Fast Imaging of Eccrine Latent Fingerprints with Nontoxic Mn-Doped

Mar 5, 2014 - Meanwhile, the levels 2 and 3 substructures of the fingerprints could also be simultaneously and clearly identified. While in the absenc...
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Fast Imaging of Eccrine Latent Fingerprints with Nontoxic Mn-Doped ZnS QDs Chaoying Xu,† Ronghui Zhou,‡ Wenwei He,§ Lan Wu,† Peng Wu,*,†,‡ and Xiandeng Hou†,‡ †

Analytical & Testing Center, and ‡Key Laboratory of Green Chemistry and Technology of MOE, College of Chemistry, Sichuan University, Chengdu 610064, China § Criminal Science and Technology Studio, Chongqing Zhongxian Police Security Bureau, Chongqing 404300, China S Supporting Information *

ABSTRACT: Fingerprints are unique characteristics of an individual, and their imaging and recognition is a top-priority task in forensic science. Fast LFP (latent fingerprint) acquirement can greatly help policemen in screening the potential criminal scenes and capturing fingerprint clues. Of the two major latent fingerprints (LFP), eccrine is expected to be more representative than sebaceous in LFP identification. Here we explored the heavy metal-free Mn-doped ZnS quantum dots (QDs) as a new imaging moiety for eccrine LFPs. To study the effects of different ligands on the LFP image quality, we prepared Mn-doped ZnS QDs with various surface-capping ligands using QDs synthesized in hightemperature organic media as starting material. The orange fluorescence emission from Mn-doped ZnS QDs clearly revealed the optical images of eccrine LFPs. Interestingly, N-acetylcysteine-capped Mn-doped ZnS QDs could stain the eccrine LFPs in as fast as 5 s. Meanwhile, the levels 2 and 3 substructures of the fingerprints could also be simultaneously and clearly identified. While in the absence of QDs or without rubbing and stamping the finger onto foil, no fluorescent fingerprint images could be visualized. Besides fresh fingerprint, aged (5, 10, and 50 days), incomplete eccrine LFPs could also be successfully stained with N-acetyl-cysteine-capped Mn-doped ZnS QDs, demonstrating the analytical potential of this method in real world applications. The method was also robust for imaging of eccrine LFPs on a series of nonporous surfaces, such as aluminum foil, compact discs, glass, and black plastic bags. he ridge pattern of skin on the human finger produces a unique fingerprint. When touching a surface, sweat excreted through the pores in the skin can be transferred to the surface to leave an impression of the ridge pattern. Such invisible impression is known as a latent fingerprint (LFP), the detection and identification of which is an indispensable strategy in individual credential and forensic science.1 Therefore, there has been intense interest in developing enhanced LFP imaging methods.2 Two major LFP origins have been explored for LFP development, namely from the eccrine and sebaceous glands. Sebaceous glands are associated with hair roots and are located throughout the body, while eccrine glands only distribute on the palms of hands.3 Therefore, LFP from eccrine is expected to be more representative in LFP identification.4 Since the amount of secretions from eccrine is much less than that from sebaceous glands, the fingerprints from eccrine glands are almost entirely invisible and demands more efforts for its visualization. Chemical imaging of LFPs with various colored or fluorescent materials has been evaluated as effective approaches to enhance the visualization of LFPs,5 which cause minimal contamination of the fingerprint. Recently, there has been a unique twist to implement the ongoing nanotechnology for

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© 2014 American Chemical Society

LFP development,3,6 primarily because of the novel and intriguing physical and electronic properties of various nanomaterials. To this end, it is possible to provide an entirely new approach for improved LFP detection with functionalized gold nanoparticles (AuNPs) via surface plasmon-based techniques7,8 or imaging mass spectrometry.9−11 Quantum dots (QDs) on the other hand, possess unique intrinsic fluorescent properties that are size-dependent at the nanoscale. As a consequence of their high luminescence, QDs bound to fingerprints can be visualized directly using UV illumination.12 A series of QDs, including CdS,12−14 CdSe,15,16 and CdTe QDs,17−20 have been explored for LFP development. However, the toxicity of these QDs, especially with Cd2+ being classified as a carcinogen,21 is of increasing concerns.22 Moreover, these LFP detection methods are also majorly based on sebaceous glands. As an alternative to common cadmium-based QDs, Mndoped ZnS QDs contain no toxic elements and have been frequently used for biosensors and bioimaging applicaReceived: December 31, 2013 Accepted: March 5, 2014 Published: March 5, 2014 3279

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tions.23−28 Besides, the highly luminescent orange emission of Mn-doped ZnS QDs can easily be visualized by human eyes. Herein, we intend to explore the LFP imaging application of Mn-doped ZnS QDs. To investigate the effect of surface ligands on the imaging quality of LFP, we prepared highly luminescent Mn-doped ZnS QDs via a high-temperature organic route29−31 and then make them water-soluble with a series of ligands. We found that Mn-doped ZnS QDs were capable of imaging of LFP from eccrine glands in a short period time of 5 s, which is one of the fastest methods for eccrine LFP imaging (Table S1 of the Supporting Information).

