Nanoplasmonic Sensing Research Articles

Nanoplasmonic sensing for studies on liposomes and extracellular vesicles

Nanoplasmonic sensing (NPS) is a comparatively new and powerful technique, which is yet to achieve its full potential across various fields of sciences. The principle behind NPS is localized surface plasmon resonance. NPS has several advantages over traditional sensing techniques when it comes to selectivity, sensitivity, concentration of analyte required, and prohibitive costs involved. The phenomenon exhibits at the resolution depth between two and a few tens of nm, which is difficult in practice or expensive to attain with various modern microscopes. Additionally, NPS is a label free technique which can measure fast and real-time interactions at the solid-liquid interface. This review highlights the applications of NPS in lipid research and the emerging field of extracellular vesicles.

Peptide Amphiphile Mediated Co‐assembly for Nanoplasmonic Sensing

AbstractAromatic interactions are commonly involved in the assembly of naturally occurring building blocks, and these interactions can be replicated in an artificial setting to produce functional materials. Here we describe a colorimetric biosensor using co‐assembly experiments with plasmonic gold and surfactant‐like peptides (SLPs) spanning a wide range of aromatic residues, polar stretches, and interfacial affinities. The SLPs programmed in DDD−(ZZ)x−FFPC self‐assemble into higher‐order structures in response to a protease and subsequently modulate the colloidal dispersity of gold leading to a colorimetric readout. Results show the strong aggregation propensity of the FFPC tail without polar DDD head. The SLPs were specific to the target protease, i.e., Mpro, a biomarker for SARS‐CoV‐2. This system is a simple and visual tool that senses Mproin phosphate buffer, exhaled breath condensate, and saliva with detection limits of 15.7, 20.8, and 26.1 nM, respectively. These results may have value in designing other protease testing methods.

Peptide Amphiphile Mediated Co-assembly for Nanoplasmonic Sensing.

Aromatic interactions are commonly involved in the assembly of naturally occurring building blocks, and these interactions can be replicated in an artificial setting to produce functional materials. Here we describe a colorimetric biosensor using co-assembly experiments with plasmonic gold and surfactant-like peptides (SLPs) spanning a wide range of aromatic residues, polar stretches, and interfacial affinities. The SLPs programmed in DDD-(ZZ)x -FFPC self-assemble into higher-order structures in response to a protease and subsequently modulate the colloidal dispersity of gold leading to a colorimetric readout. Results show the strong aggregation propensity of the FFPC tail without polar DDD head. The SLPs were specific to the target protease, i.e., Mpro , a biomarker for SARS-CoV-2. This system is a simple and visual tool that senses Mpro in phosphate buffer, exhaled breath condensate, and saliva with detection limits of 15.7, 20.8, and 26.1 nM, respectively. These results may have value in designing other protease testing methods.

Surface Activity of Surfactant–Polyelectrolyte Mixtures through Nanoplasmonic Sensing Technology

Deposition plays an important role in the active delivery and efficiency of hair and skin formulations since it allows active compounds to interact with surfaces in order to achieve the product’s desired performance characteristics. Therefore, it is essential to study the surface activity and behavior of certain compounds that are frequently used in cosmetic and pharmaceutical formulations in order to understand how they interact with relevant biological surfaces, such as hair and skin. We chose to study the surfactants and conditioning agents utilized in the formulation of conditioning shampoos, which are usually designed to be able to achieve the deposition of these substances on the hair and scalp to provide lubrication and better conditioning for hair fibers, facilitating detangling and providing a better feel. In this study, cationic polymer and salt fractions were varied to obtain eighteen different conditioning shampoo formulations in which the deposition was measured by utilizing a nanoplasmonic sensing technology instrument. Moreover, a wet combing test was performed for each of the formulations to investigate if there was any correlation between the combing force and the surface deposition. The complete study was performed using a sustainable anionic surfactant in order to compare the results with those obtained from the traditional formulations.

Biosensing Extracellular Vesicle Subpopulations in Neurodegenerative Disease Conditions.

