Lipid dynamics influenced by oligomeric states a typical pore forming toxin Listeriolysin O: Interplay between lipid free area and crowding
Developing alternate strategies against pore forming toxin (PFT) mediated bacterial virulence factors require an understanding of the cellular membrane response. Membrane-bound protein complexes involving PFTs, released by virulent bacteria are known to form pores leading to host cell lysis. However, membrane disruption and related lipid reorganization events during attack by PFTs remain largely unexplored which became the focus of our study.
In order to study the influence of LLO pore formation on lipid dynamics in a more controlled environment, experiments were carried out on SLBs over a range of LLO concentration, Cp. In a homogeneous lipid bilayer system (DOPC:Chol:3:1) as well as Ld domain of a phase separated, DOPC:DPPC:Chol::2:2:1, bilayer. Here, we have reported counter intuitive and non-monotonic variations in lipid diffusion, measured using confocal FCS, due to interplay of lipid ejection and crowding by membrane bound oligomers of LLO. Lipid diffusion was observed to have an initial enhancement followed by a gradual decline upon increasing Cp. The observed protein concentration dependent dynamical cross-over is correlated with transitions of LLO oligomeric state populations from rings to arc-like pore complexes, predicted using a proposed two-state free area based diffusion model. At low Cp, a hitherto unexplored regime of increased lipid diffusivity is attributed to lipid ejection events due to a preponderance of ring-like pore states. At higher Cp where membrane inserted arc-like pores dominate, lipid ejection is less efficient and the ensuing crowding results in a lowering of lipid diffusion. These variations in lipid dynamics are corroborated by macroscopic rheological response measurements of PFT bound vesicles.
For more information:
- Ponmalar, Ilanila I., Ramesh Cheerla, K. Ganapathy Ayappa, and Jaydeep K. Basu. “Correlated protein conformational states and membrane dynamics during attack by pore-forming toxins.” Proceedings of the National Academy of Sciences 116, no. 26 (2019): 12839-12844.
- Ilanila, I. P., K. Ganapathy Ayappa, and Jaydeep K. Basu. “Bacterial protein Listeriolysin O induces non-monotonic dynamics due to lipid ejection and crowding.” Biophysical Journal (2021).
Interplay of lipid packing and charge density in multicomponent, charged model biomembranes tunes permeation and preferential binding of charged Q2 nanoparticles
Cells respond to external stress by altering their membrane lipid composition to maintain fluidity, integrity and net charge. However, in interactions with charged nanoparticles (NPs), altering membrane charge could adversely affect its ability to transport ions across the cell membrane. Hence it is important to understand possible pathways by which cells could alter zwitterionic lipid composition to respond to nanoparticles without compromising membrane integrity and charge. Such insight is best obtained by studying model biomembranes which, however, need to replicate actual cell membranes, especially their compositional heterogeneity and charge. In our recent studies using synchrotron X-ray reflectivity (XR) measurements, we tried to monitor the interaction of cationic NPs, in the form of quantum dots, with phase-separated supported lipid bilayers as well as floating Langmuir monolayers of different compositions.
These compositions were chosen to be composed of an ordered and anionic charged lipid in combination with uncharged but variable stiffness lipids with the intention of understanding how the subtle interplay of zwitterionic lipid packing and anionic lipid charge density can affect cationic nanoparticle penetration and phase specific binding. We observe that the extent of NP penetration into the respective supported lipid bilayers, as estimated from XR data analysis, is inversely related to membrane compression moduli, which was tuned by altering the stiffness of the zwitterionic lipid component. For a particular membrane composition with discernible height difference between ordered and disordered phases, we were able to observe subtle correlations between the extent of charge on the NPs and the specificity to bind to the charged and ordered phase, contrary to that observed earlier for phase-separated model biomembranes containing no charged lipids.
Whereas for unsupported floating Langmuir monolayers, we observed that under identical subphase pH, the membrane with higher anionic charge density displays higher NP penetration. We also observe coalescence of charged lipid rafts floating amidst a more fluidic zwitterionic lipid matrix due to the phase specificity of QD binding. For both the monolayer and bilayer systems, we observed that the membrane with the higher charge density of the charged lipid domains causes a higher coverage of charged nanoparticle binding. Our results provide microscopic insight into the role of membrane rigidity and electrostatics in determining membrane permeation. This can lead to great potential benefit in rational designing of NPs for bioimaging, drug delivery applications as well as in assessing and alleviating cytotoxicity of nanoparticles.
