Amino Acid-Modified Conjugated Oligomer Self-Assembly Hydrogel

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Biological and Medical Applications of Materials and Interfaces

Amino Acid-Modified Conjugated Oligomer Self-Assembly Hydrogel for Efficient Capture and Specific Killing of Antibiotic-Resistant Bacteria Qi Zhao, Yantao Zhao, Zhuanning Lu, and Yanli Tang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b02643 • Publication Date (Web): 15 Apr 2019 Downloaded from http://pubs.acs.org on April 15, 2019

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ACS Applied Materials & Interfaces

Amino Acid-Modified Conjugated Oligomer Self-Assembly Hydrogel for Efficient Capture and Specific Killing of Antibiotic-Resistant Bacteria Qi Zhao, Yantao Zhao, Zhuanning Lu, Yanli Tang* Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710062, P. R. China. KEYWORDS: conjugated oligomer; hydrogel; antibiotic-resistant bacteria; antibacteria; capture.

ABSTRACT: Bacterial infection is one of main causes that threaten global human health. Especially, antibiotic-resistant bacteria like methicillin-resistant S. aureus (MRSA) lead to high mortality rate and more expensive treatment cost. Here, a novel aminoacid-modified conjugated oligomer OTE-D-Phe was synthesized by modifying the side-chain of conjugated oligo(thiophene ethynylene) with D-phenylalanine. By mixing Fmoc-L-Phe (9-fluorenylmethyloxycarbonyl-L-phenylalanin) with OTE-D-Phe, a new and biocompatible low molecular weight hydrogel (HG-2) was prepared through self-assembly. In solution, HG-2 can effectively capture bacteria spontaneously, such as E. coli and MRSA. Most importantly, the hydrogel has specific and strong antibacterial activity against methicillin-resistant S. aureus over methicillin-susceptible Staphylococcus aureus, Staphylococcus epidermidis and E. coli . Interestingly, when the hydrogel was put on a model surface, a piece of cloth, it also is able to selectively kill MRSA with low cell cytotoxicity. The antibacterial mechanism was investigated and demonstrated the HG-2 should interact with and physically break the cell wall and membrane, which lead to MRSA death. Therefore, this new conjugated oligomer-based hydrogel provides promising applications in disinfection and therapy of MRSA in hospital and in community.

death of bacteria6, 16, 18-20. However, they needed light source and did not show bacterial capture property in solution.

INTRODUCTION Bacterial infection is one of main causes that threaten global human health. The introduction of antibiotics has played a key role in bacterial infection therapy. However, overuse of antibiotics has led to the rapid emergence and spread of antibioticresistant bacteria.1, 2 Especially, Methicillin-resistant S. aureus (MRSA) is responsible for several severe infections in humans that are difficult to treat.3 Hospital acquired MRSA leads to high mortality rate and more expensive treatment cost. In addition, community acquired MRSA is a serious challenge to global clinicians.4 Therefore, there is an urgent need to develop a new bactericidal strategy to solve the threat of antibioticresistant microorganisms to human health. In particular, to investigate the capture of antibiotic-resistant bacteria in solution and on air-solid interface and highly effective killing of bacteria still is challenging.

Low molecular weight hydrogels (LMWHs) are a novel class of soft materials. Different from covalently coupled chemical hydrogels, most of the LMWHs are formed by the supramolecular self-assembly of small molecules. Many nanocavities will be formed in LMWHs under the cooperation of various non-covalent interactions including hydrogen bonding, π-π interactions, Van der Waals interactions and hydrophobic interactions.21 In addition, LMWGs also have many advantages, such as easy synthesis and characterization, controllable physical and chemical properties, highly ordered hydrogel structure.22 Among common LMWHs, amino acidbased hydrogels are of great importance because of their potential biocompatibility and biodegradability. 23 In recent years, amino acid functionalized LMWHs are used in various fields, such as drug release,24-28 cell culture,29, 30 tissue regeneration,31-34 water purification35, 36 wound repair,37 bactericidal,38 and so on. Especially, 9-Fluorenylmethoxycarbonyl (Fmoc)modified amino acid LMWGs have been widely used as bactericidal drug carrier and bactericidal agent.22, 23, 39 However, their bactericidal activity is still unsatisfied.

