Interactions of Bacterial Lipopolysaccharides with Gold Nanorod Surfaces Investigated by Refractometric Sensing

Factors influencing the antimicrobial mechanism of chitosan action and its derivatives: A review

Chitosan, a versatile amino polysaccharide biopolymer derived from chitin, exhibits broad-spectrum antimicrobial activity against various pathogenic microorganisms, including gram-negative and gram-positive bacteria, as well as fungi. Due to its ubiquitous use in medications, food, cosmetics, chemicals, and crops, it is an effective antibacterial agent. However, the antimicrobial performance of chitosan is influenced by multiple factors, which have been extensively investigated and reported in the literature. The goal of this review paper is to present a thorough grasp of the mechanisms of action and determining variables of chitosan and its derivatives' antibacterial activity. The article begins by providing a brief background on chitosan and its antimicrobial properties, followed by the importance of understanding the mechanism of action and factors influencing its activity".

Plasmonic nanoparticle etching-based optical sensors: current status and future prospects

Plasmonic nanoparticles are an emerging tool for developing label-free multicolorimetric sensors for biosensing and chemosensing applications. The color absorbed by nanoparticles from visible light is influenced by their size, shape, orientation, and interparticle distance. Differently sized and shaped gold and silver nanoparticles exhibit a wide range of colors, aiding in the development of label-free sensors. Etching is the process of oxidizing nanoparticles, which alters their aspect ratio, shape, plasmonic peak, and outward appearance. It is typically used to create sensitive sensing platforms. Through etching, analytes could be detected in a simple, sensitive, and selective manner. The multicolor readout of nanoparticle etching-based multicolorimetric sensors can overcome the limitations of conventional colorimetric assays and improve the accuracy of visual inspection. This review discusses different approaches for target sensing using nanoparticle etching strategies like direct etching, enzyme-mediated etching, chemical reaction-driven etching, and anti-etching-based sensors and their mechanisms. In the future, etching strategies could be modified into portable sensing devices to detect a variety of analytes, which will aid in the development of on-time, in situ, and point-of-care sensing systems.

Tuning nanoscale plasmon-exciton coupling via chemical interface damping

Understanding the exact role of each plasmon decay channel in the plasmon-exciton interaction is essential for realizing the translational potential of nanoscale plexciton hybrids. Here, using single-particle spectroscopy, we demonstrate how a particular decay channel, chemical interface damping (CID), influences the nanoscale plasmon-exciton coupling. We investigate the interaction between cyanine dye J-aggregates and gold nanorods in the presence and absence of CID. The CID effect is introduced via surface modification of the nanorods with 4-nitrothiophenol. The relative contribution of CID is systematically tuned by varying the diameter of the nanorods, while maintaining the aspect ratio constant. We show that the incorporation of the CID channel, in addition to other plasmon decay channels, reduces the plasmon-exciton coupling strength. Nanorods' diameter-dependency measurements reveal that in the absence of CID contribution, the plasmon mode-volume factor gradually dominates over the plasmon decoherence effects as the diameter of the nanorods decreases, resulting in an increase in the plasmon-exciton coupling strength. However, the situation is entirely different when the CID channel is active: plasmon dephasing determines the plasmon-exciton coupling strength by outweighing the influence of even a very small plasmon mode-volume. Most importantly, our findings indicate that CID can be used to controllably tune the plasmon-exciton coupling strength for a given plexciton system by modifying the nanoparticle's surface with suitable adsorbates without the need for altering either the plasmonic or excitonic systems. Thus, judicious exploitation of CID can be tremendously beneficial in tailoring the optical characteristics of plexciton hybrid systems to suit any targeted application.

