Stainless Steel Activation for Efficient Alkaline Oxygen Evolution in Advanced Electrolyzers.

Designing robust and cost-effective electrocatalysts for efficient alkaline oxygen evolution reaction (OER) is of great significance in the field of water electrolysis. In this study, an electrochemical strategy to activate stainless steel (SS) electrodes for efficient OER is introduced. By cycling the SS electrode within a potential window that encompasses the Fe(II)↔Fe(III) process, its OER activity can be enhanced to a great extent compared to using a potential window that excludes this redox reaction, decreasing the overpotential at current density of 100 mA cm-2 by 40 mV. Electrochemical characterization, Inductively Coupled Plasma - Optical Emission Spectroscopy, and operando Raman measurements demonstrate that the Fe leaching at the SS surface can be accelerated through a Fe → γ-Fe2O3 → Fe3O4 or FeO → Fe2+ (aq.) conversion process, leading to the sustained exposure of Cr and Ni species. While Cr leaching occurs during its oxidation process, Ni species display higher resistance to leaching and gradually accumulate on the SS surface in the form of OER-active Fe-incorporated NiOOH species. Furthermore, a potential-pulse strategy is also introduced to regenerate the OER-activity of 316-type SS for stable OER, both in the three-electrode configuration (without performance decay after 300 h at 350 mA cm-2) and in an alkaline water electrolyzer (≈30 mV cell voltage increase after accelerated stress test-AST). The AST-stabilized cell can still reach 1000 and 4000 mA cm-2 at cell voltages of 1.69 and 2.1 V, which makes it competitive with state-of-the-art electrolyzers based on ion-exchange membrane using Ir-based anodes.

Cholesterol-Containing Liposomes Decorated With Au Nanoparticles as Minimal Tunable Fusion Machinery.

Membrane fusion is essential for the basal functionality of eukaryotic cells. In physiological conditions, fusion events are regulated by a wide range of specialized proteins, operating with finely tuned local lipid composition and ionic environment. Fusogenic proteins, assisted by membrane cholesterol and calcium ions, provide the mechanical energy necessary to achieve vesicle fusion in neuromediator release. Similar cooperative effects must be explored when considering synthetic approaches for controlled membrane fusion. We show that liposomes decorated with amphiphilic Au nanoparticles (AuLips) can act as minimal tunable fusion machinery. AuLips fusion is triggered by divalent ions, while the number of fusion events dramatically changes with, and can be finely tuned by, the liposome cholesterol content. We combine quartz-crystal-microbalance with dissipation monitoring (QCM-D), fluorescence assays, and small-angle X-ray scattering (SAXS) with molecular dynamics (MD) at coarse-grained (CG) resolution, revealing new mechanistic details on the fusogenic activity of amphiphilic Au nanoparticles (AuNPs) and demonstrating the ability of these synthetic nanomaterials to induce fusion regardless of the divalent ion used (Ca2+ or Mg2+ ). The results provide a novel contribution to developing new artificial fusogenic agents for next-generation biomedical applications that require tight control of the rate of fusion events (e.g., targeted drug delivery).

α-Synuclein interacts differently with membranes mimicking the inner and outer leaflets of neuronal membranes.

The toxicity of α-synuclein (α-syn), the amyloidogenic protein responsible for Parkinson's disease, is likely related to its interaction with the asymmetric neuronal membrane. α-Syn exists as cytoplasmatic and as extracellular protein as well. To shed light on the different interactions occurring at the different α-syn localizations, we have here modelled the external and internal membrane leaflets of the neuronal membrane with two complex lipid mixtures, characterized by phase coexistence and with negative charge confined to either the ordered or the disordered phase, respectively. To this purpose, we selected a five-component (DOPC/SM/DOPE/DOPS/chol) and a four-component (DOPC/SM/GM1/chol) lipid mixtures, which contained the main membrane lipid constituents and exhibited a phase separation with formation of ordered domains. We have compared the action of α-syn in monomeric form and at different concentrations (1 nM, 40 nM, and 200 nM) with respect to lipid systems with different composition and shape by AFM, QCM-D, and vesicle leakage experiments. The experiments coherently showed a higher stability of the membranes composed by the internal leaflet mixture to the interaction with α-syn. Damage to membranes made of the external leaflet mixture was detected in a concentration-dependent manner. Interestingly, the membrane damage was related to the fluidity of the lipid domains and not to the presence of negatively charged lipids.

