High-Resolution and Universal Visualization of Latent Fingerprints

May 30, 2016 - Although fingerprints have been widely used in forensic investigations, low resolution and poor universality are still the main obstacl...
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High-Resolution and Universal Visualization of Latent Fingerprints Based on Aptamer-Functionalized Core−Shell Nanoparticles with Embedded SERS Reporters Jingjing Zhao, Kun Zhang, Yixin Li, Ji Ji, and Baohong Liu* Department of Chemistry, Institutes of Biomedical Sciences and State Key Lab of Molecular Engineering of Polymers, Fudan University, Shanghai 200433, China S Supporting Information *

ABSTRACT: Although fingerprints have been widely used in forensic investigations, low resolution and poor universality are still the main obstacles for the development of fingerprint visualization. In this paper, a facile and universal imaging protocol for latent fingerprints (LFPs) was developed by combining sandwiched SERS probes with the highly sensitive and selective recognition of aptamers. The embedded SERS probes (Au/pNTP/SiO2) successfully avoid the environment interference, ascertaining the stability and reproducibility of Raman signals, and simultaneously improve the efficiency of the fingerprint identification. This approach is operationally simple without complicated pre- or post-treatments. Moreover, the fingerprint images display the high resolution in which third-level details can be clearly identified. This is a general approach and can be used to detect various types of fingerprints, including sebaceous, eccrine, fresh LFPs, and aged LFPs on different substrates (such as smooth, scratching, semiporous, and porous surfaces). KEYWORDS: latent fingerprints, SERS imaging, sandwich structure, aptamers, lysozyme

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INTRODUCTION

At present, a variety of techniques have been developed to visualize LFPs, including fluorescence spectroscopy,5−10 mass spectrometry,3,11−15 electrochemiluminescence,16−19 multimetal deposition (MMD),20−22 nanoplasmonic imaging,4,23 infrared spectroscopy,24 Raman spectroscopy,25,26 and so on. Fluorescence spectroscopy allows fast and sensitive visualization of LFPs but usually suffers from interference from background fluorescence. The visualization of LFPs based on mass spectrometry could identify endogenous and exogenous chemicals in fingerprints. However, the fingerprints needed to be collected on a smooth thin film of a semiconductor in mass spectrometry imaging.3,12 Electrochemiluminescence methods experienced similar drawback: fingerprints had to be collected on a conductive basement.17,19 In some LFP imaging protocols based on antigen−antibody interactions, the surfaces of detection basements need complex pre- and post-treatments.8,26 Therefore, the applications of some techniques have been restricted by the specific use condition. Considering the importance of fingerprint detection in forensic identification, there remains a high demand for simple, cost-effective, nondestructive, high-resolution, and universal methods for LFP

Because of their uniqueness, fingerprints are widely used in forensic investigations and personal identification, including individual credentials, safety inspection, and access control.1 The unique pattern of fingerprints contains a series of lines corresponding to ridges and grooves that remain unchanged throughout the lifetime of a person.2 When a finger touches an object, an impression of the ridge pattern of the finger will be left. This impression is usually invisible in daylight by the naked eye and is named a latent fingerprint (LFP). Characteristic fingerprint features are generally categorized at three different levels in a hierarchical order, which refer to the first-level (pattern), second-level (minutia points), and third-level (pores and ridge contours).3,4 Among these three levels of fingerprints, the second- and third-level features are useful and sufficient for individual identification. However, it is not easy to establish their features, especially the third-level features, which typically require high resolution techniques.3 Furthermore, the visualization of LFPs is often influenced by many factors, such as surface matrix, fingerprint type, and age. Therefore, the development of high-resolution and universal protocols of fingerprint imaging is highly necessary and has attracted continuing interest in the fields of chemical and forensic sciences. © XXXX American Chemical Society