Multiepitope glycan based laser assisted fluorescent nanocomposite with dual functionality for sensing and ablation of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) infection is becoming a severe health hazard and needs early diagnosis with high specificity. However, the non-specific binding of a biosensor is a challenge to the current bacterial detection system. For the first time, we chemically synthesized a galactose tripod (GT) as a P. aeruginosa-specific ligand. We conjugated GT to a photothermally active fluorescent nanocomposite (Au@SiO2-TCPP). P. aeruginosa can be detected using Au@SiO2-TCPP-GT, and additionally ablated as well using synergistic photothermal and photodynamic therapy. Molecular dynamics and simulation studies suggested better binding of GT (binding energy = -6.6 kcal mol-1) with P. aeruginosa lectin than that of galactose monopod (GM) (binding energy = -5.9 kcal mol-1). Furthermore, a binding study was extended to target P. aeruginosa, which has a galactose-binding carbohydrate recognition domain receptor. The colorimetric assay confirmed a limit of detection (LOD) of 104 CFU mL-1. We also looked into the photosensitizing property of Au@SiO2-TCPP-GT, which is stimulated by laser light (630 nm) and causes photoablation of bacteria by the formation of singlet oxygen in the surrounding media. The cytocompatibility of Au@SiO2-TCPP-GT was confirmed using cytotoxicity assays on mammalian cell lines. Moreover, Au@SiO2-TCPP-GT also showed non-hemolytic activity. Considering the toxicity analysis and efficacy of the synthesized glycan nanocomposites, these can be utilized for the treatment of P. aeruginosa-infected wounds. Furthermore, the current glycan nanocomposites can be used for bacterial detection and ablation of P. aeruginosa in contaminated food and water samples as well.

Simple and fast colorimetric detection of lipopolysaccharide based on aptamer and SYBR Green I mediated aggregation of gold nanoparticles

Lipopolysaccharide (LPS) poses a considerable threat to food safety and human health. A colorimetric assay for LPS detection based on LPS binding aptamer (LBA) and SYBR Green I (SG) mediated aggregation of gold nanoparticles (AuNPs) was established. In the absence of LPS, the LBA was absorbed onto the AuNPs surface which prevented SG-induced aggregation of AuNPs, and the sensing system exhibited red color. When LPS was added, it interacted with the LBA, forming a complex. At higher LPS concentration, many LBAs were exhausted resulting in SG-induced aggregation of AuNPs, and color change from red to blue. The range of colorimetric detection of LPS was linear in 0-12 EU/mL, with a limit of detection of 0.1698 EU/mL. Spiked LPS in real samples and interfering substances were also identified. This assay ingeniously using the fluorescent dye SG as an effective trigger of AuNPs aggregation, is rapid and facile than most of those earlier reported LBA-based LPS assays, and there is potential to be modified to construct assays for other targets.

Optimizing Plasmonic Gold Nanorod Deposition on Glass Surfaces for High-Sensitivity Refractometric Biosensing

Owing to high surface sensitivity, gold nanorods (AuNRs) are widely used to construct surface-based nanoplasmonic biosensing platforms for label-free molecular diagnostic applications. A key fabrication step involves controlling AuNR deposition onto the target surface, which requires maximizing surface density while minimizing inter-particle aggregation, and is often achieved by surface functionalization with a self-assembled monolayer (SAM) prior to AuNR deposition. To date, existing studies have typically used a fixed concentration of SAM-forming organic molecules (0.2-10% v/v) while understanding how SAM density affects AuNR deposition and resulting sensing performance would be advantageous. Herein, we systematically investigated how controlling the (3-aminopropyl)triethoxysilane (APTES) concentration (1-30% v/v) during SAM preparation affects the fabrication of AuNR-coated glass surfaces for nanoplasmonic biosensing applications. Using scanning electron microscopy (SEM) and UV-visible spectroscopy, we identified an intermediate APTES concentration range that yielded the highest density of individually deposited AuNRs with minimal aggregation and also the highest peak wavelength in aqueous solution. Bulk refractive index sensitivity measurements indicated that the AuNR configuration had a strong effect on the sensing performance, and the corresponding wavelength-shift responses ranged from 125 to 290 nm per refractive index unit (RIU) depending on the APTES concentration used. Biosensing experiments involving protein detection and antigen-antibody interactions further demonstrated the high surface sensitivity of the optimized AuNR platform, especially in the low protein concentration range where the measurement shift was ~8-fold higher than that obtained with previously used sensing platforms.