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EXPERIMENTAL SECTION Materials. Zinc acetate (ZnAc2, 99.99%), manganese chloride (MnCl2, 99.99%), tetramethylammonium hydroxide pentahydrate (TMAH), sulfur powder (99.99%), 1-octadecene (ODE, 90%), stearic acid (SA, 95%), and oleylamine (OAm, 70%) were purchased from Sigma-Aldrich for preparation of Mn-doped ZnS QDs. Analytical-grade thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), L-cysteine (L-Cys), mercaptosuccinic acid (MSA), and N-acetyl-cysteine (N-L-Cys) were obtained from Aladdin (Shanghai, China). All chemicals were used as received without any further purification. Synthesis and Preparation of Mn-Doped ZnS QDs. Mn-doped ZnS QDs were synthesized via the “nucleationdoping” approach developed by Peng et al.29−31 Details of the synthesis can be found in the Supporting Information. Briefly, ultrasmall MnS nanoclusters were first formed with Mn2+ and S precursors. Then, Zn2+ precursors were added to form ZnS shell around the MnS nanoclusters. The obtained QDs were purified using acetone/CHCl3 extraction with QDs in the CHCl3 layer. After purification, QDs were subjected to a standard ligand exchange process32 with a series of thiols to render the QDs water-soluble (see the Supporting Information). The UV−Vis and fluorescent emission spectra of the QDs were obtained with a UV-1700 UV/vis spectrophotometer (Shimadzu, Japan) and an F-7000 spectro- fluorometer (Hitachi, Japan), respectively. Protocol for Fingerprint Development. All eccrine fingerprints were acquired from the same volunteer by rubbing and stamping the finger onto substrate such as foil mainly. Hands were thoroughly washed with soap before fingerprint deposition. The foil strips bearing the fingerprints were immersed in the aqueous solution of Mn-doped ZnS QDs for the desired time. The fingerprint images under UV irradiation (302 nm) were taken with a Nikon D300S digital camera equipping a Nikon AF-S VR 105 mm f/2.8G IF-ED Macro Lens without any filters.

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Figure 1. Characterization of Mn-doped ZnS QDs: UV−vis absorption and fluorescence emission spectra of N-L-Cys-capped Mn-doped ZnS QDs. Inset is the fluorescent photo images of the QDs before and after water-solubilization under a 302 nm UV lamp.

which should be related to the characteristic absorption of the ZnS host.31 A strong fluorescence band is observed in the range of 500−700 nm (centered at about 585 nm, Figure 1), which can be ascribed to the characteristic Mn2+ 4T1 → 6A1 transition23 and is well-beyond the autofluorescence wavelength range of typical fingerprints.33 More importantly, the typical trap state emission of ZnS appearing near 400−500 nm23 is almost totally inhibited, implying the high quality of the asprepared Mn-doped ZnS QDs. Meanwhile, the Mn-doped ZnS QDs can be successfully converted to be water soluble via a routine ligand-exchange process (inset in Figure 1), which is similar to that reported for surface modification of typical QDs using similar ligands.32 The solution of N-L-Cys-capped Mndoped ZnS QDs displays bright orange fluorescence under a UV lamp (inset in Figure 1), suggesting a high quantum yield of Mn2+ fluorescence readily applicable for fingerprint development.31 The dopant emission can be stable for at least 1 h upon UV illumination, indicating the good photostability of the Mndoped ZnS QDs. The UV−vis absorption and fluorescent emission spectra of other ligands capped Mn-doped ZnS QDs were given in Figure S2 of the Supporting Information. Imaging of Eccrine LFPs with Various Ligand-Capped Mn-Doped ZnS QDs. Due to the excellent optical properties and low toxicity of doped ZnS QDs,23 we intended to explore the application of orange-emitted Mn-doped ZnS QDs for potential LFP imaging. Practically, a fast imaging moiety may help policemen in screening the potential criminal scenes and capturing fingerprint clues. Here we define the “fast” as 5 s from the practical point of view (the required time estimated from QDs staining to subsequent fluorescent imaging). It is evident that the interactions of QDs with other subjects are majorly bridged via the surface ligands. In this vein, we prepared six common thiols capped Mn-doped ZnS QDs and compared their influence on the imaging quality of eccrine LFP. As shown in Figure 2, six common thiols containing different functional groups (amine, carboxyl, amine + carboxyl, or carboxyl + acetyl) and carbon chain lengths (2−5) were employed as ligands for Mn-doped ZnS QDs. Although Mn-doped ZnS QDs capping with these thiols can easily be prepared with relatively simple aqueous routes,23 we prepared high-quality Mn-doped ZnS QDs in an organic phase and used them as starting material for obtaining various thiol-capped QDs, which

