Ratiometric Imaging of the in Situ pH Distribution of Biofilms by Use of Fluorescent Mesoporous Silica Nanosensors

Application of biofilm dispersion-based nanoparticles in cutting off reinfection

Bacterial biofilms commonly cause chronic and persistent infections in humans. Bacterial biofilms consist of an inner layer of bacteria and an autocrine extracellular polymeric substance (EPS). Biofilm dispersants (abbreviated as dispersants) have proven effective in removing the bacterial physical protection barrier EPS. Dispersants are generally weak or have no bactericidal effect. Bacteria dispersed from within biofilms (abbreviated as dispersed bacteria) may be more invasive, adhesive, and motile than planktonic bacteria, characteristics that increase the probability that dispersed bacteria will recolonize and cause reinfection. The dispersants should be combined with antimicrobials to avoid the risk of severe reinfection. Dispersant-based nanoparticles have the advantage of specific release and intense penetration, providing the prerequisite for further antibacterial agent efficacy and achieving the eradication of biofilms. Dispersant-based nanoparticles delivered antimicrobial agents for the treatment of diseases associated with bacterial biofilm infections are expected to be an effective measure to prevent reinfection caused by dispersed bacteria. KEY POINTS: • Dispersed bacteria harm and the dispersant's dispersion mechanisms are discussed. • The advantages of dispersant-based nanoparticles in bacteria biofilms are discussed. • Dispersant-based nanoparticles for cutting off reinfection in vivo are highlighted.

Nanoarchitectonics of Bactericidal Coatings Based on CaCO3-Nanosilver Hybrids

Antimicrobial coatings provide protection against microbes colonization on surfaces. This can prevent the stabilization and proliferation of microorganisms. The ever-increasing levels of microbial resistance to antimicrobials are urging the development of alternative types of compounds that are potent across broad spectra of microorganisms and target different pathways. This will help to slow down the development of resistance and ideally halt it. The development of composite antimicrobial coatings (CACs) that can host and protect various antimicrobial agents and release them on demand is an approach to address this urgent need. In this work, new CACs based on microsized hybrids of calcium carbonate (CaCO3) and silver nanoparticles (AgNPs) were designed using a drop-casting technique. Polyvinylpyrrolidone and mucin were used as additives. The CaCO3/AgNPs hybrids contributed to endowing colloidal stability to the AgNPs and controlling their release, thereby ensuring the antibacterial activity of the coatings. Moreover, the additives PVP and mucin served as a matrix to (i) control the distribution of the hybrids, (ii) ensure mechanical integrity, and (iii) prevent the undesired release of AgNPs. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) techniques were used to characterize the 15 μm thick CAC. The antibacterial activity was determined against Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa, three bacteria responsible for many healthcare infections. Antibacterial performance of the hybrids was demonstrated at concentrations between 15 and 30 μg/cm2. Unloaded CaCO3 also presented bactericidal properties against MRSA. In vitro cytotoxicity tests demonstrated that the hybrids at bactericidal concentrations did not affect human dermal fibroblasts and human mesenchymal stem cell viability. In conclusion, this work presents a simple approach for the design and testing of advanced multicomponent and functional antimicrobial coatings that can protect active agents and release them on demand.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Surface Bio-engineered Polymeric Nanoparticles

Surface bio-engineering of polymeric nanoparticles (PNPs) has emerged as a cornerstone in contemporary biomedical research, presenting a transformative avenue that can revolutionize diagnostics, therapies, and drug delivery systems. The approach involves integrating bioactive elements on the surfaces of PNPs, aiming to provide them with functionalities to enable precise, targeted, and favorable interactions with biological components within cellular environments. However, the full potential of surface bio-engineered PNPs in biomedicine is hampered by obstacles, including precise control over surface modifications, stability in biological environments, and lasting targeted interactions with cells or tissues. Concerns like scalability, reproducibility, and long-term safety also impede translation to clinical practice. In this review, these challenges in the context of recent breakthroughs in developing surface-biofunctionalized PNPs for various applications, from biosensing and bioimaging to targeted delivery of therapeutics are discussed. Particular attention is given to bonding mechanisms that underlie the attachment of bioactive moieties to PNP surfaces. The stability and efficacy of surface-bioengineered PNPs are critically reviewed in disease detection, diagnostics, and treatment, both in vitro and in vivo settings. Insights into existing challenges and limitations impeding progress are provided, and a forward-looking discussion on the field's future is presented. The paper concludes with recommendations to accelerate the clinical translation of surface bio-engineered PNPs.

Biocompatible Rhamnolipid Self-Assemblies with pH-Responsive Antimicrobial Activity

There is an urgent need for alternative antimicrobial materials due to the growing challenge of bacteria becoming resistant to conventional antibiotics. This study demonstrates the creation of a biocompatible pH-switchable antimicrobial material by combining bacteria-derived rhamnolipids (RL) and food-grade glycerol monooleate (GMO). The integration of RL into dispersed GMO particles, with an inverse-type liquid crystalline cubic structure in the core, leads to colloidally stable supramolecular materials. The composition and pH-triggered structural transformations are studied with small-angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. The composition-structure-activity relationship is analyzed and optimized to target bacteria at acidic pH values of acute wounds. The new RL/GMO dispersions reduce Staphylococcus aureus (S. aureus) populations by 7-log after 24 h of treatment with 64 µg mL-1 of RL and prevent biofilm formation at pH = 5.0, but have no activity at pH = 7.0. Additionally, the system is active against methicillin-resistant S. aureus (MRSA) with minimum inhibitory concentration of 128 µg mL-1 at pH 5.0. No activity is found against several Gram-negative bacteria at pH 5.0 and 7.0. The results provide a fundamental understanding of lipid self-assembly and the design of lipid-based biomaterials, which can further guide the development of alternative bio-based solutions to combat bacteria.

Drosophila melanogaster as a model to study polymicrobial synergy and dysbiosis

The fruit fly Drosophila melanogaster has emerged as a valuable model for investigating human biology, including the role of the microbiome in health and disease. Historically, studies involving the infection of D. melanogaster with single microbial species have yielded critical insights into bacterial colonization and host innate immunity. However, recent evidence has underscored that multiple microbial species can interact in complex ways through physical connections, metabolic cross-feeding, or signaling exchanges, with significant implications for healthy homeostasis and the initiation, progression, and outcomes of disease. As a result, researchers have shifted their focus toward developing more robust and representative in vivo models of co-infection to probe the intricacies of polymicrobial synergy and dysbiosis. This review provides a comprehensive overview of the pioneering work and recent advances in the field, highlighting the utility of Drosophila as an alternative model for studying the multifaceted microbial interactions that occur within the oral cavity and other body sites. We will discuss the factors and mechanisms that drive microbial community dynamics, as well as their impacts on host physiology and immune responses. Furthermore, this review will delve into the emerging evidence that connects oral microbes to systemic conditions in both health and disease. As our understanding of the microbiome continues to evolve, Drosophila offers a powerful and tractable model for unraveling the complex interplay between host and microbes including oral microbes, which has far-reaching implications for human health and the development of targeted therapeutic interventions.

pH-Responsive, Charge-Reversing Layer-by-Layer Nanoparticle Surfaces Enhance Biofilm Penetration and Eradication

