Role of Free Thiol on Protein Adsorption to Gold Nanoparticles

Recent advances in smart gold nanoparticles for photothermal therapy

Gold nanoparticles (AuNPs) possess unique properties, including low toxicity and excellent optical characteristics, making them highly appealing for biomedical applications. The plasmonic photothermal effect of AuNPs has been explored to trigger localized hyperthermia. Four commonly explored gold nanoparticles (spheres, rods, stars, and cages) are produced and optimized to present the localized surface plasmon resonance effect in the near-infrared region, exploiting the increased penetration in the human body. Additionally, the production of hybrid AuNPs, combining them with other materials, such as silica, graphene, zinc oxide, polymers, and small molecules has been explored to amplify the photothermal effect (T ≥ 45ºC). This review provides an overview of AuNPs' application in photothermal therapy, describing the general synthesis processes and the main particle parameters that affect their application in photothermal therapy, including the hybrid nanomaterials. Associated with this rapid progress, surface functionalization can also improve colloidal stability, safety, and therapeutic outcomes. In this regard, we also highlight the emerging trend of applying cell-derived vesicles as biomimetic coatings, capable of evading immune recognition, increasing blood circulation, and targeting specific tissues. In addition, the challenges and future developments of AuNPs for accelerating the clinical translations are discussed in light of their therapeutic and theragnostic potential.

Optimized growth of dendritic Au nanostructures with multi-cross-linked glucose oxidase for highly catalytic activity of salivary glucose

We aim to develop a system that prominently features glucose oxidase (GOx) as the catalyst, integrated with a dendritic Au nanostructures electrode as the core component. The dendritic Au (DenAu) nanostructures are optimally electro-deposited on a flexible substrate without the use of any surfactant, template, or stabilizer, demonstrating their potential through highly sensitive flexible glucose sensor application. To determine the optimal condition for the growth of dendritic Au nanostructures, we meticulously investigated the concentration of the precursor, deposition potential/time, and stirring rate. Subsequently, the glucose oxidase (GOx) was immobilized on the fabricated sensor with dendritic Au nanostructures. Due to the effective high loading of GOx onto the dendritic Au and its high catalytic activity, the fabricated flexible glucose sensor was capable of detecting glucose over an ultra-wide dynamic range from 0.001 to 10,000 μM without any mediator. It exhibited an exceptionally high sensitivity of 678 μAmM-1 cm-2 and a low limit of detection of 0.1 μM, surpassing the performance of the sensor with bare Au. Furthermore, the fabricated flexible sensor with dendritic Au nanostructure showed practical feasibility and possibility for the detection of salivary glucose, which was evidenced by a strong correlation coefficient of 0.9935 in artificial saliva.

Multivalent nanobody engineering for enhanced physisorption and functional display on gold nanoparticles

The ease of expression and engineering of single domain antibodies, known as nanobodies, make them attractive alternatives to conventional antibodies in point-of-care diagnostics such as lateral flow assays. In lateral flow assays, gold nanoparticle bioconjugates serve as labels which display affinity molecules on the gold surface. While examples of nanobody gold nanoparticle bioconjugates exist, few utilise the simple one-step approach of physisorption owing to undesirable nanoparticle aggregation and loss of functionality. Here we show that engineering nanobodies into multivalent structures can significantly enhance their functionality when physisorbed onto gold nanoparticles. This approach enables resulting bioconjugates to withstand multiple processing steps required for long-term nanoparticle storage within lateral flow assays. Specifically, we show that the trivalent version of VHHV nanobody (VHH3) against the S1 protein of SARS-CoV-2 can be immobilised onto gold nanoparticles through passive adsorption. Unlike its monovalent and bivalent nanobody counterparts, using VHHV3 preserves nanoparticle stability under salt stress, blocking, washing, and freeze-drying conditions while maintaining picomolar sensitivity to the S1 protein. We anticipate that this facile strategy is a significant advancement towards the integration of nanobodies in lateral flow assay development.

Gold Nanoparticles in Serum and Milk and Their Effect for Label-Free Colorimetric Sensing of DNA

Label-free gold nanoparticle (AuNP)-based colorimetric biosensors have been widely used for the detection of DNA. However, the effect of the biological sample matrix has not been fully explored. In this work, we investigated the salt-induced aggregation of AuNPs as well as DNA adsorption in serum and milk. AuNPs of 13, 30, and 50 nm were used as probes. The detection was successful only in a clean buffer but failed in serum or milk. Serum and milk exhibited excellent protective properties, even 250 mM NaCl added did not induce the aggregation of AuNPs. After centrifugation of milk, the supernatant did not protect the AuNPs, whereas the redispersed pellet showed protection. The limit concentration of serum to prevent AuNPs from aggregating was 0.04% for 13 nm AuNPs and 0.01% serum for 50 nm AuNPs. In addition, serum reduced DNA adsorption, and the DNA was adsorbed to the protein corona instead of directly to the AuNP surface. These two factors can explain the difficulty of detection in protein-containing samples. This study articulates the adsorption of proteins by AuNPs in biological samples and offers useful insights into the biosensor design.

