Assembled films of nonaqueous nanoparticles, known as monolayer-protected clusters (MPCs), are investigated as adsorption platforms in protein monolayer electrochemistry (PME), a strategy for studying the electron transfer (ET) of redox proteins. Modified electrodes featuring MPC films assembled with various linking methods, including both electrostatic and covalent mechanisms, are employed to immobilize cytochrome c (cyt c) for electrochemical analysis. The background signal (non-Faradaic current) of these systems is directly related to the structure and composition of the MPC films, including nanoparticle core size, protecting ligand properties, as well as the linking mechanism utilized during assembly. Dithiol-linked films of Au225(C6)75 are identified as optimal films for PME by sufficiently discriminating against detrimental background current and exhibiting interfacial properties that are readily engineered for cyt c adsorption and electroactivity (Faradaic current). Surface concentrations and denaturation rates of adsorbed cyt c are dictated by specific manipulation of the individual MPCs composing the outer layer of the film. The use of specially designed, hydrophilic MPCs as a terminal film layer results in near-ideal cyt c voltammetry, attributed to a high degree of molecular level control of the necessary interfacial interactions and flexibility needed to create a uniform and effective binding of protein across large areas of a substrate. The electrochemical properties of cyt c at MPC films, including ET rate constants that are unaffected by the large ET distance introduced by MPC assemblies, are compared to traditional strategies employing self-assembled monolayers to immobilize cyt c. The incorporation of nanoparticles as protein adsorption platforms has implications for biosensor engineering as well as fundamental biological ET studies.

Biofilm disruption and eradication were investigated as a function of nitric oxide- (NO) releasing chitosan oligosaccharide dose with results compared to control (ie non-NO-releasing) chitosan oligosaccharides and tobramycin. Quantification of biofilm expansion/contraction and multiple-particle tracking microrheology were used to assess the structural integrity of the biofilm before and after antibacterial treatment. While tobramycin had no effect on the physical properties of the biofilm, NO-releasing chitosan oligosaccharides exhibited dose-dependent behavior with biofilm degradation. Control chitosan oligosaccharides increased biofilm elasticity, indicating that the scaffold may mitigate the biofilm disrupting power of nitric oxide somewhat. The results from this study indicate that nitric oxide-releasing chitosan oligosaccharides act as dual-action therapeutics capable of eradicating and physically disrupting P. aeruginosa biofilms.

Chitosan oligosaccharides were modified with N-diazeniumdiolates to yield biocompatible nitric oxide (NO) donor scaffolds. The minimum bactericidal concentrations and MICs of the NO donors against Pseudomonas aeruginosa were compared under aerobic and anaerobic conditions. Differential antibacterial activities were primarily the result of NO scavenging by oxygen under aerobic environments and not changes in bacterial physiology. Bacterial killing was also tested against nonmucoid and mucoid biofilms and compared to that of tobramycin. Smaller NO payloads were required to eradicate P. aeruginosa biofilms under anaerobic versus aerobic conditions. Under oxygen-free environments, the NO treatment was 10-fold more effective at killing biofilms than tobramycin. These results demonstrate the potential utility of NO-releasing chitosan oligosaccharides under both aerobic and anaerobic environments. Pseudomonas aeruginosa is an opportunistic human pathogen that frequently colonizes people with compromised immune systems, such as those with cystic fibrosis (CF) or severe burn wounds (1). The success of P. aeruginosa as a pathogen is related to its multitude of virulence factors, which increase adherence to the host cells, induce inflammation, and disrupt the host immune response (1). Furthermore, P. aeruginosa is intrinsically resistant to many antibiotics due to low membrane permeability and increased expression of ␤-lactamases and efflux pumps (2-4). In addition to this native resistance, P. aeruginosa readily adapts to antibiotic challenge by acquiring resistance genes (3, 5) and forming protective, cooperative communities known as biofilms (6, 7).While all antibiotic resistance mechanisms are not fully understood, at least three main factors reduce antibiotic efficacy against bacterial biofilms compared to planktonic cells. First, P. aeruginosa in biofilms secretes a protective layer of exopolysaccharides that prevent the diffusion of antibiotics (7). In the context of cystic fibrosis, biofilm-bound P. aeruginosa exists predominantly as the mucoid phenotype, characterized by a secreted alginate matrix that provides a physical barrier against the host immune response and antibiotics (8). This exopolysaccharide matrix also prevents the diffusion of oxygen into biofilms, causing P. aeruginosa to switch from aerobic to anaerobic respiration (9). The reduced metabolic activity of P. aeruginosa undergoing anaerobic respiration protects the bacterium against traditional antibiotics that are most effective against rapidly dividing cells, including aminoglycosides and ␤-lactams (10, 11). Finally, biofilms produce persister cells (i.e., dormant bacteria that are highly resistant to chemical disinfectants and exhibit multidrug tolerance) much more frequently than planktonic bacterial cultures (3, 7).The failure of conventional antibiotics to treat P. aeruginosa biofilms and infections necessitates the development of new antibacterial agents. Nitric oxide (NO), an endogenously produced free radical that can disperse (12, 13) and ...

Nitric oxide (NO)-releasing chitosan oligosaccharides were modified with ester functional groups to examine how the mucoadhesive nature of the scaffold impacts the ability of NO to degrade mucins from human bronchial epithelial cell cultures and clinical sputum samples collected from patients with cystic fibrosis (CF). Agarose gel electrophoresis experiments indicated that the mucoadhesive NO-releasing chitosan oligosaccharides degraded both the purified mucins and sputum, while control scaffolds (without NO release or mucoadhesive ligands) had no effect on mucin structure. Microscopic observations of sputum treated with the mucoadhesive NO-releasing chitosan oligosaccharide confirmed degradation of the mucin and DNA networks. Similarly, the viscosity and elasticity of sputum were reduced upon treatment with the mucoadhesive NO-releasing chitosan, demonstrating the potential utility of these NO-releasing scaffolds as mucolytic agents.

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O2-protected N-diazeniumdiolate-based silanes were grafted onto mesoporous silica nanoparticles to yield a scaffold with an NO payload of 2.4 μmol NO/mg and NO release half-life of 23 d. Reduced (3-log) Streptococcus mutans viable adhesion was observed for NO-releasing dental restorative materials modified with these particles relative to controls.

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