Influence of particle size on the binding activity of proteins adsorbed onto gold nanoparticles

Sustainable Formation of Gold Nanoparticle-Decorated Amyloid Fibrils for the Development of Functional Hybrid Materials

Amyloid fibrils have recently emerged as promising building blocks for functional materials due to their exceptional physicochemical stability and adaptable properties. These protein-based structures can be functionalized to create hybrid materials with a diverse range of applications. Here we report a simple eco-friendly protocol for generating amyloid fibrils from hen egg white lysozyme decorated with gold nanoparticles that can self-assemble in a hydrogel. Reactive oligomeric species act as reducing agents, enabling the efficient and simple formation of small gold nanoparticles without the need of harsh reagents. Furthermore, the protein molecules template the formation of gold nanoparticles, which are stabilized at regular intervals along the fibril axis, preserving gold nanoparticle properties at a macroscopic scale. As an illustration of potential application, we show that the gold nanoparticle functionalized hydrogel can be employed to sense and quantify creatinine using fluorescence detection. These findings reinforce the growing interest in utilizing proteins as foundational elements for functional biomaterials due to their high biocompatibility, availability, and the ability to finely tune supramolecular assemblies.

Comparative Characteristics of Immunochromatographic Test Systems for Tylosin Antibiotic in Meat Products

Tylosin (TYL) is a macrolide antibiotic widely used in animal husbandry. Due to associated health risks, there is a demand for sensitive methods for mass screening of TYL in products of animal origin. This article describes the development of lateral flow immunoassays (LFIAs) for TYL detection using direct (anti-TYL antibodies conjugated with nanoparticles) and indirect antibody labeling (anti-species antibodies conjugated with nanoparticles and combined with native anti-TYL antibodies). The choice of LFIA conditions, such as concentrations of hapten-protein conjugates, specific antibodies, and gold nanoparticle (GNP) conjugates with antibodies, as well as incubation time of reagents and the concentration of detergent in the sample buffer, is presented. The achieved limits of TYL detection using LFIAs with indirect labeling were 0.8 ng/mL (visual) and 0.07 ng/mL (instrumental), compared to 4 ng/mL (visual) and 0.4 ng/mL (instrumental) for the case of direct labeling. The sensitivity of the LFIA using the indirect format was up to seven times higher, allowing the determination of the target analyte at low concentrations. TYL detection in ground meat using LFIA with indirect antibody labeling ranged from 76-119%.

Nanocarrier-mediated cancer therapy with cisplatin: A meta-analysis with a promising new paradigm

Aims

Cisplatin is a frontline chemotherapeutic utilized to attenuate multiple cancers in the clinic. Given its side-effects, a new cisplatin formulation which could prevent cytotoxicity, metabolic deficiencies and metastasis is much needed. This study investigates whether nanocarriers can provide a better mode of drug delivery in preclinical cancer models seeking a potent anticancer therapeutic agent.

Materials and methods

The PubMed database was searched, and 242 research articles were screened from which 94 articles qualified for selection from those published by December 31, 2023 and the data was synthesized using the Review Manager software.

Key findings

Cisplatin encapsulated as a nanomedicine confirmed the versatility of nanocarriers in significantly diminishing cancer cell viability, half maximal inhibitory concentration, tumour volume, biodistribution of platinum in tumours and kidney; at p < 0.00001 and a 95% confidence interval.

Significance

An estimated 19.3 million global cancer incidence is reported with 50% mortality worldwide for which nanocarrier-mediated cisplatin therapy is most promising. Our findings offer new vistas for future cancer treatment when combined with chemo-immunotherapy that utilizes the recently advanced nanozymes.

Ultrasmall-in-Nano: Why Size Matters

Gold nanoparticles (AuNPs) are continuing to gain popularity in the field of nanotechnology. New methods are continuously being developed to tune the particles' physicochemical properties, resulting in control over their biological fate and applicability to in vivo diagnostics and therapy. This review focuses on the effects of varying particle size on optical properties, opsonization, cellular internalization, renal clearance, biodistribution, tumor accumulation, and toxicity. We review the common methods of synthesizing ultrasmall AuNPs, as well as the emerging constructs termed ultrasmall-in-nano-an approach which promises to provide the desirable properties from both ends of the AuNP size range. We review the various applications and outcomes of ultrasmall-in-nano constructs in vitro and in vivo.

