Quantification of proteins on gold nanoparticles by combining MALDI-TOF MS and proteolysis

Molecular Surface Quantification of Multifunctionalized Gold Nanoparticles Using UV-Visible Absorption Spectroscopy Deconvolution

Multifunctional gold nanoparticles (AuNPs) are of great interest, owing to their vast potential for use in many areas including sensing, imaging, delivery, and medicine. A key factor in determining the biological activity of multifunctional AuNPs is the quantification of surface conjugated molecules. There has been a lack of accurate methods to determine this for multifunctionalized AuNPs. We address this limitation by using a new method based on the deconvolution and Levenberg-Marquardt algorithm fitting of UV-visible absorption spectrum to calculate the precise concentration and number of cytochrome C (Cyt C) and zinc porphyrin (Zn Porph) bound to each multifunctional AuNP. Dynamic light scattering (DLS) and zeta potential measurements were used to confirm the functionalization of AuNPs with Cyt C and Zn Porph. Transmission electron microscopy (TEM) was used in conjunction with UV-visible absorption spectroscopy and DLS to identify the AuNP size and confirm that no aggregation had taken place after functionalization. Despite the overlapping absorption bands of Cyt C and Zn Porph, this method was able to reveal a precise concentration and number of Cyt C and Zn Porph molecules attached per AuNP. Furthermore, using this method, we were able to identify unconjugated molecules, suggesting the need for further purification of the sample. This guide provides a simple and effective method to quickly quantify molecules bound to AuNPs, giving users valuable information, especially for applications in drug delivery and biosensors.

Analyzing the surface of functional nanomaterials-how to quantify the total and derivatizable number of functional groups and ligands

Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address method- and material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5-10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization.

How to effectively prepare a sample for bottom-up proteomic analysis of nanoparticle protein corona? A critical review

Since the interest in the biomedical applications of inorganic nanoparticles (NPs) has rapidly grown over the last decades, there is a need for a thorough characterization of bio-nano interactions. NPs introduced to the body (mostly intravenously) encounter plasma proteins, that instantly create a so-called "protein corona" on the NPs surface, giving the nanomaterial a new biological identity. Type of the proteins that interact with NPs may affect the in vivo fate of NPs. For that reason, it is particularly important to establish analytical methods capable of corona protein identification. Bottom-up proteomics is most often used for that purpose. A crucial part of the experiment is sample preparation, as it is already proven that different protocols may lead to distinct results. This review is aimed at providing a characterization of two main stages of sample preparation: separation of NPs with protein corona from the unbound proteins and the digestion of corona proteins. Separation techniques such as centrifugation, magnetic separation, and chromatography and three digestion methods (in-gel, in-solution, and on-particle) are described with special emphasis paid on their advantages and disadvantages as well as their influence on the result of identification. This paper also indicates the need for standardization of protein corona identification protocols, as some of the proteins may be preferentially detected while applying a particular digestion procedure.

Mass spectrometric investigation of concentration-dependent effect of curcumin and oxidative stress on intracellular glutathione levels

Herein, we investigated the correlation between curcumin and glutathione (GSH) levels in mammalian cells using gold nanoparticles (AuNPs) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). GSH exists in high concentration in the cytosol and acts as a major antioxidant and reducing agent in organisms. Previous studies showed that curcumin, a well-known antioxidant with anti-inflammatory, anti-proliferative, and anti-carcinogenic activities, affects GSH levels in mammalian cells. However, the correlation between their levels remains controversial and has not yet been completely elucidated. This study used our recent strategy of GSH quantification, where GSH in cell lysate is captured on maleimide groups of AuNPs and analyzed using MALDI-TOF MS with isotopomer GSH (GSH*)-conjugated AuNPs as an internal standard. The comparison between GSH and GSH* relative intensities allows the quantitation of GSH in cells. In this way, GSH levels in mammalian cells were investigated after incubation with curcumin at various concentrations with or without oxidative stress. We observed that intracellular GSH levels were affected by curcumin in a concentration-dependent manner with oxidative stress; GSH levels decrease at a lower curcumin concentration, which can be recovered at increased curcumin concentrations. We also found that the GSH level increased at all curcumin concentrations after a certain incubation time. We believe our strategy can be commonly used to determine GSH levels in cells that are treated differently with various exogenous stimulants like reactive oxygen species, biofunctional natural products, and drug candidates. Graphical abstract.

