Publications
188 results found
Ma Y, Sikdar D, Fedosyuk A, et al., 2019, An auxetic thermo-responsive nanoplasmonic optical switch., ACS Applied Materials and Interfaces, ISSN: 1944-8244
Development and use of metamaterials have been gaining prominence in large part due to the possibility of creating platforms with 'disruptive' and unique optical properties. However, to date the majority of such systems produced using micro or nanotechnology, are static and can only perform certain target functions. Next-generation multifunctional smart optical metamaterials are expected to have tuneable elements with the possibility of controlling the optical properties in real time via variation in parameters such as pressure, mechanical stress, voltage, or through non-linear optical effects. Here, we address this challenge by developing a thermally controlled optical switch, based on the self-assembly of poly(N-isopropylacrylamide)-functionalised gold nanoparticles on a planar macroscale gold substrate. We show that such meta-surfaces can be tuned to exhibit substantial changes in the optical properties both in terms of wavelength and intensity, through the temperature-controlled variation of the interparticle distance within the nanoparticle monolayer as well as its separation from the substrate. This change is based on temperature induced auxetic expansion and contraction of the functional ligands. Such a system has potential for numerous applications, ranging from thermal sensors to regulated light harnessing.
Kubánková M, Lin X, Albrecht T, et al., 2019, Rapid fragmentation during seeded lysozyme aggregation revealed at the single molecule level, Analytical Chemistry, Vol: 91, Pages: 6880-6886, ISSN: 0003-2700
Protein aggregation is associated with neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. The poorly understood pathogenic mechanism of amyloid diseases makes early stage diagnostics or therapeutic intervention a challenge. Seeded polymerization that reduces the duration of the lag phase and accelerates fibril growth is a widespread model to study amyloid formation. Seeding effects are hypothesized to be important in the "infectivity" of amyloids and are linked to the development of systemic amyloidosis in vivo. The exact mechanism of seeding is unclear yet critical to illuminating the propagation of amyloids. Here we report on the lateral and axial fragmentation of seed fibrils in the presence of lysozyme monomers at short time scales, followed by the generation of oligomers and growth of fibrils.
Cai S, Sze YYJ, Ivanov A, et al., 2019, Small molecule electro-optical binding assay using nanopores, Nature Communications, Vol: 10, Pages: 1-9, ISSN: 2041-1723
The identification of short nucleic acids and proteins at the single molecule level is a major driving force for the development of novel detection strategies. Nanopore sensing has been gaining in prominence due to its label-free operation and single molecule sensitivity. However, it remains challenging to detect small molecules selectively. Here we propose to combine the electrical sensing modality of a nanopore with fluorescence-based detection. Selectivity is achieved by grafting either molecular beacons, complementary DNA, or proteins to a DNA molecular carrier. We show that the fraction of synchronised events between the electrical and optical channels, can be used to perform single molecule binding assays without the need to directly label the analyte. Such a strategy can be used to detect targets in complex biological fluids such as human serum and urine. Future optimisation of this technology may enable novel assays for quantitative protein detection as well as gene mutation analysis with applications in next-generation clinical sample analysis.
Paulose Nadappuram B, Cadinu P, Barik A, et al., 2019, Nanoscale tweezers for single-cell biopsies, Nature Nanotechnology, Vol: 14, Pages: 80-88, ISSN: 1748-3387
Much of the functionality of multicellular systems arises from the spatial organization and dynamic behaviours within and between cells. Current single-cell genomic methods only provide a transcriptional ‘snapshot’ of individual cells. The real-time analysis and perturbation of living cells would generate a step change in single-cell analysis. Here we describe minimally invasive nanotweezers that can be spatially controlled to extract samples from living cells with single-molecule precision. They consist of two closely spaced electrodes with gaps as small as 10–20 nm, which can be used for the dielectrophoretic trapping of DNA and proteins. Aside from trapping single molecules, we also extract nucleic acids for gene expression analysis from living cells without affecting their viability. Finally, we report on the trapping and extraction of a single mitochondrion. This work bridges the gap between single-molecule/organelle manipulation and cell biology and can ultimately enable a better understanding of living cells.