RESULTS AND DISCUSSION

Characterization of Mn-Doped ZnS QDs. In this research, Mn-doped ZnS QDs were explored as the imaging moiety for fingerprints (see the Supporting Information). Mndoped ZnS QDs were first prepared via the “nucleation-doping” approach developed by Peng et al. (about 4.0 nm, Figure S1 of the Supporting Information)29−31 and then subjected to ligand exchange with six commonly used bifunctional thiols for watersolubilization.32 As shown in Figure 1, (with N-L-Cys-capped Mn-doped ZnS QDs as an example), the UV−Vis absorption spectra of Mn-doped ZnS QDs showed almost featureless absorption (without the distinguished absorption onset) in the UV region with the absorption edge located at about 335 nm, 3280

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Figure 2. Comparison of the imaging of LFPs from eccrine with different ligand-capped Mn-doped ZnS QDs. L-Cys:L-cysteine, TGA:thioglycolic acid, MPA:3-mercaptopropionic acid, MSA:mercaptosuccinic acid, and N-L-Cys:N-acetyl-cysteine. In all investigations, the concentrations of QDs were set at the same based on their absorbance at 280 nm (see the Supporting Information).

inorganic salts (such as chloride, bromide, iodide, fluoride, and phosphate) and organic materials (such as amino acids, fatty acids, and urea).2 The retaining of QDs by the secretions from eccrine glands may be based on interactions such as hydrophobic and electrostatic interactions. From the structures of all the ligands used in this work, it is evident that N-L-Cys has longest carbon chain and an acetyl group. Probably in all, the carbon chain and the carboxyl as well as acetyl groups in N-LCys permit fast and better interactions between N-L-Cys and secretions from eccrine. Selectivity of using N-L-Cys-Capped Mn-Doped ZnS QDs as Fast Imaging Moiety for Eccrine LFPs. The amount of secretions from eccrine glands is relatively small, and the eccrine LFPs are barely visible under either daylight (Figure 3A) or fluorescent excitation (Figure S6 of the Supporting Information), which thus demands fast visualization for forensic applications (especially in the criminal scenes). In the presence of N-L-Cys-capped Mn-doped ZnS QDs, the eccrine LFPs can be quickly imaged within 5 s (Figure 3C). Besides, although the amount of secretions from the volunteer varies day-by-day, fast imaging of the eccrine LFPs is still highly reproducible (Figure S7 of the Supporting Information). However, in the absence of eccrine LFPs but only QDs, no fingerprints can be detected (Figure 3B), demonstrating the selectivity of using N-L-Cyscapped Mn-doped ZnS QDs as contrast agents for eccrine LFPs. The substructures of LFPs in principle form the basis of fingerprint identification, and their unambiguous imaging is critical for forensic identification of individuals. The eccrine LFP staining with N-L-Cys-capped Mn-doped ZnS QDs for 5 s (Figure 3C) displays a well-resolved ridge flow and pattern configuration (level 1). In addition to level 1 details, level 2 (ridge termination, bifurcation, and crossover) characteristics of the LFP are also clearly observed (Figure 3D), thus suggesting strong interactions between QDs and eccrine excretions in a short period of time (5 s). Several level 3 details (pores), namely the sweat pores from which the sweat is secreted, could also be observed along the ridges. The level 3 detail is used by forensic officers in some countries for confirmation of an identification match. Overall, the successful identification of these substructures clearly demonstrates the effectiveness of using N-L-Cys-capped Mn-doped ZnS QDs for fast eccrine LFP development.