Microbes entrenched within biofilms can withstand 1000-fold higher concentrations of antibiotics, in part due to the viscous extracellular matrix that sequesters and attenuates antimicrobial activity. Nanoparticle (NP)-based therapeutics can aid in delivering higher local concentrations throughout biofilms as compared to free drugs alone, thereby enhancing the efficacy. Canonical design criteria dictate that positively charged nanoparticles can multivalently bind to anionic biofilm components and increase biofilm penetration. However, cationic particles are toxic and are rapidly cleared from circulation in vivo, limiting their use. Therefore, we sought to design pH-responsive NPs that change their surface charge from negative to positive in response to the reduced biofilm pH microenvironment. We synthesized a family of pH-dependent, hydrolyzable polymers and employed the layer-by-layer (LbL) electrostatic assembly method to fabricate biocompatible NPs with these polymers as the outermost surface. The NP charge conversion rate, dictated by polymer hydrophilicity and the side-chain structure, ranged from hours to undetectable within the experimental timeframe. LbL NPs with an increasingly fast charge conversion rate more effectively penetrated through, and accumulated throughout, wildtype (PAO1) and mutant overexpressing biomass (ΔwspF) Pseudomonas aeruginosa biofilms. Finally, tobramycin, an antibiotic known to be trapped by anionic biofilm components, was loaded into the final layer of the LbL NP. There was a 3.2-fold reduction in ΔwspF colony forming units for the fastest charge-converting NP as compared to both the slowest charge converter and free tobramycin. These studies provide a framework for the design of biofilm-penetrating NPs that respond to matrix interactions, ultimately increasing the efficacious delivery of antimicrobials.

Dual fluorescent hollow silica nanofibers for in situ pH monitoring using an optical fiber

This study reports a sensitive and robust pH sensor based on dual fluorescent doped hollow silica nanofibers (hSNFs) for in situ and real-time pH monitoring. Fluorescein isothiocyanate (FITC) and tris(2,2'-bipyridyl)dichlororuthenium(ii) hexahydrate (Ru(BPY)3) were chosen as a pH sensitive dye and reference dye, respectively. hSNFs were synthesized using a two-step method in a reverse micelle system and were shown to have an average length of 6.20 μm and average diameter of 410 nm. The peak intensity ratio of FITC/Ru(BPY)3 was used to calibrate to solution pH changes. An optical-fiber-based fluorescence detection system was developed that enabled feasible and highly efficient near-field fluorescence detection. The developed system enables fully automated fluorescence detection, where components including the light source, detector, and data acquisition unit are all controlled by a computer. The results show that the developed pH sensor works in a linear range of pH 4.0-9.0 with a fast response time of less than 10 s and minimal sample volume of 50 μL, and can be stored under dark conditions for one month without failure. In addition, the as-prepared hSNF-based pH sensors also have excellent long-term durability. Experimental results from ratiometric sensing confirm the high feasibility, accuracy, stability and simplicity of the dual fluorescent hSNF sensors for the detection of pH in real samples.

Mesoporous Silica Nanoparticles as a Potential Nanoplatform: Therapeutic Applications and Considerations

With advances in nanotechnology, nanoparticles have come to be regarded as carriers of therapeutic agents and have been widely studied to overcome various diseases in the biomedical field. Among these particles, mesoporous silica nanoparticles (MSNs) have been investigated as potential nanocarriers to deliver drug molecules to various target sites in the body. This review introduces the physicochemical properties of MSNs and synthesis procedures of MSN-based nanoplatforms. Moreover, we focus on updating biomedical applications of MSNs as a carrier of therapeutic or diagnostic cargo and review clinical trials using silica-nanoparticle-based systems. Herein, on the one hand, we pay attention to the pharmaceutical advantages of MSNs, including nanometer particle size, high surface area, and porous structures, thus enabling efficient delivery of high drug-loading content. On the other hand, we look through biosafety and toxicity issues associated with MSN-based platforms. Based on many reports so far, MSNs have been widely applied to construct tissue engineering platforms as well as treat various diseases, including cancer, by surface functionalization or incorporation of stimuli-responsive components. However, even with the advantageous aspects that MSNs possess, there are still considerations, such as optimizing physicochemical properties or dosage regimens, regarding use of MSNs in clinics. Progress in synthesis procedures and scale-up production as well as a thorough investigation into the biosafety of MSNs would enable design of innovative and safe MSN-based platforms in biomedical fields.

Precise Localization and Simultaneous Bacterial Eradication of Biofilms Based on Nanocontainers with Successive Responsive Property toward pH and ATP

The bacterial colonization of surfaces and subsequent biofilm formation are a great threat in medical therapy and clinical diagnosis. The complex internal structure and composition sets an enormous obstacle for the localization and removal of biofilms. In this study, we proposed a novel biofilm-targeted nanocontainer with successive responsive property toward pH and ATP for precise localization and simultaneous bacterial eradication, with an acidic and adenosine triphosphate (ATP)-rich microenvironment within biofilms, formed due to the accumulation of fatty acids and ATP in the three-dimensional enclosed structure, integrated as two successive indicators to improve the precision of biofilm identification and removal. The biofilm-targeted nanocontainer was composed of a ATP-responsive zeolitic imidazolate framework-90 (ZIF-90) core loaded with Rho 6G and doxorubicin hydrochloride (DOX) encapsulated in the pH-responsive amorphous calcium carbonate/poly(acrylic acid) (ACC/PAA) shell. In the presence of biofilms, the ACC/PAA shell and ZIF-90 core were successively degraded by the accumulated H⁺ and ATP within biofilms, resulting in the release of fluorescence indicators and antimicrobial agents. On the other hand, to meet the application requirements of different biofilm scenarios, the pH response ability of the nanocontainers could be adjusted by changing the metallic ions (Ni²⁺, Zn²⁺, and Cu²⁺) doped into the structure of the ACC/PAA shell. Owing to excellent water dispersion of the pH/ATP double-responsive ZIF-90@Zn-ACC/PAA nanocontainer, precise localization and simultaneous bacterial eradication was successfully realized via a simple spray process. The successive pH/ATP two-step unlocking processes endowed the nanocontainers high precision for localization and simultaneous eradication of biofilms, which made the proposed nanocontainers high promising in food safety and medical treatment.

A Heterocatalytic Metal-Organic Framework to Stimulate Dispersal and Macrophage Combat with Infectious Biofilms

Eradication of infectious biofilms is becoming increasingly difficult due to the growing number of antibiotic-resistant strains. This necessitates development of nonantibiotic-based, antimicrobial approaches. To this end, we designed a heterocatalytic metal-organic framework composed of zirconium 1,4-dicarboxybenzene (UiO-66) with immobilized Pt nanoparticles (Pt-NP/UiO-66). Pt-NP/UiO-66 enhanced singlet-oxygen generation compared with Pt nanoparticles or UiO-66, particularly in an acidic environment. Singlet-oxygen generation degraded phosphodiester bonds present in eDNA gluing biofilms together and therewith dispersed biofilms. Remaining biofilms possessed a more open structure. Concurrently, Pt-NP/UiO-66 stimulated macrophages to adapt a more M1-like, "fighting" phenotype, moving faster toward their target bacteria and showing increased bacterial killing. As a combined effect of biofilm dispersal and macrophage polarization, a subcutaneous Staphylococcus aureus biofilm in mice was more readily eradicated by Pt-NP/UiO-66 than by Pt nanoparticles or UiO-66. Therewith, heterocatalytic Pt-NP/UiO-66 metal-organic frameworks constitute a nonantibiotic-based strategy to weaken protective matrices and disperse infectious biofilms, while strengthening macrophages in bacterial killing.