Quantitative Super-Resolution Microscopy to Assess Adhesion of Neuronal Cells on Single-Layer Graphene Substrates.

Single Layer Graphene (SLG) has emerged as a critically important nanomaterial due to its unique optical and electrical properties and has become a potential candidate for biomedical applications, biosensors, and tissue engineering. Due to its intrinsic 2D nature, SLG is an ideal surface for the development of large-area biosensors and, due to its biocompatibility, can be easily exploited as a substrate for cell growth. The cellular response to SLG has been addressed in different studies with high cellular affinity for graphene often detected. Still, little is known about the molecular mechanism that drives/regulates the cellular adhesion and migration on SLG and SLG-coated interfaces with respect to other substrates. Within this scenario, we used quantitative super-resolution microscopy based on single-molecule localization to study the molecular distribution of adhesion proteins at the nanoscale level in cells growing on SLG and glass. In order to reveal the molecular mechanisms underlying the higher affinity of biological samples on SLG, we exploited stochastic optical reconstruction microscopy (STORM) imaging and cluster analysis, quantifying the super-resolution localization of the adhesion protein vinculin in neurons and clearly highlighting substrate-related correlations. Additionally, a comparison with an epithelial cell line (Chinese Hamster Ovary) revealed a cell dependent mechanism of interaction with SLG.

Emergence of Electric Fields at the Water-C12E6 Surfactant Interface.

We study the properties of the interface of water and the surfactant hexaethylene glycol monododecyl ether (C12E6) with a combination of heterodyne-detected vibrational sum frequency generation (HD-VSFG), Kelvin-probe measurements, and molecular dynamics (MD) simulations. We observe that the addition of the hydrogen-bonding surfactant C12E6, close to the critical micelle concentration (CMC), induces a drastic enhancement in the hydrogen bond strength of the water molecules close to the interface, as well as a flip in their net orientation. The mutual orientation of the water and C12E6 molecules leads to the emergence of a broad (∼3 nm) interface with a large electric field of ∼1 V/nm, as evidenced by the Kelvin-probe measurements and MD simulations. Our findings may open the door for the design of novel electric-field-tuned catalytic and light-harvesting systems anchored at the water-surfactant-air interface.

Cholesterol Hinders the Passive Uptake of Amphiphilic Nanoparticles into Fluid Lipid Membranes.

Plasma membranes represent pharmacokinetic barriers for the passive transport of site-specific drugs within cells. When engineered nanoparticles (NPs) are considered as transmembrane drug carriers, the plasma membrane composition can affect passive NP internalization in many ways. Among these, cholesterol-regulated membrane fluidity is probably one of the most biologically relevant. Herein, we consider small (2-5 nm in core diameter) amphiphilic gold NPs capable of spontaneously and nondisruptively entering the lipid bilayer of plasma membranes. We study their incorporation into model 1,2-dioleoyl-sn-glycero-3-phosphocholine membranes with increasing cholesterol content. We combine dissipative quartz crystal microbalance experiments, atomic force microscopy, and molecular dynamics simulations to show that membrane cholesterol, at biologically relevant concentrations, hinders the molecular mechanism for passive NP penetration within fluid bilayers, resulting in a dramatic reduction in the amount of NP incorporated.

Correlative nanoscopy: A multimodal approach to molecular resolution.

Atomic force microscopy (AFM) is a nano-mechanical tool uniquely suited for biological studies at the molecular scale. AFM operation is based on mechanical interaction between the tip and the sample, a mechanism of contrast capable of measuring different information, including surface topography, mechanical, and electrical properties. However, the lack of specificity highlights the need to integrate AFM data with other techniques providing compositional hints. In particular, optical microscopes based on fluorescence as a mechanism of contrast can access the local distribution of specific molecular species. The coupling between AFM and super-resolved fluorescence microscopy solves the resolution mismatch between AFM and conventional fluorescence optical microscopy. Recent advances showed that also the inherently label-free imaging capabilities of the AFM are fundamental to complement the fluorescence images. In this review, we have presented a brief historical view on correlative microscopy, and, finally, we have summarized the progress of correlative AFM-super-resolution microscopy in biological research.

Non-disruptive uptake of anionic and cationic gold nanoparticles in neutral zwitterionic membranes.