Extracellular vesicles (EVs) are secreted nanoparticles that are involved in intercellular communication and that modulate a wide range of biological processes in normal and disease conditions. However, EVs are highly heterogeneous in terms of origin in the cell, size, and density. As a result, complex protocols are required to identify and characterize specific EV subpopulations, limiting biomedical applications, notably in diagnostics. Here, we show that combining quartz crystal microbalance with dissipation (QCM-D) and nanoplasmonic sensing (NPS) provides a facile method to track the viscoelastic properties of small EVs. We applied this multisensing strategy to analyze small EVs isolated by differential ultracentrifugation from knock-in mouse striatal cells expressing either a mutated allele or wild-type allele of huntingtin (Htt), the Huntington's disease gene. Our results validate the sensing strategy coupling QCM-D and NPS and suggest that the mass and viscoelastic dissipation of EVs can serve as potent biomarkers for sensing the intercellular changes associated with the neurodegenerative condition.

Dual-Phase Nanoplasmonic Sensing Platform for Monitoring Blood Protein Adsorption and its Coagulation in Vitro

Dual-Phase Nanoplasmonic Sensing Platform for Monitoring Blood Protein Adsorption and its Coagulation in Vitro

CO and O2 Adsorption and CO Oxidation on Pt Nanoparticles by Indirect Nanoplasmonic Sensing.

We used indirect nanoplasmonic sensing (INPS) coupled with mass spectrometry to study CO and oxygen adsorption as well as CO oxidation, on Pt nanoparticles, in the Torr pressure range. Due to an optimization of the physical parameters of our plasmonic sample, we obtain a highly sensitive probe that can detect gas adsorption of a few hundredths of a monolayer, even with a very low number density of Pt particles. Moreover and for the first time, a similarity is observed between the sign and the evolution of the localized surface plasmon resonance (LSPR) peak shift and the work function measurements for CO and oxygen chemisorption. Controlling the size, shape, and surface density of Pt particles, the turnover frequency (TOF) has also been accurately determined. For similar experimental conditions, the TOF is close to those measured on Pt/oxide powder catalysts and Pt(100) single crystals.

Influence of Sensor Coating and Topography on Protein and Nanoparticle Interaction with Supported Lipid Bilayers.

Supported lipid bilayers (SLBs) have proven to be valuable model systems for studying the interactions of proteins, peptides, and nanoparticles with biological membranes. The physicochemical properties (e.g., topography, coating) of the solid substrate may affect the formation and properties of supported phospholipid bilayers, and thus, subsequent interactions with biomolecules or nanoparticles. Here, we examine the influence of support coating (SiO2 vs Si3N4) and topography [sensors with embedded vs protruding gold nanodisks for nanoplasmonic sensing (NPS)] on the formation and subsequent interactions of supported phospholipid bilayers with the model protein cytochrome c and with cationic polymer-wrapped quantum dots using quartz crystal microbalance with dissipation monitoring and NPS techniques. The specific protein and nanoparticle were chosen because they differ in the degree to which they penetrate the bilayer. We find that bilayer formation and subsequent non-penetrative association with cytochrome c were not significantly influenced by substrate composition or topography. In contrast, the interactions of nanoparticles with SLBs depended on the substrate composition. The substrate-dependence of nanoparticle adsorption is attributed to the more negative zeta-potential of the bilayers supported by the silica vs the silicon nitride substrate and to the penetration of the cationic polymer wrapping the nanoparticles into the bilayer. Our results indicate that the degree to which nanoscale analytes interact with SLBs may be influenced by the underlying substrate material.

Real time nanoplasmonic sensing for monitoring CH3NH3PbI3 perovskite formation in mesoporous TiO2 films

The formation of methylammonium lead iodide (CH3NH3PbI3) perovskite into mesoporous titania (TiO2) scaffold via a sequential deposition method is known to offer high quality films for good photovoltaic device performance. The local kinetics at the lower interface between the mesoporous TiO2 film and the collecting electrode govern perovskite growth and formation. Here, we have used a NanoPlasmonic Sensing (NPS) approach with gold (Au) nanosensors to monitor the formation of CH3NH3PbI3 perovskite at the lower interface of up to 650 nm mesoporous TiO2 films. This technique provides time-resolved spectral shifts of the localized surface plasmon resonance at different operating temperatures and methylammonium iodide (CH3NH3I3) concentrations by recording changes in the local vicinity of the Au nanosensors at the mesoporous TiO2 film interface. Analytical studies included ellipsometry, scanning electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. The results show that both the intensity of the NPS response and NPS rate constants are correlated with the operating concentrations and temperatures of CH3NH3I3 as well as CH3NH3PbI3 perovskite growth in mesoporous TiO2.

