Article www.acsanm.org
Cite This: ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Adhesion and Bactericidal Properties of a Wettability-Controlled Artificial Nanostructure Kazuki Nakade,† Keisuke Jindai,† Takashi Sagawa,‡ Hiroaki Kojima,‡ Tomohiro Shimizu,† Shoso Shingubara,† and Takeshi Ito*,† †
Graduate School of Science and Engineering, Kansai University, Yamatecho 3-3-35, Suita, Osaka 564-8060, Japan National Institute of Information and Communications Technology, Iwaoka 588-2, Iwaokacho, Kobe, Hyogo 651-2492, Japan
‡
Downloaded via 37.230.213.56 on October 20, 2018 at 09:22:47 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: The adhesion behavior and bactericidal properties of the nanostructured surface of Si nanopillar array, which mimicked a cicada wing surface, were evaluated using Escherichia coli. Wettability of the nanostructured surface was controlled by using self-assembled monolayer (SAM). The adhesion behavior was strongly dependent on the wettability of the surface and whether it was a nanostructured or a flat surface. The number of adhered cells on the nanostructured surface was higher than that on the flat Au surface. In addition, the cell membrane was more strongly damaged at a higher contact angle than at a lower contact angle on the nanostructured surface. Time-lapse imaging was used to analyze the changes in fluorescence intensity caused by the effusion of an intercellular fluid, including fluorescent protein (mCherry), at the single cell level on the cicada wing surface and the artificial nanostructured surface. We found that there were three stages of changes in the fluorescence intensity gradient. KEYWORDS: bactericidal properties, adhesion properties, nanostructured surface, fluorescence imaging, metal-assisted chemical etching
1. INTRODUCTION Several living organisms, including plants, insects, and animals, have acquired functional nano- and microstructures along the course of evolution. There are studies that focus on their function−structure relationship and try to mimic them artificially. Especially, the transparent wings of cicadas and dragonflies are very attractive. Chemical compounds of the wing surface, such as proteins, chitin, and cuticular waxes, account for their surface hydrophobicity.1 In addition, rough surfaces increased the contact angle of water (wettability for water), a phenomenon known as the lotus effect.2 The contact angle of water on the wings can reach 140°. The nonreflective surface is achieved due to cone-shaped nanostructures that can change the refraction index gently from the top of the surface to the bottom. Some research groups have applied this optical characteristic to devices.3−5 Recently, many reports described nanostructure-based bactericidal materials; for example, nanostructured surfaces of cicada wings,1,6−8 dragonfly wings,6,9,10 and gecko fingers11,12 showed bactericidal properties. Bactericidal activity is not attributed to chemical properties but to physical properties of the nanostructure; cell membranes are stretched on the nanostructure surface, and then they break. Metal ions such as Ag and CuO,13−15 antibiotic agents,16−18 and antimicrobial compounds19−21 are currently used as antibacterial agents. © XXXX American Chemical Society
However, these materials do not have long-term stability and might be harmful to humans. Nanostructured materials can overcome such defects because their bactericidal properties depend on the physical condition of the nanostructure. Researchers use fluorescent DNA staining such as SYTO 9 and propidium iodide (PI) to determine whether cells adhering to the nanostructure surface are dead or alive.1,6−12 SYTO 9 diffuses into the cell cytoplasm through the cell membrane and stains DNA green. In contrast, PI only enters the cell cytoplasm and stains DNA red, when the cell membrane is damaged. This technology is easy to use and commercially available. However, PI can diffuse into the cytoplasm even if the cell membrane is only slightly damaged and still alive. We used PI and SYTO 9 to distinguish the cell damage caused by an artificial nanostructured surface dependent on wettability. In addition, we observed the leakage of fluorescent protein (mCherry), which was expressed in the cytoplasm of Escherichia coli, as an indicator of damage in the cell membrane. We used E. coli in the bactericidal properties tests since it is a well-known Gram-negative bacterium and its experiments have been established for its cultivation and gene Received: August 8, 2018 Accepted: October 1, 2018