guarantee that the expected difference in LFP imaging is originated from the surface ligands. As can be seen from Figure 2, all carboxyl-terminated (including N-L-Cys) QDs can stain eccrine LFPs in 5 s, in which N-L-Cys-capped QDs give the best and reproducible imaging quality. On the contrary, amine-terminated (including L-Cys) QDs can hardly be retained by the fingerprint in such a short period of time. After incubating the LFPs with various ligand-capped QDs for 10 min, all QDs can be captured by LFPs. But still, amine-terminated QDs give poor resolution and carboxyl-terminated QDs show better imaging quality for LFPs (data not shown). For potential application at the scene of a crime for forensic investigation, it is evident that N-L-Cyscapped Mn-doped ZnS QDs can provide high-quality eccrine fingerprints in a very short period of time. After staining, the fluorescence of the LFP image can last for at least 50 days and fade out only slightly (Figure S3 of the Supporting Information). It should be noted that the least time required for LFP visualization with Superglue (cyanoacrylate fuming, a standard technique being adopted at the forensic crime scene for examination of invisible fingerprints34) is about 10 min to obtain a high-quality fingerprint image (Figure S4 of the Supporting Information). Therefore, N-L-Cys-capped Mndoped ZnS QDs could be employed as a superfast staining moiety for eccrine LFPs (Table S1 of the Supporting Information). Meanwhile, sebaceous LFPs can also be stained as well but was not as fast as that for eccrine LFPs (see the Supporting Information). To further confirm the role of N-L-Cys in fast staining of eccrine LFPs, water-soluble N-L-Cys-capped Mn-doped ZnS QDs were also prepared directly with an aqueous route.35 Eccrine LFPs staining with the resultant Mn-doped ZnS QDs could also be achieved in 5 s (Figure S5 of the Supporting Information), indicating that the fast staining of eccrine LFPs could be majorly ascribed to the interaction between N-L-Cys with secretions from eccrine. Lastly, N-L-Cys is expected to add long-term colloidal stability of Mn-doped ZnS QDs as compared with TGA and MPA, since N-L-Cys has longer carbon chain and branched structure for protecting dissolved oxygen from etching the QDs surface.36 The exact mechanisms of fast staining of eccrine LFPs with N-L-Cys-capped Mn-doped ZnS QDs were not very clear at the present stage. Eccrine sweat consists of 98−99% water, various 3281

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Figure 4. Comparison of the eccrine LFP stained by N-L-Cys-capped Mn-doped ZnS QDs (left) and a blue inkpad (right). Parts of the similar minutia points of the two fingerprints were labeled on the images.

bags in 5 s. Although the amounts of QDs deposited on different surfaces vary (different brightness), sufficient contrast between the background and orange ridge could be obtained, which is crucial for forensic investigations. The successful fingerprint development on different surfaces clearly demonstrates the reliability of this method for fast imaging of eccrine LFPs. To further demonstrate the robustness of this method for practical use, aged eccrine fingerprints (5, 10, and 50 days) were developed with N-L-Cys-capped Mn-doped ZnS QDs for 5 s. As shown in Figure S9 of the Supporting Information, the fingerprint ridge details could still be quickly visualized, although the amount of QDs deposited on the ridge of a fingerprint became smaller as the age lengthened. Moreover, the substructures of the 50-day old fingerprint can still be easily identified (Figure S10 of the Supporting Information), demonstrating the effectiveness of this method. In a real crime scene, incomplete fingerprint may be frequently encountered. Establishing the identity of a suspect (or victim) based on partial fingerprints is also very important for law enforcement agencies. Accordingly, the performance of this method for staining of incomplete eccrine fingerprints was also investigated. As shown in Figure 5, N-L-Cys-capped Mndoped ZnS QDs could also image incomplete fingerprints in 5 s. After careful minutiae extraction, at least 17 similar minutia

Figure 3. Selectivity evaluation of using N-L-Cys-capped Mn-doped ZnS QDs as the imaging moiety for eccrine LFPs: (A) aluminum foil with eccrine fingerprint but no QDs, (B) fluorescent image of aluminum foil without eccrine fingerprint after immersing in solution of N-L-Cys-capped Mn-doped ZnS QDs for 5 s, (C) fluorescent image of aluminum foil with eccrine fingerprint after immersing in solution of N-L-Cys-capped Mn-doped ZnS QDs for 5 s, and (D) magnified images (3×, from corresponding areas in C) showing the details of level 2 and level 3 characteristics of LFPs. All fluorescent images were excited with a 302 nm UV lamp.