Recently, water-soluble conjugated oligomers have been widely studied because they have broad-spectrum and highly efficient antibacterial properties and antiviral activities.5-12 These oligomers, such as cationic oligo(p-phenylene vinylene) (OPV),13 oligo(p-phenylene ethynylene)s (OPEs),14, 15 oligo(thiophene ethynylene) (OTE),16 contain hydrophobic delocalized π-conjugated backbones and positively charged ionic side chains (quaternary ammonium salts and imidazolium salts). Under both electrostatic and hydrophobic interactions, they exhibit a strong affinity for bacterial membrane. Conjugated oligomers thus are adsorbed on the surface of the bacteria and then enter into the bacterial cells.17 Under light irradiation, reactive oxygen species (ROS) can be generated in the proximity of the bacterial membrane and inside cells, resulting in peroxidation of the phospholipids of the bacterial membrane, the leakage of contents from the cytoplasm and eventually the

In this work, we aim to create a new LMWH bactericidal material to achieve advantages containing effective capture and highly efficient antibacterial activity against MRSA without light irradiation. Firstly, by virtue of D-phenylalanine providing increased intermolecular π-π stacking interactions to promote gel formation, the amino acid-modified conjugated oligomer (OTE-D-Phe) was synthesized by introducing the Dphenylalanine group in the side chain of the OTE. Then, a novel supramolecular self-assembly hydrogel was fabricated based on OTE-D-Phe and Fmoc-L-phenylalanine (Fmoc-L-

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Scheme 1. Schematic presentation of structure of gels and the capture of bacteria and specific killing of MRSA by HG-2.

filtration system. E. coli and MRSA were purchased from China general microbiological culture collection center. UVvis absorption spectra were taken on a Shimadzu UV-2600 spectrophotometer. The fluorescence spectra were recorded on a Hitachi F-7000 spectrophotometer equipped with a xenon lamp. The Accuri C6 flow cytometer equipped with a 488 nm laser (Becton Dickinson, Franklin Lakes, NJ) was used to study the antibacterial activity. Photographs of agar plates were obtained from Bio-Rad GelDoc XR imager. Rheological properties of LWMT were characterized on a rheometer (ARG2, TA Instruments). Fourier transform infrared spectra were measured on an FTIR (Bruker, Germany) and Nicolet iS10 (Thermo scientific) system.

Phe). In solution, the hydrogel can spontaneously capture MRSA and E. coli efficiently. Furthermore, it demonstrates specific antibacterial activity against MRSA (Scheme 1). When the hydrogel was put on a model solid surface, it also shows specific antibacterial activity against MRSA. The conjugated oligomer-based hydrogel will have promising biomedical applications including disinfection and therapy of MRSA in hospital and in community. Materials and Method 3-Thiopheneacetic acid, N-iodosuccinimide, 2ethynylthiophene, bis(triphenylphosphine) palladium (II) dichloride, copper (I) iodide, L-proline, D-phenylalanine, N-(9fluorenylmethoxycarbonyl)-L-phenylalanine (Fmoc-L-Phe), 1hydroxybenzotriazole (HOBt) and 1-(3dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) were purchased from J&K Chemical Ltd. and Aladdin Industrial Corporation and used without further purification. The SYTO 9 and SYTO 24 were purchased from Thermo Fisher Scientific Inc. The propidium iodide (PI) and medium components were purchased from Solarbio. Cor. All solutions were prepared with ultrapure water purified using a Millipore

