365 nm light, respectively. As shown in the Fig. 1c, the red emission peak at 640 nm of the ratiometric probe was gradually quenched upon the continuous addition of uranyl ions, whereas the green emission peak at 525 nm was unchanged. As fluorescence intensity ratios (I525/I640) of the ratiometric probe increased, the resultant fluorescence color continuously changed from red to green (the inset of Fig. 1c), which could be easily observed by the naked eye under a UV lamp.


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Figure 1. HRTEM images of (a) C-dots and (b) MPA@CdTe QDs; (c) Ratiometric fluorescent spectra of the probe (λex= 365 nm) in the presence of uranyl ions (0−250 nM) in ultrapure water. The inset photograph shows the corresponding visible fluorescent color changes of the probe under UV light excitation, respectively; (d) Plots of quenching efficiency of the fluorescence versus uranyl content in ultrapure water. Fig. 1d displays the calibration curve based on the intensity ratio (I525/I640) of the probe versus the concentrations of uranyl ions. The value of I525/I640 was gradually increased with the


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increasing uranyl ions concentrations in the range from 0 to 250 nM, resulting in a linear fitting with a coefficient of 0.9999 (R2), which can be employed for the measurement of uranyl ions. The detection limit was calculated to be as low as 4 nM based on a signal-to-noise ratio of 3, which was much lower when compared with other fluorescent methods for the detection of uranyl ions.16, 39-40 Selectivity and anti-interference of the ratiometric fluorescent probe The selectivity of the probe to uranyl ions against other environmentally relevant metal ions, including Na+, K+, Cd2+, Ba2+, Zn2+, Mg2+, In3+, Co2+, Mn2+, Al3+, Ag+, Ni2+, Ca2+, Al3+, Fe3+, Pb2+, Hg2+, and Cu2+, was carefully examined. The concentrations of the metal ions were chosen on the basis of real application conditions, in which the alkaline earth metal ions are the most abundant. In addition, some transition metal ions like Ag+ and Cu2+ can be readily removed through pretreatment with sulfide before fluorescence measurement. It was reported that Cu2+ and Ag+ could quench the fluorescence of MPA@CdTe QDs due to ions exchange41 or coordination between Cu2+ and the thiol group on the QDs surface,42-43 and it would influence the selectivity towards uranyl. To eliminate the influence of silver and copper ions on the detection, we have utilized sodium sulfide to remove these ions by precipitation which showed the best efficiency than EDTA to remove these ions. Appropriate amount of Na2S solution was introduced to the sensing system before detection, and it can help to precipitate and separate Cu2+ and Ag+ from the target solutions. To validate the probe, the anti-interference ability of the method against other metal ions was synchronously examined. As shown in the Fig. 2, except for Cu2+ and Ag+ ions, the intensity ratios (I525/I640)0/(I525/I640) of the ratiometric probe exhibited a negligible change after adding other metal ions. Later, 1 equiv of uranyl ions was added into the mixture, respectively. The


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results showed that the presence of coexisting ions of higher concentrations than that of uranyl ions had no obvious interference on the uranyl ion sensing. For Cu2+ and Ag+ ions, the same result can be found after introducing the sodium sulfide agent. These results indicated high selectivity and anti-interference of the ratiometric fluorescent probe to uranyl ions, which would be practical for visual determination of uranyl ions.

Figure 2. Selectivity and anti-interference study of the ratiometric probe in ultrapure water against other metal ions. (I525/I640)0 and (I525/I640) were the ratios of fluorescence intensities with and without cations or uranyl ions, respectively). The absorption spectrum of CdTe-MPA QDs is nearly identical to that after mixing with uranyl ions, and there is no spectral overlap between them, which exclude fluorescence resonance energy transfer for the quenching mechanism. The zeta potential of MPA@CdTe QDs was measured to be -26.73 mV, which is consistent with the carboxylic groups of MPA on the surface of QDs. In addition, dynamic light scattering (DLS) measurements were carried on MPA@CdTe QDs with and without uranyl ions. The dynamic light scatting result shows that the dynamic sizes of the particles have no obvious change after interaction with uranyl ions (Fig. S14), excluding the possibility of MPA@CdTe QDs aggregation. It has been speculated the


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uranyl ions and the surface functional groups of MPA might form a complex, which further quenching the fluorescence of MPA@CdTe QDs through photo-induced electron transfer. On-site measurement of uranyl ions by smartphone To assess the utility of the probe, a portable detection device for uranyl ions was designed and developed based on smartphone. For the measurement, 10 μL of different concentration of uranyl ion solution (represented by “S”) was dropped into the as-prepared probe solution (represented by “P”) (as shown in Fig. S15). After the complete reaction, the mixture solution was reiteratively deposited on the test strip and drying in the room temperature 5 min for the color change to be stabilized. Then the test strip was put in the strip slot and performed by device, and the fluorescence image of test paper was recognized and colorimetric analyzed by App. Finally, the measurement value was displayed on the screen. The smartphone-based concentration detection system mainly consisted of a removable smartphone-linked device and an APP program. The smartphone-linked device was used to acquire the fluorescence image information in strips. To fabricate the smartphone accessory device, a 3D model device was previously designed using CAD program, and the relevant specifications were imported into a 3D printer. Finally, the accessory device was printed out by using a thermoplastic polymer as the ink. As shown in Fig. 3, there are mainly three parts in the accessory device, a low-cost regulator, a light source with 365 nm output and an enclosed dark cavity. The regulator was used to control the voltage and supply power for the UV light UV light. In order to maintain a stable and reliable operating environment, the applied voltage was set to 4.1 V and the current was limited to 700 mA. The UV light (1 W output power) used as the light source to illuminate the test strip was soldered onto a printed circuit board and powered by USB interface through the regulator. The dark cavity contained a strip slot to place the test strip


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and a filter to cut off stray light. Especially, the distance and angle of the slot were fixed between UV light and the smartphone camera, which could ensure the photography location. The dark condition could eliminate the influence from other light source and diminish all possible variables except the color of test strips.

