Co-reporter:Zhiling Zhu, Fei Yu, Haoqing Chen, Jun Wang, ... Chengzhi Cai
Acta Biomaterialia 2017 Volume 64(Volume 64) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.actbio.2017.10.008
Bacterial interference using non-pathogenic Escherichia coli 83972 is a novel strategy for preventing catheter-associated urinary tract infection (CAUTI). Crucial to the success of this strategy is to establish a high coverage and stable biofilm of the non-pathogenic bacteria on the catheter surface. However, this non-pathogenic strain is sluggish to form biofilms on silicone as the most widely used material for urinary catheters. We have addressed this issue by modifying the silicone catheter surfaces with mannosides that promote the biofilm formation, but the stability of the non-pathogenic biofilms challenged by uropathogens over long-term remains a concern. Herein, we report our study on the stability of the non-pathogenic biofilms grown on propynylphenyl mannoside-modified silicone. The result shows that 94% non-pathogenic bacteria were retained on the modified silicone under >0.5 Pa shear stress. After being challenged by three multidrug-resistant uropathogenic isolates in artificial urine for 11 days, large amounts (>4 × 106 CFU cm−2) of the non-pathogenic bacteria remained on the surfaces. These non-pathogenic biofilms reduced the colonization of the uropathogens by >3.2-log.Statement of SignificanceIn bacterial interference, the non-pathogenic Escherichia coli strains are sluggish to form biofilms on the catheter surfaces, due to rapid removal by urine flow. We have demonstrated a solution to this bottleneck by pre-functionalization of mannosides on the silicone surfaces to promote E. coli biofilm formation. A pre-conjugated high affinity propynylphenyl mannoside ligand tethered to the nanometric amino-terminated poly(amido amine) (PAMAM) dendrimer is used for binding to a major E. coli adhesin FimH. It greatly improves the efficiency for the catheter modification, the non-pathogenic biofilm coverage, as well as the (long-term) stability for prevention of uropathogen infections.Download high-res image (71KB)Download full-size image
Co-reporter:Quan Chen, Zhiling Zhu, Jun Wang, Analette I. Lopez, ... Lijuan Zhang
Acta Biomaterialia 2017 Volume 50(Volume 50) pp:
Publication Date(Web):1 March 2017
DOI:10.1016/j.actbio.2017.01.011
Bacterial interference is an alternative strategy to fight against device-associated bacterial infections. Pursuing this strategy, a non-pathogenic bacterial biofilm is used as a live, protective barrier to fence off pathogen colonization. In this work, biofilms formed by probiotic Escherichia coli strain Nissle 1917 (EcN) are investigated for their potential for long-term bacterial interference against infections associated with silicone-based urinary catheters and indwelling catheters used in the digestive system, such as feeding tubes and voice prostheses. We have shown that EcN can form stable biofilms on silicone substrates, particularly those modified with a biphenyl mannoside derivative. These biofilms greatly reduced the colonization by pathogenic Enterococcus faecalis in Lysogeny broth (LB) for 11 days.Statement of SignificanceBacterial interference is an alternative strategy to fight against device-associated bacterial infections. Pursuing this strategy, we use non-pathogenic bacteria to form a biofilm that serves as a live, protective barrier against pathogen colonization. Herein, we report the first use of preformed probiotic E. coli Nissle 1917 biofilms on the mannoside-presenting silicone substrates to prevent pathogen colonization. The biofilms serve as a live, protective barrier to fence off the pathogens, whereas current antimicrobial/antifouling coatings are subjected to gradual coverage by the biomass from the rapidly growing pathogens in a high-nutrient environment. It should be noted that E. coli Nissle 1917 is commercially available and has been used in many clinical trials. We also demonstrated that this probiotic strain performed significantly better than the non-commercial, genetically modified E. coli strain that we previously reported.Download high-res image (189KB)Download full-size image
Co-reporter:Guoting Qin;Chi Ming Yam;Amit Kumar;J. Manuel Lopez-Romero;Sha Li;Toan Huynh;Yan Li;Bin Yang;Rafael Contreras-Caceres
RSC Advances (2011-Present) 2017 vol. 7(Issue 24) pp:14466-14476
Publication Date(Web):2017/03/03
DOI:10.1039/C6RA28497C
A series of oligo(ethylene glycol) (OEG)-terminated monolayers were prepared by photo-activated grafting of OEG-alkenes with the general formula CH2CH(CH2)m(OCH2CH2)nOCH3 (abbreviated as Cm+2EGn, m = 8, 9; n = 3–7) on hydrogen-terminated silicon (111) surfaces using different deposition conditions. The films were characterized by contact-angle goniometry, ellipsometry, X-ray photoelectron spectroscopy (XPS) and tested for protein resistance. Films prepared under a higher vacuum showed a higher thickness and exhibited better protein resistance with increasing ethylene glycol (EG) units. Remarkably, the films prepared from C10EGn were generally thicker than those from their corresponding homologues C11EGn, and displayed better resistance to protein adsorption, which were probably due to the odd–even effect from the alkyl chain. Prepared under high vacuum conditions (∼10−5 mbar), the C10EG7 films with a thickness of 40 Å adsorbed <0.8% (the detection limit of N 1s XPS) monolayer of fibrinogen in a standard assay. The films remained protein-resistant (adsorbed <3% monolayer of fibrinogen) even after 28 days in phosphate buffered saline (PBS) at 37 °C or 17 days in MC3T3-E1 cell culture with 10% fetal bovine serum at 37 °C. Therefore, the C10EG7 films prepared under high vacuum conditions represent the most protein-resistant and stable films on non-oxidized silicon substrates.
