Fabrication of corona-free nanoparticles with tunable hydrophobicity

Zwitterionic Stealth Dye-Loaded Polymer Nanoparticles for Intracellular Imaging

Intracellular applications of fluorescent nanoparticles (NPs) as probes and labels are currently limited by significant molecular crowding and the high level of complexity encountered inside living cells. The solution is to develop very small, bright, and noninteracting (stealth) NPs. Combining these properties requires implementing the stealth behavior through the thinnest possible hydrophilic shell. Here, we propose a one-step process for preparing ultrasmall and bright stealth NPs based on a zwitterionic (ZI) methacrylate-based copolymer. Dye-loaded polymer NPs are assembled through nanoprecipitation of the copolymer together with the salt of a rhodamine B derivative and a bulky hydrophobic counterion to achieve high particle brightness. We found that 10 mol % ZI groups in the polymer yield NPs of less than 15 nm that are stable in physiological salt conditions and practically resistant to protein adsorption, as suggested by fluorescence correlation spectroscopy. The combination of the very small size with the nonfouling nature of these particles enables spreading of ZI polymer NPs in the whole cytosol after their microinjection into living cells. In addition, single-particle tracking showed up to four times faster diffusion of ZI NPs in the cytosol compared to PEGylated NPs. The obtained dye-loaded ZI polymer NPs open the route to intracellular single-particle tracking and biosensing applications.

Gold nanoclusters for biomedical applications: toward in vivo studies

In parallel with the rapidly growing and widespread use of nanomedicine in the clinic, we are also witnessing the development of so-called theranostic agents that combine diagnostic and therapeutic properties.

Overcoming Hurdles in Nanoparticle Clinical Translation: The Influence of Experimental Design and Surface Modification

Nanoparticles are becoming an increasingly popular tool for biomedical imaging and drug delivery. While the prevalence of nanoparticle drug-delivery systems reported in the literature increases yearly, relatively little translation from the bench to the bedside has occurred. It is crucial for the scientific community to recognize this shortcoming and re-evaluate standard practices in the field, to increase clinical translatability. Currently, nanoparticle drug-delivery systems are designed to increase circulation, target disease states, enhance retention in diseased tissues, and provide targeted payload release. To manage these demands, the surface of the particle is often modified with a variety of chemical and biological moieties, including PEG, tumor targeting peptides, and environmentally responsive linkers. Regardless of the surface modifications, the nano-bio interface, which is mediated by opsonization and the protein corona, often remains problematic. While fabrication and assessment techniques for nanoparticles have seen continued advances, a thorough evaluation of the particle's interaction with the immune system has lagged behind, seemingly taking a backseat to particle characterization. This review explores current limitations in the evaluation of surface-modified nanoparticle biocompatibility and in vivo model selection, suggesting a promising standardized pathway to clinical translation.

One-pot synthesis and characterization of ovalbumin-conjugated gold nanoparticles: A comparative study of adjuvanticity against the physical mixture of ovalbumin and gold nanoparticles

Only few adjuvants are licensed for use in humans and there is a need to develop safe and improved vaccine adjuvants. In this study, we report the one-pot synthesis of antigen ovalbumin (OVA)-conjugated gold nanoparticles (OVA@GNPs). A systematical study was performed by comparing OVA@GNPs with the simple mixture of OVA and gold nanoparticles (OVA+GNPs), including their physiochemical properties through spectrometric and electrophoretic analysis, in vitro stability, cytotoxicity and cellular uptake, and in vivo humoral immune responses following subcutaneous and transcutaneous immunization in mice. The results demonstrate a much stronger interaction between protein and GNPs in OVA@GNPs than OVA+GNPs, which makes OVA@GNPs more stable under in vitro conditions than OVA+GNPs with the ability to induce 4 times higher OVA-specific serum IgG titers following subcutaneous immunization. We also show the dose sparing of OVA@GNPs, as the dosage for aluminum adjuvant required to reach to an equivalent OVA-specific antibody titer was almost five times higher than OVA@GNPs. However, we found that the co-administration of small-sized GNPs had a limited ability for the transcutaneous delivery of OVA. These results demonstrate the potential application of one-pot synthesis approach for producing antigen protein-conjugated gold nanoparticles for vaccine delivery.