Ma Y, Zagar C, Klemme DJ, et al., 2018, A tunable nanoplasmonic mirror at an electrochemical interface, ACS Photonics, Vol: 5, Pages: 4604-4616, ISSN: 2330-4022
Designing tunable optical metamaterials is one of the great challenges in photonics. Strategies for reversible tuning of nanoengineered devices are currently being sought through electromagnetic or piezo effects. For example, bottom-up self-assembly of nanoparticles at solid | liquid or liquid | liquid interfaces can be used to tune optical responses by varying their structure either chemically or through applied voltage. Here, we report on a fully reversible tunable-color mirror based on a TiN-coated Ag substrate immersed in an aqueous solution of negatively charged Au-nanoparticles (NPs). Switching electrode potential can be used to fully control the assembly/disassembly of NPs at the electrode | electrolyte interface within a 0.6 V wide electrochemical window. The plasmon coupling between the electrode and the adsorbed NP array at high positive potentials produces a dip in the optical reflectance spectrum, creating the "absorber" state. Desorption of NPs at low potentials eliminates the dip, returning the system to the reflective "mirror" state. The intensity and wavelength of the dip can be finely tuned through electrode-potential and electrolyte concentration. The excellent match between the experimental data and the theory of optical response for such system allows us to extract valuable information on equilibrium and kinetic properties of NP-assembly/disassembly. Together with modeling of the latter, this study promotes optimization of such meta-surfaces for building electrotunable reflector devices.
Xue L, Cadinu P, Paulose Nadappuram B, et al., 2018, Gated single-molecule transport in double-barreled nanopores, ACS Applied Materials and Interfaces, Vol: 10, Pages: 38621-38629, ISSN: 1944-8244
Single-molecule methods have been rapidly developing with the appealing prospect of transforming conventional ensemble-averaged analytical techniques. However, challenges remain especially in improving detection sensitivity and controlling molecular transport. In this article, we present a direct method for the fabrication of analytical sensors that combine the advantages of nanopores and field-effect transistors for simultaneous label-free single-molecule detection and manipulation. We show that these hybrid sensors have perfectly aligned nanopores and field-effect transistor components making it possible to detect molecular events with up to near 100% synchronization. Furthermore, we show that the transport across the nanopore can be voltage-gated to switch on/off translocations in real time. Finally, surface functionalization of the gate electrode can also be used to fine tune transport properties enabling more active control over the translocation velocity and capture rates.
Al Sulaiman D, Cadinu P, Ivanov AP, et al., 2018, Chemically modified hydrogel-filled nanopores: a tunable platform for single-molecule sensing, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 18, Pages: 6084-6093, ISSN: 1530-6984
Label-free, single-molecule sensing is an ideal candidate for biomedical applications that rely on the detection of low copy numbers in small volumes and potentially complex biofluids. Among them, solid-state nanopores can be engineered to detect single molecules of charged analytes when they are electrically driven through the nanometer-sized aperture. When successfully applied to nucleic acid sensing, fast transport in the range of 10–100 nucleotides per nanosecond often precludes the use of standard nanopores for the detection of the smallest fragments. Herein, hydrogel-filled nanopores (HFN) are reported that combine quartz nanopipettes with biocompatible chemical poly(vinyl) alcohol hydrogels engineered in-house. Hydrogels were modified physically or chemically to finely tune, in a predictable manner, the transport of specific molecules. Controlling the hydrogel mesh size and chemical composition allowed us to slow DNA transport by 4 orders of magnitude and to detect fragments as small as 100 base pairs (bp) with nanopores larger than 20 nm at an ionic strength comparable to physiological conditions. Considering the emergence of cell-free nucleic acids as blood biomarkers for cancer diagnostics or prenatal testing, the successful sensing and size profiling of DNA fragments ranging from 100 bp to >1 kbp long under physiological conditions demonstrates the potential of HFNs as a new generation of powerful and easily tunable molecular diagnostics tools.