Co-reporter:Zhiling Zhu;Haoqing Chen;Siheng Li;Xunmo Yang;Eric Bittner
Catalysis Science & Technology (2011-Present) 2017 vol. 7(Issue 12) pp:2474-2485
Publication Date(Web):2017/06/20
DOI:10.1039/C7CY00587C
Ancillary ligands, especially the tripodal ligands such as tris(triazolylmethyl)amines, have been widely used to accelerate Cu-catalyzed azide–alkyne cycloaddition (CuAAC, a “click” reaction). However, the relationship between the activity of these Cu(I) complexes and their stability against air oxidation and ligand dissociation/exchange was seldom studied, which is critical for the applications of CuAAC in many biological systems. In this work, we synthesized twenty-one Cu(I) tripodal ligands varying in chelate arm length (five to seven atoms), donor groups (triazolyl, pyridyl and phenyl), and steric hindrance. The effects of these variables on the CuAAC reaction, air oxidation, and ligand dissociation were evaluated. Reducing the chelate arm length to five atoms, decreasing steric hindrance, or using a relatively weakly binding ligand can significantly increase the CuAAC reactivity of the Cu(I) complexes, but the concomitant higher degree of oxidation cannot be avoided, which leads to rapid degradation of a histidine-containing peptide as a model of proteins. The oxidation of the peptide can be reduced by attaching oligo(ethylene glycol) chains to the ligands as sacrificial reagents. Using electrospray ionization mass spectrometry (ESI-MS), we directly observed the tri- and di-copper(I)-acetylide complexes in the CuAAC reaction in the [5,5,5] ligand system and a small amount of di-Cu(I)-acetylide in the [5,5,6] ligand system. Only the mono-Cu(I) ligand adducts were observed in the [6,6,6] and [5,6,6] ligand systems.
Co-reporter:Siheng Li;Lin Wang;Fei Yu;Zhiling Zhu;Dema Shobaki;Haoqing Chen;Mu Wang;Jun Wang;Guoting Qin;Uriel J. Erasquin;Li Ren;Yingjun Wang
Chemical Science (2010-Present) 2017 vol. 8(Issue 3) pp:2107-2114
Publication Date(Web):2017/02/28
DOI:10.1039/C6SC02297A
We demonstrated that the copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction could be performed inside live mammalian cells without using a chelating azide. Under optimized conditions, the reaction was performed in human ovary cancer cell line OVCAR5 in which newly synthesized proteins were metabolically modified with homopropargylglycine (HPG). This model system allowed us to estimate the efficiency of the reaction on the cell membranes and in the cytosol using mass spectrometry. We found that the reaction was greatly promoted by a tris(triazolylmethyl)amine CuI ligand tethering a cell-penetrating peptide. Uptake of the ligand, copper, and a biotin-tagged azide in the cells was determined to be 69 ± 2, 163 ± 3 and 1.3 ± 0.1 μM, respectively. After 10 minutes of reaction, the product yields on the membrane and cytosolic proteins were higher than 18% and 0.8%, respectively, while 75% of cells remained viable. By reducing the biothiols in the system by scraping or treatment with N-ethylmalemide, the reaction yield on the cytosolic proteins was greatly improved to ∼9% and ∼14%, respectively, while the yield on the membrane proteins remained unchanged. The results indicate that out of many possibilities, deactivation of the current copper catalysts by biothiols is the major reason for the low yield of the CuAAC reaction in the cytosol. Overall, we have improved the efficiency for the CuAAC reaction in live cells by 3-fold. Despite the low yield inside live cells, products that strongly bind to the intracellular targets can be detected by mass spectrometry. Hence, the in situ CuAAC reaction can be potentially used for screening of cell-specific enzyme inhibitors or biomarkers containing 1,4-substituted 1,2,3-triazoles.
Co-reporter:Siheng Li, Honghao Cai, Jilin He, Haoqing Chen, Srujana Lam, Tao Cai, Zhiling Zhu, Steven J. Bark, and Chengzhi Cai
Bioconjugate Chemistry 2016 Volume 27(Issue 10) pp:2315
Publication Date(Web):September 1, 2016
DOI:10.1021/acs.bioconjchem.6b00267
The copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction is a powerful tool for bioconjugation of biomolecules, particularly proteins and peptides. The major drawback limiting the use of the CuAAC reaction in biological systems is the copper-mediated formation of reactive oxygen species (ROS), leading to the oxidative degradation of proteins or peptides. From the studies on a limited number of proteins and peptides, it is known that, in general, the copper mediated oxidative damage is associated with the copper coordination environment and solvent accessibility. However, there is a lack of data to help estimate the extent of copper-mediated oxidation on a wide range of proteins and peptides. To begin to address this need, we quantitatively measured the degree of copper-mediated oxidation on libraries of 1200 tetrapeptides and a model protein (bovine serum albumin, BSA) using liquid chromatography mass spectrometry (LC-MS). The collected data will be useful to researchers planning to use the CuAAC reaction for bioconjugaton on peptides or proteins.