Cefotaxime Mediated Synthesis of Gold Nanoparticles: Characterization and Antibacterial Activity

Cefotaxime (CTX) is a third-generation cephalosporin antibiotic with broad-spectrum activity against Gram negative and Gram positive bacteria. However, like other third-generation cephalosporin antibiotics, its efficacy is declining due to the increased prevalence of multidrug-resistant (MDR) pathogens. Recent advances in nanotechnology have been projected as a practical approach to combat MDR microorganisms. Therefore, in the current study, gold nanoparticles (AuNPs) were prepared using cefotaxime sodium, which acted as a reducing and capping agent, besides having well-established antibacterial activity. The synthesized cefotaxime-loaded gold nanoparticles (C-AuNPs) were characterized by UV-Visible spectroscopy, FTIR, TEM and DLS. In addition, the in vitro antibacterial activity of C-AuNPs was assessed against both Gram-positive and Gram-negative bacteria. UV-Visible spectroscopy verified the formation of C-AuNPs, while TEM and DLS verified their nano-size. In addition, CTX loading onto AuNPs was confirmed by FTIR. Furthermore, the colloidal stability of the synthesized C-AuNPs was ascribed to the higher net negative surface charge of C-AuNPs. Most importantly, the synthesized C-AuNPs showed superior antibacterial activity and lower minimum inhibitory concentration (MIC) values against Gram-negative (Escherichia coli, Klebsiella oxytoca, Pseudomonas aeruginosa) and gram-positive (Staphylococcus aureus) bacteria, compared with pure CTX. Collectively, CTX was successfully adopted, as reducing and capping agent, to synthesize stable, nano-sized spherical C-AuNPs. Furthermore, loading CTX onto AuNPs could efficiently restore and/or boost the antibacterial activity of CTX against resistant Gram-negative and Gram-positive bacteria.

Investigation of Nanoparticle Metallic Core Antibacterial Activity: Gold and Silver Nanoparticles against Escherichia coli and Staphylococcus aureus

Multidrug-resistant (MDR) bacteria constitute a global health issue. Over the past ten years, interest in nanoparticles, particularly metallic ones, has grown as potential antibacterial candidates. However, as there is no consensus about the procedure to characterize the metallic nanoparticles (MNPs; i.e., metallic aggregates) and evaluate their antibacterial activity, it is impossible to conclude about their real effectiveness as a new antibacterial agent. To give part of the answer to this question, 12 nm gold and silver nanoparticles have been prepared by a chemical approach. After their characterization by transmission electronic microscopy (TEM), Dynamic Light Scattering (DLS), and UltraViolet-visible (UV-vis) spectroscopy, their surface accessibility was tested through the catalytic reduction of the 4-nitrophenol, and their stability in bacterial culture medium was studied. Finally, the antibacterial activities of 12 nm gold and silver nanoparticles facing Staphylococcus aureus and Escherichia coli have been evaluated using the broth microdilution method. The results show that gold nanoparticles have a weak antibacterial activity (i.e., slight inhibition of bacterial growth) against the two bacteria tested. In contrast, silver nanoparticles have no activity on S. aureus but demonstrate a high antibacterial activity against Escherichia coli, with a minimum inhibitory concentration of 128 µmol/L. This high antibacterial activity is also maintained against two MDR-E. coli strains.

Interactions of Gold and Silver Nanoparticles with Bacterial Biofilms: Molecular Interactions behind Inhibition and Resistance

Many bacteria have the capability to form a three-dimensional, strongly adherent network called 'biofilm'. Biofilms provide adherence, resourcing nutrients and offer protection to bacterial cells. They are involved in pathogenesis, disease progression and resistance to almost all classical antibiotics. The need for new antimicrobial therapies has led to exploring applications of gold and silver nanoparticles against bacterial biofilms. These nanoparticles and their respective ions exert antimicrobial action by damaging the biofilm structure, biofilm components and hampering bacterial metabolism via various mechanisms. While exerting the antimicrobial activity, these nanoparticles approach the biofilm, penetrate it, migrate internally and interact with key components of biofilm such as polysaccharides, proteins, nucleic acids and lipids via electrostatic, hydrophobic, hydrogen-bonding, Van der Waals and ionic interactions. Few bacterial biofilms also show resistance to these nanoparticles through similar interactions. The nature of these interactions and overall antimicrobial effect depend on the physicochemical properties of biofilm and nanoparticles. Hence, study of these interactions and participating molecular players is of prime importance, with which one can modulate properties of nanoparticles to get maximal antibacterial effects against a wide spectrum of bacterial pathogens. This article provides a comprehensive review of research specifically directed to understand the molecular interactions of gold and silver nanoparticles with various bacterial biofilms.