Nanoscale Technologies for Prevention and Treatment of Heart Failure: Challenges and Opportunities

The adult myocardium has a limited regenerative capacity following heart injury, and the lost cells are primarily replaced by fibrotic scar tissue. Suboptimal efficiency of current clinical therapies to resurrect the infarcted heart results in injured heart enlargement and remodeling to maintain its physiological functions. These remodeling processes ultimately leads to ischemic cardiomyopathy and heart failure (HF). Recent therapeutic approaches (e.g., regenerative and nanomedicine) have shown promise to prevent HF postmyocardial infarction in animal models. However, these preclinical, clinical, and technological advancements have yet to yield substantial enhancements in the survival rate and quality of life of patients with severe ischemic injuries. This could be attributed largely to the considerable gap in knowledge between clinicians and nanobioengineers. Development of highly effective cardiac regenerative therapies requires connecting and coordinating multiple fields, including cardiology, cellular and molecular biology, biochemistry and chemistry, and mechanical and materials sciences, among others. This review is particularly intended to bridge the knowledge gap between cardiologists and regenerative nanomedicine experts. Establishing this multidisciplinary knowledge base may help pave the way for developing novel, safer, and more effective approaches that will enable the medical community to reduce morbidity and mortality in HF patients.

Zwitterion-Functionalized Detonation Nanodiamond with Superior Protein Repulsion and Colloidal Stability in Physiological Media

Nanodiamond (ND) is a versatile and promising material for bioapplications. Despite many efforts, agglomeration of nanodiamond and the nonspecific adsorption of proteins on the ND surface when exposed to biofluids remains a major obstacle for biomedical applications. Here, the functionalization of detonation nanodiamond with zwitterionic moieties in combination with tetraethylene glycol (TEG) moieties immobilized by click chemistry to improve the colloidal dispersion in physiological media with strong ion background and for the simultaneous prevention of nonspecific interactions with proteins is reported. Based on five building blocks, a series of ND conjugates is synthesized and their performance is compared in biofluids, such as fetal bovine serum (FBS) and Dulbecco's modified Eagle medium (DMEM). The adsorption of proteins is investigated via dynamic light scattering (DLS) and thermogravimetric analysis. The colloidal stability is tested with DLS monitoring over prolonged periods of time in various ratios of water/FBS/DMEM and at different pH values. The results show that zwitterions efficiently promote the anti-fouling properties, whereas the TEG linker is essential for the enhanced colloidal stability of the particles.

Tailoring the component of protein corona via simple chemistry

Control over the protein corona of nanomaterials allows them to function better. Here, by taking graphene/gold as examples, we comprehensively assessed the association of surface properties with the protein corona. As revealed by in vitro measurements and computations, the interaction between graphene/gold and HSA/IgE was inversely correlated with the hydroxyl group availability, whereas the interaction between that and ApoE was comparatively less relevant. Molecular simulations revealed that the number and the distribution of surface hydroxyl groups could regulate the manner in which nanomaterials interact with proteins. Moreover, we validated that ApoE pre-adsorption before injection enhances the blood circulation of nanomaterials relative to their pristine and IgE-coated counterparts. This benefit can be attributed to the invulnerability of the complementary system provided by ApoE, whose encasement does not increase cytotoxicity. Overall, this study offers a robust yet simple way to create protein corona enriched in dysopsonins to realize better delivery efficacy.

The interaction between proteins and nanomaterials is complex and of interest for controlling nanoparticle fate. Here, using experimental and computational methods, the authors report on the effect of hydroxyl groups on protein interaction and how they can be used to enhance circulation times.

Impact of Protein Corona in Nanoflare-Based Biomolecular Detection and Quantification

Selective detection and precise quantification of biomolecules in intracellular settings play a pivotal role in the diagnostics and therapeutics of diseases, including various cancers and infectious epidemics. Because of this clinical relevance, nanoprobes with high sensitivity, wide tunability, and excellent biological stability have become of high demand. In particular, nanoflares based on gold nanoparticles have emerged as an attractive candidate for intracellular detection due to their efficient cellular uptake, enhanced binding affinity with complementary targets, and improved biological compatibility. However, nanoprobes, including these nanoflares, are known to be susceptible to the adsorption of proteins present in the biological environment, which leads to the formation of a so-called protein corona layer on their surface, leading to an altered targeting efficiency and cellular uptake. In this work, we leverage the nanoflares platform to demonstrate the effect of protein corona on biomolecular detection, quantification, as well as biological stability against enzymatic degradation. Nanoflares incubated in a biologically relevant concentration of serum albumin proteins (0.50 wt %) were shown to result in more than 20% signal reduction in target detection, with a decrease varying proportionally with the protein concentrations. In addition, similar signal reduction was observed for different serum proteins, and PEG backfilling was found to be ineffective in mitigating the negative impact induced by the corona formation. Furthermore, nuclease resistance in nanoflares was also severely compromised by the presence of the corona shell (∼2-fold increase in hydrolysis activity). This work demonstrates the consequences of an in situ formed protein corona layer on molecular detection/quantification and biological stability of nanoflares in the presence of nuclease enzymes, highlighting the importance of calibrating similar nanoprobes in proper biological media to improve the accuracy of molecular detection and quantification.

