One-Pot Synthesis of Fluorescent Silicon Nanoparticles for Sensitive

Article pubs.acs.org/ac

One-Pot Synthesis of Fluorescent Silicon Nanoparticles for Sensitive and Selective Determination of 2,4,6-Trinitrophenol in Aqueous Solution Yangxia Han,†,‡ Yonglei Chen,*,†,‡ Jie Feng,†,‡ Juanjuan Liu,†,‡ Sudai Ma,†,‡ and Xingguo Chen*,†,‡,§ †

State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China Department of Chemistry, Lanzhou University, Lanzhou 730000, China § Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, Lanzhou 730000, China ‡

S Supporting Information *

ABSTRACT: Because 2,4,6-trinitrophenol (TNP) and its analogues such as 2,4,6-trinitrotoluene (TNT) possess similar chemical structures and properties, the reliable and accurate detection of TNP from its analogues still remains a challenging task. In the present work, a selective and sensitive method based on the water-soluble silicon nanoparticles (SiNPs) for the determination of TNP was established. The SiNPs with good thermostability and excellent antiphotobleaching capability were prepared via a simple one-pot method. Compared with the synthesized time of other nanomaterials with respect to the detection of TNP, this method avoided a multistep and time-consuming synthesis procedure. Significantly, the fluorescence of the SiNPs could be remarkably quenched by TNP via an inner filter effect. A wide linear range was obtained from 0.02 to 120 μg/mL with a limit of detection of 6.7 ng/mL. The method displayed excellent selectivity toward TNP over other nitroaromatic explosives. The proposed fluorescent method was successfully applied to the analysis of TNP. Moreover, a straightforward and convenient fluorescent filter paper sensor was developed for the detection of TNP, providing a valuable platform for TNP sensing in public safety and security. ilicon nanoparticles (SiNPs), as a new type of fluorescent nanomaterial with low toxicity and good stability, have been demonstrated to be environmentally friendly fluorescent probes and have attracted much interest. In addition, the superb optical, electronic, and mechanical properties of siliconbased nanostructures enable them to play an important role in a variety of applications. However, most SiNPs studied to date are hydrophobic. To realize water-solubility of SiNPs, extensive efforts have been devoted to modifying SiNP surfaces with hydrophilic species.1−3 In addition to relatively complicated modification, procedures such as multistep procedures may produce adverse effects on the physical or chemical properties of the SiNPs. Therefore, despite those advances, further efforts are required to develop strategies for facile synthesis of watersoluble SiNPs for broad applications. Up to now, several methods have been developed to synthesize water-dispersible SiNPs used for biological imaging,4−10 but there are few studies on selective and sensitive detection of various analytes using SiNPs,11,12 especially for 2,4,6-trinitrophenol (TNP). TNP is a kind of important nitroaromatic explosive chemical with strong electron-withdrawing groups. It possesses an explosive ability stronger than that of 2,4,6-trinitrotoluene (TNT).13 It is also widely used in the dye industry, rocket fuel, fireworks, pharmaceuticals, chemical laboratories, and so

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© 2017 American Chemical Society

on.14−16 The permissible level for TNP in drinking water is set to be 0.5 mg/L with an allowable daily intake (ADI) of 1− 37 μg/(kg per day).17 Therefore, its extensive use can contaminate soil and groundwater and may further lead to skin irritation, anemia, cancer, abnormal liver functioning, and damage to respiratory organs when people inhale, ingest, or touch it.18−20 Because of its contamination to environment and the risk to human health, sensitive and selective detection of TNP has attracted increasing attention.21 In addition, nitroaromatic explosives such as dinitrotoluene (DNT), nitrobenzene (NB), and especially TNT often interfere the detection of TNP because nitroaromatic explosives and TNP possess extremely similar chemical structures and properties.22 Therefore, it becomes an important and challenging task for selective and sensitive detection of TNP in the presence of structurally similar interference compounds. Up to now, a number of analytical methods such as surface enhanced Raman spectrometry,23 high performance liquid chromatography,24 dynamic light scattering,25 enzyme linked immunosorbent assay,26 solid phase microextraction-ion mobility spectrometry, Received: November 16, 2016 Accepted: February 10, 2017 Published: February 10, 2017 3001