Ivanov AP, Edel JB, 2018, Scissoring genes with light, NATURE CHEMISTRY, Vol: 10, Pages: 800-801, ISSN: 1755-4330
Rakers V, Cadinu P, Edel JB, et al., 2018, Development of microfluidic platforms for the synthesis of metal complexes and evaluation of their DNA affinity using online FRET melting assays, Chemical Science, Vol: 9, Pages: 3459-3469, ISSN: 2041-6520
Guanine-rich DNA sequences can fold into quadruple-stranded structures known as G-quadruplexes. These structures have been proposed to play important biological roles and have been identified as potential drug targets. As a result, there is increasing interest in developing small molecules that can bind to G-quadruplexes. So far, these efforts have been mostly limited to conventional batch synthesis. Furthermore, no quick on-line method to assess new G-quadruplex binders has been developed. Herein, we report on two new microfluidic platforms to: (a) readily prepare G-quadruplex binders (based on metal complexes) in flow, quantitatively and without the need for purification before testing; (b) a microfluidic platform (based on FRET melting assays of DNA) that enables the real-time and on-line assessment of G-quadruplex binders in continuous flow.
Cadinu P, Campolo G, Pud S, et al., 2018, Double barrel nanopores as a new tool for controlling single-molecule transport, Nano Letters, Vol: 18, Pages: 2738-2745, ISSN: 1530-6984
The ability to control the motion of single biomolecules is key to improving a wide range of biophysical and diagnostic applications. Solid-state nanopores are a promising tool capable of solving this task. However, molecular control and the possibility of slow readouts of long polymer molecules are still limited due to fast analyte transport and low signal-to-noise ratios. Here, we report on a novel approach of actively controlling analyte transport by using a double-nanopore architecture where two nanopores are separated by only a ∼ 20 nm gap. The nanopores can be addressed individually, allowing for two unique modes of operation: (i) pore-to-pore transfer, which can be controlled at near 100% efficiency, and (ii) DNA molecules bridging between the two nanopores, which enables detection with an enhanced temporal resolution (e.g., an increase of more than 2 orders of magnitude in the dwell time) without compromising the signal quality. The simplicity of fabrication and operation of the double-barrel architecture opens a wide range of applications for high-resolution readout of biological molecules.
Kornyshev AA, Sikdar D, Edel JB, et al., 2018, Towards Electrotuneable Nanoplasmonic Fabry–Perot Interferometer, Scientific Reports, Vol: 8, ISSN: 2045-2322
Directed voltage-controlled assembly and disassembly of plasmonic nanoparticles (NPs) at electrified solid–electrolyte interfaces (SEI) offer novel opportunities for the creation of tuneable optical devices. We apply this concept to propose a fast electrotuneable, NP-based Fabry–Perot (FP) interferometer, comprising two parallel transparent electrodes in aqueous electrolyte, which form the polarizable SEI for directed assembly–disassembly of negatively charged NPs. An FP cavity between two reflective NP-monolayers assembled at such interfaces can be formed or deconstructed under positive or negative polarization of the electrodes, respectively. The inter-NP spacing may be tuned via applied potential. Since the intensity, wavelength, and linewidth of the reflectivity peak depend on the NP packing density, the transmission spectrum of the system can thus be varied. A detailed theoretical model of the system’s optical response is presented, which shows excellent agreement with full-wave simulations. The tuning of the peak transmission wavelength and linewidth is investigated in detail. Design guidelines for such NP-based FP systems are established, where transmission characteristics can be electrotuned in-situ, without mechanically altering the cavity length.