Dental plaque-inspired versatile nanosystem for caries prevention and tooth restoration

Dental caries is one of the most prevalent human diseases resulting from tooth demineralization caused by acid production of bacteria plaque. It remains challenges for current practice to specifically identify, intervene and interrupt the development of caries while restoring defects. In this study, inspired by natural dental plaque, a stimuli-responsive multidrug delivery system (PMs@NaF-SAP) has been developed to prevent tooth decay and promote enamel restoration. Classic spherical core-shell structures of micelles dual-loaded with antibacterial and restorative agents are self-assembled into bacteria-responsive multidrug delivery system based on the pH-cleavable boronate ester bond, followed by conjugation with salivary-acquired peptide (SAP) to endow the nanoparticle with strong adhesion to tooth enamel. The constructed PMs@NaF-SAP specifically adheres to tooth, identifies cariogenic conditions and intelligently releases drugs at acidic pH, thereby providing antibacterial adhesion and cariogenic biofilm resistance, and restoring the microarchitecture and mechanical properties of demineralized teeth. Topical treatment with PMs@NaF-SAP effectively diminishes the onset and severity of caries without impacting oral microbiota diversity or surrounding mucosal tissues. These findings demonstrate this novel nanotherapy has potential as a promising biomedical application for caries prevention and tooth defect restoration while resisting biofilm-associated diseases in a controlled manner activated by pathological bacteria.

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Nanomaterials can adhere to tooth and target acidic biofilms specifically.

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Application of caries prevention and tooth defect restoration.

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Guidance for the innovation of the existing post-defect restoration strategies.

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The multidrug delivery system exerts antibacterial and restorative abilities on demand.

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Bacteria-responsive system resists biofilm-associated diseases in a controlled manner.

Biomimetic Transparent Nanoplasmonic Meshes by Reverse-Nanoimprinting for Bio-Interfaced Spatiotemporal Multimodal SERS Bioanalysis

Multicellular systems, such as microbial biofilms and cancerous tumors, feature complex biological activities coordinated by cellular interactions mediated via different signaling and regulatory pathways, which are intrinsically heterogeneous, dynamic, and adaptive. However, due to their invasiveness or their inability to interface with native cellular networks, standard bioanalysis methods do not allow in situ spatiotemporal biochemical monitoring of multicellular systems to capture holistic spatiotemporal pictures of systems-level biology. Here, a high-throughput reverse nanoimprint lithography approach is reported to create biomimetic transparent nanoplasmonic microporous mesh (BTNMM) devices with ultrathin flexible microporous structures for spatiotemporal multimodal surface-enhanced Raman spectroscopy (SERS) measurements at the bio-interface. It is demonstrated that BTNMMs, supporting uniform and ultrasensitive SERS hotspots, can simultaneously enable spatiotemporal multimodal SERS measurements for targeted pH sensing and non-targeted molecular detection to resolve the diffusion dynamics for pH, adenine, and Rhodamine 6G molecules in agarose gel. Moreover, it is demonstrated that BTNMMs can act as multifunctional bio-interfaced SERS sensors to conduct in situ spatiotemporal pH mapping and molecular profiling of Escherichia coli biofilms. It is envisioned that the ultrasensitive multimodal SERS capability, transport permeability, and biomechanical compatibility of the BTNMMs can open exciting avenues for bio-interfaced multifunctional sensing applications both in vitro and in vivo.

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

The advent of implanted medical devices has greatly improved the quality of life and increased longevity. However, infection remains a significant risk because bacteria can colonize device surfaces and form biofilms that are resistant to antibiotics and the host's immune system. Several factors contribute to this resistance, including heterogeneous biochemical and pH microenvironments that can affect bacterial growth and interfere with antibiotic biochemistry; dormant regions in the biofilm with low oxygen, pH, and metabolites; slow bacterial growth and division; and poor antibody penetration through the biofilm, which may also be regions with poor acid product clearance. Measuring pH in biofilms is thus key to understanding their biochemistry and offers potential routes to detect and treat latent infections. This review covers the causes of biofilm pH changes and simulations, general findings of metabolite-dependent pH gradients, methods for measuring pH in biofilms, effects of pH on biofilms, and pH-targeted antimicrobial-based approaches.

A core/shell nanogenerator achieving pH-responsive nitric oxide release for treatment of infected diabetic wounds

Nitric oxide is critical for eliminating infection and promoting regeneration in diabetic wounds. However, clinical uses of nitric oxide are limited by its high activity and lack of specificity in targeting infections. Herein, we develop an intelligent nitric oxide nanogenerator comprising isosorbide dinitrate (ISDN)-coated copper sulfide (CuS)/calcium carbonate (CaCO₃) core/shell nanoparticles (CuS@CaCO₃-ISDN) to target the acidic microenvironment of the infected diabetic wounds. Meaningfully, triggered by acid decomposition of CaCO₃, this nanogenerator can achieve a responsive and accelerated release of nitric oxide from ISDN through enzyme-mimicking redox processes that involve CuS nanoparticles and then inactivate biofilm bacteria through the pathways of oxidative stress and disruption of adenosine triphosphate (ATP)-related energy metabolism. Moreover, after eliminating the infection, the pH-responsive release of nitric oxide can promote the proliferation of blood vessels and tissue regeneration and accelerate diabetic wound closure. This study expands the use of nitric oxide donors in wound treatment by developing the enzyme-mimicking release strategy, and the pH-responsive core/shell nanogenerator is promising for a variety of anti-infection therapeutic applications.

Charge-switchable MOF nanocomplex for enhanced biofilm penetration and eradication

Bacterial biofilm is notorious for causing chronic infections, whose antibiotic treatment is bringing about severe multidrug resistance and environmental contamination. Stimuli-responsive nanocarriers have become encouraging materials to combat biofilm infections with high efficiency and low side effect. Herein, a charge-switchable and pH-responsive nanocomplex is fabricated via a facile aqueous one-pot zeolitic imidazolate framework-8 (ZIF-8) encapsulation of proteinase K (PK) and photosensitizer Rose Bengal (RB), for enzymatic and photodynamic therapies (PDT) against biofilm infections. Once encountering in acidic microenvironment, the surface charge of nanocomplex can switch self-adaptively from negative to positive, hence remarkably facilitating the biofilm penetration of nanocomplex. After acid-induced decomposition of nanocomplex, the released PK degrades biofilm matrix and loosens its structure, promoting diffusion of RB inside the biofilm. Afterwards, upon visible light illumination, the RB generates highly reactive oxygen species (ROS), which can readily and efficiently kill the remained bacteria even in the biofilm core. The charge-assisted penetration makes PK and RB fully functional, resulting in a cooperative effect concerning high biofilm eradication capacity, as testified by biofilm models both in vitro and in vivo. The green synthesis and good therapeutic performance of the nanocomplex manifests its considerable potential as a nontoxic and effective platform for biofilm treatment.

