Engineering the nanoparticle-protein interface: applications and possibilities

Porphysome Engineered With Specific Protein Binding Sites as a Multimodal Theranostic Nanocarrier for Targeted Protein Delivery

The immobilization of proteins on the surface of carriers is challenging due to the loss of protein structure and function in this process. Here, we report the development of the protein immobilization on the surface of the metallated-porphyrin complex in the porphysome nanocarrier. The conjugated Ni-porphyrin to fatty acid (as a tail) has been synthesized and independently placed at the depth of the bilayer center of Dipalmitoylphosphatidylcholine (DPPC) in which the Ni-porphyrin was at the polar region of the membrane and is thus superficial. This porphysome (DPPC: Ni-porphyrin, 4 : 1 mole ratio) was formed by supramolecular self-assembly with a diameter of 173±7 nm and zeta potential -8.5±3.4 mv, which exhibited no significant toxicity at the experimental concentrations and acceptable cellular uptake on MCF-7 cells. The physicochemical properties and specific protein binding sites of the firefly luciferase as a model protein into the porphysome (1 : 2 mole ratio) show the conjugation efficiency about 80 % and the conformation of protein was completely maintained. Furthermore, bioluminescence assay and SDS-PAGE confirmed the preservation of protein function. The stabilized platform of porphyrin-lipid structure can potentially improve the efficacy of protein functionality for a particular display, shifting porphysomes from a simple carrier to a therapeutic agent.

Brain-targeted drug delivery - nanovesicles directed to specific brain cells by brain-targeting ligands

Neurodegenerative diseases are characterized by extensive loss of function or death of brain cells, hampering the life quality of patients. Brain-targeted drug delivery is challenging, with a low success rate this far. Therefore, the application of targeting ligands in drug vehicles, such as lipid-based and polymeric nanoparticles, holds the promise to overcome the blood-brain barrier (BBB) and direct therapies to the brain, in addition to protect their cargo from degradation and metabolization. In this review, we discuss the barriers to brain delivery and the different types of brain-targeting ligands currently in use in brain-targeted nanoparticles, such as peptides, proteins, aptamers, small molecules, and antibodies. Moreover, we present a detailed review of the different targeting ligands used to direct nanoparticles to specific brain cells, like neurons (C4-3 aptamer, neurotensin, Tet-1, RVG, and IKRG peptides), astrocytes (Aquaporin-4, D4, and Bradykinin B2 antibodies), oligodendrocytes (NG-2 antibody and the biotinylated DNA aptamer conjugated to a streptavidin core Myaptavin-3064), microglia (CD11b antibody), neural stem cells (QTRFLLH, VPTQSSG, and NFL-TBS.40-63 peptides), and to endothelial cells of the BBB (transferrin and insulin proteins, and choline). Reports demonstrated enhanced brain-targeted delivery with improved transport to the specific cell type targeted with the conjugation of these ligands to nanoparticles. Hence, this strategy allows the implementation of high-precision medicine, with reduced side effects or unwanted therapy clearance from the body. Nevertheless, the accumulation of some of these nanoparticles in peripheral organs has been reported indicating that there are still factors to be improved to achieve higher levels of brain targeting. This review is a collection of studies exploring targeting ligands for the delivery of nanoparticles to the brain and we highlight the advantages and limitations of this type of approach in precision therapies.

The Molecular Footprint of Peptides on the Surface of Ultrasmall Gold Nanoparticles (2 nm) Is Governed by Steric Demand

Ultrasmall gold nanoparticles were functionalized with peptides of two to seven amino acids that contained one cysteine molecule as anchor via a thiol-gold bond and a number of alanine residues as nonbinding amino acid. The cysteine was located either in the center of the molecule or at the end (C-terminus). For comparison, gold nanoparticles were also functionalized with cysteine alone. The particles were characterized by UV spectroscopy, differential centrifugal sedimentation (DCS), high-resolution transmission electron microscopy (HRTEM), and small-angle X-ray scattering (SAXS). This confirmed the uniform metal core (2 nm diameter). The hydrodynamic diameter was probed by 1H-DOSY NMR spectroscopy and showed an increase in thickness of the hydrated peptide layer with increasing peptide size (up to 1.4 nm for heptapeptides; 0.20 nm per amino acid in the peptide). 1H NMR spectroscopy of water-dispersed nanoparticles showed the integrity of the peptides and the effect of the metal core on the peptide. Notably, the NMR signals were very broad near the metal surface and became increasingly narrow in a distance. In particular, the methyl groups of alanine can be used as probe for the resolution of the NMR spectra. The number of peptide ligands on each nanoparticle was determined using quantitative 1H NMR spectroscopy. It decreased with increasing peptide length from about 100 for a dipeptide to about 12 for a heptapeptide, resulting in an increase of the molecular footprint from about 0.1 to 1.1 nm2.

Boosting one-step degradation of shrimp shell waste to produce chitin oligosaccharides at smart nanoscale enzyme reactor with liquid-solid system

Chitin oligosaccharides (CTOS) possess potential applications in food, medicine, and agriculture. However, lower mass transfer and catalytic efficiency are the main kinetic limitations for the production of CTOS from shrimp shell waste (SSW) and crystalline chitin. Chemical or physical methods are usually used for pretreatment to improve chitinase hydrolysis efficiency, but this is not eco-friendly and cost-effective. To address this challenge, a chitinase nanoreactor with the liquid-solid system (BcChiA1@ZIF-8) was manufactured to boost the one-step degradation of SSW and crystalline chitin. Compared with free enzyme, the catalytic efficiency of BcChiA1@ZIF-8 on colloidal chitin was significantly improved to 142 %. SSW and crystalline chitin can be directly degraded by BcChiA1@ZIF-8 without any pretreatments. The yield of N, N'-diacetylchitobiose [(GlcNAc)2] from SSW and N-acetyl-D-glucosamine (GlcNAc) from crystalline chitin was 2 times and 3.1 times than that of free enzyme, respectively. The reason was that BcChiA1@ZIF-8 with a liquid-solid system enlarged the interface area, increased the collision frequency between enzyme and substrate, and improved the large-substrates binding activity of chitinase. Moreover, the biphasic system exhibited excellent stability, and the design showed universal applicability. This strategy provided novel guidance for other polysaccharide biosynthesis and the conversion of environmental waste into carbohydrates.

Biomolecules meet organic frameworks: from synthesis strategies to diverse applications

Biomolecules are essential in pharmaceuticals, biocatalysts, biomaterials, etc., but unfortunately they are extremely susceptible to extraneous conditions. When biomolecules meet porous organic frameworks, significantly improved thermal, chemical, and mechanical stabilities are not only acquired for raw biomolecules, but also molecule sieving, substrate enrichment, chirality property, and other functionalities are additionally introduced for application expansions. In addition, the intriguing synergistic effect stemming from elaborate and concerted interactions between biomolecules and frameworks can further enhance application performances. In this paper, the synthesis strategies of the so-called bio-organic frameworks (BOFs) in recent years are systematically reviewed and classified. Additionally, their broad applications in biomedicine, catalysis, separation, sensing, and imaging are introduced and discussed. Before ending, the current challenges and prospects in the future for this infancy-stage but significant research field are also provided. We hope that this review will offer a concise but comprehensive vision of designing and constructing multifunctional BOF materials as well as their full explorations in various fields.