Received: March 18, 2016 Accepted: May 30, 2016

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DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces imaging on various surfaces. It is rare to find a fingerprint imaging platform that simultaneously meets these requirements. Recently, an LFP detection method based on upconversion nanoparticles was reported, and the universality was greatly improved, but the second-level features of fingerprints were vague.27 Surface-enhanced Raman scattering (SERS) spectroscopy, as a nonphotobleaching, nondestructive, and noninvasive technique, has the integrated advantages of single-molecule sensitivity, narrow spectroscopic fingerprints, and anti-interference with water; thus, SERS has been applied as a robust tool for biological detection and imaging. For instance, this noninvasive, label-free technique was used to monitor and visualize the metabolism of an antitumor drug in living cells28 to map the glycan expression of cancerous cells29 and to visualize the distribution of molecules in cells and cellular transport pathways.30 At present, the visualization of LFPs based on SERS imaging is rarely reported.25,26 SERS imaging of LFPs was implemented through an interaction between antigen and antibody, where the detection substrates need a time-consuming pretreatment (∼26 h).26 Detailed features of the fingerprints and the universality of detection basements were not investigated. Herein, we report a facile imaging strategy for LFPs by combining SERS with the highly sensitive and selective recognition of aptamers. Aptamers are short single-stranded oligonucleotides that can fold into specific three-dimensional structures in the presence of targets to realize specific recognition. Compared with antigen−antibody interactions, the recognition of aptamers displays many exceptional properties, such as flexible design, mild synthetic conditions, easy modification, good biochemical stability, and high specificity and affinity.6,9 Lysozyme, one of the polypeptide components found in human sweat, is universal in fingerprints.27 Therefore, a lysozyme-binding aptamer (denoted LBA) was chosen as a general targeting reagent for LFPs. We prepared LBA-modified sandwich-structured Au/pNTP/SiO2 SERS probes. SERS report molecules (pNTP) embedded between the Au core and the silica shell were successful at avoiding interference of the external environment, which ascertained the stability and reproducibility of SERS signals. In addition, the totally free surface of the silica shell could, as much as possible, be modified with LBA, which was helpful for improving the efficiency of the fingerprint identification. By modification-sandwiched SERS probes with aptamers selected against lysozyme, LFPs were successfully detected and recorded. Moreover, this universal approach was operationally simple without any complicated pre- or post-treatment and could be used to detect various types of fingerprints containing sebaceous, eccrine, fresh LFPs, and aged LFPs on different substrates with legible second-level features. This simple, universal, and high resolution imaging strategy greatly promotes the application of fingerprint imaging.