Click-Engineered, Bioresponsive, and Versatile Particle-Protein-Dye System

We present a multifunctional polymer based nanoparticle platform for personalized nanotheranostic applications, which include photodynamic therapy and active targeting. In this system, poly(propargyl acrylate) (PA) particles were surface-modified with organic ligands and fluorophores (the payload) through an environmentally-sensitive linker. An azide modified bovine serum albumin (azBSA) was employed as the linker. This system prevents opsonization and, upon digestion, releases the payload. Attachment of the emitting payload to the particle through azide-modified bovine serum albumin (BSA) quenches emission, which can be again activated with digestion of the azBSA. The emission "turn-on" at a specific location will increase the signal-to-noise ratio. By utilizing human head and neck squamous carcinoma cells (UMSCC22A), photodynamic therapy studies with these particles gave promising reductions in cell growth. Additionally, the particle-protein-dye system is versatile as different fluorophores (such as silicon phthalocyanine or cyanine 3) can be attached to the protein and the same activation/deactivation behavior is observed. Active targeting can be employed to enhance the concentration of the payload in the designated tumor. Human lung carcinoma cells (A549) were utilized in toxicity studies where PA-azBSA particles were modified with a Survivin targeting ligand and indicated an enhanced cell death with the modified particles relative to the "free" Survivin targeting ligand.

Characterization of glycan isomers using magnetic carbon nanoparticles as a MALDI co-matrix

Matrix-assisted laser desorption ionization-in source decay (MALDI-ISD) analysis is a useful technique in the structural analysis of glycans. Our recent publication demonstrated that magnetic carbon nanoparticles (MCNPs), used as a MALDI co-matrix, significantly enhanced ISD efficiency for glycomic analysis by MALDI-TOF. In this study, MCNPs were used for the structural study of isomeric glycans. Results from the standard glycans confirmed easy distinction of positional and linkage isomers without the need for further derivatization of glycan molecules. Extensive glycosidic and cross-ring fragmented ions provided different fragment patterns for various glycan isomers. Core- and branch-fucosylated isomers were distinguished by several unique ions, and pseudo-MS³ data were used to recognize the fucosylated branch. Although no diagnostic fragment ion was observed for 2,3- and 2,6-linked sialic acid isomers, their MALDI-ISD patterns were found to be significantly different (P < 0.05). Furthermore, the method introduced in this study could not only be used for the identification of glycan isomers but has also proved effective for the isomeric structural confirmation of gangliosides. GD1a and GD1b gangliosides were easily distinguished by the diagnostic ion originated from GD1a, produced by Z_4αZ_2β cleavages. Moreover, liquid chromatography coupled with MALDI-TOF was applied to analyze N-glycan isomers derived from a pooled human blood serum sample, providing an alternative method of isomeric glycomic analysis of biological specimens.

Magnetic carbon nanoparticles as a MALDI co-matrix enable isomeric characterization of glycans in biological samples.

Functionalized gold nanoparticles for sample preparation: A review

Sample preparation is a crucial step for the reliable and accurate analysis of both small molecule and biopolymers which often involves processes such as isolation, pre-concentration, removal of interferences (purification), and pre-processing (e.g., enzymatic digestion) of targets from a complex matrix. Gold nanoparticle (GNP)-assisted sample preparation and pre-concentration has been extensively applied in many analytical procedures in recent years due to the favorable and unique properties of GNPs such as size-controlled synthesis, large surface-to-volume ratio, surface inertness, straightforward surface modification, easy separation requiring minimal manipulation of samples. This review article primarily focuses on applications of GNPs in sample preparation, in particular for bioaffinity capture and biocatalysis. In addition, their most common synthesis, surface modification and characterization methods are briefly summarized. Proper surface modification for GNPs designed in accordance to their target application directly influence their functionalities, e.g., extraction efficiencies, and catalytic efficiencies. Characterization of GNPs after synthesis and modification is worthwhile for monitoring and controlling the fabrication process to ensure proper quality and functionality. Parameters such as morphology, colloidal stability, and physical/chemical properties can be assessed by methods such as surface plasmon resonance, dynamic light scattering, ζ-potential determinations, transmission electron microscopy, Taylor dispersion analysis, and resonant mass measurement, among others. The accurate determination of the surface coverage appears to be also mandatory for the quality control of functionality of the nanoparticles. Some promising applications of (functionalized) GNPs for bioanalysis and sample preparation are described herein.