Calcium Dependent Reversible Aggregation of Escherichia coli Biomimicking Vesicles Enables Formation of Supported Vesicle Layers on Silicon Dioxide

The importance of using biomimicking membranes for various biological applications is rising, as such models are relevant for imitating real organisms. In addition, biomimicking membranes are usually much more repeatable in preparation and easier to handle during analysis than real organisms or biological membranes. In this work we developed a method for the adsorption of intact small unilamellar Escherichia coli (E. coli) vesicles (size Z-average of 73 nm) on SiO2 substrate material. We describe the adsorption process based on the use of two surface sensitive techniques, i.e., nanoplasmonic sensing (NPS) and quartz crystal microbalance (QCM). The acquired data show that the adsorption follows a two-step process. The first step is a slow adsorption of E. coli vesicle aggregates held together by 5 mM of calcium (size Z-average of 531 nm). The Z-average of the aggregates decreased almost three times when the calcium concentration was decreased to 0.1 mM. This suggests that the aggregates were disassembling to some extent when calcium was removed from the system. With both techniques, i.e., NPS and QCM, we observed a second rapid adsorption step after the solution was changed to deionized water. In this second step, the aggregates started to fall apart as the calcium concentration dropped, and the released vesicles started to adsorb onto unoccupied spots at the SiO2 surface of the sensors. Extensive release of mass from the surface was confirmed by QCM, where it was reflected by a sharp increase of frequency, while NPS, due to its lower sensing depth of a few tens of nanometers, did not record such a change. Taken together, we have developed a protocol to form a supported vesicle layer of E. coli vesicles on SiO2 surface using sodium 4-(2-hydroxyethyl)piperazine-1-ethanesulfonate buffer, thus enabling the preparation of E. coli biomimicking supported vesicle layers for interaction studies of compounds of interest. The immobilization happens via a two-step adsorption process.

Nanoplasmonic sensing of CH3NH3PbI3 perovskite formation in mimic of solar cell photoelectrodes

Hybrid metal-halide perovskites have emerged as leading class of semiconductors for photovoltaic devices with remarkable light harvesting efficiencies. The formation of methylammonium lead iodide (CH3NH3PbI3) perovskite into mesoporous titania (TiO2) scaffold by a sequential deposition technique is known to offer better control over the perovskite morphology. The growth reactions at the mesoporous TiO2 film depend on reactants concentration in the host matrix and the reaction activation energy. Here, we are characterizing formation of CH3NH3PbI3 perovskite in mimic solar cell photoelectrodes utilizing the developed NanoPlasmonic Sensing (NPS) approach. Based on dielectric changes at the TiO2 mesoporous film interface, the technique provides time-resolved spectral shifts of the localized surface plasmon resonance that varies widely depending on the different operating temperatures and methylammonium iodide (CH3NH3I) concentrations. Analytical studies included Ellipsometry, Scanning Electron Microscopy, and X-ray diffraction. The results show that perovskite conversion can be obtained at lower CH3NH3I concentrations if reaction activation energy is lowered. A significant finding is that the NPS response at 350 nm mesoporous TiO2 can widely change from red shifts to blue shifts depending on extent of conversion and morphology of perovskite formed at given reaction conditions.

Assessment of Ruthenium Dye N719 Adsorption Kinetics in Mesoporous TiO2 Films of Dye-Sensitized Solar Cells via Nanoplasmonic Sensing

A dye monolayer formation on a semiconductor surface is critical for efficient dye-sensitized solar cells. The role of dye is to absorb light and convert it to photoelectrons, which are injected into the semiconductor conduction band as device current. We measured dye N719 adsorption via optical techniques including indirect nanoplasmonic sensing. The adsorption rate constant of dye N719 in mimic TiO2 photoelectrodes is determined as ka = 983 M−1 s−1. Dye adsorption for ruthenium dyes N3, N749, and Z907, coated onto TiO2 photoelectrodes of varying thicknesses ranging from 3 μm to 10 μm, was conducted and related to fabricated dye-sensitized solar cell efficiency. Analytical studies included scanning electron microscopy and ellipsometry, X-ray diffraction, and UV-Vis spectroscopy, as well as quantum efficiency and current-voltage device characterizations. The results show greatest enhancement of device performance for dye N719 in spite of multilayer formation, which often is underestimated when addressing the dynamic competing factors that reverse thick-film device performance.