DOI: 10.1021/acs.analchem.6b04509 Anal. Chem. 2017, 89, 3001−3008

Article

Analytical Chemistry

The as-prepared fluorescent SiNPs emitted a green fluorescence with a quantum yield of about 7.1% and exhibited good thermostability and excellent photostability and water solubility. It was found that the FL intensity of the obtained SiNPs decreased with the addition of TNP. On the basis of this phenomenon, a selective and sensitive method to detect TNP was developed. The proposed fluorescent method was successfully applied to detect TNP in water samples with satisfactory results. In addition, a fluorescent filter paper sensor was developed for the detection of TNP, providing a straightforward and convenient platform for TNP sensing in public safety and security.

and electrochemical methods have been applied to detect nitroaromatic explosives.27,28 Unfortunately, some drawbacks such as high cost, complex operation of sophisticated instruments, complicated extraction procedures, and especially low distinguishing ability between TNP and TNT in these methods impede their widespread applications. In contrast, fluorescent methods have attracted more attention owing to their high sensitivity, good selectivity, operational simplicity, real-time detection, low cost, and portability.20,29 Therefore, a series of fluorescence (FL) methods for the detection of nitroaromatic explosives was developed based on nanocomposites such as ZnS:Mn2+@allyl mercaptan and 8hydroxyquinoline aluminum (Alq3)-based composite nanospheres,13,30 graphitic carbon nitride (g-C3N4) nanosheets,22 Cd(II)-based metal−organic frameworks (MOF), and nitrogen-doped carbon nanodots (N-doped CNDs).31,32 However, these fluorescent probes suffer limitations when detecting explosives, especially for TNP, such as multistep and timeconsuming synthesis procedure of the materials, high toxicity to the environment, and utilization of organic media, all of which restrict their far-ranging application. Therefore, it is necessary to develop a simple and time-efficient method for synthesizing novel nanomaterial and establishing a harmless, facile, timesaving, highly selective and sensitive method for the determination of TNP in aqueous phase using the nanomaterial as a probe. In this study, water-soluble SiNPs were synthesized with a relatively straightforward one-pot hydrothermal method using N-[3-(trimethoxysilyl)propyl]- ethylenediamine (DAMO) and catechol as the silicon source and reductant, respectively (Scheme 1). Catechol was chosen as the precursor for the

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EXPERIMENTAL SECTION Synthesis of SiNPs. The SiNPs were prepared by adding 2.0 mL of DAMO to 10 mL of deionized water with stirring. Then, 11.0 mg of catechol was added to the above solution by stirring for 1 min. The mixture solution was then transferred into a Teflon-lined autoclave and processed under 200 °C for 4 h. Further, various amounts of catechol and 2.0 mL of DAMO were mixed to prepare SiNPs in a similar way. Then, the asprepared SiNPs were cooled to room temperature and purified through a dialysis tube (1000 Da, molecular weight cutoff) for about 6 h. The obtained SiNPs were stored at 4 °C for further characterization and detection of TNP. In addition, the SiNPs were prepared with catechol and APTES/APTMS instead of DAMO and processed in a similar way. Fluorescence Detection of TNP. The stock solution of TNP was prepared by dissolving it into the deionized water with a final concentration of 2.0 mg/mL. Different concentrations of TNP solution were prepared by diluting the stock solution into the deionized water. The obtained SiNPs were diluted 1000-fold with 10.0 mM PBS buffer solution (pH 7.4) for the fluorescence measurements. The typical procedure was as follows: 3.0 mL of the SiNP dilute solution was mixed with various concentrations of TNP, and the mixture was shaken thoroughly. The fluorescence emission spectra were recorded under excitation wavelength at 430 nm after 1 min. The working curve was mapped by logarithmic value of F0/F of SiNPs and the concentration of TNP (F0 and F are the fluorescence intensity of SiNPs in the absence and presence of TNP, respectively). The selectivity of the SiNP probe toward TNP was evaluated by adding inorganic ion solutions or nitroaromatic explosive solutions instead of TNP in a similar way. All experiments were performed at room temperature.