RESULTS AND DISCUSSION Synthesis and Characterization of Amino AcidFunctioned OTE. The synthesis of amino acid-modified OTE is shown in Scheme 2. OTE-D-Phe and OTE-L-Pro were synthesized by a similar procedure from the starting compound 3thiopheneacetic acid. The intermediate compound 3 was obtained by iodination and esterification reactions. Then compound 4 was afforded by a Sonogashira coupling reaction between compound 3 and 2-ethynylthiophene in the presence of

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Scheme 2. Synthesis of OTE-D-Phe and OTE-L-Pro: (I) NIS, CH2Cl2/AcOH, r.t. 11 h; (II) H2SO4 (Con.), MeOH, 75 oC, 4 h; (III) 2-ethynylthiophene, Pd(PPh3)2Cl2/CuI, diethylamine/CHCl3, r. t. 10 h; (IV) NaOH (0.5 M), MeOH/THF, r.t. 5 h; (V) Lproline, EDC/HOBt, triethylamine /DCM, 0 oC for 1 h and r. t. for 12 h; (VI) D-phenylalanine, EDC/HOBt, triethylamine /DCM, 0 oC for 1 h and r. t. for 12 h.

and transparent hydrogel (named HG-2) through hydrogen bonding, Van der Waals interactions, π-π interactions and hydrophobic interactions. However, only an aqueous suspension was obtained when we tried to prepare a hydrogel from FmocL-Phe and OTE-L-Pro (molar ratio of 5:1) by the same gelation strategy (named HG-3). Because the introduction of proline does not provide enough interaction force compared to the phenylalanine on the side chain of OTE, a hydrogel could not be formed by self-assembly. Furthermore, to investigate the mechanical strength of gels, the dynamic rheology was performed. As shown in Figure S1 (Supporting Information), the yield stress (τ) of HG-1 and HG-2 are 189 and 62 Pa, respectively. The values demonstrate the relative good network structures of gels.

bis(triphenylphosphine)palladium (II) dichloride and copper (I) iodide in trichloromethane at room temperature overnight. After ester hydrolysis, OTE-D-Phe and OTE-L-Pro can be obtained by a condensation reaction between OTE-COOH and L-proline or D-phenylalanine in the presence of EDC and HOBt. The chemical structures of intermediates, such as OTECOOH, OTE-L-Pro and OTE-D-Phe were characterized by HRMS, 1H NMR and 13C NMR. The synthesis has the advantages of mild conditions, easy operation and high yields, which facilitates large-scale preparation of these amino acid functioned OTEs. In addition, the absorption and emission spectra of OTE-D-Phe and OTE-L-Pro were measured in water. As shown in Figure 1a, both OTE-D-Phe and OTE-L-Pro have a maximum absorption peak at 363 nm, and the maximum emission peaks are at 426 (a shoulder peak at 446 nm) and 409 nm (a shoulder peak at 429 nm) in water, respectively. Compared with the reported cationic water-soluble conjugated oligomer OTE, both the maximum absorption peak and maximum emission peak of the two amino acid-modified OTE compounds blue shift.16 It is possible that the amino acidmodified OTE with poor water-solubility could self-assemble into vesicles in water, which will affect the conjugation of OTE main chain, resulting in blue-shift in spectra.

It was reported that the π-π stacking interactions and hydrogen bonding played key roles in gel formation [39]. Hence, the fluorescence spectroscopy was employed to study the molecular arrangement of small molecules within gels. As shown in Figure S2a (Supporting Information), the maximum emission peak appears at 423 nm and 441 nm in the complex of FmocL-Phe and OTE-D-Phe solution, while the maximum emission for HG-2 hydrogel centers at 449 nm when the excitation wavelength is 369 nm. The similar red-shift of maximum emission can be observed in HG-1 (Figure S2b, Supporting Information). These results demonstrate that π-π stacking interactions exist in the gel phase 39. Meanwhile, the Fourier transform infrared (FTIR) spectroscopy was used to investigate the role of intermolecular hydrogen bonding in the gels formation. As shown in Figure S3 (Supporting Information), the characteristic C=O stretching band peaks in HG-1 and HG2 hydrogel phases redshift from 1716 cm-1 to 1602 and 1600 cm-1, respectively, compared to that in solution phase. These results indicate that the intermolecular hydrogen bonding motifs present in gels.