Co-reporter:Orawan Khantamat, Chien-Hung Li, Fei Yu, Andrew C. Jamison, Wei-Chuan Shih, Chengzhi Cai, and T. Randall Lee
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 7) pp:3981
Publication Date(Web):January 22, 2015
DOI:10.1021/am506516r
Catheter-related infections (CRIs) are associated with the formation of pathogenic biofilms on the surfaces of silicone catheters, which are ubiquitous in medicine. These biofilms provide protection against antimicrobial agents and facilitate the development of bacterial resistance to antibiotics. The application of photothermal agents on catheter surfaces is an innovative approach to overcoming biofilm-generated CRIs. Gold nanoshells (AuNSs) represent a promising photothermal tool, because they can be used to generate heat upon exposure to near-infrared (NIR) radiation, are biologically inert at physiological temperatures, and can be engineered for the photothermal ablation of cells and tissue. In this study, AuNSs functionalized with carboxylate-terminated organosulfur ligands were attached to model catheter surfaces and tested for their effectiveness at killing adhered Enterococcus faecalis (E. faecalis) bacteria. The morphology of the AuNSs was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while the elemental composition was characterized by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Furthermore, optical and photothermal properties were acquired by ultraviolet–visible (UV-vis) spectroscopy and thermographic imaging with an infrared camera, respectively. Bacterial survival studies on AuNS-modified surfaces irradiated with and without NIR light were evaluated using a colony-formation assay. These studies demonstrated that AuNS-modified surfaces, when illuminated with NIR light, can effectively kill E. faecalis on silicone surfaces.Keywords: catheter-related infections; E. faecalis; gold nanoshells; photothermal; polydimethylsiloxane; surface plasmon resonance;
Co-reporter:Zhiling Zhu, Jun Wang, Analette I. Lopez, Fei Yu, Yongkai Huang, Amit Kumar, Siheng Li, Lijuan Zhang and Chengzhi Cai
Biomaterials Science 2015 vol. 3(Issue 6) pp:842-851
Publication Date(Web):27 Apr 2015
DOI:10.1039/C5BM00076A
Prevention of pathogenic colonization on medical devices over a long period of time remains a great challenge, especially in a high-nutrient environment that accelerates the production of biomass leading to biofouling of the device. Since biofouling and the subsequent pathogen colonization is eventually inevitable, a new strategy using non-pathogenic bacteria as living guards against pathogenic colonization on medical devices has attracted increasing interest. Crucial to the success of this strategy is to pre-establish a high coverage and stable biofilm of benign bacteria on the surface. Silicone elastomers are one of the most widely used materials in biomedical devices. In this work, we modified silicone surfaces to promote formation of high coverage and stable biofilms by a non-pathogenic Escherichia coli strain 83972 with type 1 fimbriae (fim+) to interfere with the colonization of an aggressive biofilm-forming, uropathogenic Enterococcus faecalis. Although it is well known that mannoside surfaces promote the initial adherence of fim+ E. coli through binding to the FimH receptor at the tip of the type 1 fimbriae, it is not clear whether the fast initial adherence could lead to a high coverage and stable protective biofilm. To explore the role of mannoside ligands, we synthesized a series of alkyl and aryl mannosides varied in the structure and immobilized them on silicone surfaces pre-coated with a poly(amidoamine) (PAMAM) dendrimer. We found that stable and densely packed benign E. coli biofilms were formed on the surfaces presenting biphenyl mannoside with the highest initial adherence of fim+ E. coli. These non-pathogenic biofilms prevented the colonization of E. faecalis for 11 days at a high concentration (108 CFU mL−1, 100000 times above the diagnostic threshold for urinary tract infection) in the nutrient-rich Lysogeny Broth (LB) media. The result shows a correlation among the initial adherence of fim+ E. coli 83972, the coverage and long-term stability of the resulting biofilms, as well as their efficiency for preventing the pathogen colonization.
Co-reporter:G. T. Qin, A. Lopez, C. Santos, A. M. McDermott and C. Z. Cai
Biomaterials Science 2015 vol. 3(Issue 5) pp:771-778
Publication Date(Web):07 Apr 2015
DOI:10.1039/C5BM00055F
Antimicrobial peptides (AMPs) are part of the immune system in a wide range of organisms. They generally carry positive charges under physiological conditions, allowing them to accumulate on the negatively charged bacterial membrane as the first step of bactericidal action. The concentration range of AMPs necessary for rapid killing of bacteria tested in vitro is much higher than levels found at epithelial surfaces and body fluids in vivo, and close to the a level that is toxic to the host cells. It is likely that AMPs in vivo are localized and act cooperatively to enhance antimicrobial activity, while the global concentration is low thus demonstrating low toxicity to host cells. Herein we employed well-defined mixed self-assembled monolayers (SAMs) to localize LL-37, one of the most studied AMPs, via electrostatic interactions. We systematically varied the surface density of LL-37, and found that the immobilized AMPs not only attracted bacteria Pseudomonas aeruginosa to the surface, but also killed nearly all bacteria when above a threshold density. More significantly, the AMPs displayed low toxicity to human corneal epithelial cells. The results indicated that localization of AMPs on suitable polyanion substrates facilitated the bactericidal activity while minimizing the cytotoxicity of AMPs.
Co-reporter:Rafael Contreras-Caceres, Catherine M. Santos, Siheng Li, Amit Kumar, Zhiling Zhu, Satya S. Kolar, Miguel A. Casado-Rodriguez, Yongkai Huang, Alison McDermott, Juan Manuel Lopez-Romero, Chengzhi Cai
Journal of Colloid and Interface Science 2015 Volume 458() pp:112-118
Publication Date(Web):15 November 2015
DOI:10.1016/j.jcis.2015.07.033
In this work perfluorinated substrates fabricated from SiO2 glass slides are modified with oligo(ethylene glycol) (OEG) units for long-term resistance of cell adhesion purposes, based on fluorous interactions and click chemistry. Specifically, fluorous substrates, prepared by treatment of glass slides with 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane (FAS17), were coated with ethynyl-OEG-C8F17, followed by covalent attachment of an azido-OEG via copper-catalyzed azide-alkyne cycloaddition (CuAAC) “click” reaction. We demonstrate that the resultant surface avoid fibrinogen adsorption and resisted cell adhesion for over 14 days. X-ray photoemission spectroscopy (XPS) analysis and contact angle goniometry measurements confirm the presence of the OEG molecules on the fluorous substrates. Bright field optical images show total absence of 3T3 fibroblast cells on the OEG modified fluorinated substrate for 1 and 5 days, and a remarkably decrease of cell adhesion at 14 days.
