Self-Interaction Nanoparticle Spectroscopy: A Nanoparticle-Based Protein Interaction Assay

Nanomaterials-enriched sensors for detection of chiral pharmaceuticals

Advancements in nanoscience and nanotechnology have opened new pathways to fabricate novel nanostructures with interesting properties that would be used for different applications. In this respect, nanostructures comprising chirality are one of the most rapidly developing research fields encompassing chemistry, physics and biology. Chirality, also known as mirror asymmetry, describes the geometrical property of an object that is not superimposable on its mirror image. This characteristic plays a crucial role because these identical forms of chiral species in pharmaceuticals or food additives may exhibit different effects on living organisms. Therefore, chiral analysis is an important field of modern chemical analysis in health-related industries that are reliant on the production of enantiomeric compounds involving pharmaceuticals. This review covers the recent advances dealing with the synthesis, design and advantageous analytical performance of nanomaterials-enriched sensors used for chiral pharmaceuticals. We conclude this review with the challenges existing in this research field and our perspectives on some potential strategies with cutting-edge approaches for the rational design of sensors for chiral pharmaceuticals. We expect this comprehensive review will inspire future studies in nanomaterials-enriched chiral sensors.

Protein-nanoparticle interactions and a new insight

The study of protein-nanoparticle interactions provides knowledge about the bio-reactivity of nanoparticles, and creates a database of nanoparticles for applications in nanomedicine, nanodiagnosis, and nanotherapy. The problem arises when nanoparticles come in contact with physiological fluids such as plasma or serum, wherein they interact with the proteins (or other biomolecules). This interaction leads to the coating of proteins on the nanoparticle surface, mostly due to the electrostatic interaction, called 'corona'. These proteins are usually partially unfolded. The protein corona can deter nanoparticles from their targeted functionalities, such as drug/DNA delivery at the site and fluorescence tagging of diseased tissues. The protein corona also has many repercussions on cellular intake, inflammation, accumulation, degradation, and clearance of the nanoparticles from the body depending on the exposed part of the proteins. Hence, the protein-nanoparticle interaction and the configuration of the bound-proteins on the nanosurface need thorough investigation and understanding. Several techniques such as DLS and zeta potential measurement, UV-vis spectroscopy, fluorescence spectroscopy, circular dichroism, FTIR, and DSC provide valuable information in the protein-nanoparticle interaction study. Besides, theoretical simulations also provide additional understanding. Despite a lot of research publications, the fundamental question remained unresolved. Can we aim for the application of functional nanoparticles in medicine? A new insight, given by us, in this article assumes a reasonable solution to this crucial question.

Review of optical sensing and manipulation of chiral molecules and nanostructures with the focus on plasmonic enhancements [Invited]

Chiral molecules are ubiquitous in nature; many important synthetic chemicals and drugs are chiral. Detecting chiral molecules and separating the enantiomers is difficult because their physiochemical properties can be very similar. Here we review the optical approaches that are emerging for detecting and manipulating chiral molecules and chiral nanostructures. Our review focuses on the methods that have used plasmonics to enhance the chiroptical response. We also review the fabrication and assembly of (dynamic) chiral plasmonic nanosystems in this context.

Antimicrobial and Amyloidogenic Activity of Peptides. Can Antimicrobial Peptides Be Used against SARS-CoV-2?

At present, much attention is paid to the use of antimicrobial peptides (AMPs) of natural and artificial origin to combat pathogens. AMPs have several points that determine their biological activity. We analyzed the structural properties of AMPs, as well as described their mechanism of action and impact on pathogenic bacteria and viruses. Recently published data on the development of new AMP drugs based on a combination of molecular design and genetic engineering approaches are presented. In this article, we have focused on information on the amyloidogenic properties of AMP. This review examines AMP development strategies from the perspective of the current high prevalence of antibiotic-resistant bacteria, and the potential prospects and challenges of using AMPs against infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Particle Detection and Characterization for Biopharmaceutical Applications: Current Principles of Established and Alternative Techniques