Self-Sufficient and Highly Efficient Gold Sandwich Upconversion Nanocomposite Lasers for Stretchable and Bio-applications

Multifunctional lanthanide-doped upconversion nanoparticles (UCNPs) have spread their wings in the fields of flexible optoelectronics and biomedical applications. One of the ongoing challenges lies in achieving UCNP-based nanocomposites, which enable a continuous-wave (CW) laser action at ultralow thresholds. Here, gold sandwich UCNP nanocomposites [gold (Au¹)-UCNP-gold (Au²)] capable of exhibiting lasing at ultralow thresholds under CW excitation are demonstrated. The metastable energy-level characteristics of lanthanides are advantageous for creating population inversion. In particular, localized surface plasmon resonance-based electromagnetic hotspots in the nanocomposites and the huge enhancement of scattering coefficient for the formation of coherent closed loops due to multiple scattering facilitate the process of stimulated emissions as confirmed by theoretical simulations. The nanocomposites are subjected to stretchable systems for enhancing the lasing action (threshold ∼ 0.06 kW cm^-2) via a light-trapping effect. The applications in bioimaging of HeLa cells and antibacterial activity (photothermal therapy) are demonstrated using the newly designed Au¹-UCNP-Au² nanocomposites.

Chitosan Stabilized Silver Nanoparticles for the Electrochemical Detection of Lipopolysaccharide: A Facile Biosensing Approach for Gram-Negative Bacteria

Negatively charged lipopolysaccharide (LPS), a major endotoxin and component of the outer membrane of several Gram-negative bacteria, provides a useful biomarker for the indirect detection of these pathogens. For instance, Escherichia coli (E. coli) is a pathogenic bacterium that causes infections in almost all age groups, and has been implicated in food and water contamination. Current diagnostic and detection methods tend to be labor-intensive or expensive, necessitating the need for an easy, sensitive, rapid, and low-cost method. We report on the synthesis and use of positively charged chitosan stabilized silver nanoparticles (Chi-AgNPs) as a sensitive electrochemical nanobiosensor for the detection of LPS. Chi-AgNPs were synthesized through a facile, single step protocol, and characterized for size, charge, and morphology. Glassy carbon electrodes modified with Chi-AgNPs resulted in an enhancement of signal in the presence of both LPS and E. coli. Detection was accomplished over a large concentration range (several orders of magnitude) of 0.001–100 ng/mL and 10–10⁷ CFU/mL. The biosensors can reliably detect LPS and E. coli at very low concentrations. Chi-AgNPs have potential as low cost, sensitive nanobiosensors for Gram-negative bacteria due to strong electrostatic interaction with LPS present in their outer membranes.

Ionic Environment Affects Bacterial Lipopolysaccharide Packing and Function

The interaction of lipopolysaccharides (LPS) with metal cations strongly affects the stability and function of the Gram-negative bacterial outer membrane. The sensitivity of deep rough (Re) LPS packing and function to the ionic environment, as affected by cation valency and ionic radius, has been determined using molecular dynamics simulations and Langmuir balance experiments. The degree of LPS aggregation within the LPS models in the presence of different cations is assessed by measuring the effective mean molecular area (Â_m) of each LPS molecule projected onto the interfacial plane at the end of the equilibration. These results are compared to the LPS mean molecular area from experimental measurements in which the LPS monolayers are assembled at the air-water interface using a Langmuir film balance. We found that packing of the LPS arrays is sensitive to the ionic radius and ion valency of the cations present in solution during LPS array packing. Using enhanced sampling of the free energy for the intercalation of oligo(allylamine HCl) (OAH) into deep rough Salmonella enterica LPS bilayers, we obtained the affinity of the core section of LPS to OAH as a function of the nature of the metal cations present in solution. We found that packing of the solvated LPS bilayer models is sensitive to ionic radius and ion valency of the neutralizing cations. This further suggests that ion bridging and steric barriers rather than charge shielding are important factors in mitigating ligand intercalation under conditions with low ionic concentrations.

Emerging antibacterial nanomedicine for enhanced antibiotic therapy

This review highlights the different mechanisms of current nano-antibiotic systems for combatting serious antibiotic resistance of bacteria.

