Resonance Elastic Light Scattering Research Articles

Supramolecular interactions of oxidative stress biomarker glutathione with fluorone black

Oxidative stress biomarkers, including glutathione (GSH) and related compounds, are involved in a variety of interactions enabling redox potential maintenance in living cells and protection against radicals. Since the oxidative stress is promoting and, in many cases, inducing serious illnesses, monitoring of GSH levels can aid in diagnostics and disease prevention. Herein, we report on the discovery of the formation of a supramolecular ensemble of GSH with fluorone black (9-phenyl fluorone, FB) which is optically active and enables sensitive determination of GSH by resonance elastic light scattering (RELS). We have found that supramolecular interactions of GSH with FB can be probed with spectroscopic, RELS, and electrochemical methods. Our investigations show that RELS intensity for FB solutions increases with GSH concentration while fluorescence emission of FB is not affected, as quenching begins only above 0.8mM GSH. The UV–Vis difference spectra show a positive peak at 383nm and a negative peak at 458nm, indicating a higher-energy absorbing complex in comparison to the non-bonded FB host. Supramolecular interactions of FB with GSH have also been corroborated by electrochemical measurements involving two configurations of FB-GSH ensembles on electrodes: (i) an inverted orientation on Au-coated quartz crystal piezoelectrode (Au@SG-FB), with strong thiolate bonding to gold, and (ii) a non-inverted orientation on glassy carbon electrode (GCE@FB-GS), with weak π-π stacking attachment and efficient charge mediation through the ensemble. The formation of a supramolecular ensemble with hydrogen bonding has also been confirmed by quantum mechanical calculations. The discovery of supramolecular FB-GSH ensemble formation enables elucidating the mechanisms of strong RELS responses, changes in UV–Vis absorption spectra, and the electrochemical reactivity. Also, it provides new insights to the understanding of the efficient charge-transfer in redox potential homeostasis which is likely based on an intermediate formation of a similar type of supramolecular ensembles.

Mitochondria–based biosensors with piezometric and RELS transduction for potassium uptake and release investigations

Dysfunctional mitochondria appear to be involved in many diseases through their role in respiration, reactive oxygen species generation, and energy production. To aid in the design of new biosensors based on mitochondria (MT), we have investigated the feasibility of detecting ion fluxes through the MT-membrane K+-ion channels using piezosensors with MTs immobilized either by hydrogen bonding or thin polypyrrole (PPy) binding film. We have demonstrated for the first time that the mitochondria-based piezosensors are able to detect ion fluxes and thus be utilized for drug development aimed at ion channel opener- or inhibitor-function. The quartz crystal resonator responding only to mass changes in the lower part of the MT film, penetrated by the acoustic wave, is able to detect a pronounced cationic dynamics in PPy-bonded MT piezosensors despite of the undoped-PPy preference for pure anion dynamics. The control experiments performed by resonance elastic light scattering (RELS) confirmed MT swelling/shrinking, ion dynamics, and osmotic water transfer in MTs, as well as the effects of exposure to a drug valinomycin at sub-nanomolar concentrations.

Double-shell gold nanoparticle-based DNA-carriers with poly- l-lysine binding surface

In view of the prospective applications of polyamine coatings in functional gold nanoparticles for use as carriers in gene delivery systems, in tissue repair and as bactericidal and virucidal non-toxic vehicle, we have investigated the interactions of poly- l-lysine (PLL) with gold nanoparticles (AuNP). Since direct binding of PLL to AuNP is not strong at neutral pH, we have focused on PLL interactions with carboxylated self-assembled monolayers (SAM) on AuNP, such as the citrate-capped AuNP. The double-shell nanoparticles AuNP@Cit/PLL thus produced do not contain any toxic thiols. We have observed strong electrostatic interactions between polycationic chains of PLL and AuNP@Cit in weakly acidic to weakly alkaline solutions (pH 5–9), as evidenced by the bathochromic shift of the local surface plasmon (SP) band and strong increase in resonance elastic light scattering (RELS) intensity. The stoichiometry of interactions evaluated on the basis of RELS data indicates on a hyper-Langmuirian type of interactions with stoichiometric coefficient n = 1.35 (PLL : AuNP@Cit). From the RELS titration data, a shift of the deprotonation constant for the bound PLL has been determined ( pK a = 11.6 for the bound PLL vs. 10.48 for the free PLL). The deprotonation of PLL leads to AuNP aggregate disassembly, evidenced by sharp RELS decline and hypsochromic shift of SP band. We have found that under these conditions, a residual aggregation due to the interparticle interactions between β-sheets of PLL overcoat become predominant. The molecular dynamics simulations indicate that multiple hydrogen bonds can also be formed between the PLL linker and the shell molecules of AuNP@Cit. The double-shell nanoparticles, AuNP@Cit/PLL, have been shown to attract DNA molecules using highly sensitive RELS measurements presenting the proof-of-concept for the suitability of this non-toxic nanostructured material for gene delivery applications. The advantage of the proposed material is no toxicity related to the ligand release in gene delivery processes in contrast to the thiol-functionalized AuNP.