Gold Nanoparticles (AuNPs) as Reactive Matrix for Detection of Trace Levels of HCN in Air by Laser Desorption/Ionization Mass Spectrometry (LDI-MS)

Under direct laser desorption/ionization mass spectrometric conditions, the irradiation of target spots made of gold nanoparticle residues generates a series of peaks at m/z 197, 394, 591… representing Au_n^- ions (n = 1-3). In contrast, spectra recorded from gold nanoparticles directly mixed with an alkali cyanide exhibited an additional peak at m/z 249, indicating an abundant generation of gaseous [Au(CN)₂]^- ions upon irradiation. The relative intensity of the m/z 249 peak surged when the amount of cyanide in the mixture was increased. Most remarkably, a peak at m/z 249 was observed even from neat AuNPs upon irradiation, if a nearby spot, which was not irradiated, happened to bear a cyanide sample. We postulated that traces of HCN emanating from the headspace of aqueous cyanide solution during the sample-plate preparation is sufficient to convert gold to AuCN, which is subsequently detected as [Au(CN)₂]^-. Further experiments demonstrated that the relative intensity of the m/z 249 peak diminishes exponentially as the AuNP spot becomes more distant from the putative HCN source. Eventually, the method was developed as an efficient procedure to detect HCN or alkali cyanides. Using KCN, the detection limits were determined to be below 10 pg of CN^- per spot. The method also demonstrated that, upon crushing, the seeds or roots of certain fruits and vegetables such as apple, peach, radish, and cassava, but not carrot, release HCN in amounts detectable by this method. Graphical Abstract.

Liposome-encapsulated fish oil protein-tagged gold nanoparticles for intra-articular therapy in osteoarthritis

AIM

To provide multilayered combination therapies encompassing nanoparticles and organic peptides and to assess their efficacy in the treatment of arthritis.

MATERIALS & METHODS

Fish oil protein (FP) was isolated from fish oil glands and tagged with spherical gold nanoparticles (GNPs). Tagged GNPs were encapsulated in DPPC liposomes (FP-GNP-DPPC) and characterized.

RESULTS & CONCLUSION

FP increased the hydrophilicity of GNP, while encapsulation of FP-GNP within liposomes increased the hydrophobicity. In vitro release studies of FP-GNP-DPPC exhibited sustained release of FP in simulated synovial fluid. FP-GNP-DPPC injected into intra-articular joints of rats displayed anti-osteoarthritic effects in osteoarthritic rat model. This is the first study to report the anti-osteoarthritic activity of FP and DPPC encapsulated FP-GNP liposomes.

Dual Maleimide Tagging for Relative and Absolute Quantitation of Cysteine-Containing Peptides by MALDI-TOF MS

A dual maleimide (DuMal) tagging method has been developed for both relative and absolute quantitation of cysteine-containing peptides (CCPs) in combination with MALDI-TOF mass spectrometry. A pair of maleimides with minimal differences in their chemical structures, N-methylmaleimide and Nethylmaleimide, have been chosen to allow for the rapid (≈minutes) tagging of CCPs in the Michael addition reaction with high efficiency. It has been validated that the DuMal tagging technique is sensitive and reliable in the quantitative analysis of CCPs. Absolute quantitation of CCPs can be achieved with a detection limit as low as 7.3 nm. Relative quantitation of CCPs can be performed in various sample mixtures with consistent results (coefficient of variation <5 %). The DuMal tagging technique provides a sensitive and accurate approach for the quantitation of biomolecules containing thiol reactive sites; thus it is promising for protein detection, disease diagnosis, and biomarker discovery associated with post-translational modifications of cysteines.

Opportunities for glyconanomaterials in personalized medicine

In this feature article we discuss the particular relevance of glycans as components or targets of functionalized nanoparticles (NPs) for potential applications in personalized medicine but we will not enter into descriptions for their preparation. For a more general view covering the preparation and applications of glyconanomaterials the reader is referred to a number of recent reviews. The combination of glyco- and nanotechnology is already providing promising new tools for more personalized solutions to diagnostics and therapy. Current applications relevant to personalized medicine include drug targeting, localized radiation therapy, imaging of glycan expression of cancer cells, point of care diagnostics, cancer vaccines, photodynamic therapy, biosensors, and glycoproteomics.