Chiral NIR-II fluorescent Ag2S quantum dots with stereospecific biological interactions and tumor accumulation behaviors

Near-infrared II (NIR-II) fluorescent nanoprobes hold great potential for biomedical applications. Elucidating the relationship between surface properties of NIR-II nanoprobes and their biological behaviors is particularly important for future probe design and their performance optimization. Despite the rapid development of NIR-II nanoprobes, the distinct role of surface chirality on their biological fates has rarely been exploited. Herein, chiral NIR-II fluorescent Ag₂S quantum dots (QDs) are synthesized to investigate the relationship between their chirality and biological functions at both in vitro and in vivo levels. D-/L-Ag₂S QDs exhibit significant differences on their interactions with serum proteins, which further affect the cellular uptake. As a result, D-Ag₂S QDs can be internalized with higher efficiency (over 2-fold) than that of L-Ag₂S QDs. Moreover, in vivo studies reveal that the chirality determines the primary localization of these chiral QDs, where a more efficient renal elimination of D-Ag₂S QDs was observed than that of L-Ag₂S QDs. Importantly, D-Ag₂S QDs show preferential accumulation in tumor region than that of L-Ag₂S QDs in orthotopic kidney tumor model, which points out a new avenue of enhancing targeting capabilities of nanoprobes by engineering their surface chirality.

Gold Nanoparticles Augment N-Terminal Cleavage and Splicing Reactions in Mycobacterium tuberculosis SufB

Protein splicing is a self-catalyzed event where the intervening sequence intein cleaves off, joining the flanking exteins together to generate a functional protein. Attempts have been made to regulate the splicing rate through variations in temperature, pH, and metals. Although metal-regulated protein splicing has been more captivating to researchers, metals were shown to only inhibit splicing reactions that confine their application. This is the first study to show the effect of nanoparticles (NPs) on protein splicing. We found that gold nanoparticles (AuNPs) of various sizes can increase the splicing efficiency by more than 50% and the N-terminal cleavage efficiency by more than 45% in Mycobacterium tuberculosis SufB precursor protein. This study provides an effective strategy for engineering splicing-enhanced intein platforms. UV-vis absorption spectroscopy, isothermal titration calorimetry (ITC), and transmission electron microscopy (TEM) confirmed AuNP interaction with the native protein. Quantum mechanics/molecular mechanics (QM/MM) analysis suggested a significant reduction in the energy barrier at the N-terminal cleavage site in the presence of gold atom, strengthening our experimental evidence on heightened the N-terminal cleavage reaction. The encouraging observation of enhanced N-terminal cleavage and splicing reaction can have potential implementations from developing a rapid drug delivery system to designing a contemporary protein purification system.

Retention of Activity by Antibodies Immobilized on Gold Nanoparticles of Different Sizes: Fluorometric Method of Determination and Comparative Evaluation

Antibody–nanoparticle conjugates are widely used analytical reagents. An informative parameter reflecting the conjugates’ properties is the number of antibodies per nanoparticle that retain their antigen-binding ability. Estimation of this parameter is characterized by a lack of simple, reproducible methods. The proposed method is based on the registration of fluorescence of tryptophan residues contained in proteins and combines sequential measurements of first the immobilized antibody number and then the bound protein antigen number. Requirements for the measurement procedure have been determined to ensure reliable and accurate results. Using the developed technique, preparations of spherical gold nanoparticles obtained by the most common method of citrate reduction of gold salts (the Turkevich–Frens method) and varying in average diameter from 15 to 55 nm have been characterized. It was shown that the number of antibodies (immunoglobulins G) bound by one nanoparticle ranged from 30 to 194 during adsorptive unoriented monolayer immobilization. C-reactive protein was considered as the model antigen. The percentage of antibody valences that retained their antigen-binding properties in the conjugate increased from 17 to 34% with an increase in the diameter of gold nanoparticles. The proposed method and the results of the study provide tools to assess the capabilities of the preparations of gold nanoparticles and their conjugates as well as the expediency of seeking the best techniques for various practical purposes.

Solution NMR of Nanoparticles in Serum: Protein Competition Influences Binding Thermodynamics and Kinetics

The spontaneous formation of a protein corona on a nanoparticle surface influences the physiological success or failure of the synthetic nanoparticle as a drug carrier or imaging agent used in vivo. A quantitative understanding of protein-nanoparticle interactions is therefore critical for the development of nanoparticle-based therapeutics. In this perspective, we briefly discuss the challenges and limitations of current approaches used for studying protein-nanoparticle binding in a realistic biological medium. Subsequently, we demonstrate that solution nuclear magnetic resonance (NMR) spectroscopy is a powerful tool to monitor protein competitive binding in a complex serum medium in situ. Importantly, when many serum proteins are competing for a gold nanoparticle (AuNP) surface, solution NMR is able to detect differences in binding thermodynamics, and kinetics of a tagged protein. Combined with other experimental approaches, solution NMR is an invaluable tool to understand protein behavior in the nanoparticle corona.