Scheme 1. (A) Synthetic Strategy of the SiNPs and (B) Schematic Illustration of Fabricated SiNPs for TNP Detection

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RESULTS AND DISCUSSION Characterization. The morphologies of the as-prepared SiNPs were confirmed by typical transmission electron microscopy (TEM) images. As shown in Figure 1, the obtained SiNPs were well dispersed and uniform in size, and their size was about 2.4−3.6 nm with an average diameter of 3.3 nm. Figure 1C displayed the EDS pattern of SiNPs, indicating that SiNPs contained C, N, O, and Si. The Fourier transform infrared (FT-IR) spectrum (Figure 1D) was used to identify the surface functional groups presented in the SiNPs. The absorption peaks at 3367 and 3293 cm−1 were assigned to stretching vibrations of O−H and N−H, respectively.34 The absorption peaks at 2932 and 1468 cm−1 were attributed to C− H unsaturated stretching vibration and C−H bending vibration, and the strong signal at 1604 cm−1 was assigned to the bending vibration of N−H,5 while the relatively broad peak at 781 cm−1

following reasons: First, catechol can act as a reductant to prepare SiNPs. Second, the strong donor group (−OH) of catechol usually causes dramatic changes in fluorescent parameters (mainly including the intersystem crossing rate constant) and further increases the fluorescence quantum yield.33 Third, the π−π* transition of the CC bond of catechol can enhance the fluorescence emission. In addition, the hydroxyl groups of catechol can improve the water solubility of the SiNPs, and hydrogen bonding interactions may occur between the hydroxyl groups of SiNPs and TNP. Therefore, the TNP can be determined in aqueous solutions using the SiNPs. Compared with previously published reports with respect to the detection of TNP,13,22,30 this method avoided a multistep and time-consuming synthesis procedure. 3002


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Figure 1. (A) TEM image, (B) corresponding size distribution histogram, (C) EDS pattern, and (D) FT-IR spectrum of the SiNPs.

Figure 2. High resolution XPS spectra of the SiNPs: (A) full range, (B) C 1s, (C) N 1s, (D) O 1s, (E) Si 2p, respectively. (F) Fluorescence excitation spectrum (a), emission spectrum (b), and UV−vis absorption spectrum of SiNPs (c).

indicated the presence of a N−H wagging vibration.35 The peak at 1349 cm−1 was assigned to C−N stretching vibrations,4 and the presence of bands at 1039 cm−1 and 1125−1030 cm−1 due to Si−C asymmetric deformation and Si−O−Si stretching vibrations, respectively.36 In addition, the Si−O−H group showed a strong peak involving Si−O stretching at 932 cm−1, and a peak belonging to a secondary amine was also clearly visible at 693 cm−1.35 These results indicated that there were abundant hydroxyl and amino groups on the surface of the

SiNPs, and the presence of these functional hydrophilic groups on the surface greatly improved the water solubility and stability of the SiNPs. The surface composition for the SiNPs was further performed by X-ray photoelectron spectroscopy (XPS) (Figure 2). Figure 2A presents five major peaks at 102.2, 153.3, 284.8, 398.8, and 531.9 eV which corresponded to Si 2p, Si 2s, C 1s, N 1s, and O 1s, respectively. The high resolution C 1s XPS spectrum of SiNPs (Figure 2B) indicated the presence of C−Si (283.9 eV), C−C/CC (284.6 eV), C−N (285.3 3003


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Figure 3. (A) Normalized FL intensity of the SiNPs after incubation at different temperatures for 10 min. (B) Normalized FL intensity of the SiNPs at different pH values.