A
DOI: 10.1021/acsanm.8b01340 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Nano Materials
were grown in TB containing 1 mM arabinose and 50 μg/mL ampicillin at 30 °C with shaking at 170 rpm, until OD550 = 0.6. Cells were suspended in motility buffer twice, and the cell suspensions were diluted with motility buffer to obtain OD600 = 0.2. 2.4. Observation of Attached Cells. After the cell suspension (20 μL) was dropped either on the cicada wing or on Si surfaces with nanopillars, a coverslip was put over it and fixed using a double-sided tape (0.1 mm thick). To ensure that the cell suspension covered the whole area of these nanostructured surfaces, the dropped suspension was pushed out by the coverslip. The chamber was held for 1 min to allow cell adherence onto the nanostructured surfaces. Then, the chamber was turned over to prevent the cells from falling from the solution onto the cicada wing or nanopillar surface because of gravity during observation. Cells attached on nanostructured surfaces were observed with a phase contrast microscope, and fluorescence microscope (Eclipse TiE, Nikon, Tokyo, Japan) equipped with 20× objective lenses (CFI S Plan Fluor ELWD 20X, NA = 0.45, Nikon) and 2.5× C-mount relay lens (VM2.5X, Nikon). Total magnification was set to 50×. E. coli cells, stained with SYTO 9/PI or expressing mCherry, were illuminated with epifluorescence from a mercury lamp. To observe the fluorescence from SYTO 9, the GFP HQ filter set (excitation filter: 470/40 nm; dichroic mirror: 495 nm; emission filter: 525/50 nm; Nikon Japan) was used. To observe the fluorescence from PI and mCherry, the FITC filter set (excitation filter: 540/25 nm; dichroic mirror: 565 nm; emission filter: 605/55 Nikon, Japan) was used. The fluorescence images were captured using a CCD camera (DMK23G618; The Imaging Source, Bremen, Germany). To reduce fluorophore quenching, excitation light was irradiated only for 1 s in each capturing process. After the acquisition of the fluorescence images, phase-contrast images were also recorded to confirm the position of the E. coli cells. 2.5. Kinetic Analysis of Fluorescence Intensity of mCherry Expressed in E. coli Cells. The time course of the fluorescence intensity of mCherry expressed in cells was analyzed by ImageJ.28,29 The fluorescence intensity was quantified from the average value of brightness in fluorescence images of each cell body. 2.6. Fabrication of Si Nanopillar Array and Preparation of Surface Wettability. Previously, researchers had tried to fabricate nano- and microstructures and had reported their bactericidal properties.6,30,31 However, conventional techniques do not control the structure precisely. Here, we adopted metal-assisted chemical etching (MachEtch)25 to prepare Si nanopillar arrays as shown in Figure 1a. Briefly, after the Si wafer was cleaned with piranha solution for 30 min, it was dipped in ammonia solution for 1 h to make it more hydrophilic (see Supporting Information Figure S1). This condition was beneficial to coat PS beads closely arranged.1 The Si wafer was coated with the PS bead suspension using a spin-coater at 1000 rpm for 30 s to have a monolayer of the PS beads.2 The PS beads on the Si wafer were carved with O2 plasma using the dry etching equipment (BP-1, Samco Ltd., Tokyo, Japan) to decrease the diameter of the beads.3 A thin layer of Au was deposited on the Si by magnetron sputtering.4 Si under the Au layer was etched selectively using MachEtch.32,33,56 The Au layer and PS beads were removed by chemical etching and O2 plasma, respectively. Finally, nanostructured Si substrate was obtained. Figure 1b shows a cross-section SEM image of the fabricated nanopillar array. The pillars had a cylindrical shape and spread all over the surface. After MachEtch, the surface was hydrophilic since Si was oxidized with hydrogen peroxide. After etching SiO2 thin layer by dipping in a buffer solution of HF and NH4F, the contact angle increased from 23° to 80°. Our experiments were performed with a hydrophobic surface of Si nanopillar. 2.7. Control of the Surface Wettability of the Nanostructure. We prepared two physical conditions: flat surface and nanostructured surface. Both were composed of Au/SiO2/Si. Wettability was particularly controlled by the ratio of the reagents, as explained below. After the Au thin layer (10 nm) was deposited on the nanostructured or flat Si substrate, it was dipped in ethanol and dissolved with surface treatment reagents to get self-assembled monolayer (SAM). Wettability was controlled by changing the