Immobilization of Thiol-Modified Horseradish Peroxidase on Gold Nanoparticles Enhances Enzyme Stability and Prevents Proteolytic Digestion

The specificity and efficiency of enzyme-mediated reactions have the potential to positively impact many biotechnologies; however, many enzymes are easily degraded. Immobilization on a solid support has recently been explored to improve enzyme stability. This study aims to gain insights and facilitate enzyme adsorption onto gold nanoparticles (AuNPs) to form a stable bioconjugate through the installation of thiol functional groups that alter the protein chemistry. In specific, the model enzyme, horseradish peroxidase (HRP), is thiolated via Traut's reagent to increase the robustness and enzymatic activity of the bioconjugate. This study compares HRP and its thiolated analog (THRP) to deduce the impact of thiolation and AuNP-immobilization on the enzyme activity and stability. HRP, THRP, and their corresponding bioconjugates, HRP-AuNP and THRP-AuNP, were analyzed via UV-vis spectrophotometry, circular dichroism, zeta potential, and enzyme-substrate kinetics assays. Our data show a 5-fold greater adsorption for THRP on the AuNP, in comparison to HRP, that translated to a 5-fold increase in the THRP-AuNP bioconjugate activity. The thiolated and immobilized HRP exhibited a substantial improvement in stability at elevated temperatures (50 °C) and storage times (1 month) relative to the native enzyme in solution. Moreover, HRP, THRP, and their bioconjugates were incubated with trypsin to assess the susceptibility to proteolytic digestion. Our results demonstrate that THRP-AuNP bioconjugates maintain full enzymatic activity after 18 h of incubation with trypsin, whereas free HRP, free THRP, and HRP-AuNP conjugates are rendered inactive by trypsin treatment. These results highlight the potential for protein modification and immobilization to substantially extend enzyme shelf life, resist protease digestion, and enhance biological function to realize enzyme-enabled biotechnologies.

Thiolation-Based Protein-Protein Hydrogels for Improved Wound Healing

The limitations of protein-based hydrogels, including their insufficient mechanical properties and restricted biological functions, arise from the highly specific functions of proteins as natural building blocks. A potential solution to overcome these shortcomings is the development of protein-protein hydrogels, which integrate structural and functional proteins. In this study, a protein-protein hydrogel formed by crosslinking bovine serum albumin (BSA) and a genetically engineered intrinsically disordered collagen-like protein (CLP) through Ag─S bonding is introduced. The approach involves thiolating lysine residues of BSA and crosslinking CLP with Ag+ ions, utilizing thiolation of BSA and the free-cysteines of CLP. The resulting protein-protein hydrogels exhibit exceptional properties, including notable plasticity, inherent self-healing capabilities, and gel-sol transition in response to redox conditions. In comparison to standalone BSA hydrogels, these protein-protein hydrogels demonstrate enhanced cellular viability, and improved cellular migration. In vivo experiments provide conclusive evidence of accelerated wound healing, observed not only in murine models with streptozotocin (Step)-induced diabetes but also in zebrafish models subjected to UV-burn injuries. Detailed mechanistic insights, combined with assessments of proinflammatory cytokines and the expression of epidermal differentiation-related proteins, robustly validate the protein-protein hydrogel's effectiveness in promoting wound repair.

A review on gold nanoparticles as an innovative therapeutic cue in bone tissue engineering: Prospects and future clinical applications

Bone damage is a complex orthopedic problem primarily caused by trauma, cancer, or bacterial infection of bone tissue. Clinical care management for bone damage remains a significant clinical challenge and there is a growing need for more advanced bone therapy options. Nanotechnology has been widely explored in the field of orthopedic therapy for the treatment of a severe bone disease. Among nanomaterials, gold nanoparticles (GNPs) along with other biomaterials are emerging as a new paradigm for treatment with excellent potential for bone tissue engineering and regenerative medicine applications. In recent years, a great deal of research has focused on demonstrating the potential for GNPs to provide for enhancement of osteogenesis, reduction of osteoclastogenesis/osteomyelitis, and treatment of bone cancer. This review details the latest understandings in regards to GNPs based therapeutic systems, mechanisms, and the applications of GNPs against various bone disorders. The present review aims to summarize i) the mechanisms of GNPs in bone tissue remodeling, ii) preparation methods of GNPs, and iii) functionalization of GNPs and its decoration on biomaterials as a delivery vehicle in a specific bone tissue engineering for future clinical application.

SERS-based immunoassay on a plasmonic syringe filter for improved sampling and labeling efficiency of biomarkers

Rapid, sensitive, and quantitative detection of biomarkers is needed for early diagnosis of disease and surveillance of infectious outbreaks. Here, we exploit a plasmonic syringe filter and surface-enhanced Raman spectroscopy (SERS) in the development of a rapid detection system, using human IgG as a model diagnostic biomarker. The novel assay design facilitates multiple passages of the sample and labeling solution through the detection zone enabling us to investigate and maximize sampling efficiency to the capture substrate. The vertical flow immunoassay process in this study involves the utilization of filter paper embedded with gold nanoparticles (AuNPs) to form a plasmonic substrate. Capture antibody (anti-human IgG) is then immobilized onto the prepared plasmonic paper and inserted into a vertical flow device (syringe filter holder). Sample solution is passed through the filter paper and the target antigen (human IgG) is selectively captured by the immobilized antibody to form an antibody-antigen complex. Next, functionalized AuNPs as extrinsic Raman labels (ERLs) are passed through the filter paper to label the captured biomarker molecules forming a layered structure. This sandwiched geometry enhances plasmonic coupling and SERS signal to provide highly sensitive detection of biomolecules. Systematic studies to investigate the impact of multiple infuse/withdraw cycles of the sample and labeling solutions reveal that antigen and ERL binding are maximized with 10 and 20 cycles, respectively. The optimized assay achieves a detection limit of ∼0.2 ng mL-1 for human IgG with a total assay time of less than 5 minutes, meeting the demands for rapid point of care diagnostics. Additionally, the optimized platform was implemented in the quantitative analysis of the SARS-CoV-2 nucleocapsid protein, the typical target in commercial, FDA-approved rapid antigen tests for COVID-19.