Efficient Chlorostannate Modification of Magnetite Nanoparticles for Their Biofunctionalization

Magnetite nanoparticles (MNPs) are highly favored materials for a wide range of applications, from smart composite materials and biosensors to targeted drug delivery. These multifunctional applications typically require the biofunctional coating of MNPs that involves various conjugation techniques to form stable MNP-biomolecule complexes. In this study, a cost-effective method is developed for the chlorostannate modification of MNP surfaces that provides efficient one-step conjugation with biomolecules. The proposed method was validated using MNPs obtained via an optimized co-precipitation technique that included the use of degassed water, argon atmosphere, and the pre-filtering of FeCl2 and FeCl3 solutions followed by MNP surface modification using stannous chloride. The resulting chlorostannated nanoparticles were comprehensively characterized, and their efficiency was compared with both carboxylate-modified and unmodified MNPs. The biorecognition performance of MNPs was verified via magnetic immunochromatography. Mouse monoclonal antibodies to folic acid served as model biomolecules conjugated with the MNP to produce nanobioconjugates, while folic acid-gelatin conjugates were immobilized on the test lines of immunochromatography lateral flow test strips. The specific trapping of the obtained nanobioconjugates via antibody-antigen interactions was registered via the highly sensitive magnetic particle quantification technique. The developed chlorostannate modification of MNPs is a versatile, rapid, and convenient tool for creating multifunctional nanobioconjugates with applications that span in vitro diagnostics, magnetic separation, and potential in vivo uses.

Manipulating Physicochemical Properties of Biosensor Platform with Polysuccinimide-Silica Nanocomposite for Enhanced Protein Detection

As point-of-care testing (POCT) is becoming the new paradigm of medical diagnostics, there is a growing need to develop reliable POCT devices that can be conveniently operated in a minimally invasive manner. However, the clinical potential of POCT diagnostics is yet to be realized, mainly due to the limited and inconsistent amount of collected samples on these devices, undermining their accuracy. This study proposes a new biosensing platform modified with a functional polysuccinimide (PSI)-silica nanoparticle (SNP) composite system that can substantially increase the protein conjugation efficiency by modulating physicochemical interaction with proteins by several hundred percent from an unmodified device. The efficacy of this PSI-SNP system is further validated by applying it on the surface of a microneedle array (MN), which has emerged as a promising POCT device capable of accessing interstitial fluid through minimal penetration of the skin. This PSI-SNP MN is demonstrated to detect a wide array of proteins with high sensitivity on par with conventional whole serum analysis, validated by in vivo animal testing, effectively displaying broad applicability in biomedical engineering.

Self-Assembled Monolayers of Gemini-Type Amphiphilic Hexabenzocoronenes on Gold: Contribution of Their Triethylene Glycol Side Chains to Self-Assembly Formation

We report on a two-dimensional self-assembled structure of a supramolecule with hydrophilic oligoethylene glycol (EG) units, which are capable of stronger electrostatic interactions than van der Waals (vdW) interactions between alkyl chains. For this purpose, hexabenzocoronene (HBC) with two hydrophobic dodecyl chains on one side of the HBC core and two hydrophilic triethylene glycol (TEG) chains on the other side of the HBC core (HBCGemini) and HBCGemini with a trinitrofluorenone (TNF) added to the end of one TEG chain (HBCTNFGemini) were employed. Scanning tunneling microscopy (STM) revealed the presence of multiple two-dimensional self-assembled structures in each of HBCGemini and HBCTNFGemini deposited on the gold substrate in vacuum. The role of polar functional groups in these observations is discussed based on semiempirical molecular orbital simulations. Two types of 2D organized structures of HBC-TEG were observed: one with rectangular and relatively dense unit cells and the other with nearly square and relatively sparse unit cells. In both organized structures, the phenyl group TEG units and alkyl chains were considered to be the main molecular interactions with each other. On the other hand, in HBCTNFGemini, three types of organized structures were observed, which could be explained by the mechanism of interdigitation of the TEG-containing side-chain moieties to form a dimeric core. The EG units are more flexible than the alkyl chains and thus can interact flexibly with the hydrophobic HBC core, and the glycol side chains facilitate the intermolecular interactions as well as the alkyl chains.

Surface functionalized nanoparticles: A boon to biomedical science

The rapid development of nanomedicine has increased the likelihood that manufactured nanoparticles will one day come into contact with people and the environment. A variety of academic fields, including engineering and the health sciences, have taken a keen interest in the development of nanotechnology. Any significant development in nanomaterial-based applications would depend on the production of functionalized nanoparticles, which are believed to have the potential to be used in fields like pharmaceutical and biomedical sciences. The functionalization of nanoparticles with particular recognition chemical moieties does result in multifunctional nanoparticles with greater efficacy while at the same time minimising adverse effects, according to early clinical studies. This is because of traits like aggressive cellular uptake and focused localization in tumours. To advance this field of inquiry, chemical procedures must be developed that reliably attach chemical moieties to nanoparticles. The structure-function relationship of these functionalized nanoparticles has been extensively studied as a result of the discovery of several chemical processes for the synthesis of functionalized nanoparticles specifically for drug delivery, cancer therapy, diagnostics, tissue engineering, and molecular biology. Because of the growing understanding of how to functionalize nanoparticles and the continued work of innovative scientists to expand this technology, it is anticipated that functionalized nanoparticles will play an important role in the aforementioned domains. As a result, the goal of this study is to familiarise readers with nanoparticles, to explain functionalization techniques that have already been developed, and to examine potential applications for nanoparticles in the biomedical sciences. This review's information is essential for the safe and broad use of functionalized nanoparticles, particularly in the biomedical sector.

Surface Functionalised Parenteral Nanoemulsions for Active and Homotypic Targeting to Melanoma

Despite recent progressions in cancer genomic and immunotherapies, advanced melanoma still represents a life threat, pushing to optimise new targeted nanotechnology approaches for specific drug delivery to the tumour. To this aim, owing to their biocompatibility and favourable technological features, injectable lipid nanoemulsions were functionalised with proteins owing to two alternative approaches: transferrin was chemically grafted for active targeting, while cancer cell membrane fragments wrapping was used for homotypic targeting. In both cases, protein functionalisation was successfully achieved. Targeting efficiency was preliminarily evaluated using flow cytometry internalisation studies in two-dimensional cellular models, after fluorescence labelling of formulations with 6-coumarin. The uptake of cell-membrane-fragment-wrapped nanoemulsions was higher compared to uncoated nanoemulsions. Instead, the effect of transferrin grafting was less evident in serum-enriched medium, since such ligand probably undergoes competition with the endogenous protein. Moreover, a more pronounced internalisation was achieved when a pegylated heterodimer was employed for conjugation (p < 0.05).