Confirmation of the Accuracy and Reliability of Using N-L-Cys-Capped Mn-Doped ZnS QDs as Fast Imaging Moiety for Eccrine LFPs. At the beginning of the 19th century, scientists found there were two major key characteristics in identifying the similarity of two fingerprints (i.e., the ridge patterns of two individuals are extremely variable and such patterns will not change during their whole life). Therefore, assessing the accuracy and reliability of a LFP visualization method is of great importance for potential practical use.37 To confirm the accuracy of eccrine LFP imaging with the proposed method, we further compared eccrine fingerprint images stained by N-L-Cys-capped Mn-doped ZnS QDs with that previously captured with a blue inkpad. As shown in Figure 4, the macrodetails such as friction ridge flow, pattern type, and singular points of the two images are generally the same. Besides, a lot of similar minutia points of the two images can be identified (with 14 points labeled in Figure 4), implying that they are from the same individual. Therefore, the accuracy of this method was confirmed. To investigate versatility of fast staining of eccrine LFPs with N-L-Cys-capped Mn-doped ZnS QDs, LFPs deposited on several other nonporous surfaces were investigated. As shown in Figure S8 of the Supporting Information, fingerprint images can also be taken from compact discs, glass, and black plastic

Figure 5. Comparison of the incomplete eccrine LFP stained by N-LCys-capped Mn-doped ZnS QDs in 5 s (a) with a fingerprint stained by a blue inkpad (b). Seventeen similar minutia points of the two fingerprints were identified and labeled on the images. 3282

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points could be identified between the incomplete fingerprint and that stained by the blue inkpad, indicating that the proposed N-L-Cys-capped Mn-doped ZnS QDs may be practically useful in real forensic applications.

(15) Sametband, M.; Shweky, I.; Banin, U.; Mandler, D.; Almog, J. Chem. Commun. 2007, 1142−1144. (16) Wang, Y. F.; Yang, R. Q.; Wang, Y. J.; Shi, Z. X.; Li, J. J. Forensic Sci. Int. 2009, 185, 96−99. (17) Yu, X. J.; Liu, J. J.; Zuo, S. L.; Yu, Y. C.; Cai, K. Y.; Yang, R. Q. Forensic Sci. Int. 2013, 231, 125−130. (18) Cheng, K. H.; Ajimo, J.; Chen, W. J. Nanosci. Nanotechnol. 2008, 8, 1170−1173. (19) Gao, F.; Lv, C. F.; Han, J. X.; Li, X. Y.; Wang, Q.; Zhang, J.; Chen, C.; Li, Q.; Sun, X. F.; Zheng, J. C.; Bao, L. R.; Li, X. J. Phys. Chem. C 2011, 115, 21574−21583. (20) Yu, X. J.; Zuo, S. L.; Xiong, H.; Yu, Y. C.; Liu, J. J.; Yang, R. Q. ChemPlusChem 2013, 78, 244−249. (21) Wu, P.; Li, C. H.; Chen, J. B.; Zheng, C. B.; Hou, X. D. Appl. Spectrosc. Rev. 2012, 47, 327−370. (22) Bottrill, M.; Green, M. Chem. Commun. 2011, 47, 7039−7050. (23) Wu, P.; Yan, X.-P. Chem. Soc. Rev. 2013, 42, 5489−5521. (24) Wang, H.-F.; Wu, Y.-Y.; Yan, X.-P. Anal. Chem. 2013, 85, 1920− 1925. (25) Zhang, L.; Cui, P.; Zhang, B.; Gao, F. Chem.Eur. J. 2013, 19, 9242−9250. (26) Wu, P.; Zhao, T.; Tian, Y. F.; Wu, L.; Hou, X. D. Chem.Eur. J. 2013, 19, 7473−7479. (27) Ren, H.-B.; Wu, B.-Y.; Chen, J.-T.; Yan, X.-P. Anal. Chem. 2011, 83, 8239−8244. (28) Wu, P.; Miao, L.-N.; Wang, H.-F.; Shao, X.-G.; Yan, X.-P. Angew. Chem., Int. Ed. 2011, 50, 8118−8121. (29) Pradhan, N.; Goorskey, D.; Thessing, J.; Peng, X. G. J. Am. Chem. Soc. 2005, 127, 17586−17587. (30) Pradhan, N.; Peng, X. G. J. Am. Chem. Soc. 2007, 129, 3339− 3347. (31) Zhang, W. J.; Li, Y.; Zhang, H.; Zhou, X. G.; Zhong, X. H. Inorg. Chem. 2011, 50, 10432−10438. (32) Pradhan, N.; Battaglia, D. M.; Liu, Y. C.; Peng, X. G. Nano Lett. 2007, 7, 312−317. (33) Lambrechts, S. A. G.; van Dam, A.; de Vos, J.; van Weert, A.; Sijen, T.; Aalders, M. C. G. Forensic Sci. Int. 2012, 222, 89−93. (34) Day, J. S.; Edwards, H. G. M.; Dobrowski, S. A.; Voice, A. M. Spectrochim. Acta, Part A 2004, 60, 1725−1730. (35) Chen, Z. Q.; Lian, C.; Zhou, D.; Xiang, Y.; Wang, M.; Ke, M.; Liang, L. B.; Yu, X. F. Chem. Phys. Lett. 2010, 488, 73−76. (36) Aldana, J.; Wang, Y. A.; Peng, X. G. J. Am. Chem. Soc. 2001, 123, 8844−8850. (37) Ulery, B. T.; Hicklin, R. A.; Buscaglia, J.; Roberts, M. A. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 7733−7738.

