Underlying Mechanisms for the Modulation of Self-Assembly and the Intrinsic Fluorescent Properties of Amino Acid-Functionalized Gold Nanoparticles

Amyloid inspired single amino acid (phenylalanine)-based supramolecular functional assemblies: from disease to device applications

In the evolving landscape of biomolecular supramolecular chemistry, recent studies on phenylalanine (Phe) have revealed important insights into the versatile nature of this essential aromatic amino acid. Phe can spontaneously self-assemble into fibrils with amyloid-like properties linked to the neurological disorder phenylketonuria (PKU). Apart from its pathological implications, Phe also displays complex phase behavior and can undergo structural changes in response to external stimuli. Its ability to co-assemble with other amino acids opens up new possibilities for studying biomolecular interactions. Furthermore, Phe's coordination with metal ions has led to the development of enzyme-mimicking catalytic systems for applications in organic chemistry, environmental monitoring, and healthcare. Research on L and D enantiomers of Phe, particularly on bio-MOFs, has highlighted their potential in advanced technologies, including bioelectronic devices. This review provides a comprehensive overview of the advancements in Phe-based supramolecular assemblies, emphasizing their interdisciplinary relevance. The Phe assemblies show great potential for future therapeutic and functional biomaterial developments, from disease treatments to innovations in bionanozymes and bioelectronics. This review presents a compelling case for the ongoing exploration of Phe's biomolecular supramolecular chemistry as a fundamental framework for developing sustainable and efficient methodologies across various scientific disciplines.

Freeze-Thaw-Induced Patterning of Extracellular Vesicles with Artificial Intelligence for Breast Cancers Identifications

Extracellular vesicles (EVs) play a crucial role in the occurrence and progression of cancer. The efficient isolation and analysis of EVs for early cancer diagnosis and prognosis have gained significant attention. In this study, for the first time, a rapid and visually detectable method termed freeze-thaw-induced floating patterns of gold nanoparticles (FTFPA) is proposed, which surpasses current state-of-the-art technologies by achieving a 100 fold improvement in the limit of detection of EVs. Notably, it allows for multi-dimensional visualizations of EVs through site-specific oligonucleotide incorporation. This capability empowers FTFPA to accurately identify EVs derived from subtypes of breast cancers with artificial intelligence algorithms. Intriguingly, learning the freezing-thawing-microstructures of EVs with a random forest algorithm is not only able to distinguish their original cell lines (with an accuracy of 95.56%), but also succeed in processing clinical samples (n = 156) to identify EVs by their healthy donors, breast lump and breast cancer subtypes (Luminal A, Triple-negative breast cancer, and Luminal B) with an accuracy of 83.33%. Therefore, this AI-empowered micro-visualization method establishes a rapid and precise point-of-care platform that is applicable to both fundamental research and clinical settings.

Fabrication and characterization of whey protein isolate-tryptophan nanoparticles by pH-shifting combined with heat treatment

L-Tryptophan (Trp) is an essential amino acid with numerous health benefits. However, incorporating Trp into food products is limited due to its pronounced bitter taste. Encapsulating Trp in nanoparticles by using other natural biopolymers is a potential strategy to mask the bitter taste of Trp in the final products. Whey protein isolate (WPI), composed of alpha-lactalbumin (α-LA), bovine serum albumin (BSA), and beta-lactoglobulin (β-LG), has played a crucial role in delivering bioactive compounds. In order to incorporate Trp within WPI, the present study used a combination of pH-shifting andthermal treatment to fabricatewhey protein isolate-tryptophan nanoparticles (WPI-Trp-NPs). During the pH-shifting technique, WPI unfolds at high pH, such as pH 11, and the dissociated WPI molecules are refolded when pH is shifted back to neutral, creating particles with uniform dispersion and encapsulating smaller particles surrounding them in solution. Further, the well-distributed nanoparticles formed by pH-shifting might encourage the formation of more uniform nanoparticles during subsequent thermal treatment. TheWPI-Trp particles have an average particle size of 110.1 nm and a low average PDI of 0.20. Fluorescence spectroscopy confirmed the encapsulation of Trp by WPI, which shows higher fluorescence when the Trp is encapsulated by the WPI. Surface hydrophobicity, circular dichroism, particle size, free sulfhydryl, and antioxidant activity were used to characterize the WPI-Trp-NPs. WPI-Trp-NPs formed by pH-shifting combined with heating showed a higher surface hydrophobicity and free sulfhydryl content than the untreated WPI-Trp mixture. The conversion of α-helix into random coil in the WPI secondary structure indicated a more disordered structure of the modified whey protein. Molecular docking results indicate the interactions between Trp and WPI, including alpha-lactalbumin (α-LA), bovine serum albumin, and beta-lactoglobulin (β-LG), were mainly driven by hydrophobic interactions and hydrogen bonding. The binding affinity between Trp and these proteins was ranked as α-LA>BSA>β-LG. The combination of pH-shifting and heating improved the functionalityof WPI and was an effective way to fabricate WPI-Trp nanoparticles.