DNA-Directed Protein Anchoring on Oligo/Alkanethiol-Coated Gold Nanoparticles: A Versatile Platform for Biosensing Applications

Herein, we report on a smart biosensing platform that exploits gold nanoparticles (AuNPs) functionalized through ssDNA self-assembled monolayers (SAM) and the DNA-directed immobilization (DDI) of DNA-protein conjugates; a novel, high-sensitivity optical characterization technique based on a miniaturized gel electrophoresis chip integrated with online thermal lens spectrometry (MGEC-TLS), for the high-sensitivity detection of antigen binding events. Specifically, we characterized the physicochemical properties of 20 nm AuNPs covered with mixed SAMs of thiolated single-stranded DNA and bio-repellent molecules, referred to as top-terminated oligo-ethylene glycol (TOEG6), demonstrating high colloidal stability, optimal binder surface density, and proper hybridization capacity. Further, to explore the design in the frame of cancer-associated antigen detection, complementary ssDNA fragments conjugated with a nanobody, called C8, were loaded on the particles and employed to detect the presence of the HER2-ECD antigen in liquid. At variance with conventional surface plasmon resonance detection, MGEC-TLS characterization confirmed the capability of the assay to titrate the HER2-ECD antigen down to concentrations of 440 ng/mL. The high versatility of the directed protein-DNA conjugates immobilization through DNA hybridization on plasmonic scaffolds and coupled with the high sensitivity of the MGEC-TLS detection qualifies the proposed assay as a potential, easily operated biosensing strategy for the fast and label-free detection of disease-relevant antigens.

Charge and hydrophobicity of amyloidogenic protein/peptide templates regulate the growth and morphology of gold nanoparticles

Biomolecules are known to interact with metals and produce nanostructured hybrid materials with diverse morphologies and functions. In spite of the great advancement in the principles of biomimetics for designing complex nano-bio structures, the interplay between the physical properties of biomolecules such as sequence, charge, and hydrophobicity with predictable morphology of the resulting nanomaterials is largely unknown. Here, using various amyloidogenic proteins/peptides and their corresponding fibrils in combination with different pH, we show defined principle for gold nanocrystal growth into triangular and supra-spheres with high prediction. Using a combination of different biophysical and structural techniques, we establish the mechanism of nucleation and crystal growth of gold nanostructures and show the effective isolation of intact nanostructures from amyloid templates using protein digestion. This study will significantly advance our design principle for bioinspired materials for specific functions with great predictability.

Ferritin: A Promising Nanoreactor and Nanocarrier for Bionanotechnology

The essence of bionanotechnology lies in the application of nanotechnology/nanomaterials to solve the biological problems. Quantum dots and nanoparticles hold potential biomedical applications, but their inherent problems such as low solubility and associated toxicity due to their interactions at nonspecific target sites is a major concern. The self-assembled, thermostable, ferritin protein nanocages possessing natural iron scavenging ability have emerged as a potential solution to all the above-mentioned problems by acting as nanoreactor and nanocarrier. Ferritins, the cellular iron repositories, are hollow, spherical, symmetric multimeric protein nanocages, which sequester the excess of free Fe(II) and synthesize iron biominerals (Fe₂O₃·H₂O) inside their ∼5-8 nm central cavity. The electrostatics and dynamics of the pore residues not only drives the natural substrate Fe²⁺ inside ferritin nanocages but also uptakes a set of other metals ions/counterions during in vitro synthesis of nanomaterial. The current review aims to report the recent developments/understanding on ferritin structure (self-assembly, surface/pores electrostatics, metal ion binding sites) and chemistry occurring inside these supramolecular protein cages (protein mediated metal ion uptake and mineralization/nanoparticle formation) along with its surface modification to exploit them for various nanobiotechnological applications. Furthermore, a better understanding of ferritin self-assembly would be highly useful for optimizing the incorporation of nanomaterials via the disassembly/reassembly approach. Several studies have reported the successful engineering of these ferritin protein nanocages in order to utilize them as potential nanoreactor for synthesizing/incorporating nanoparticles and as nanocarrier for delivering imaging agents/drugs at cell specific target sites. Therefore, the combination of nanoscience (nanomaterials) and bioscience (ferritin protein) projects several benefits for various applications ranging from electronics to medicine.

Stimuli-Responsive Adaptive Nanotoxin to Directly Penetrate the Cellular Membrane by Molecular Folding and Unfolding

Biological nanomachines, including proteins and nucleic acids whose function is activated by conformational changes, are involved in every biological process, in which their dynamic and responsive behaviors are controlled by supramolecular recognition. The development of artificial nanomachines that mimic the biological functions for potential application as therapeutics is emerging; however, it is still limited to the lower hierarchical level of the molecular components. In this work, we report a synthetic machinery nanostructure in which actuatable molecular components are integrated into a hierarchical nanomaterial in response to external stimuli to regulate biological functions. Two nanometers core-sized gold nanoparticles are covered with ligand layers as actuatable components, whose folding/unfolding motional response to the cellular environment enables the direct penetration of the nanoparticles across the cellular membrane to disrupt intracellular organelles. Furthermore, the pH-responsive conformational movements of the molecular components can induce the apoptosis of cancer cells. This strategy based on the mechanical motion of molecular components on a hierarchical nanocluster would be useful to design biomimetic nanotoxins.

Designing Functional Bionanoconstructs for Effective In Vivo Targeting

The progress achieved over the last three decades in the field of bioconjugation has enabled the preparation of sophisticated nanomaterial–biomolecule conjugates, referred to herein as bionanoconstructs, for a multitude of applications including biosensing, diagnostics, and therapeutics. However, the development of bionanoconstructs for the active targeting of cells and cellular compartments, both in vitro and in vivo, is challenged by the lack of understanding of the mechanisms governing nanoscale recognition. In this review, we highlight fundamental obstacles in designing a successful bionanoconstruct, considering findings in the field of bionanointeractions. We argue that the biological recognition of bionanoconstructs is modulated not only by their molecular composition but also by the collective architecture presented upon their surface, and we discuss fundamental aspects of this surface architecture that are central to successful recognition, such as the mode of biomolecule conjugation and nanomaterial passivation. We also emphasize the need for thorough characterization of engineered bionanoconstructs and highlight the significance of population heterogeneity, which too presents a significant challenge in the interpretation of in vitro and in vivo results. Consideration of such issues together will better define the arena in which bioconjugation, in the future, will deliver functional and clinically relevant bionanoconstructs.

