Turn-on Fluorescent Detection of Hydrogen Peroxide and Triacetone

Letter Cite This: Anal. Chem. 2019, 91, 6967−6970

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Turn-on Fluorescent Detection of Hydrogen Peroxide and Triacetone Triperoxide via Enhancing Interfacial Interactions of a Blended System Xinting Yu,†,‡,# Yanjun Gong,‡,§,# Wei Xiong,‡,§ Mei Li,*,† Jincai Zhao,‡,§ and Yanke Che*,‡,§

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†

School of Materials Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China ‡ Key Laboratory of Photochemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China § University of Chinese Academy of Sciences, Beijing 100049, China S Supporting Information *

ABSTRACT: In this work, we report the fabrication of a blend consisting of fluorescent 1 nanofibers and amberlyst-15 particles as a turn-on fluorescence sensor for trace TATP vapors. Fluorescence imaging and lifetime analysis reveal that the interface between 1 nanofibers and amberlyst-15 particles exhibits stronger photoluminescence than the unblended areas because of the formed strong hydrogen bonding between. Furthermore, the interfacial adhesion between 1 nanofibers and amberlyst-15 particles can be amplified by H2O2, which in turn gives rise to rapid and remarkable fluorescence enhancement. When exposed to TATP vapors, the amberlyst-15 component can rapidly decompose TATP into H2O2 that gives sensitive fluorescence enhancement responses of the blend. On the basis of this detection mechanism, fluorescence detection of TATP with rapid response (ca. 5 s) and high sensitivity (ca. 0.1 ppm) is achieved. Here, the resulting blend combines the pretreatment of TATP and detection responses and thereby simplifies the senor fabrication for the practical application.

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TATP vapor and then used interpenetrated binary nanofibers to detect the resulting H2O2.5 Despite these advances, the pretreat method has to be used in advance and be separated from the sensing materials. This obviously complicates the sensor fabrication and delays the sensor response time. To address this, we have tried to directly mix the solid acid catalysis with the binary nanofibers to detect TATP. Unfortunately, amberlyst-15 caused severe fluorescence quenching of the binary nanofibers and attenuated the sensing performance. Therefore, new molecular systems that are compatible with the solid acid catalysis need to be developed. In addition, such composite should exhibit fast response to the resulting H2O2. In this work, we fabricate a blend consisting of fluorescent 1 nanofibers and solid acid (amberlyst-15) particles as a turn-on fluorescence sensor for trace TATP vapors (Figure 1). We demonstrate that the interfacial adhesion between 1 nanofibers and amberlyst-15 particles can be enhanced by H2O2, which thereby gives rise to rapid and remarkable fluorescence enhancement. Importantly, the amberlyst-15 component can

riacetone triperoxide (TATP) is a high-powered explosive and easy to prepare from the acid catalyzed reaction of acetone and hydrogen peroxide.1−3 Use of TATP by terrorists has threatened humankind and homeland security. Therefore, sensitive and selective detection of TATP has attracted intensive attention.1−14 However, although various technologies, such as ion mobility spectroscopy (IMS),13,15 have been applied to detect TATP, these methods generally suffer from one or more disadvantages including high cost, complicated operation, poor portability, and poor limit of detection (LOD). As a simple, fast, cost-effective, and highly sensitive method, fluorescence sensors have been widely used to detect various explosives, particularly nitro-containing explosives.3,5,16−27 However, these fluorescence sensors generally exhibited no responses to TATP because TATP has no nitro or chromophoric groups; very limited examples have reported to be able to detect TATP, particularly in the gas phase.2,5,6,28 Therefore, sensitive detection of TATP still poses significant challenges for fluorescence sensors. Suslick and co-workers developed an elegant method where a solid acid catalysis, i.e., amberlyst-15, was used to decompose TATP into H2O2 for subsequent detection in a colorimetric sensor array.1 Recently, we have used this method to pretreat © 2019 American Chemical Society

Received: March 11, 2019 Accepted: May 13, 2019 Published: May 13, 2019 6967

DOI: 10.1021/acs.analchem.9b01255 Anal. Chem. 2019, 91, 6967−6970

Letter

Analytical Chemistry

Figure 1. Schematic diagram of the fluorescence enhancement of a blend consisting of fluorescent 1 nanofibers and amberlyst-15 particles because of the increased interfacial adhesion by H2O2 that can originate from the decomposition of TATP.