Application of Localized Surface Plasmon Resonance Spectroscopy to Investigate a Nano-Bio Interface

The accurate determination of events at the interface between a biological system and nanomaterials is necessary for efficacy and safety evaluation of novel nano-enabled medical products. Investigating the interaction of proteins with nanoparticles (NPs) and the formation of protein corona on nanosurfaces is particularly challenging from the methodological point of view due to the multiparametric complexity of such interactions. This study demonstrated the application of localized surface plasmon resonance (LSPR) spectroscopy as a low-cost and rapid biosensing technique that can be used in parallel with other sophisticated methods to monitor nano-bio interplay. Interaction of citrate-coated gold NPs (AuNPs) with human plasma proteins was selected as a case study to evaluate the applicability and value of scientific data acquired by LSPR as compared to fluorescence spectroscopy, which is one of the most used techniques to study NP interaction with biomolecules. LSPR results obtained for interaction of AuNPs with bovine serum albumin, glycosylated human transferrin, and non-glycosylated recombinant human transferrin correlated nicely with the adsorption constants obtained by fluorescence spectroscopy. This ability, complemented by its fast operation and reliability, makes the LSPR methodology an attractive option for the investigation of a nano-bio interface.

Optical Density Optimization of Malaria Pan Rapid Diagnostic Test Strips for Improved Test Zone Band Intensity

For the last few decades, the immunochromatographic assay has been used for the rapid detection of biological markers in infectious diseases in humans and animals The assay, also known as lateral flow assay, is utilized for the detection of antigen or antibody in human infectious diseases. There are a series of steps involved in the development of these immuno-chromatographic test kits, from gold nano colloids preparation to nitrocellulose membrane coating (NCM). These tests are mostly used for qualitative assays by a visual interpretation of results. For the interpretation of the results, the color intensity of the test zone is therefore very significant. Herein, the study was performed on a malaria antigen test kit. Several studies have reported the use of gold nanoparticles (AuNPs) with varying diameters and its binding with various concentrations of protein in order to optimize tests. However, none of these studies have reported how to fix (improve) test zone band intensity (color), if different sized AuNPs were synthesized during a reaction and when conjugated equally with same amount of protein. Herein, different AuNPs with average diameter ranging from 10 nm to 50 nm were prepared and conjugated equally with protein concentration of 150 µg/mL with K_D = 1.0 × 10⁻³. Afterwards, the developed kits’ test zone band intensity for all different sizes AuNPs was fixed to the same band level (high) by utilization of an ultraviolet-visible spectrophotometer. The study found that the same optical density (OD) has the same test zone band intensity irrespective of AuNP size. This study also illustrates the use of absorption maxima (λ max) techniques to characterize AuNPs and to prevent wastage of protein while developing immunochromatographic test kits.

Biological Behavior Regulation of Gold Nanoparticles via the Protein Corona

One of the difficulties in the translation of gold nanoparticles (GNPs) into clinical practice is the formation of the protein corona (PC) that causes the discrepancy between the in vitro and in vivo performance of GNPs. The PC formed on the surface of GNPs gives them a biological identity instead of an initial synthetic one. In most instances, this biological identity increases the particle size, leads to more clearance by the reticuloendothelial system, and causes less uptake by target cells. However, the performance of GNPs can still be improved by rewriting their original surface chemistry via the PC. This review specifically focuses on discussing the main influence factors, including the biological environment and physicochemical properties of GNPs, which affect the production and status of the PC. The status of the PC such as the amount, thickness, and composition subsequently influence the biological behavior of GNPs, especially their cellular uptake, cytotoxicity, biodistribution, and tumor targeting. Further understanding and revealing the impacts of the PC on the biological behavior of GNPs can be a promising and important strategy to regulate and improve the performance of GNP-based biosystems in the future.

Biosynthesized Quantum Dot for Facile and Ultrasensitive Electrochemical and Electrochemiluminescence Immunoassay

Nanomaterials are commonly utilized for amplified immunoassay of biomarkers. However, traditional nanomaterial-based immunoassay usually requires a time-consuming and labor-intensive nanoparticle modification and conjugation process, which impedes their practical applications. Here, a new immunoassay method based on biosynthesized nanomaterials is developed with versatile functions for facile and ultrasensitive detection of cancer biomarker. In this method, the utilized biosynthesized quantum dots (BQDs) allow convenient antibody conjugation and electrode modification, and demonstrate excellent electrochemical and electrochemiluminescent responses. The differential pulse voltammetric, faradaic impedance spectroscopy, and electrochemiluminescent measurements with the BQD-modified electrode show detection limits at picomolar levels as well as good specificity toward human prostate-specific antigen detection. The inherent recognization capability as well as the inherent electrochemical and electrochemiluminescence features thus enable BQDs as good candidates for facile immunosensors with high sensitivity. Such a biosynthesized nanomaterial-based approach opens up the possibility of using innovative designs for nanoparticle-based assays, and developing reliable and practical methods for early disease diagnosis.