Sensing nanoparticle-protein corona using nanoparticle enhanced Laser Induced Breakdown Spectroscopy signal enhancement

Recently nanoparticle enhanced Laser Induced Breakdown Spectroscopy (NELIBS) is getting a growing interest as an effective alternative method for improving the analytical performance of LIBS. On the other hand, the plasmonic effect during laser ablation can be used for a different task rather than elemental analysis. In this paper, the dependence of NELIBS emission signal enhancement on nanoparticle-protein solutions dried on a reference substrate (metallic titanium) was investigated. Two proteins were studied: Human Serum Albumin (HSA) and Cytochrome C (CytC). Both proteins have a strong affinity for the gold nanoparticles (AuNPs) due to the bonding between the single free exterior thiol (associated with a cysteine residue) and the gold surface to form a stable protein corona. Then, since the protein sizes are vastly different, a different number of protein units is needed to cover AuNP surface to form a protein layer. The NP-protein solution was dropped and dried onto the titanium substrate. Then the NELIBS signal enhancement of Ti emission lines was correlated to the solution characteristics as determined with Dynamic Light Scattering (DLS), Surface Plasmon Resonance (SPR) spectroscopy and Laser Doppler Electrophoresis (LDE) for ζ-potential determination. Moreover, the dried solutions were studied with TEM (Transmission Electron Microscopy) for the inspection of the inter-particle distance. The structural effect of the NP-protein conjugates on the NELIBS signal reveals that NELIBS can be used to determine the number of protein units required to form the nanoparticle-protein corona with good accuracy. Although the investigated NP-protein systems are simple cases in biological applications, this work demonstrates, for the first time, a different use of NELIBS that is beyond elemental analysis and it opens the way for sensing the nanoparticle protein corona.

Stimuli-Responsive Three-Dimensional DNA Nanomachines Engineered by Controlling Dynamic Interactions at Biomolecule-Nanoparticle Interfaces

Stimuli-responsive nanomachines are attractive tools for biosensing, imaging, and drug delivery. Herein, we demonstrate that the orientation of macromolecules and subsequent dynamic interactions at the biomolecule-nanoparticle (bio-nano) interfaces can be rationally controlled to engineer stimuli-responsive DNA nanomachines. The success of this design principle was demonstrated by engineering a series of antibody-responsive DNA walkers capable of moving persistently on a three-dimensional track made of DNA functionalized gold nanoparticles. We show that drastically different responses to antibodies could be achieved using DNA walkers of identical sequences but with varying number or sites of modifications. We also show that multiple interfacial factors could be combined to engineer stimuli-responsive DNA nanomachines with high sensitivity and modularity. The potential of our strategy for practical uses was finally demonstrated for the amplified detection of antibodies and small molecules in both buffer and human serum samples. Unlike many DNA-based nanomachines, the performance of which could be significantly hindered by the matrix of serum, our system shows a matrix-enhanced sensitivity as a result of the engineering approach at the bio-nano interface.

Systematic Modification and Evaluation of Enzyme-Loaded Chitosan Nanoparticles

Polymeric-based nano drug delivery systems have been widely exploited to overcome protein instability during formulation. Presently, a diverse range of polymeric agents can be used, among which polysaccharides, such as chitosan (CS), hyaluronic acid (HA) and cyclodextrins (CDs), are included. Due to its unique biological and physicochemical properties, CS is one of the most used polysaccharides for development of protein delivery systems. However, CS has been described as potentially immunogenic. By envisaging a biosafe cytocompatible and haemocompatible profile, this paper reports the systematic development of a delivery system based on CS and derived with HA and CDs to nanoencapsulate the model human phenylalanine hydroxylase (hPAH) through ionotropic gelation with tripolyphosphate (TPP), while maintaining protein stability and enzyme activity. By merging the combined set of biopolymers, we were able to effectively entrap hPAH within CS nanoparticles with improvements in hPAH stability and the maintenance of functional activity, while simultaneously achieving strict control of the formulation process. Detailed characterization of the developed nanoparticulate systems showed that the lead formulations were internalized by hepatocytes (HepG2 cell line), did not reveal cell toxicity and presented a safe haemocompatible profile.

Protein-Based Nanohydrogels for Bioactive Delivery

Hydrogels possess a unique three-dimensional, cross-linked network of polymers capable of absorbing large amounts of water and biological fluids without dissolving. Nanohydrogels (NGs) or nanogels are composed of diverse types of polymers of synthetic or natural origin. Their combination is bound by a chemical covalent bond or is physically cross-linked with non-covalent bonds like electrostatic interactions, hydrophobic interactions, and hydrogen bonding. Its remarkable ability to absorb water or other fluids is mainly attributed to hydrophilic groups like hydroxyl, amide, and sulphate, etc. Natural biomolecules such as protein- or peptide-based nanohydrogels are an important category of hydrogels which possess high biocompatibility and metabolic degradability. The preparation of protein nanohydrogels and the subsequent encapsulation process generally involve use of environment friendly solvents and can be fabricated using different proteins, such as fibroins, albumin, collagen, elastin, gelatin, and lipoprotein, etc. involving emulsion, electrospray, and desolvation methods to name a few. Nanohydrogels are excellent biomaterials with broad applications in the areas of regenerative medicine, tissue engineering, and drug delivery due to certain advantages like biodegradability, biocompatibility, tunable mechanical strength, molecular binding abilities, and customizable responses to certain stimuli like ionic concentration, pH, and temperature. The present review aims to provide an insightful analysis of protein/peptide nanohydrogels including their preparation, biophysiochemical aspects, and applications in diverse disciplines like in drug delivery, immunotherapy, intracellular delivery, nutraceutical delivery, cell adhesion, and wound dressing. Naturally occurring structural proteins that are being explored in protein nanohydrogels, along with their unique properties, are also discussed briefly. Further, the review also covers the advantages, limitations, overview of clinical potential, toxicity aspects, stability issues, and future perspectives of protein nanohydrogels.

Investigating the use of conducting oligomers and redox molecules in CdS-MoFeP biohybrids

In this work we report the effect of incorporating conducting oligophenylenes and a cobaltocene-based redox mediator on photodriven electron transfer between thioglycolic acid (TGA) capped CdS nanorods (NR) and the native nitrogenase MoFe protein (MoFeP) by following the reduction of H⁺ to H₂. First, we demonstrate that the addition of benzidine-a conductive diphenylene- to TGA-CdS and MoFeP increased catalytic activity by up to 3-fold as compared to CdS-MoFeP alone. In addition, in comparing the use of oligophenylenes composed of one (p-phenylenediamine), two (benzidine) or three (4,4''-diamino-p-terphenyl)phenylene groups, the largest gain in H₂ was observed with the addition of benzidine and the lowest with phenylenediamine. As a comparison to the conductive oligophenylenes, a cobaltocene-based redox mediator was also tested with the TGA-CdS NRs and MoFeP. However, adding either cobaltocene diacid or diamine caused negligible gains in H₂ production and at higher concentrations, caused a significant decrease. Agarose gel electrophoresis revealed little to no detectable interaction between benzidine and TGA-CdS but strong binding between cobaltocene and TGA-CdS. These results suggest that the tight binding of the cobaltocene mediator to CdS may hinder electron transfer between CdS and MoFe and cause the mediator to undergo continuous reduction/oxidation events at the surface of CdS.