Figure 4. (A) Fluorescence responses of SiNPs upon addition of various concentrations of TNP (from top to bottom, 0, 0.02, 0.08, 0.2, 1, 4, 6, 10, 20, 30, 50, 80, and 120 μg/mL) in a pH 7.4 PBS solution. Inset: photographs of SiNPs in the absence (left) and presence (right) of TNP under UV light (365 nm). (B) Logarithmic value of F0/F of SiNPs as a function of the concentration of TNP. F0 and F are the fluorescence intensity of SiNPs in the absence and presence of TNP, respectively.

eV), and C−OH/C−O−C (286.0 eV) groups, respectively.37 The XPS spectrum of N 1s (Figure 2C) exhibited three fitted peaks which were ascribed to N−Si (398.3 eV), C−N−C (399.0 eV), and N−(C)3 (400.3 eV).34 Two peaks at 530.7 and 531.7 eV were attributed to Si−O in the XPS spectrum of O 1s (Figure 2D),35 and the peak at 532.4 eV corresponded to C− O.38 The Si 2p spectrum (Figure 2E) exhibited three peaks at 101.0, 101.8, and 102.5 eV, which were associated with Si−C, Si−N and Si−O groups, respectively.39 The surface components of the SiNPs conducted by XPS were in accordance with the FT-IR results. In addition, the optical properties of the obtained SiNPs were confirmed by UV−vis absorption and fluorescence spectra (Figure 2F). It can be seen that the UV− vis spectrum of the SiNPs exhibited two characteristic absorption bands centered at 290 and 422 nm, and the former was assigned to the π−π* transition of the CC bond (curve c).40 The peak at 422 nm may be originated from the trapping surface state, leading to strong emission.41 The fluorescence emission peak of the SiNPs appeared at 512 nm (curve b) when the excitation wavelength was at 430 nm (curve a). Figure S1 was the fluorescence emission spectrum of the SiNPs at various excitation wavelengths (390−470 nm). The fluorescence emission peak did not shift with the change excitation wavelength, indicating no size-dependent emission behavior.5 Stability of the SiNPs. To test the effect of the amount of catechol on the detection of TNP, the weight ratios of DAMO and catechol were studied. As shown in Figure S2, the F0 − F value was higher than others when the catechol was 11.0 mg and DAMO was 2.0 mL. Therefore, 11.0 mg was selected as the optimum catechol amount. The FL intensity of SiNPs in this method was observed to be very stable even under the

concentration of NaCl as high as 100 mM in the solution (Figure S3), showing excellent salt tolerance. As shown in Figure S4, the FL intensity of the obtained SiNPs remained relatively stable after irradiation of the fluorescent material at 430 nm for 60 min, indicating that they had excellent antiphotobleaching capability. Moreover, it can be seen from Figure 3A that the FL intensity of SiNPs remained almost unchanged when the temperature increased from 5 to 85 °C. Furthermore, the impact of the pH on the fluorescence of the SiNPs was also conducted. From Figure 3B, it should be noticed that the FL intensity was weak and remained nearly constant at pH 4.0−8.0, and then the fluorescence was enhanced obviously when the pH was >8. This pH-dependent fluorescence property can be attributed to the variation in surface charge of SiNPs owing to protonation−deprotonation.42 Fluorescence Sensing of TNP Based on the SiNP Probe. As mentioned previously, the obtained SiNPs were highly water soluble because of the enriched amino and hydroxyl groups on the nanoparticle surface, facilitating their applications as fluorescence probes in aqueous media. Besides, the as-prepared fluorescent SiNPs with DAMO had a quantum yield of about 7.1%, which was higher than that of the SiNPs prepared with APTES or APTMS (APTES: 1.0%, APTMS: 2.0%). To obtain higher sensitivity of the detection of TNP, DAMO was chosen as the source of silane molecules for SiNPs preparation. Under an excitation wavelength of 430 nm, the SiNPs emitted strong green fluorescence that can be quenched by the added TNP (inset in Figure 4A). Considering a probe for security-screening needs on the scene, rapid response to the target explosive is necessary. The response time of the as3004


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Figure 5. (A) FL intensity response (F/F0) of the SiNPs to 600 μg/mL inorganic interference ions (black bars) and the subsequent addition of 60 μg/mL TNP (red bars). (B) FL intensity response (F/F0) of the SiNPs to 60 μg/mL nitroaromatic explosives (black bars) and the subsequent addition of 60 μg/mL TNP (red bars).