Determination of the Main Phase Transition Temperature of Phospholipids by Nanoplasmonic Sensing

Our study demonstrates that nanoplasmonic sensing (NPS) can be utilized for the determination of the phase transition temperature (Tm) of phospholipids. During the phase transition, the lipid bilayer undergoes a conformational change. Therefore, it is presumed that the Tm of phospholipids can be determined by detecting conformational changes in liposomes. The studied lipids included 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). Liposomes in gel phase are immobilized onto silicon dioxide sensors and the sensor cell temperature is increased until passing the Tm of the lipid. The results show that, when the system temperature approaches the Tm, a drop of the NPS signal is observed. The breakpoints in the temperatures are 22.5 °C, 41.0 °C, and 55.5 °C for DMPC, DPPC, and DSPC, respectively. These values are very close to the theoretical Tm values, i.e., 24 °C, 41.4 °C, and 55 °C for DMPC, DPPC, and DSPC, respectively. Our studies prove that the NPS methodology is a simple and valuable tool for the determination of the Tm of phospholipids.

Effect of Surface Coverage of Gold Nanoparticles on the Refractive Index Sensitivity in Fiber-Optic Nanoplasmonic Sensing.

A simple theoretical model was developed to analyze the extinction spectrum of gold nanoparticles (AuNPs) on the fiber core and glass surfaces in order to aid the determination of the surface coverage and surface distribution of the AuNPs on the fiber core surface for sensitivity optimization of the fiber optic particle plasmon resonance (FOPPR) sensor. The extinction spectrum of AuNPs comprises of the interband absorption of AuNPs, non-interacting plasmon resonance (PR) band due to isolated AuNPs, and coupled PR band of interacting AuNPs. When the surface coverage is smaller than 12.2%, the plasmon coupling effect can almost be ignored. This method is also applied to understand the refractive index sensitivity of the FOPPR sensor with respect to the non-interacting PR band and the coupled PR band. In terms of wavelength sensitivity at a surface coverage of 18.6%, the refractive index sensitivity of the coupled PR band (205.5 nm/RIU) is greater than that of the non-interacting PR band (349.1 nm/RIU). In terms of extinction sensitivity, refractive index sensitivity of the coupled PR band (−3.86/RIU) is similar to that of the non-interacting PR band (−3.93/RIU). Both maximum wavelength and extinction sensitivities were found at a surface coverage of 15.2%.

Nanoplasmonic Sensing and Capillary Electrophoresis for Fast Screening of Interactions between Phosphatidylcholine Biomembranes and Surfactants.

Nanoplasmonic sensing (NPS), based on localized surface plasmon resonance, with sensors composed of glass covered with golden nanodisks and overlaid with a SiO2 coating was applied in this study. Egg phosphatidylcholine (eggPC), being an easily accessible membrane-forming lipid, was used for preparation of biomimicking membranes. Small unilamellar vesicles with an approximate hydrodynamic diameter of 30 nm, formed by sonication in 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid buffer, were adsorbed within 10 min on the sensor surface either as intact vesicles or as a planar bilayer. The adsorbed biomembrane systems were further utilized for interaction studies with four different well-known surfactants (negatively and positively charged, zwitterionic, and nonionic) and each surfactant was tested at concentrations below and above the critical micelle concentration (CMC). Our results allowed the evaluation of different NPS patterns for every particular supported membrane system, surfactant, and its concentration. The most significant effect on the membrane was achieved upon the introduction of zwitterionic surfactant micelles, which in fact completely solubilized and removed the lipid membranes from the sensor surface. Other surfactant micelles interacted with the membranes and formed mixed structures remaining on the sensor surface. The studies performed at the concentrations below the CMCs of the surfactants showed that different mixed systems were formed. Depending on the supported membrane system and the type of surfactant, the mixed systems indicated different formation kinetics. Additionally, the final water rinse revealed the stability of the formed systems. To investigate the effect of the studied surfactants on the overall surface charge of the biomembrane, capillary electrophoresis (CE) experiments were carried out in parallel with the NPS analysis. The electroosmotic flow mobility of an eggPC-coated fused silica capillary was used to measure the total surface charge of the biomembrane after its treatment with the surfactants. Our results indicated in general good correlation between CE and NPS data. However, some discrepancies were seen while applying either zwitterionic or positively charged surfactants. This confirmed that CE analysis was able to provide additional data about the investigated systems. Taken together, the combination of NPS and CE proved to be an efficient way to describe the nature of interactions between biomimicking membranes and amphiphilic molecules.