Effects of Orientation on the Stability and Affinity of Antibody-GNP Conjugation

In medicine, gold nanoparticles are widely used because of its unique properties. They are usually attached to a monoclonal antibody in treatment and diagnosis. Computational and laboratory work has demonstrated that the structure of the protein can change after interaction with gold nanoparticle and the effect of nanoparticle on the protein is dependent on the type of bond between them. Thus, finding out how nanoparticles affect the protein structure can help us to design the optimal complex of gold nanoparticle-antibody. In the present study, docking and molecular dynamic simulation were performed to obtain an insight at the molecular level in the binding of immunoglobulin G to the Gold nanoparticles, the structure change in immunoglobulin G, and binding energies of Fab and Fc domains of Immunoglobulin G to the GNP. We found the Fab region was more stable than the Fc region when bound to the GNP surface and it also had less structural changes. In neutral pH, Van der Waals interactions contribute more to the Fab-GNP interaction compared to electrostatic interactions; However, in Fc-GNP interaction, the main contributor is the electrostatic energy.

Optimization and Structural Stability of Gold Nanoparticle-Antibody Bioconjugates

Gold nanoparticles (AuNPs) bound with biomolecules have emerged as suitable biosensors exploiting unique surface chemistries and optical properties. Many efforts have focused on antibody bioconjugation to AuNPs resulting in a sensitive bioconjugate to detect specific types of bacteria. Unfortunately, bacteria thrive under various harsh environments, and an understanding of bioconjugate stability is needed. Here, we show a method for optimizing Listeria monocytogenes polyclonal antibodies bioconjugation mechanisms to AuNPs via covalent binding at different pH values, from 2 to 11, and 2-(N-morpholino)ethanesulfonic acid (MES), 3-(N-morpholino)propanesulfonic acid, NaOH, HCl conditions. By fitting Lorentz curves to the amide I and II regions, we analyze the stability of the antibody secondary structure. This shows an increase in the apparent breakdown of the antibody secondary structure during bioconjugation as pH decreases from 7.9 to 2. We find variable adsorption efficiency, measured as the percentage of antibody adsorbed to the AuNP surface, from 17 to 27% as pH increases from 2 to 6 before decreasing to 8 and 13% at pH 7.9 and 11, respectively. Transmission electron microscopy (TEM) analysis reveals discrepancies between size and morphological changes due to the corona layer assembly from antibody binding to single nanoparticles versus aggregation or cluster self-assembly into large aggregates. The corona layer formation size increases from 3.9 to 5.1 nm from pH 2 to 6, at pH 7.9, there is incomplete corona formation, whereas at pH 11, there is a corona layer formed of 6.4 nm. These results indicate that the covalent binding process was more efficient at lower pH values; however, aggregation and deactivation of the antibodies were observed. We demonstrate that optimum bioconjugation condition was determined at pH 6 and MES buffer-type by indicators of covalent bonding and stability of the antibody secondary structure using Fourier transform-infrared, the morphological characteristics and corona layer formation using TEM, and low wavelength shifts of ultraviolet-visible after bioconjugation.

Probing the biological obstacles of nanomedicine with gold nanoparticles

Despite massive growth in nanomedicine research to date, the field still lacks fundamental understanding of how certain physical and chemical features of a nanoparticle affect its ability to overcome biological obstacles in vivo and reach its intended target. To gain fundamental understanding of how physical and chemical parameters affect the biological outcomes of administered nanoparticles, model systems that can systematically manipulate a single parameter with minimal influence on others are needed. Gold nanoparticles are particularly good model systems in this case as one can synthetically control the physical dimensions and surface chemistry of the particles independently and with great precision. Additionally, the chemical and physical properties of gold allow particles to be detected and quantified in tissues and cells with high sensitivity. Through systematic biological studies using gold nanoparticles, insights toward rationally designed nanomedicine for in vivo imaging and therapy can be obtained. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Inner-View of Nanomaterial Incited Protein Conformational Changes: Insights into Designable Interaction