manipulation. Cells were dropped on the surface of cicada wings; subsequently, the fluorescence intensity change in each cell due to the effusion of cytoplasmic proteins including mCherry was monitored. When fluorescence intensity decreased and was lost, the cell was declared dead. The experimental protocol mentioned above was repeated with the artificial nanostructured surfaces to see whether the fluorescence intensity changed compared to that of cicada wings. An important step for bactericidal behavior is the adhesion of bacteria to the material surface because adhesion is the first step in the nanostructure-based bactericidal material. Adhesion of E. coli to the material surface is dependent on the structural features and the chemical properties of the surface of the cell itself.22−24 Friedlander et al. reported that the adhesion speed of E. coli to the microstructure is lower than that of a flat surface for up to 2 h after dropping the culture on the surface.22 However, the number of adhered E. coli to the microstructure was much higher than that adhered to a flat surface after 24 h of incubation. In addition, flagella played an important role in the adhesion to the material surface because they can sense its physicochemical properties.23 We had reported that bactericidal properties increased with the height of Si nanopillars, fabricated using metal-assisted chemical etching (MachEtch).25 In this study, we show that the number of adhered cells depends on the wettability of the flat and nanostructured surfaces by controlling the wettability of a Si nanopillar using a self-assembled monolayer (SAM). In addition, we show that the damage to the cell membrane, which is the bactericidal property, is strongly dependent on surface wettability.
2. MATERIALS AND METHODS 2.1. Chemicals. PI, hydrogen peroxide, sulfonic acid, nitric acid, hydrochloric acid, and ammonia−water were purchased from WAKO Chemicals (Tokyo, Japan). SYTO 9 was obtained from Thermo Fisher Scientific (Tokyo, Japan). 11-Mercapto-1-undecanol (HSCH2(CH2)9CH2OH) and 1-dodecanthiol (CH3(CH2)11SH) were obtained from Sigma-Aldrich (Tokyo, Japan). Hydrofluoric acid was obtained from Daikin Industries, Ltd. (Osaka, Japan). Polystyrene beads (PS beads) (diameter: 200 nm) were obtained from Funakoshi Co., Ltd. (Tokyo, Japan). P-type Si wafer (crystal orientation: 100; diameter: 101.6 mm) was purchased from SUMCO Co. (Tokyo, Japan). 2.2. Preparation of Cicada Wings. Cicada (Cryptotympana facialis) specimens were collected from university areas. Their wings were cut from their body and kept in a vacuum chamber after sonication in ethanol. Before the bactericidal test, sonication was performed again in ethanol. Afterward, the wings were dried and cut using a cutter and fixed on a glass plate with double-sided tape. 2.3. Growth and Preparation of E. coli. RP437, a wild-type (WT) E. coli strain, was used to observe the adhesion to the nanostructured surfaces because it has been used to study E. coli motility and chemotaxis.26 WT E. coli cells were grown in Tryptone broth (TB) (1% bactotryptone, 0.5% NaCl) at 30 °C with shaking at 170 rpm, until OD550 = 0.6. Cultured cells were suspended in motility buffer (10 mM potassium phosphate buffer pH 7.0; 0.1 mM EDTA2K pH 7.0; and 10 mM NaCl, 75 mM KCl) twice. The cell suspension was diluted with motility buffer to obtain OD600 = 0.2. For staining cells with SYTO 9 and PI, 1 mL of the diluted cell suspension was mixed with 3.3 mM SYTO 9 DMSO solution and 10 mM PI DMSO solution. After mixing, the cell suspension was allowed to stand for 15 min. For fluorescence measurement of mCherry, this protein was cloned into the bacterial expression vector pBAD24 with the arabinose PBAD promoter.27 The constructed plasmid (pBAD24-mCherry) was transformed in RP437. The RP437 cells harboring pBAD24-mCherry B
DOI: 10.1021/acsanm.8b01340 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Nano Materials
Figure 3. Number of attached cells on the flat (red circles) and nanostructured surface (blue squares) dependent on the contact angle. Cell counting was performed using microscopy 60 s after dropping the suspension of bacteria (20 μL).