The potential toxicity of ligand-protected nanoparticles (NPs) on biological targets is crucial for their clinical translation. A number of studies are aimed at investigating the molecular mechanisms shaping the interactions between synthetic NPs and neutral plasma membranes. The role played by the NP surface charge is still widely debated. We compare, via liposome leakage assays, the perturbation induced by the penetration of sub-6 nm anionic and cationic Au NPs into model neutral lipid membranes composed of the zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Our charged Au NPs are functionalized by a mixture of the apolar 1-octanethiol and a ω-charged thiol which is either the anionic 11-mercapto-1-undecanesulfonate or the cationic (11-mercaptoundecyl)-N,N,N-trimethylammonium. In both cases, the NP uptake in the bilayer is confirmed by quartz crystal microbalance investigations. Our leakage assays show that both negatively and positively charged Au NPs do not induce significant membrane damage on POPC liposomes when penetrating into the bilayer. By means of molecular dynamics simulations, we show that the energy barrier for membrane penetration is the same for both NPs. These results suggest that the sign of the NP surface charge, per se, does not imply different physicochemical mechanisms of interaction with zwitterionic lipid membranes.

Amphiphilic gold nanoparticles perturb phase separation in multidomain lipid membranes.

Amphiphilic gold nanoparticles with diameters in the 2-4 nm range are promising as theranostic agents thanks to their spontaneous translocation through cell membranes. This study addresses the effects that these nanoparticles may have on a distinct feature of plasma membranes: lipid lateral phase separation. Atomic force microscopy, quartz crystal microbalance, and molecular dynamics are combined to study the interaction between model neuronal membranes, which spontaneously form ordered and disordered lipid domains, and amphiphilic gold nanoparticles having negatively charged surface functionalization. Nanoparticles are found to interact with the bilayer and form bilayer-embedded ordered aggregates. Nanoparticles also suppress lipid phase separation, in a concentration-dependent fashion. A general, yet simple thermodynamic model is developed to show that the change of lipid-lipid enthalpy is the dominant driving force towards the nanoparticle-induced destabilization of phase separation.

Graphene-enhanced differentiation of neuroblastoma mouse cells mediated by poly-D-lysine.

We compared the proliferation and differentiation of mouse neuroblastoma Neuro 2A cell line on single layer graphene and glass substrates. Quantitative and qualitative analysis of the cell proliferation and differentiation were performed, considering also the effect of a common adhesion factor, namely polylysine. We observed that on graphene substrates the cells proliferate faster with respect to glass; additionally, the presence of the adhesion factor enhances the difference and, remarkably, boosts the cell differentiation on the graphene-based interface. To understand the mechanism underlying a different cell behavior on the same adhesion coating, we carried out a physicochemical investigation of the studied interfaces (glass and graphene, bare and polylysine coated) by several techniques. In particular, we employed infrared spectroscopy to gain information on polylysine conformation, and atomic force microscopy force-distance curves to study adhesion properties at the surface. The results indicate that polylysine has an enhanced binding affinity for graphene, as well as a different molecular arrangement on graphene with respect to glass. These properties act as surface cues to trigger the cell response.

Bioresin-based superhydrophobic coatings with reduced bacterial adhesion.

HYPOTHESIS: Certain biobased polymers or natural compounds can be effectively used in superhydrophobic coating formulations to reduce environmental impact of fluorinated compounds and related bioaccumulation and toxicity problems. Many environmental concerns have thus far been raised in relation to toxicity of solvents and C8 fluorine chemicals. Elimination of these important elements from non-wettable coating formulations can jeopardize non-wetting performance significantly. However, intelligent and innovative approaches that introduce ecofriendly resins and compounds in superhydrophobic coating formulations without significantly altering self-cleaning superhydrophobicity are possible and being reported. EXPERIMENTS: Superhydrophobic coatings based on a biomass-derived bioresin polyfurfuryl alcohol (PFA) were prepared. The coatings were made by blending PFA resin with a C6 perfluorinated acrylic copolymer PFAC in solution and subsequent spray coating. Silica nanoparticles were also added in order to repel some common oils. Coating morphology, chemical and thermal properties, biocompatibility and bacterial adhesion properties were studied in detail. FINDINGS: Coatings having 50 wt% bioresin revealed equal water-repellency performance comapred to 100% PFAC-based coatings. Healthy cell growth was maintained on the coatings with no cell toxicity using human cell line, HeLa cells. Superhydrophobic coatings demonstrated very low bacterial adhesion to E. coli, S. aureus and Ps. aeruginosa indicating promising biofouling resistance. The coatings did not require any post thermal annealing. This would cause significant energy savings for large-scale adaptation.