Biofilm-responsive encapsulated-phage coating for autonomous biofouling mitigation in water storage systems

Biofilms in water storage systems may harbor pathogens that threaten public health. Chemical disinfectants are marginally effective in eradicating biofilms due to limited penetration, and often generate harmful disinfection byproducts. To enhance biofouling mitigation in household water storage tanks, we encapsulated bacteriophages (phages) in chitosan crosslinked with tri-polyphosphate and 3-glycidoxypropyltrimethoxysilane. Phages served as self-propagating green biocides that exclusively infect bacteria. This pH-responsive encapsulation (244 ± 11 nm) enabled autonomous release of phages in response to acidic pH associated with biofilms (corroborated by confocal microscopy with pH-indicator dye SNARF-4F), but otherwise remained stable in pH-neutral tap water for one month. Encapsulated phages instantly bind to plasma-treated plastic and fiberglass surfaces, providing a facile coating method that protects surfaces highly vulnerable to biofouling. Biofilm formation assays were conducted in tap water amended with 200 mg/L glucose to accelerate growth and attachment of Pseudomonas aeruginosa, an opportunistic pathogen commonly associated with biofilms in drinking water distribution and storage systems. Biofilms formation on plastic surfaces coated with encapsulated phages decreased to only 6.7 ± 0.2% (on a biomass basis) relative to the uncoated controls. Likewise, biofilm surface area coverage (4.8 ± 0.2 log CFU/mm²) and live/dead fluorescence ratio (1.80) were also lower than the controls (6.6 ± 0.2 log CFU/mm² and live/dead ratio of 11.05). Overall, this study offers proof-of-concept of a chemical-free, easily implementable approach to control problematic biofilm-dwelling bacteria and highlights benefits of this bottom-up biofouling control approach that obviates the challenge of poor biofilm penetration by biocides.

Sensors in a Flash! Oxygen Nanosensors for Microbial Metabolic Monitoring Synthesized by Flash Nanoprecipitation

Flash nanoprecipitation (FNP) is an efficient and scalable nanoparticle synthesis method that has not previously been applied to nanosensor fabrication. Current nanosensor fabrication methods have traditionally exhibited poor replicability and consistency resulting in high batch-to-batch variability, highlighting the need for a more tunable and efficient method such as FNP. We used FNP to fabricate nanosensors to sense oxygen based on an oxygen-sensitive dye and a reference dye, as a tool for measuring microbial metabolism. We used fluorescence spectroscopy to optimize nanosensor formulations, calibrate the nanosensors for oxygen concentration determination, and measure oxygen concentrations through oxygen-sensitive dye luminescence. FNP provides an effective platform for making sensors capable of responding to oxygen concentration in gas-bubbled solutions as well as in microbial environments. The environments we tested the sensors in arePseudomonas aeruginosa biofilms andSaccharomyces cerevisiae liquid cultures─both settings where oxygen concentration is highly dependent on microbial activity. With FNP now applied to nanosensor fabrication, future nanosensor applications can take advantage of improved product quality through better replicability and consistency while maintaining the original function of the nanosensor.

Interaction between Engineered Pluronic Silica Nanoparticles and Bacterial Biofilms: Elucidating the Role of Nanoparticle Surface Chemistry and EPS Matrix

Nanoparticles (NPs) are considered a promising tool in the context of biofilm control. Many studies have shown that different types of NPs can interfere with the bacterial metabolism and cellular membranes, thus making them potential antibacterial agents; however, fundamental understanding is still lacking on the exact mechanisms involved in these actions. The development of NP-based approaches for effective biofilm control also requires a thorough understanding of how the chosen nanoparticles will interact with the biofilm itself, and in particular with the biofilm self-produced extracellular polymeric matrix (EPS). This work aims to provide advances in the understanding of the interaction between engineered fluorescent pluronic silica (PluS) nanoparticles and bacterial biofilms, with a main focus on the role of the EPS matrix in the accumulation and diffusion of the particles in the biofilm. It is demonstrated that particle surface chemistry has a key role in the different lateral distribution and specific affinity to the biofilm matrix components. The results presented in this study contribute to our understanding of biofilm-NP interactions and promote the principle of the rational design of smart nanoparticles as an important tool for antibiofilm technology.

Multicolor Polystyrene Nanosensors for the Monitoring of Acidic, Neutral, and Basic pH Values and Cellular Uptake Studies

A first tricolor fluorescent pH nanosensor is presented, which was rationally designed from biocompatible carboxylated polystyrene nanoparticles and two analyte-responsive molecular fluorophores. Its fabrication involved particle staining with a blue-red-emissive dyad, consisting of a rhodamine moiety responsive to acidic pH values and a pH-inert quinoline fluorophore, followed by the covalent attachment of a fluorescein dye to the particle surface that signals neutral and basic pH values with a green fluorescence. These sensor particles change their fluorescence from blue to red and green, depending on the pH and excitation wavelength, and enable ratiometric pH measurements in the pH range of 3.0-9.0. The localization of the different sensor dyes in the particle core and at the particle surface was confirmed with fluorescence microscopy utilizing analogously prepared polystyrene microparticles. To show the application potential of these polystyrene-based multicolor sensor particles, fluorescence microscopy studies with a human A549 cell line were performed, which revealed the cellular uptake of the pH nanosensor and the differently colored emissions in different cell organelles, that is, compartments of the endosomal-lysosomal pathway. Our results demonstrate the underexplored potential of biocompatible polystyrene particles for multicolor and multianalyte sensing and bioimaging utilizing hydrophobic and/or hydrophilic stimuli-responsive luminophores.

Monitoring and imaging pH in biofilms utilizing a fluorescent polymeric nanosensor

Biofilms are ubiquitous in nature and in the man-made environment. Given their harmful effects on human health, an in-depth understanding of biofilms and the monitoring of their formation and growth are important. Particularly relevant for many metabolic processes and survival strategies of biofilms is their extracellular pH. However, most conventional techniques are not suited for minimally invasive pH measurements of living biofilms. Here, a fluorescent nanosensor is presented for ratiometric measurements of pH in biofilms in the range of pH 4.5–9.5 using confocal laser scanning microscopy. The nanosensor consists of biocompatible polystyrene nanoparticles loaded with pH-inert dye Nile Red and is surface functionalized with a pH-responsive fluorescein dye. Its performance was validated by fluorometrically monitoring the time-dependent changes in pH in E. coli biofilms after glucose inoculation at 37 °C and 4 °C. This revealed a temperature-dependent decrease in pH over a 4-h period caused by the acidifying glucose metabolism of E. coli. These studies demonstrate the applicability of this nanosensor to characterize the chemical microenvironment in biofilms with fluorescence methods.

Nanocarriers for combating biofilms: advantages and challenges

Bacterial biofilms are highly resistant to antibiotics and pose a great threat to human and animal health. The control and removal of bacterial biofilms have become an important topic in the field of bacterial infectious diseases. Nanocarriers show great anti-biofilm potential because of their small particle size and strong permeability. In this review, the advantages of nanocarriers for combating biofilms are analyzed. Nanocarriers can act on all stages of bacterial biofilm formation and diffusion. They can improve the scavenging effect of biofilm by targeting biofilm, destroying extracellular polymeric substances, and enhancing the biofilm permeability of antimicrobial substances. Nanocarriers can also improve the antibacterial ability of antimicrobial drugs against bacteria in biofilm by protecting the loaded drugs and controlling the release of antimicrobial substances. Additionally, we emphasize the challenges faced in using nanocarrier formulations and translating them from a preclinical level to the clinical setting.