The data clearly show that the number of adhered cells increased with the contact angle on both the flat and nanostructured surfaces. In addition, the number of adhered cells on the nanostructured surface reached a plateau on contact angles higher than 100°, and it was 1.5 times larger than that on the flat Au surface as a whole. Figure 4 shows the time-dependent active cell ratio on the wettability controlled nanostructured surface. As written above,
Figure 1. (a) Schematic images of the fabrication process of the Si nanowire by MachEtch (metal-assisted chemical etching). (b) Crosssection SEM image of fabricated nanowires. Scale bar of the SEM images represents 100 nm. reagents ratio as shown in Figure 2. In this case, the dipping time was 24 h at 25 °C. The same treatments (different reagent ratios) were
Figure 2. Contact angles of flat (red circles) and nanostructured surface (blue squares) for water droplet dependent on the molar ratio of 11-mercapto-1-undecanol and 1-dodecanethiol.
Figure 4. Time-dependent active cell ratio with different surface wettability evaluated by surface contact angles. The active cell ratio was calculated as the ratio of green cells to the sum of adhered cells. Red circles, blue squares, and black triangles show the active cell ratio with the contact angle of 100°, 70°, and 10°, respectively.
applied to the nanostructure and the flat surface, the contact angles on the nanostructure were changed from 140° to 10°, and those on the flat surface were changed from 105° to 15°. Based on the results, the contact angle on the nanostructured surface increased. This property is known as the lotus effect.
SYTO 9 can diffuse into the cell cytoplasm through the cell membrane and stain DNA green. In contrast, PI can enter the cell cytoplasm and stain DNA red when the cell membrane is damaged. Therefore, adhered cells without membrane damaged were colored green. The vertical axis of Figure 4 represents the ratio of the green cell to the adhered cells, called the active cell ratio. Here, the amount of adhered cells was the sum of red and green cells. The active cell ratio with a high contact angle of 100° decreased drastically and subsequently reached almost 0 after 15 min. In contrast, the active cell ratio on the hydrophilic surface decreased gradually. This data
3. RESULTS AND DISCUSSION 3.1. Adhesion and Membrane Damage of E. coli on the Nanostructured Surfaces Dependent on Wettability. We monitored the changes in the number of E. coli cells adhered to the sample surface through microscopy. Two physical conditions, flat and nanostructured surfaces, were prepared with changing wettability. Figure 3 shows the amount of adhered cells per unit area 60 s after dropping the suspension of E. coli on the flat and nanostructured surfaces. C
DOI: 10.1021/acsanm.8b01340 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Nano Materials
images just after the start of the monitoring and after 30 min. These images show that once the cell attached to the cicada wing, it did not deviate and stayed on-site. The fluorescence images show that the fluorescence on the upper right section disappeared after 30 min. These data suggest that the cell cytoplasm from trapped E. coli was effused to the environment. Because the effused cell cytoplasm might be a nutrient source for free bacteria, they accumulate at the trapped cells (see Movie S3). For the artificial nanostructure, the decrease in fluorescence intensities on adhered cells was similar to the one on the cicada wing, as shown in Figure 5b. The condition of the nanostructure was as follows: pitch, 200 nm; height, 850 nm; diameter, 150 nm; contact angle, 80°. Fluorescence disappeared on some cells. The data show that the mimicked nanostructure has the same bactericidal properties as the natural nanostructure of the cicada wing. The time course of the fluorescence intensity change at the single cell level on the cicada wing was analyzed for 20 cells as shown in Figure 6a. Three stages of changes in fluorescence
shows that the cell membrane was damaged even on the hydrophilic surface. From these results, we conclude that the membrane damage is strongly dependent on surface wettability, that is, the interaction between the nanostructure and cell membrane determined by the physical properties of the nanostructure. Because the cicada wing has a superhydrophobic surface, the membrane damage of attached cells occurred quickly, which might reflect the strong bactericidal effect. 3.2. Single Cell Analysis of Fluorescence Intensity. Analysis of the instance of cell death is very important to understand the mechanism that confers bactericidal property. We performed time-lapse imaging on the cicada wing surface through phase contrast microscopy and fluorescence microscopy simultaneously. With phase contrast microscopy, we could monitor the attachment process of the cell on the surface clearly. Fluorescence intensity of the attached cells expressing mCherry was monitored and normalized just after the attachment on the surface. Fluorescence images and phase contrast images are provided in the Supporting Information (Movie S2: fluorescence images; Movie S3: phase contrast images). The phase contrast images showed that free E. coli swam toward the trapped E. coli and aggregates. The fluorescence intensity of the cell gradually decreased and eventually disappeared after its attachment to the surface. Figure 5a shows the phase contrast images and fluorescence
Figure 6. Time-dependent fluorescence intensity changes by singlecell analysis. (a) Suspension of the bacteria was dropped on the cicada wing surface. (b) Suspension of the bacteria was dropped on the Si nanopillar surface.