Elucidating the Role of Surface Coating in the Promotion or Prevention of Protein Corona around Quantum Dots

Nonspecific interactions in biological media can lead to the formation of a protein corona around nanocolloids, which tends to alter their behavior and limit their effectiveness when used as probes for imaging or sensing applications. Yet, understanding the corona buildup has been challenging. We hereby investigate these interactions using luminescent quantum dots (QDs) as a model nanocolloid system, where we carefully vary the nature of the hydrophilic block in the surface coating, while maintaining the same dihydrolipoic acid (DHLA) bidentate coordinating motif. We first use agarose gel electrophoresis to track changes in the mobility shift upon exposure of the QDs to protein-rich media. We find that QDs capped with DHLA (which presents a hydrophobic alkyl chain terminated with a carboxyl group) promote corona formation, in a concentration-dependent manner. However, when a polyethylene glycol block or a zwitterion group is appended onto DHLA, it yields a coating that prevents corona buildup. Our results clearly confirm that nonspecific interactions with protein-rich media are strongly dependent on the nature of the hydrophilic motif used. Additional gel experiments using SDS-PAGE have allowed further characterization of the corona protein, and showed that mainly a soft corona forms around the DHLA-capped QDs. These findings will be highly informative when designing nanocolloids that can find potential use in biological applications.

Biomimetic Immunomagnetic Nanoparticles with Minimal Nonspecific Biomolecule Adsorption for Enhanced Isolation of Circulating Tumor Cells

Immunomagnetic micro/nanoparticles (IMNs) have been widely used to isolate rare circulating tumor cells (CTCs) from blood samples for early diagnosis of cancers. However, when entering into biofluids, IMNs nonspecifically adsorb biomolecules and the in situ formed biomolecule corona covers IMN surface ligands and weakens the targeting capabilities of IMNs. In this work, we demonstrated that by surface coating of IMNs with red blood cell (RBC)-derived vesicles, the obtained biomimetic particles (RBC-IMNs) basically adsorb no biomolecules and maintain the CTC targeting ability when exposed to plasma. Compared to IMNs, RBC-IMNs exhibited an excellent cell isolation efficiency in spiked blood samples, which was improved to 95.71% from 60.22%. Furthermore, by using RBC-IMNs, we successfully isolated CTCs in 28 out of 30 prostate cancer patient blood samples and further showed the robustness of RBC-IMNs in downstream cell sequencing. The work presented here provides a new insight into developing targeted nanomaterials for biological and medical applications.

Shielding and stealth effects of zwitterion moieties in double-functionalized silica nanoparticles

Surface functionalization of silica nanoparticles (SiO₂NPs) has been considered as a promising strategy to develop target-specific nanostructures. However, finding a chemical functionalization that can be used as an active targeting moiety while preserving the nanoparticles colloidal stability in biological fluids is still challenging. We present here a dual surface modification strategy for SiO₂NPs where a zwitterion (ZW) and a biologically active group (BAG) (amino, mercapto or carboxylic functionalities) are simultaneously grafted on the nanoparticles' surface. The rationale behind this strategy is to generate colloidally stable nanoparticles and avoid the nonspecific protein adsorption due to ZW groups insertion, while the effective interaction with biosystems is guaranteed by the BAGs presence. The biological efficacy was tested against VERO cells, E. coli bacteria and Zika viruses and a similar trend was observed for all tested particles. The desirable "stealth property" to prevent nonspecific protein adhesion also generated a ZW shielding effect of the BAG functionality hindering their proper interaction and activity in cells, bacteria and viruses.

Monitoring the Changes of pH in Lysosomes during Autophagy and Apoptosis by Plasmon Enhanced Raman Imaging

Lysosomes are acidic organelles that not only participate in intracellular degradation but also relate to various cellular functions. Abnormal pH in lysosomes would lead to lysosomal dysfunction, which may further result in many diseases. In this work, we statistically analyze the pH change in the lysosomes of HeLa cells model by using surface enhanced Raman scattering (SERS) imaging technique. We prepared a plasmon Raman pH probe and localized the pH probe to lysosomes via an incubation-depletion method. The pH profiles within lysosomes during the process of cellular autophagy and apoptosis were monitored in situ by SERS imaging. The pH in lysosomes decreased slightly during the process of autophagy, while the pH in lysosomes increased during apoptosis. The phenomenon, in general, is consistent with our current biological knowledge. However, we did not observe significant variation of pH between different individual cells. This information might provide an in depth understanding about the relationship of lysosomal pH with fundamental cellular functions and mechanism of diseases.