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analytical grade and used as received without further purification. Ultrapure Milli-Q water (Millipore) was used throughout the experiments. Preparation of Sandwiched-Structure Au/pNTP/SiO2 SERS Nanoprobes. The Au nanoparticles (Au NPs) were synthesized according to the Frens’ method.31 In brief, 613 μL of HAuCl4·4H2O (1%) solution and 500 μL of trisodium citrate dihydrate (1%) were added to a round flask containing 50 mL of deionized water. After being boiled for 20 min, the reaction mixture was removed from the oil bath and cooled to room temperature. Then, 300 μL of pNTP (1 mM) ethanol solution was added to the Au NP solution, and the mixture was stirred for 4 h to form a self-assembled submonolayer of pNTP on the Au NP surface. A thin silica shell was then coated on the pNTP-labeled Au NPs following the procedure of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS).32 Briefly, 600 μL of APTMS (1 mM) was added to the flask and stirred for 15 min. Then, 4.8 mL of sodium silicate solution (0.54% (w/w)) was added and stirred for 30 min in a 90 °C oil bath. After the mixture was cooled in an ice bath to room temperature, 300 μL of APTMS (1 mM) was added to the flask and stirred for 15 min to increase the content of amino groups on the surface of the silica shell. Immobilization of LBA onto Au/pNTP/SiO2 SERS nanoprobes. The aptamers selected against lysozyme were attached to the surface of Au/pNTP/SiO2 nanoparticles following the reported methods through the formation of a triazine-functionalized surface.33−35 After centrifugation and being washed three times with ethanol and three times with acetonitrile, amino-modified Au/pNTP/ SiO2 SERS nanoprobes were further reacted with 2,4,6-trichloro-1,3,5triazine in acetonitrile (3 mL, 0.2 M) at room temperature for 4 h.33−35 Then, the surface-activated nanoprobes were centrifuged (7000 rpm for 10 min) and washed three times with acetonitrile and two times with ethanol, deionized water, and borate buffer. The obtained Au/pNTP/SiO2 nanoprobes were redispersed in 2 mL of borate buffer (pH 8.4). 5′-Amine-modified lysozyme-binding aptamer (5.6 nmol) was dissolved in 0.4 mL of borate buffer and then added to the activated Au/pNTP/SiO2 nanoprobes. The mixture was slightly shaken at room temperature overnight. Finally, the LBA-modified Au/pNTP/SiO2 SERS nanoprobes were centrifuged and washed three times with borate buffer to remove the free LBA. The supernatant was collected to measure the concentration of free LBA by UV/vis spectroscopy. Characterization. The shape and diameter of the as-prepared Au NPs and Au/pNTP/SiO2-LBA nanoparticles were characterized with a JEOL JEM-2011 transmission electron microscope (TEM) operated at an acceleration voltage of 200 kV by dispersing the sample on a copper grid with a carbon film. In addition, scanning TEM (STEM) and energy dispersion spectrum (EDS) of Au/pNTP/SiO2-LBA nanoparticles were also collected on this TEM. UV−vis spectra were measured on an Agilent HP8453 spectrophotometer using a quartz cuvette with a 1 cm optical pathway. Raman spectra of Au/pNTP/ SiO2-LBA nanoparticles were obtained with a Horiba XploRA confocal Raman microspectrometer with a 638 nm laser; the laser power at the sample spot was 2.4 mW, and data was recorded with an acquisition time of 10 s. Samples for SERS measurements were drop-cast onto glass slides using a micropipette with 10 μL followed by drying at 60 °C. Fingerprint Collection and Incubation. Sebaceous and eccrine fingerprints were collected by different procedures. First, volunteers were asked to wash their hands, which were dried with N2 prior to fingerprint collection. To obtain sebaceous fingerprints, they gently ran their fingers across their foreheads and slightly pressed their fingers on the chosen substrates that were precleaned with ethanol and dried with N2. To produce eccrine fingerprints, volunteers warmed their hands in PE gloves for “sweating” and then stamped their fingertips on the surface of the clean substrate. Fingerprint samples were subjected to the incubation procedure after being aged for 16 h. First, 200 μL of Au/pNTP/SiO2-LBA nanoprobes (0.01 mg/mL) was cast onto the fingerprint substrates and incubated for 30 min at room temperature in a wet chamber. Then, the excess nonbonded

EXPERIMENTAL SECTION

Chemicals. Tetrachloroauric acid tetrahydrate (HAuCl4·4H2O), pnitrothiophenol (pNTP), acetonitrile, and ethanol were purchased from Sinopharm Chemical Reagent (Shanghai, China). Trisodium citrate dehydrate (Na3C6O7·2H2O) and 2,4,6-trichloro-1,3,5-triazine were obtained from Aladdin Reagent (Shanghai, China). (3Aminopropyl)trimethoxysilane (APTMS) and sodium silicate solution were purchased from Sigma-Aldrich. The sequence of the lysozymebinding aptamer (designated LBA) is 5′-NH2-TTTTTTATCAGGGCTAAAGAGTGCAGAGTTACTTAG-3′ and was synthesized by Sangon Biotech (Shanghai, China). All other chemicals were at least of B

DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces Scheme 1. Synthesis of Au/pNTP/SiO2-LBA SERS Nanoprobes

Figure 1. (A) TEM image of the as-prepared Au NPs. (B) TEM image of Au/pNTP/SiO2 SERS nanoprobes. The inset is the higher-magnification image (bar = 5.0 nm). (C) STEM images of Au/pNTP/SiO2 NPs using the electron, Au, S, Si, and O signals and the superimposed image of the STEM images of S and Si (bar = 25.0 nm). The inset is the TEM image (bar = 10.0 nm). (D) Extinction spectra of pure Au NPs (navy line), Au/ pNTP/SiO2 SERS nanoprobes (purple line), and Au/pNTP/SiO2-LBA SERS nanoprobes (red line). (E) SERS spectra of pNTP-functionalized Au NPs (blue line), Au/pNTP/SiO2 SERS nanoprobes (orange line), and Au/pNTP/SiO2-LBA SERS nanoprobes (violet line). nanoparticles were carefully rinsed out with deionized water, and the fingerprint substrates were dried with N2. Raman Imaging of Latent Fingerprints. Raman imaging was carried out with a Horiba XploRA confocal Raman microspectrometer imaging system with 638 nm laser (2.4 mW power) using a 10× objective lens (numerical aperture of 0.24); every data point was acquired with an acquisition time of 0.1 s. The Raman spectra were acquired in the wavenumber range of 1200−1500 cm−1, and the vibration band at 1350 cm−1 was chosen to image the LFPs. The