Detection and characterization of particles in the visible and subvisible size range is critical in many fields of industrial research. Commercial particle analysis systems have proliferated over the last decade. Despite that growth, most systems continue to be based on well-established principles, and only a handful of new approaches have emerged. Identifying the right particle-analysis approach remains a challenge in research and development. The choice depends on each individual application, the sample, and the information the operator needs to obtain. In biopharmaceutical applications, particle analysis decisions must take product safety, product quality, and regulatory requirements into account. Biopharmaceutical process samples and formulations are dynamic, polydisperse, and very susceptible to chemical and physical degradation: improperly handled product can degrade, becoming inactive or in specific cases immunogenic. This article reviews current methods for detecting, analyzing, and characterizing particles in the biopharmaceutical context. The first part of our article represents an overview about current particle detection and characterization principles, which are in part the base of the emerging techniques. It is very important to understand the measuring principle, in order to be adequately able to judge the outcome of the used assay. Typical principles used in all application fields, including particle–light interactions, the Coulter principle, suspended microchannel resonators, sedimentation processes, and further separation principles, are summarized to illustrate their potentials and limitations considering the investigated samples. In the second part, we describe potential technical approaches for biopharmaceutical particle analysis as some promising techniques, such as nanoparticle tracking analysis (NTA), micro flow imaging (MFI), tunable resistive pulse sensing (TRPS), flow cytometry, and the space- and time-resolved extinction profile (STEP^®) technology.

Smartphone-based colorimetric chiral recognition of ibuprofen using aptamers-capped gold nanoparticles

Sensitive and fast detection of ibuprofen enantiomers is very critical for required routine monitoring and risk assessment of trace pollutants in water samples. Here a simple, rapid and highly sensitive android smartphone application for chiral recognition was developed. Aptamer-capped gold nanoparticles (AuNPs) was demonstrated as an efficient detection platform for (S)-(+)-ibuprofen (S-Ibu) and (R)-(-)-ibuprofen (R-Ibu). Detachment of an enantioselective aptamer from the AuNPs surface and binding with an enantiomer of Ibu lead to AuNPs aggregation, which allows a rapid enantiodiscrimination of Ibu by monitoring the absorbance changes of AuNPs solution in the UV-vis spectrum. Under optimal conditions, the limit of detection for S-Ibu and R-Ibu was 1.24 and 3.91 pg/mL, respectively. These probes showed good chiral recognition ability in mixed samples (i.e. S-Ibu + R-Ibu) and environmental samples. These advantages can be further developed by quantitative measurement with smartphone, which opens new opportunities for on-site detection of trace chiral pollutants in a simple and practical manner.

Site Selection: a Case Study in the Identification of Optimal Cysteine Engineered Antibody Drug Conjugates

As the antibody drug conjugate (ADC) community continues to shift towards site-specific conjugation technology, there is a growing need to understand how the site of conjugation impacts the biophysical and biological properties of an ADC. In order to address this need, we prepared a carefully selected series of engineered cysteine ADCs and proceeded to systematically evaluate their potency, stability, and PK exposure. The site of conjugation did not have a significant influence on the thermal stability and in vitro cytotoxicity of the ADCs. However, we demonstrate that the rate of cathepsin-mediated linker cleavage is heavily dependent upon site and is closely correlated with ADC hydrophobicity, thus confirming other recent reports of this phenomenon. Interestingly, conjugates with high rates of cathepsin-mediated linker cleavage did not exhibit decreased plasma stability. In fact, the major source of plasma instability was shown to be retro-Michael mediated deconjugation. This process is known to be impeded by succinimide hydrolysis, and thus, we undertook a series of mutational experiments demonstrating that basic residues located nearby the site of conjugation can be a significant driver of succinimide ring opening. Finally, we show that total antibody PK exposure in rat was loosely correlated with ADC hydrophobicity. It is our hope that these observations will help the ADC community to build "design rules" that will enable more efficient prosecution of next-generation ADC discovery programs.

A novel colorimetric sensor for sensitive determination of R-citalopram based on the plasmonic properties of silver nanoparticles

A simple and reliable colorimetric method for visual differentiation between the S-citalopram and R-citalopram enantiomers in aqueous solution based on the inherent chirality of silver nanoparticles as a colorimetric probe was presented.