Probing the adsorption of nonionic micelles on different-sized nanoparticles by scattering techniques

The interaction of nanoparticles with surfactants is extensively used in a wide range of applications from enhancing colloidal stability to phase separation processes as well as in the synthesis of noble functional materials. The interaction is highly specific depending on the charged nature of the surfactant. In the case of nonionic surfactants, the micelles adsorb on the surface of nanoparticles. The adsorption of nonionic surfactant C12E10 as a function of surfactant concentration for two different sizes of anionic silica nanoparticles (16 and 27 nm) has been examined using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). SANS measurements have been carried out under different contrast-matched conditions, where nanoparticles, as well as surfactant micelles, have been contrast-matched to the solvent. The adsorption of micelles is determined from the contrast-matched condition of silica nanoparticles with the solvent. SANS data under surfactant contrast-matched condition suggest that there is no modification in the structure and/or interaction of the silica nanoparticles in presence of nonionic micelles. The adsorption of micelles on nanoparticles is found to follow an exponential behavior with respect to the surfactant concentration. These results are consistent with the variation of hydrodynamic size of nanoparticle-surfactant system in DLS. The study on different-sized nanoparticles shows that the lower curvature enhances the packing fraction whereas the loss of surface-to-volume ratio suppresses the fraction of adsorbed micelles with the increase in the nanoparticle size. The adsorption coefficient has higher value for the larger size of the nanoparticles. In the mixed system of two sizes of nanoparticles, no preferential selectivity of micelle adsorption is observed.

Modulating the biological function of protein by tailoring the adsorption orientation on nanoparticles

Protein orientation in nanoparticle-protein conjugates plays a crucial role in binding to cell receptors and ultimately, defines their targeting efficiency. Therefore, understanding fundamental aspects of the role of protein orientation upon adsorption on the surface of nanoparticles (NPs) is vital for the development of clinically important protein-based nanomedicines. In this work, new insights on the effect of the different orientation of cytochrome c (cyt c) bound to gold nanoparticles (GNPs) using various ligands on its apoptotic activity is reported. Time-of-Flight Secondary-Ion Mass Spectrometry (ToF-SIMS), electrochemical and circular dichroism (CD) analyses are used to investigate the characteristics of cyt c orientation and structure on functionalized GNPs. These studies indicate that the orientation and position of the heme ring inside the cyt c structure can be altered by changing the surface chemistry on the GNPs. A difference in the apoptosis inducing capability because of different orientation of cyt c bound to the GNPs is observed. These findings indicate that the biological activity of a protein can be modulated on the surface of NPs by varying its adsorption orientation. This study will impact on the rational design of new nanoscale biosensors, bioelectronics, and nanoparticle-protein based drugs.

Alpha-Synuclein-Nanoparticle Interactions: Understanding, Controlling and Exploiting Conformational Plasticity

Alpha-synuclein (αS) is an extensively studied protein due to its involvement in a group of neurodegenerative disorders, including Parkinson's disease, and its documented ability to undergo aberrant self-aggregation resulting in the formation of amyloid-like fibrils. In dilute solution, the protein is intrinsically disordered but can adopt multiple alternative conformations under given conditions, such as upon adsorption to nanoscale surfaces. The study of αS-nanoparticle interactions allows us to better understand the behavior of the protein and provides the basis for developing systems capable of mitigating the formation of toxic aggregates as well as for designing hybrid nanomaterials with novel functionalities for applications in various research areas. In this review, we summarize current progress on αS-nanoparticle interactions with an emphasis on the conformational plasticity of the biomolecule.

Comparative study on formation of protein coronas under three different serum origins

Nanomaterials form a complex called "protein corona" by contacting with protein-containing biological fluids such as serum when they are exposed to physiological environments. The characteristics of these proteins, which are one of the substantial factors in cellular response, are affected by the interactions between the nanomaterials and the biological systems. Many studies have investigated the biological behaviors of nanomaterials by conducting experiments in vitro and in vivo; however, the origin of the biological materials used is rather inconsistent. This is due to the fact that the composition of the protein coronas may differ depending on the animal origin, not on the composition or size of the nanoparticles. The resulting differences in the composition of the protein coronas can lead to different conclusions. To identify the differences in protein corona formation among sera of different species, we investigated protein coronas of gold and silica nanoparticles in serum obtained from various species. Using comparative proteomic analysis, common proteins adsorbed onto each nanoparticle among the three different sera were identified as highly abundant proteins in the serum. These findings indicate that protein corona formation is dependent on the serum population rather than the size or type of the nanoparticles. Additionally, in the physiological classification of protein coronas, human serum (HS) was found to be rich in apolipoproteins. In conclusion, our data indicate that HS components are different from those of bovine or mouse, indicating that the serum species origin should be carefully considered when selecting a biological fluid.

Nanobioconjugates for Signal Amplification in Electrochemical Biosensing

Nanobioconjugates are hybrid materials that result from the coalescence of biomolecules and nanomaterials. They have emerged as a strategy to amplify the signal response in the biosensor field with the potential to enhance the sensitivity and detection limits of analytical assays. This critical review collects a myriad of strategies for the development of nanobioconjugates based on the conjugation of proteins, antibodies, carbohydrates, and DNA/RNA with noble metals, quantum dots, carbon- and magnetic-based nanomaterials, polymers, and complexes. It first discusses nanobioconjugates assembly and characterization to focus on the strategies to amplify a biorecognition event in biosensing, including molecular-, enzymatic-, and electroactive complex-based approaches. It provides some examples, current challenges, and future perspectives of nanobioconjugates for the amplification of signals in electrochemical biosensing.

Promising insights into the kosmotropic effect of magnetic nanoparticles on proteins: The pivotal role of protein corona formation

Increasing concerns about biosafety of nanoparticles (NPs) has raised the need for detailed knowledge of NP interactions with biological molecules especially proteins. Herein, the concentration-dependent effect of magnetic NPs (MNPs) on bovine serum albumin and hen egg white lysozyme was explored. The X-ray diffraction patterns, zeta potential, and dynamic light scattering measurements together with scanning electron microscopy images were employed to characterize MNPs synthesized through coprecipitation method. Then, we studied the behavior of two model proteins with different surface charges and structural properties on interaction with Fe₃ O₄ . A thorough investigation of protein-MNP interaction by the help of intrinsic fluorescence at different experimental conditions revealed that affinity of proteins for MNPs is strongly affected by the similarity of protein and MNP surface charges. MNPs exerted structure-making kosmotropic effect on both proteins under a concentration threshold; however, binding strength was found to determine the extent of stabilizing effect as well as magnitude of the concentration threshold. Circular dichroism spectra showed that proteins with less resistance to conformational deformations are more prone to secondary structure changes upon adsorption on MNPs. By screening thermal aggregation of proteins in the presence of Fe₃ O₄ , it was also found that like chemical stability, thermal stability is influenced to a higher extent in more strongly bound proteins. Overall, this report not only provides an integrated picture of protein-MNP interaction but also sheds light on the molecular mechanism underling this process.

A custom-made functionalization method to control the biological identity of nanomaterials

Here we propose a one-step strategy to endow nanomaterials with a custom-designed bio-identity. This study designs a universal 'nanomaterial binding domain' that can be genetically attached to any protein ensuring precise and spontaneous protein orientation. We demonstrate how, despite the simplicity of the method, the bioconjugation achieved: (i) is highly efficient, even in the presence of competing proteins, (ii) is stable at extreme physiological conditions (pH ranges 5.2-9.0; NaCl concentrations 0-1 M); (iii) prevents unwanted protein biofouling days after incubation in biologically-relevant conditions; and finally, (iv) avoids nanoparticle interaction with promiscuous unspecific receptors. In summary, this protein biocoating technique, applicable to a wide array of nano-designs, integrates material science and molecular biology procedures to create hybrid nanodevices with well-defined surfaces and predictable biological behaviors, opening a chapter in precision nanodiagnostics, nanosensing or nanotherapeutic applications.