movement steps (i.e., center-to-center distance of the laser spot movement) of the X,Y stage for the imaging of the LFPs on the substances were set at 40 × 40 μm.

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RESULTS AND DISCUSSION

LBA-modified sandwich-structured Au/pNTP/SiO2 SERS nanoprobes were synthesized with a layer-by-layer approach, which is illustrated in Scheme 1. First, Au NPs were prepared C

DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 2. (A) SERS imaging of a latent fingerprint on a glass surface using Au/pNTP/SiO2-LBA nanoprobes. In this SERS image, the second- and third-level details can be identified. (B) Cross-sectional gray values over six parallel ridges as indicated by the white line in A. (C) (a−e) Second-level details of the latent fingerprint in A. (f) Second-level details of a latent fingerprint not shown, and the inset is the third-level details. Inset bar (yellow) = 40 μm. Bar (white) = 150 μm.

by using the Frens’ method as previously reported.31 Subsequently, Au NPs were labeled with pNTP as the Raman reporter to form a submonomolecular layer through the sulfur− gold interaction. This dense packing of pNTP molecules on the Au NP surface with uniform orientation could effectively improve the reproducibility of the SERS signal. Then, a thin silica shell was coated on the pNTP-labeled Au NPs following the modified procedure of SHINERS,32 giving rise to the formation of sandwich-structured Au/pNTP/SiO2 SERS probes. Finally, 5′-amine-modified aptamers were functionalized on the surface of sandwich-structured Au/pNTP/SiO2 nanoparticles via a two-step process.33−35 APTMS ethanol solution was first introduced into the Au/pNTP/SiO2 NP solution to generate an amine-modified surface. Then, 2,4,6trichloro-1,3,5-triazine was added to generate a triazinefunctionalized surface for further modification with aminoterminated aptamers. Lysozyme is a universal polypeptide component in human sweat and serves an indispensable role in the defense systems of the skin. Previous research has shown that the recognition of lysozyme using the aptamer has high selectivity and affinity.27 The aptamers selected against lysozyme are short single-stranded oligonucleotides and remain in their single-stranded state in the absence of lysozyme. In the presence of lysozyme, the aptamers will fold into their specific and complex three-dimensional structures and then bind to the lysozyme. Therefore, Au/pNTP/SiO2-LBA SERS nanoprobes could be deposited on the location of fingerprint ridges after the recognition of lysozyme by the nanoconjugate. The construction process of Au/pNTP/SiO2-LBA SERS nanoprobes was simple without a complex reaction or expensive instruments. TEM images in Figure 1A showed that the asprepared Au NPs were uniform and monodispersed with an average size of 55.6 ± 3.0 nm (see Figure S2A). The TEM image of the sandwich-structured Au/pNTP/SiO2 nanoparticles is shown in Figure 1B, and a light ring coating the dark gold core could be clearly identified, indicating that Au NPs were successfully and completely encapsulated with the thin silica shell. The higher-magnification TEM image inserted