For more information, please refer:
Chaudhury, A., Debnath, K., Bu, W., Jana, N. R., & Basu, J. K. (2021). Penetration and preferential binding of charged nanoparticles to mixed lipid monolayers: interplay of lipid packing and charge density. Soft Matter, 17(7), 1963-1974. DOI: 10.1039/D0SM01945C
Chaudhury, A., Varshney, G. K., Debnath, K., Das, G., Jana, N. R., & Basu, J. K. (2021). Compressibility of Multicomponent, Charged Model Biomembranes Tunes Permeation of Cationic Nanoparticles. Langmuir, 37(12), 3550-3562. DOI: 10.1021/acs.langmuir.0c03408
Hybrid devices consisting of single layer graphene (SLG) and semiconductor quantum dots (QDs) can lead to the formation of optoelectronic devices with enhanced sensitivity and can have extensive applications in the field of the photodetector and photovoltaics. The optical properties of the resultant hybrid material are controlled by the interplay of energy transfer between QDs and charge transfer between the QDs and SLG. By studying the steady-state and time-resolved photoluminescence spectroscopy of hybrid QD−SLG devices, we observe a subtle interplay of short- and long-range energy transfer between cadmium selenide (CdSe) QDs in a compact monolayer solid film placed in close proximity to an SLG and the charge transfer from the QD solid to SLG. At larger separation, δ, between the compact monolayer QD and SLG, the emission properties are dominated by mutual energy transfer between the QDs. At relatively smaller separation the emission from QDs, which is strongly quenched, is dominated by charge transfer between QDs and SLG. In addition, we are also able to tune the relative strength of energy and charge transfer by electrostatic doping through the back gate voltage, which provides a novel pathway to tune emission properties of these devices for possible applications as photodetectors, in photovoltaics, and for sensing.
For more information, see “Electrical Tuning of Optical Properties of Quantum Dot−Graphene Hybrid Devices: Interplay of Charge and Energy Transfer.” Riya Dutta, Saloni Kakkar, Praloy Mondal, Neha Chauhan, and J. K. Basu*. https://pubs.acs.org/doi/full/10.1021/acs.jpcc.1c00643
Room-Temperature Coupling of Single Photon Emitting Quantum Dots to Localized and Delocalized Modes in a Plasmonic Nanocavity Array
Single photon sources, especially those based on solid state quantum emitters, are key elements in future quantum technologies. What is required is the development of broadband, high quantum efficiency, room temperature single photon sources, which can also be tunably coupled to optical cavities, which could lead to development of all optical quantum communication platforms. In this regard, the deterministic coupling of Single photon sources to plasmonic nanocavity arrays has great advantage due to long propagation length and delocalized nature of surface lattice resonances . Guided by these considerations, we report experiments on the room temperature tunable coupling of single photon emitting colloidal quantum dots to localised surface plasmon and surface lattice resonances modes in plasmonic nanocavity arrays. Using time-resolved photoluminescence measurement on isolated colloidal quantum dots, we report significant advantage of surface lattice resonances in realizing much higher Purcell e_ect, despite large dephasing of colloidal quantum dots, with values of ~22 and ~6 for coupling to the lattice and localized modes, respectively. We present measurements on the antibunching of colloidal quantum dots coupled to these modes with g(2)(0) values in the quantum domain, providing evidence for effective cooperative behavior. We present a density matrix treatment of the coupling of colloidal quantum dots to plasmonic and lattice modes enabling us to model the experimental results on Purcell factors as well as on the antibunching. We also provide experimental evidence of indirect excitation of remote colloidal quantum dots mediated by the lattice modes and propose a model to explain these observations. Our study demonstrates the possibility of developing nanophotonic platforms for single photon operations and communications with broadband quantum emitters and plasmonic nanocavity arrays since these arrays can generate entanglement between to spatially separated quantum emitters.
For more information, see Ravindra Kumar Yadav, Wenxiao Liu,Ran Li, Teri W. Odom, Girish S. Agarwal, and Jaydeep K Basu. Room-Temperature Coupling of Single Photon Emitting Quantum Dots to Localized and Delocalized Modes in a Plasmonic Nanocavity Array. ACS Photonics (2021). DOI: https://doi.org/10.1021/acsphotonics.0c01635
Temperature-Driven Grafted Nanoparticle Penetration into Polymer Melt: Role of Enthalpic and Entropic Interactions
Polymer nanocomposites (PNCs) are hybrid materials formed by mixing nanoparticles into pure polymers, with amalgamate properties of polymers and nanoparticles, which find synergistic applications in electronic, optical, and biomedical fields. In order to realize these applications, a good homogeneous nanoparticle dispersion is required. So, it is very important to study the penetration and thermal stability of nanoparticles in PNCs. Understanding the fundamentals of nanoparticle (NP) penetration into soft matter systems is indispensable for numerous applications ranging from targeted nanoparticle-based drug delivery to generating hybrid polymer nanocomposite materials. Hence, it is crucial to identify the parameters which control the extent of NP penetration. We study the penetration of polystyrene-grafted Au nanoparticles (PGNPs) into an entropically/enthalpically coupled soft polymer film. The system consists of two layers: ultrathin monolayer of ordered grains of PGNPs on top of a bulk polymer film. To study enthalpic effects on nanoparticle penetration, PGNP monolayer was coupled to two different polymers, polystyrene (PS) and poly(tert-butyl acrylate) (PtBA). When the temperature of the system is increased toward the glass transition temperature of underlying films, the width and extent of penetration of the PGNP layer depends on the Flory−Huggins parameter between the graft chain of the PGNPs and the underlying matrix polymer. In athermal cases (PGNP/PS) (χ = 0), the initially compact monolayer undergoes structural disordering and individual PGNPs penetrate into PS films to form a broad layer. However, in the second case (PGNP/PtBA) (χ ≈ 0.26), unfavourable enthalpic interactions results in PGNPs penetrating together as a monolayer into PtBA leading to the formation of a narrow layer of PGNP. The extent of PGNP penetration is improved upon increasing the entropic and enthalpic compatibility between PGNPs and underlying bulk layer. We have done molecular dynamics simulation studies, where the time evolution of PGNP penetration into a bottom polymer layer is found to be similar to that in experiments.