intensity gradient were observed as follows. (1) Wing surface attachment; fluorescence intensity did not change for a few minutes. Six of 20 cells showed this property, which suggests that the state is not an artifact. This state is attributed to a point where the flagella are attached to the membrane, but the cytoplasm is intact. (2) A gradual decrease in fluorescence intensity; this was the longest stage as the cell cytoplasm effused gradually due to minor scratches at the interface
Figure 5. (a) Microscopy images at 0 and 30 min after dropping the suspension of the bacteria on the cicada wing surface. Upper figures are phase contrast images, and lower figures are fluorescence images. (b) Fluorescence microscopy images at 0 and 30 min after dropping the suspension of bacteria on the Si nanopillar surface. D
DOI: 10.1021/acsanm.8b01340 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Nano Materials
at the nanostructured surface did not depend on the material component. In addition, K3 was much larger than K2 on both surfaces. These data indicate that stages 2 and 3 might be attributed to different phenomena. In addition, the data prove that the bactericidal property was due to the nanostructure. On the basis of the results, we propose the following model to show that the bactericidal effect of the nanostructure depends on the motility and adhesion properties of flagellum. A bacterium searches for its favorite hydrophobic surface relying on sensors present in its flagellum. Consequently, the flagella are the first cellular structures to make contact with the nanostructure and adhere to it. Then, flagellum get entangled at the nanostructure, but the cell can still move. Then, the cell hits on the nanostructure and suffers abrasions that cause the cell cytoplasm effuse gradually. Over time, the small abrasions grow into major scars that cause the cytoplasm to effuse drastically. Finally, the cell dies. We will further research the bactericidal property focusing on the dependence of the motility and adhesion properties of the flagellum more deeply in the future to prove this hypothesis.
between the outer membrane and the nanostructure. (3) A drastic decrease in fluorescence intensity; the magnitude of the fluorescence change became substantial within 2 or 3 min. These data indicate that cell rupture progressed rapidly. Ivanova et al. reported that AFM (atomic force microscopy) tip was decreased gently after contact, and it was suddenly decreased a few hundred nm over ∼220 s on the observation of Pseudomonas aeruginosa cell on a cicada wing (Psaltoda claipennis).1 Our results agree with the reports mentioned above, if our recommended first stage is eliminated. Our recommended second stage was maintained from 3 to 17 min; this may depend on the cell or its direction when attached. Figure 6b shows the time course of fluorescence intensity change at the single cell level on the mimicked Si nanopillar for 20 cells. There were three stages of changes in fluorescence intensity gradient, similar to those in the cicada wing. Five of the 20 cells showed the first stage which lasted for a very short period of time. We analyzed the time constant (K) from the gradient of fluorescence intensity change on stages 2 and 3, which were recorded both on the cicada wing surface and on the Si nanopillars. The time constant was calculated with the following equation:
4. CONCLUSION We evaluated the adhesion properties of the nanostructure surface compared to that of the flat surface based on wettability. The surface properties were controlled by SAM. The number of adhered cells increased with the contact angle on both the flat and nanostructured surfaces. In addition, the number of cells adhered to the nanostructured surface was larger than that to the flat Au surface. Furthermore, the membrane damage was also strongly dependent on surface wettability. Our results indicate that the cicada wing surface is appropriate to collect and kill bacteria essentially because of its superhydrophobic nanostructure. Effusion of intercellular fluid was confirmed on E. coli adhering on the cicada wing surface by monitoring the decrease in fluorescent protein expressed in E. coli, which indicated that E. coli cells adhering to the nanostructure of the wing were destroyed. Decrease in fluorescence intensity gradient was divided into three stages: just trapped on the nanostructure, small effusion, and large effusion. The same phenomenon was observed on the artificial nanostructured surface. This proves that the bactericidal property depends on the nanostructure.