Thermal Properties and Segmental Dynamics of Polymer Melt Chains Adsorbed on Solid Surfaces.

The glass transition of supported polystyrene (PS) and poly(2-vinylpyridine) (P2VP) thin films in the vicinity of the substrate interface was studied by using a nanoplasmonic sensing (NPS) method. This "nanocalorimetric" approach utilizes localized surface plasmon resonance from two-dimensional arrangements of sensor nanoparticles deposited on SiO2-coated glass substrates. The NPS results demonstrated the existence of a high glass transition temperature ( Tg,high) along with the bulk glass transition temperature ( Tg,bulk ≈ 100 °C for PS and P2VP) within the thin films: Tg,high ≈ 160 °C for PS and Tg,high ≈ 200 °C for P2VP. To understand the origin of the Tg,high, we also studied the thermal transitions of lone polymer chains strongly adsorbed onto the substrate surface using solvent rinsing. Interestingly, the NPS data indicated that the Tg,high is attributed to the adsorbed polymer chains. To provide a better understanding of the mechanism of the Tg,high, molecular dynamics simulations were performed on a PS film adsorbed on hydrophobic and hydrophilic substrates. The simulation results illuminated the presence of a higher density region closest to the substrate surface regardless of the magnitude of the polymer-solid interactions. We postulate that the highly packed chain conformation reduces the free volume at the substrate interface, resulting in the Tg,high. Moreover, the simulation results revealed that the deviation of the Tg,high from the bulk Tg,bulk becomes larger as the polymer-substrate interaction increases, which is in line with the experimental findings.

Counting charges on membrane-bound peptides.

Quantifying the number of charges on peptides bound to interfaces requires reliable estimates of (i) surface coverage and (ii) surface charge, both of which are notoriously difficult parameters to obtain, especially at solid/water interfaces. Here, we report the thermodynamics and electrostatics governing the interactions of l-lysine and l-arginine octamers (Lys8 and Arg8) with supported lipid bilayers prepared from a 9 : 1 mixture of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DMPG) from second harmonic generation (SHG) spectroscopy, quartz crystal microbalance with dissipation monitoring (QCM-D) and nanoplasmonic sensing (NPS) mass measurements, and atomistic simulations. The combined SHG/QCM-D/NPS approach provides interfacial charge density estimates from mean field theory for the attached peptides that are smaller by a factor of approximately two (0.12 ± 0.03 C m-2 for Lys8 and 0.10 ± 0.02 C m-2 for Arg8) relative to poly-l-lysine and poly-l-arginine. These results, along with atomistic simulations, indicate that the surface charge density of the supported lipid bilayer is neutralized by the attached cationic peptides. Moreover, the number of charges associated with each attached peptide is commensurate with those found in solution; that is, Lys8 and Arg8 are fully ionized when attached to the bilayer. Computer simulations indicate Lys8 is more likely than Arg8 to "stand-up" on the surface, interacting with lipid headgroups through one or two sidechains while Arg8 is more likely to assume a "buried" conformation, interacting with the bilayer through up to six sidechains. Analysis of electrostatic potential and charge distribution from atomistic simulations suggests that the Gouy-Chapman model, which is widely used for mapping surface potential to surface charge, is semi-quantitatively valid; despite considerable orientational preference of interfacial water, the apparent dielectric constant for the interfacial solvent is about 30, due to the thermal fluctuation of the lipid-water interface.