A centrifugation-based physicochemical characterization method for the interaction between proteins and nanoparticles

Nanomedicine requires in-depth knowledge of nanoparticle-protein interactions. These interactions are studied with methods limited to large or fluorescently labelled nanoparticles as they rely on scattering or fluorescence-correlation signals. Here, we have developed a method based on analytical ultracentrifugation (AUC) as an absorbance-based, label-free tool to determine dissociation constants (KD), stoichiometry (Nmax), and Hill coefficient (n), for the association of bovine serum albumin (BSA) with gold nanoparticles. Absorption at 520 nm in AUC renders the measurements insensitive to unbound and aggregated proteins. Measurements remain accurate and do not become more challenging for small (sub-10 nm) nanoparticles. In AUC, frictional ratio analysis allows for the qualitative assessment of the shape of the analyte. Data suggests that small-nanoparticles/protein complexes significantly deviate from a spherical shape even at maximum coverage. We believe that this method could become one of the established approaches for the characterization of the interaction of (small) nanoparticles with proteins.

Colorimetric detection of lead(ii) ions based on accelerating surface etching of gold nanorods to nanospheres: the effect of sodium thiosulfate

The lead ion-participated etching of gold nanorods leads to qualitative spectral change from double bands to single band LSPR, which results in a distinct irreversible color change of the gold colloid from blue to red.

High-throughput assay for measuring monoclonal antibody self-association and aggregation in serum

Subcutaneous delivery is one of the preferred administration routes for therapeutic monoclonal antibodies (mAbs). High antibody dosing requirements and small injection volumes necessitate formulation and delivery of highly concentrated mAb solutions. Such elevated antibody concentrations can lead to undesirable solution behaviors such as mAb self-association and aggregation, which are relatively straightforward to detect using various biophysical methods because of the high purity and concentration of antibody formulations. However, the biophysical properties of mAbs in serum can also impact antibody activity, but these properties are less well understood because of the difficulty characterizing mAbs in such a complex environment. Here we report a high-throughput assay for directly evaluating mAb self-association and aggregation in serum. Our approach involves immobilizing polyclonal antibodies specific for human mAbs on gold nanoparticles, and then using these conjugates to capture human antibodies at a range of subsaturating to saturating mAb concentrations in serum. Antibody aggregation is detected at subsaturating mAb concentrations via blue-shifted plasmon wavelengths due to the reduced efficiency of capturing mAb aggregates relative to monomers, which reduces affinity cross-capture of mAbs by multiple conjugates. In contrast, antibody self-association is detected at saturating mAb concentrations via red-shifted plasmon wavelengths due to attractive interparticle interactions between immobilized mAbs. The high-throughput nature of this assay along with its compatibility with unusually dilute mAb solutions (0.1-10 μg per mL) should make it useful for identifying antibody candidates with high serum stability during early antibody discovery.

Improving monoclonal antibody selection and engineering using measurements of colloidal protein interactions

A limitation of using mAbs as therapeutic molecules is their propensity to associate with themselves and/or with other molecules via nonaffinity (colloidal) interactions. This can lead to a variety of problems ranging from low solubility and high viscosity to off-target binding and fast antibody clearance. Measuring such colloidal interactions is challenging given that they are weak and potentially involve diverse target molecules. Nevertheless, assessing these weak interactions-especially during early antibody discovery and lead candidate optimization-is critical to preventing problems that can arise later in the development process. Here we review advances in developing and implementing sensitive methods for measuring antibody colloidal interactions as well as using these measurements for guiding antibody selection and engineering. These systematic efforts to minimize nonaffinity interactions are expected to yield more effective and stable mAbs for diverse therapeutic applications. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3356-3363, 2014.

High-throughput screening for developability during early-stage antibody discovery using self-interaction nanoparticle spectroscopy