Facet-Specific Adsorption of Tripeptides at Aqueous Au Interfaces: Open Questions in Reconciling Experiment and Simulation

The adsorption of three homo-tripeptides, HHH, YYY, and SSS, at the aqueous Au interface is investigated, using molecular dynamics simulations. We find that consideration of surface facet effects, relevant to experimental conditions, opens up new questions regarding interpretations of current experimental findings. Our well-tempered metadynamics simulations predict the rank ordering of the tripeptide binding affinities at aqueous Au(111) to be YYY > HHH > SSS. This ranking differs with that obtained from existing experimental data which used surface-immobilized Au nanoparticles as the target substrate. The influence of Au facet on these experimental findings is then considered, via our binding strength predictions of the relevant amino acids at aqueous Au(111) and Au(100)(1 × 1). The Au(111) interface supports an amino acid ranking of Tyr > HisA ≃ HisH > Ser, matching that of the tripeptides on Au(111), while the ranking on Au(100) is HisA > Ser ≃ Tyr ≃ HisH, with only HisA showing non-negligible binding. The substantial reduction in Tyr amino acid affinity for Au(100) vs Au(111) offers one possible explanation for the experimentally observed weaker adsorption of YYY on the nanoparticle-immobilized substrate compared with HHH. In a separate set of simulations, we predict the structures of the adsorbed tripeptides at the two aqueous Au facets, revealing facet-dependent differences in the adsorbed conformations. Our findings suggest that Au facet effects, where relevant, may influence the adsorption structures and energetics of biomolecules, highlighting the possible influence of the structural model used to interpret experimental binding data.

Quantification of Cell-Penetrating Peptide Associated with Polymeric Nanoparticles Using Isobaric-Tagging and MALDI-TOF MS/MS

High sensitivity quantification of the putative cell-penetrating peptide di-arginine-histidine (RRH) associated with poly (ethyl-cyanoacrylate) (PECA) nanoparticles was achieved without analyte separation, using a novel application of isobaric-tagging and high matrix-assisted laser desorption/ionization coupled to time-of-flight (MALDI-TOF) mass spectrometry. Isobaric-tagging reaction equilibrium was reached after 5 min, with 90% or greater RRH peptide successfully isobaric-tagged after 60 min. The accuracy was greater than 90%, which indicates good reliability of using isobaric-tagged RRH as an internal standard for RRH quantification. The sample intra- and inter-spot coefficients of variations were less than 11%, which indicate good repeatability. The majority of RRH peptides in the nanoparticle formulation were physically associated with the nanoparticles (46.6%), whereas only a small fraction remained unassociated (13.7%). The unrecovered RRH peptide (~40%) was assumed to be covalently associated with PECA nanoparticles. Graphical Abstract ᅟ.

Electrostatic Interactions and Protein Competition Reveal a Dynamic Surface in Gold Nanoparticle-Protein Adsorption

Gold nanoparticle- (AuNP-) protein conjugates are potentially useful in a broad array of diagnostic and therapeutic applications, but the physical basis of the simultaneous adsorption of multiple proteins onto AuNP surfaces remains poorly understood. Here, we investigate the contribution of electrostatic interactions to protein-AuNP binding by studying the pH-dependent binding behavior of two proteins, GB3 and ubiquitin. For both proteins, binding to 15-nm citrate-coated AuNPs closely tracks with the predicted net charge using standard pK_a values, and a dramatic reduction in binding is observed when lysine residues are chemically methylated. This suggests that clusters of basic residues are involved in binding, and using this hypothesis, we model the pK_a shifts induced by AuNP binding. Then, we employ a novel NMR-based approach to monitor the binding competition between GB3 and ubiquitin in situ at different pH values. In light of our model, the NMR measurements reveal that the net charge, binding association constant, and size of each protein play distinct roles at different stages of protein adsorption. When citrate-coated AuNPs and proteins first interact, net charge appears to dominate. However, as citrate molecules are displaced by protein, the surface chemistry changes, and the energetics of binding becomes far more complex. In this case, we observed that GB3 is able to displace ubiquitin at intermediate time scales, even though it has a lower net charge. The thermodynamic model for binding developed here could be the first step toward predicting the binding behavior in biological fluids, such as blood plasma.