Cholesterol affects the interaction between an ionic liquid and phospholipid vesicles. A study by differential scanning calorimetry and nanoplasmonic sensing

The present work aims at studying the interactions between cholesterol-rich phosphatidylcholine-based lipid vesicles and trioctylmethylphosphonium acetate ([P8881][OAc]), a biomass dissolving ionic liquid (IL). The effect of cholesterol was assayed by using differential scanning calorimetry (DSC) and nanoplasmonic sensing (NPS) measurement techniques. Cholesterol-enriched dipalmitoyl-phosphatidylcholine vesicles were exposed to different concentrations of the IL, and the derived membrane perturbation was monitored by DSC. The calorimetric data could suggest that the binding and infiltration of the IL are delayed in the vesicles containing cholesterol. To clarify our findings, NPS was applied to quantitatively follow the resistance of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine incorporating 0, 10, and 50mol% of cholesterol toward the IL exposure over time. The membrane perturbation induced by different concentrations of IL was found to be a concentration dependent process on cholesterol-free lipid vesicles. Moreover, our results showed that lipid depletion in cholesterol-enriched lipid vesicles is inversely proportional to the increasing amount of cholesterol in the vesicles. These findings support that cholesterol-rich lipid bilayers are less susceptible toward membrane disrupting agents as compared to membranes that do not incorporate any sterols. This probably occurs because cholesterol tightens the phospholipid acyl chain packing of the plasma membranes, increasing their resistance and reducing their permeability.

Gold nano disks arrays for localized surface plasmon resonance based detection of PSA cancer marker

Here in, we report prostate specific antigen (PSA) detection method using DNA aptamer functionalized gold nano disks array. The approach is based on DNA aptamer–PSA specific interaction and the localized surface plasmon resonance (LSPR) extinction λ max shifts of the transmitted light (UV–vis). The specific interaction results in a stable dynamic equilibrium. The concentration effect on equilibrium time has been described. We also describe the relationship between the aptamer concentration and the plasmon response. Using 2nM DNA aptamer on gold nano arrays, a detectable linear range from 1.7ng/mL to 20.4ng/mL was obtained with the R2 value>0.99. The limit of detection (LOD) value was found 1.49ng/mL. Finite difference time domain (FDTD) simulations were plotted for the gold substrate in air and water. Great agreement was found between the experimental and simulated shifts in both the cases. The refractive index sensitivities (S) of experimental spectra (113nm/RIU) and simulated spectra (116nm/RIU) were also found in good agreement. These results indicate that this NanoPlasmonic Sensing (NPS) detection platform is most suitable for the pre-biopsy test of prostate cancer patients. The DNA aptamers have been used as specific receptors for biomarkers for the first time; it provided the method with great potential for monitoring other biological interaction due to its great versatility and resistance to denaturation. Furthermore, substrate is recoverable which gives it clear advantage over most of the prevalent methods.

Theoretical Investigation on Coupled Plasmon Waveguide Resonance in Real and Complex Domain for High Precision Nanoplasmonic Sensing

Numerical investigations on modified multilayer coupled plasmonic structure, termed as coupled plasmon waveguide resonance (CPWR) structure, have been presented in real as well as complex plane domain. Coupling of waveguide resonance and plasmonic resonance results in dual resonance. Reflectance, field enhancement, and phase-dependent resonant behavior have been analyzed in angular interrogation for three different metal layers in order to optimize the structure with proper choice of metal layers. The resonance parameters have also been theoretically investigated in differential angular regime for better comparison of the shape of different resonance curves. Complex amplitude reflection and transmission co-efficients are analyzed with circular graphical plots in the complex plane. Simultaneous observations of the real and imaginary parts as well as amplitude and phase of the reflection and transmission co-efficients have been demonstrated. Different conventional optical polymers have been considered as waveguide layer materials and their respective real and complex plane analyses demonstrate the comparison for the proper choice of the waveguide layer. Moreover, the resonance parameters and the differential plots in real as well as complex plane for coarse and precise measurement have also been investigated for nanoplasmonic sensing applications to provide improved resolution.