K = −ln(N (t + Δt )/N (t ))/Δt
Here, N(t) is the fluorescence intensity at time t. Because N(t) is a nondimensional variable, the kinetic constant is the same as the time constant. Figure 7 shows the average time constants in stage 2 (K2: red) and stage 3 (K3: blue) observed on the cicada wing (left
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsanm.8b01340. Figure S1: images on the contact angle measurement after piranha cleaning (left) and after dipping in ammonia solution (right) (PDF) Movie S2: time-lapse fluorescence images recorded every 5 min after dropping the suspension of bacteria (AVI) Movie S3: time-lapse phase contrast images recorded every 5 min after dropping the suspension of bacteria (AVI)
Figure 7. Average of time constants (K2 and K3) were calculated using fluorescence intensity change for 20 cells, adhered on the cicada wing (left column) and the mimicked Si nanopillar (right column). Red and blue bars show K2 and K3, respectively.
column) and the Si nanopillar (right column), respectively. These values were calculated from 20 cells, which are shown in Figure 6a,b. Error bars show the standard deviation of the values for 20 cells. These values were almost the same on the surface of the cicada wing and the mimicked Si nanopillar. In fact, K2 at the cicada wing and Si nanopillar were calculated as 4.94 × 10−2 and 5.09 × 10−2 min−1, respectively. K3 at the cicada wing and Si nanopillar were calculated as 3.55 and 2.31 min−1, respectively. We also evaluated the time constant due to photobleaching of mCherry. The value was 1.92 × 10−3 min, which was too small compared to that of K2 and K3. These results indicate that the decrease in the fluorescence intensity
■
AUTHOR INFORMATION
Corresponding Author
*(T.I.) E-mail
[email protected]. ORCID
Takeshi Ito: 0000-0001-8559-5565 E
DOI: 10.1021/acsanm.8b01340 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Nano Materials Notes
and Gram-Positive Bacteria. Environ. Sci. Technol. 2010, 44, 5210− 5215. (15) Azam, A.; Ahmed, A. S.; Oves, M.; Khan, M. S.; Memic, A. Size-Dependent Antimicrobial Properties of CuO Nanoparticles Against Gram-Positive and -Negative Bacterial Strains. Int. J. Nanomed. 2012, 7, 3527−3535. (16) Oda, Y.; Kanaoka, S.; Sato, T.; Aoshima, S.; Kuroda, K. Block Versus Random Amphiphilic Copolymers as Antibacterial Agents. Biomacromolecules 2011, 12, 3581−3591. (17) Ghosh, C.; Manjunath, G. B.; Akkapeddi, P.; Yarlagadda, V.; Hoque, J.; Uppu, D. S. S. M.; Konai, M. M.; Haldar, J. Small Molecular Antibacterial Peptoid Mimics: The Simpler the Better! J. Med. Chem. 2014, 57, 1428−1436. (18) Parhi, A. K.; Zhang, Y.; Saionz, K. W.; Pradhan, P.; Kaul, M.; Trivedi, K.; Pilch, D. S.; LaVoie, E. J. Antibacterial Activity of Quinoxalines, Quinazolines, and 1,5-Naphthyridines. Bioorg. Med. Chem. Lett. 2013, 23, 4968−4974. (19) Condell, O.; Iversen, C.; Cooney, S.; Power, K. A.; Walsh, C.; Burgess, C.; Fanning, S. Efficasy of Biocides Used in the Modern Food Industry to Control Salmonella Enterica, and Links between Biocide Tolerance and Resistance to Clinically Relevant Antimicrobial Compounds. Appl. Environ. Microbiol. 