Figure 6. (A) UV−vis absorption spectra of the SiNPs and TNP as well as the theoretical and experimental spectra based on the mixture of the SiNPs and TNP. (B) UV−vis absorption spectrum of TNP (a), fluorescent excitation spectrum (b), and emission spectrum of SiNPs (c). (C) Suppressed efficiency (E, %) of observed (black line, Eobsd) and corrected (red line, Ecor) fluorescence intensity. (D) Influence of TNP concentrations on the corrected fluorescence intensity ratio (Fcor,0/Fcor; for data, see Table S3) of SiNPs.

inorganic ions (K+, Ca2+, Mg2+, Mn2+, Fe2+, Fe3+, Zn2+, Cu2+, 2− 2− − Ba2+, Ni2+, Co2+, NO−3 , NO−2 , SO2− 3 , SO4 , CO3 , and HCO3 ) and organic compounds (DNB, DNBA, DNT, NB, NT and TNT) that may be present in water samples were tested under the same test conditions. As shown in Figure 5, no obvious fluorescence quenching was observed for these interferences. Meanwhile, the anti-interference capability of the SiNP solution was also investigated by adding a mixture consisting of TNP and other potential interferences into the sensing system. Little influence on the FL intensity was observed compared to that on the system in which only TNP existed. Possible Mechanism of the FL Response of the SiNPs to TNP. Generally, the possible quenching mechanisms of the fluorescent materials are as follows: inner filter effect (IFE),43 Förster resonant energy transfer (FRET),44,45 the formation of a donor−acceptor charge-transfer complex,46 dynamic quench-

prepared SiNPs to TNP was investigated. As demonstrated in Figure S5, the fluorescence quenching was quite rapid and achieved within half a minute when the SiNPs and TNP solutions were mixed, indicating that the SiNP probe was a rapid sensing tool for explosive analysis. As shown in Figure 4A, a quite large fluorescence quenching was observed after addition of different concentrations TNP into SiNP solutions. A significant linear correlation (R2 = 0.998) existed between the quenching efficiency [log(F0/F)] and the TNP concentration in the range of 0.02−120 μg/mL (Figure 4B). The limit of detection (3 s/k, in which s is the standard deviation for the blank solution and k is the slope of the calibration curve) was estimated to be 6.7 ng/mL, which was lower than those of many other methods, as shown in Table S1. Selectivity of the SiNPs for TNP. To investigate the selectivity of the SiNP probe toward TNP, the interferences of 3005


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fluorescence excitation spectrum of the SiNPs even was superior to that of TNP (Figure S8), which was in accordance with the order of the quenching efficiency of those nitroaromatic explosives containing hydroxyl (Figure S9), further indicating that IFE played a leading role in the quenching mechanism. The selectivity of SiNPs toward TNP could also be explained by the UV−vis absorption spectra of nitroaromatics. As shown in Figure S10, in addition to TNP, there was no overlap between the UV−vis absorption spectra of nitroaromatic compounds and the emission spectrum of fluorescence SiNPs. These results revealed that the SiNP probe presented an excellent selectivity for TNP detection. In general, fluorescence can be quenched through DQE or SQE. Both DQE and SQE through the ground-state complex formation model could be theoretically described by the Stern− Volmer equation (eq 2):