in Figure 1B indicated that the thickness of the silica shell was approximately 2.4 nm. The ultrathin silica shell was essential for extending the strong electromagnetic field from the gold core to the shell surface. The elemental composition from the EDS measurement also revealed that the silica layer was successfully formed at the Au surface (see Figure S2B). For the sandwich structure to be further confirmed, the spatial distributions of the Au core, silica shell, and embedded molecular layer (pNTP) were simultaneously investigated by STEM. From Figure 1C, we could find that the STEM images of Au and S were very similar, indicating that pNTP molecules took the shape of the Au NPs. Furthermore, the superimposed STEM image of S and Si clearly displayed that the pNTP molecular layer retained its integrity, and the molecules did not spill out to the surface of the silica shell.36 All of the results presented above demonstrate that we had successfully obtained the designed sandwich nanostructures. Such nanostructures were helpful for avoiding environmental interference for the SERS signal and improving the efficiency of the fingerprint identification. In addition, the optical properties of Au/pNTP/SiO2-LBA nanoparticles were also discussed, indicating that these nanoparticles were ideal SERS nanoprobes for the LFP imaging. As shown in Figure 1D, the localized surface plasmon band of the bare Au NPs was located at 525 nm, and no considerable shift of that was observed after they were labeled by pNTP and coated by the silica shell, indicating that the nanoparticles still maintained the monodisperse state after the surface modification.37 However, the plasmon band of Au NPs red-shifted and broadened after bonding with LBA. At the same time, a typical absorption band at 260 nm emerged, indicating LBA was successful conjugated to Au/pNTP/SiO2 nanoparticles. pNTP is one of the common Raman reporter molecules owing to the strong interaction of sulfur−gold or sulfur−silver. Characteristic bands of pNTP on the surface of Au NPs are located at 723, 857, 1082, 1350, and 1573 cm−1, and they are assigned to the C−S stretching, C−H wagging, C−S stretching, O−N−O stretching, and the phenyl-ring mode, respectively, as shown in Figure 1E. There was no D

DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

identification of partial fingerprints or other cases with ambiguous second-level details.17 In addition, this approach using Au/pNTP/SiO2-LBA nanoprobes for SERS imaging was free from the interference of external pollutants such as dust and fibers. Under an optical microscope, it could be seen clearly that two paper fibers were located on the pattern of the fingerprint, which is shown in Figure S3A. However, the paper fibers disappeared in the SERS image of the fingerprint (Figure S3B), which indicated that the pattern of the fingerprint could not be affected by the external pollutant in the SERS image. To estimate the universality of this fingerprint imaging method based on the sandwiched SERS nanoprobes and aptamer recognition, we determined the applicability of this method on different surfaces. A fingerprint on a scratching (decorative pattern) surface such as a stainless steel knife was incubated with Au/pNTP/SiO2-LBA nanoprobes. Subsequently, a clear pattern of the fingerprint is seen, as shown in Figure S4(a−f) with higher magnification, and the core part of the LFP is clearly displayed in Figure 3A, even including the

remarkable change of the SERS enhancement of Au NPs after the layer-by-layer modification (Figure 1E), confirming that the silica shell coated on the surface of Au/pNTP nanoparticles was thin enough to facilitate the application of Au/pNTP/SiO2LBA SERS nanoprobes in the imaging of LFPs. Furthermore, the amount of LBA immobilized onto Au/pNTP/SiO 2 nanoparticles was calculated according to Lambert−Beer’s Law.35 The calculation process is shown in the Supporting Information, and the amount of LBA immobilized per Au/ pNTP/SiO2 nanoparticle was estimated to be 320. The performance of Au/pNTP/SiO2-LBA nanoprobes in SERS imaging was evaluated by detecting a latent fingerprint collected on a glass surface. Glass substances are very common in daily life, and criminal suspects can always be identified through detection of LFPs left on glass substances in forensic investigations. A smooth glass microscope slide was chosen as a representative glass surface for fingerprint imaging. Importantly, the glass slide was just precleaned with ethanol and dried with nitrogen without any complicated premodification prior to fingerprint collection. Subsequently, the fingerprint collected on a glass microscope slide was incubated with Au/pNTP/ SiO2-LBA nanoprobes, and the nanoprobes were deposited on the papillary ridges of LFPs through the recognition of LBA to lysozyme. Prior to the deposition of Au/pNTP/SiO2-LBA nanoprobes, we could see a faintly spatial pattern (first-level features) of the fingerprint under an optical microscope in which the dark ridge deposits contrasted with the bright substrate (no figure shown here). The pattern of the fingerprint was more legible after deposition of the SERS probes, whereas the second- and third-level details of an LFP could not be clearly identified. Then, the fingerprint was imaged by the SERS imaging technique. It was obvious that the characteristic band of pNTP at 1350 cm−1 was the most prominent (Figure 1E) and was thus used for the SERS image. A representative mapping of the fingerprint obtained by the SERS imaging technique is shown in Figure 2A, displaying a well-resolved ridge and furrow without any interference from substrate. The SERS image of the LFP was collected by mapping different regions of the LFP in sequence and then these pictures were merged with each other using the software. The cross-sectional gray values over six parallel ridges of the white line in Figure 2A were shown in Figure 2B, indicating the remarkable variation of gray values from ridge to furrow in the SERS mapping image. The dark furrow had a smaller gray value, whereas the bright ridge had a larger one. Moreover, the average of distinction in the gray value was more than 100, suggesting that the fingerprint visualization was enhanced by the SERS imaging. Impressively, the second- and third-level details of the LFP could also be clearly observed as shown in Figure 2A. The second-level details, including the ridge interrupt (a), termination (b), lake (c), core (d), and bifurcation (e), are amplified in Figure 2C. The crossover in Figure 2C(f) was one part of another LFP not shown in the paper. Actually, these second-level details are the basis of fingerprint identification; thus, their unambiguous imaging is vital for practical identification. The third-level details, namely the sweat pores, were also clearly observed along the ridges in Figure 2, which are always difficult to visualize in some other reported methods.6,21,27 One sweat pore was truncated and is shown in the inset of Figure 2C(f), presenting a perfect pore shape with a diameter of around 100 μm. In some countries, the third-level details are used to confirm an identification match in forensic identification, in particular, to assist the