Nanoparticle bioreactivity critically depends upon interaction between proteins and nanomaterials (NM). The formation of the "protein corona" (PC) is the effect of such nanoprotein interactions. PC has a wide usage in pharmaceuticals, drug delivery, medicine, and industrial biotechnology. Therefore, a detailed in-vitro, in-vivo, and in-silico understanding of nanoprotein interaction is fundamental and has a genuine contemporary appeal. NM surfaces can modify the protein conformation during interaction, or NMs themselves can lead to self-aggregations. Both phenomena can change the whole downstream bioreactivity of the concerned nanosystem. The main aim of this review is to understand the mechanistic view of NM-protein interaction and recapitulate the underlying physical chemistry behind the formation of such complicated macromolecular assemblies, to provide a critical overview of the different models describing NM induced structural and functional modification of proteins. The review also attempts to point out the current limitation in understanding the field and highlights the future scopes, involving a plausible proposition of how artificial intelligence could be aided to explore such systems for the prediction and directed design of the desired NM-protein interactions.

Protein-gold nanoparticle interactions and their possible impact on biomedical applications

In the past few years, concerns of protein-gold nanoparticles (AuNP) interaction have been continuously growing in numerous potential biomedical applications. Despite the advances in tunable size, shape and excellent biocompatibility, unpredictable adverse effects related with protein corona (PC) have critically affected physiological to therapeutic responses. The complexity and uncontrollability of AuNP-PC formation limited the clinical applications of AuNP, e.g. AuNP-based drug delivery systems or imaging agent. Thus, even intensive attempts have been made for in vitro characterizations of PC around AuNP, the extrapolation of these data into in vivo PC responses still lags far behind. However, with accumulated knowledge of corona formation and the unique properties of AuNP, we are now encouraged to move forward to seeking positive exploitations. Herein, we summarize recent researches on interaction of protein and AuNP, aiming at provide a comprehensive understanding of such interaction associated with subsequent biomedical impacts. Importantly, the emerging trends in exploiting of potential applications and opportunities based on protein-AuNP interaction were discussed as well.

STATEMENT OF SIGNIFICANCE

Gold nanoparticles (AuNPs) have shown great potentials in biomedical areas. However, its practical use is highly limited by protein corona, formed as a result of protein-AuNP interaction. This protein corona surrounding AuNPs is a new identity and the real substance that the organs and cells firstly encounter, and finally makes the behavior of AuNPs in vivo uncontrollable and unpredictable. Therefore, comprehensively understanding such interaction is of great significance for predicting the in vivo fate of AuNPs and for designing advanced AuNPs systems. In this review, we would provide a detailed description of protein-AuNP interaction and launch an interesting discussion on how to use such interaction for smart and controlled AuNPs delivery, which would be a topic of widespread interest.

Mathematical Model of Serodiagnostic Immunochromatographic Assay

This article describes the mathematical model for an immunochromatographic assay for the detection of specific immunoglobulins against a target antigen (antibodies) in blood/serum (serodiagnosis). The model utilizes an analytical (non-numerical) approach and allows the calculation of the kinetics of immune complexes' formation in a continuous-flow system using commonly available software, such as Microsoft Excel. The developed model could identify the nature of the influence of immunochemical interaction constants and reagent concentrations on the kinetics of the formation of the detected target complex. On the basis of the model, recommendations are developed to decrease the detection limit for an immunochromatographic assay of specific immunoglobulins.

A non-enzyme cascade amplification strategy for colorimetric assay of disease biomarkers

A non-enzyme cascade amplification strategy for colorimetric assay of disease biomarkers with substantially enhanced detection sensitivity has been developed.

Apolipoprotein E genotyping using PCR-GoldMag lateral flow assay and its clinical applications

A polymerase chain reaction-gold magnetic nanoparticles lateral flow assay (PCR-GoldMag LFA) has been developed via integrating multiplex amplification refractory mutation system PCR (multi-ARMS-PCR) with GoldMag-based LFA for the visual detection of single-nucleotide polymorphisms (SNPs). This assay was applied to genotype Apolipoprotein E (ApoE). ApoE genotyping is important due to the predictive value for the development of coronary artery disease and Alzheimer's disease. The method requires two steps: i) Simultaneous amplifications of the two polymorphic codons (ApoE 158 and 112), performed in separated reactions using multi-ARMS-PCR; and ii) detection of the wild-type and mutant PCR products via dual immunoreactions, which can be performed in ~5 min. Within two LFAs, anti-digoxin antibody-conjugated GoldMag probes bind digoxin-labeled wild-type PCR products, and anti-fluorescein isothiocyanate (FITC) antibody-conjugated GoldMag probes bind FITC-labeled mutant PCR products. All PCR products are biotin labeled and are detected by streptavidin-coated regions on the LFA strip, resulting in a red color. The current approach is capable of detecting the SNPs of ApoE in ~1.5 h, with a broad detection range from 10–1,000 ng of genomic DNA. Thus, the present protocol may facilitate simple, fast and cost-effective screening for important SNPs, as demonstrated by the evaluation of the prevalence of ApoE variants in a Han Chinese cohort.