ing effect (DQE), and static quenching effect (SQE).47 To explore the quenching mechanism between TNP and SiNPs, a corresponding experiment was conducted to evaluate each of these quenching effects. First, UV−vis spectra in the presence of SiNPs and/or TNP were studied. As shown in Figure 6A, the experimental UV−vis absorption spectrum of SiNPs upon the addition of the TNP was almost completely overlapped by the theoretical one. This phenomenon implied that the interaction between TNP and the SiNPs was weak, and no Meisenheimer complex (the electron-withdrawing analyte, TNP, readily reacts with electron-donating primary amino groups to form the Meisenheimer complex) between them could be formed.22,48,49 In addition, it was considered to be a FRET quenching mechanism when a spectral overlap occurred between the UV− vis absorption spectrum of a quencher and the emission spectrum of a fluorescence agent. As demonstrated in Figure 6B, the emission spectrum of SiNPs was scarcely overlapped with the absorption spectrum of TNP, indicating FRET probably did not exist in the fluorescence quenching mechanism. Subsequently, the role of IFE in the entire suppression process in our system was also studied. As displayed in Figure 6B, there was a large spectral overlap between the absorption spectrum of TNP and the excitation spectrum of the fluorescent SiNPs. In addition, the corresponding fluorescence lifetime was investigated by adding different concentrations of TNP into the SiNP solutions. As shown in Table S2 and Figure S6, there were no obvious changes of fluorescence lifetime among these different SiNP solutions. It suggested that the TNP induced fluorescence quenching of SiNPs was considered to stem from IFE. To verify this hypothesis, corrections were made by taking into consideration of the cuvette geometry used in the fluorescence measurements and absorption characteristics of the aqueous solution of the SiNPs and TNP with eq 1:50 Fcor 2.3dAex 2.3sAem 10 gAem = −dAex Fobsd 1 − 10−sAem 1 − 10

F0 = 1 + KSV[Q ] (2) F where F0 and F are the steady-state fluorescence intensities in the absence and presence of the quencher, respectively; KSV is the Stern−Volmer constant, and [Q] is the concentration of TNP. In this study, there was no linear relationship between the corrected fluorescence intensity ratio (Fcor,0/Fcor, Table S3) of SiNPs and the concentration of TNP, as depicted in Figure 6D. As a result, it seemed that the quenching mechanism of DQE and SQE were negligible. As discussed above, IFE was considered to be the main possible mechanism for fluorescence quenching of SiNPs by TNP. Analysis of TNP in Water Samples. To further investigate the selectivity of this proposed method, the mixture of TNP and other nitroaromatics was analyzed via this strategy. As shown in Table 1, the values found for TNP in the mixture

Table 1. Determination of TNP in Mixed Samples

(1)

where Fobsd is the observed maximum FL intensity and Fcor is the corrected maximum FL intensity after removing IFE from Fobsd; Aex and Aem are the absorbance at the maximum excitation wavelength (λ = 430 nm) and maximum emission wavelength (λ = 512 nm), respectively. As presented in Figure S7, g is the distance between the edge of the excitation beam and the edge of cuvette (g = 0.40 cm); s is the thickness of the excitation beam (s = 0.10 cm), and d is the width of the cuvette (d = 1.00 cm). The terms g, s, and d depend upon the geometry of the measurement. The maximum value of the correction factor (CF) could not exceed 3; otherwise, the correction is not convincing.34 The CF of IFE at each concentration of TNP was calculated according to eq 1. Table S3 summarizes the CF of IFE; Eobsd and Ecor are the observed and corrected fluorescence quenching efficiencies after addition of different concentrations of TNP into the SiNP solution, respectively. The results demonstrated that the suppressed efficiency of IFE for TNP to SiNPs reached as high as 92% of the total suppressed efficiency, indicating that suppressed efficiency mainly came from IFE (Figure 6C). In addition, the UV−vis absorption spectra of some nitroaromatic explosives containing hydroxyl such as DNP and PNP were investigated. It was observed that the overlap between the absorption spectrum of DNP or PNP and

sample

composition of solution (μg/mL)

1 2 3 4 5 6 7 8

TNP (1) TNP (1) + DNB (5) TNP (1) + DNBA (5) TNP (1) + DNT (5) TNP (1) + NB (5) TNP (1) + NT (5) TNP (1) + TNT (5) TNP (1) + DNB (5) + DNBA (5) + DNT (5) + NB (5) + NT (5) + TNT (5)

TNP found (μg/mL)

recovery (%)

RSD (%, n = 3)