Reversible Control of Protein Corona Formation on Gold Nanoparticles Using Host-Guest Interactions

When nanoparticles (NPs) are exposed to biological media, proteins are adsorbed, forming a so-called protein corona (PC). This cloud of protein aggregates hampers the targeting and transport capabilities of the NPs, thereby compromising their biomedical applications. Therefore, there is a high interest in the development of technologies that allow control over PC formation, as this would provide a handle to manipulate NPs in biological fluids. We present a strategy that enables the reversible disruption of the PC using external stimuli, thereby allowing a precise regulation of NP cellular uptake. The approach, demonstrated for gold nanoparticles (AuNPs), is based on a biorthogonal, supramolecular host-guest interactions between an anionic dye bound to the AuNP surface and a positively charged macromolecular cage. This supramolecular complex effectively behaves as a zwitterionic NP ligand, which is able not only to prevent PC formation but also to disrupt a previously formed hard corona. With this supramolecular stimulus, the cellular internalization of AuNPs can be enhanced by up to 30-fold in some cases, and even NP cellular uptake in phagocytic cells can be regulated. Additionally, we demonstrate that the conditional cell uptake of purposely designed gold nanorods can be used to selectively enhance photothermal cell death.

Enzyme Immobilization on Maghemite Nanoparticles with Improved Catalytic Activity: An Electrochemical Study for Xanthine

Generally, enzyme immobilization on nanoparticles leads to nano-conjugates presenting partially preserved, or even absent, biological properties. Notwithstanding, recent research demonstrated that the coupling to nanomaterials can improve the activity of immobilized enzymes. Herein, xanthine oxidase (XO) was immobilized by self-assembly on peculiar naked iron oxide nanoparticles (surface active maghemite nanoparticles, SAMNs). The catalytic activity of the nanostructured conjugate (SAMN@XO) was assessed by optical spectroscopy and compared to the parent enzyme. SAMN@XO revealed improved catalytic features with respect to the parent enzyme and was applied for the electrochemical studies of xanthine. The present example supports the nascent knowledge concerning protein conjugation to nanoparticle as a means for the modulation of biological activity.

Building block and rapid synthesis of catecholamines-inorganic nanoflowers with their peroxidase-mimicking and antimicrobial activities

Protein incorporated flower-shaped hybrid nanostructures have received highly considerable attention due to their greatly enhanced catalytic activities and stabilities. Up to date, proteins, enzymes (mostly considered as proteins), and amino acids (as the building blocks of peptides and proteins) have been used as organic components of the hybrid nanoflowers. Herein, we present a rational strategy to rapidly form catecholamines (dopamine, epinephrine and norepinephrine)-copper ion (Cu2+) incorporated nanoflowers (cNFs) mostly in 3 hours and show their peroxidase-mimic catalytic, dye degradation and antimicrobial activities through Fenton-like reaction mechanism. We systematically studied effects of experimental parameters including catecholamine concentrations, reaction time and reaction pH values, on formation of the cNFs. We also explained that norepinephrine nanoflower (neNF) with its porous structure, high surface area, polar surface property behaves as an efficient Fenton agent by exhibiting highly much catalytic activities compared to dopamine nanoflower (dNF) and epinephrine nanoflower (epNF). We claim that the NFs formed using nonprotein molecules can be used in designing new generation nanobiocatalytics, antimicrobial agents, nanobiosensors and pharmaceutical products.

Multichannel DNA Sensor Array Fingerprints Cell States and Identifies Pharmacological Effectors of Catabolic Processes

Cells at disease onset are often associated with subtle changes in the expression level of a single or few molecular components, making traditionally used biomarker-driven clinical diagnosis a challenging task. We demonstrate here the design of a DNA nanosensor array with multichannel output that identifies the normal or pathological state of a cell based on the alteration of its global proteomic signature. Fluorophore-encoded single-stranded DNA (ssDNA) strands were coupled via supramolecular interaction with a surface-functionalized gold nanoparticle quencher to generate this integrated sensor array. In this design, ssDNA sequences exhibit dual roles, where they provide differential affinities with the receptor gold nanoparticle as well as act as transducer elements. The unique interaction mode of the analyte molecules disrupts the noncovalent supramolecular complexation, generating simultaneous multichannel fluorescence output to enable signature-based analyte identification via a linear discriminant analysis-based machine learning algorithm. Different cell types, particularly normal and cancerous cells, were effectively distinguished using their fluorescent fingerprints. Additionally, this DNA sensor array displayed excellent sensitivity to identify cellular alterations associated with chemical modulation of catabolic processes. Importantly, pharmacological effectors, which could modulate autophagic flux, have been effectively distinguished by generating responses from their global protein signatures. Taken together, these studies demonstrate that our multichannel DNA nanosensor is well suited for rapid identification of subtle changes in a complex mixture and thus can be readily expanded for point-of-care clinical diagnosis, high-throughput drug screening, or predicting the therapeutic outcome from a limited sample volume.

Bare Iron Oxide Nanoparticles: Surface Tunability for Biomedical, Sensing and Environmental Applications

Surface modification is widely assumed as a mandatory prerequisite for the real applicability of iron oxide nanoparticles. This is aimed to endow prolonged stability, electrolyte and pH tolerance as well as a desired specific surface chemistry for further functionalization to these materials. Nevertheless, coating processes have negative consequences on the sustainability of nanomaterial production contributing to high costs, heavy environmental impact and difficult scalability. In this view, bare iron oxide nanoparticles (BIONs) are arousing an increasing interest and the properties and advantages of pristine surface chemistry of iron oxide are becoming popular among the scientific community. In the authors’ knowledge, rare efforts were dedicated to the use of BIONs in biomedicine, biotechnology, food industry and environmental remediation. Furthermore, literature lacks examples highlighting the potential of BIONs as platforms for the creation of more complex nanostructured architectures, and emerging properties achievable by the direct manipulation of pristine iron oxide surfaces have been little studied. Based on authors’ background on BIONs, the present review is aimed at providing hints on the future expansion of these nanomaterials emphasizing the opportunities achievable by tuning their pristine surfaces.