Preparation and Characterization of Hydrogels. In this study, we used a glucono-δ-lactone-triggered gelation strategy to controllably prepare single-component and two-component hydrogels (Scheme 1). The aged hydrogels are formed upon cooling at room temperature within dozens of hours. Due to commercial Fmoc-L-Phe presenting gelation and antibacterial properties, to decrease the usage of OTE-L-Pro and OTE-DPhe, two kinds of gels were prepared by mixing Fmoc-L-Phe with OTE-L-Pro or OTE-D-Phe through the strategy. As the control, a white and opaque gel (named HG-1) was obtained from Fmoc-L-Phe firstly. Interestingly, as shown in Figure 1b, Fmoc-L-Phe/OTE-D-Phe (molar ratio of 5:1) formed a yellow



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Figure 1. (a) Normalized absorption and fluorescence spectra of OTE-D-Phe (red), OTE-L-Pro (black) and OTE (blue) in water; (b) The photos of HG-1, HG-2 and HG-3; (c) The SEM images of HG-1, HG-2 and HG-3. mance was detected for HG-3 because HG-3 has no hydrogel Then the morphology of self-assembled gels was measured morphology. These results indicate that the HG-2 with rough by SEM. Gels were first dropped on silicon wafer and then fiber network can spontaneously capture and efficiently sepadried under vacuum freeze for 24 h. As shown in Figure 1c, rate bacteria from solution. With the excellent capture properuniform fibrous network structures can be observed in HG-1 ties for bacteria, HG-2 is expected to be applied for protection gel and HG-2 hydrogel, while HG-3 does not form a fibrous from infection of pathogens both in air and in liquid. network structure, which indicates the nanofibrous network structure is the basis of hydrogel formation. In addition, comFurthermore, we separated the precipitate and studied the pared with the thin nanofibers and compact structure of HG-1 bactericidal activity of HG-2 against E. coli and MRSA. The hydrogel, the nanofibers in HG-2 hydrogel are thicker and precipitate containing bacteria and HG-2 was resuspended rougher, and the holes between nanofibers are bigger, which is with fresh culture medium and then cultured for another 15 h. benefit to bind and kill bacteria. Also, we studied the zeta poThe results were shown in Figure 2b. MRSA captured by HGtential of the hydrogels. The results are shown in Table S 1 2 no longer reproduce, which means MRSA were killed com(Supporting Information). The zeta potentials are -40.4 ± 0.4, pletely by HG-2. However, after being captured by HG-2 and 43.6 ± 0.5 and -43.1 ± 0.6 mV for HG-1, HG-2 and HG-3, incubated for 15 h, the O.D. value of E. coli still increase respectively, which result from amino acid that is modified on greatly as same as the control, which represent the HG-2 has the side chain of small molecules. no effect on E. coli. The OTE-D-Phe-containing hydrogel HG2 is able to selectively inactivate MRSA over E. coli, which Capture and Antibacterial Activity in Solution. To invescould result from the different cell membrane composition of tigate the capture of bacteria by the hydrogels, the experiments gram-negative and gram-positive bacteria 40. Also, as reported of bacteria incubating with HG-1, HG-2, and HG-3 were carby our group previously16, OTE oligomer can specifically kill ried out, respectively. In this assay, the cell density of both 9 S. aureus under low concentration. Because HG-2 was formed MRSA and E. coli suspensions are about 1×10 CFU/mL. The from OTE-D-phe and Fmoc-L-phe, the antibacterial activity of concentration of Fmoc-L-Phe (HG-1) is 200 μM. Also, the HG-2 should benefit from the introduction of OTE. It is worth concentration of Fmoc-L-Phe in both HG-1 and HG-2 is 200 noting that the presence of hydrophobic and v type structure of μM, and the concentration of OTE-D-Phe in HG-2 and OTEOTE in the HG-2 may play a very important role in providing L-Pro in HG-3 is 40 μM. As shown in Figure 2a, HG-2 specific antibacterial activity against MRSA. To obtain indemonstrates great capture performance to both E. coli and sights into the antibacterial mechanism of the HG-2, the morMRSA in dark after incubation for 1 hour, which is attributed phological changes of MRSA cells on HG-1 and HG-2 were to the thicker and rougher nanofibers of HG-2. The obvious investigated. Due to HG-1 showing no antibacterial activity precipitate was observed at the bottom of tube. However, HG(discussion in following paragraph), MRSA cells captured by 1 and HG-3 have weak capture properties. At least 70% E. coli HG-1 was used as the control. To gain in situ morphology of cells are remained, and about 94% S. aureus are kept in the MRSA cells, after cells being captured by hydrogels and the solution after incubating with HG-1, resulting from the smooth supernatant being carefully discarded, the precipitation in and compact structure of HG-1. No distinct capture perfor-