Chromatin Compaction Multiscale Modeling: A Complex Synergy Between Theory, Simulation, and Experiment.

Understanding the mechanisms that trigger chromatin compaction, its patterns, and the factors they depend on, is a fundamental and still open question in Biology. Chromatin compacts and reinforces DNA and is a stable but dynamic structure, to make DNA accessible to proteins. In recent years, computational advances have provided larger amounts of data and have made large-scale simulations more viable. Experimental techniques for the extraction and reconstitution of chromatin fibers have improved, reinvigorating theoretical and experimental interest in the topic and stimulating debate on points previously considered as certainties regarding chromatin. A great assortment of approaches has emerged, from all-atom single-nucleosome or oligonucleosome simulations to various degrees of coarse graining, to polymer models, to fractal-like structures and purely topological models. Different fiber-start patterns have been studied in theory and experiment, as well as different linker DNA lengths. DNA is a highly charged macromolecule, making ionic and electrostatic interactions extremely important for chromatin topology and dynamics. Indeed, the repercussions of varying ionic concentration have been extensively examined at the computational level, using all-atom, coarse-grained, and continuum techniques. The presence of high-curvature AT-rich segments in DNA can cause conformational variations, attesting to the fact that the role of DNA is both structural and electrostatic. There have been some tentative attempts to describe the force fields governing chromatin conformational changes and the energy landscapes of these transitions, but the intricacy of the system has hampered reaching a consensus. The study of chromatin conformations is an intrinsically multiscale topic, influenced by a wide range of biological and physical interactions, spanning from the atomic to the chromosome level. Therefore, powerful modeling techniques and carefully planned experiments are required for an overview of the most relevant phenomena and interactions. The topic provides fertile ground for interdisciplinary studies featuring a synergy between theoretical and experimental scientists from different fields and the cross-validation of respective results, with a multi-scale perspective. Here, we summarize some of the most representative approaches, and focus on the importance of electrostatics and solvation, often overlooked aspects of chromatin modeling.

Poly(furfuryl alcohol)-Polycaprolactone Blends.

Poly(furfuryl alcohol) (PFA) is a bioresin synthesized from furfuryl alcohol (FA) that is derived from renewable saccharide-rich biomass. In this study, we compounded this bioresin with polycaprolactone (PCL) for the first time, introducing new functional polymer blends. Although PCL is biodegradable, its production relies on petroleum precursors such as cyclohexanone oils. With the method proposed herein, this dependence on petroleum-derived precursors/monomers is reduced by using PFA without significantly modifying some important properties of the PCL. Polymer blend films were produced by simple solvent casting. The blends were characterized in terms of surface topography by atomic force microscopy (AFM), chemical interactions between PCL and PFA by attenuated total reflection-Fourier transform infrared (ATR-FTIR), crystallinity by XRD, thermal properties by differential scanning calorimetry (DSC), and mechanical properties by tensile tests and biocompatibility by direct and indirect toxicity tests. PFA was found to improve the gas barrier properties of PCL without compromising its mechanical properties, and it demonstrated sustained antioxidant effect with excellent biocompatibility. Our results indicate that these new blends can be potentially used in diverse applications ranging from food packing to biomedical devices.

Polymer Coating and Lipid Phases Regulate Semiconductor Nanorods' Interaction with Neuronal Membranes: A Modeling Approach.

The interplay between nanoparticles (NPs) and cell membranes is extremely important with regard to using NPs in biology applications. With the aim of unraveling the dominating factors on the molecular scale, we have studied the interaction between polymer-coated semiconductor nanorods (NRs) made of cadmium selenium/cadmium sulfur and model lipid membranes. The zeta potential (ζ) of the NRs was tuned from having a negative value (-24 mV) to having a positive one (+11 mV) by changing the amine content in the polymer coating. Supported lipid bilayers (SLBs) and lipid monolayers (LMs) were used as model membranes. Lipid mixtures containing anionic or cationic lipids were employed in order to change the membrane ζ from -77 to +49 mV; lipids with saturated hydrophobic chains were used to create phase-separated gel domains. NR adsorption to the SLBs was monitored by quartz crystal microbalance with dissipation monitoring; interactions with LMs with the same lipid composition were measured by surface pressure-area isotherms. The results showed that the NRs only interact with the model membrane if the mutual Δζ is higher than 70 mV; at the air-water interface, positively charged NRs remove lipids from the anionic lipid mixtures, and the negative ones penetrate the space between the polar heads in the cationic mixtures. However, the presence of gel domains in the membrane inhibits this interaction. The results of the Derjaguin-Landau-Verwey-Overbeek model frame indicate that the interaction occurs not only due to electrostatic and van der Waals forces, but also due to steric and/or hydration forces.