Present Scenario of Bioconjugates in Cancer Therapy: A Review

Cancer is one of the deadliest diseases and poses a risk to people all over the world. Surgery, chemo, and radiation therapy have been the only options available until today to combat this major problem. Chemotherapeutic drugs have been used for treatment for more than 50 years. Unfortunately, these drugs have inherent cytotoxicities and tumor cells have started inducing resistance against these drugs. Other common techniques such as surgery and radiotherapy have their own drawbacks. Therefore, such techniques are incompetent tools to alleviate the disease efficiently without any adverse effects. This scenario has inspired researchers to develop alternative techniques with enhanced therapeutic effects and minimal side effects. Such techniques include targeted therapy, liposomal therapy, hormonal therapy, and immunotherapy, etc. However, these therapies are expensive and not effective enough. Furthermore, researchers have conjugated therapeutic agents or drugs with different molecules, delivery vectors, and/or imaging modalities to combat such problems and enhance the therapeutic effect. This conjugation technique has led to the development of bioconjugation therapy, in which at least one molecule is of biological origin. These bioconjugates are the new therapeutic strategies, having prospective synergistic antitumor effects and have potency to overcome the complications being produced by chemo drugs. Herein, we provide an overview of various bioconjugates developed so far, as well as their classification, characteristics, and targeting approach for cancer. Additionally, the most popular nanostructures based on their organic or inorganic origin (metallic, magnetic, polymeric nanoparticles, dendrimers, and silica nanoparticles) characterized as nanocarriers are also discussed. Moreover, we hope that this review will provide inspiration for researchers to develop better bioconjugates as therapeutic agents.

Covalently Binding of Bovine Serum Albumin to Unsaturated Poly(Globalide-Co-ε-Caprolactone) Nanoparticles by Thiol-Ene Reactions

When nanoparticles (NPs) are introduced to a biological fluid, different proteins (and other biomolecules) rapidly get adsorbed onto their surface, forming a protein corona capable of giving to the NPs a new "identity" and determine their biological fate. Protein-nanoparticle conjugation can be used in order to promote specific interactions between living systems and nanocarriers. Non-covalent conjugates are less stable and more susceptible to desorption in biological media, which makes the development of engineered nanoparticle surfaces by covalent attachment an interesting topic. In this work, the surface of poly(globalide-co-ε-caprolactone) (PGlCL) nanoparticles containing double bonds in the main polymer chain is covalently functionalized with bovine serum albumin (BSA) by thiol-ene chemistry, producing conjugates which are resistant to dissociation. The successful formation of the covalent conjugates is confirmed by flow cytometry (FC) and fluorescence correlation spectroscopy (FCS). Transmission electron microscopy (TEM) allows the visualization of the conjugate formation, and the presence of a protein layer surrounding the NPs can be observed. After conjugation with BSA, NPs present reduced cell uptake by HeLa and macrophage RAW264.7 cells, in comparison to uncoated NP. These results demonstrate that it is possible to produce stable conjugates by covalently binding BSA to PGlCL NP through thiol-ene reaction.

Enhanced Biocatalytic Activity of Recombinant Lipase Immobilized on Gold Nanoparticles

BACKGROUND

Bacterial lipases especially Pseudomonas lipases are extensively used for different biotechnological applications.

OBJECTIVES

With the better understanding and progressive needs for improving its activity in accordance with the growing market demand, we aimed in this study to improve the recombinant production and biocatalytic activity of lipases via surface conjugation on gold nanoparticles.

METHODS

The full length coding sequences of lipase gene (lipA), lipase specific foldase gene (lipf) and dual cassette (lipAf) gene were amplified from the genomic DNA of Pseudomonas aeruginosa PA14 and cloned into the bacterial expression vector pRSET-B. Recombinant lipases were expressed in E. coli BL-21 (DE3) pLysS then purified using nickel affinity chromatography and the protein identity was confirmed using SDS-PAGE and Western blot analysis. The purified recombinant lipases were immobilized through surface conjugation with gold nanoparticles and enzymatic activity was colorimetrically quantified.

RESULTS

Here, two single expression plasmid systems pRSET-B-lipA and pRSET-B-lipf and one dual cassette expression plasmid system pRSET-B-lipAf were successfully constructed. The lipolytic activities of recombinant lipases LipA, Lipf and LipAf were 4870, 426 and 6740 IUmg-1, respectively. However, upon immobilization of these recombinant lipases on prepared gold nanoparticles (GNPs), the activities were 7417, 822 and 13035 IUmg-1, for LipA-GNPs, Lipf-GNPs and LipAf-GNPs, respectively. The activities after immobilization have been increased 1.52 and 1.93 -fold for LipA and LipAf, respectively.

CONCLUSION

The lipolytic activity of recombinant lipases in the bioconjugate was significantly increased relative to the free recombinant enzyme where immobilization had made the enzyme attain its optimum performance.

The Role of Ligands in the Chemical Synthesis and Applications of Inorganic Nanoparticles

The design of nanoparticles is critical for their efficient use in many applications ranging from biomedicine to sensing and energy. While shape and size are responsible for the properties of the inorganic nanoparticle core, the choice of ligands is of utmost importance for the colloidal stability and function of the nanoparticles. Moreover, the selection of ligands employed in nanoparticle synthesis can determine their final size and shape. Ligands added after nanoparticle synthesis infer both new properties as well as provide enhanced colloidal stability. In this article, we provide a comprehensive review on the role of the ligands with respect to the nanoparticle morphology, stability, and function. We analyze the interaction of nanoparticle surface and ligands with different chemical groups, the types of bonding, the final dispersibility of ligand-coated nanoparticles in complex media, their reactivity, and their performance in biomedicine, photodetectors, photovoltaic devices, light-emitting devices, sensors, memory devices, thermoelectric applications, and catalysis.

Enhancing Enzyme Immobilization on Carbon Nanotubes via Metal-Organic Frameworks for Large-Substrate Biocatalysis

Biocatalysis of large-sized substrates finds wide applications. Immobilizing the involved enzymes on solid supports improves biocatalysis yet faces challenges such as enzyme structural perturbation, leaching, and low cost-efficiencies, depending on immobilization strategies/matrices. Carbon nanotubes (CNTs) are attractive matrices but challenged by enzyme leaching (physical adsorption) or perturbation (covalent linking). Zeolitic imidazolate frameworks (ZIFs) overcome these issues. However, our recent study [ J. Am. Chem. Soc., 2018, 140, 16032-16036] showed reduced cost-efficiency as enzymes trapped below the ZIF surfaces cannot participate in biocatalysis; the enzyme-ZIF composites are also unstable under acidic conditions. In this work, we demonstrate the feasibility of using ZIFs to immobilize enzymes on CNT surfaces on two model enzymes, T4 lysozyme and amylase, both of which showed negligible leaching and retained catalytic activity under neutral and acidic conditions. To better understand the behavior of enzymes on CNTs and CNT-ZIF, we characterized enzyme orientation on both matrices using site-directed spin-labeling (SDSL)-electron paramagnetic resonance (EPR), which is immune to the complexities caused by CNT and ZIF background signals and enzyme-matrix interactions. Our structural investigations showed enhanced enzyme exposure to the solvent compared to enzymes in ZIFs alone; orientation of enzymes in matrices itself is directly related to substrate accessibility and, therefore, essential for understanding and improving catalytic efficiency. To the best of our knowledge, this is the first time ZIFs and one-pot synthesis are employed to anchor large-substrate enzymes on CNT surfaces for biocatalysis. This is also the first report of enzyme orientation on the CNT surface and upon trapping in CNT-ZIF composites. Our results are essential for guiding the rational design of CNT-ZIF combinations to improve enzyme stabilization, loading capacity, and catalytic efficiency.