Co-reporter:Lin Wang, Meirong Zhao, Siheng Li, Uriel J. Erasquin, Hao Wang, Li Ren, Changyi Chen, Yingjun Wang, and Chengzhi Cai
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 11) pp:8401
Publication Date(Web):April 21, 2014
DOI:10.1021/am501309d
We show that coating of decellularized extracellular matrix (DC-ECM) on substrate surfaces is an efficient way to generate a platform mimicking the native ECM environment. Moreover, the DC-ECM can be modified with a peptide (QK) mimicking vascular endothelial growth factor without apparently compromising its integrity. The modification was achieved through metabolic incorporation of a “clickable” handle to DC-ECM followed by rapid attachment of the QK peptide with an azido tag using copper-catalyzed click reaction. The attachment of the QK peptide on to DC-ECM in this way further enhanced the angiogenic responses (formation of branched tubular networks) of endothelial cells.Keywords: angiogenesis; copper-catalyzed click chemistry; decellularization; extracellular matrix; QK peptide;
Co-reporter:Catherine M. Santos, Amit Kumar, Satya S. Kolar, Rafael Contreras-Caceres, Alison McDermott, and Chengzhi Cai
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 24) pp:12789
Publication Date(Web):November 22, 2013
DOI:10.1021/am404591n
We report a practical method for biofunctionalization of fluoropolymers based on noncovalent, fluorous interactions and click chemistry that allows incorporation of biomolecules under physiological solutions. We demonstrate the method by immobilization of an antimicrobial peptide (AMP) on fluorous thin films and fluorosilicone contact lens. The fluorous surfaces were dip-coated with fluorous-tagged oligo(ethylene) chain terminated with a reactive group, such as an alkynyl group. This simple step generates a “clickable” surface. The noncovalent fluorous interaction was strong enough to allow subsequent covalent attachment of IG-25, a truncated version of the most extensively studied human AMP LL-37. The attachment was through copper-catalyzed click reaction between the alkynyl group on the surface and the azido-OEG tag at the N-terminus of IG-25. In comparison to surfaces presenting IG-25 randomly bound via carbodiimide chemistry, the surfaces presenting IG-25 tethering to the surface at the N-terminus via click chemistry displayed higher antibacterial activities against an ocular pathogen Pseudomonas aeruginosa (strain PA-O1).Keywords: antimicrobial peptides; click chemistry; contact lens; fluorinated polymers; LL-37;
Co-reporter:Lin Wang, Uriel J. Erasquin, Meirong Zhao, Li Ren, Martin Yi Zhang, Gary J. Cheng, Yingjun Wang, and Chengzhi Cai
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 8) pp:2885
Publication Date(Web):July 20, 2011
DOI:10.1021/am2004398
In this article, we present the first report on the antibacterial activity and cytotoxicity of poly(amidoamine) (PAMAM) dendrimers immobilized on three types of titanium-based substrates with and without calcium phosphate coating. We show that the amino-terminated PAMAM dendrimers modified with various percentages (0–60%) of poly(ethylene glycol) (PEG) strongly adsorbed on the titanium-based substrates. The resultant dendrimer films effectively inhibited the colonization of the Gram-negative bacteria Pseudomonas aeruginosa (strain PAO1) and, to a lesser extent, the Gram-positive bacteria Staphylococcus aureus (SA). The antibacterial activity of the films was maintained even after storage of the samples in PBS for up to 30 days. In addition, the dendrimer films had a low cytotoxicity to human bone mesenchymal stem cells (hMSCs) and did not alter the osteoblast gene expression promoted by the calcium phosphate coating.Keywords: antibacterial coatings; dendrimer; mesenchcymal stem cell; microarc oxidation; titanium;
Co-reporter:Amit Kumar, King Li and Chengzhi Cai
Chemical Communications 2011 vol. 47(Issue 11) pp:3186-3188
Publication Date(Web):31 Jan 2011
DOI:10.1039/C0CC05376G
Oxidation of protein (bovine albumin serum) by air still occurred under the copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction conditions even in the presence of a Cu(I)-stabilizing tris(triazole) ligand. Anaerobic conditions not only avoided the oxidation of the protein, but also greatly accelerated the CuAAC reaction using a water-soluble bis(triazole) Cu(I) ligand.
Co-reporter:Dr. Yan Li;Dr. Catherine M. Santos;Dr. Amit Kumar;Dr. Meirong Zhao;Analette I. Lopez;Dr. Guoting Qin;Dr. Alison M. McDermott;Dr. Chengzhi Cai
Chemistry - A European Journal 2011 Volume 17( Issue 9) pp:2656-2665
Publication Date(Web):
DOI:10.1002/chem.201001533
Abstract
We describe an effective approach for the covalent immobilization of antimicrobial peptides (AMPs) to bioinert substrates via CuI-catalyzed azide–alkyne cycloaddition (CuAAC). The bioinert substrates were prepared by surface hydrosilylation of oligo(ethylene glycol) (OEG) terminated alkenes on hydrogen-terminated silicon surfaces. To render the OEG monolayers “clickable”, mixed monolayers were prepared using OEG-alkenes with and without a terminal alkyne protected by a trimethylgermanyl (TMG) group. The mixed monolayers were characterized by X-ray photoelectron spectroscopy (XPS), elliposometry and contact angle measurement. The TMG protecting group can be readily removed to yield a free terminal alkyne by catalytic amounts of CuI in an aqueous media. This step can then be combined with the subsequent CuAAC reaction. Thus, the immobilization of an azide modified AMP (N3-IG-25) was achieved in a one-pot deprotection/coupling reaction. Varying the ratio of the two alkenes in the deposition mixture allowed for control over the density of the alkynyl groups in the mixed monolayer, and subsequently the coverage of the AMPs on the monolayer. These samples allowed for study of the dependence of antimicrobial activities on the AMP density. The results show that a relative low coverage of AMPs (∼1.6×1013 molecule per cm2) is sufficient to significantly suppress the viability of Pseudomonas aeruginosa, while the surface presenting the highest density of AMPs (∼2.8×1013 molecule per cm2) is still cyto-compatible. The remarkable antibacterial activity is attributed to the long and flexible linker and the site-specific “click” immobilization, which may facilitate the covalently attached peptides to interact with and disrupt the bacterial membranes.
Co-reporter:Yan Li, Jun Wang, and Chengzhi Cai
Langmuir 2011 Volume 27(Issue 6) pp:2437-2445
Publication Date(Web):February 9, 2011
DOI:10.1021/la104060j
Microwave (MW) irradiation was used for the grafting of azido-labeled oligo(ethylene oxide) (OEG) on alkynyl-terminated nonoxidized silicon substrates via copper-catalyzed “click” reaction. The “clickable” monolayers were prepared by photografting of an α,ω-alkynene, where the alkynyl terminus was protected by a trimethylgermanyl (TMG) group, onto hydrogen-terminated Si(111) surfaces. X-ray photoelectron spectroscopy (XPS) was primarily employed to characterize the monolayers, and the data obtained were utilized to calculate the surface density of the TMG-alkynyl-functionalized substrate. MW-assisted one-pot deprotection/click reaction was optimized on the surfaces using azido-tagged OEG derivatives. Using MW instead of conventional heating led to a substantial improvement in the rate of the reaction while suppressing the oxidation of the silicon interface and OEG degradation. The antifouling property of the resulting substrates was evaluated using fibrinogen as a model protein. Results show that the OEG-modification reduced the protein adsorption by >90%.