Effect of Lipid Corona on Phenylalanine-Functionalized Gold Nanoparticles to Develop Stable and Corona-Free Systems

Conventional gold nanoparticles (Au NPs) have many limitations, such as aggregation and subsequent precipitation in the medium of high ionic strength and protein molecules. Furthermore, when exposed to biological fluids, nanoparticles form a protein corona, which controls different biological processes such as the circulation lifetime, drug release profile, biodistribution, and in vivo cellular distribution. These limitations reduce the functionality of Au NPs in targeted delivery, bioimaging, gene delivery, drug delivery, and other biomedical applications. To circumvent these problems, there are numerous attempts to design corona-free and stable nanoparticles. Here, we report for the first time that lipid corona (coating of lipid) formation on phenylalanine-functionalized Au NPs (AuPhe NPs) imparts excellent stability against the high ionic strength of bivalent metal ions, amino acids, and proteins of different charges as compared to bare nanoparticles. Moreover, this work is focused on the ability of lipid corona formation on AuPhe NPs to prevent protein adsorption in the presence of cell culture medium (CCM), oppositely charged protein (e.g., histone 3), and human serum albumin (HSA). The results demonstrate that the lipid corona successfully protects the AuPhe NPs from protein adsorption, leading to the development of corona-free character. This unique achievement has profound implications for enhancing the biomedical utility and safety of these nanoparticles.

Investigating the synergistic effects of high-pressure homogenization and pH shifting on the formation of tryptophan-rich nanoparticles

A combined treatment of high-pressure homogenization (HPH) and pH-shifting on the mixture of α-lactalbumin (α-LA) and tryptophan (Trp) was used to fabricate nanoparticles (α-LA-Trp-NP). The optimal α-LA/Trp ratio (5:1), HPH pressure (206.8 MPa), and recirculation time (40 min) was found to produce small α-LA-Trp-NP (243.0 ± 7.2 nm) with a narrow particle size distribution. Comparing the size and morphology of α-LA-NPs with α-LA-Trp-NPs indicated that the presence of Trp significantly affected the size and morphology of the NPs in the dry form. The stability of the α-LA-Trp-NPs was improved by using the combination of HPH and pH-shifting. The α-LA-Trp-NPs showed better freeze-thaw stability and retained the particle characteristics with heat treatment at 63 °C, 30 min after the freeze-thaw cycle. α-LA-Trp-NPs were also observed to have remarkable stability against pH changes and thermal treatments at 63 °C, 30 min, and 90 °C, 2 min.