Peveler WJ, Noimark S, Al-Azawi H, et al., 2018, Covalently attached antimicrobial surfaces using BODIPY: improving efficiency and effectiveness, ACS Applied Materials and Interfaces, Vol: 10, Pages: 98-104, ISSN: 1944-8244
The development of photoactivated antimicrobial surfaces that kill pathogens through the production of singlet oxygen has proved very effective in recent years, with applications in medical devices and hospital touch surfaces, to improve patient safety and well being. However, many of these surfaces require a swell-encapsulation-shrink strategy to incorporate the photoactive agents in a polymer matrix, and this is resource intensive, given that only the surface fraction of the agent is active against bacteria. Furthermore, there is a risk that the agent will leach from the polymer and thus raises issues of biocompatibility and patient safety. Here, we describe a more efficient method of fabricating a silicone material with a covalently attached monolayer of photoactivating agent that uses heavy-atom triplet sensitization for improved singlet oxygen generation and corresponding antimicrobial activity. We use boron-dipyrromethane with a reactive end group and incorporated Br atoms, covalently attached to poly(dimethylsiloxane). We demonstrate the efficacy of this material in producing singlet oxygen and killing Staphylococcus aureus and suggest how it might be easily modifiable for future antimicrobial surface development.
Aizpurua J, Arnolds H, Baumberg J, et al., 2017, Ultrasensitive and towards single molecule SERS: general discussion, FARADAY DISCUSSIONS, Vol: 205, Pages: 291-330, ISSN: 1359-6640
Barik A, Zhang Y, Grassi R, et al., 2017, Graphene-edge dielectrophoretic tweezers for trapping of biomolecules, Nature Communications, Vol: 8, Pages: 1-9, ISSN: 2041-1723
The many unique properties of graphene, such as the tunable optical, electrical, and plasmonic response make it ideally suited for applications such as biosensing. As with other surface-based biosensors, however, the performance is limited by the diffusive transport of target molecules to the surface. Here we show that atomically sharp edges of monolayer graphene can generate singular electrical field gradients for trapping biomolecules via dielectrophoresis. Graphene-edge dielectrophoresis pushes the physical limit of gradient-force-based trapping by creating atomically sharp tweezers. We have fabricated locally backgated devices with an 8-nm-thick HfO2 dielectric layer and chemical-vapor-deposited graphene to generate 10× higher gradient forces as compared to metal electrodes. We further demonstrate near-100% position-controlled particle trapping at voltages as low as 0.45 V with nanodiamonds, nanobeads, and DNA from bulk solution within seconds. This trapping scheme can be seamlessly integrated with sensors utilizing graphene as well as other two-dimensional materials.
Sze JYY, Ivanov AP, Cass AEG, et al., 2017, Single molecule multiplexed nanopore protein screening in human serum using aptamer modified DNA carriers, Nature Communications, Vol: 8, Pages: 1-10, ISSN: 2041-1723
The capability to screen a range of proteins at the single-molecule level with enhanced selectivity in biological fluids has been in part a driving force in developing future diagnostic and therapeutic strategies. The combination of nanopore sensing and nucleic acid aptamer recognition comes close to this ideal due to the ease of multiplexing, without the need for expensive labelling methods or extensive sample pre-treatment. Here, we demonstrate a fully flexible, scalable and low-cost detection platform to sense multiple protein targets simultaneously by grafting specific sequences along the backbone of a double-stranded DNA carrier. Protein bound to the aptamer produces unique ionic current signatures which facilitates accurate target recognition. This powerful approach allows us to differentiate individual protein sizes via characteristic changes in the sub-peak current. Furthermore, we show that by using DNA carriers it is possible to perform single-molecule screening in human serum at ultra-low protein concentrations.
Montelongo Y, Sikdar D, Ma Y, et al., 2017, Electrotunable nanoplasmonic liquid mirror., Nature materials, Vol: 16, Pages: 1127-1135, ISSN: 1476-1122
Recently, there has been a drive to design and develop fully tunable metamaterials for applications ranging from new classes of sensors to superlenses among others. Although advances have been made, tuning and modulating the optical properties in real time remains a challenge. We report on the first realization of a reversible electrotunable liquid mirror based on voltage-controlled self-assembly/disassembly of 16 nm plasmonic nanoparticles at the interface between two immiscible electrolyte solutions. We show that optical properties such as reflectivity and spectral position of the absorption band can be varied in situ within ±0.5 V. This observed effect is in excellent agreement with theoretical calculations corresponding to the change in average interparticle spacing. This electrochemical fully tunable nanoplasmonic platform can be switched from a highly reflective 'mirror' to a transmissive 'window' and back again. This study opens a route towards realization of such platforms in future micro/nanoscale electrochemical cells, enabling the creation of tunable plasmonic metamaterials.