Figure 3. (A) SERS imaging of the core part of a latent fingerprint on a stainless steel surface using Au/pNTP/SiO2-LBA nanoprobes. (B) SERS imaging of the pattern of the latent fingerprint on a PVDF membrane surface using Au/pNTP/SiO2-LBA nanoprobes. (C) SERS imaging of the core part of a latent fingerprint on a Petri dish surface using Au/pNTP/SiO2-LBA nanoprobes (bar = 500 μm).

second-level details, such as the ridge interrupt, termination, lake, core, and bifurcation, indicating that the method was suitable for imaging LFP on a scratching surface. A poly(vinylidene fluoride) (PVDF) membrane (average pore size: 0.2 μm) was used as a representative porous substrate for SERS imaging of LFPs. The obtained SERS image of LFPs collected on a PVDF membrane is shown in Figure 3B and Figure S5. The pattern and second-level details containing termination and bifurcation could be clearly identified, further showing that this SERS imaging protocol could be used on a porous surface. Additionally, a plastic Petri dish was also chosen as a representative semiporous substrate for fingerprint imaging. In this case, the fingerprint, instead of a fresh one, was placed and left for more than one month. Similar imaging of the LFP on the plastic surface was obtained as exhibited in Figure 3C. The pattern and second-level details of the fingerprint could be clearly identified, indicating that not only fresh but also aged LFPs can be visually imaged by this strategy. The core part of the pattern of LPFs in Figure 3C was different from that in Figure 3A because these fingerprints were from a ring and index finger, respectively. Therefore, these images of fingerprints E

DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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spectroscopy and electrochemiluminescence, which enables it to visualize various types of fingerprints containing sebaceous, eccrine, fresh LFPs, and aged LFPs on different substrates with legible second-level features. Compared with most previously reported imaging approaches of LFP, the present method also has the remarkable advantage of high resolution, such that third-level details can also be clearly presented. In addition, this approach has the potential to detect endogenous and exogenous chemicals in the fingerprint by selecting corresponding aptamers. However, a relatively long imaging time is a problem that cannot be ignored for SERS imaging of latent fingerprints. In an effort to accelerate the time barrier, further work is in progress to construct a more highly SERS-active substrate. This simple, universal, high resolution and nondestructive imaging protocol greatly promotes the application of fingerprint imaging in the field of forensic investigation.

clearly illustrate that this is a general strategy and can be used successfully to visualize LFPs on various types of substrates. All of the fingerprints collected on various substrates were sebaceous fingerprints. Considering that lysozyme is one of the polypeptide components in human sweat, this SERS imaging approach based on lysozyme-binding aptamers should thus also be suitable for detecting eccrine fingerprints, also known as sweat fingerprints, the SERS imaging result of which is displayed in Figure 4A. The detailed features of eccrine