Nimmi Das A and Swain, A and Begam, N and Bhattacharyya, A and Basu, JK ,“Temperature-Driven Grafted Nanoparticle Penetration into Polymer Melt: Role of Enthalpic and Entropic Interactions” Macromolecules, 53, 8674-8682 (2020).
Observation of photonic spin-momentum locking due to coupling of achiral metamaterials and quantum dots
Chiral interfaces provide a new platform to execute quantum control of light-matter interactions. One phenomenon which has emerged from engineering such nanophotonic interfaces is spin-momentum locking akin to similar reports in electronic topological materials and phases. While there are reports of spin-momentum locking with combination of chiral emitters and/or chiral metamaterials with directional far field excitation it is not readily observable with both achiral emitters and metamaterials. Here, we report the observation of photonic spin-momentum locking in the form of directional and chiral emission from achiral quantum dots (QDs) evanescently coupled to achiral hyperbolic metamaterials (HMM). Efficient coupling between QDs and the metamaterial leads to emergence of these photonic topological modes which can be detected in the far field. We provide theoretical explanation for the emergence of spin-momentum locking through rigorous modeling based on photon Green’s function where pseudo spin of light arises from coupling of QDs to evanescent modes of HMM.
For more information, see Ravindra Kumar Yadav, Wenxiao Liu, SRK Chaitanya Indukuri, Adarsh B. Vasista, G. V. Pavan Kumar, Girish S. Agarwal, and Jaydeep Kumar Basu. Observation of photonic spin-momentum locking due to coupling of achiral metamaterials and quantum dots.Journal of Physics: Condensed Matter, 2020, 33, 015701.
Strongly coupled exciton-surface lattice resonances engineer long-range energy propagation
Achieving propagation lengths in hybrid systems involving plasmonic components beyond typical values of tens of m is important for advancing quantum plasmonics applications. Here we report long-range optical energy propagation in hybrid photonic devices due to excitons in semiconductor quantum dots (SQDs) strongly coupled to surface lattice resonances (SLRs) in a proximal silver nanoparticle array. By using a unique photoluminescence (PL) microscopy scheme we provide evidence for the detection of an exciton-SLR (ESLR) strongly coupled mode at least 600 m away from the region of excitation. We also observe existence of additional energy propagation the range of which goes well beyond that of the ESLR mode and is dependent on the magnitude of strong coupling, g. Cavity quantum electrodynamics (cQED) calculations correctly capture the nature of the experimentally observed PL spectra for consistent values of g, while coupled dipole (CD) calculations show a SQD number dependent electric field decay profile away from excitation region which is consistent with the experimental spatial PL profile. Our results suggest an exciting new direction wherein SLRs or high-quality plasmonic modes can be used to mediate long-range interactions between SQDs, having various possible applications in optoelectronics, sensing and quantum information science.
For more information, see Yadav, Ravindra Kumar, Matthew Otten, Weijia Wang, Cristian L. Cortes, David J. Gosztola, Gary P. Wiederrecht, Stephen K. Gray, Teri W. Odom, and Jaydeep Kumar Basu. "Strongly coupled exciton-surface lattice resonances engineer long-range energy propagation." Nano Letters (2020). DOI: 10.1021/acs.nanolett.0c01236.
Colloidal quantum dot (CQD) assemblies exhibit interesting optoelectronic properties when coupled to optical resonators ranging from Purcell-enhanced emission to the emergence of hybrid electronic and photonic polariton states in the weak and strong coupling limits, respectively. Here, experiments exploring the weak-to-strong coupling transition in CQD–plasmonic lattice hybrid devices at room temperature are presented for varying CQD concentrations. To interpret these results, generalized retarded Fano–Anderson and effective medium models are developed. Individual CQDs are found to interact locally with the lattice yielding Purcell-enhanced emission. At high CQD densities, polariton states emerge as two-peak structures in the photoluminescence, with a third polariton peak, due to collective CQD emission, appearing at still higher CQD concentrations. Our results demonstrate that CQD–lattice plasmon devices represent a highly flexible platform for the manipulation of collective spontaneous emission using lattice plasmons, which could find applications in optoelectronics, ultrafast optical switches, and quantum information science.
For more information, see:
“Room Temperature Weak-to-Strong Coupling and the Emergence of Collective Emission from Quantum Dots Coupled to Plasmonic Arrays.” , Yadav, Ravindra Kumar, Marc R. Bourgeois, Charles Cherqui, Xitlali G. Juarez, Weijia Wang, Teri W. Odom, George C. Schatz, and Jaydeep Kumar Basu. ACS Nano (2020). DOI: 10.1021/acsnano.0c02785.