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CONCLUSION In summary, we have developed a method of fast imaging of eccrine LFPs based on N-L-Cys-capped Mn-doped ZnS QDs. Excellent eccrine LFP images were obtained after staining of the eccrine LFPs with Mn-doped ZnS QDs for 5 s, with clear illustration of the levels 2 and 3 substructures. The method is robust for imaging of eccrine LFPs on a series of nonporous surfaces, such as aluminum foil, glass, compact discs, and black plastic bags. It was also demonstrated that the aged (up to 50 days) and incomplete LFPs could be successfully stained with N- L-Cys-capped Mn-doped ZnS QDs. This method is promising for potential application at the scene of a crime for forensic investigations.

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ASSOCIATED CONTENT

S Supporting Information *

Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86 28 8541 2798. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We appreciate the financial support of this project from the National Natural Science Foundation of China (Grant 21205084) and the Basic Research Program of Sichuan Province (Grant 2011JY0016).

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REFERENCES

(1) Bell, S. Annu. Rev. Anal. Chem. 2009, 2, 297−319. (2) Hazarika, P.; Russell, D. A. Angew. Chem., Int. Ed. 2012, 51, 3524−3531. (3) Choi, M. J.; McDonagh, A. M.; Maynard, P.; Roux, C. Forensic Sci. Int. 2008, 179, 87−97. (4) Spindler, X.; Hofstetter, O.; McDonagh, A. M.; Roux, C.; Lennard, C. Chem. Commun. 2011, 47, 5602−5604. (5) Shan, X. N.; Patel, U.; Wang, S. P.; Iglesias, R.; Tao, N. J. Science 2010, 327, 1363−1366. (6) Wolfheis, O. S. Angew. Chem., Int. Ed. 2009, 48, 2268−2269. (7) Li, K.; Qin, W. W.; Li, F.; Zhao, X. C.; Jiang, B. W.; Wang, K.; Deng, S. H.; Fan, C. H.; Li, D. Angew. Chem., Int. Ed. 2013, 52, 11542−11545. (8) Song, W.; Mao, Z.; Liu, X. J.; Lu, Y.; Li, Z. S.; Zhao, B.; Lu, L. H. Nanoscale 2012, 4, 2333−2338. (9) Lim, A. Y.; Ma, J.; Boey, Y. C. F. Adv. Mater. 2012, 24, 4211− 4216. (10) Tang, H. W.; Lu, W.; Che, C. M.; Ng, K. M. Anal. Chem. 2010, 82, 1589−1593. (11) Liu, Y. Y.; Ma, X. X.; Lin, Z. Q.; He, M. J.; Han, G. J.; Yang, C. D.; Xing, Z.; Zhang, S. C.; Zhang, X. R. Angew. Chem., Int. Ed. 2010, 49, 4435−4437. (12) Menzel, E. R.; Savoy, S. M.; Ulvick, S. J.; Cheng, K. H.; Murdock, R. H.; Sudduth, M. R. J. Forensic Sci. 2000, 45, 545−551. (13) Bouldin, K. K.; Menzel, E. R.; Takatsu, M.; Murdock, R. H. J. Forensic Sci. 2000, 45, 1239−1242. (14) Dilag, J.; Kobus, H.; Ellis, A. V. Forensic Sci. Int. 2013, 228, 105− 114. 3283

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