Bioinspired Amino Acid Based Materials in Bionanotechnology: From Minimalistic Building Blocks and Assembly Mechanism to Applications

Inspired by natural hierarchical self-assembly of proteins and peptides, amino acids, as the basic building units, have been shown to self-assemble to form highly ordered structures through supramolecular interactions. The fabrication of functional biomaterials comprised of extremely simple biomolecules has gained increasing interest due to the advantages of biocompatibility, easy functionalization, and structural modularity. In particular, amino acid based assemblies have shown attractive physical characteristics for various bionanotechnology applications. Herein, we propose a review paper to summarize the design strategies as well as research advances of amino acid based supramolecular assemblies as smart functional materials. We first briefly introduce bioinspired reductionist design strategies and assembly mechanism for amino acid based molecular assembly materials through noncovalent interactions in condensed states, including self-assembly, metal ion mediated coordination assembly, and coassembly. In the following part, we provide an overview of the properties and functions of amino acid based materials toward applications in nanotechnology and biomedicine. Finally, we give an overview of the remaining challenges and future perspectives on the fabrication of amino acid based supramolecular biomaterials with desired properties. We believe that this review will promote the prosperous development of innovative bioinspired functional materials formed by minimalistic building blocks.

Insight into the Lysozyme-Induced Aggregation of Aromatic Amino Acid-Functionalized Gold Nanoparticles: Impact of the Protein Conjugation and Lipid Corona on the Aggregation Phenomena

The aggregation and subsequent precipitation of gold nanoparticles (Au NPs) in the presence of protein molecules restrict the usefulness of NPs in biomedical applications. Till now, the influence of different properties of Au NPs (size, surface charge, surface coatings) and proteins (surface charge, chemical modification, folded and unfolded states) and pH and ionic strength of the solution on the aggregation of both Au NPs and proteins has been thoroughly discussed in the literature. However, the underlying different mechanistic pathways of the protein concentration-dependent aggregation of both Au NPs and proteins are poorly understood. The impact of the lipid corona on the protein-induced Au NP aggregation has remained an unresolved issue. In this context, we investigate the interaction of the negatively charged aromatic amino acid (phenylalanine and tyrosine)-functionalized gold nanoparticles (Au-AA NPs) with the positively charged globular protein lysozyme at different protein concentrations and compare the results with those of conventional citrate-functionalized Au NPs (Au-Cit NPs). Next, we conjugate lipids and proteins to Au NPs to impede the aggregation of Au NPs induced by the lysozyme. Our results reveal that the aggregation mechanism of the Au-AA NPs is distinctly different at low and high protein concentrations with the uniqueness of the Au-AA NPs over the Au-Cit NPs. Furthermore, we find that human serum albumin (HSA) protein-conjugated Au-AA and Au-Cit NPs are more effective in preventing the lysozyme-induced Au NP aggregation than bovine serum albumin (BSA)-conjugated Au NPs. For the first time, we also report the significant role of "hard" and "soft" lipid coronas in the aggregation of amino acid (phenylalanine)-functionalized gold nanoparticles in the presence of lysozyme protein.

Luminescent Gold Nanoclusters for Bioimaging: Increasing the Ligand Complexity

Fluorescence, and more in general, photoluminescence (PL), presents important advantages for imaging with respect to other diagnostic techniques. In particular, detection methodologies exploiting fluorescence imaging are fast and versatile; make use of low-cost and simple instrumentations; and are taking advantage of newly developed powerful, low-cost, light-based electronic devices, such as light sources and cameras, used in huge market applications, such as civil illumination, computers, and cellular phones. Besides the aforementioned simplicity, fluorescence imaging offers a spatial and temporal resolution that can hardly be achieved with alternative methods. However, the two main limitations of fluorescence imaging for bio-application are still (i) the biological tissue transparency and autofluorescence and (ii) the biocompatibility of the contrast agents. Luminescent gold nanoclusters (AuNCs), if properly designed, combine high biocompatibility with PL in the near-infrared region (NIR), where the biological tissues exhibit higher transparency and negligible autofluorescence. However, the stabilization of these AuNCs requires the use of specific ligands that also affect their PL properties. The nature of the ligand plays a fundamental role in the development and sequential application of PL AuNCs as probes for bioimaging. Considering the importance of this, in this review, the most relevant and recent papers on AuNCs-based bioimaging are presented and discussed highlighting the different functionalities achieved by increasing the complexity of the ligand structure.