Conjugation of Bovine Serum Albumin With ZnO Nanosphere-A Novel Approach for Ultra-Low Level Mercury Ion Detection

Solution-processed bovine serum albumin conjugated with ZnO nanosphere (BCZ) have been synthesized for ultra-low level mercury ion detection. Simple drop casting technique was adopted to fabricate such a mercury ion (Hg²⁺) detection scheme. Morphological and optical characterization of the BCZ was performed by Transmission Electron Microscopy (TEM), UV-Vis and Fluorescence spectroscopic technique prior to device fabrication. The working principle of the BCZ device for Hg²⁺ detection depends upon the variation of conductance with various concentration of Hg²⁺. An extensive study was carried out to investigate the effect of Hg²⁺ upon transport properties of BCZ. The ultra-low level of Hg²⁺ sensing was performed using this electrical detection technique. More importantly, this proposed BCZ based detection technique is found to be simple, inexpensive and very fast in responding (response time  ∼ 2.5 s) to heavy metal ion with a limit of detection (LOD) 0.03 fg/ml (S/ [Formula: see text]3).

Identification and Localization of Gold Nanoparticles in Potassium Ion Pores: Implications for Kir Blockade

INTRODUCTION

In our previous study, we found that negatively charged gold nanoparticles with spermidine have the potential of blocking inwardly rectifying potassium channels (Kir), both at the cellular and the tissue level.

METHODS

For the purpose of the present study, we purified the cytoplasmic domain of the Kir 3.1 receptor from Escherichia coli. Using single particles with surface coating by transmission electron microscopy, we identified the gold nanoparticles at the cytoplasmic side of the human Kir channel.

RESULTS

Energy-dispersive X-ray spectroscopy showed the presence of the gold deposits in the cytoplasmic domain of the Kir receptor.

CONCLUSION

In conclusion, we could identify undecagold in the ion pore of the Kir3.1 channel in order to clarify its direct blocking effect in the Kir ion pore by undecagold.

Understanding the mechanism of replacement of citrate from the surface of gold nanoparticles by amino acids: a theoretical and experimental investigation and their biological application

The present study explores the physicochemical aspects needed for the appropriate in vitro synthesis and surface modification behavior of gold nanoparticles (AuNPs) in the presence of amino acids (AA).

Green synthesis of bacterial mediated anti-proliferative gold nanoparticles: inducing mitotic arrest (G2/M phase) and apoptosis (intrinsic pathway)

The physiochemical and biological properties of microbial derived gold nanoparticles have potential applications in various biomedical domains as well as in cancer therapy. We have fabricated anti-proliferative bacterial mediated gold nanoparticles (b-Au NPs) using a culture supernatant of Streptomyces clavuligerus and later characterized them by UV-visible, TEM, DLS, XRD and FT-IR spectroscopic techniques. The capping agent responsible for the nanoparticle formation was characterized based on SDS-PAGE and MALDI-TOF-MS analyses. They were tested for anticancer activity in A549, HeLa and DU145 cell lines. The biocompatibility and non-toxic nature of the nanoparticles were tested on normal human lung cell line (MRC-5). The b-Au NPs induced the cell cycle arrest in G2/M phase and also inhibited the microtubule assembly in DU145 cells. Mechanistic studies, such as ROS, MMP, Cyt-c, GSH, caspases 9, 8 and 3 activation and the Annexin V-FITC staining, along with the above parameters tested provided sufficient evidence that the b-Au NPs induced apoptosis through the intrinsic pathway. The results supported the use of b-Au NPs for future therapeutic application in cancer therapy and other biomedical applications.

Bridging the divide between human and environmental nanotoxicology

The need to assess the human and environmental risks of nanoscale materials has prompted the development of new metrological tools for their detection, quantification and characterization. Some of these methods have tremendous potential for use in various scenarios of nanotoxicology. However, in some cases, the limited dialogue between environmental scientists and human toxicologists has hampered the full exploitation of these resources. Here we review recent progress in the development of methods for nanomaterial analysis and discuss the use of these methods in environmental and human toxicology. We highlight the opportunities for collaboration between these two research areas.