Interactions between gold nanoparticles with different morphologies and human serum albumin

Introduction: Three different shapes of gold nanoparticles were synthesized in this experiment. At the same time, studies compared their effects with human serum albumin (HSA). Methods: Gold nanoparticles (AuNPs) with three different morphologies, such as, nanospheres (AuNSs), nanorods (AuNRs), and nanoflowers (AuNFs) were synthesized via a seeding method and their characteristic absorption peaks were detected using ultraviolet-visible (UV-vis) absorption spectroscopy, Telectron microscopy (TEM), Dynamic Light Scattering (DLS) and Zeta potential measurements, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) to study the interactions between them and HSA. By comparing the thermodynamic parameters and quenching mechanism of the three materials, similarities and differences were determined in their interactions with HSA. Results: The results showed that with an increase in the concentration of the AuNPs with the three different morphologies, the UV-vis absorption peak intensity of the mixed solution increased, but its fluorescence intensity was quenched. This indicates that the three types of AuNPs interact with HSA, and that the interactions between them represent a static quenching process, which is consistent with the conclusions derived from three-dimensional fluorescence experiments. Through variable-temperature fluorescence experiments, the binding constants, number of binding sites, and thermodynamic parameters of the interactions between the three types of AuNPs and HSA were determined. The Gibbs free energy changes were <0, indicating that the reactions of the three types of AuNPs with HSA are spontaneous, resulting in associated matter. Binding constant measurements indicated that the strongest binding took place between the AuNFs and HSA. In addition, the results of fluorescence, CD spectroscopy, and FTIR showed that three different shapes of AuNPs can induce conformational changes in HSA and reduce the α-helix content. Among them, AuNFs have the smallest ability to induce conformational changes. Discussion: According to studies, AuNFs interact more favorably with HSA. This can be used as a reference for the administration of drugs containing AuNPs.

Multifaceted roles of pollen in the management of cancer

Oral drug delivery of microparticles demonstrates shortcomings like aggregation, decreased loading capacity and batch-to-batch variation, which limits its scale-up. Later, porous structures gained attention because of their large surface-to-volume ratio, high loading capacity and ability to carry biomacromolecules, which undergo degradation in GIT. But there are pitfalls like non-uniform particle size distribution, the impact of porogen properties, and harsh chemicals. To circumvent these drawbacks, natural carriers like pollen are explored in drug delivery, which withstands harsh environments. This property helps to subdue the acid-sensitive drug in GIT. It shows uniform particle size distribution within the species. On the other side, they contain phytoconstituents like flavonoids and polysaccharides, which possess various pharmacological applications. Therefore, pollen has the capability as a carrier system and therapeutic agent. This review focuses on pollen's microstructure, composition and utility in cancer management. The extraction strategies, characterisation techniques and chemical structure of sporopollenin exine capsule, its use in the oral delivery of antineoplastic drugs, and emerging cancer treatments like photothermal therapy, immunotherapy and microrobots have been highlighted. We have mentioned a note on the anticancer activity of pollen extract. Further, we have summarised the regulatory perspective, bottlenecks and way forward associated with pollen.

Immunochromatographic assay for miroestrol and deoxymiroestrol, its cross-reactivity, and application in Pueraria mirifica (white Kwao Krua) analysis

INTRODUCTION

Miroestrol (Mi) and deoxymiroestrol (Dmi) are trace, yet potent, phytooestrogens found in white Kwao Krua [Pueraria candollei var. mirifica (Airy Shaw & Suvat.) Niyomdham, PM]. However, the analysis of these substances is difficult because of complex matrix effects and their various analogues. In addition, alteration in the cross-reactivity of a gold nanoparticle (AuNP)-based immunochromatographic assay (ICA) resulting from the electrostatic adsorption between antibodies and AuNPs has not yet been evaluated.

OBJECTIVES

This study aims to develop, characterise, and validate ICA with a monoclonal antibody exhibiting similar reactivity against Mi and Dmi (MD-mAb).

MATERIALS AND METHODS

The ICA performance was validated for cross-reactivity and performance in comparison with those of indirect competitive enzyme-linked immunosorbent assays (icELISAs) with MD-mAb and mAb exhibiting specificity against Mi (Mi-mAb).

RESULTS

The ICA showed a limit of detection (LOD) at 1 and 16 μg/mL for Mi and Dmi, respectively. The cross-reactivity of the ICA with Dmi was lower (6.25%) than that observed with the icELISA (120%). Cross-reactivity of ICA against other compounds of the PM was also correlated with those of icELISA; no false-positive/negative results were observed. The repeatability and reproducibility of the ICA were confirmed. The results obtained using ICA in samples of PM are correlated with the concentrations determined through icELISAs.

CONCLUSION

An ICA with MD-mAb was constructed and validated. However, direct conjugation via the electrostatic adsorption of mAb-AuNPs was expected to alter the cross-reactivity of ICA, especially that of the analyte analogue Dmi.