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- Citations: 24
Crick CR, Albella P, Kim H-J, et al., 2017, Low-Noise Plasmonic Nanopore Biosensors for Single Molecule Detection at Elevated Temperatures, ACS Photonics, Vol: 4, Pages: 2835-2842, ISSN: 2330-4022
Advanced single molecular analysis is a key stepping stone for the rapid sensing and characterization of biomolecules. This will only be made possible through the implementation of versatile platforms, with high sensitivities and the precise control of experimental conditions. The presented work details an advancement of this technology, through the development of a low-noise Pyrex/silicon nitride/gold nanopore platform. The nanopore is surrounded by a plasmonic bullseye structure and provides targeted and controllable heating via laser irradiation, which is directed toward the center of the pore. The device architecture is investigated using multiwavelength laser heating experiments and 'individual DNA molecules are detected under controlled heating. The plasmonic features, optimized through numerical simulations, are tuned to the wavelength of incident light, ensuring a platform that provides substantial heating with high signal-to-noise.
Cadinu P, Cadinu P, Paulose Nadappuram B, et al., 2017, Single Molecule Trapping and Sensing Using Dual Nanopores Separated by a Zeptoliter Nanobridge., Nano letters, Vol: 17, Pages: 6376-6384, ISSN: 1530-6984
There is a growing realization, especially within the diagnostic and therapeutic community, that the amount of information enclosed in a single molecule can not only enable a better understanding of biophysical pathways, but also offer exceptional value for early stage biomarker detection of disease onset. To this end, numerous single molecule strategies have been proposed, and in terms of label-free routes, nanopore sensing has emerged as one of the most promising methods. However, being able to finely control molecular transport in terms of transport rate, resolution, and signal-to-noise ratio (SNR) is essential to take full advantage of the technology benefits. Here we propose a novel solution to these challenges based on a method that allows biomolecules to be individually confined into a zeptoliter nanoscale droplet bridging two adjacent nanopores (nanobridge) with a 20 nm separation. Molecules that undergo confinement in the nanobridge are slowed down by up to 3 orders of magnitude compared to conventional nanopores. This leads to a dramatic improvement in the SNR, resolution, sensitivity, and limit of detection. The strategy implemented is universal and as highlighted in this manuscript can be used for the detection of dsDNA, RNA, ssDNA, and proteins.
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- Citations: 17
Ren R, Zhang Y, Paulose Nadappuram B, et al., 2017, Nanopore extended field effect transistor for selective single molecule biosensing, Nature Communications, Vol: 8, Pages: 1-9, ISSN: 2041-1723
There has been a significant drive to deliver nanotechnological solutions to biosensing, yet there remains an unmet need in the development of biosensors that are affordable, integrated, fast, capable of multiplexed detection, and offer high selectivity for trace analyte detection in biological fluids. Herein, some of these challenges are addressed by designing a new class of nanoscale sensors dubbed nanopore extended field-effect transistor (nexFET) that combine the advantages of nanopore single-molecule sensing, field-effect transistors, and recognition chemistry. We report on a polypyrrole functionalized nexFET, with controllable gate voltage that can be used to switch on/off, and slow down single-molecule DNA transport through a nanopore. This strategy enables higher molecular throughput, enhanced signal-to-noise, and even heightened selectivity via functionalization with an embedded receptor. This is shown for selective sensing of an anti-insulin antibody in the presence of its IgG isotype.