Nanomaterials for Biosensing Lipopolysaccharide

Lipopolysaccharides (LPS) are endotoxins, hazardous and toxic inflammatory stimulators released from the outer membrane of Gram-negative bacteria, and are the major cause of septic shock giving rise to millions of fatal illnesses worldwide. There is an urgent need to identify and detect these molecules selectively and rapidly. Pathogen detection has been done by traditional as well as biosensor-based methods. Nanomaterial based biosensors can assist in achieving these goals and have tremendous potential. The biosensing techniques developed are low-cost, easy to operate, and give a fast response. Due to extremely small size, large surface area, and scope for surface modification, nanomaterials have been used to target various biomolecules, including LPS. The sensing mechanism can be quite complex and involves the transformation of chemical interactions into amplified physical signals. Many different sorts of nanomaterials such as metal nanomaterials, magnetic nanomaterials, quantum dots, and others have been used for biosensing of LPS and have shown attractive results. This review considers the recent developments in the application of nanomaterials in sensing of LPS with emphasis given mainly to electrochemical and optical sensing.

Sensitive method for endotoxin determination in nanomedicinal product samples

Aim: Nanomaterials and nanomedicinal products tend to interfere with various commonly used assays, including regulatory required endotoxin detection methods for medicines. We developed a method to quantify endotoxin levels that is compatible with nanomaterials and nanomedicinal products. Materials & methods: The method is based on measuring endotoxin indirectly via 3-hydroxylated fatty acids of lipid-A, using Ultra High Performance Liquid Chromatography coupled with mass spectrometry. The outcome was related to results of the commonly used Limulus Amebocyte Lysate method. Results: The ultra high performance liquid chromatography coupled with mass spectrometry method has clear advantages compared with other endotoxin determination assays; particularly the absence of nanospecific interference. Conclusion: The method is sensitive, straightforward and accurate in determining and quantifying endotoxin in nanomedicinal product samples.

Probing the influence of cell surface polysaccharides on nanodendrimer binding to Gram-negative and Gram-positive bacteria using single-nanoparticle force spectroscopy

The safe use and design of nanoparticles (NPs) ask for a comprehensive interpretation of their potentially adverse effects on (micro)organisms. In this respect, the prior assessment of the interactions experienced by NPs in the vicinity of - and in contact with - complex biological surfaces is mandatory. It requires the development of suitable techniques for deciphering the processes that govern nano-bio interactions when a single organism is exposed to an extremely low dose of NPs. Here, we used atomic force spectroscopy (AFM)-based force measurements to investigate at the nanoscale the interactions between carboxylate-terminated polyamidoamine (PAMAM) nanodendrimers (radius ca. 4.5 nm) and two bacteria with very distinct surface properties, Escherichia coli and Lactococcus lactis. The zwitterionic nanodendrimers exhibit a negative peripheral surface charge and/or a positive intraparticulate core depending on the solution pH and salt concentration. Following an original strategy according to which a single dendrimer NP is grafted at the very apex of the AFM tip, the density and localization of NP binding sites are probed at the surface of E. coli and L. lactis mutants expressing different cell surface structures (presence/absence of the O-antigen of the lipopolysaccharides (LPS) or of a polysaccharide pellicle). In line with electrokinetic analysis, AFM force measurements evidence that adhesion of NPs onto pellicle-decorated L. lactis is governed by their underlying electrostatic interactions as controlled by the pH-dependent charge of the peripheral and internal NP components, and the negatively-charged cell surface. In contrast, the presence of the O-antigen on E. coli systematically suppresses the adhesion of nanodendrimers onto cells, may the apparent NP surface charge be determined by the peripheral carboxylate groups or by the internal amine functions. Altogether, this work highlights the differentiated roles played by surface polysaccharides in mediating NP attachment to Gram-positive and Gram-negative bacteria. It further demonstrates that the assessment of NP bioadhesion features requires a critical analysis of the electrostatic contributions stemming from the various structures composing the stratified cell envelope, and those originating from the bulk and surface NP components. The joint use of electrokinetics and AFM provides a valuable option for rapidly addressing the binding propensity of NPs to microorganisms, as urgently needed in NP risk assessments.

Green synthesis of catalytic gold/bismuth oxyiodide nanocomposites with oxygen vacancies for treatment of bacterial infections