0.97 0.92 1.02 0.98 0.95 1.01 0.97 0.93

97.2 92.5 102.4 98.5 95.0 101.1 96.8 93.3

1.3 0.7 3.3 0.7 2.1 2.1 3.3 2.6

were in accordance with the expected ones, and no obvious interference was observed, suggesting a very good selectivity. To evaluate the applicability of the assay method, the fluorescent response of the SiNP sensor for TNP was tested in Yellow River water, Yangtze River water, and tap water samples. The recoveries of this method were carried out on the samples by spiking a series of known concentrations of TNP. As shown in Table 2, it can be seen that the RSD was below 3.5%, and the recoveries of TNP in the real samples varied from 98.6 to 103.3%. These results demonstrated the excellent reproducibility and accuracy of the SiNP sensor for selective monitoring of TNP in environmental water samples. 3006



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CONCLUSION In summary, water-soluble SiNPs were synthesized in a simple one-pot method and used as a fluorescent probe without further modification for TNP sensing. The as-prepared SiNPs displayed excellent salt tolerance, thermostability, and antiphotobleaching. It was found that the green fluorescence of SiNPs could be quenched owing to the IFE mechanism between TNP and SiNPs. The probe was successfully applied to detect TNP in water samples with satisfactory recoveries (98.6−103.3%). In addition, a fluorescent SiNP filter paper sensor was favorably fabricated for the rapid and convenient detection of TNP. This method, with its simplicity and excellent selectivity and sensitivity, can be used as a promising tool for TNP analysis in a practical environment.

Table 2. Detection of TNP in Different Water Samples sample Yellow River water Yangtze River water tap water

spiked (μg/mL)

found (μg/mL)

recovery (%)

RSD (%, n = 3)

1 5 10 1 5 10 1 5 10

0.99 4.93 10.04 1.01 5.04 10.27 0.99 4.99 10.33

98.7 98.6 100.4 101.5 100.7 102.7 99.2 99.7 103.3

1.5 0.9 1.0 3.5 1.7 0.5 2.0 1.9 1.1

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Visual Detection of TNP by Paper Sensor. Considering the simplicity and rapidity of a fluorescence sensor for the detection of explosives, a facile paper sensor was developed for visual detection of TNP. Under the irradiation of 365 nm UV light, the fluorescence of the SiNP paper sensor was quenched in varying degrees by adding different concentrations of TNP (Figure 7b). The selectivity of the SiNP paper sensor was

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.analchem.6b04509. Details on the reagents, materials, apparatus, and characterization, analysis of TNP in water samples, preparation of the paper sensor, and additional figures (S1−S10) and tables (S1−S3) (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Tel.: 86-931-8912763; Fax: 86-931-8912582; E-mail: chyl@ lzu.edu.cn. *Tel.: 86-931-8912763; Fax: 86-931-8912582; E-mail: [email protected]. ORCID

Xingguo Chen: 0000-0002-7982-1519 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for financial support from the National Natural Science Foundation of China (Grant 21675068) and the Specialized Research Fund for the Doctoral Program of Higher Education (Grant 20130211110039).

Figure 7. Photographs of the filter paper trips with the mixture of SiNPs and TNP in the daylight (a), with the mixture of SiNPs and TNP under 365 nm UV light (b), with the mixture of SiNPs and nitroaromatics (including DNB, DNBA, NB, NT, DNT, and TNT) under 365 nm UV light (c), and with the mixture of SiNPs and nitroaromatics (including DNB, DNBA, NB, NT, DNT, TNT, and TNP) under 365 nm UV light (d). The concentration of the nitroaromatic solutions are 0, 0.01, 0.05, 0.1, 0.5, and 1 mg/mL from left to right.

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tested to detect other nitroaromatic compounds (including TNT, DNT, DNB, NB, NT, and DNBA) under the same conditions. As shown in Figure 7c, no obvious fluorescence quenching was observed in the presence of nitroaromatic interferences. Meanwhile, the anti-interference performance of the paper sensor was also evaluated by dropping a mixture consisting of TNP and other potential interferences into the sensing system. A remarkable fluorescence quenching appeared with the dropping of the mixture of TNP and nitroaromatic interferences (Figure 7d). All of these results indicated that the paper sensor provided a convenient fluorescent platform for TNP detection with high sensitivity and selectivity. 3007


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