lauri A, Velleman L, Xiao X, et al., 2017, 3D Confocal Raman Tomography to Probe Field Enhancements inside Supercluster Metamaterials, ACS Photonics, Vol: 4, Pages: 2070-2077, ISSN: 2330-4022
Spherical colloidal superclusters, composed from sub-100 nm plasmonic nanoparticles, have been proposed to possess collective plasmonic modes imbued with large field enhancements and tunable spectral response extending from the visible to infrared regions. Here, we report the experimental verification of collective near-IR plasmonic modes inside single superclusters, with dimensions ranging from 0.77 μm up to 2 μm. Raman reporters, coated onto the nanoparticle building blocks, were used as local probes of the electric field enhancement inside the metamaterial. By performing diffraction-limited 3D Raman tomography we were able to build up the electric field intensity distribution within the superclusters. We demonstrate that plasmonic responses of superclusters vary according to their size and excitation wavelength, in accordance with theoretical predictions of their tunable optical properties. The existence of three-dimensional internal collective modes in these superclusters enables the excitation of a large number of electromagnetic hot-spots, validating these self-assembled structures as promising candidates for molecular spectroscopy.
Velleman L, Scarabelli L, Sikdar D, et al., 2017, Monitoring plasmon coupling and SERS enhancement through in situ nanoparticle spacing modulation, Faraday Discussions, Vol: 205, Pages: 67-83, ISSN: 1364-5498
Self-assembled nanoparticle (NP) arrays at liquid interfaces provide a unique optical response which has opened the door to new tuneable metamaterials and for sensing and optical applications. NPs can spontaneously assemble at the liquid-liquid interface, forming an ordered, self-healing, low-defect 2D film. The close proximity of the NPs at the interface results in collective plasmonic modes with a spectral response dependent on the distance between the NPs and induces large field enhancements within the gaps. In this study, we assembled spherical and rod-shaped gold NPs with the aim of improving our understanding of NP assembly processes at liquid interfaces, working towards finely controlling their structure and producing tailored optical and enhanced Raman signals. We systematically tuned the assembly and spacing between NPs through increasing or decreasing the degree of electrostatic screening between NPs with the addition of electrolyte or pH adjustment. The in situ modulation of nanoparticle positioning on the same sample allowed us to monitor plasmon coupling and the resulting SERS enhancement processes in real time, with sub-nm precision.
Lin X, Ivanov AP, Edel JB, 2017, Selective single molecule nanopore sensing of proteins using DNA aptamer-functionalised gold nanoparticles, Chemical Science, Vol: 8, Pages: 3905-3912, ISSN: 2041-6539
Single molecule detection methods, such as nanopore sensors have found increasing importance in applications ranging from gaining a better understanding of biophysical processes to technology driven solutions such as DNA sequencing. However, challenges remain especially in relation to improving selectivity to probe specific targets or to alternatively enable detection of smaller molecules such as small-sized proteins with a sufficiently high signal-to-noise ratio. In this article, we propose a solution to these technological challenges by using DNA aptamer-modified gold nanoparticles (AuNPs) that act as a molecular carrier through the nanopore sensor. We show that this approach offers numerous advantages including: high levels of selectivity, efficient capture from a complex mixture, enhanced signal, minimized analyte-sensor surface interactions, and finally can be used to enhance the event detection rate. This is demonstrated by incorporating a lysozyme binding aptamer to a 5 nm AuNP carrier to selectively probe lysozyme within a cocktail of proteins. We show that nanopores can reveal sub-complex molecular information, by discriminating the AuNP from the protein analyte, indicating the potential use of this technology for single molecule analysis of different molecular analytes specifically bound to AuNP.
Gielen F, Butz M, Rees EJ, et al., 2017, Quantitative affinity determination by fluorescence anisotropy measurements of individual nanoliter droplets, Analytical Chemistry, Vol: 89, Pages: 1092-1101, ISSN: 0003-2700
Fluorescence anisotropy measurements of reagents compartmentalized into individual nanoliter droplets are shown to yield high-resolution binding curves from which precise dissociation constants (Kd) for protein–peptide interactions can be inferred. With the current platform, four titrations can be obtained per minute (based on ∼100 data points each), with stoichiometries spanning more than 2 orders of magnitude and requiring only tens of microliters of reagents. In addition to affinity measurements with purified components, Kd values for unpurified proteins in crude cell lysates can be obtained without prior knowledge of the concentration of the expressed protein, so that protein purification can be avoided. Finally, we show how a competition assay can be set up to perform focused library screens, so that compound labeling is not required anymore. These data demonstrate the utility of droplet compartments for the quantitative characterization of biomolecular interactions and establish fluorescence anisotropy imaging as a quantitative technique in a miniaturized droplet format, which is shown to be as reliable as its macroscopic test tube equivalent.