Scanning Kelvin Probe Microscopy: Challenges and Perspectives towards Increased Application on Biomaterials and Biological Samples.

We report and comment on the possible increase of application of scanning Kelvin probe microscopy (SKPM) for biomaterials, biological substrates, and biological samples. First, the fundamental concepts and the practical limitations of SKPM are presented, pointing out the difficulties in proper probe calibration. Then, the most relevant literature on the use of SKPM on biological substrates and samples is briefly reviewed. We report first about biocompatible surfaces used as substrates for subsequent biological applications, such as cultures of living cells. Then, we briefly review the SKPM measurements made on proteins, DNA, and similar biomolecular systems. Finally, some considerations about the perspectives for the use of SKPM in the field of life sciences are made. This work does not pretend to provide a comprehensive view of this emerging scenario, yet we believe that it is time to put these types of application of SKPM under focus, and to face the related challenges, such as measuring in liquid and quantitative comparison with other techniques for the electrical potential readout.

Toxic HypF-N Oligomers Selectively Bind the Plasma Membrane to Impair Cell Adhesion Capability.

The deposition of fibrillar protein aggregates in human organs is the hallmark of several pathological states, including highly debilitating neurodegenerative disorders and systemic amyloidoses. It is widely accepted that small oligomers arising as intermediates in the aggregation process, released by fibrils, or growing in secondary nucleation steps are the cytotoxic entities in protein-misfolding diseases, notably neurodegenerative conditions. Increasing evidence indicates that cytotoxicity is triggered by the interaction between nanosized protein aggregates and cell membranes, even though little information on the molecular details of such interaction is presently available. In this work, we propose what is, to our knowledge, a new approach, based on the use of single-cell force spectroscopy applied to multifunctional substrates, to study the interaction between protein oligomers, cell membranes, and/or the extracellular matrix. We compared the interaction of single Chinese hamster ovary cells with two types of oligomers (toxic and nontoxic) grown from the N-terminal domain of the Escherichia coli protein HypF. We were able to quantify the affinity between both oligomer type and the cell membrane by measuring the mechanical work needed to detach the cells from the aggregates, and we could discriminate the contributions of the membrane lipid and protein fractions to such affinity. The fundamental role of the ganglioside GM1 in the membrane-oligomers interaction was also highlighted. Finally, we observed that the binding of toxic oligomers to the cell membrane significantly affects the functionality of adhesion molecules such as Arg-Gly-Asp binding integrins, and that this effect requires the presence of the negatively charged sialic acid moiety of GM1.

Amyloid and membrane complexity: The toxic interplay revealed by AFM.

Lipid membranes play a fundamental role in the pathological development of protein misfolding diseases. Several pieces of evidence suggest that the lipid membrane could act as a catalytic surface for protein aggregation. Furthermore, a leading theory indicates the interaction between the cell membrane and misfolded oligomer species as the responsible for cytotoxicity, hence, for neurodegeneration in disorders such as Alzheimer's and Parkinson's disease. The definition of the mechanisms that drive the interaction between pathological protein aggregates and plasma membrane is fundamental for the development of effective therapies for a large class of diseases. Atomic force microscopy (AFM) has been employed to study how amyloid aggregates affect the cell physiological properties. Considerable efforts were spent to characterize the interaction with model systems, i.e., planar supported lipid bilayers, but some works also addressed the problem directly on living cells. Here, an overview of the main works involving the use of the AFM on both model system and living cells will be provided. Different kind of approaches will be presented, as well as the main results derived from the AFM analysis.

Biocompatibility of a Magnetic Tunnel Junction Sensor Array for the Detection of Neuronal Signals in Culture.