How eluents define proteomic fingerprinting of protein corona on nanoparticles

Nanoparticles (NPs) have broad application prospects in the field of biomedicine due to their excellent physicochemical properties. When entering biological fluids, NPs inevitably encountered proteins and were subsequently surrounded by them, forming the termed protein corona (PC). As PC has been evidenced to have critical roles in deciding the biological fates of NPs, how to precisely characterize PC is vital to promote the clinical translation of nanomedicine by understanding and harnessing NPs' behaviors. During the centrifugation-based separation techniques for the PC preparation, direct elution has been most widely used to strip proteins from NPs due to its simpleness and robustness, but the roles of multifarious eluents have never been systematically declared. Herein, seven eluents composed of three denaturants, sodium dodecyl sulfate (SDS), dithiothreitol (DTT), and urea (Urea), were applied to detach PC from gold nanoparticles (AuNPs) and silica nanoparticles (SiNPs), and eluted proteins in PC have been carefully characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and chromatography coupled tandem mass spectrometry (LC-MS/MS). Our results showed that SDS and DTT were the main contributors to the efficient desorption of PC on SiNPs and AuNPs, respectively. The molecular reactions between NPs and proteins were explored and verified by SDS-PAGE analysis of PC formed in the serums pretreated with protein denaturing or alkylating agents. The proteomic fingerprinting analysis indicated the difference of the eluted proteins brought by the seven eluents was the abundance rather than the species. The enrichment of some opsonins and dysopsonins in a special elution reminds us that the possibility of biased judgments on predicting NPs' biological behaviors under different elution conditions. The synergistic effects or antagonistic effects among denaturants for eluting PC were manifested in a nanoparticle-type dependent way by integrating the properties of the eluted proteins. Collectively, this study not only underlines the urgent need of choosing the appropriate eluents for identifying PC robustly and unbiasedly, but also provides an insight into the understanding of molecular interactions during PC formation.

Controlled Temporal Release of Serum Albumin Immobilized on Gold Nanoparticles

Proteins adsorbed to gold nanoparticles (AuNPs) form bioconjugates and are critical to many emerging technologies for drug delivery, diagnostics, therapies, and other biomedical applications. A thorough understanding of the interaction between the immobilized protein and AuNP is essential for the bioconjugate to perform as designed. Here, we explore a correlation between the number of solvent-accessible thiol groups on a protein and the protein desorption rate from the AuNP surface in the presence of a competing protein. The chemical modification of human serum albumin (HSA) was carried out to install additional free thiols using Traut's reagent and create a library of HSA analogues by tailoring the molar excess of the Traut's reagent. We pre-adsorbed HSA variants onto the AuNP surface, and the resulting bioconjugates were then exposed to IgG antibody, and protein exchange was monitored as a function of time. We found that the rate of HSA displacement from the AuNP correlated with the experimentally measured number of accessible free thiol groups. Additionally, bioconjugates were synthesized using thiolated analogues of bovine serum albumin (BSA) and suspended in serum as a model for a complex sample matrix. Similarly, desorption rates with serum proteins were modulated with solvent-accessible thiols on the immobilized protein. These results further highlight the key role of Au-S bonds in the formation of protein-AuNP conjugates and provide a pathway to systematically control the number of free thiols on a protein, enabling the controlled release of protein from the surface of AuNP.

In Situ and Ex Situ Raman Studies of Cysteine’s Behavior on a Titanium Surface in Buffer Solution

In this paper, surface-enhanced Raman spectroscopy (SERS) was used to investigate the adsorption process of cysteine (Cys). Studies were carried out in the presence of phosphate-buffered saline solution (PBS), at pH 7.4, and acidified to pH 5, 3, and 1, on the surface of Ti for implant application. In situ SERS spectra obtained for the Cys/Ti solution system, after 24 h of immersion time, indicated that the buffer solution strongly influences the adsorption behavior of Cys on the Ti surface. This results in a decrease in Cys adsorption on the Ti surface, in the range of pH 7.4 to 3. The strong interaction between a sulfur atom of Cys and a Ti surface was observed only at pH = 1, under strongly acidic conditions. In contrast, ex situ SERS spectra recorded for the same samples but in a dried Cys/Ti system show a completely different behavior of Cys on the Ti surface. Formation of a disulfide (S-S) bond has occurred as a result of the dimerization or aggregation of Cys molecules on the Ti surface. Detailed analysis of the adsorption behavior of Cys on the Ti surface can be very important in the preparation of bioactive materials (i.e., coated by organic layers).

Structure and activity of native and thiolated α-chymotrypsin adsorbed onto gold nanoparticles

A detailed understanding of protein-nanoparticle interactions is critical to realize the full potential of bioconjugate-enabled technologies. Parameters that lead to conformational changes in protein structure upon adsorption must be identified and controlled to mitigate loss of biological function. We hypothesized that the installation of thiol functional groups on a protein will facilitate robust adsorption to gold nanoparticles (AuNPs) and prevent protein unfolding to achieve thermodynamic stability. Here we investigated the adsorption behavior of α-chymotrypsin (ChT) and a thiolated analog of α-chymotrypsin (T-ChT) with AuNPs. ChT, which does not present any free thiols, was modified with 2-iminothiolane (Traut's reagent) to synthesize T-ChT consisting of two free thiols. Protein adsorption to AuNPs was monitored with dynamic light scattering and UV-vis spectrophotometry, and fluorescence spectra were acquired to assess changes in protein structure induced by interaction with the AuNP. The biological function of ChT, T-ChT, and respective bioconjugates were compared using a colorimetric enzymatic assay. The thiolated analog exhibited a greater affinity for the AuNP than the unmodified ChT, as determined from adsorption isotherms. The ChT protein formed a soft protein corona in which the enzyme denatures with prolonged exposure to AuNPs and, subsequently, lost enzymatic function. Conversely, the T-ChT formed a robust hard corona on the AuNP and retained structure and function. These data support the hypothesis, provide further insight into protein-AuNP interactions, and identify a simple chemical approach to synthesize robust and functional conjugates.