Reply to Comment on “Multimodal coupling of optical transitions and plasmonic oscillations in rhodamine B modified gold nanoparticles” by I. Blakey

In answer to Blakey’s comment concerning the role of solution absorbance on emission spectra of gold nanoparticles (AuNP) recorded under the resonance elastic light scattering (RELS) conditions of a synchronous scan with λem = λex, we provide new evidence of a complex behaviour of plasmonic responses of functionalized AuNP down to very low concentrations, CAuNP = 7 pM. We have demonstrated that there is no threshold on the RELS spectra and that from the lowest concentration under study there is a continuous shift of the RELS peak toward longer waves. Since the absorbance of a 7 pM AuNP solution is A < 0.008, there cannot be any direct effect of A on λmax for the RELS peak and the observed approximately-linear correlation between λmax and ASP is therefore an expression of a dependence of λmax on CAuNP.

Multimodal coupling of optical transitions and plasmonic oscillations in rhodamine B modified gold nanoparticles

The optical properties of a photoluminescent dye rhodamine B (RhB) interacting with gold nanoparticles (AuNP) have been investigated using plasmonic absorbance, fluorescence, and resonance elastic light scattering (RELS) spectroscopy. We have found that these interactions result in a multimodal coupling that influence optical transitions in RhB. In absorbance measurements, we have observed for the first time the coupling resulting in strong screening of RhB π-π* transitions, likely caused by a contact adsorption of RhB on a conductive surface of AuNP. The nanoparticles quench also very efficiently the RhB fluorescence. We have determined that the static quenching mechanism with a non-Förster fluorescence resonance energy transfer (FRET) from RhB molecules to AuNP is involved. The Stern-Volmer dependence F(0)/F = f(Q) shows an upward deviation from linearity, attributed to the ultra-high quenching efficiency of AuNP leading to the new extended Stern-Volmer model. A sharp RELS peak of RhB alone (λ(max) = 566 nm) has been observed for the first time and attributed to the resonance fluorescence and enhanced scattering. This peak is completely quenched in the presence of AuNP(22nm). Our quantum mechanical calculations confirm that the distance between AuNP surface and conjugated π-electron system in RhB is well within the range of plasmonic fields extending from AuNP. The optical transition coupling to plasmonic oscillations and the efficient energy transfer due to the interactions of fluorescent dyes with nanoparticles are important for biophysical studies of life processes and applications in nanomedicine.

Resonance Elastic Light Scattering and Plasmonic Phenomena in Glutathione-Mediated Gold Nanoparticle Assembly

The resonance elastic light scattering (RELS) spectroscopy has been applied to study the interactions of glutathione (GSH) with citrate-capped gold nanoparticles (AuNP). A strong dependence of GSH-induced gold nanoparticle assembly on nanoparticle size has been found. The RELS intensity measurements were carried out in a short reaction time (τ = 60 s) after injection of GSH. The strong interparticle interactions between AuNP are due to zwitterionic forces and intermolecular hydrogen bonding. The AuNP assembly has been confirmed using the surface plasmon UV-Vis spectroscopy. A fast initial adsorption rate of GSH on a clean Au surface, v = 2.4 ng cm-2 s-1, has been measured using a nanogravimetric flow-cell with piezoelectric QC/Au resonator. The adsorption/desorption processes have been evaluated. The RELS spectroscopy has been found as a very sensitive tool for studying interparticle interactions and its applications can be extended to monitor reactivities and assembly of other monolayer-protected metal clusters.