The discovery of monoclonal antibodies (mAbs) that bind to a particular molecular target is now regarded a routine exercise. However, the successful development of mAbs that (1) express well, (2) elicit a desirable biological effect upon binding, and (3) remain soluble and display low viscosity at high concentrations is often far more challenging. Therefore, high throughput screening assays that assess self-association and aggregation early in the selection process are likely to yield mAbs with superior biophysical properties. Here, we report an improved version of affinity-capture self-interaction nanoparticle spectroscopy (AC-SINS) that is capable of screening large panels of antibodies for their propensity to self-associate. AC-SINS is based on concentrating mAbs from dilute solutions around gold nanoparticles pre-coated with polyclonal capture (e.g., anti-Fc) antibodies. Interactions between immobilized mAbs lead to reduced inter-particle distances and increased plasmon wavelengths (wavelengths of maximum absorbance), which can be readily measured by optical means. This method is attractive because it is compatible with dilute and unpurified mAb solutions that are typical during early antibody discovery. In addition, we have improved multiple aspects of this assay for increased throughput and reproducibility. A data set comprising over 400 mAbs suggests that our modified assay yields self-interaction measurements that are well-correlated with other lower throughput assays such as cross-interaction chromatography. We expect that the simplicity and throughput of our improved AC-SINS method will lead to improved selection of mAbs with excellent biophysical properties during early antibody discovery.

Rapid analysis of antibody self-association in complex mixtures using immunogold conjugates

A key challenge in developing therapeutic antibodies is their highly variable propensities to self-associate at high antibody concentrations (>50 mg/mL) required for subcutaneous delivery. Identification of monoclonal antibodies (mAbs) in the initial discovery process that not only have high binding affinity but also have high solubility and low viscosity would simplify the development of safe and effective antibody therapeutics. Unfortunately, the low purities, small quantities and large numbers of antibody candidates during the early discovery process are incompatible with current methods of measuring antibody self-association. We report a method (affinity-capture self-interaction nanoparticle spectroscopy, AC-SINS) capable of identifying mAbs with low self-association propensity that is robust even at low mAb concentrations (5-50 μg/mL) and in the presence of cell culture media. Gold nanoparticles are coated with polyclonal antibodies specific for human antibodies, and then human mAbs are captured from dilute antibody solutions. We find that the wavelength of maximum absorbance (plasmon wavelength) of antibody-gold conjugates--which red-shifts as the distance between particles is reduced due to attractive mAb self-interactions--is well correlated with light scattering measurements conducted at several orders of magnitude higher antibody concentrations. The generality of AC-SINS makes it well suited for use in diverse settings ranging from antibody discovery to formulation development.

The colorimetric detection of Pb2+ by using sodium thiosulfate and hexadecyl trimethyl ammonium bromide modified gold nanoparticles

A simple, rapid colorimetric detection method for Pb(2+) in aqueous solution has been developed by using sodium thiosulfate (Na2S2O3) and hexadecyl trimethyl ammonium bromide (CTAB) modified gold nanoparticles (Au NPs). Na2S2O3 was added into the Au NP solution and thiosulfate ions (S2O3(2-)) were adsorbed on the surface of the Au NPs due to electrostatic interactions. Au atoms on the surface of the Au NPs were then oxidized to Au(i) by the O2 that existed in the solution in presence of thiosulfate. The addition of Pb(2+) (the final concentration was lower than 10 μM), accelerated the leaching of the Au NPs, and Pb-Au alloys also formed on the surface of the Au NPs. There was an obvious decrease in the surface plasmon resonance (SPR) absorption of the Au NPs. The lowest concentration for Pb(2+) that could be detected by the naked eye was 0.1 μM and using UV-vis spectroscopy was 40 nM. This is lower than the lead toxic level defined by the US Environmental Protection Agency (US EPA), which is 75 nM. In this method, CTAB, as a stabilizing agent for Au NPs, can accelerate the adsorption of S2O3(2-) on the surface of the Au NPs, which shortened the detection time to within 30 min. Moreover, this detection method is simple, cheap and environmentally friendly.

Impact of polymer shell on the formation and time evolution of nanoparticle-protein corona

The study of protein corona formation on nanoparticles (NPs) represents an actual main issue in colloidal, biomedical and toxicological sciences. However, little is known about the influence of polymer shells on the formation and time evolution of protein corona onto functionalized NPs. Therefore, silica-poly(ethylene glycol) core-shell nanohybrids (SNPs@PEG) with different polymer molecular weights (MW) were synthesized and exhaustively characterized. Bovine serum albumin (BSA) at different concentrations (0.1-6 wt%) was used as model protein to study protein corona formation and time evolution. For pristine SNPs and SNPs@PEG (MW=350 g/mol), zeta potential at different incubation times show a dynamical evolution of the nanoparticle-protein corona. Oppositely, for SNPs@PEG with MW≥2000 g/mol a significant suppression of corona formation and time evolution was observed. Furthermore, AFM investigations suggest a different orientation (side-chain or perpendicular) and penetration depth of BSA toward PEGylated surfaces depending on the polymer length which may explain differences in protein corona evolution.