In silico profiling nanoparticles: predictive nanomodeling using universal nanodescriptors and various machine learning approaches

Rational nanomaterial design is urgently demanded for new nanomaterial development with desired properties. However, computational nanomaterial modeling and virtual nanomaterial screening are not applicable for this purpose due to the complexity of nanomaterial structures. To address this challenge, a new computational workflow is established in this study to virtually profile nanoparticles by (1) constructing a structurally diverse virtual gold nanoparticle (GNP) library and (2) developing novel universal nanodescriptors. The emphasis of this study is the second task by developing geometrical nanodescriptors that are suitable for the quantitative modeling of GNPs and virtual screening purposes. The feasibility, rigor and applicability of this novel computational method are validated by testing seven GNP datasets consisting of 191 unique GNPs of various nano-bioactivities and physicochemical properties. The high predictability of the developed GNP models suggests that this workflow can be used as a universal tool for nanomaterial profiling and rational nanomaterial design.

Ligand density on nanoparticles: A parameter with critical impact on nanomedicine

Nanoparticles modified with ligands for specific targeting towards receptors expressed on the surface of target cells are discussed in literature towards improved delivery strategies. In such concepts the ligand density on the surface of the nanoparticles plays an important role. How many ligands per nanoparticle are best for the most efficient delivery? Importantly, this number may be different for in vitro and in vivo scenarios. In this review first viruses as "biological" nanoparticles are analyzed towards their ligand density, which is then compared to the ligand density of engineered nanoparticles. Then, experiments are reviewed in which in vitro and in vivo nanoparticle delivery has been analyzed in terms of ligand density. These results help to understand which ligand densities should be attempted for better targeting. Finally synthetic methods for controlling the ligand density of nanoparticles are described.

Concepts of nanoparticle cellular uptake, intracellular trafficking, and kinetics in nanomedicine

Nanoparticle-based therapeutics and diagnostics are commonly referred to as nanomedicine and may significantly impact the future of healthcare. However, the clinical translation of these technologies is challenging. One of these challenges is the efficient delivery of nanoparticles to specific cell populations and subcellular targets in the body to elicit desired biological and therapeutic responses. It is critical for researchers to understand the fundamental concepts of how nanoparticles interact with biological systems to predict and control in vivo nanoparticle transport for improved clinical benefit. In this overview article, we review and discuss cellular internalization pathways, summarize the field`s understanding of how nanoparticle physicochemical properties affect cellular interactions, and explore and discuss intracellular nanoparticle trafficking and kinetics. Our overview may provide a valuable resource for researchers and may inspire new studies to expand our current understanding of nanotechnology-biology interactions at cellular and subcellular levels with the goal to improve clinical translation of nanomedicines.

Bioorthogonal nanozymes: progress towards therapeutic applications

Bioorthogonal nanocatalysts in the form of 'nanozymes', are promising tools for generating imaging and therapeutic molecules in living systems. These systems use transformations developed by synthetic chemists to effect transformations that cannot be performed by cellular machinery. This emerging platform is rapidly evolving towards the creation of smart nanodevices featuring the capabilities of their enzyme prototypes, modulating catalytic activity through structure as well as chemical and physical signals. Here we describe different strategies to fabricate these nanocatalysts and their potential in diagnostic and therapeutic applications.

Role of Ligand Conformation on Nanoparticle-Protein Interactions

Engineered biomedical nanoparticles (NPs) administered via intravenous routes are prone to associate to serum proteins. The protein corona can mask the NP surface functionalization and hamper the delivery of the NP to its biological target. The design of corona-free NPs relies on our understanding of the chemical-physical features of the NP surface driving the interaction with serum proteins. Here, we address, by computational means, the interaction between human serum albumin (HSA) and a prototypical monolayer-protected Au nanoparticle. We show that both the chemical composition (charge, hydrophobicity) and the conformational preferences of the ligands decorating the NP surface affect the NP propensity to bind HSA.

Label-free plasmonic nanostar probes to illuminate in vitro membrane receptor recognition

Protein-ligand recognition is a key activity where chemical signals are communicated to cells to activate various biochemical pathways, which are important for understanding membrane signaling and drug interactions. Gold nanostars are highly attractive for biological applications due to their readily modified surface chemistry, facile synthesis and optical properties. The increase in electromagnetic field at their branches increases the surface enhanced Raman scattering (SERS) making them ideal candidates as label free in vitro probes that can be used to detect a variety of cellular activities. However, the use of particles in vitro is complicated by the adsorption of proteins, which forms the protein corona. In this paper we demonstrate gold nanostars as label free in vitro probes to study the interaction between αvβ3 integrin and RGD. Nanostars functionalized with cyclic-RDGFC reduced the formation of the protein corona, due to its zwitterionic nature, indicating a small peptide approach to minimizing protein absorption. Additionally, the functionalized nanostars evince a SERS response from their interaction with αvβ3 integrin representative of the amino acids present at the binding site which is also retained in a complex biological matrix. The nanostars were used in vitro to selectively detect αvβ3 integrin on the membrane of human metastatic colon cancer cells. By exploiting the intense SERS and tunable plasmon resonance properties of gold nanostars functionalized with cyclic RGDFC, we have demonstrated a label free approach to investigate the chemical interactions associated with protein-ligand binding from both purified proteins and membrane bound receptors in cells.