The impact of engineered nanomaterials on the environment: Release mechanism, toxicity, transformation, and remediation

The presence and longevity of nanomaterials in the ecosystem, as well as their properties, account for environmental toxicity. When nanomaterials in terrestrial and aquatic systems are exposed to the prevailing environmental conditions, they undergo various transformations such as dissociation, dissolution, and aggregation, which affects the food chain. The toxicity of nanomaterials is influenced by a variety of factors, including environmental factors and its physico-chemical characteristics. Bioaccumulation, biotransformation, and biomagnification are the mechanisms that have been identified for determining the fate of nanomaterials. The route taken by nanomaterials to reach living cells provides us with information about their toxicity profile. This review discusses the recent advances in the transport, transformation, and fate of nanomaterials after they are released into the environment. The review also discusses how nanoparticles affect lower trophic organisms through direct contact, the impact of nanoparticles on higher trophic organisms, and the possible options for remediation.

Physisorption of Affinity Ligands Facilitates Extracellular Vesicle Detection with Low Non-Specific Binding to Plasmonic Gold Substrates

Plasmonic biosensors are increasingly being used for the analysis of extracellular vesicles (EVs) originating from disease areas. However, the high non-specific binding of EVs to a gold-sensing surface has been a critical problem and hindered the true translational potential. Here, we report that direct antibody immobilization on the plasmonic gold surface via physisorption shows excellent capture of cancer-derived EVs with ultralow non-specific binding even at very high concentrations. Contrary to commonly used methods that involve thiol-based linker attachment and an EDC/sulfo-NHS reaction, we show a higher specific capture rate and >50-fold lower non-specific on citrate-capped plain and nanopatterned gold surfaces. The method provides a simple, fast, and reproducible means to functionalize plasmonic gold surfaces with antibodies for robust EV biosensing.

Gold nanomaterials for oral cancer diagnosis and therapy: Advances, challenges, and prospects

Early diagnosis and treatment of oral cancer are vital for patient survival. Since the oral cavity accommodates the second largest and most diverse microbiome community after the gut, the diagnostic and therapeutic approaches with low invasiveness and minimal damage to surrounding tissues are keys to preventing clinical intervention-related infections. Gold nanoparticles (AuNPs) are widely used in the research of cancer diagnosis and therapy due to their excellent properties such as surface-enhanced Raman spectroscopy, surface plasma resonance, controlled synthesis, the plasticity of surface morphology, biological safety, and stability. AuNPs had been used in oral cancer detection reagents, tumor-targeted therapy, photothermal therapy, photodynamic therapy, and other combination therapies for oral cancer. AuNPs-based noninvasive diagnosis and precise treatments further reduce the clinical intervention-related infections. This review is focused on the recent advances in research and application of AuNPs for early screening, diagnostic typing, drug delivery, photothermal therapy, radiotherapy sensitivity treatment, and combination therapy of oral cancer. Distinctive reports from the literature are summarized to highlight the latest advances in the development and application of AuNPs in oral cancer diagnosis and therapy. Finally, this review points out the challenges and prospects of possible applications of AuNPs in oral cancer diagnosis and therapy.

Interactions of proteins with metal-based nanoparticles from a point of view of analytical chemistry - Challenges and opportunities

Interactions of proteins with nanomaterials draw attention of many research groups interested in fundamental phenomena. However, alongside with valuable information regarding physicochemical aspects of such processes and their mechanisms, they more and more often prove to be useful from a point of view of bioanalytics. Deliberate use of processes based on adsorption of proteins on nanoparticles (or vice versa) allows for a development of new analytical methods and improvement of the existing ones. It also leads to obtaining of nanoparticles of desired properties and functionalities, which can be used as elements of analytical tools for various applications. Due to interactions with nanoparticles, proteins can also gain new functionalities or lose their interfering potential, which from perspective of bioanalytics seems to be very inviting and attractive. In the framework of this article we will discuss the bioanalytical potential of interactions of proteins with a chosen group of nanoparticles, and implementation of so driven processes for biosensing. Moreover, we will show both positive and negative (opportunities and challenges) aspects resulting from the presence of proteins in media/samples containing metal-based nanoparticles or their precursors.

Antibody-Incorporated Nanomedicines for Cancer Therapy

Antibody-based cancer therapy, one of the most significant therapeutic strategies, has achieved considerable success and progress over the past decades. Nevertheless, obstacles including limited tumor penetration, short circulation half-lives, undesired immunogenicity, and off-target side effects remain to be overcome for the antibody-based cancer treatment. Owing to the rapid development of nanotechnology, antibody-containing nanomedicines that have been extensively explored to overcome these obstacles have already demonstrated enhanced anticancer efficacy and clinical translation potential. This review intends to offer an overview of the advancements of antibody-incorporated nanoparticulate systems in cancer treatment, together with the nontrivial challenges faced by these next-generation nanomedicines. Diverse strategies of antibody immobilization, formats of antibodies, types of cancer-associated antigens, and anticancer mechanisms of antibody-containing nanomedicines are provided and discussed in this review, with an emphasis on the latest applications. The current limitations and future research directions on antibody-containing nanomedicines are also discussed from different perspectives to provide new insights into the construction of anticancer nanomedicines.