We have developed a simple and green solution for the synthesis of catalytic gold-doped bismuth oxyiodide (Au/BiOI) nanocomposites at room temperature from an aqueous mixture of gold ions, bismuth ions, and iodide ions. Au nanoparticles (NPs) were formed in situ and doped into BiOI nanosheets. The oxygen vacancies generated in BiOI give rise to its oxidase-like activity, and Au doping facilitated the reaction leading to a 4-fold higher oxidase-like activity of the Au/BiOI nanocomposite. The Au/BiOI nanocomposites showed wide spectrum antimicrobial activity not only against non-multidrug-resistant E. coli, K. pneumoniae, S. enteritidis, S. aureus, and B. subtilis bacteria, but also against multidrug-resistant bacteria, methicillin-resistant S. aureus (MRSA). The gold doping reduced the minimal inhibitory concentration value by ∼2000-fold for the Au/BiOI nanocomposite, in comparison with only BiOI nanoparticles. The bactericidal property of the Au/BiOI nanocomposite arose from the combined effect of the disruption of the bacterial membrane through a strong interaction of the nanocomposite with the bacteria and the generation of reactive oxygen species. Also, the Au/BiOI nanocomposite is highly biocompatible, which has been demonstrated in vitro by analysis of cytotoxicity and hemolysis, and in vivo by evaluating ocular tissue responses. Furthermore, intrastromal administration of Au/BiOI nanocomposites can effectively alleviate S. aureus-induced bacterial keratitis in rabbits, suggesting a significant disinfectant benefit in preclinical studies. The Au/BiOI nanocomposites show great potential for the inactivation of bacterial pathogens in an aqueous environment and treatment of bacterial infection-induced diseases.

Amplifying the signal of localized surface plasmon resonance sensing for the sensitive detection of Escherichia coli O157:H7

Gold nanorods (Au NRs) based localized surface plasmon resonance (LSPR) sensors have been widely employed in various fields including biology, environment and food safety detection, but their size- and shape-dependent sensitivity limits their practical applications in sensing and biological detection. In our present work, we proposed an approach to maximally amplify the signal of Au NRs based LSPR sensing by coating an optimized thickness of mesoporous silica onto Au NRs. The plasmonic peaks of Au NRs@SiO₂ with different shell thickness showed finely linear response to the change of surrounding refractive index. The optimized thickness of mesoporous silica of Au NRs@SiO₂ not only provided high stability for LSPR sensor,but also displayed much higher sensitivity (390 nm/RIU) than values of Au NRs from previous reports. The obtained Au NRs@SiO₂ based LSPR sensor was further used in practical application for selectively detection of the E. coli O157:H7, and the detection limit achieved 10 CFU, which is much lower than conventional methods such as electrochemical methods and lateral-flow immunochromatography.

Use of Nanoparticle Contrast Agents for Cell Tracking with Computed Tomography

Efforts to develop novel cell-based therapies originated with the first bone marrow transplant on a leukemia patient in 1956. Preclinical and clinical examples of cell-based treatment strategies have shown promising results across many disciplines in medicine, with recent advances in immune cell therapies for cancer producing remarkable response rates, even in patients with multiple treatment failures. However, cell-based therapies suffer from inconsistent outcomes, motivating the search for tools that allow monitoring of cell delivery and behavior in vivo. Noninvasive cell imaging techniques, also known as cell tracking, have been developed to address this issue. These tools can allow real-time, quantitative, and long-term monitoring of transplanted cells in the recipient, providing insight on cell migration, distribution, viability, differentiation, and fate, all of which play crucial roles in treatment efficacy. Understanding these parameters allows the optimization of cell choice, delivery route, and dosage for therapy and advances cell-based therapy for specific clinical uses. To date, most cell tracking work has centered on imaging modalities such as MRI, radionuclide imaging, and optical imaging. However, X-ray computed tomography (CT) is an emerging method for cell tracking that has several strengths such as high spatial and temporal resolution, and excellent quantitative capabilities. The advantages of CT for cell tracking are enhanced by its wide availability and cost effectiveness, allowing CT to become one of the most popular clinical imaging modalities and a key asset in disease diagnosis. In this review, we will discuss recent advances in cell tracking methods using X-ray CT in various applications, in addition to predictions on how the field will progress.

Endotoxin Contamination in Nanomaterials Leads to the Misinterpretation of Immunosafety Results

Given the presence of engineered nanomaterials in consumers' products and their application in nanomedicine, nanosafety assessment is becoming increasingly important. In particular, immunosafety aspects are being actively investigated. In nanomaterial immunosafety testing strategies, it is important to consider that nanomaterials and nanoparticles are very easy to become contaminated with endotoxin, which is a widespread contaminant coming from the Gram-negative bacterial cell membrane. Because of the potent inflammatory activity of endotoxin, contaminated nanomaterials can show inflammatory/toxic effects due to endotoxin, which may mask or misidentify the real biological effects (or lack thereof) of nanomaterials. Therefore, before running immunosafety assays, either in vitro or in vivo, the presence of endotoxin in nanomaterials must be evaluated. This calls for using appropriate assays with proper controls, because many nanomaterials interfere at various levels with the commercially available endotoxin detection methods. This also underlines the need to develop robust and bespoke strategies for endotoxin evaluation in nanomaterials.