Conjugation of an α-Helical Peptide to the Surface of Gold Nanoparticles

We are interested in functionalizing gold nanoparticles (AuNPs) with proteins using a biomimetic approach in which an intermediate peptide "glue" directs the orientation of a protein relative to the AuNP surface. The first step toward this goal is described in the present article. Specifically, we show that ∼5 nm AuNPs can be functionalized with a mixed self-assembled monolayer (SAM) consisting of oligo(ethylene glycol) alkanethiols terminated with either hydroxyl or azide groups, and that the resulting materials are stable and soluble in water. The azide groups on the surface of the AuNPs can be subsequently linked to alkyne-functionalized peptides via a copper-catalyzed azide-alkyne cycloaddition (click) reaction. Analysis of the resulting material by Fourier transform infrared and circular dichroism spectroscopy demonstrates that the peptide is covalently linked to the SAM and that it exists in an α-helical conformation. In addition to our intended purpose of using these highly structured, biomimetic materials to orient proteins, they may also be useful for applications involving interactions between nanoparticles and cells.

Enzyme self-assembly on naked iron oxide nanoparticles for aminoaldehyde biosensing

The preservation of enzymatic activity is a fundamental requirement for exploiting hybrid nano-bio-conjugates, and the control over protein-nanoparticle interactions, leading to stable and catalytically active hybrids, represents the key for designing new biosensing platforms. In this scenario, surface active maghemite nanoparticles (SAMNs) represent a new class of naked magnetic nanoparticles, displaying peculiar electrocatalytic features and the ability to selectively bind proteins. Recombinant aminoaldehyde dehydrogenase from tomato (SlAMADH1) was used as a model protein, and successfully immobilized by self-assembly on the surface of naked SAMNs, where its enzymatic activity resulted preserved for more than 6 months. The hybrid nanomaterial (SAMN@SlAMADH1) was characterized by UV-Vis spectroscopy, mass spectrometry, and TEM microscopy, and applied for the development of a biosensor for the determination of aminoaldehydes in alcoholic beverages. Measurements were carried out in a low volume electrochemical flow cell comprising a SAMN modified carbon paste electrode for the coulometric determination of the NADH produced during the enzymatic catalysis. The present findings, besides representing the first example of an electrochemical biosensor for aminoaldehydes in an alcoholic matrix, open the door to the use of immobilized enzymes on naked metal oxides nanomaterials for biosensing.

Methotrexate-Loaded Solid Lipid Nanoparticles: Protein Functionalization to Improve Brain Biodistribution

Glioblastoma is the most common and invasive primary tumor of the central nervous system and normally has a negative prognosis. Biodistribution in healthy animal models is an important preliminary study aimed at investigating the efficacy of chemotherapy, as it is mainly addressed towards residual cells after surgery in a region with an intact blood⁻brain barrier. Nanoparticles have emerged as versatile vectors that can overcome the blood⁻brain barrier. In this experimental work, solid lipid nanoparticles, prepared using fatty acid coacervation, have been loaded with an active lipophilic ester of cytotoxic drug methotrexate, and functionalized with either transferrin or insulin, two proteins whose receptors are abundantly expressed on the blood⁻brain barrier. Functionalization has been achieved by grafting a maleimide moiety onto the nanoparticle's surface and exploiting its reactivity towards thiolated proteins. The nanoparticles have been tested in vitro on a blood⁻brain barrier cellular model and in vivo for biodistribution in Wistar rats. Drug metabolites, in particular 7-hydroxymethotrexate, have also been investigated in the animal model. The data obtained indicate that the functionalization of the nanoparticles improved their ability to overcome the blood⁻brain barrier when a PEG spacer between the proteins and the nanoparticle's surface was used. This is probably because this method provided improved ligand⁻receptor interactions and selectivity for the target tissue.

Structure and Interaction of Nanoparticle-Protein Complexes

The integration of nanoparticles with proteins is of high scientific interest due to the amazing potential displayed by their complexes, combining the nanoscale properties of nanoparticles with the specific architectures and functions of the protein molecules. The nanoparticle-protein complexes, in particular, are useful in the emerging field of nanobiotechnology (nanomedicine, drug delivery, and biosensors) as the nanoparticles having sizes comparable to that of living cells can access and operate within the cell. The understanding of nanoparticle interaction with different protein molecules is a prerequisite for such applications. The interaction of the two components has been shown to result in conformational changes in proteins and to affect the surface properties and colloidal stability of the nanoparticles. In this feature article, our recent studies exploring the driving interactions in nanoparticle-protein systems and resultant structures are presented. The anionic colloidal silica nanoparticles and two globular charged proteins [lysozyme and bovine serum albumin (BSA)] have been investigated as model systems. The adsorption behavior of the two proteins on nanoparticles is found to be completely different, but they both give rise to similar phase transformation from one phase to two phase in respective nanoparticle-protein systems. The presence of protein induces the short-range and long-range attraction between the nanoparticles with lysozyme and BSA, respectively. The observed phase behavior and its dependence on various physiochemical parameters (e.g., nanoparticle size, ionic strength, and solution pH) have been explained in terms of underlying interactions.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Tuning Nanoparticle-Micelle Interactions and Resultant Phase Behavior

The evolution of the interaction between an anionic nanoparticle and a nonionic surfactant and their resultant phase behavior in aqueous solution in the presence of electrolyte and ionic surfactants have been studied. The mixed system of anionic silica nanoparticles (Ludox LS30) with nonionic surfactant decaethylene glycol monododecylether (C12E10) forms a highly stable clear phase over a wide concentration range of surfactant. Small-angle neutron scattering (SANS) and dynamic light scattering data show that the surfactant micelles adsorb on the surface of the nanoparticle, resulting in micellar-decorated nanoparticle structures. With the addition of a small amount of electrolyte into this system, the stability gets disturbed substantially and turns to a two-phase (turbid) system. The evolution of interaction in this system has been examined, and it was found that micelle-induced long-range depletion attraction (modeled by a double Yukawa potential) between nanoparticles leads to their aggregation. Interestingly, the addition of anionic surfactant sodium dodecyl sulfate (SDS) in this two-phase system transforms it to a transparent one-phase state, suppressing the depletion-mediated aggregation of nanoparticles. This is attributed to the formation of anionic C12E10-SDS mixed micelles, and it is their repulsive micelle-micelle interaction that disrupts the depletion phenomenon. On the other hand, the addition of cationic surfactant dodecyl trimethylammonium bromide (DTAB) to the turbid LS30-C12E10 electrolyte system shows no change in the turbidity arising from an aggregated nanoparticle system. The driving interaction, in this case, is different from that of the surfactant-mediated depletion attraction; it is due to the attraction between the nanoparticles mediated by the presence of oppositely charged DTAB micelles between them, resulting in a charge-driven bridging aggregation of nanoparticles. Each of these multicomponent systems has been investigated using contrast variation SANS measurements for different contrast conditions where the role of individual components (nanoparticle or surfactant) in the mixed system has been selectively studied. These results thus show that nanoparticle-surfactant micelle interactions can be tuned by the presence of electrolyte and/or choice of surfactant combination.