2012, 78, 3087−3097. (20) Ferreira, C.; Pereira, A. M.; Pereira, M. C.; Melo, L. F.; Simoes, M. Physiological Changes Induced by the Quaternary Ammonium Compound Benzyldimethyldodecylammonium Chloride on Pseudomonas f luorescens. J. Antimicrob. Chemother. 2011, 66, 1036−1043. (21) Elshaarawy, R. F. M.; Janiak, C. Toward New Classes of Potent Antibiotics: Synthesis and Antimicrobial Activity of Novel Metallosaldach−Imidazolium Salts. Eur. J. Med. Chem. 2014, 75, 31−42. (22) Friedlander, R. S.; Vlamakis, H.; Kim, P.; Khan, M.; Kolter, R.; Aizenberg, J. Bacterial Flagella Explore Microscale Hummocks and Hollows to Increase Adhesion. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 5624−5629. (23) Friedlander, R. S.; Vogel, N.; Aizenberg, J. Role of Flagella in Adhesion of Escherichia coli to Abiotic Surfaces. Langmuir 2015, 31, 6137−6144. (24) Li, B.; Logan, B. E. Bacterial Adhesion to Glass and MetalOxide Surface. Colloids Surf., B 2004, 36, 81−90. (25) Ito, T.; Nakade, K.; Asai, N.; Shimizu, T.; Shingubara, S. Antibacterial Property of Si Nanopillar Array Fabricated Using Metal Assisted Etching; Mimic A Cicada Wing. ECS Trans. 2017, 75, 1−5. (26) Parkinson, J. S.; Houts, S. E. Isolation and Behavior of Escherichia coli Deletion Mutants Lacking Chemotaxis Functions. J. Bacteriol. 1982, 151, 106−113. (27) Guzman, L. M.; Belin, D.; Carson, M. J.; Beckwith, J. Tight Regulation, and High-Level Expression by Vectors Containing the Arabinose PBAD Promoter. J. Bacteriol. 1995, 177, 4121−4130. (28) Schneider, C. A.; Rasband, W. S.; Eliceiri, K. W. NIH Image to ImageJ: 25 Years of Image Analysis. Nat. Methods 2012, 9, 671−675. (29) Abramoff, M. D.; Magalhães, P. J.; Ram, S. J. Image Processing with Image. J. Biophotonics Int. 2004, 11, 36−42. (30) Linklater, D. P.; Juodkazis, S.; Ivanova, E. P. Nanofabrication of Mechano-Bactericidal Surfaces. Nanoscale 2017, 9, 16564. (31) Bhadra, C. M.; Werner, M.; Baulin, V. A.; Truong, V. K.; Kobaisi, M. A.; Nguyen, S. H.; Balcytis, A.; Juodkazis, S.; Wang, J. Y.; Mainwaring, D. E.; Crawford, R. J.; Ivanova, E. P. Subtle Variations in Surface Properties of Black Silicon Surfaces Influence the Degree of Bactericidal Efficiency. Nano-Micro Lett. 2018, 10, 10−36. (32) Huang, Z.; Geyer, N.; Werner, P.; de Boor, J.; Gösele, U. MetalAssisted Chemical Etching of Silicon: A review. Adv. Mater. 2011, 23, 285−308. (33) Li, X.; Bohn, P. W. Metal-Assisted Chemical Etching in HF/ H2O2 Produces Porous Silicon. Appl. Phys. Lett. 2000, 77, 2572− 2574.
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was partially supported by JSPS KAKENHI Grant JP18K19008 and MEXT-Supported Program for the Strategic Research Foundation at Private Universities, “Creation of 3D nano-micro structures and its application to biomimetics and medicine”, 2015−2019.