Antibacterial and Biofilm-Eradicating Activities of pH-Responsive Vesicles against Pseudomonas aeruginosa

The formation of biofilms by a microcolony of bacteria is a significant burden on the healthcare industry due to difficulty eradicating it. In this study, pH-responsive vesicles capable of releasing apramycin (APR), a model aminoglycoside antibiotic, in response to the low pH typical of establishedPseudomonas aeruginosa biofilms resulted in improved eradication of existing biofilms in comparison to the free drug. The amphiphilic polymeric vesicle (PV) comprised of block polymer poly (ethylene glycol)-block-poly 2-(dimethylamino) ethyl methacrylate (mPEG-b-pDEAEMA) averaged 128 nm. The drug encapsulation content of APR in PV/APR was confirmed to be 28.2%, and the drug encapsulation efficiency was confirmed to be 51.2%. At pH 5.5, PV/APR released >90% APR after 24 h compared to <20% at pH 7.4. At pH 5.5, protonation of the pDEAEMA block results in a zeta potential of +23 mV compared to a neutral zeta potential of +2.2 mV at pH 7.4. Confocal microscopy, flow cytometry, and scanning electron microscopy reveal that the positively charged vesicles can compromise the integrity of the planktonic bacterial membrane in a pH-dependent manner. In addition, PV/APR is able to diffuse into mature biofilms to release APR in the acidic milieu of biofilm bacteria, and PV/APR was more efficient at eliminating preexisting biofilms compared to free APR at 128 and 256 μg/mL. This study reveals that dynamic charge density in response to pH can lead to differential levels of interactions with the biofilm and bacterial membrane. This effectively results in enhanced antibacterial and antibiofilm properties against both planktonic and difficult-to-treat biofilm bacteria at concentrations significantly lower than those of the free drug. Overall, this pH-responsive vesicle could be especially promising for treating biofilm-associated infectious diseases.

A pH-Gated Functionalized Hollow Mesoporous Silica Delivery System for Photodynamic Sterilization in Staphylococcus aureus Biofilm

Multidrug-resistant bacteria are increasing, particularly those embedded in microbial biofilm. These bacteria account for most microbial infections in humans. Traditional antibiotic treatment has low efficiency in sterilization of biofilm-associated pathogens, and thus the development of new approaches is highly desired. In this study, amino-modified hollow mesoporous silica nanoparticles (AHMSN) were synthesized and used as the carrier to load natural photosensitizer curcumin (Cur). Then glutaraldehyde (GA) and polyethyleneimine (PEI) were used to seal the porous structure of AHMSN by the Schiff base reaction, forming positively charged AHMSN@GA@PEI@Cur. The Cur delivery system can smoothly diffuse into the negatively charged biofilm of Staphylococcus aureus (S. aureus). Then Cur can be released to the biofilm after the pH-gated cleavage of the Schiff base bond in the slightly acidic environment of the biofilm. After the release of the photosensitizer, the biofilm was irradiated by the blue LED light at a wavelength of 450 nm and a power of 37.4 mV/cm² for 5 min. Compared with the control group, the number of viable bacteria in the biofilm was reduced by 98.20%. Therefore, the constructed pH-gated photosensitizer delivery system can efficiently target biofilm-associated pathogens and be used for photodynamic sterilization, without the production of antibiotic resistance.

pH-Responsive Fluorescent Polymer-Drug System for Real-Time Detection and In Situ Eradication of Bacterial Biofilms

Bacterial biofilms encased in extracellular polymeric substances to create protected microenvironments are typically challenging to disperse by common antibiotics and cannot be in situ visualized under current modalities. Herein, a pH-responsive branched polymer [poly(MBA-AEPZ)-AEPZ-NA] capable of overcoming antibiotic resistance and real-time visualizing biofilms for fluorescence imaging-guided infection control is reported. The positively charged polymer can effectively penetrate bacterial biofilms, neutralize the anionic character, and then disrupt the structural integrity, thus significantly promoting the transport of antibiotics into biofilms. The polymer shows a weak fluorescence emission intensity under physiological conditions (pH 7.4) but emits intense green-light emission within the localized biofilm microenvironment (pH 5.5) to real-time visualize bacterial biofilms. A therapeutic system made of the polymer and a model antibiotic can significantly reduce the dosages of the drug, thereby minimizing biofilm-induced drug resistance. Notably, a green fluorescent polymer responding to localized pH conditions is demonstrated in living zebrafish. This work confirmed that combinations of the pH-responsive branched polymer and antibiotics could be administered to overcome drug resistance and realize fluorescence imaging-guided treatment of bacterial biofilm infections.

Applications and Biocompatibility of Mesoporous Silica Nanocarriers in the Field of Medicine

Mesoporous silica nanocarrier (MSN) preparations have a wide range of medical applications. Studying the biocompatibility of MSN is an important part of clinical transformation. Scientists have developed different types of mesoporous silica nanocarriers (MSNs) for different applications to realize the great potential of MSNs in the field of biomedicine, especially in tumor treatment. MSNs have achieved good results in diagnostic bioimaging, tissue engineering, cancer treatment, vaccine development, biomaterial application and diagnostics. MSNs can improve the therapeutic efficiency of drugs, introduce new drug delivery strategies, and provide advantages that traditional drugs lack. It is necessary not only to innovate MSNs but also to comprehensively understand their biological distribution. In this review, we summarize the various medical uses of MSN preparations and explore the factors that affect their distribution and biocompatibility in the body based on metabolism. Designing more reasonable therapeutic nanomedicine is an important task for the further development of the potential clinical applications of MSNs.

MacAB-TolC Contributes to the Development of Acinetobacter baumannii Biofilm at the Solid–Liquid Interface

Acinetobacter baumannii has emerged as one of the most problematic bacterial pathogens responsible for hospital-acquired and community infections worldwide. Besides its high capacity to acquire antibiotic resistance mechanisms, it also presents high adhesion abilities on inert and living surfaces leading to biofilm development. This lifestyle confers additional protection against various treatments and allows it to persist for long periods in various hospital niches. Due to their remarkable antimicrobial tolerance, A. baumannii biofilms are difficult to control and ultimately eradicate. Further insights into the mechanism of biofilm development will help to overcome this challenge and to develop novel antibiofilm strategies. To unravel critical determinants of this sessile lifestyle, the proteomic profiles of two A. baumannii strains (ATTC17978 and SDF) grown in planktonic stationary phase or in mature solid–liquid (S-L) biofilm were compared using a semiquantitative proteomic study. Of interest, among the 69 common proteins determinants accumulated in the two strains at the S-L interface, we sorted out the MacAB-TolC system. This tripartite efflux pump played a role in A. baumannii biofilm formation as demonstrated by using ΔmacAB-tolC deletion mutant. Complementary approaches allowed us to get an overview of the impact of macAB-tolC deletion in A. baumannii physiology. Indeed, this efflux pump appeared to be involved in the envelope stress response occurring in mature biofilm. It contributes to maintain wild type (WT) membrane rigidity and provides tolerance to high osmolarity conditions. In addition, this system is probably involved in the maintenance of iron and sulfur homeostasis. MacAB-TolC might help this pathogen face and adapt to deleterious conditions occurring in mature biofilms. Increasing our knowledge of A. baumannii biofilm formation will undoubtedly help us develop new therapeutic strategies to tackle this emerging threat to human health.