Mechanistic Pathway of Lipid Phase-Dependent Lipid Corona Formation on Phenylalanine-Functionalized Gold Nanoparticles: A Combined Experimental and Molecular Dynamics Simulation Study

In recent years, the underlying mechanism of formation of the lipid corona and its stability have begun to garner interest in the nanoscience community. However, until now, very little is known about the role of different properties of nanoparticles (NPs) (surface charge density, hydrophobicity, and size) in lipid corona formation. Apart from the physicochemical properties of NPs, the different properties of lipids remain elusive in lipid corona formation. In the present contribution, we have investigated the interaction of phenylalanine-functionalized gold NPs (Au-Phe NPs) with different zwitterionic lipid vesicles of different phase states (sol-gel and liquid crystalline at room temperature) as a function of lipid concentration. The main objective of the present work is to understand how the lipid phase affects lipid corona formation and lipid-induced aggregation in various media. Our results establish that the lipid phase state, area per lipid head group, and the buffer medium play important roles in lipid-induced aggregation. The lipid corona occurs for NPs at high lipid concentration, irrespective of the phase states and area per lipid head group of the lipid bilayer. Notably, the lipid corona also forms at a low concentration of lipid vesicles in the liquid crystalline phase (1,2-dioleoyl-sn-glycero-3-phosphocholine). The corona formation brings in remarkable stability to NPs against freeze-thaw cycles. Based on the stability, for the first time, we classify lipid corona as "hard lipid corona" and "soft lipid corona". This distinct classification will help to develop suitable nanomaterials for various biomedical applications.

Inhibiting protein aggregation with nanomaterials: The underlying mechanisms and impact factors

Protein aggregation is correlated with the onset and progression of protein misfolding diseases (PMDs). Inhibiting the generation of toxic aggregates of misfolded proteins has been proposed as a therapeutic approach for PMDs. Due to their unique properties, nanomaterials have been extensively investigated for their ability to inhibit protein aggregation and have shown great potential in the diagnosis and treatment of PMDs. However, the precise mechanisms by which nanomaterials interact with amyloidogenic proteins and the factors influencing these interactions remain poorly understood. Consequently, developing a rational design strategy for nanomaterials that target specific proteins in PMDs has been challenging. In this review, we elucidate the effects of nanomaterials on protein aggregation and describe the mechanisms through which nanomaterials interfere with protein aggregation. The major factors impacting protein-nanomaterial interaction such as size, charge, concentration, surface modification and morphology that can be rationally addressed to achieve the desired effects of nanomaterials on protein aggregation are summarized. The prospects and challenges to the clinical application of nanomaterials for the treatment of PMDs are also discussed.

Effect of Metal Ions on the Intrinsic Blue Fluorescence Property and Morphology of Aromatic Amino Acid Self-Assembly

Metal ions are known to strongly bind with different proteins and peptides, resulting in alteration of their different physicochemical properties. In this work, we investigate the effect of metal ions of different nuclear charges and sizes on the intrinsic blue luminescence of the self-assembled structures formed by aromatic amino acids, namely, phenylalanine and tryptophan, using spectroscopic and imaging techniques. The study reveals that the intrinsic blue fluorescence of amino acid assemblies is influenced by metal ions and the pH of the medium. The metal ions with a higher charge to radius ratio promote clusterization which results in the enhancement of the intrinsic fluorescence, an effect known as "clusteroluminescence" of the amino acids aggregates. The imaging study reveals that metal ions with a higher charge to size ratio inhibit the large fibrillation of aromatic amino acids by promoting the formation of small nonfibrillar aggregates through increased hydrophobicity in the medium. The nanoaggregates are assumed to be responsible for the enhancement in the blue "clusteroluminescence".

Self-assembly of artificial sweetener aspartame adversely affects phospholipid membranes: plausible reason for its deleterious effects

The prolonged intake of the artificial sweetener aspartame is known to have deleterious effects. Our biophysical experimentations indicate that aspartame forms self-assembled cytotoxic fibrillar etiologies that affect the intrinsic integrity of the phospholipid membrane bilayer through electrostatic interaction and hydrophobic insertion, thereby making the membrane less rigid and more heterogeneous.