Co-reporter:Yan Li, Meirong Zhao, Jun Wang, Kai Liu, and Chengzhi Cai
Langmuir 2011 Volume 27(Issue 8) pp:4848-4856
Publication Date(Web):March 21, 2011
DOI:10.1021/la104853t
We have developed a general method combining photochemical grafting and copper-catalyzed click chemistry for biofunctionalization of titanium substrates. The UV-activated grafting of an α,ω-alkenyne onto TiO2/Ti substrates provided a “clickable” thin film platform. The selective attachment of the vinyl end of the molecule to the surface was achieved by masking the alkynyl end with a trimethylgermanyl (TMG) protecting group. Subsequently, various oligo(ethylene glycol) (OEG) derivatives terminated with an azido group were attached to the TMG-alkynyl modified titanium surface via a one-pot deprotection/click reaction. The films were characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, ellipsometry, and atomic force microscopy (AFM). We showed that the titanium surface presenting click-immobilized OEG substantially suppressed the nonspecific attachment of protein and cells as compared to the unmodified titanium substrate. Furthermore, glycine-arginine-glycine-aspartate (GRGD), a cell adhesion peptide, was coimmobilized with OEG on the platform. We demonstrated that the resultant GRGD-presenting thin film on Ti substrates can promote the specific adhesion and spreading of AsPC-1 cells.
Co-reporter:Guoting Qin, Jianhua Gu, Kai Liu, Zhongdang Xiao, Chi Ming Yam, and Chengzhi Cai
Langmuir 2011 Volume 27(Issue 11) pp:6987-6994
Publication Date(Web):April 28, 2011
DOI:10.1021/la1047358
Micro- and nanopatterns of biomolecules on inert, ultrathin platforms on nonoxidized silicon are ideal interfaces between silicon-based microelectronics and biological systems. We report here the local oxidation nanolithography with conductive atomic force microscopy (cAFM) on highly protein-resistant, oligo(ethylene glycol) (OEG)-terminated alkyl monolayers on nonoxidized silicon substrates. We propose a mechanism for this process, suggesting that it is possible to oxidize only the top ethylene glycol units to generate carboxylic acid and aldehyde groups on the film surface. We show that avidin molecules can be attached selectively to the oxidized pattern and the density can be varied by altering the bias voltage during cAFM patterning. Biotinylated molecules and nanoparticles are selectively immobilized on the resultant avidin patterns. Since one of the most established methods for immobilization of biomolecules is based on avidin–biotin binding and a wide variety of biotinylated biomolecules are available, this approach represents a versatile means for prototyping any nanostructures presenting these biomolecules on silicon substrates.
Co-reporter:Analette I. Lopez, Amit Kumar, Megan R. Planas, Yan Li, Thuy V. Nguyen, Chengzhi Cai
Biomaterials 2011 32(19) pp: 4336-4346
Publication Date(Web):
DOI:10.1016/j.biomaterials.2011.02.056
Co-reporter:Dr. Yan Li ;Dr. Chengzhi Cai
Chemistry – An Asian Journal 2011 Volume 6( Issue 10) pp:2592-2605
Publication Date(Web):
DOI:10.1002/asia.201100294
Abstract
Copper-catalyzed azide–alkyne cycloaddition (CuAAC), combined with the chemical stability of the SiC-bound organic layer, serves as an efficient tool for the modification of silicon substrates, particularly for the immobilization of complex biomolecules. This review covers recent advances in the preparation of alkynyl- or azido-terminated “clickable” platforms on non-oxidized silicon and their further derivatization by means of the CuAAC reaction. The exploitation of these “click”-functionalized organic thin films as model surfaces to study many biological events was also addressed, as they are directly relevant to the on-going effort of creating silicon-based molecular electronics and chemical/biomolecular sensors.
Co-reporter:Guoting Qin ; Catherine Santos ; Wen Zhang ; Yan Li ; Amit Kumar ; Uriel J. Erasquin ; Kai Liu ; Pavel Muradov ; Barbara Wells Trautner
Journal of the American Chemical Society 2010 Volume 132(Issue 46) pp:16432-16441
Publication Date(Web):October 29, 2010
DOI:10.1021/ja1025497
Biofunctionalization of silicon substrates is important to the development of silicon-based biosensors and devices. Compared to conventional organosiloxane films on silicon oxide intermediate layers, organic monolayers directly bound to the nonoxidized silicon substrates via Si−C bonds enhance the sensitivity of detection and the stability against hydrolytic cleavage. Such monolayers presenting a high density of terminal alkynyl groups for bioconjugation via copper-catalyzed azide−alkyne 1,3-dipolar cycloaddition (CuAAC, a “click” reaction) were reported. However, yields of the CuAAC reactions on these monolayer platforms were low. Also, the nonspecific adsorption of proteins on the resultant surfaces remained a major obstacle for many potential biological applications. Herein, we report a new type of “clickable” monolayers grown by selective, photoactivated surface hydrosilylation of α,ω-alkenynes, where the alkynyl terminal is protected with a trimethylgermanyl (TMG) group, on hydrogen-terminated silicon substrates. The TMG groups on the film are readily removed in aqueous solutions in the presence of Cu(I). Significantly, the degermanylation and the subsequent CuAAC reaction with various azides could be combined into a single step in good yields. Thus, oligo(ethylene glycol) (OEG) with an azido tag was attached to the TMG−alkyne surfaces, leading to OEG-terminated surfaces that reduced the nonspecific adsorption of protein (fibrinogen) by >98%. The CuAAC reaction could be performed in microarray format to generate arrays of mannose and biotin with varied densities on the protein-resistant OEG background. We also demonstrated that the monolayer platform could be functionalized with mannose for highly specific capturing of living targets (Escherichia coli expressing fimbriae) onto the silicon substrates.
Co-reporter:Amit Kumar, Uriel J. Erasquin, Guoting Qin, King Li and Chengzhi Cai
Chemical Communications 2010 vol. 46(Issue 31) pp:5746-5748
Publication Date(Web):28 Jun 2010
DOI:10.1039/C0CC00784F
A versatile and stable liposomal platform is developed for rapid optimization of its peripheral composition. The platform is based on polydiacetylene lipids terminated with alkynyl groups. Conditions for copper-catalyzed azide–alkyne cycloaddition (a “click” reaction) are optimized for rapid attachment of azides with controlled composition onto the liposomes.
