Supported lipid bilayer templated J-aggregate growth: role of stabilizing cation-pi interactions and headgroup packing

Supramolecular polymers: A perspective on the stability, biocompatibility and regulatory aspects

Supramolecular polymers represent a distinctive class of polymers exhibiting similarities with covalent polymers, while also showcasing distinctive attributes such as responsiveness, reversibility, self-healing, and dynamism, which are conferred upon them by non-covalent interactions including hydrogen bonding, electrostatic interactions, van der Waals forces, π-π arrangements, and donor-acceptor interactions, among others. The noteworthy features of these supramolecular polymers have attracted considerable interest across diverse fields of science and technology, spanning electrochemistry, environmental science, drug delivery and tissue engineering. Nonetheless, the prevailing research focus in the realm of supramolecular polymers revolves around the advancement of novel methodologies aimed at synthesizing a broad spectrum of polymers characterized by diverse topologies. However, to fully capitalize on their potential applications within these domains, it is imperative to scrutinize these versatile polymers through the lens of thermodynamic and kinetic stability. Moreover, their integration into healthcare and medical realms necessitates rigorous assessment of safety and biocompatibility attributes. Thus, the present review endeavours to critically evaluate supramolecular polymers from perspectives of stability, safety, and regulatory considerations, thereby elucidating their potential for translation into commercial domains.

Biodegradable lipid bilayer-assisted indocyanine green J- aggregates for photothermal therapy: Formulation, in vitro toxicity and in vivo clearance

Indocyanine green (ICG) J-aggregates (IJA) are a unique form of aggregation that exhibits superior properties to monomeric ICG. Despite their higher photoacoustic (PA) signals for imaging and heating stability during photothermal therapy (PTT), they exhibit low stability under a biological milieu. Our group previously proposed a simple procedure for in-situ preparation of IJA into liposomes, accelerating their formation and optical properties. To comprehend their potential applications, we systematically investigated the effect of the lipid bilayer composition on ICG J-aggregation and stability. Moreover, their in vitro compatibility and photothermal toxicity in monolayers and cancer spheroids, besides their in vivo biodistribution and clearance were evaluated. Our findings revealed the importance of high cholesterol and PEG-lipid content and low charged lipids (∼ 5 mol %) in liposomes to promote a high IJA/ICG ratio and, thus, high heating stability. More importantly, IJA-liposomes revealed high biocompatibility in monolayer and cancer spheroids with efficient photothermal toxicity. Finally, IJA-liposomes were cleared from the body without toxicity. Interestingly, IJA-liposomes mainly showed lower affinity to the liver than monomeric ICG, resulting in higher renal clearance. Overall, our biodegradable IJA-liposomes could be an excellent alternative to gold-based agents suitable for PA imaging and cancer PTT.

Sensitive Detection of Biomolecular Adsorption by a Low-Density Surfactant Layer Using Sum-Frequency Vibrational Spectroscopy

Small molecules or proteins interact with a biomembrane in various ways for molecular recognition, structure stabilization, and transmembrane signaling. In this study, 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), having a choline group, was used to investigate this interaction by using sum-frequency vibrational spectroscopy. The sum-frequency spectrum characteristic of a neat monolayer changed to that of a bare air/water interface at a larger molecular area of the DPTAP molecules due to local laser heating. Upon introduction of the aromatic molecules in the subphase at around 120 Å2 per molecule, the sum-frequency signal suddenly reappeared due to molecular adhesion, and this was utilized to probe the adsorption of the aromatic ring molecules in the water subphase to the choline headgroup of the DPTAP by cation-π interaction. The onset concentrations of this sum-frequency signal change allowed a comparison of the relative interaction strengths between different aromatic molecules. A zwitterionic surfactant molecule (DPPC) was found to interact weakly compared to the cationic DPTAP molecule.

Repurposing ICG enables MR/PA imaging signal amplification and iron depletion for iron-overload disorders

Precise and noninvasive theranostic methods to quantify and deplete focal iron are of crucial importance for iron-overload disorders. Here, we developed an indocyanine green (ICG)–based imaging platform to reveal Fe³⁺ in vitro and in vivo. The high sensitivity and specificity of ICG-Fe interaction facilitated MR images with a marked correlation between T₁ signal intensity ratio (T₁SIR) changes and Fe³⁺ concentration in rodent models and humans. On the basis of these findings, a rational design for coordination-driven self-assembly ICG-Lecithin (ICG/Leci) was proposed to determine Fe³⁺. The enhancement of photoacoustic signal at 890 nm with increasing Fe³⁺ concentration showed an over 600% higher linear slope than that of T₁SIR changes in animal models. ICG/Leci also promoted a 100% increase in iron depletion in the liver compared with deferoxamine. The high MR sensitivity and superior photoacoustic contrast, combined with enhanced iron depletion, demonstrate that ICG/Leci is a promising theranostic agent for simultaneous detection and treatment of iron-overload disorders.

Liposome-Templated Indocyanine Green J- Aggregates for In Vivo Near-Infrared Imaging and Stable Photothermal Heating

Indocyanine green (ICG) is an FDA-approved near-infrared fluorescent dye that has been used in optical imaging and photothermal therapy. Its rapid in vivo clearance and photo-degradation have limited its application. ICG pharmacokinetics and biodistribution have been improved via liposomal encapsulation, while its photothermal stability has been enhanced by ICG J-aggregate (IJA) formation. In the present work, we report a simple approach to engineer a nano-sized, highly stable IJA liposomal formulation. Our results showed that lipid film hydration and extrusion method led to efficient IJA formation in rigid DSPC liposomes, as supported by molecular dynamics modeling. The engineered DSPC-IJA formulation was nano-sized, and with spectroscopic and photothermal properties comparable to free IJA. Promisingly, DSPC-IJA exhibited high fluorescence, which enabled its in vivo tracking, showing prolonged blood circulation and significantly higher tumor fluorescence signals, compared to free ICG and IJA. Furthermore, DSPC-IJA demonstrated high photo-stability in vivo after multiple cycles of 808 nm laser irradiation. Finally, doxorubicin was loaded into liposomal IJA to utilize the co-delivery capabilities of liposomes. In conclusion, with both liposomes and ICG being clinically approved, our novel liposomal IJA could offer a clinically relevant theranostic platform enabling multimodal imaging and combinatory chemo- and photothermal cancer therapy.

Structural templating of J-aggregates: Visualizing bis(monoacylglycero)phosphate domains in live cells

Identifying the key structural and dynamical determinants that drive the association of biomolecules, whether in solution, or perhaps more importantly in a membrane environment, has critical implications for our understanding of cellular dynamics, processes, and signaling. With recent advances in high-resolution imaging techniques, from the development of new molecular labels to technical advances in imaging methodologies and platforms, researchers are now reaping the benefits of being able to directly characterize and quantify local dynamics, structures, and conformations in live cells and tissues. These capabilities are providing unique insights into association stoichiometries, interactions, and structures on sub-micron length scales. We previously examined the role of lipid headgroup chemistry and phase state in guiding the formation of pseudoisocyanine (PIC) dye J-aggregates on supported planar bilayers [Langmuir, 25, 10719]. We describe here how these same J-aggregates can report on the in situ formation of organellar membrane domains in live cells. Live cell hyperspectral confocal microscopy using GFP-conjugated GTPase markers of early (Rab5) and late (Rab7) endosomes revealed that the PIC J-aggregates were confined to domains on either the limiting membrane or intralumenal vesicles (ILV) of late endosomes, known to be enriched in the anionic lipid bis(monoacylglycero)phosphate (BMP). Correlated confocal fluorescence - atomic force microscopy performed on endosomal membrane-mimetic supported planar lipid bilayers confirmed BMP-specific templating of the PIC J-aggregates. These data provide strong evidence for the formation of BMP-rich lipid domains during multivesicular body formation and portend the application of structured dye aggregates as markers of cellular membrane domain structure, size, and formation.

Stable J-aggregation enabled dual photoacoustic and fluorescence nanoparticles for intraoperative cancer imaging

J-aggregates display nanoscale optical properties which enable their use in fluorescence and photoacoustic imaging applications. However, control over their optical properties in an in vivo setting is hampered by the conformational lability of the J-aggregate structure in complex biological environments. J-aggregating nanoparticles (JNP) formed by self-assembly of bacteriopheophorbide-lipid (Bchl-lipid) in lipid nanovesicles represents a novel strategy to stabilize J-aggregates for in vivo bioimaging applications. We find that 15 mol% Bchl-lipid embedded within a saturated phospholipid bilayer vesicle was optimal in terms of maximizing Bchl-lipid dye loading, while maintaining a spherical nanoparticle morphology and retaining spectral properties characteristic of J-aggregates. The addition of cholesterol maintains the stability of the J-aggregate absorption band for up to 6 hours in the presence of 90% FBS. In a proof-of-concept experiment, we successfully applied JNPs as a fluorescence contrast agent for real-time intraoperative detection of metastatic lymph nodes in a rabbit head-and-neck cancer model. Lymph node metastasis delineation was further verified by visualizing the JNP within the excised lymph node using photoacoustic imaging. Using JNPs, we demonstrate the possibility of using J-aggregates as fluorescence and photoacoustic contrast agents and may potentially spur the development of other nanomaterials that can stably induce J-aggregation for in vivo cancer bioimaging applications.

Correlative optical and scanning probe microscopies for mapping interactions at membranes

Innovative approaches for real-time imaging on molecular-length scales are providing researchers with powerful strategies for characterizing molecular and cellular structures and dynamics. Combinatorial techniques that integrate two or more distinct imaging modalities are particularly compelling as they provide a means for overcoming the limitations of the individual modalities and, when applied simultaneously, enable the collection of rich multi-modal datasets. Almost since its inception, scanning probe microscopy has closely associated with optical microscopy. This is particularly evident in the fields of cellular and molecular biophysics where researchers are taking full advantage of these real-time, in situ, tools to acquire three-dimensional molecular-scale topographical images with nanometer resolution, while simultaneously characterizing their structure and interactions though conventional optical microscopy. The ability to apply mechanical or optical stimuli provides an additional experimental dimension that has shown tremendous promise for examining dynamic events on sub-cellular length scales. In this chapter, we describe recent efforts in developing these integrated platforms, the methodology for, and inherent challenges in, performing coupled imaging experiments, and the potential and future opportunities of these research tools for the fields of molecular and cellular biophysics with a specific emphasis on the application of these coupled approaches for the characterization of interactions occurring at membrane interfaces.

Nucleation and growth of elastin-like peptide fibril multilayers: an in situ atomic force microscopy study

Controlling how molecules assemble into complex supramolecular architectures requires careful consideration of the subtle inter- and intra-molecular interactions that control their association. This is particularly crucial in the context of assembly at interfaces, where both surface chemistry and structure can play a role in directing structure formation. We report here the results of a study into the self-assembly of the elastin-like peptide EP I on structurally modified highly ordered pyrolytic graphite, including the role of spatial confinement on fibril nucleation and the growth of oriented fibril multilayers. In situ atomic force microscopy performed in fluid and at elevated temperature provided direct evidence of frustrated fibril nuclei and oriented growth of independent fibril domains. These results portend the application of this in situ strategy for studies of the nucleation and growth mechanisms of other fibril- and amyloid-forming proteins.