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Figure 2. (a) Capture of bacteria by HG-1, HG-2 and HG-3 for E. coli and MRSA. [MRSA] = [E.coli] = 1×109 CFU/mL. The concentration of Fmoc-L-Phe in all gels was 200 μM. The concentration of OTE-D-Phe in HG-2 and OTE-L-Pro in HG-3 was 40 μM. (b) Bacteria Viability of E. coli and MRSA captured by HG-2. (c) SEM photographs of MRSA cells captured by HG-1 and (d) HG2 after direct lyophilization for 12 h. The scale bar is 2.0 µm. activity on E. coli. Furthermore, the relationship between the concentration of HG-2 and the viability of MRSA was studied. As shown in Figure 3b, the bactericidal effect gradually enhances with the increasing of HG-2 concentration. When the concentration increases to 40 μM, the bactericidal rate reaches the plateau. To clarify the antibacterial activity of HG-2 against other species, the methicillin-susceptible Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis) were used in the study. Under the same experimental condition, HG-2 shows no obvious antibacterial activity against S. epidermidis. Toward methicillin-susceptible S. aureus, HG-2 demonstrates biocidal activity at higher concentration. When the concentration of HG-2 is 40 µM, the viability of methicillin-susceptible S. aureus is 76% (Figure 4b), however, the viability of MRSA is 10%. These results indicate that HG-2 has a highly effective and specific antibacterial activity against MRSA. Furthermore, the biocidal ability

centrifuge tube was directly dried under lyophilization for 12 h. As shown in Figure 2c, MRSA cells on HG-1 exhibit complete and smooth morphology, although the size of cells reduces inevitably during drying. In contrast, no whole cells were observed for MRSA captured by HG-2 (Figure 2d). All cells are broken and only debris are observed on the hydrogel, which means MRSA cells are killed physically by HG-2. The hydrophobic OTE should interact with and physically break the cell membrane by inserting into lipid domains. To further support the conclusion, the live/dead bacterial staining assay was carried out. As shown in Figure S4 (Supporting Information), MRSA bacteria are stained red after contact with the HG-2 hydrogel for 30 min and 60 min, while almost no red bacteria are found in the control. These results further confirm that the bacterial cell wall and membrane are disrupted after contact with HG-2 because red-fluorescent propidium iodide could penetrate only bacteria with destroyed cell walls and membranes. Therefore, HG-2 demonstrates specific killing of MRSA captured on its surface or inside, which provides promising applications in clinical treatment and medical materials. Antibacterial Activity in Hydrogel-Containing Nutrient Agar Medium. During the capture investigation, it is found that HG-2 has great capture property and HG-1 can partly capture bacteria. Thus, the antibacterial activity of HG-1 and HG-2 against MRSA and E. coli were studied. The bacteria solution was incubated with the hydrogel-containing NA medium for 15 h. As shown in Figure 3a, HG-1, made from Fmoc-L-Phe, has no antibacterial activity against MRSA and E. coli. It is noted that HG-2 shows high biocidal ability against MRSA, which is owing to the delivery of OTE-D-Phe from the NA medium. However, HG-2 has no antibacterial