rapidly decompose TATP into H2O2 that in turn gives sensitive fluorescence enhancement of the blend. This response mechanism allows rapid turn-on fluorescence responses (ca. 5 s) and high sensitivity (0.1 ppm) to trace TATP. Molecule 1 (N-[4-methanol phenyl) methyl]-N′-(1-dodecyl) perylene-3,4,9,10-tetracarboxylic acid bisimide, Figure 1), was chosen in this work because molecule 1 is chemically stable in the presence of strong acid and possesses hydroxyl group to form hydrogen bonding with amberlyst-15 (a solid acid) to some extent. Given that hydrogen bonding can effectively restrict the vibration of hydroxyl substituents to enhance the chromophore photoluminescence,29 we envisage that H2O2 may modulate the hydrogen bonding interactions between 1 nanofibers and amberlyst-15 catalysis and thereby give sensitive fluorescence responses. We fabricated a 1 nanofibers−amberlyst-15 blend by injecting 1 mL of chloroform solution of 1 (0.074 mM) into 10 mL of ethanol containing a predispersed 1 mg of amberlyst-15 (see details in the Supporting Information). Figure 2a shows the morphology of the resulting blend consisting of 1 nanofibers and solid acid (amberlyst-15) particles after 3 days of aging. A closer examination by scanning electron microscopy (SEM) shows that some 1 nanofibers bound with amberlyst-15 particles (Figure 2b and Figure S1). To explore the modulation effect of intermolecular interactions on photoluminescence, we recorded the fluorescence image of the resulting blend that presented the region-resolved photoluminescence. As shown in Figure 2c, the interface between 1 nanofibers and amberlyst-15 particles exhibited stronger fluorescence than the areas of entangled 1 nanofibers. The fluorescence quantum yield (FQY) of the composite was determined to be ca. 32% when excited by visible light (450−550 nm), which is much higher than that of pure 1 nanofibers (ca. 19%)30 and of amberlyst-15 particles (almost nonemissive). These results indicate that the hydrogen-bonding interactions at the interfaces between 1 nanofibers and amberlyst-15 particles can greatly enhance the photoluminescence likely by restricting the vibration of hydroxyl groups to reduce nonradiative decays. The modulation of fluorescence via interfacial interactions was further illustrated by the regionresolved fluorescence lifetime profile (Figure 2d,e). Apparently, the fluorescence lifetime of the interfaces between 1 nanofibers and amberlyst-15 particles was longer than that of areas containing only 1 nanofibers (Figure 2e). Specifically, the fluorescence lifetime of the interfaces is 4.2 ns, which is much longer than that of pure 1 nanofibers (Figure 2f). These results

Figure 2. (a) SEM image of the 1 nanofibers−amberlyst-15 blend deposited onto a silica substrate. (b) Magnified SEM image of the 1 nanofibers−amberlyst-15 blend. (c) Fluorescence-mode optical microscopic image of the 1 nanofibers−amberlyst-15 blend. (d) Bright-field CLSM image and (e) fluorescence lifetime imaging of the 1 nanofibers−amberlyst-15 blend. (f) Decay curves of areas 1−3 (red) and areas 4−6 (black) as marked in (e).

indicate that the strong hydrogen-bonding interactions between 1 nanofibers and amberlyst-15 particles can reduce nonradiative decays and thereby enhance the photoluminescence. We also fabricated different blends with various mass ratios of amberlyst-15 particles relative to 1 nanofibers that were kept at a fixed value (see details in the Supporting Information). Figure S2 showed that the FQY of 1 nanofibers−amberlyst-15 blend initially increased with the proportion of amberlyst-15 particles and then decreased after the mass ratio of amberlyst-15 particles to 1 nanofibers was higher than 20:1. This can be explained by the fact that a proper amount of amberlyst-15 particles can effectively enhance the photoluminescence of 1 nanofibers via interfacial hydrogen-bonding interactions, while an excess of amberlyst-15 particles would absorb too much exciting light. The latter would outcompete the enhancement effect and result in the decreased photoluminescence of the blend. For experimental convenience, we used a blend with the highest FYQ, i.e., the blend with the mass ratio of amberlyst-15 particles to 1 nanofibers at 20:1 in the following experiments. Having demonstrated that the strength of interfacial interactions is closely associated with the photoluminescence of the blends as observed above, we expected that the modulation of the interfacial interactions by specific molecules would cause fluorescence changes that can be used as the detection signal. To support this hypothesis, we first explored if H2O2 that can increase the interaction between 1 nanofibers and amberlyst-15 particles via extra hydrogen-bonding interactions and thereby restrict the vibration of hydroxyl groups to reduce nonradiative decays and to enhance the emission. We performed the sensing experiments for H2O2 vapors in a homemade optical chamber31,32 that contained the precast blend and used an Ocean Optics USB4000 fluorometer to monitor H2O2-induced fluorescent responses. As shown in Figure 3a and Figure S3, the 6968