Magnetoencephalography has been established nowadays as a crucial in vivo technique for clinical and diagnostic applications due to its unprecedented spatial and temporal resolution and its non-invasive methods. However, the innate nature of the biomagnetic signals derived from active biological tissue is still largely unknown. One alternative possibility for in vitro analysis is the use of magnetic sensor arrays based on Magnetoresistance. However, these sensors have never been used to perform long-term in vitro studies mainly due to critical biocompatibility issues with neurons in culture. In this study, we present the first biomagnetic chip based on magnetic tunnel junction (MTJ) technology for cell culture studies and show the biocompatibility of these sensors. We obtained a full biocompatibility of the system through the planarization of the sensors and the use of a three-layer capping of SiO2/Si3N4/SiO2. We grew primary neurons up to 20 days on the top of our devices and obtained proper functionality and viability of the overlying neuronal networks. At the same time, MTJ sensors kept their performances unchanged for several weeks in contact with neurons and neuronal medium. These results pave the way to the development of high performing biomagnetic sensing technology for the electrophysiology of in vitro systems, in analogy with Multi Electrode Arrays.

Developmental refinement of synaptic transmission on micropatterned single layer graphene.

Interfacing neurons with graphene, a single atomic layer of sp2 hybridized C-atoms, is a key paradigm in understanding how to exploit the unique properties of such a two-dimensional system for neural prosthetics and biosensors development. In order to fabricate graphene-based circuitry, a reliable large area patterning method is a requirement. Following a previously developed protocol, we monitored the in vitro neuronal development of geometrically ordered neural network growing onto patterned Single Layer Graphene (SLG) coated with poly-D-lysine. The microscale patterns were fabricated via laser micromachining and consisted of SLG stripes separated by micrometric ablated stripes. A comprehensive analysis of the biointerface was carried out combining the surface characterization of SLG transferred on the glass substrates and Immunohistochemical (IHC) staining of the developing neural network. Neuronal and glial cells proliferation, as well as cell viability, were compared on glass, SLG and SLG-patterned surfaces. Further, we present a comparative developmental study on the efficacy of synaptic transmission on control glass, on transferred SLG, and on the micropatterned SLG substrates by recording miniature post synaptic currents (mPSCs). The mPSC frequencies and amplitudes obtained on SLG-stripes, SLG only and on glass were compared. Our results indicate a very similar developmental trend in the three groups, indicating that both SLG and patterned SLG preserve synaptic efficacy and can be potentially exploited for the fabrication of large area devices for neuron sensing or stimulation. STATEMENT OF SIGNIFICANCE: This paper compares the morphological and functional development of neural networks forming on glass, on Single Layer Graphene (SLG) and on microsized patterned SLG substrates after neuron spontaneous migration. Neurons developing on SLG are viable after two weeks in vitro, and, on SLG, glial cell proliferation is enhanced. The functionality of the neural networks is demonstrated by measuring the development of neuron synapses in the first and second week in vitro. Preserving the neuron synaptic efficacy, both homogeneous and patterned interfaces based on graphene can be potentially exploited for the fabrication of large area devices for neuron sensing or stimulation, as well as for next generation of bio-electronic systems, to be used as brain-interfaces.

Selective Targeting of Neurons with Inorganic Nanoparticles: Revealing the Crucial Role of Nanoparticle Surface Charge.

Nanoparticles (NPs) are increasingly used in biomedical applications, but the factors that influence their interactions with living cells need to be elucidated. Here, we reveal the role of NP surface charge in determining their neuronal interactions and electrical responses. We discovered that negatively charged NPs administered at low concentration (10 nM) interact with the neuronal membrane and at the synaptic cleft, whereas positively and neutrally charged NPs never localize on neurons. This effect is shape and material independent. The presence of negatively charged NPs on neuronal cell membranes influences the excitability of neurons by causing an increase in the amplitude and frequency of spontaneous postsynaptic currents at the single cell level and an increase of both the spiking activity and synchronous firing at neural network level. The negatively charged NPs exclusively bind to excitable neuronal cells, and never to nonexcitable glial cells. This specific interaction was also confirmed by manipulating the electrophysiological activity of neuronal cells. Indeed, the interaction of negatively charged NPs with neurons is either promoted or hindered by pharmacological suppression or enhancement of the neuronal activity with tetrodotoxin or bicuculline, respectively. We further support our main experimental conclusions by using numerical simulations. This study demonstrates that negatively charged NPs modulate the excitability of neurons, revealing the potential use of NPs for controlling neuron activity.