Kim M, Ivanov A, Edel J, 2017, Nanofluidics Preface, NANOFLUIDICS, 2ND EDITION, Editors: Edel, Ivanov, Kim, Publisher: ROYAL SOC CHEMISTRY, Pages: VII-IX, ISBN: 978-1-84973-404-2
Velleman L, Sikdar D, Turek V, et al., 2016, Tuneable 2D self-assembly of plasmonic nanoparticles at liquid | liquid interfaces, Nanoscale, Vol: 8, Pages: 19229-19241, ISSN: 2040-3372
Understanding the structure and assembly of nanoparticles at liquid | liquid interfaces is paramount to their integration into devices for sensing, catalysis, electronics and optics. However, many difficulties arise when attempting to resolve the structure of such interfacial assemblies. In this article we use a combination of X-ray diffraction and optical reflectance to determine the structural arrangement and plasmon coupling between 12.8 nm diameter gold nanoparticles assembled at a water | 1,2-dichloroethane interface. The liquid | liquid interface provides a molecularly flat and defect-correcting platform for nanoparticles to self-assemble. The amount of nanoparticles assembling at the interface can be controlled via the concentration of electrolyte within either the aqueous or organic phase. At higher electrolyte concentration more nanoparticles can settle at the liquid | liquid interface resulting in a decrease in nanoparticle spacing as observed from X-ray diffraction experiments. The coupling of plasmons between the nanoparticles as they come closer together is observed by a red-shift in the optical reflectance spectra. The optical reflectance and the X-ray diffraction data are combined to introduce a new ‘plasmon ruler’. This allows extraction of structural information from simple optical spectroscopy techniques, with important implications in understanding the structure of nanoparticle films at liquid interfaces and their self-assembly.
Panich S, Sleiman MH, Steer I, et al., 2016, Real-Time Monitoring of Ligand Binding to G-Quadruplex and Duplex DNA by Whispering Gallery Mode Sensing, ACS Sensors, Vol: 1, Pages: 1097-1102, ISSN: 2379-3694
The therapeutic potential of small molecules targeting G-quadruplexes has gained credibility since such structures were shown to form in human cells and to be highly prevalent in the human genome, most notably at telomere ends and in oncogene promoters. Herein, we perform whispering gallery mode (WGM) sensing for monitoring DNA–small molecule interactions. Unlike most existing technologies, WGM sensing offers numerous advantages including high sensitivity, real-time analysis, easy access to kinetic parameters, and much lower cost than current gold standards. In this work, interactions of five known DNA-binding ligands with either G-quadruplex or duplex DNA immobilized on a sphere microresonator have been assessed. The induced shift of the resonant mode from quadruplex (or duplex)–ligand binding was used to estimate kinetic parameters. Association and dissociation rate constants (kon and koff, respectively) as well as dissociation equilibrium constants (KD) were measured for these five ligands binding to both duplex and quadruplex DNA.
Crick CR, Noimark S, Peveler WJ, et al., 2016, Advanced Compositional Analysis of Nanoparticle-polymer Composites Using Direct Fluorescence Imaging, Jove-Journal of Visualized Experiments, Vol: 113, ISSN: 1940-087X
The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise composition of these materials is essential, especially in the design of surface catalysts, where the surface concentration of the active component determines the activity of the material. Antimicrobial materials which utilize nanoparticles are a particular focus of this technology. Recently swell encapsulation has emerged as a technique for inserting antimicrobial nanoparticles into a host polymer matrix. Swell encapsulation provides the advantage of localizing the incorporation to the external surfaces of materials, which act as the active sites of these materials. However, quantification of this nanoparticle uptake is challenging. Previous studies explore the link between antimicrobial activity and surface concentration of the active component, but this is not directly visualized. Here we show a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of CdSe/ZnS nanoparticles can be accurately visualized through cross-sectional fluorescence imaging. Using this method, we can quantify the uptake of nanoparticles via swell encapsulation and measure the surface concentration of encapsulated particles, which is key in optimizing the activity of functional materials.