Viral nanoparticles can elude protein barriers: exploiting rather than imitating nature

Protein-corona formation in body fluids and/or entrapment of nanoparticles in protein matrices (e.g. food and mucus) can hinder the delivery of nanoparticles, irrespective of the route of administration. Here we demonstrate that certain viral nanoparticles (VNPs) can evade the adhesion of a broad panel of macromolecules from several biological milieus. We also show that the permeability of VNPs through mucin gels is far superior to that of synthetic nanoparticles. The non-sticky nature of VNPs implies that they will be able to readily cross most non-specific protein and glycoprotein barriers encountered, ubiquitously, upon administration through mucosal, and non-mucosal routes.

Solution NMR Spectroscopy with Isotope-Labeled Cysteine (13C and 15N) Reveals the Surface Structure of l-Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)

Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as ¹³C-labeled and ¹⁵N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including ¹H-¹³C-heteronuclear single-quantum coherence and ¹³C-¹³C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy (¹H-, ¹³C-, and ¹H-¹³C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au₁₇₄(cysteine)₆₇.

In Situ Characterization of Protein Corona Formation on Silica Microparticles Using Confocal Laser Scanning Microscopy Combined with Microfluidics

In biological fluids, proteins bind to particles, forming so-called protein coronas. Such adsorbed protein layers significantly influence the biological interactions of particles, both in vitro and in vivo. The adsorbed protein layer is generally described as a two-component system comprising "hard" and "soft" protein coronas. However, a comprehensive picture regarding the protein corona structure is lacking. Herein, we introduce an experimental approach that allows for in situ monitoring of protein adsorption onto silica microparticles. The technique, which mimics flow in vascularized tumors, combines confocal laser scanning microscopy with microfluidics and allows the study of the time-evolution of protein corona formation. Our results show that protein corona formation is kinetically divided into three different phases: phase 1, proteins irreversibly and directly bound (under physiologically relevant conditions) to the particle surface; phase 2, irreversibly bound proteins interacting with preadsorbed proteins, and phase 3, reversibly bound "soft" protein corona proteins. Additionally, we investigate particle-protein interactions on low-fouling zwitterionic-coated particles where the adsorption of irreversibly bound proteins does not occur, and on such particles, only a "soft" protein corona is formed. The reported approach offers the potential to define new state-of-the art procedures for kinetics and protein fouling experiments.

Length of the Stabilizing Zwitterionic Poly(2-methacryloyloxyethyl phosphorycholine) Block Influences the Activity of the Conjugated Arsenic Drug in Drug-Directed Polymerization-Induced Self-Assembly Particles

We report on the synthesis of poly(2-methacryloyloxyethyl phosphorycholine-co-PENAO)-block-poly(methyl methacrylate) core-shell nanoparticles which carry different chain lengths of zwitterionic 2-methacryloyloxyethyl phosphorycholine (MPC) on a nanoparticle surface. The particles, 30-40 nm in size, were readily obtained by polymerization-induced self-assembly (PISA) of the corresponding arsenic-based MPC polymers as the stabilizer block and methyl methacrylate (MMA) as the core-forming block. Zwitterionic nanoparticles are ideal candidates for protein-repellent materials. Herein, we show how the decrease of zwitterionic chain lengths tunes the reactivity and cytotoxicity of the organoarsenical anticancer drug PENAO (4-(N-(S-penicillaminylacetyl)amino) phenylarsonous acid). More cytotoxic (5-fold) nanoparticles were obtained when the MPC chain lengths were condensed from 37 to 13 repeating units. To gain a better understanding of the behavior of the drug-directed PISA particles, small-angle neutron scattering (SANS) experiments were conducted, evidencing that having PENAO located in the hydrophilic building block indeed influences the physiochemical micelle structure in terms of core radius (r_core), SLD, shell thickness, and aggregation number.

Protein⁻Polyelectrolyte Interaction: Thermodynamic Analysis Based on the Titration Method †

This review discussed the mechanisms including theories and binding stages concerning the protein⁻polyelectrolyte (PE) interaction, as well as the applications for both complexation and coacervation states of protein⁻PE pairs. In particular, this review focused on the applications of titration techniques, that is, turbidimetric titration and isothermal titration calorimetry (ITC), in understanding the protein⁻PE binding process. To be specific, by providing thermodynamic information such as pHc, pHφ, binding constant, entropy, and enthalpy change, titration techniques could shed light on the binding affinity, binding stoichiometry, and driving force of the protein⁻PE interaction, which significantly guide the applications by utilization of these interactions. Recent reports concerning interactions between proteins and different types of polyelectrolytes, that is, linear polyelectrolytes and polyelectrolyte modified nanoparticles, are summarized with their binding differences systematically discussed and compared based on the two major titration techniques. We believe this short review could provide valuable insight in the understanding of the structure⁻property relationship and the design of applied biomedical PE-based systems with optimal performance.