Figure 3. (a) Viability of E. coli and MRSA bacteria in agar medium containing HG-1 and HG-2. (b) Viability of MRSA, S. aureus and S. epidermidis in agar medium containing various concentrations of HG-2.



should be attributed to OTE-D-Phe that is one of components of HG-2. Due to the HG-3 containing L-proline-modified OTE (OTE-L-Pro), the killing ability against MRSA also were studied (Figure S5, Supporting Information). When the final concentration of OTE-L-Pro is 80 μM, the inhibition rates of HG3 against MRSA are 49% that is far lower than that of HG-2. When the final concentration of OTE-L-Pro is 160 μM, the bactericidal activity of HG-3 against MRSA is 85%. This result indicates that both HG-2 and HG-3 have antibacterial activity because they all contain amino acid-modified OTE. Interestingly, the hydrogel HG-2 present higher antibacterial ability than aqueous suspension HG-3, which may result from that the hydrophobic interaction between OTE-D-Phe and bacteria is stronger than that between OTE-L-Pro and bacteria 40 . In summary, among the self-assembly hydrogels, HG-2 shows both excellent capture ability and highly efficient and specific antibacterial activity against MRSA.

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Phe-containing hydrogel could selectively kill MRSA over E. coli, which may result from the different antibacterial mechanism of OTE-D-Phe in hydrogel and in solution. Antibacterial Activity of HG-2 on Surface. In order to investigate the potential of clinical applications of HG-2, the bactericidal activity of the HG-1/ HG-2-coated on model surface, a cotton cloth used to manufacture surgical gown were measured. The cotton cloth which is 1 square centimeter was sterilized before using. Hydrogel was spread on the cloth, followed by incubating with bacteria for 30 min in dark. Then bacteria captured on the cloth were smeared on the cultural dish and incubated for 15 h. The plate photographs are shown in Figure 4. In the center of the plate is a hydrogel-coated cloth. The circle around the cloth is the bacterial colony. If the hydrogel has bactericidal activity, there are few or no colonies. In contrast, a ring-shaped colony will appear after culturing. Figure 4 shows that lots of E. coli grow around the hydrogelcoated cloths, which means that HG-1 and HG-2 have no bactericidal activity against E. coli. However, HG-2 has highly efficient bactericidal activity against MRSA because of no bacterial colony appear on the plate. These results indicate that HG-2 coated on surface also has an efficient and specific bactericidal activity against MRSA without the need of light source.

In addition, the antibacterial activity of small molecules including Fmoc-L-Phe, OTE-D-Phe and OTE-L-Pro were investigated toward E. coli and MRSA. Due to the poor watersolubility of small molecules, these molecules were dissolved in DMSO. Their biocidal activities were determined by incubation with bacteria suspensions (2 x 10 -7 CFU/mL) for 30 min or 60 min at room temperature. As shown in Figure S6 (Supporting Information), when the concentration of small molecules is 0.8 µM, no MRSA bacteria are dead. When the concentration of OTE-D-Phe increases, the antibacterial activity enhances. Also, the antibacterial activity is a little better after incubating for 60 min than that for 30 min. Finally, 10 uM OTE-D-Phe can kill over 90% MRSA. However, Fmoc-LPhe and OTE-L-Pro have no biocidal ability against MRSA even the concentration reaches 10 uM after incubation for 60 min. The similar results are obtained for E. coli. Due to the different resistance of amino acid (D-and L-amino acid) to bacterial proteases, the L-amino acids (L-Phe and L-Pro) are more susceptible to hydrolysis by protease as they are proteinogenic amino acids, which possibly leads to the different antibacterial activity of small molecules 41. At this case, OTE-DPhe may form vesicles in solution and could kill both MRSA and E. coli at the higher concentration, however, the OTE-D-