Sikdar D, Hasan SB, Urbakh M, et al., 2016, Unravelling the optical responses of nanoplasmonic mirror-on-mirror metamaterials., Physical Chemistry Chemical Physics, Vol: 18, Pages: 20486-20498, ISSN: 1463-9084
Mirror-on-mirror platforms based on arrays of metallic nanoparticles, arranged top-down or self-assembled on a thin metallic film, have interesting optical properties. Interaction of localized surface-plasmons in nanoparticles with propagating surface-plasmons in the film underpins the exotic features of such platforms. Here, we present a comprehensive theoretical framework which emulates such a system using a five-layer-stack model and calculate its reflectance, transmittance, and absorbance spectra. The theory rests on dipolar quasi-static approximations incorporating image-forces and effective medium theory. Systematically tested against full-wave simulations, this simple approach proves to be adequate within its obvious applicability limits. It is used to study optical signals as a function of nanoparticle dimensions, interparticle separation, metal film thickness, the gap between the film and nanoparticles, and incident light characteristics. Several peculiar features are found, e.g., quenching of reflectivity in certain frequency domains or shift of the reflectivity spectra. Schemes are proposed to tailor those as functions of the mentioned parameters. Calculating the system's optical responses in seconds, as compared to much longer running simulations, this theory helps to momentarily unravel the role of each system parameter in light reflection, transmission, and absorption, facilitating thereby the design and optimisation of novel mirror-on-mirror systems.
Freedman KJ, Crick CR, Albella P, et al., 2016, On-Demand Surface and Tip Enhanced Raman Spectroscopy Using Dielectrophoretic Trapping and Nanopore Sensing, ACS Photonics, Vol: 3, Pages: 1036-1044, ISSN: 2330-4022
Surface enhanced Raman spectroscopy (SERS) and tip-enhanced Raman Spectroscopy (TERS) have shown great promise in the detection and analysis of trace analytes throughout numerous fields of study. Both SERS and TERS utilize nanoscale plasmonic surface features to increase the intensity of observed Raman signals by many orders of magnitude (> 108). One of the major factors limiting the wider and more routine implementation of the enhanced Raman phenomena, is in the difficulty of forming consistent and reliable plasmonic substrates with well defined “hot-spots”. We address this limitation by designing a platform which can be used for both SERS and TERS respectively. The presented technique allows for rapid, controlled, “on-demand”, and reversible formation of a SERS substrate using dielectrophorisis (DEP) at the end of a nanoscale pipette. This drives gold nanoparticles in solution to concentrate and self-assemble at the tip of the pipette, where analytes can be detected effectively using SERS. An additional benefit of the platform is that the nanopipette containing a nanopore can be used for detection of individual nanoparticles facilitated by the added enhancement originating from the nanopipette tip enhanced signal. Complementing the experimental results are simulations highlighting the mechanism for SERS substrate formation and TERS detection.
Elani Y, Solvas XC, Edel JB, et al., 2016, Microfluidic generation of encapsulated droplet interface bilayer networks (multisomes) and their use as cell-like reactors., Chemical Communications, Vol: 52, Pages: 5961-5964, ISSN: 1364-548X
Compartmentalised structures based on droplet interface bilayers (DIBs), including multisomes and compartmentalised vesicles, are seen by many as the next generation of biomimetic soft matter devices. Herein, we outline a microfluidic approach for the construction of miniaturised multisomes of pL volumes in high-throughput and demonstrate their potential as vehicles for in situ chemical synthesis.
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