Small protein sequences can induce cellular uptake of complex nanohybrids

In this letter, we report on the ability of functional fusion proteins presenting a lytic gamma peptide, to promote interactions with HeLa cells and delivery of large hybrid nanostructures.

Anionic nanoparticle-lipid membrane interactions: the protonation of anionic ligands at the membrane surface reduces membrane disruption

Monolayer-protected gold nanoparticles (Au NPs) are promising biomedical tools with applications in diagnosis and therapy, thanks to their biocompatibility and versatility. Here we show how the NP surface functionalization can drive the mechanism of interaction with lipid membranes. In particular, we show that the spontaneous protonation of anionic carboxylic groups on the NP surface can make the NP-membrane interaction faster and less disruptive.

The interaction between anionic Au nanoparticles and model lipid membranes is facilitated by the spontaneous protonation of the NP ligand carboxylate groups, COO⁻˙ → COOH, in the lipid headgroup region.

Cationic Silver Nanoclusters as Potent Antimicrobials against Multidrug-Resistant Bacteria

Bacterial multidrug resistance (MDR) is a serious healthcare issue caused by the long-term subtherapeutic clinical treatment of infectious diseases. Nanoscale engineering of metal nanoparticles has great potential to address this issue by tuning the nano-bio interface to target bacteria. Herein, we report the use of branched polyethylenimine-functionalized silver nanoclusters (bPEI-Ag NCs) to selectively kill MDR pathogenic bacteria by combining the antimicrobial activity of silver with the selective toxicity of bPEI toward bacteria. The minimum inhibitory concentration of bPEI-Ag NCs was determined against 12 uropathogenic MDR strains and found to be 10- to 15-fold lower than that of PEI and 2- to 3-fold lower than that of AgNO₃ alone. Cell viability and hemolysis assays demonstrated the biocompatibility of bPEI-Ag NCs with human fibroblasts and red blood cells, with selective toxicity against MDR bacteria.

Dual Functionalization of Nanoparticles for Generating Corona-Free and Noncytotoxic Silica Nanoparticles

Protein coronas form on the surfaces of nanomaterials in biological fluids. This layer of proteins affects the properties of nanomaterials, altering their behavior and masking engineered functionality. The use of nonfouling moieties reduces or prevents corona formation; however, these ligands typically complicate functionalization. We present here a surface modification strategy for silica nanoparticles using specific molar ratios of zwitterionic and amine moieties. Through proper balance of ligands, we were able to generate particles that featured reactive "handles", while retaining nonfouling properties, high hemocompatibility, and low cytotoxicity.

Mass spectrometry and Monte Carlo method mapping of nanoparticle ligand shell morphology

Janus, patchy, stripe-like, or random arrangements of molecules within the ligand shell of nanoparticles affect many properties. Among all existing ligand shell morphology characterization methods, the one based on mass spectroscopy is arguably the simplest. Its greatest limitation is that the results are qualitative. Here, we use a tailor-made Monte Carlo type program that fits the whole MALDI spectrum and generates a 3D model of the ligand shell. Quantitative description of the ligand shell in terms of nearest neighbor distribution and characteristic length scale can be readily extracted by the model, and are compared with the results of other characterization methods. A parameter related to the intermolecular interaction is extracted when this method is combined with NMR. This approach could become the routine method to characterize the ligand shell morphology of many nanoparticles and we provide an open access program to facilitate its use.

Determining the arrangement of ligands on a nanoparticle is challenging, given the limitations of existing characterization tools. Here, the authors describe an accessible method for resolving ligand shell morphology that uses simple MALDI-TOF mass spectrometry measurements in conjunction with an open-access Monte Carlo fitting program.

Elemental and optical imaging evaluation of zwitterionic gold nanoclusters in glioblastoma mouse models

We report in this study the in vivo biodistribution of ultra-small luminescent gold (Au) particles (∼1.5 nm core size; 17 kDa), so-called nanoclusters (NCs), stabilized by bidentate zwitterionic molecules in subcutaneous (s.c.) and orthotopic glioblastoma mice models. Particular investigations on renal clearance and tumor uptake were performed using highly sensitive advanced imaging techniques such as multi-elemental Laser-Induced Breakdown Spectroscopy (LIBS) imaging and in-line X-ray Synchrotron Phase Contrast Tomography (XSPCT). Results show a blood circulation time of 6.5 ± 1.3 min accompanied by an efficient and fast renal clearance through the cortex of the kidney with a 66% drop between 1 h and 5 h. With a similar size range, these Au NCs are 5 times more fluorescent than the well-described Au₂₅GSH₁₈ NCs in the near-infrared (NIR) region and present significantly stronger tumor uptake and retention illustrated by an in vivo s.c. tumor-to-skin ratio of 1.8 measured by non-invasive optical imaging and an ex vivo tumor-to-muscle of 6.1. This work highlights the pivotal role of surface coating in designing optimum Au NC candidates for cancer treatment.