The potential of protein-nanomaterial interaction for advanced drug delivery

Nanomaterials, like nanoparticles, micelles, nano-sheets, nanotubes and quantum dots, have great potentials in biomedical fields. However, their delivery is highly limited by the formation of protein corona upon interaction with endogenous proteins. This new identity, instead of nanomaterial itself, would be the real substance the organs and cells firstly encounter. Consequently, the behavior of nanomaterials in vivo is uncontrollable and some undesired effects may occur, like rapid clearance from blood stream; risk of capillary blockage; loss of targeting capacity; and potential toxicity. Therefore, protein-nanomaterial interaction is a great challenge for nanomaterial systems and should be inhibited. However, this interaction can also be used to functionalize nanomaterials by forming a selected protein corona. Unlike other decoration using exogenous molecules, nanomaterials functionalized by selected protein corona using endogenous proteins would have greater promise for clinical use. In this review, we aim to provide a comprehensive understanding of protein-nanomaterial interaction. Importantly, a discussion about how to use such interaction is launched and some possible applications of such interaction for advanced drug delivery are presented.

Size and surface chemistry of nanoparticles lead to a variant behavior in the unfolding dynamics of human carbonic anhydrase

The adsorption induced conformational changes of human carbonic anhydrase I (HCAi) and pseudo wild type human carbonic anhydrase II truncated at the 17th residue at the N-terminus (trHCAii) were studied in presence of nanoparticles of different sizes and polarities. Isothermal titration calorimetry (ITC) studies showed that the binding to apolar surfaces is affected by the nanoparticle size in combination with the inherent protein stability. 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence revealed that HCAs adsorb to both hydrophilic and hydrophobic surfaces, however the dynamics of the unfolding at the nanoparticle surfaces drastically vary with the polarity. The size of the nanoparticles has opposite effects depending on the polarity of the nanoparticle surface. The apolar nanoparticles induce seconds timescale structural rearrangements whereas polar nanoparticles induce hours timescale structural rearrangements on the same charged HCA variant. Here, a simple model is proposed where the difference in the timescales of adsorption is correlated with the energy barriers for initial docking and structural rearrangements which are firmly regulated by the surface polarity. Near-UV circular dichorism (CD) further supports that both protein variants undergo structural rearrangements at the nanoparticle surfaces regardless of being "hard" or "soft". However, the conformational changes induced by the apolar surfaces differ for each HCA isoform and diverge from the previously reported effect of silica nanoparticles.

Harvesting Low Molecular Weight Biomarkers Using Gold Nanoparticles

We developed and characterized a platform based on gold (Au) nanoparticles (NPs) coated with poly(acrylic acid) (PAA) for harvesting positively charged, low molecular weight (LMW) proteins. The particles are synthesized using a layer by layer (LbL) procedure: first the gold NPs are coated with positively charged polyethylenimine (PEI) and subsequently with PAA. This simple procedure produces stable PAA-PEI-Au (PPAu) NPs with high selectivity and specificity. PPAu NPs successfully harvested, separated, and detected various LMW proteins and peptides from serum containing a complex mixture of abundant high molecular weight (HMW) proteins, including bovine serum albumin (BSA) and Immunoglobulin G (IgG). In addition, PPAu NPs selectively harvested and separated LMW proteins from serum in the presence of another positively charged competing protein. Furthermore, PPAu NPs successfully harvested a LMW biomarker in a mock diseased state. This system can be applied in various biomedical applications where selective harvesting and identifying of LMW proteins is required. A particularly useful application for this system can be found in early cancer diagnosis as described hereinafter.

Measuring antibody coatings on gold nanoparticles by optical spectroscopy

Coating thickness estimates of coated gold nanoparticles was achieved to avoid reduction of diagnostic sensitivity from excess antibody.

Detection of unamplified genomic DNA by a PNA-based microstructured optical fiber (MOF) Bragg-grating optofluidic system

Microstructured optical fibers containing microchannels and Bragg grating inscribed were internally functionalized with a peptide nucleic acid (PNA) probe specific for a gene tract of the genetically modified Roundup Ready soy. These fibers were used as an optofluidic device for the detection of DNA by measuring the shift in the wavelength of the reflected IR light. Enhancement of optical read-out was obtained using streptavidin coated gold-nanoparticles interacting with the genomic DNA captured in the fiber channels (0%, 0.1%, 1% and 10% RR-Soy), enabling to achieve statistically significant, label-free, and amplification-free detection of target DNA in low concentrations, low percentages, and very low sample volumes. Computer simulations of the fiber optics based on the finite element method (FEM) were consistent with the formation of a layer of organic material with an average thickness of 39 nm for the highest percentage (10% RR soy) analysed.