Co-reporter:Guoting Qin, Rui Zhang, Boris Makarenko, Amit Kumar, Wayne Rabalais, J. Manuel López Romero, Rodrigo Rico and Chengzhi Cai
Chemical Communications 2010 vol. 46(Issue 19) pp:3289-3291
Publication Date(Web):26 Mar 2010
DOI:10.1039/B925708J
Thin films terminated with oligo(ethylene glycol) (OEG) could be photochemically grafted onto ultrathin silicon carbide layers that were generated on silicon substrates via carbonization with acetylene at 820 °C. The OEG coating reduced the non-specific adsorption of fibrinogen on the substrates by 99.5% and remained resistant after storage in PBS for 4 weeks at 37 °C.
Co-reporter:GuoTing Qin
Science China Chemistry 2010 Volume 53( Issue 1) pp:36-44
Publication Date(Web):2010 January
DOI:10.1007/s11426-010-0030-2
Functionalization of silicon substrate surfaces with a stable monolayer for resisting non-specific adsorption of proteins has attracted great interest, since it is directly relevant to the development of miniature, silicon-based biosensors and implantable microdevices, such as silicon-neuron interfaces. This brief review summarizes our contribution to the development of robust monolayers grown by surface hydrosilylation on atomically flat, hydrogen-terminated silicon surfaces. The review also outlines our strategy and progress on the fabrication of single molecule patterns on such monolayer platforms.
Co-reporter:Guoting Qin and Chengzhi Cai
Chemical Communications 2009 (Issue 34) pp:5112-5114
Publication Date(Web):30 Jul 2009
DOI:10.1039/B911155G
The observation that oligo(ethylene glycol) (OEG)-terminated monolayers remained highly protein-resistant for a month at 37 °C in PBS buffer while they degraded faster in air can be rationalized by a proposed mechanism formulated from a model study using the first internal hydroperoxide of OEG.
Co-reporter:Catherine M. Santos, Amit Kumar, Wen Zhang and Chengzhi Cai
Chemical Communications 2009 (Issue 20) pp:2854-2856
Publication Date(Web):09 Apr 2009
DOI:10.1039/B821148E
The first covalent modification of thin films non-covalently immobilized via fluorous interactions was demonstrated with “click” reactions in 70–80% yields.
Co-reporter:Analette I. Lopez, Rose Y. Reins, Alison M. McDermott, Barbara W. Trautner and Chengzhi Cai
Molecular BioSystems 2009 vol. 5(Issue 10) pp:1148-1156
Publication Date(Web):03 Jul 2009
DOI:10.1039/B904746H
We have investigated the antibacterial activity and cytotoxicity of a series of amino-terminated poly(amidoamine) (PAMAM) dendrimers modified with poly(ethylene glycol) (PEG) groups. The antibacterial activity of the PAMAM dendrimers and their derivatives against the common ocular pathogens, Pseudomonas aeruginosa and Staphylococcus aureus, was evaluated by their minimum inhibitory concentrations (MICs). For the unmodified third and fifth generation (G3 and G5) amino-terminated dendrimers, the MICs against both P. aeruginosa and S. aureus were in the range of 6.3–12.5 μg mL−1, comparable to that of the antimicrobial peptide LL-37 (1.3–12.5 μg mL−1) and within the wide range of 0.047–128 μg mL−1 for the fluoroquinolone antibiotics. PEGylation of the dendrimers decreased their antibacterial activities, especially for the Gram-positive bacteria (S. aureus). The reduction in potency is likely due to the decrease in the number of protonated amino groups and shielding of the positive charges by the PEG chains, thus decreasing the electrostatic interactions of the dendrimers with the negatively-charged bacterial surface. Interestingly, localization of a greater number of amino groups on G5 vs. G3 dendrimers did not improve the potency. Significantly, even a low degree of PEGylation, e.g. 6% with EG11 on G3 dendrimer, greatly reduced the cytotoxicity towards human corneal epithelial cells while maintaining a high potency against P. aeruginosa. The cytotoxicity of the PEGylated dendrimers to host cells is much lower than that reported for antimicrobial peptides. Furthermore, the MICs of these dendrimers against P. aeruginosa are more than two orders of magnitude lower than other antimicrobial polymers reported to date. These results motivate further exploration of the potential of cationic dendrimers as a new class of antimicrobial agents that may be less likely to induce bacterial resistance than standard antibiotics.
Co-reporter:Chi Ming Yam, Juan Manuel Lopez-Romero, Jianhua Gu and Chengzhi Cai
Chemical Communications 2004 (Issue 21) pp:2510-2511
Publication Date(Web):27 Sep 2004
DOI:10.1039/B401499E
Atomically flat, homogeneous, and protein-resistant monolayers can be readily prepared on H–Si(111) surfaces by photo-induced hydrosilylation of α-oligo(ethylene glycol)-ω-alkenes.
Co-reporter:Zhongdang Xiao, Chengzhi Cai and Xiaobin Deng
Chemical Communications 2001 (Issue 16) pp:1442-1443
Publication Date(Web):19 Jul 2001
DOI:10.1039/B104306B
Robust sub-micrometer ring structures are easily prepared
using SiCl3-terminated dendrimers.
Co-reporter:Guoting Qin, Zhiling Zhu, Siheng Li, Alison M. McDermott, Chengzhi Cai
Biomaterials (April 2017) Volume 124() pp:
Publication Date(Web):April 2017
DOI:10.1016/j.biomaterials.2017.01.046
In this work, we developed a simple method to load drugs into commercially available contact lenses utilizing fluorous chemistry. We demonstrated this method using model compounds including fluorous-tagged fluorescein and antibiotic ciprofloxacin. We showed that fluorous interactions facilitated the loading of model molecules into fluorocarbon-containing contact lenses, and that the release profiles exhibited sustained release. Contact lenses loaded with fluorous-tagged ciprofloxacin exhibited antimicrobial activity against Pseudomonas aeruginosa in vitro, while no cytotoxicity towards human corneal epithelial cells was observed. To mimic the tear turnover, we designed a porcine eye infection model under flow conditions. Significantly, the modified lenses also exhibited antimicrobial efficacy against Pseudomonas aeruginosa in the ex vivo infection model. Overall, utilizing fluorous chemistry, we can construct a drug delivery system that exhibits high drug loading capacity, sustained drug release, and robust biological activity.