High-throughput analysis of concentration-dependent antibody self-association

Monoclonal antibodies are typically monomeric and nonviscous at low concentrations, yet they display highly variable associative and viscous behavior at elevated concentrations. Although measurements of antibody self-association are critical for understanding this complex behavior, traditional biophysical methods are not capable of characterizing such concentration-dependent self-association in a high-throughput manner. Here we describe a nanoparticle-based method, termed self-interaction nanoparticle spectroscopy, that is capable of rapidly measuring concentration-dependent self-interactions for three human monoclonal antibodies with unique solution behaviors. We demonstrate that gold nanoparticles conjugated with antibodies at low protein concentrations (<40 μg/mL) display self-association behavior (as measured by the interparticle distance-dependent plasmon wavelength) that is well correlated with static light-scattering measurements obtained at three orders of magnitude higher antibody concentrations. Using this methodology, we find that the antibodies display a complex pH-dependent self-association behavior that is strongly influenced by the solution ionic strength. Importantly, we find that a polyclonal human antibody is nonassociative for all solution conditions evaluated in this work, suggesting that antibody self-association is more specific than previously realized. We expect that our findings will guide rational manipulation of antibody phase behavior, and enable studies that elucidate sequence and structural determinants of antibody self-association.

Colorimetric chiral recognition of enantiomers using the nucleotide-capped silver nanoparticles

Chiral recognition is among the important and special modes of molecular recognition. It is highly desirable to develop a simple, rapid, sensitive, and high-throughput routine assay for chiral recognition. In this study, we demonstrate that nucleotide-capped Ag nanoparticles (AgNPs) can be used as an ultrahigh efficiency enantioseparation and detection platform for D- and L-cysteine. The aggregation of AgNPs is selectively induced by an enantiomer of cysteine, which allowed the rapid colorimetric enantiodiscrimination of cysteine without any prior derivatization and specific instruments and left an excess of the other enantiomer in the solution, thus resulting in enantioseparation. This is the first application of a nucleotide-capped AgNP-based biosensing platform for chiral recognition and opens new opportunities for design of more novel enantiosensing strategies and enantiospecific adsorbents and expansion of its application in different fields.

Highly selective and sensitive visualizable detection of Hg2+ based on anti-aggregation of gold nanoparticles

For the widely used gold nanoparticles (AuNPs)-based colorimetric probes, AuNPs generally change from dispersion to aggregation state accompanying with corresponding color turning from red to blue. Although colorimetric probes based on the anti-aggregation of AuNPs show exceptional selectivity and sensitivity, few examples have been reported in literature. A facile but highly sensitive and selective colorimetric probe based on the anti-aggregation of AuNPs transferred from the deactivation of aggregation agent 4,4'-dipyridyl by Hg(2+) was developed in this work. This reported probe is suitable for real-time detection of Hg(2+) in water with a detection limit of 3.0 ppb for Hg(2+), and exhibits a selectivity toward Hg(2+) by two orders of magnitude over other metal ions. The dynamic range of this probe can be conveniently tuned by adjusting the amount of 4,4'-dipyridyl used.

Improving the solubility of anti-LINGO-1 monoclonal antibody Li33 by isotype switching and targeted mutagenesis

Monoclonal antibodies (Mabs) are a favorite drug platform of the biopharmaceutical industry. Currently, over 20 Mabs have been approved and several hundred others are in clinical trials. The anti-LINGO-1 Mab Li33 was selected from a large panel of antibodies by Fab phage display technology based on its extraordinary biological activity in promoting oligodendrocyte differentiation and myelination in vitro and in animal models of remyelination. However, the Li33 Fab had poor solubility when converted into a full antibody in an immunoglobulin G1 framework. A detailed analysis of the biochemical and structural features of the antibody revealed several possible reasons for its propensity to aggregate. Here, we successfully applied three molecular approaches (isotype switching, targeted mutagenesis of complementarity determining region residues, and glycosylation site insertion mutagenesis) to address the solubility problem. Through these efforts we were able to improve the solubility of the Li33 Mab from 0.3 mg/mL to >50 mg/mL and reduce aggregation to an acceptable level. These strategies can be readily applied to other proteins with solubility issues.