Interaction Mechanisms and Interface Configuration of Cysteine Adsorbed on Gold, Silver, and Copper Nanoparticles

Cysteine-protected metal nanoparticles (NPs) have shown interesting physicochemical properties of potential utility in biomedical applications and in the understanding of protein folding. Herein, cysteine interaction with gold, silver, and copper NPs is characterized by Raman spectroscopy and density functional theory calculations to elucidate the molecular conformation and adsorption sites for each metal. The experimental analysis of Raman spectra upon adsorption with respect to free cysteine indicates that while the C-S bond and carboxyl group are similarly affected by adsorption on the three metal NPs, the amino group is sterically influenced by the electronegativity of each metal, causing a greater modification in the case of gold NPs. A theoretical approach that takes into consideration intermolecular interactions using two cysteine molecules is proposed using a S-metal-S interface motif anchored to the metal surface. These interactions generate the stabilization of an organo-metallic complex that combines gauche (P_H) and anti (P_C) rotameric conformers of cysteine on the surface of all three metals. Similarities between the calculated Raman spectra and experimental data confirm the thiol and carboxyl as adsorption groups for gold, silver, and copper NPs and suggest the formation of monomeric "staple motifs" that have been found in the protecting monolayer of atomic-precise thiolate-capped metal nanoclusters.

Exosome detection via surface-enhanced Raman spectroscopy for cancer diagnosis

As nanoscale extracellular vesicles, exosomes are secreted by various cell types, and they are widely distributed in multiple biological fluids. Studies have shown that tumor-derived exosomes can carry a variety of primary tumor-specific molecules, which may represent a novel tool for the early detection of cancer. However, the clinical translation of exosomes remains a challenge due to the requirement of large quantities of samples when enriching the cancer-related exosomes in biological fluids, the insufficiency of traditional techniques for exosome subpopulations, and the complex exosome isolation of the current commercially available exosome phenotype profiling approaches. The evolving surface-enhanced Raman scattering (SERS) technology, with properties of unique optoelectronics, easy functionalization, and the particular interaction between light and nanoscale metallic materials, can achieve sensitive detection of exosomes without large quantities of samples and multiplexed phenotype profiling, providing a new mode of real-time and noninvasive analysis for cancer patients. In the present review, we mainly discussed exosome detection based on SERS, especially SERS immunoassay. The basic structure and function of exosomes were firstly introduced. Then, recent studies using the SERS technique for cancer detection were critically reviewed, which mainly included various SERS substrates, biological modification of SERS substrates, SERS-based exosome detection, and the combination of SERS and other technologies for cancer diagnosis. This review systematically discussed the essential aspects, limitations, and considerations of applying SERS technology in the detection and analysis of cancer-derived exosomes, which could provide a valuable reference for the early diagnosis of cancer through SERS technology. STATEMENT OF SIGNIFICANCE: Surface-enhanced Raman scattering (SERS) has been applied to exosomes detection to obtain better diagnostic results. In past three years, several reviews have been published in exosome detection, which were narrowly focus on methods of exosome detection. Selection and surface functionalization of the substrate and the combination detection with different methods based on SERS will provide new strategies for the detection of exosomes. This review will focus on the above aspects. This emerging detection method is constantly evolving and contributing to the early discovery of diseases in the future.

Role of Sporopollenin Shell Interfacial Properties in Protein Adsorption

Sporopollenin shells isolated from natural pollen grains have received attention in translational and applied research in diverse fields of drug delivery, vaccine delivery, and wastewater remediation. However, little is known about the sporopollenin shell's potential as an adsorbent. Herein, we have isolated sporopollenin shells from four structurally diverse pollen species, black walnut, marsh elder, mugwort, and silver birch, to study protein adsorption onto sporopollenin shells. We investigated three major interfacial properties, surface area, surface functional groups, and surface charge, to elucidate the mechanism of protein adsorption onto sporopollenin shells. We showed that sporopollenin shells have a moderate specific surface area (<12 m²/g). Phosphoric acid and potassium hydroxide treatments that were used to isolate sporopollenin shells from natural pollen grains also result in the functionalization of sporopollenin shell surfaces with ionizable groups of carboxylic acid and carboxylate salt. As a result, sporopollenin shells exhibit a negative ζ potential in the range of -75 to -82 mV at pH 10 when dispersed in water. The ζ potentials of sporopollenin shells remain negative in the pH range of 2.5-11, with the absolute value of ζ potential showing a decrease with the decrease in pH. The negative surface charge promotes the adsorption of protein onto the sporopollenin shell via electrostatic interaction. Despite having a moderate surface area, sporopollenin shells adsorb a significant amount of lysozyme (145-340 μg lysozyme per mg of sporopollenin shells). Lysozyme adsorption onto sporopollenin shells alters the surface, and the surface charge becomes positive at acidic pH. Overall, this study demonstrates the potential of sporopollenin shells to adsorb proteins, highlights the critical role of sporopollenin shell's interfacial properties in protein adsorption, and identifies the mechanism of protein adsorption on sporopollenin shells.