Polymer mediated layer-by-layer assembly of different shaped gold nanoparticles

Gold nanoparticles (GNPs) have a wide range of properties with potential applications in electronics, optics, catalysis, and sensing. In order to demonstrate that dense, stable, and portable samples could be created for these applications, multiple layers of GNPs were assembled via drop casting on glass substrates by layer-by-layer (LBL) techniques. Two cationic polyelectrolytes, poly(diallyldimethylammonium chloride) and polyethyleneimine, one anionic polyelectrolyte, poly(sodium 4-styrene sulfonate), and one neutral polymer, polyvinylpyrrolidone, were combined with four different shapes of GNPs (spherical, rod, triangular prismatic, and octahedral) to prepare thin films. A subset of these polymer nanoparticle combinations were assembled into thin films. Synthesized GNPs were characterized via dynamic light scattering, UV-vis spectroscopy, and transmission electron microscopy and the LBL thin films were characterized using UV-vis spectroscopy and atomic force microscopy. Sensing applications of the nanoparticles in solution and thin films were tested by monitoring the localized surface plasmon resonance of the GNPs. LBL thin films were prepared ranging from 25 to 100 layers with optical densities at plasmon from 0.5 to 3.0. Sensitivity in solutions ranged from 14 to 1002nm/refractive index units (RIU) and films ranged from 18.8 to 135.1nm/RIU suggesting reduced access to the GNPs within the films.

Association models for binding of molecules to nanostructures

The interaction between nanoparticles and molecules determines the activity of nanostructures.

Sensitivity Tuning through Additive Heterogeneous Plasmon Coupling between 3D Assembled Plasmonic Nanoparticle and Nanocup Arrays

Plasmonic substrates have fixed sensitivity once the geometry of the structure is defined. In order to improve the sensitivity, significant research effort has been focused on designing new plasmonic structures, which involves high fabrication costs; however, a method is reported for improving sensitivity not by redesigning the structure but by simply assembling plasmonic nanoparticles (NPs) near the evanescent field of the underlying 3D plasmonic nanostructure. Here, a nanoscale Lycurgus cup array (nanoLCA) is employed as a base colorimetric plasmonic substrate and an assembly template. Compared to the nanoLCA, the NP assembled nanoLCA (NP-nanoLCA) exhibits much higher sensitivity for both bulk refractive index sensing and biotin-streptavidin binding detection. The limit of detection of the NP-nanoLCA is at least ten times smaller when detecting biotin-streptavidin conjugation. The numerical calculations confirm the importance of the additive plasmon coupling between the NPs and the nanoLCA for a denser and stronger electric field in the same 3D volumetric space. Tunable sensitivity is accomplished by controlling the number of NPs in each nanocup, or the number density of the hot spots. This simple yet scalable and cost-effective method of using additive heterogeneous plasmon coupling effects will benefit various chemical, medical, and environmental plasmon-based sensors.

Interactions between bacterial surface and nanoparticles govern the performance of "chemical nose" biosensors

Rapid and portable diagnosis of pathogenic bacteria can save lives lost from infectious diseases. Biosensors based on a "chemical nose" approach are attracting interest because they are versatile but the governing interactions between bacteria and the biosensors are poorly understood. Here, we use a "chemical nose" biosensor based on gold nanoparticles to explore the role of extracellular polymeric substances in bacteria-nanoparticle interactions. We employ simulations using Maxwell-Garnett theory to show how the type and extent of aggregation of nanoparticles influence their colorimetric response to bacteria. Using eight different species of Gram-positive and Gram-negative bacteria, we demonstrate that this "chemical nose" can detect and identify bacteria over two orders of magnitude of concentration (89% accuracy). Additionally, the "chemical nose" differentiates between binary and tertiary mixtures of the three most common hospital-isolated pathogens: Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa (100% accuracy). We demonstrate that the complex interactions between nanoparticles and bacterial surface determine the colorimetric response of gold nanoparticles and thus, govern the performance of "chemical nose" biosensors.