Understanding the elusive protein corona of thermoresponsive nanogels

Aim: We analyzed the protein corona of thermoresponsive, poly(N-isopropylacrylamide)- or poly(N-isopropylmethacrylamide)-based nanogels. Materials & methods: Traces of protein corona detected after incubation in human serum were characterized by proteomics and dynamic light scattering in undiluted serum. Results: Apolipoprotein B-100 and albumin were the main components of the protein coronae. For dendritic polyglycerol-poly(N-isopropylacrylamide) nanogels at 37°C, an increase in adsorbed immunoglobulin light chains was detected, followed by partially reversible nanogel aggregation. All nanogels in their hydrophilic state are colloidally stable in serum and bear a dysopsonin-rich protein corona. Conclusion: We observed strong changes in NG stability upon slight alterations in the composition of the protein coronae according to nanogel solvation state. Nanogels in their hydrophilic state possess safe protein coronae.

Surface Modifications of Nanoparticles for Stability in Biological Fluids

Due to the high surface: volume ratio and the extraordinary properties arising from the nanoscale (optical, electric, magnetic, etc.), nanoparticles (NPs) are excellent candidates for multiple applications. In this context, nanoscience is opening a wide range of modern technologies in biological and biomedical fields, among others. However, one of the main drawbacks that still delays its fast evolution and effectiveness is related to the behavior of nanomaterials in the presence of biological fluids. Unfortunately, biological fluids are characterized by high ionic strengths which usually induce NP aggregation. Besides this problem, the high content in biomacromolecules—such as lipids, sugars, nucleic acids and, especially, proteins—also affects NP stability and its viability for some applications due to, for example, the formation of the protein corona around the NPs. Here, we will review the most common strategies to achieve stable NPs dispersions in high ionic strength fluids and, also, antifouling strategies to avoid the protein adsorption.

Biodistribution studies of ultrasmall silicon nanoparticles and carbon dots in experimental rats and tumor mice

Ultrasmall clearable nanoparticles possess enormous potential as cancer imaging agents. In particular, biocompatible silicon nanoparticles (Si NPs) and carbon quantum dots (CQDs) hold great potential in this regard. Their facile surface functionalization easily allows the introduction of different labels for in vivo imaging. However, to date, a thorough biodistribution study by in vivo positron emission tomography (PET) and a comparative study of Si vs. C particles of similar size are missing. In this contribution, ultrasmall (size <5 nm) Si NPs and CQDs were synthesized and characterized by high-resolution transmission electron microscopy (HR-TEM), Fourier-transform infrared (FTIR), absorption and steady-state emission spectroscopy. Subsequent functionalization of NPs with a near-infrared dye (Kodak-XS-670) or a radiolabel (64Cu) enabled a detailed in vitro and in vivo study of the particles. For radiolabeling experiments, the bifunctional chelating agent S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) was conjugated to the amino surface groups of the respective NPs. Efficient radiolabeling of NOTA-functionalized NPs with the positron emitter 64Cu was found. The biodistribution and PET studies showed a rapid renal clearance from the in vivo systems for both variants of the nanoparticles. Interestingly, the different derivatives investigated exhibited significant differences in the biodistribution and pharmacokinetic properties. This can mostly be attributed to different surface charge and hydrophilicity of the NPs, arising from the synthetic strategy used to prepare the particles.

Stable and oxidant responsive zwitterionic nanoclusters

Zwitterions are promising ligands for the fabrication of non-toxic and non-interacting biomaterials. Sulfonamide-based monothiol zwitterionic ligands on gold nanocluster (AuNC) surfaces provide nanomaterials with stable colloidal properties and intense red emission in biological environments. The fluorescence intensity of the nanocluster can be modulated by reactive oxygen species (e.g. ˙OH), allowing for quantitative and selective sensing of antioxidants (e.g. ascorbic acid) in real time.