Simultaneous Stabilization and Functionalization of Gold Nanoparticles via Biomolecule Conjugation: Progress and Perspectives

Gold nanoparticles (AuNPs) are used in various biological applications because of their small surface area-to-volume ratios, ease of synthesis and modification, low toxicity, and unique optical properties. These properties can vary significantly with changes in AuNP size, shape, composition, and arrangement. Thus, the stabilization of AuNPs is crucial to preserve the properties required for biological applications. In recent years, various polymer-based physical and chemical methods have been extensively used for AuNP stabilization. However, a new stabilization approach using biomolecules has recently attracted considerable attention. Biomolecules such as DNA, RNA, peptides, and proteins are representative of the biomoieties that can functionalize AuNPs. According to several studies, biomolecules can stabilize AuNPs in biological media; in addition, AuNP-conjugated biomolecules can retain certain biological functions. Furthermore, the presence of biomolecules on AuNPs significantly enhances their biocompatibility. This review provides a representative overview of AuNP functionalization using various biomolecules. The strategies and mechanisms of AuNP functionalization using biomolecules are comprehensively discussed in the context of various biological fields.

Surface engineering strategies of gold nanomaterials and their applications in biomedicine and detection

Gold nanomaterials have potential applications in biosensors and biomedicine due to their controllable synthesis steps, high biocompatibility, low toxicity and easy surface modification. However, there are still various limitations including low water solubility and stability, which greatly affect their applications. In addition, some synthetic methods are very complicated and costly. Therefore, huge efforts have been made to improve their properties. This review mainly introduces the strategies for surface modification of gold nanomaterials, such as amines, biological small molecules and organic small molecules as well as the biological applications of these functionalized AuNPs. We aim to provide effective ideas for better functionalization of gold nanomaterials in the future.

Serum albumin guided plasmonic nanoassemblies with opposite chiralities

Chiral assemblies by combining natural biomolecules with plasmonic nanostructures hold great promise for plasmonic enhanced sensing, imaging, and catalytic applications. Herein, we demonstrate that human serum albumin (HSA) and porcine serum albumin (PSA) can guide the chiral assembly of gold nanorods (GNRs) with left-handed chiroptical responses opposite to those by a series of other homologous animal serum albumins (SAs) due to the difference of their surface charge distributions. Under physiological pH conditions, the assembly of HSA or PSA with GNRs yielded left-handed twisted aggregates, while bovine serum albumin (BSA), sheep serum albumin, and equine serum albumin behaved on the contrary. The driving force for the chiral assembly is mainly attributed to electrostatic interaction. The opposite chiroptical signals acquired are correlated with the chiral surface charge distributions of the tertiary structures of SAs. Moreover, the chirality of the assembly induced by both HSA and BSA can be enhanced or reversed by adjusting the pH values. This work provides new insights into the modulation of protein-induced chiral assemblies and promotes their applications.

High-Affinity Points of Interaction on Antibody Allow Synthesis of Stable and Highly Functional Antibody-Gold Nanoparticle Conjugates

Many emerging nanobiotechnologies rely on the proper function of proteins immobilized on gold nanoparticles. Often, the surface chemistry of the AuNP is engineered to control the orientation, surface coverage, and structure of the adsorbed protein to maximize conjugate function. Here, we chemically modified antibody to investigate the effect of protein surface chemistries on adsorption to AuNPs. A monoclonal anti-horseradish peroxidase IgG antibody (anti-HRP) was reacted with N-succinimidyl acrylate (NSA) or reduced dithiobissuccinimidyl propionate (DSP) to modify lysine residues. Zeta potential measurements confirmed that both chemical modifications reduced the localized regions of positive charge on the protein surface, while the DSP modification incorporated additional free thiols. Dynamic light scattering confirmed that native and chemically modified antibodies adsorbed onto AuNPs to form bioconjugates; however, adsorption kinetics revealed that the NSA-modified antibody required significantly more time to allow for the formation of a hard corona. Moreover, conjugates formed with the NSA-modified antibody lost antigen-binding function, whereas unmodified and DSP-modified antibodies adsorbed onto AuNPs to form functional conjugates. These results indicate that high-affinity functional groups are required to prevent protein unfolding and loss of function when adsorbed on the AuNP surface. The reduced protein charge and high-affinity thiol groups on the DSP-modified antibody enabled pH-dependent control of protein orientation and the formation of highly active conjugates at solution pHs (<7.5) that are inaccessible with unmodified antibody due to conjugate aggregation. This study establishes parameters for protein modification to facilitate the formation of highly functional and stable protein-AuNP conjugates.

Ultrasensitive detection of specific IgE based on nanomagnetic capture and separation with a AuNP-anti-IgE nanobioprobe for signal amplification

The accurate detection of allergen specific IgE (sIgE) is fundamental in the diagnosis of allergic diseases. The present commercial platforms fail to meet the need for personalized diagnosis, due to the unsuitable allergen-fixation model and large amounts of serum consumption. In this work, we developed a nano-capturer Fe₃O₄@SiO₂-NTA with an enhanced signal by taking advantage of a AuNP-anti-IgE nanobioprobe for precise and highly sensitive quantification detection of sIgE in serum of allergic patients. The recombinant allergen was immobilized on Fe₃O₄@SiO₂-NTA through the interaction between its His-tag and Ni-NTA, which is more consistent with the real binding mode of allergens with sIgE in vivo than the present clinically used allergen-fixation methods. Numerous horseradish peroxidase (HRP)-labeled anti-IgE were modified onto one AuNP to detect the sIgE probed by Fe₃O₄@SiO₂-NTA@rCanf1. Once one anti-IgE binds to sIgE, other HRP-labeled anti-IgE modified on the same AuNP would all create signals, resulting in a significantly amplified chemiluminescence (CL) signal. Our results showed that this immunosensor could realize fast, accurate, low-cost and highly sensitive sIgE detection in serum samples. In vitro experiments demonstrated a 0.02 ng mL^-1 detection limit, which was lower than that of any standard analyzer used for allergy immunoassays. Furthermore, our method was utilized for the diagnosis of clinical samples. The results were in good agreement with those obtained by the clinical gold standard ImmunoCAP, with 1000 times less serum consumption than ImmunoCAP. Therefore, the presented immunosensor holds great promise to improve clinical sIgE quantitative detection and constitutes a potentially useful tool for clinical diagnosis and subsequent individual treatment of allergic diseases.