Finally, to investigate the activity of the hydrogel-coated cloth on the inhibition of bacterial growth, we observed the colonies of MRSA and E. coli around the HG-2-coated cloth. First, the bacteria were smeared to the cultural plate surface. Then the HG-2-coated cloth was placed on the surface of the plate and incubated for 15 h in dark. As shown in Figure 5, lots of E. coli bacteria grow around the cloth, which means HG-2 has no inhibition activity against E. coli. However, the growth of MRSA around the cloth is completely inhibited and no bacteria appear near the cloth. These results indicate that HG-2 coated on surface also has high and specific inhibition activity against MRSA. These results represent that HG-2 hydrogel is a promising agent in biomedical applications such as implants, being used as a wound dressing, or daily antiseptic to keep from infections of MRSA.

Figure 4. Bactericidal activity of HG-1-coated and HG-2-coated cloths against E. coli and MRSA in dark. The cotton cloth is 1 square centimeter.


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Figure 5. Inhibition activity of HG-2-coated cloths against E. coli and MRSA in dark. The cotton cloth is 1 square centimeter.

Figure 6. Cell viability of A549 incubation with HG-1 (a), HG-2 (b) and HG-3 (c) at different concentrations for 24 h.

antibacterial activity against MRSA captured by hydrogel. When HG-2 was coated on surface, it also showed extremely strong and specific killing of MRSA without light irradiation. Noted that HG-2 does not have significant cytotoxicity. Therefore, HG-2 is promising in wide biomedical applications such as the treatment of drug-resistant bacteria infections, disinfection of devices and daily antiseptic to keep from infections of MRSA.

A great biocompatibility is very important for a material to be applied in biomedical field. Thus the toxicity of HG-1, HG2 and HG-3 were studied based on the model cell A549. As shown in Figure 6, HG-1, prepared only by Fmoc-L-Phe, shows very low toxicity when the concentration is 800 μM. Also, HG-2 presents great biocompatibility even the OTE-DPhe concentration reach 120 μM, while the concentration of Fmoc-L-Phe is 600 μM in the HG-2. When the concentration of OTE-D-Phe is added to 160 μM, the cell viability decreases. HG-3 demonstrates the very similar biocompatibility with HG-2. Because only 40 μM HG-2 can kill over 90% MRSA, HG-2 exhibits great and specific antibacterial activity against MRSA and low toxicity, which opens up a new window for biomedical applications in hospital and in community.

ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Synthesis of conjugated oligomers, preparation of hydrogels, bacteria incubation, antibacterial activities of hydrogels, Figure S1-Figure S6, and Table S1.

CONCLUSIONS In conclusion, we design and synthesize new Dphenylalanine and L-proline-modified conjugated oligomers, OTE-D-Phe and OTE-L-Pro, and prepare hydrogel HG-1, HG2 and suspension HG-3 by "self-assembly" gelation strategy. Among these hydrogels, HG-2 behaves a thicker and rougher nanofiber, which demonstrates an obvious advantage in effectively capturing model bacteria MRSA and E. coli. Most importantly, HG-2 also represents highly efficient and specific

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Prof. Y. L. Tang); Fax: +86-2981530727; Tel: +86-29-81530844.

ORCID Yanli Tang: 0000-0002-9979-6808



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ACKNOWLEDGMENT We thank Dr. Kaiqiang Liu (School of Chemistry & Chemical Engineering, Shaanxi Normal University) for the help of measurement of rheological properties. We are grateful for the financial support from the National Natural Science Foundation of China (Grants 21675106), the Natural Science Basic Research Plan in Shaanxi Province of China (grant 2017JM2019), Fundamental Research Funds for the Central Universities (no. GK201901003), and the 111 Project (Grant B14041).

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Amino Acid-Modified Conjugated Oligomer Self-Assembly Hydrogel

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