Bacteria-Responsive Biopolymer-Coated Nanoparticles for Biofilm Penetration and Eradication

Biofilm infections are common and can be extremely difficult to treat. Bacteria-responsive nanoparticles that respond to multiple bacterial stimuli have the potential to successfully prevent and eradicate biofilms. Here, we...

Plasmonic Au@Ag@mSiO2 Nanorattles for In Situ Imaging of Bacterial Metabolism by Surface-Enhanced Raman Scattering Spectroscopy

It is well known that microbial populations and their interactions are largely influenced by their secreted metabolites. Noninvasive and spatiotemporal monitoring and imaging of such extracellular metabolic byproducts can be correlated with biological phenotypes of interest and provide new insights into the structure and development of microbial communities. Herein, we report a surface-enhanced Raman scattering (SERS) hybrid substrate consisting of plasmonic Au@Ag@mSiO₂ nanorattles for optophysiological monitoring of extracellular metabolism in microbial populations. A key element of the SERS substrate is the mesoporous silica shell encapsulating single plasmonic nanoparticles, which furnishes colloidal stability and molecular sieving capabilities to the engineered nanostructures, thereby realizing robust, sensitive, and reliable measurements. The reported SERS-based approach may be used as a powerful tool for deciphering the role of extracellular metabolites and physicochemical factors in microbial community dynamics and interactions.

Electrografted anthraquinone to monitor pH at the biofilm-anode interface in a wastewater microbial fuel cell

Electrografted anthraquinone on graphite was used as a probe to monitor the pH change at the biofilm-electrode interface at the anode of a microbial fuel cell inoculated with wastewater. The grafting procedure was optimized so that the pH-dependent electrochemical response of the grafted quinone did not overlay with that of the electroactive biofilm. The variation of the formal potential of the grafted quinone as a function of pH was linear over the pH range 1-10 with a slope of - 64 mV. This allowed to monitor the interfacial pH change over three weeks of biofilm colonization of the electrode. During that time the interfacial pH decreased from neutrality to 5.3 while the anolyte only acidified down to pH 6.2. This finding is relevant as local pH change usually leads to alterations of the bioenergetics process of microbial communities and hence on the performance of bioelectrochemical devices.

pH-Responsive Hybrid Nanoparticles for Imaging Spatiotemporal pH Changes in Biofilm-Dentin Microenvironments

Engineering highly sensitive nanomaterials to monitor spatiotemporal pH changes has rather broad applications in studying various biological systems. Intraoral/biofilm-tooth pH is the single parameter that has demonstrated accurate assessment of dental caries risk, reflecting the summative integrated outcome of the complicated interactions between three etiological factors, namely, microorganisms/biofilm, diet/carbohydrates, and tooth/saliva/host. However, there is little to no technology/system capable of accurately probing simultaneously both the micro-pH profiles in dentin tissues and acidogenic oral biofilms and examining the pathophysiologic acid attacks with high spatial/temporal resolution. Therefore, a highly sensitive pH-responsive hybrid nanoparticle (pH-NP) is developed and coupled with an ex vivo tooth-biofilm caries model to simulate and study the key cariogenic determinants/steps. The pH-NP emits two distinct fluorescences with mutually inversely proportional intensities that vary accordingly to the proximity pH and with a ratiometric output sensitivity of 13.4-fold across a broad clinically relevant pH range of 3.0-8.0. Using [H⁺], in addition to pH, to calculate the "area-under-curve" corroborates the "minimum-pH" in semiquantifying the demineralizing potential in each biofilm-dentin zones/depth. The data mechanistically elucidates a two-pronged cariogenic effect of a popular-acidic-sweet-drink, in inundating the biofilm/tooth-system with H⁺ ions from both the drink and the metabolic byproducts of the biofilm.

Stimuli-responsive nanocarriers for bacterial biofilm treatment

ABSTRACT

Bacterial biofilm infections have been threatening the human's life and health globally for a long time because they typically cause chronic and persistent infections. Traditional antibiotic therapies can hardly eradicate biofilms in many cases, as biofilms always form a robust fortress for pathogens inside, inhibiting the penetration of drugs. To address the issues, many novel drug carriers emerged as promising strategies for biofilm treatment. Among them, stimuli-responsive nanocarriers have attracted much attentions for their intriguing physicochemical properties, such as tunable size, shape and surface chemistry, especially smart drug release characteristic. Based on the microenvironmental difference between biofilm infection sites and normal tissue, many stimuli, such as bacterial products accumulating in biofilms (enzymes, glutathione, etc.), lower pH and higher H₂O₂ levels, have been employed and proved in favor of "on-demand" drug release for biofilm elimination. Additionally, external stimuli including light, heat, microwave and magnetic fields are also able to control the drug releasing behavior artificially. In this review, we summarized recent advances in stimuli-responsive nanocarriers for combating biofilm infections, and mainly, focusing on the different stimuli that trigger the drug release.

摘要

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Liposomes with Water as a pH-Responsive Functionality for Targeting of Acidic Tumor and Infection Sites

A lipid named DCPA was synthesized under microwave-assisted heating. DCPA possesses a pyridine betaine, hydrophilic group that can be complexed with water through hydrogen bonding (DCPA-H2 O). DCPA-H2 O liposomes became protonated relatively fast already at pH<6.8, due to the high HOMO binding energy of DCPA-H2 O. In murine models, DCPA-H2 O liposomes had longer blood circulation times than natural DPPC or cationic DCPM liposomes, while after tail-vein injection DCPA-H2 O liposomes targeted faster to solid tumors and intra-abdominal infectious biofilms. Therapeutic efficacy in a murine, infected wound-healing model of tail-vein injected ciprofloxacin-loaded DCPA-H2 O liposomes exceeded the ones of clinically applied ciprofloxacin as well as of ciprofloxacin-loaded DPPC or DCPM liposomes.

Fluorescent nanosensors reveal dynamic pH gradients during biofilm formation

Understanding the dynamic environmental microniches of biofilms will permit us to detect, manage and exploit these communities. The components and architecture of biofilms have been interrogated in depth; however, little is known about the environmental microniches present. This is primarily because of the absence of tools with the required measurement sensitivity and resolution to detect these changes. We describe the application of ratiometric fluorescent pH-sensitive nanosensors, as a tool, to observe physiological pH changes in biofilms in real time. Nanosensors comprised two pH-sensitive fluorophores covalently encapsulated with a reference pH-insensitive fluorophore in an inert polyacrylamide nanoparticle matrix. The nanosensors were used to analyse the real-time three-dimensional pH variation for two model biofilm formers: (i) opportunistic pathogen Pseudomonas aeruginosa and (ii) oral pathogen Streptococcus mutans. The detection of sugar metabolism in real time by nanosensors provides a potential application to identify therapeutic solutions to improve oral health.