Co-reporter:Siheng Li, Lin Wang, Fei Yu, Zhiling Zhu, Dema Shobaki, Haoqing Chen, Mu Wang, Jun Wang, Guoting Qin, Uriel J. Erasquin, Li Ren, Yingjun Wang and Chengzhi Cai
Chemical Science (2010-Present) 2017 - vol. 8(Issue 3) pp:NaN2114-2114
Publication Date(Web):2016/11/25
DOI:10.1039/C6SC02297A
We demonstrated that the copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction could be performed inside live mammalian cells without using a chelating azide. Under optimized conditions, the reaction was performed in human ovary cancer cell line OVCAR5 in which newly synthesized proteins were metabolically modified with homopropargylglycine (HPG). This model system allowed us to estimate the efficiency of the reaction on the cell membranes and in the cytosol using mass spectrometry. We found that the reaction was greatly promoted by a tris(triazolylmethyl)amine CuI ligand tethering a cell-penetrating peptide. Uptake of the ligand, copper, and a biotin-tagged azide in the cells was determined to be 69 ± 2, 163 ± 3 and 1.3 ± 0.1 μM, respectively. After 10 minutes of reaction, the product yields on the membrane and cytosolic proteins were higher than 18% and 0.8%, respectively, while 75% of cells remained viable. By reducing the biothiols in the system by scraping or treatment with N-ethylmalemide, the reaction yield on the cytosolic proteins was greatly improved to ∼9% and ∼14%, respectively, while the yield on the membrane proteins remained unchanged. The results indicate that out of many possibilities, deactivation of the current copper catalysts by biothiols is the major reason for the low yield of the CuAAC reaction in the cytosol. Overall, we have improved the efficiency for the CuAAC reaction in live cells by 3-fold. Despite the low yield inside live cells, products that strongly bind to the intracellular targets can be detected by mass spectrometry. Hence, the in situ CuAAC reaction can be potentially used for screening of cell-specific enzyme inhibitors or biomarkers containing 1,4-substituted 1,2,3-triazoles.
Co-reporter:Zhiling Zhu, Haoqing Chen, Siheng Li, Xunmo Yang, Eric Bittner and Chengzhi Cai
Catalysis Science & Technology (2011-Present) 2017 - vol. 7(Issue 12) pp:NaN2485-2485
Publication Date(Web):2017/04/26
DOI:10.1039/C7CY00587C
Ancillary ligands, especially the tripodal ligands such as tris(triazolylmethyl)amines, have been widely used to accelerate Cu-catalyzed azide–alkyne cycloaddition (CuAAC, a “click” reaction). However, the relationship between the activity of these Cu(I) complexes and their stability against air oxidation and ligand dissociation/exchange was seldom studied, which is critical for the applications of CuAAC in many biological systems. In this work, we synthesized twenty-one Cu(I) tripodal ligands varying in chelate arm length (five to seven atoms), donor groups (triazolyl, pyridyl and phenyl), and steric hindrance. The effects of these variables on the CuAAC reaction, air oxidation, and ligand dissociation were evaluated. Reducing the chelate arm length to five atoms, decreasing steric hindrance, or using a relatively weakly binding ligand can significantly increase the CuAAC reactivity of the Cu(I) complexes, but the concomitant higher degree of oxidation cannot be avoided, which leads to rapid degradation of a histidine-containing peptide as a model of proteins. The oxidation of the peptide can be reduced by attaching oligo(ethylene glycol) chains to the ligands as sacrificial reagents. Using electrospray ionization mass spectrometry (ESI-MS), we directly observed the tri- and di-copper(I)-acetylide complexes in the CuAAC reaction in the [5,5,5] ligand system and a small amount of di-Cu(I)-acetylide in the [5,5,6] ligand system. Only the mono-Cu(I) ligand adducts were observed in the [6,6,6] and [5,6,6] ligand systems.
Co-reporter:Guoting Qin, Rui Zhang, Boris Makarenko, Amit Kumar, Wayne Rabalais, J. Manuel López Romero, Rodrigo Rico and Chengzhi Cai
Chemical Communications 2010 - vol. 46(Issue 19) pp:NaN3291-3291
Publication Date(Web):2010/03/26
DOI:10.1039/B925708J
Thin films terminated with oligo(ethylene glycol) (OEG) could be photochemically grafted onto ultrathin silicon carbide layers that were generated on silicon substrates via carbonization with acetylene at 820 °C. The OEG coating reduced the non-specific adsorption of fibrinogen on the substrates by 99.5% and remained resistant after storage in PBS for 4 weeks at 37 °C.
Co-reporter:Guoting Qin and Chengzhi Cai
Chemical Communications 2009(Issue 34) pp:NaN5114-5114
Publication Date(Web):2009/07/30
DOI:10.1039/B911155G
The observation that oligo(ethylene glycol) (OEG)-terminated monolayers remained highly protein-resistant for a month at 37 °C in PBS buffer while they degraded faster in air can be rationalized by a proposed mechanism formulated from a model study using the first internal hydroperoxide of OEG.
Co-reporter:Amit Kumar, King Li and Chengzhi Cai
Chemical Communications 2011 - vol. 47(Issue 11) pp:NaN3188-3188
Publication Date(Web):2011/01/31
DOI:10.1039/C0CC05376G
Oxidation of protein (bovine albumin serum) by air still occurred under the copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction conditions even in the presence of a Cu(I)-stabilizing tris(triazole) ligand. Anaerobic conditions not only avoided the oxidation of the protein, but also greatly accelerated the CuAAC reaction using a water-soluble bis(triazole) Cu(I) ligand.
Co-reporter:Amit Kumar, Uriel J. Erasquin, Guoting Qin, King Li and Chengzhi Cai
Chemical Communications 2010 - vol. 46(Issue 31) pp:NaN5748-5748
Publication Date(Web):2010/06/28
DOI:10.1039/C0CC00784F
A versatile and stable liposomal platform is developed for rapid optimization of its peripheral composition. The platform is based on polydiacetylene lipids terminated with alkynyl groups. Conditions for copper-catalyzed azide–alkyne cycloaddition (a “click” reaction) are optimized for rapid attachment of azides with controlled composition onto the liposomes.