Colorimetric detection of DNA using unmodified metallic nanoparticles and peptide nucleic acid probes

We have developed a colorimetric assay for DNA detection based on the aggregation of unmodified metallic nanoparticles. Charge neutral peptide nucleic acids (PNA) are used as a "coagulant" of citrate anion-coated particles and as hybridization probe. In the absence of a complementary target DNA, free PNA molecules in solution induce aggressive particle aggregation because of the removal of charge repulsion as a result of PNA coating on nanoparticles. When a complementary DNA is present and PNA-DNA complexes are formed, the particles remain stable because the negative charges of the DNA strands in the complexes adsorbed on the particle surface ensure sufficient charge repulsions. In this method, no probe immobilization is needed and PNA-DNA hybridization occurs in a homogeneous phase. The assay results are displayed as rapidly as the changes in color and/or in UV-vis adsorption spectra of the colloidal solutions. We have validated the assay principle using gold- and silver-nanoparticles (AuNPs and AgNPs), with the involvement of a shorter (13 mer) and a longer (22 mer) probe sequences. A specific DNA can be detected in the presence of at least 10 times of interference DNA, and the detection limit is at a DNA/PNA ratio of 0.05. When NaCl is added to accelerate the particle aggregation, the selectivity is further improved, and single-base-mismatch discrimination is achieved. A two-component assay using a mixture of AuNPs and AgNPs has also been constituted, aiming to improve the result accuracy by making use of the multiple aggregation signatures from the two types of particles. For single-base-mismatch discrimination, the AgNPs offer a higher sensitivity than AuNPs by showing more obvious spectra and color alternation, and the two-component assay offers three parameters in the UV-vis adsorption spectra.

Analytical strategies for detecting nanoparticle-protein interactions

A significant increase in biomedical applications of nanomaterials and their potential toxicity demands versatile analytical techniques to determine protein-nanoparticle (NP) interactions. These diverse analytical techniques are reviewed. Spectroscopic methods play a significant role in studying binding affinity, binding ratio, and binding mechanisms. To elucidate NP-proteome interactions, chromatography and electrophoresis techniques are applied to separate NP-bound proteins and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to identify these proteins. Since NP-protein binding is a dynamic event, surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) are methods of choice to study the kinetics of NP-protein binding.

Single-Walled Carbon Nanotubes Probing the Denaturation of Lysozyme

Resonance Raman spectroscopy measurements of lysozyme-bound single-walled carbon nanotubes have been made during different stages of the chemically and thermally induced misfolding and of the denaturation process of nanotube-bound lysozymes. Changes to the Raman intensity of single-walled carbon nanotubes (SWNTs) have been observed during the denaturation of lysozyme. The Raman intensity changes are attributed to excitonic transition energy (Eii ) shifts of the SWNTs during the denaturation of lysozyme. The Eii shift of SWNTs was confirmed by photoluminescence measurements.

A simple, reliable and sensitive colorimetric visualization of melamine in milk by unmodified gold nanoparticles

In this paper, we report a simple, reliable and sensitive colourimetric visualization of melamine in milk products using citrate-stabilized gold nanoparticles (Au NPs). Upon exposure to ppb-level melamine, gold nanoparticle solution exhibits a highly sensitive colour change from red to blue and rapid aggregation kinetics within the initial 5 min, which can directly be seen with the naked eye and monitored by UV-vis absorbance spectra. As confirmed by the comparison with six other typical amino compounds, the melamine molecule itself contains multiple strong-binding sites to the surface of Au NPs and thus plays a role of molecular linker to efficiently crosslink Au NPs. Further evidence is that the sensitivity is significantly improved when NaHSO(4) is added to promote the ligand exchange between citrate and melamine at the surface of Au NPs. The NaHSO(4)-optimized Au NPs system provides a rapid colourimetric assay for the rapid detection of melamine down to approximately 25 ppb in real milk products.