Selective, pH-Dependent Colorimetric and Fluorimetric Detection of Quadruplex DNA with 4-Dimethylamino(phenyl)-Substituted Berberine Derivatives

The 9- and 12-dimethylaminophenyl-substituted berberine derivatives 3 a and 3 b were readily synthesized by Suzuki-Miyaura reactions and shown to be useful fluorescent probes for the optical detection of quadruplex DNA (G4-DNA). Their association with the nucleic acids was investigated by spectrometric titrations, CD and LD spectroscopy, and with DNA-melting analysis. Both ligands bind to duplex DNA by intercalation and to G4-DNA by terminal π stacking. At neutral conditions, they bind with higher affinity (Kb =105 -106  M-1 ) to representative quadruplex forming oligonucleotides 22AG, c-myc, c-kit, and a2, than to duplex calf thymus (ct) DNA (Kb =5-7×104  M-1 ). At pH 5, however, the affinity of 3 a towards G4-DNA 22AG is higher (Kb =1.2×106  M-1 ), whereas the binding constant towards ct DNA is lower (Kb =3.9×103  M-1 ) than under neutral conditions. Notably, the association of the ligand with DNA results in characteristic changes of the absorption and emission properties under specific conditions, which may be used for optical DNA detection. Other than the parent berberine, the ligands do not show a noticeable increase of their very low intrinsic emission intensity upon association with DNA at neutral conditions. In contrast, a fluorescence light-up effect was observed upon association to duplex (Φfl =0.01) and quadruplex DNA (Φfl =0.04) at pH 5. This fluorimetric response to G4-DNA association in combination with the distinct, red-shifted absorption under these conditions provides a simple and conclusive optical detection of G4-DNA at lower pH.

Methanogenesis at High Temperature, High Ionic Strength and Low pH in the Volcanic Area of Dallol, Ethiopia

The Dallol geothermal area originated as a result of seismic activity and the presence of a shallow underground volcano, both due to the divergence of two tectonic plates. In its ascent, hot water dissolves and drags away the subsurface salts. The temperature of the water that comes out of the chimneys is higher than 100 °C, with a pH close to zero and high mineral concentration. These factors make Dallol a polyextreme environment. So far, nanohaloarchaeas, present in the salts that form the walls of the chimneys, have been the only living beings reported in this extreme environment. Through the use of complementary techniques: culture in microcosms, methane stable isotope signature and hybridization with specific probes, the methanogenic activity in the Dallol area has been assessed. Methane production in microcosms, positive hybridization with the Methanosarcinales probe and the δ¹³C_CH4-values measured, show the existence of extensive methanogenic activity in the hydrogeothermic Dallol system. A methylotrophic pathway, carried out by Methanohalobium and Methanosarcina-like genera, could be the dominant pathway for methane production in this environment.

Stability and Performance Study of Fluorescent Organosilica pH Nanosensors

Long-term stability and function are key challenges for optical nanosensors operating in complex biological environments. While much focus is rightly placed on issues related to specificity, sensitivity, reversibility, and response time, many nanosensors are not capable of transducing accurate results over prolonged time periods. Sensors could fail over time due to the degradation of scaffold material, degradation of signaling dyes and components, or a combination of both. It is critical to investigate how such degradative processes affect sensor output, as the consequences could be severe. Herein, we used fluorescent core-shell organosilica pH nanosensors as a model system, incubating them in a range of common aqueous solutions over time at different temperatures, and then searched for changes in fluorescence signal, particle size, and evidence of silica degradation. We found that these ratiometric nanosensors produced stable optical signals after aging for 30 days at 37 °C in standard saline buffers with and without 10% fetal bovine serum, and without any evidence of material degradation. Next, we evaluated their performance as real-time pH nanosensors in bacterial suspension cultures, observing a close agreement with a pH electrode for control nanosensors, yet observing obvious deviations in signal based on the aging conditions. The results show that while the organosilica scaffold does not degrade appreciably over time, careful selection of dyes and further systematic investigations into the effects of salt and protein levels are required to realize long-term stable nanosensors.

Acclimation of microorganisms for an efficient production of volatile fatty acids and biogas from mezcal vinasses in a dark fermentation process

Mezcal is an alcoholic artisanal drink made from agave plants in Mexico. Its production causes the generation of wastewater called vinasses, which are highly polluting residues due to its concentration of organic matter as chemical oxygen demand (COD) (35,000-122,000 mg/L) and acidity (pH < 4). Due to their organic content, these residues can be used in dark fermentation to obtain biogas, which is rich in hydrogen. In this work, the acclimation of inoculum by means of a dark fermentation process, in the presence of toxic compounds from mezcal vinasses was studied. The strategy of increasing the initial concentration of vinasse in each treatment cycle in a sequencing batch reactor (SBR) reactor was applied. It was possible to obtain a maximum biogas production of 984 ± 187 mL/L, from vinasses (18,367 ± 1,200 mg COD/L), with an organic matter removal efficiency of 20 ± 1%. A maximum generation of volatile fatty acids (VFA) of 980 ± 538 mg/L equivalent to a production of 74 ± 21% of the influent concentration and removal rate of organic matter of 1,125 ± 234 mg COD/L d^-1 equivalent to a removal efficiency of 20 ± 4% was obtained from vinasses with a concentration of 19,648 ± 1,702 mg COD/L.

Halochromic Polymer Nanosensors for Simple Visual Detection of Local pH in Coatings

Replacing metallic structures before critical damage is beneficial for safety and for saving energy and resources. One simple approach consists in visually monitoring the early stage of corrosion, and related change of pH, of coated metals. We prepare smart nanoparticle additives for coatings which act as a pH sensor. The nanoparticles are formed with a terpolymer containing two dyes as side chains, acting as donor and acceptor for a FRET process. Real time monitoring of the extent of localized corrosion on metallic structures is then carried out with a smartphone camera. Colored pH mapping can be then manually retrieved by an operator or automatically recorded by a surveillance camera.

Synthesis and self-assembly of curcumin-modified amphiphilic polymeric micelles with antibacterial activity

BACKGROUND

The ubiquitous nature of bacterial biofilms combined with the enhanced resistance towards antimicrobials has led to the development of an increasing number of strategies for biofilm eradication. Such strategies must take into account the existence of extracellular polymeric substances, which obstruct the diffusion of antibiofilm agents and assists in the maintenance of a well-defended microbial community. Within this context, nanoparticles have been studied for their drug delivery efficacy and easily customised surface. Nevertheless, there usually is a requirement for nanocarriers to be used in association with an antimicrobial agent; the intrinsically antimicrobial nanoparticles are most often made of metals or metal oxides, which is not ideal from ecological and biomedical perspectives. Based on this, the use of polymeric micelles as nanocarriers is appealing as they can be easily prepared using biodegradable organic materials.

RESULTS

In the present work, micelles comprised of poly(lactic-co-glycolic acid) and dextran are prepared and then functionalised with curcumin. The effect of the functionalisation in the micelle's physical properties was elucidated, and the antibacterial and antibiofilm activities were assessed for the prepared polymeric nanoparticles against Pseudomonas spp. cells and biofilms. It was found that the nanoparticles have good penetration into the biofilms, which resulted in enhanced antibacterial activity of the conjugated micelles when compared to free curcumin. Furthermore, the curcumin-functionalised micelles were efficient at disrupting mature biofilms and demonstrated antibacterial activity towards biofilm-embedded cells.

CONCLUSION

Curcumin-functionalised poly(lactic-co-glycolic acid)-dextran micelles are novel nanostructures with an intrinsic antibacterial activity tested against two Pseudomonas spp. strains that have the potential to be further exploited to deliver a secondary bioactive molecule within its core.