■
REFERENCES
(1) Ivanova, E. P.; Hasan, J.; Webb, H. K.; Truong, V. K.; Watson, G. S.; Watson, J. A.; Baulin, V. A.; Pogodin, S.; Wang, J. Y.; Tobin, M. J.; Lobbe, C.; Crawford, R. J. Natural Bactericidal Surfaces: Mechanical Rupture of Pseudomonas aeruginosa Cells by Cicada Wings. Small 2012, 8, 2489−2494. (2) Nosonovsky, M.; Bhushan, B. Roughness Optimization for Biomimetic Surperhydrophobic Surface. Microsyst. Technol. 2005, 11, 535−549. (3) Huang, Y. F.; Jen, Y. J.; Chen, L. C.; Chen, K. H.; Chattopadhyay, S. Design for Approaching Cicada-Wing Reflectance in Low- and High-Index Biomimetic Nanostructures. ACS Nano 2015, 9, 301−311. (4) Lv, M. Y.; Teng, H. Y.; Chen, Z. Y.; Zhao, Y. M.; Zhang, X.; Liu, L.; Wu, Z.; Liu, L. M.; Xu, H. J. Low-Cost Au Nanoparticle-Decorated Cicada Wing as Sensitive and Recyclable Substrates for Surface Enhanced Raman Scattering. Sens. Actuators, B 2015, 209, 820−827. (5) Chen, Y. C.; Huang, Z.-S.; Yang, H. Cicada-Wing-Inspired SelfCleaning Antireflection Coatings on Polymer Substrate. ACS Appl. Mater. Interfaces 2015, 7, 25495−25505. (6) Ivanova, E. P.; Hasan, J.; Webb, H. K.; Gervinskas, G.; Juodkazis, S.; Truong, V. K.; Wu, A. H. F.; Lamb, R. N.; Baulin, V. A.; Watson, G. S.; Watson, J. A.; Mainwaring, D. E.; Crawford, R. J. Bactericidal Activity of Black Silicon. Nat. Commun. 2013, 4, 2838. (7) Kelleher, S. M.; Habimana, O.; Lawler, J.; O’Reilly, B.; Daniels, S.; Casey, E.; Cowley, A. Cicada Wing Surface Topography: An Investigation into the Bactericidal Properties of Nanostructural Features. ACS Appl. Mater. Interfaces 2016, 8, 14966−14974. (8) Nowlin, K.; Boseman, A.; Covell, A.; LaJeunesse, D. AdhesionDependent Rupturing of Saccharomyces Cerevisiae on Biological Antimicrobial Nanostructured Surfaces. J. R. Soc., Interface 2015, 12, 20140999. (9) Mainwaring, D. E.; Nguyen, S. H.; Webb, H.; Jakubov, T.; Tobin, M.; Lamb, R. N.; Wu, A. H. -F.; Marchant, R.; Crawford, R. J.; Ivanova, E. P. The Nature of Inherent Bactericidal Activity: Insights from the Nanotopology of Three Species of Dragonfly. Nanoscale 2016, 8, 6527−6534. (10) Bandara, C. D.; Singh, S.; Afara, I. O.; Wolff, A.; Tesfamichael, T.; Ostrikov, L.; Oloyede, A. Bactericidal Effects of Natural Nanotopography of Dragonfly Wing on Escherichia coli. ACS Appl. Mater. Interfaces 2017, 9, 6746−6760. (11) Watson, G. S.; Green, D. W.; Schwarzkopf, L.; Li, X.; Cribb, B. W.; Myhra, S.; Watson, J. A. A Gecko Skin Micro/Nano Structure − A Low Adheshion, Superhydrophopbic, Anti-wetting, Self-cleaning, Biocompatible, Antibactericidal Surface. Acta Biomater. 2015, 21, 109−122. (12) Green, D. W.; Lee, K. K.; Watson, J. A.; Kim, H.-Y.; Yoon, K.S.; Kim, E.-J.; Lee, J.-M.; Watson, G. S.; Jung, H.-S. High Quality Bioreplication of Intricate Nanostructures from A Fragile Gecko Skin Surface with Bactericidal Properties. Sci. Rep. 2017, 7, 41023. (13) Marambio-Jones, C.; Hoek, E. M. V. A Review of the Antibacterial Effects of Silver Nanomaterials and Potential Implications for Human Health and the Environment. J. Nanopart. Res. 2010, 12, 1531−1551. (14) Suresh, A. K.; Pelletier, D. A.; Wang, W.; Moon, J.-W.; Gu, B.; Mortensen, N. P.; Allison, D. P.; Joy, D. C.; Phelps, T. J.; Doktycz, M. J. Silver Nanocrystallties: Biofabrication Using Shewanella oneidensis, and an Evaluation of Their Comparative Toxicity on Gram-Negative F
DOI: 10.1021/acsanm.8b01340 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