Rupture of Lipid Membranes Induced by Amphiphilic Janus Nanoparticles

The surface coatings of nanoparticles determine their interaction with biomembranes, but studies have been limited almost exclusively to nanoparticles with a uniform surface chemistry. Although nanoparticles are increasingly made with complex surface chemistries to achieve multifunctionalities, our understanding of how a heterogeneous surface coating affects particle-biomembrane interaction has been lagging far behind. Here we report an investigation of this question in an experimental system consisting of amphiphilic "two-faced" Janus nanoparticles and supported lipid membranes. We show that amphiphilic Janus nanoparticles at picomolar concentrations induce defects in zwitterionic lipid bilayers. In addition to revealing the various effects of hydrophobicity and charge in particle-bilayer interactions, we demonstrate that the Janus geometry-the spatial segregation of hydrophobicity and charges on particle surface-causes nanoparticles to bind more strongly to bilayers and induce defects more effectively than particles with uniformly mixed surface functionalities. We combine experiments with computational simulation to further elucidate how amphiphilic Janus nanoparticles extract lipids to rupture intact lipid bilayers. This study provides direct evidence that the spatial arrangement of surface functionalities on a nanoparticle, rather than just its overall surface chemistry, plays a crucial role in determining how it interacts with biological membranes.

Interaction of spin-labeled HPMA-based nanoparticles with human blood plasma proteins - the introduction of protein-corona-free polymer nanomedicine

In this paper, we revised the current understanding of the protein corona that is created on the surface of nanoparticles in blood plasma after an intravenous injection. We have focused on nanoparticles that have a proven therapeutic outcome. These nanoparticles are based on two types of biocompatible amphiphilic copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA): a block copolymer, poly(ε-caprolactone) (PCL)-b-poly(HPMA), and a statistical HPMA copolymer bearing cholesterol moieties, which have been tested both in vitro and in vivo. We studied the interaction of nanoparticles with blood plasma and selected blood plasma proteins by electron paramagnetic resonance (EPR), isothermal titration calorimetry, dynamic light scattering, and cryo-transmission electron microscopy. The copolymers were labeled with TEMPO radicals at the end of hydrophobic PCL or along the hydrophilic HPMA chains to monitor changes in polymer chain dynamics caused by protein adsorption. By EPR and other methods, we were able to probe specific interactions between nanoparticles and blood proteins, specifically low- and high-density lipoproteins, immunoglobulin G, human serum albumin (HSA), and human plasma. It was found that individual proteins and plasma have very low binding affinity to nanoparticles. We observed no hard corona around HPMA-based nanoparticles; with the exception of HSA the proteins showed no detectable binding to the nanoparticles. Our study confirms that a classical "hard corona-soft corona" paradigm is not valid for all types of nanoparticles and each system has a unique protein corona that is determined by the nature of the NP material.

Zwitterionic peptide-capped gold nanoparticles for colorimetric detection of Ni2+

Zwitterionic nanoparticles are typically utilized as nanoprobes and delivery vehicles in nanomedicine and therapeutics due to their resistance to interferences. Their high stability also shows great potential to be applied in sensing applications. Here, we report a selective, sensitive and rapid colorimetric sensing of nickel ions (Ni²⁺) using zwitterionic polypeptide, EKEKEKPPPPC (EK)₃, capped gold nanoparticles (AuNP-(EK)₃). By taking advantage of the alternate carboxylic (-COOH)/amine (-NH₂) groups, the zwitterionic peptide can function dually by being able to sense metal ions and maintain colloidal stability. Ni²⁺ can trigger the aggregation of the AuNP-(EK)₃ nanoprobe, which results in a red-to-purple color change of the AuNP-(EK)₃ solution. Our 40 nm AuNP-(EK)₃ nanoprobe can detect Ni²⁺ as low as 34 nM within 15 min with a linear range of 60-160 nM, and is stable in soil, urine and water samples. We demonstrate that the aggregation mechanism of the nanoprobe is due to the interactions between the -NH₂ group of glutamic acid at the N-terminus of the peptide and Ni²⁺, and the aggregation process is reversible. Furthermore, the slight modification of two amino acid sequences at the N-terminus allows the nanoprobe to retain its stability, even in a high ionic strength medium. We believe that by adjusting or extending the peptide sequences, new metal ion selective peptides could be created.

Surface Engineering of Nanoparticles for Targeted Delivery to Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-associated deaths worldwide. There is a lack of efficient therapy for HCC; the only available first-line systemic drug, sorafenib, can merely improve the average survival by two months. Among the efforts to develop an efficient therapy for HCC, nanomedicine has drawn the most attention, owing to its unique features such as high drug-loading capacity, intrinsic anticancer activities, integrated diagnostic and therapeutic functionalities, and easy surface engineering with targeting ligands. Despite its tremendous advantages, no nanomedicine can be effective unless it successfully targets the tumor site, which is a challenging task. In this review, the features of HCC are described, and the physiological hurdles that prevent nanoparticles from targeting HCC are discussed. Then, the surface physicochemical factors of nanoparticles that can influence targeting efficiency are discussed. Finally, a thorough description of the physiological barriers that nanomedicine must conquer before uptake by HCC cells if possible is provided, as well as the surface engineering approaches to nanomedicine to achieve targeted delivery to HCC cells. The physiological hurdles and corresponding solutions summarized in this review provide a general guide for the rational design of HCC targeting nanomedicine systems.