DOI: 10.1021/acs.analchem.9b01255 Anal. Chem. 2019, 91, 6967−6970

Letter

Analytical Chemistry

turn-on fluorescence responses were also fast, i.e., ca. 5 s (Figure 3d), which indicates that the decomposition of TATP into H2O2 by amberlyst-15 particles is rapid. Also the recovery of fluorescence responses is ca. 60 s (Figure S5d). Importantly, the application of the blend can simplify the sensor fabrication without sacrificing the detection sensitivity and speed of TATP vapors. Finally, the selectivity of the 1 nanofibers−amberlyst-15 blend to H2O2 and TATP vapors against various potential interferents, which is critical to the practical application, was evaluated. We previously reported that pure 1 nanofibers exhibited considerable fluorescence enhancement when exposed to diethyl chlorophosphate (DCP) vapors and hydrogen chloride (HCl).30 Intriguingly, exposure of the 1 nanofibers−amberlyst-15 blend to DCP and HCl vapors gave rise to the turn-off fluorescence responses (Figure 4a,b). These phenomena should

Figure 3. (a) Turn-on fluorescence responses of the 1 nanofibers− amberlyst-15 blend monitored in the range 670−710 nm upon exposure to H2O2 vapors at different concentrations. (b) Response time of the 1 nanofibers−amberlyst-15 blend to 2 ppm of H2O2 vapor. (c) Turn-on fluorescence responses of the 1 nanofibers−amberlyst-15 blend monitored in the range 670−710 nm upon exposure to TATP vapors at different concentrations. (d) Response time of the 1 nanofibers−amberlyst-15 blend to 0.3 ppm TATP vapor.

1 nanofibers−amberlyst-15 blend exhibited enhanced fluorescence responses when exposed to diluted H2O2 vapors. The limit of detection (LOD) reached as low as 0.2 ppm. Furthermore, these turn-on fluorescence responses were fast, which was determined to be ca. 5 s (Figure 3b), which thereby facilitates the practical application. In addition, the blend allowed the multiple detection (Figure S4), and the recovery of fluorescence responses (ca. 50 s, see Figure S5b), which was favorable for practical applications. Given that pure 1 nanofibers exhibited negligible responses to H2O2 and TATP vapors (Figure S6) and amberlyst-15 particles had no photoluminescence, we hypothesized that interface interactions between 1 nanofibers and amberlyst-15 particles were strengthened by H2O2 molecules, which thereby enhanced the photoluminescence. To support this hypothesis, we recorded and compared the fluorescence images of the composite before and after exposure to H2O2 vapor (Figure S7). As expected, the interfaces between 1 nanofibers and amberlyst-15 particles exhibited enhanced fluorescence and other areas remained the same luminescent intensity (Figure S7). This result suggests that H2O2 can increase the interface interactions likely because of the formed extra hydrogen bonding that glues together 1 nanofibers and amberlyst-15 particles that loosely stacked (Figure 1). The enhanced interface interactions enable the restriction of the vibration of hydroxyl groups and thereby enhance the emission by reducing the nonradiative decays. Importantly, this detection mechanism gave rise to a rapid and considerable fluorescence enhancement responses needed for the sensitivity. Having achieved the sensitive detection of H2O2 vapors, we next investigated the possibility of the 1 nanofibers−amberlyst15 blend to detect TATP vapors. The presence of amberlyst-15 particles is expected to effectively decompose TATP into H2O2 for the detection.1 Indeed, exposure of the blend to trace TATP vapors gave rise to marked fluorescence enhancement, as shown in Figure 3c. Notably, the LOD of TATP vapor was even lower than that of H2O2, reaching 0.1 ppm. This can be explained by the fact that the lack of water in TATP vapor may avoid a competitive interaction of water with the resulting H2O2 and thereby caused stronger fluorescence responses. Notably, the