Detection of adenosine triphosphate through polymerization-induced aggregation of actin-conjugated gold/silver nanorods

We have developed a simple and selective nanosensor for the optical detection of adenosine triphosphate (ATP) using globular actin-conjugated gold/silver nanorods (G-actin-Au/Ag NRs). By simply mixing G-actin and Au/Ag NRs (length ~56 nm and diameter ~12 nm), G-actin-Au/Ag NRs were prepared which were stable in physiological solutions (25 mM Tris-HCl, 150 mM NaCl, 5.0 mM KCl, 3.0 mM MgCl2 and 1.0 mM CaCl2; pH 7.4). Introduction of ATP into the G-actin-Au/Ag NR solutions in the presence of excess G-actin induced the formation of filamentous actin-conjugated Au/Ag NR aggregates through ATP-induced polymerization of G-actin. When compared to G-actin-modified spherical Au nanoparticles having a size of 13 nm or 56 nm, G-actin-Au/Ag NRs provided better sensitivity for ATP, mainly because the longitudinal surface plasmon absorbance of the Au/Ag NR has a more sensitive response to aggregation. This G-actin-Au/Ag NR probe provided high sensitivity (limit of detection 25 nM) for ATP with remarkable selectivity (>10-fold) over other adenine nucleotides (adenosine, adenosine monophosphate and adenosine diphosphate) and nucleoside triphosphates (guanosine triphosphate, cytidine triphosphate and uridine triphosphate). It also allowed the determination of ATP concentrations in plasma samples without conducting tedious sample pretreatments; the only necessary step was simple dilution. Our experimental results are in good agreement with those obtained from a commercial luciferin-luciferase bioluminescence assay. Our simple, sensitive and selective approach appears to have a practical potential for the clinical diagnosis of diseases (e.g. cystic fibrosis) associated with changes in ATP concentrations.

New derivative of carnosine for nanoparticle assemblies

Carnosine (β-alanyl-l-histidine) is an endogenous dipeptide, extensively studied owing to its multifunctional activity exhibited in tissues of several animal species. This natural compound may act as a physiological buffer, ion-chelating agent (especially for copper(II) and zinc(II)), antioxidant and antiglycating agent. The main limit for the therapeutical uses of carnosine is the rapid hydrolysis mostly in human plasma by carnosinase. The chemical derivatization of carnosine is a promising strategy to improve the bioavailability of the dipeptide and facilitating the site-specific transport to different tissues. On this basis, a new carnosine derivative with biotin was synthesized and structurally characterized by NMR and MS measurements, with aim of exploiting the avidin-biotin technology that offers a universal system for selective delivery of any biotinylated agent. The stability of the new carnosine derivative towards the hydrolytic action of serum carnosinase as well as the copper(II) binding ability of the carnosine-biotin conjugate were also assessed. The binding affinity of the new molecular entity to avidin and streptavidin, investigated by a spectrophotometric assay, was exploited to functionalize avidin- and streptavidin-gold nanoparticles with the carnosine-biotin conjugate.

Tuning dye-to-particle interactions toward luminescent gold nanostars

Light-matter interactions are of great interest for potential biological applications (bioimaging, biosensing, phototherapy). For such applications, sharp nanostructures exhibit interesting features since their extinction bands (surface plasmon resonance) cover a large bandwidth in the whole visible wavelength region due to the existence of "hot spots" located at the end of the tips. In this context, gold nanostars appear to be interesting objects. However, their study remains difficult, mainly due to complicated synthetic methods and further functionalization. This paper reports the synthesis, functionalization, and photophysics of luminescent hybrid gold nanostars prepared using a layer-by-layer (LbL) deposition method for the tuning of chromophore-to-particle distances together with the impact of the spectral overlap between the plasmon and the emission/absorption of the dyes. Several luminescent dyes with different optical signatures were selectively adsorbed at the nanoparticle surface. The optimized systems, exhibiting the highest luminescence recovery, clearly showed that overlap must be as low as possible. Also, the fluorescence intensities were quenched in close vicinity of the metal surface and revealed a distance-dependence with almost full recovery of the dyes emission for 11 LbL layers, which corresponded to 15 nm distances evaluated on dried samples. The photophysics of the luminescent core-shell particles were carried out in suspension and correlated with the response of isolated single objects.