Figure 3. Photograph and structure of the smartphone based platform device for uranyl detection.

Figure 4. The major modules of the “Concentration Detection” App, showing the components of the practical APP.


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Current color recognition technology mainly relies on the reading RGB (red green blue) intensity value of images, however, when there is a slight change in color, the RGB values alone are not necessarily sufficient.44-45 In order to make up for this deficiency, multiple analyzing of color and chromaticity through precise algorithms was adopted in our color recognition technology. Thus, any grabbed color can be quickly and accurately converted to corresponding concentration values. According to multiple color analysis technology, our group further designed an image identification smartphone App “Concentration Detection”. As shown in Fig. 4, the home menu of “Concentration Detection” App main contains three parts. The first section is used for detecting the sample concentrations. Once the detection instruction was started, the referential color and sample color were displayed simultaneously in a row on the result page, and the concentration was calculated and presented clearly below. The second part is used for system setting, which can setup the concentration ranges and select the target elements or compounds. The reference data is open for compiling and updating, for example, different concentration ranges and new detection targets can be imported to the data base. The third section provides the relevant information about the App (copyright, version, etc.). The App is currently operated on an Android system, and it can be easily converted to other operating systems. The program using an open-source java can be re-edited and improved in the future. To set up a standard uranyl ions colorimetric reference chart, a series of different known concentrations of uranyl ions were added into three kinds of ratiometric fluorescent probe solutions with different mass ratios of 1:1, 1:2, and 1:3, respectively. The resultant probe solution was dropped on test strip for further evaluation. It was clearly seen from Fig. 5 that with the increasing amounts of uranyl ions, the color of test paper under UV light was gradually


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converted from red to green, and the broader color change could be obtained by hybridizing the MPA@CdTe QDs and C-dots solution with a mass ratios of 1:1. The correspondence between the color of the reacted probe solution on testing paper and the concentrations of uranyl ions was recorded and uploaded to “Concentration Detection” App as a reference standard for colorimetric identification. Through the App of “Concentration Detection’’, the concentrations of uranyl ions contained in the sample could be obtained rapidly. The limit of detection of the APP was estimated based on the identification mechanism of the vision algorithms of Open CV, which accurately matched the reference image through the multidimensional calculation. So the limit of detection for uranyl ions relied on the precision of reference color chart and was estimate to be 0.5 μM in this APP.

Figure 5. Different concentrations of uranyl ions-induced color of three kinds of ratimetric fluorescent probe solutions (mass ratios of MPA@CdTe QDs and C-dots: 1:1, 1:2, 1:3) on test strip under UV light. To further verify its practicability, the smartphone-based detection platform was further evaluated for monitoring uranyl ions in real samples. The evaluation was carried out with spike and recovery experiments. A series of amounts of uranyl ions were added into real samples of lake water, tap water and mineral water, which was pretreated by using of 0.45 μm Suporfilters. The screenshots of the recognition results of uranyl concentration in different water sample by


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App was displayed on Fig. 6. It clearly showed that the APP can effectively compare the sample test strips with control group and produced the results. The detailed recovery values were calculated to be from 80%-100% based on the detection results (Table S2). The results of the spike and recovery test showed that the smartphone-based detection platform offered a new potential application in various environment sensing.

Figure 6. The resultant images of spiked real samples of lake water, tap water, and mineral water by the “Concentration Detection” App.

CONCLUSION

In conclusion, it has been demonstrated that a smartphone-based ratiometric fluorescence detection platform was developed for rapid and on-site analysis of uranyl ions in aqueous solution. The designed ratiometric fluorescence probe exhibited high sensitivity and selectivity for uranyl ions in a wide concentration range. The possible interference from some transition metal ions such as copper and silver can be eliminated by the addition of sodium sulfide during the detection, which greatly enhanced the selectivity and anti-interference. Such a smartphone


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platform for uranyl detection has been successfully applied in various real water samples, which shows practical application in environmental monitoring. ASSOCIATED CONTENT Supporting Information Emission spectra of ratiometric probe; dynamic responses of probe to uranyl ions; photostability of ratiometric probe; characterization with UV-vis, FT-IR, TEM, XRD, dynamic light scattering, zeta potential, intensity ratio (I525/I640) study of ratiometric probe; steps for detecting uranyl ions; pH effect on CdTe and the strips, table of recovery study. AUTHOR INFORMATION * Corresponding author: E-mail: [email protected]. Tel: +86 1371873619; E-mail: [email protected]. Tel: +86 13855167314. Author Contributions: The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. || Xinfeng Chen and Qingsong Mei have contributed equally to this work. ACKNOWLEDGMENT The study was financially supported from the National Key Re-search and Development Program of China (2017YFA0207003), the National Natural Science Foundation of China (21475134, 21775042, and 21675158) and the Fundamental Research Funds for the Central Universities (2016ZZD06). REFERENCES


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Rapid and On-Site Detection of Uranyl Ions via Ratiometric

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