Figure 4. Fluorescence quenching of the 1 nanofibers−amberlyst-15 blend recorded in the range 670−710 nm upon exposure to DCP (a) and HCl (b) at different concentrations. (c) Fluorescence responses of the 1 nanofibers−amberlyst-15 blend to H2O2, TATP, and various potential interferents.

result from the competitive interactions between DCP or HCl and the blend interface that weaken the interactions between 1 nanofibers and amberlyst-15 particles and thereby reduce the photoluminescence. Furthermore, the resulting decrease in photoluminescence of the blend interface outcompeted the DCP- or HCl-induced increase in photoluminescence of pure 1 nanofibers parts;30 the net effect resulted in fluorescence quenching. Importantly, these quenching responses enabled 1 nanofibers−amberlyst-15 blend to access the easy discrimination of H2O2 and TATP from DCP and HCl. Other than DCP and HCl, other potential interferents at relatively high concentration, including common organic solvents and water, were tested under identical conditions. As shown in Figure 4c and Figure S8, the 1 nanofibers−amberlyst-15 blend exhibited either negligible fluorescence responses when exposed to most organic interferents or quenching fluorescence responses to amines. Even though some interferents caused modest fluorescence enhancement, these fluorescence responses were quickly recovered because of the volatile nature and the 6969

DOI: 10.1021/acs.analchem.9b01255 Anal. Chem. 2019, 91, 6967−6970

Analytical Chemistry

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insufficient interactions with the blend. Organic amines caused the fluorescence quenching because of the electron transfer mechanism and these opposite quenching responses would not interfere with the selectivity of the 1 nanofibers−amberlyst-15 blend for TATP (Figure 4c). The above negligible or distinct fluorescence response behaviors demonstrate that the 1 nanofibers−amberlyst-15 blend processes high selectivity for H2O2 and TATP against various interferents. Finally, we have also performed the detection of TATP in mixed systems. As shown in Figures S9 and S10, the mixed interferents (e.g., hair spray) caused only slight decreasing in fluorescence responses of TATP, which further indicating the high selectivity for H2O2 and TATP the 1 nanofibers−amberlyst-15 blend. In conclusion, we have fabricated a 1 nanofibers−amberlyst15 blend for the rapid, sensitive, and selective detection of TATP in the vapor phase based on turn-on fluorescence responses. We demonstrate that the amberlyst-15 component in the blend can rapidly decompose TATP into H2O2, which enables the enhancement of the interfacial interactions of 1 nanofibers and amberlyst-15 particles and gives sensitive fluorescence enhancement responses. This new response mechanism allows rapid turn-on fluorescence responses (ca. 5 s) and high sensitivity (0.1 ppm) to trace TATP. In contrast, various interferents have no sufficient interactions with the 1 nanofibers−amberlyst-15 blend and give rise to negligible fluorescence responses. Here, we highlight that the 1 nanofibers−amberlyst-15 blend enables the combination of the pretreatment and detection process and thereby simplifies the senor fabrication for the practical application.

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REFERENCES

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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.9b01255. Synthetic procedure, fabrication of the 1 nanofibersamberlyst-15 blend, property and fluorescence sensing characterizations, SEM images, fluorescence quantum yields, fluorescence enhancing profiles, and optical microscopic images (PDF)

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Letter

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Fax: +86-10-82617315 (Y.C.). *E-mail: [email protected]. Fax: +86-531-89631226 (M.L.). ORCID

Mei Li: 0000-0002-5766-5842 Yanke Che: 0000-0002-9671-3704 Author Contributions #

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by NSFC (Nos. 21577147, 21590811), the International Cooperation Foundation of Qilu University of Technology (No. QLUTGJHZ2018023) and International Intelligent Foundation of Qilu University of Technology (No. QLUTGJYZ2018024) and the “Key Research Program of Frontier Sciences” (No. QYZDY-SSW-SLH028) of the Chinese Academy of Sciences. 6970

DOI: 10.1021/acs.analchem.9b01255 Anal. Chem. 2019, 91, 6967−6970