Facet selectivity in gold binding peptides: exploiting interfacial water structure

Peptide sequences that can discriminate between gold facets under aqueous conditions offer a promising route to control the growth and organisation of biomimetically-synthesised gold nanoparticles. Knowledge of the interplay between sequence, conformations and interfacial properties is essential for predictable manipulation of these biointerfaces, but the structural connections between a given peptide sequence and its binding affinity remain unclear, impeding practical advances in the field. These structural insights, at atomic-scale resolution, are not easily accessed with experimental approaches, but can be delivered via molecular simulation. A current unmet challenge lies in forging links between predicted adsorption free energies derived from enhanced sampling simulations with the conformational ensemble of the peptide and the water structure at the surface. To meet this challenge, here we use an in situ combination of Replica Exchange with Solute Tempering with Metadynamics simulations to predict the adsorption free energy of a gold-binding peptide sequence, AuBP1, at the aqueous Au(111), Au(100)(1 × 1) and Au(100)(5 × 1) interfaces. We find adsorption to the Au(111) surface is stronger than to Au(100), irrespective of the reconstruction status of the latter. Our predicted free energies agree with experiment, and correlate with trends in interfacial water structuring. For gold, surface hydration is predicted as a chief determining factor in peptide-surface recognition. Our findings can be used to suggest how shaped seed-nanocrystals of Au, in partnership with AuBP1, could be used to control AuNP nanoparticle morphology.

Structure and properties of citrate overlayers adsorbed at the aqueous Au(111) interface

One of the most common means of gold nanoparticle (AuNP) biofunctionalization involves the manipulation of precursor citrate-capped AuNPs via ligand displacement. However, the molecular-level structural characteristics of the citrate overlayer adsorbed at the aqueous Au interface at neutral pH remain largely unknown. Access to atomistic-scale details of these interfaces will contribute much needed insight into how AuNPs can be manipulated and exploited in aqueous solution. Here, the structures of such citrate overlayers adsorbed at the aqueous Au(111) interface at pH 7 are predicted and characterized using atomistic molecular dynamics simulations, for a range of citrate surface densities. We find that the overlayers are disordered in the surface density range considered, and that many of their key characteristics are invariant with surface density. In particular, we predict the overlayers to have 3-D, rather than 2-D, morphologies, with the anions closest to the gold surface being oriented with their carboxylate groups pointing away from the surface. We predict both striped and island morphologies for our overlayers, depending on the citrate surface density, and in all cases we find bare patches of the gold surface are present. Our simulations suggest that both citrate-gold adsorption and citrate-counterion pairing contribute to the stability of these citrate overlayer morphologies. We also calculate the free energy of adsorption at the aqueous Au(111) interface of a single citrate molecule, and compare this with the corresponding value for a single arginine molecule. These findings enable us to predict the conditions under which ligand displacement of surface-adsorbed citrate by arginine may take place. Our findings represent the first steps toward elucidating a more elaborate, detailed atomistic-scale model relating to the biofunctionalization of citrate-capped AuNPs.

Surface modification and bioconjugation of FeCo magnetic nanoparticles with proteins

Magnetic Fe70Co30 nanoparticles with a cubic shape and a mean size of 15±1.5 nm were fabricated using a magnetron-sputtering-based gas phase condensation deposition method. The particles had a high saturation magnetization of 220 emu/g, which is much higher than that of commercially available iron oxide nanoparticles. The FeCo nanoparticles were modified by 3-aminopropyltriethoxy silane and subsequently activated by glutaraldehyde, leading to successful attachment of aldehyde groups onto nanoparticle surfaces. Three proteins, namely streptavidin, PAPP-A antibody and Nectin-4 antibody, were immobilized on glutaraldehyde activated FeCo nanoparticles, and their loading levels were quantitatively evaluated. Our results show that loading capabilities are 95 μg of streptavidin, 128 μg of PAPP-A, and 125 μg of Nectin-4 antibody per milligram of FeCo nanoparticles, and that the three immobilized proteins retain their binding bioactivity. The protein-FeCo conjugates may find valuable applications involving magnetic separation and purification of proteins and cells, and the magnetic detection of biomolecules.

Challenges and opportunities in the advancement of nanomedicines

Nanomedicine-based approaches to cancer treatment face several challenges that differ from those encountered by conventional medicines during clinical development. A systematic exploration of these issues has led us to identify the following needs and opportunities for further development: (1) robust and general methods for the accurate characterization of nanoparticle size, shape, and composition; (2) scalable approaches for producing nanomedicines with optimized bioavailability and excretion profiles; (3) particle engineering for maintaining low levels of nonspecific cytotoxicity and sufficient stability during storage; (4) optimization of surface chemistries for maximum targeted delivery and minimum nonspecific adsorption; (5) practical methods for quantifying ligand density and distributions on multivalent nanocarriers; and (6) the design of multifunctional nanomedicines for novel combination therapies with supportable levels of bioaccumulation.