Polyelectrolyte-coated gold magnetic nanoparticles for immunoassay development: toward point of care diagnostics for syphilis screening

Immediate response for disease control relies on simple, inexpensive, and sensitive diagnostic tests, highly sought after for timely and accurate test of various diseases, including infectious diseases. Composite Fe3O4/Au nanoparticles have attracted considerable interest in diagnostic applications due to their unique physical and chemical properties. Here, we developed a simple coating procedure for gold magnetic nanoparticles (GMNs) with poly(acrylic acid) (PAA). PAA-coated GMNs (PGMNs) were stable and monodispersed and characterized by Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscopy, UV-visible scanning spectrophotometry, thermogravimetric analysis, and Zetasizer methodologies. For diagnostic application, we established a novel lateral flow immunoassay (LFIA) strip test system where recombinant Treponema pallidum antigens (r-Tp) were conjugated with PGMNs to construct a particle probe for detection of anti-Tp antibodies. Intriguingly, the particle probes specifically identified Tp antibodies with a detection limitation as low as 1 national clinical unit/mL (NCU/mL). An ample pool of 1020 sera samples from three independent hospitals were obtained to assess our PGMNs-based LFIA strips, which exhibited substantially high values of sensitivity and specificity for all clinical tests (higher than 97%) and, therefore, proved to be a suitable approach for syphilis screening at a point-of-care test manner.

Graphene oxide-induced conformation changes of glucose oxidase studied by infrared spectroscopy

The adsorption of proteins on the surface of nanomaterials can induce changes in the structure and biological activity of the proteins. Although there have been a number of studies aimed at developing an understanding of the interactions of proteins with surfaces of nanomaterials, a detailed description of the actual state of the adsorbed proteins or the functional consequences of protein adsorption onto nanomaterials has yet to be reported. In this study, the conformation changes of glucose oxidase (GOx) induced by adsorption on graphene oxide (GO) sheets were investigated by quantitative second-derivative infrared analysis and two-dimensional infrared correlation spectroscopy (2D IR). The adsorption of GOx on GO sheets resulted in the conversion of α-helix to β-sheet structures and therefore led to substantial conformation changes of GOx, even the unfolding of the protein. These alterations in the conformation of GOx caused a significant decrease in the catalytic activity of the enzyme for glucose oxidation. This study demonstrates that nanomaterials can strongly influence the conformation and activity of adsorbed proteins. In addition to the importance of this effect in cases of the direct adsorption of proteins on nanomaterials, the results have implications for proteins adsorbed on materials with nanometer-scale surface roughness.

The influence of nanostructured materials on biointerfacial interactions

Control over biointerfacial interactions in vitro and in vivo is the key to many biomedical applications: from cell culture and diagnostic tools to drug delivery, biomaterials and regenerative medicine. The increasing use of nanostructured materials is placing a greater demand on improving our understanding of how these new materials influence biointerfacial interactions, including protein adsorption and subsequent cellular responses. A range of nanoscale material properties influence these interactions, and material toxicity. The ability to manipulate both material nanochemistry and nanotopography remains challenging in its own right, however, a more in-depth knowledge of the subsequent biological responses to these new materials must occur simultaneously if they are ever to be affective in the clinic. We highlight some of the key technologies used for fabrication of nanostructured materials, examine how nanostructured materials influence the behavior of proteins and cells at surfaces and provide details of important analytical techniques used in this context.

How do proteins unfold upon adsorption on nanoparticle surfaces?

Owing to their many outstanding features, such as small size, large surface area, and cell penetration ability, nanoparticles have been increasingly used in medicine and biomaterials as drug carriers and diagnostic or therapeutic agents. However, our understanding of the interactions of biological entities, especially proteins, with nanoparticles is far behind the explosive development of nanotechnology. In typical protein-nanoparticle interactions, two processes (i.e., surface binding and conformational changes in proteins) are intermingled with each other and have not yet been quantitatively described. Here, by using a stopped-flow fast mixing technique, we were able to shed light on the kinetics of the adsorption-induced protein unfolding on nanoparticle surfaces in detail. We observed a biphasic denaturation behavior of protein GB1 on latex nanoparticle surfaces. Such kinetics can be adequately described by a fast equilibrium adsorption followed by a slow reversible unfolding of GB1. On the basis of this model, we quantitatively measured all rate constants that are involved in this process, from which the free-energy profile is constructed. This allows us to evaluate the effects of environmental factors, such as pH and ionic strength, on both the adsorption and the conformational change in GB1 on the latex nanoparticle surface. These studies provide a general physical picture of the adsorption-induced unfolding of proteins on nanoparticle surfaces and a quantitative description of the energetics of each transition. We anticipate that it will greatly advance our current understanding of protein-nanoparticle interactions and will be helpful for the rational control of such interactions in biomedical applications.