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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/acsami.6b03352. Calculation of the amount of LBA immobilized onto Au/ pNTP/SiO2 SERS nanoprobes, size-histogram of asprepared Au NPs based on TEM measurements, EDS spectrum of the Au/pNTP/SiO2 nanoparticles, amplifying SERS imaging of the pattern of LFPs on the stainless steel surface, and amplifying SERS imaging of the pattern of LFPs on the PVDF membrane (PDF)

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Figure 4. (A) SERS imaging of the pattern of eccrine fingerprints on a smooth glass surface using Au/pNTP/SiO2-LBA nanoprobes. (B) Optical images of the pattern of eccrine (a) and sebaceous (b) fingerprints (bar = 120 μm) and corresponding SERS imaging of the pattern of eccrine (c) and sebaceous (d) fingerprints (bar = 150 μm).

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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fingerprints containing second- and third-level details could be clearly distinguished. The imaging results of sebaceous and eccrine fingerprints based on this approach were similar, further indicating good universality. However, the amount of Au/ pNTP/SiO2-LBA nanoprobes deposited on eccrine fingerprints was more than that on sebaceous fingerprints (Figure 4B). This might be associated with an increased amount of lysozyme in eccrine fingerprints. Additionally, among various components in eccrine fingerprints, polypeptides and proteins are highly useful for disease diagnosis and therapy. The visualization of eccrine fingerprints is promising for detecting biomarkers with medical value.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21175028 and 21375022) and China Postdoctoral Science Foundation (2015M580287).

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REFERENCES

(1) Yang, S.; Wang, C.-F.; Chen, S. A Release-Induced Response for the Rapid Recognition of Latent Fingerprints and Formation of InkjetPrinted Patterns. Angew. Chem., Int. Ed. 2011, 50, 3706−3709. (2) Hazarika, P.; Russell, D. A. Advances in Fingerprint Analysis. Angew. Chem., Int. Ed. 2012, 51, 3524−3531. (3) Tang, X.; Huang, L.; Zhang, W.; Zhong, H. Chemical Imaging of Latent Fingerprints by Mass Spectrometry Based on Laser Activated Electron Tunneling. Anal. Chem. 2015, 87, 2693−2701. (4) Li, K.; Qin, W.; Li, F.; Zhao, X.; Jiang, B.; Wang, K.; Deng, S.; Fan, C.; Li, D. Nanoplasmonic Imaging of Latent Fingerprints and Identification of Cocaine. Angew. Chem., Int. Ed. 2013, 52, 11542− 11545. (5) van Dam, A.; Schwarz, J. C. V.; de Vos, J.; Siebes, M.; Sijen, T.; van Leeuwen, T. G.; Aalders, M. C. G.; Lambrechts, S. A. G. Oxidation Monitoring by Fluorescence Spectroscopy Reveals the Age of Fingermarks. Angew. Chem., Int. Ed. 2014, 53, 6010−6010. (6) Wood, M.; Maynard, P.; Spindler, X.; Lennard, C.; Roux, C. Visualization of Latent Fingermarks Using an Aptamer-Based Reagent. Angew. Chem., Int. Ed. 2012, 51, 12272−12274. (7) Wolfbeis, O. S. Nanoparticle-Enhanced Fluorescence Imaging of Latent Fingerprints Reveals Drug Abuse. Angew. Chem., Int. Ed. 2009, 48, 2268−2269.

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CONCLUSIONS SERS imaging of an LFP with aptamer-modified and sandwichstructured nanoprobes (Au/pNTP/SiO2-LBA) is apparently a general yet effective and nondestructive approach. Embedded Raman reporter molecules (pNTP) ascertain the stability and reproducibility of SERS signals, and the totally free surface of the silica shell improves the efficiency of the fingerprint identification. In comparison with reported SERS imaging strategies of LFPs, there is no need for complicated and timeconsuming pre- and post-treatment of detectable substrates; thus, the procedure in this approach has been greatly reduced. This approach is also safe because it does not involve hazardous substances that are typically used in conventional fume or dustbrushing methods. Moreover, the universality of this protocol is greatly improved compared with methods based on mass F

DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

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DOI: 10.1021/acsami.6b03352 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX