Coupling Lipid Nanoparticle Structure and Automated Single-Particle Composition Analysis to Design Phospholipase-Responsive Nanocarriers.

Lipid nanoparticles (LNPs) are versatile structures with tunable physicochemical properties that are ideally suited as a platform for vaccine delivery and RNA therapeutics. A key barrier to LNP rational design is the inability to relate composition and structure to intracellular processing and function. Here Single Particle Automated Raman Trapping Analysis (SPARTA) is combined with small-angle X-ray and neutron scattering (SAXS/SANS) techniques to link LNP composition with internal structure and morphology and to monitor dynamic LNP-phospholipase D (PLD) interactions. This analysis demonstrates that PLD, a key intracellular trafficking mediator, can access the entire LNP lipid membrane to generate stable, anionic LNPs. PLD activity on vesicles with matched amounts of enzyme substrate is an order of magnitude lower, indicating that the LNP lipid membrane structure can be used to control enzyme interactions. This represents an opportunity to design enzyme-responsive LNP solutions for stimuli-responsive delivery and diseases where PLD is dysregulated.

Sub-picomolar lateral flow antigen detection with two-wavelength imaging of composite nanoparticles.

Lateral flow tests, commonly based on metal plasmonic nanoparticles, are rapid, robust, and low-cost. However, improvements in analytical sensitivity are required to allow detection of low-abundance biomarkers, for example detection of low antigen concentrations for earlier or asymptomatic diagnosis of infectious diseases. Efforts to improve sensitivity often require changes to the assay. Here, we developed optical methods to improve the sensitivity of absorption-based lateral flow tests, requiring no assay modifications to existing tests. We experimentally compared five different lock-in and subtraction-based methods, exploiting the narrow plasmonic peak of gold nanoparticles for background removal by imaging at different light wavelengths. A statistical framework and three fitting models were used to compare limits of detection, giving a 2.0-5.4-fold improvement. We then demonstrated the broad applicability of the method to an ultrasensitive assay, designing 530 nm composite nanoparticles to increase the particle volume, and therefore light absorption per particle, whilst retaining the plasmonic peak to allow background removal and without adding any assay steps. This multifaceted, modular approach gave a combined 58-fold improvement in the fundamental limit of detection using a biotin-avidin model over 50 nm gold nanoparticles with single-wavelength imaging. Applying to a sandwich assay for the detection of HIV capsid protein gave a limit of detection of 170 fM. Additionally, we developed an open-source software tool for performing the detection limit analysis used in this work.

Design of Lipid-Based Nanocarriers via Cation Modulation of Ethanol-Interdigitated Lipid Membranes.

Short-chain alcohols (i.e., ethanol) can induce membrane interdigitation in saturated-chain phosphatidylcholines (PCs). In this process, alcohol molecules intercalate between phosphate heads, increasing lateral separation and favoring hydrophobic interactions between opposing acyl chains, which interpenetrate forming an interdigitated phase. Unraveling mechanisms underlying the interactions between ethanol and model lipid membranes has implications for cell biology, biochemistry, and for the formulation of lipid-based nanocarriers. However, investigations of ethanol-lipid membrane systems have been carried out in deionized water, which limits their applicability. Here, using a combination of small- and wide-angle X-ray scattering, small-angle neutron scattering, and all-atom molecular dynamics simulations, we analyzed the effect of varying CaCl2 and NaCl concentrations on ethanol-induced interdigitation. We observed that while ethanol addition leads to the interdigitation of bulk phase 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers in the presence of CaCl2 and NaCl regardless of the salt concentration, the ethanol-induced interdigitation of vesicular DPPC depends on the choice of cation and its concentration. These findings unravel a key role for cations in the ethanol-induced interdigitation of lipid membranes in either bulk phase or vesicular form.

Employing defined bioconjugates to generate chemically functionalised gold nanoparticles for in vitro diagnostic applications.

Novel methods for introducing chemical and biological functionality to the surface of gold nanoparticles serve to increase the utility of this class of nanomaterials across a range of applications. To date, methods for functionalising gold surfaces have relied upon uncontrollable non-specific adsorption, bespoke chemical linkers, or non-generalisable protein-protein interactions. Herein we report a versatile method for introducing functionality to gold nanoparticles by exploiting the strong interaction between chemically functionalised bovine serum albumin (f-BSA) and citrate-capped gold nanoparticles (AuNPs). We establish the generalisability of the method by introducing a variety of functionalities to gold nanoparticles using cheap, commercially available chemical linkers. The utility of this approach is further demonstrated through the conjugation of the monoclonal antibody Ontruzant to f-BSA-AuNPs using inverse electron-demand Diels-Alder (iEDDA) click chemistry, a hitherto unexplored chemistry for AuNP-IgG conjugation. Finally, we show that the AuNP-Ontruzant particles generated via f-BSA-AuNPs have a greater affinity for their target in a lateral flow format when compared to conventional physisorption, highlighting the potential of this technology for producing sensitive diagnostic tests.

Tumor-Targeting Cholesterol-Decorated DNA Nanoflowers for Intracellular Ratiometric Aptasensing.

Probing endogenous molecular profiles is of fundamental importance to understand cellular function and processes. Despite the promise of programmable nucleic-acid-based aptasensors across the breadth of biomolecular detection, target-responsive aptasensors enabling intracellular detection are as of yet infrequently realized. Several challenges remain, including the difficulties in quantification/normalization of quencher-based intensiometric signals, stability issues of the probe architecture, and complex sensor operations often necessitating extensive structural modeling. Here, the biomimetic crystallization-empowered self-assembly of a tumor-targetable DNA-inorganic hybrid nanocomposite aptasensor is presented, which enables Förster resonance energy transfer (FRET)-based quantitative interpretation of changes in the cellular target abundance. Leveraging the design programmability and high-throughput fabrication of rolling circle amplification-driven DNA nanoarchitecture, this designer platform offers a method to self-assemble a robust nanosensor from a multifunctionality-encoded template that includes a cell-targeting aptamer, a ratiometric aptasensor, and a cholesterol-decorating element. Taking prostate cancer cells and intracellular adenosine triphosphate molecules as a model system, a synergistic effect in the targeted delivery by cholesterol and aptamers, and the feasibility of quantitative intracellular aptasensing are demonstrated. It is envisioned that this approach provides a highly generalizable strategy across wide-ranging target systems toward a biologically deliverable nanosensor that enables quantitative monitoring of the abundance of endogenous biomolecules.

Iodide-Mediated Rapid and Sensitive Surface Etching of Gold Nanostars for Biosensing.

Iodide-mediated surface etching can tailor the surface plasmon resonance of gold nanostars through etching of the high-energy facets of the nanoparticle protrusions in a rapid and sensitive way. By exploring the underlying mechanisms of this etching and the key parameters influencing it (such as iodide, oxygen, pH, and temperature), we show its potential in a sensitive biosensing system. Horseradish peroxidase-catalyzed oxidation of iodide enables control of the etching of gold nanostars to spherical gold nanoparticles, where the resulting spectral shift in the surface plasmon resonance yields a distinct color change of the solution. We further develop this enzyme-modulated surface etching of gold nanostars into a versatile platform for plasmonic immunoassays, where a high sensitivity is possible by signal amplification via magnetic beads and click chemistry.

Surface enhanced Raman scattering artificial nose for high dimensionality fingerprinting.

Label-free surface-enhanced Raman spectroscopy (SERS) can interrogate systems by directly fingerprinting their components' unique physicochemical properties. In complex biological systems however, this can yield highly overlapping spectra that hinder sample identification. Here, we present an artificial-nose inspired SERS fingerprinting approach where spectral data is obtained as a function of sensor surface chemical functionality. Supported by molecular dynamics modeling, we show that mildly selective self-assembled monolayers can influence the strength and configuration in which analytes interact with plasmonic surfaces, diversifying the resulting SERS fingerprints. Since each sensor generates a modulated signature, the implicit value of increasing the dimensionality of datasets is shown using cell lysates for all possible combinations of up to 9 fingerprints. Reliable improvements in mean discriminatory accuracy towards 100% are achieved with each additional surface functionality. This arrayed label-free platform illustrates the wide-ranging potential of high-dimensionality artificial-nose based sensing systems for more reliable assessment of complex biological matrices.

Shape-controlled synthesis and in situ characterisation of anisotropic Au nanomaterials using liquid cell transmission electron microscopy.

Understanding the mechanisms behind crystal nucleation and growth is a fundamental requirement for the design and production of bespoke nanomaterials with controlled sizes and morphologies. Herein, we select gold (Au) nanoparticles as the model system for our study due to their representative applications in biology, electronics and optoelectronics. We investigate the radiation-induced in situ growth of gold (Au) particles using liquid cell transmission electron microscopy (LCTEM) and study the growth kinetics of non-spherical Au structures. Under controlled electron fluence, liquid flow rate and Au3+ ion supply, we show the favoured diffusion-limited growth of multi-twinned nascent Au seed particles into branched structures when using thin liquid cells (100 nm and 250 nm) in LCTEM, whereas faceted structures (e.g., spheres, rods, and prisms) formed when using a 1 µm thick liquid cell. In addition, we observed that anisotropic Au growth could be modulated by Au-binding amyloid fibrils, which we ascribe to their capability to regulate Au3+ ion diffusion and mass transfer in solution. We anticipate that this study will provide new perspectives on the shape-controlled synthesis of anisotropic metallic nanomaterials using LCTEM.

Effect of Formulation Method, Lipid Composition, and PEGylation on Vesicle Lamellarity: A Small-Angle Neutron Scattering Study.

Liposomes are well-established systems for drug delivery and biosensing applications. The design of a liposomal carrier requires careful choice of lipid composition and formulation method. These determine many vesicle properties including lamellarity, which can have a strong effect on both encapsulation efficiency and the efflux rate of encapsulated active compounds. Despite this, a comprehensive study on how the lipid composition and formulation method affect vesicle lamellarity is still lacking. Here, we combine small-angle neutron scattering and cryogenic transmission electron microscopy to study the effect of three different well-established formulation methods followed by extrusion through 100 nm polycarbonate membranes on the resulting vesicle membrane structure. Specifically, we examine vesicles formulated from the commonly used phospholipids 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC), 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) via film hydration followed by (i) agitation on a shaker or (ii) freeze-thawing, or (iii) the reverse-phase evaporation vesicle method. After extrusion, up to half of the total lipid content is still assembled into multilamellar structures. However, we achieved unilamellar vesicle populations when as little as 0.1 mol % PEG-modified lipid was included in the vesicle formulation. Interestingly, DPPC with 5 mol % PEGylated lipid produces a combination of cylindrical micelles and vesicles. In conclusion, our results provide important insights into the effect of the formulation method and lipid composition on producing liposomes with a defined membrane structure.

Taking connected mobile-health diagnostics of infectious diseases to the field.

Mobile health, or 'mHealth', is the application of mobile devices, their components and related technologies to healthcare. It is already improving patients' access to treatment and advice. Now, in combination with internet-connected diagnostic devices, it offers novel ways to diagnose, track and control infectious diseases and to improve the efficiency of the health system. Here we examine the promise of these technologies and discuss the challenges in realizing their potential to increase patients' access to testing, aid in their treatment and improve the capability of public health authorities to monitor outbreaks, implement response strategies and assess the impact of interventions across the world.

Activatable cell-biomaterial interfacing with photo-caged peptides.

Spatio-temporally tailoring cell-material interactions is essential for developing smart delivery systems and intelligent biointerfaces. Here we report new photo-activatable cell-material interfacing systems that trigger cellular uptake of various cargoes and cell adhesion towards surfaces. To achieve this, we designed a novel photo-caged peptide which undergoes a structural transition from an antifouling ligand to a cell-penetrating peptide upon photo-irradiation. When the peptide is conjugated to ligands of interest, we demonstrate the photo-activated cellular uptake of a wide range of cargoes, including small fluorophores, proteins, inorganic (e.g., quantum dots and gold nanostars) and organic nanomaterials (e.g., polymeric particles), and liposomes. Using this system, we can remotely regulate drug administration into cancer cells by functionalizing camptothecin-loaded polymeric nanoparticles with our synthetic peptide ligands. Furthermore, we show light-controlled cell adhesion on a peptide-modified surface and 3D spatiotemporal control over cellular uptake of nanoparticles using two-photon excitation. We anticipate that the innovative approach proposed in this work will help to establish new stimuli-responsive delivery systems and biomaterials.

Residue-Specific Solvation-Directed Thermodynamic and Kinetic Control over Peptide Self-Assembly with 1D/2D Structure Selection.

Understanding the self-organization and structural transformations of molecular ensembles is important to explore the complexity of biological systems. Here, we illustrate the crucial role of cosolvents and solvation effects in thermodynamic and kinetic control over peptide association into ultrathin Janus nanosheets, elongated nanobelts, and amyloid-like fibrils. We gained further insight into the solvation-directed self-assembly (SDSA) by investigating residue-specific peptide solvation using molecular dynamics modeling. We proposed the preferential solvation of the aromatic and alkyl domains on the peptide backbone and protofibril surface, which results in volume exclusion effects and restricts the peptide association between hydrophobic walls. We explored the SDSA phenomenon in a library of cosolvents (protic and aprotic), where less polar cosolvents were found to exert a stronger influence on the energetic balance at play during peptide propagation. By tailoring cosolvent polarity, we were able to achieve precise control of the peptide nanostructures with 1D/2D shape selection. We also illustrated the complexity of the SDSA system with pathway-dependent peptide aggregation, where two self-assembly states ( i.e., thermodynamic equilibrium state and kinetically trapped state) from different sample preparation methods were obtained.

Surface Dynamics and Ligand-Core Interactions of Quantum Sized Photoluminescent Gold Nanoclusters.

Quantum-sized metallic clusters protected by biological ligands represent a new class of luminescent materials; yet the understanding of structural information and photoluminescence origin of these ultrasmall clusters remains a challenge. Herein we systematically study the surface ligand dynamics and ligand-metal core interactions of peptide-protected gold nanoclusters (AuNCs) with combined experimental characterizations and theoretical molecular simulations. We show that the peptide sequence plays an important role in determining the surface peptide structuring, interfacial water dynamics and ligand-Au core interaction, which can be tailored by controlling peptide acetylation, constituent amino acid electron donating/withdrawing capacity, aromaticity/hydrophobicity and by adjusting environmental pH. Specifically, emission enhancement is achieved through increasing the electron density of surface ligands in proximity to the Au core, discouraging photoinduced quenching, and by reducing the amount of surface-bound water molecules. These findings provide key design principles for understanding the surface dynamics of peptide-protected nanoparticles and maximizing the photoluminescence of metallic clusters through the exploitation of biologically relevant ligand properties.

Elastic serum-albumin based hydrogels: mechanism of formation and application in cardiac tissue engineering.

Hydrogels are promising materials for mimicking the extra-cellular environment. Here, we present a simple methodology for the formation of a free-standing viscoelastic hydrogel from the abundant and low cost protein serum albumin. We show that the mechanical properties of the hydrogel exhibit a complicated behaviour as a function of the weight fraction of the protein component. We further use X-ray scattering to shed light on the mechanism of gelation from the formation of a fibrillary network at low weight fractions to interconnected aggregates at higher weight fractions. Given the match between our hydrogel elasticity and that of the myocardium, we investigated its potential for supporting cardiac cells in vitro. Interestingly, these hydrogels support the formation of several layers of myocytes and significantly promote the maintenance of a native-like gene expression profile compared to those cultured on glass. When confronted with a multicellular ventricular cell preparation, the hydrogels can support macroscopically contracting cardiac-like tissues with a distinct cell arrangement, and form mm-long vascular-like structures. We envisage that our simple approach for the formation of an elastic substrate from an abundant protein makes the hydrogel a compelling biomedical material candidate for a wide range of cell types.

Duplex-Specific Nuclease-Amplified Detection of MicroRNA Using Compact Quantum Dot-DNA Conjugates.

Advances in nanotechnology have provided new opportunities for the design of next-generation nucleic acid biosensors and diagnostics. Indeed, combining advances in functional nanoparticles, DNA nanotechnology, and nuclease-enzyme-based amplification can give rise to new assays with advantageous properties. In this work, we developed a microRNA (miRNA) assay using bright fluorescent quantum dots (QDs), simple DNA probes, and the enzyme duplex-specific nuclease. We employed an isothermal target-recycling mechanism, where a single miRNA target triggers the cleavage of many DNA signal probes. The incorporation of DNA-functionalized QDs enabled a quantitative fluorescent readout, mediated by Förster resonance energy transfer (FRET)-based interaction with the DNA signal probes. Our approach splits the reaction in two, performing the enzyme-mediated amplification and QD-based detection steps separately such that each reaction could be optimized for performance of the active components. Target recycling gave ca. 3 orders of magnitude amplification, yielding highly sensitive detection with a limit of 42 fM (or 1.2 amol) of miR-148, with excellent selectivity versus mismatched sequences and other miRNAs. Furthermore, we used an alternative target (miR-21) and FRET pair for direct and absolute quantification of miR-21 in RNA extracts from human cancer and normal cell lines.

Fate of Liposomes in the Presence of Phospholipase C and D: From Atomic to Supramolecular Lipid Arrangement.

Understanding the origins of lipid membrane bilayer rearrangement in response to external stimuli is an essential component of cell biology and the bottom-up design of liposomes for biomedical applications. The enzymes phospholipase C and D (PLC and PLD) both cleave the phosphorus-oxygen bonds of phosphate esters in phosphatidylcholine (PC) lipids. The atomic position of this hydrolysis reaction has huge implications for the stability of PC-containing self-assembled structures, such as the cell wall and lipid-based vesicle drug delivery vectors. While PLC converts PC to diacylglycerol (DAG), the interaction of PC with PLD produces phosphatidic acid (PA). Here we present a combination of small-angle scattering data and all-atom molecular dynamics simulations, providing insights into the effects of atomic-scale reorganization on the supramolecular assembly of PC membrane bilayers upon enzyme-mediated incorporation of DAG or PA. We observed that PC liposomes completely disintegrate in the presence of PLC, as conversion of PC to DAG progresses. At lower concentrations, DAG molecules within fluid PC bilayers form hydrogen bonds with backbone carbonyl oxygens in neighboring PC molecules and burrow into the hydrophobic region. This leads initially to membrane thinning followed by a swelling of the lamellar phase with increased DAG. At higher DAG concentrations, localized membrane tension causes a change in lipid phase from lamellar to the hexagonal and micellar cubic phases. Molecular dynamics simulations show that this destabilization is also caused in part by the decreased ability of DAG-containing PC membranes to coordinate sodium ions. Conversely, PLD-treated PC liposomes remain stable up to extremely high conversions to PA. Here, the negatively charged PA headgroup attracts significant amounts of sodium ions from the bulk solution to the membrane surface, leading to a swelling of the coordinated water layer. These findings are a vital step toward a fundamental understanding of the degradation behavior of PC lipid membranes in the presence of these clinically relevant enzymes, and toward the rational design of diagnostic and drug delivery technologies for phospholipase-dysregulation-based diseases.

Platinum Nanocatalyst Amplification: Redefining the Gold Standard for Lateral Flow Immunoassays with Ultrabroad Dynamic Range.

Paper-based lateral flow immunoassays (LFIAs) are one of the most widely used point-of-care (PoC) devices; however, their application in early disease diagnostics is often limited due to insufficient sensitivity for the requisite sample sizes and the short time frames of PoC testing. To address this, we developed a serum-stable, nanoparticle catalyst-labeled LFIA with a sensitivity surpassing that of both current commercial and published sensitivities for paper-based detection of p24, one of the earliest and most conserved biomarkers of HIV. We report the synthesis and characterization of porous platinum core-shell nanocatalysts (PtNCs), which show high catalytic activity when exposed to complex human blood serum samples. We explored the application of antibody-functionalized PtNCs with strategically and orthogonally modified nanobodies with high affinity and specificity toward p24 and established the key larger nanoparticle size regimes needed for efficient amplification and performance in LFIA. Harnessing the catalytic amplification of PtNCs enabled naked-eye detection of p24 spiked into sera in the low femtomolar range (ca. 0.8 pg·mL-1) and the detection of acute-phase HIV in clinical human plasma samples in under 20 min. This provides a versatile absorbance-based and rapid LFIA with sensitivity capable of significantly reducing the HIV acute phase detection window. This diagnostic may be readily adapted for detection of other biomolecules as an ultrasensitive screening tool for infectious and noncommunicable diseases and can be capitalized upon in PoC settings for early disease detection.

Self-Assembled 2D Free-Standing Janus Nanosheets with Single-Layer Thickness.

We report the thermodynamically controlled growth of solution-processable and free-standing nanosheets via peptide assembly in two dimensions. By taking advantage of self-sorting between peptide ß-strands and hydrocarbon chains, we have demonstrated the formation of Janus 2D structures with single-layer thickness, which enable a predetermined surface heterofunctionalization. A controlled 2D-to-1D morphological transition was achieved by subtly adjusting the intermolecular forces. These nanosheets provide an ideal substrate for the engineering of guest components (e.g., proteins and nanoparticles), where enhanced enzyme activity was observed. We anticipate that sequence-specific programmed peptides will offer promise as design elements for 2D assemblies with face-selective functionalization.

Sequence-Dependent Self-Assembly and Structural Diversity of Islet Amyloid Polypeptide-Derived ß-Sheet Fibrils.

Determining the structural origins of amyloid fibrillation is essential for understanding both the pathology of amyloidosis and the rational design of inhibitors to prevent or reverse amyloid formation. In this work, the decisive roles of peptide structures on amyloid self-assembly and morphological diversity were investigated by the design of eight amyloidogenic peptides derived from islet amyloid polypeptide. Among the segments, two distinct morphologies were highlighted in the form of twisted and planar (untwisted) ribbons with varied diameters, thicknesses, and lengths. In particular, transformation of amyloid fibrils from twisted ribbons into untwisted structures was triggered by substitution of the C-terminal serine with threonine, where the side chain methyl group was responsible for the distinct morphological change. This effect was confirmed following serine substitution with alanine and valine and was ascribed to the restriction of intersheet torsional strain through the increased hydrophobic interactions and hydrogen bonding. We also studied the variation of fibril morphology (i.e., association and helicity) and peptide aggregation propensity by increasing the hydrophobicity of the peptide side group, capping the N-terminus, and extending sequence length. We anticipate that our insights into sequence-dependent fibrillation and morphological diversity will shed light on the structural interpretation of amyloidogenesis and development of structure-specific imaging agents and aggregation inhibitors.

Plasmonic Chirality Imprinting on Nucleobase-Displaying Supramolecular Nanohelices by Metal-Nucleobase Recognition.

Supramolecular self-assembly is an important process that enables the conception of complex structures mimicking biological motifs. Herein, we constructed helical fibrils through chiral self-assembly of nucleobase-peptide conjugates (NPCs), where achiral nucleobases are helically displayed on the surface of fibrils, comparable to polymerized nucleic acids. Selective binding between DNA and the NPC fibrils was observed with fluorescence polarization. Taking advantage of metal-nucleobase recognition, we highlight the possibility of deposition/assembly of plasmonic nanoparticles onto the fibrillar constructs. In this approach, the supramolecular chirality of NPCs can be adaptively imparted to metallic nanoparticles, covering them to generate structures with plasmonic chirality that exhibit significantly improved colloidal stability. The self-assembly of rationally designed NPCs into nanohelices is a promising way to engineer complex, optically diverse nucleobase-derived nanomaterials.