Voltammetric detection of vitamin D employing Au-MoS2 hybrid as immunosensing platform

A voltammetric immunosensor based on molybdenum sulphide (MoS₂) and gold nanoparticles (Au NPs) for the determination of 25-hydroxy vitamin D₃ (25(OH)D₃) is reported. Anti-vit D (Ab-25(OH)D₃) was immobilized onto the cysteamine-modified MoS₂ and Au NPs which were deposited onto a fluoride tin oxide (FTO) electrode (Ab/Cys/Au/MoS₂/FTO). The MoS₂ sheets were prepared by hydrothermal method followed by an in situ growth of Au film onto the MoS₂/FTO surface. Self-assembled monolayer (SAM) of cysteamine was synthesized onto the Au/MoS₂/FTO which acts as a linker to covalently bind Ab-25(OH)D₃. The Ab-25(OH)D₃-immobilized Cys/Au/MoS₂/FTO was used to detect 25(OH)D₃ using differential pulse voltammetry. The electrochemical system provided an anodic peak current at a potential of +0.21 V vs. Ag/AgCl (satd. KCl) of ferricyanide/ferrocyanide redox couple. The detection principle relies on the inhibition of electron transfer at the electrode surface owing to the hindrance caused by the formation of immune complex between Ab-25(OH)D₃ and 25(OH)D₃. The immunosensor shows linear response from 1 pg mL^-1 to 100 ng mL^-1 25(OH)D₃ and a sensitivity of 189 μA [log (pg mL^-1)]^-1 cm^-2 along with a low limit of detection (LOD) of 0.38 pg mL^-1. The immunosensor is highly selective towards 25(OH)D₃ and presented a long shelf life of 28 days. Also, the immunosensor exhibits satisfactory performance towards spiked human serum samples with recovery between 95.1 and 102% (RSD 1.15-3.22%).

Probing the Mechanism of Antibody-Triggered Aggregation of Gold Nanoparticles

The unique physicochemical properties of gold nanoparticles (AuNPs) provide many opportunities to develop novel biomedical technologies. The surface chemistry of AuNPs can be engineered to perform a variety of functions, including targeted binding, cellular uptake, or stealthlike properties through the immobilization of biomolecules, such as proteins. It is well established that proteins can spontaneously adsorb onto AuNPs, to form a stable and functional bioconjugate; however, the protein-AuNP interaction may result in the formation of less desirable protein-AuNP aggregates. Therefore, it is imperative to investigate the protein-AuNP interaction and elucidate the mechanism by which protein triggers AuNP aggregation. Herein, we systematically investigated the interaction of immunoglobulin G (IgG) antibody with citrate-capped AuNPs as a function of solution pH. We found that the addition of antibody triggers the aggregation of AuNPs for pH < 7.5, whereas a monolayer of antibody adsorbs onto the AuNP to form a stable bioconjugate when the antibody is added to AuNPs at pH ≥ 7.5. Our data identifies electrostatic bridging between the antibody and the negatively charged AuNPs as the mechanism by which aggregation occurs and rules out protein unfolding and surface charge depletion as potential causes. Furthermore, we found that the electrostatic bridging of AuNPs is reversible within the first few hours of interaction, but the protein-AuNP interactions strengthen over 24 h, after which the protein-AuNP aggregate is irreversibly formed. From this data, we developed a straightforward approach to acrylate the basic residues on the antibody to prevent protein-induced aggregation of AuNP over a wide pH range. The results of this study provide additional insight into antibody-nanoparticle interactions and provide a pathway to control the interaction with the potential to enhance the conjugate function.

Advances in Gold Nanoparticle-Based Combined Cancer Therapy

According to the global cancer observatory (GLOBOCAN), there are approximately 18 million new cancer cases per year worldwide. Cancer therapies are largely limited to surgery, radiotherapy, and chemotherapy. In radiotherapy and chemotherapy, the maximum tolerated dose is presently being used to treat cancer patients. The integrated development of innovative nanoparticle (NP) based approaches will be a key to address one of the main issues in both radiotherapy and chemotherapy: normal tissue toxicity. Among other inorganic NP systems, gold nanoparticle (GNP) based systems offer the means to further improve chemotherapy through controlled delivery of chemotherapeutics, while local radiotherapy dose can be enhanced by targeting the GNPs to the tumor. There have been over 20 nanotechnology-based therapeutic products approved for clinical use in the past two decades. Hence, the goal of this review is to understand what we have achieved so far and what else we can do to accelerate clinical use of GNP-based therapeutic platforms to minimize normal tissue toxicity while increasing the efficacy of the treatment. Nanomedicine will revolutionize future cancer treatment options and our ultimate goal should be to develop treatments that have minimum side effects, for improving the quality of life of all cancer patients.