Co-reporter:Catherine M. Santos, Amit Kumar, Wen Zhang and Chengzhi Cai
Chemical Communications 2009(Issue 20) pp:
Publication Date(Web):
DOI:10.1039/B821148E
Co-reporter:G. T. Qin, A. Lopez, C. Santos, A. M. McDermott and C. Z. Cai
Biomaterials Science (2013-Present) 2015 - vol. 3(Issue 5) pp:NaN778-778
Publication Date(Web):2015/04/07
DOI:10.1039/C5BM00055F
Antimicrobial peptides (AMPs) are part of the immune system in a wide range of organisms. They generally carry positive charges under physiological conditions, allowing them to accumulate on the negatively charged bacterial membrane as the first step of bactericidal action. The concentration range of AMPs necessary for rapid killing of bacteria tested in vitro is much higher than levels found at epithelial surfaces and body fluids in vivo, and close to the a level that is toxic to the host cells. It is likely that AMPs in vivo are localized and act cooperatively to enhance antimicrobial activity, while the global concentration is low thus demonstrating low toxicity to host cells. Herein we employed well-defined mixed self-assembled monolayers (SAMs) to localize LL-37, one of the most studied AMPs, via electrostatic interactions. We systematically varied the surface density of LL-37, and found that the immobilized AMPs not only attracted bacteria Pseudomonas aeruginosa to the surface, but also killed nearly all bacteria when above a threshold density. More significantly, the AMPs displayed low toxicity to human corneal epithelial cells. The results indicated that localization of AMPs on suitable polyanion substrates facilitated the bactericidal activity while minimizing the cytotoxicity of AMPs.
Co-reporter:Zhiling Zhu, Jun Wang, Analette I. Lopez, Fei Yu, Yongkai Huang, Amit Kumar, Siheng Li, Lijuan Zhang and Chengzhi Cai
Biomaterials Science (2013-Present) 2015 - vol. 3(Issue 6) pp:NaN851-851
Publication Date(Web):2015/04/27
DOI:10.1039/C5BM00076A
Prevention of pathogenic colonization on medical devices over a long period of time remains a great challenge, especially in a high-nutrient environment that accelerates the production of biomass leading to biofouling of the device. Since biofouling and the subsequent pathogen colonization is eventually inevitable, a new strategy using non-pathogenic bacteria as living guards against pathogenic colonization on medical devices has attracted increasing interest. Crucial to the success of this strategy is to pre-establish a high coverage and stable biofilm of benign bacteria on the surface. Silicone elastomers are one of the most widely used materials in biomedical devices. In this work, we modified silicone surfaces to promote formation of high coverage and stable biofilms by a non-pathogenic Escherichia coli strain 83972 with type 1 fimbriae (fim+) to interfere with the colonization of an aggressive biofilm-forming, uropathogenic Enterococcus faecalis. Although it is well known that mannoside surfaces promote the initial adherence of fim+ E. coli through binding to the FimH receptor at the tip of the type 1 fimbriae, it is not clear whether the fast initial adherence could lead to a high coverage and stable protective biofilm. To explore the role of mannoside ligands, we synthesized a series of alkyl and aryl mannosides varied in the structure and immobilized them on silicone surfaces pre-coated with a poly(amidoamine) (PAMAM) dendrimer. We found that stable and densely packed benign E. coli biofilms were formed on the surfaces presenting biphenyl mannoside with the highest initial adherence of fim+ E. coli. These non-pathogenic biofilms prevented the colonization of E. faecalis for 11 days at a high concentration (108 CFU mL−1, 100000 times above the diagnostic threshold for urinary tract infection) in the nutrient-rich Lysogeny Broth (LB) media. The result shows a correlation among the initial adherence of fim+ E. coli 83972, the coverage and long-term stability of the resulting biofilms, as well as their efficiency for preventing the pathogen colonization.
.jpg)
![Propanoic acid, 3-[2-[2-[2-[2-[2-(2-azidoethoxy)ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]-](/data/chemimg/3739600/361189-66-4.png)
![Propanoic acid, 3-[2-[2-[2-[2-[2-(2-azidoethoxy)ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]-](/data/chemimg/3739600/361189-66-4_b.png)
![Hexadecanoic acid,1,1'-[(1R)-1-[(phosphonooxy)methyl]-1,2-ethanediyl] ester, sodium salt (1:1)](http://img.cochemist.com/ccimg/169100/169051-60-9.png)
![Hexadecanoic acid,1,1'-[(1R)-1-[(phosphonooxy)methyl]-1,2-ethanediyl] ester, sodium salt (1:1)](http://img.cochemist.com/ccimg/169100/169051-60-9_b.png)
![2H-1-Benzopyran-2-one, 7-hydroxy-3-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]-](/data/chemimg/3722500/1202867-60-4.png)
![2H-1-Benzopyran-2-one, 7-hydroxy-3-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]-](/data/chemimg/3722500/1202867-60-4_b.png)
![Ethanol, 2-[2-[2-(2-azidoethoxy)ethoxy]ethoxy]-](/data/chemimg/976600/86770-67-4.png)
![Ethanol, 2-[2-[2-(2-azidoethoxy)ethoxy]ethoxy]-](/data/chemimg/976600/86770-67-4_b.png)
![3',6'-Dihydroxy-3H-spiro[isobenzofuran-1,9'-xanthen]-3-one](http://img.cochemist.com/ccimg/2400/2321-07-5.png)
![3',6'-Dihydroxy-3H-spiro[isobenzofuran-1,9'-xanthen]-3-one](http://img.cochemist.com/ccimg/2400/2321-07-5_b.png)
![Ethanol, 2,2',2''-[nitrilotris(methylene-1H-1,2,3-triazole-4,1-diyl-2,1-ethanediyloxy-2,1-ethanediyloxy-2,1-ethanediyloxy)]tris-](/data/chemimg/3722500/1163732-93-1.png)
![Ethanol, 2,2',2''-[nitrilotris(methylene-1H-1,2,3-triazole-4,1-diyl-2,1-ethanediyloxy-2,1-ethanediyloxy-2,1-ethanediyloxy)]tris-](/data/chemimg/3722500/1163732-93-1_b.png)