MSNs-Based Nanocomposite for Biofilm Imaging and NIR-Activated Chem/Photothermal/Photodynamic Combination Therapy

Bacterial infections caused by biofilms are severe clinical problems, resulting in high drug resistance by limiting the penetration of antibiotics. Herein, a near-infrared (NIR)-activated chem/photodynamic/photothermal combined therapeutic agent is proposed by loading fluorescein isothiocyanate (FITC), ultrasmall copper sulfide nanoparticles (Cu_2-xSNPs), and ε-polylysine (PLL) onto mesoporous silica nanoparticles (MSNs) through a layer-by-layer self-assembly approach. FITC-doped MSNs are prepared to monitor the permeability and accumulation of nanocomposites into biofilms. MSNs can also act as hosts for the synthesis of ultrasmall Cu_2-xSNPs, which has effective photodynamic and photothermal ablation against bacteria under NIR light irradiation. Moreover, biodegradable PLL introduced can not only enhance adhesion toward the bacterial surface to increase the effectiveness of phototherapy but also damage bacteria through electrostatic interaction. As a result, the prepared nanocomposites could not only penetrate biofilms but also ablate biofilms through combined chem/photodynamic/photothermal effects under NIR light irradiation. Furthermore, the nanocomposites could treat bacterial infections in vivo with negligible tissue toxicity. Overall, the finely designed nanocomposites are anticipated to display promising applications in imaging-guided chem/photodynamic/photothermal combined therapy for bacterial infections.

Enzyme-Functionalized Mesoporous Silica Nanoparticles to Target Staphylococcus aureus and Disperse Biofilms

BACKGROUND

Staphylococcus aureus biofilms pose a unique challenge in healthcare due to their tolerance to a wide range of antimicrobial agents. The high cost and lengthy timeline to develop novel therapeutic agents have pushed researchers to investigate the use of nanomaterials to deliver antibiofilm agents and target biofilm infections more efficiently. Previous studies have concentrated on improving the efficacy of antibiotics by deploying nanoparticles as nanocarriers. However, the dispersal of the extracellular polymeric substance (EPS) matrix in biofilm-associated infections is also critical to the development of novel nanoparticle-based therapies.

METHODS

This study evaluated the efficacy of enzyme-functionalized mesoporous silica nanoparticles (MSNs) against methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) biofilms. MSNs were functionalized with the enzyme lysostaphin, which causes cell lysis of S. aureus bacteria. This was combined with two other enzyme functionalized MSNs, serrapeptase and DNase I which will degrade protein and eDNA in the EPS matrix, to enhance eradication of the biofilm. Cell viability after treatment with enzyme-functionalized MSNs was assessed using a MTT assay and CLSM, while crystal violet staining was used to assess EPS removal.

RESULTS

The efficacy of all three enzymes against S. aureus cells and biofilms was significantly improved when they were immobilized onto MSNs. Treatment efficacy was further enhanced when the three enzymes were used in combination against both MRSA and MSSA. Regardless of biofilm maturity (24 or 48 h), near-complete dispersal and killing of MRSA biofilms were observed after treatment with the enzyme-functionalized MSNs. Disruption of mature MSSA biofilms with a polysaccharide EPS was less efficient, but cell viability was significantly reduced.

CONCLUSION

The combination of these three enzymes and their functionalization onto nanoparticles might extend the therapeutic options for the treatment of S. aureus infections, particularly those with a biofilm component.

Surface functionalization-dependent localization and affinity of SiO2 nanoparticles within the biofilm EPS matrix

The contribution of the biofilm extracellular polymeric substance (EPS) matrix to reduced antimicrobial susceptibility in biofilms is widely recognised. As such, the direct targeting of the EPS matrix is a promising biofilm control strategy that allows for the disruption of the matrix, thereby allowing a subsequent increase in susceptibility to antimicrobial agents. To this end, surface-functionalized nanoparticles (NPs) have received considerable attention. However, the fundamental understanding of the interactions occurring between engineered NPs and the biofilm EPS matrix has not yet been fully elucidated. An insight into the underlying mechanisms involved when a NP interacts with the EPS matrix will aid in the design of more efficient NPs for biofilm control. Here we demonstrate the use of highly specific fluorescent probes in confocal laser scanning microscopy (CLSM) to illustrate the distribution of EPS macromolecules within the biofilm. Thereafter, a three-dimensional (3D) colocalization analysis was used to assess the affinity of differently functionalized silica NPs (SiNPs) and EPS macromolecules from Pseudomonas fluorescens biofilms. Results show that both the charge and surface functional groups of SiNPs dramatically affected the extent to which SiNPs interacted and localized with EPS macromolecules, including proteins, polysaccharides and DNA. Hypotheses are also presented about the possible physicochemical interactions which may be dominant in EPS matrix-NP interactions. This research not only develops an innovative CLSM-based methodology for elucidating biofilm-nanoparticle interactions but also provides a platform on which to build more efficient NP systems for biofilm control.

Biofilm interfacial acidity evaluation by pH-Responsive luminescent nanoparticle films

Biofilms are dense bacterial colonies that may adhere to the surfaces of medical devices and are major contributors to infections. These colonies are characterized by a self-produced matrix of extracellular polymeric substances (EPS). Bacterial biofilms are difficult to treat with the commonly used antibiotics partially because of their poor diffusion through the EPS and therefore require new targeted strategies to effectively fight them. Biofilms may produce an acidic microenvironment which can be exploited to design such targeted treatment strategies. However, there is currently a lack of high-throughput ways to determine the acidity of biofilms at their interface with the medical device. Here, a novel all-inorganic pH responsive system is developed from luminescent carbonated hydroxyapatite nanoparticles doped with Eu³⁺ ions which can determine the biofilm acidity fluorometrically due to carbonate removal in acidic environments that directly affects the nanoparticle luminescence. The pH responsive nanoparticles are in-situ deposited during their production onto substrates on which a variety of clinically-relevant biofilms are grown. The acidity of their interfacial (micro)environment depends on the bacterial species and strain even when differences in biofilm biomass are considered.

Engineering Inorganic Nanoflares with Elaborate Enzymatic Specificity and Efficiency for Versatile Biofilm Eradication

Nanozyme has emerged as a versatile nanocatalyst yet is constrained with limited catalytic efficiency and specificity for various biomedical applications. Herein, by elaborately integrating the recognition/transduction carbon dots (CDs) with platinum nanoparticles (PtNPs), an exquisite CDs@PtNPs (CPP) nanoflare is engineered as an efficient and substrate-specific peroxidase-mimicking nanozyme for high-performance biosensing and antibacterial applications. The intelligent CPP-catalyzed hydrogen peroxide (H₂ O₂ )-generated reactive oxygen species realize the sensitive diagnosis-guided enhanced disinfection of pathogens. Significantly, the CPP nanozyme shows the prominent biofilm eradication and wound healing in vivo by virtue of endogenous H₂ O₂ in acidic infection tissues, which can substantially preclude the annoying antibiotics resistance. A fundamental understanding on the present CPP nanoflare would not only facilitate the advancement of various prospective biocatalysts, but also establish a multifunctional means for versatile biosensing and smart diagnostic applications.