Detection of Oxidative Stress Biomarker Homocysteine Utilizing Resonance Elastic Light Scattering

Homocysteine is a biomarker of oxidative stress and a risk factor for many disorders, including cardiovascular and Alzheimer's disease. We have investigated new methods for the development of homocysteine assays based on gold nanoparticles (AuNP) in solutions and modified solid gold piezoelectrodes. In this work, we have applied sensitive resonance elastic light scattering (RELS) and plasmonic UV-Vis spectroscopy to monitor homocysteine-induced AuNP assembly. The assembly of AuNP frameworks by covalent binding of interparticle glutaraldehyde nanobridges has been utilized for sensitive homocysteine determination. The selectivity of a glutaraldehyde crosslinking reactions toward homocysteine has been exploited to discriminate against other aminoacids. The measurements of a homocysteine adsorption on a solid Au electrode, carried out using the electrochemical quartz crystal nanogravimetry (EQCN), have shown that a multilayer film, with thickness of up to 3 equivalent monolayers, is formed in the zwitterionic pH range of homocysteine.

Rapid functionalization of metal nanoparticles by moderator-tunable ligand-exchange process for biosensor designs

A new method for rapid functionalization of metal nanoparticles based on a moderator-tunable 2D nucleation and growth of ligand-exchange domains has been developed for the design of biosensors with nanoparticle-enhanced sensory films and other applications. The proposed functionalization of gold nanoparticles proceeds through the nucleation and avalanche growth of ligand-exchange domains in the self-assembled monolayer film on a gold nanoparticle surface. The nucleation and growth is controllable by a moderator molecule. The experimental system described presents a ligand-exchange process at citrate-capped gold nanoparticles, with homocysteine acting as the incoming ligand and glutathione as the moderator. The kinetics of the nucleation and growth driven ligand-exchange is characterized by a sigmoidal switching function and differs from that of the usually observed Langmuirian pseudo-first-order process corresponding to the random place-exchange. The ultra-fast functionalization process was monitored using resonance elastic light scattering (RELS) spectroscopy and confirmed by UV–vis plasmonic band absorbance measurements.

Resonance elastic light scattering (RELS) spectroscopy of fast non-Langmuirian ligand-exchange in glutathione-induced gold nanoparticle assembly

The interactions of a biomolecule glutathione (GSH) with citrate-capped gold nanoparticles (AuNP) have been investigated to evaluate the viability of a rapid GSH-capture by gold nanoparticle carriers, as a model system for applications ranging from designing nanoparticle-enhanced functional biosensor interfaces to nanomedicine. The measurements, performed using resonance elastic light scattering (RELS) spectroscopy, have shown a strong dependence of GSH-induced scattering cross-section on gold nanoparticle size. A large increase in RELS intensity after injection of GSH, in a short reaction time ( τ = 60 s), has been observed for small AuNP (5 nm dia.) and ascribed to the fast ligand-exchange followed by AuNP assembly. The unexpected non-Langmuirian concentration dependence of scattering intensity for AuNP 5nm indicates on a 2D nucleation and growth mechanism of the ligand-exchange process. The ligand-exchange and small nanoparticle ensemble formation followed by relaxation have been observed in long term (10 h) monitoring of GSH–AuNP interactions by RELS. The results of molecular dynamics and quantum mechanical calculations corroborate the mechanism of the formation of hydrogen-bonded GSH-linkages and interparticle interactions and show that the assembly is driven by multiple H-bonding between GSH-capped AuNP and electrostatic zwitterionic interactions. The RELS spectroscopy has been found as a very sensitive tool for studying interparticle interactions. The application of RELS can be expanded to monitor reactivities and assembly of other monolayer-protected metal clusters, especially in very fast processes which cannot be followed by other techniques.

Resonance Elastic Light Scattering and Plasmonic Phenomena in Glutathione-Mediated Gold Nanoparticle Assembly

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Detection of Oxidative Stress Biomarker Homocysteine Utilizing Resonance Elastic Light Scattering

not Available.

Ligand exchange effects in gold nanoparticle assembly induced by oxidative stress biomarkers: Homocysteine and cysteine

The interactions of oxidative stress biomarkers: homocysteine (Hcys) and cysteine (Cys) with the multifunctional gold nanoparticles, important in view of novel biomedical applications in diagnostics and therapy, have been investigated using resonance elastic light scattering (RELS), UV–Vis plasmonic spectroscopy, and high-resolution TEM imaging. The Hcys-induced assembly of gold nanoparticles has been observed for non-ionic surfactant-capped gold nanoparticles as well as for negatively-charged citrate-capped gold nanoparticles. We have observed for the first time the de-aggregation of citrate-capped gold nanoparticle ensembles followed by their conversion to citrate-linked Hcys-capped nanoparticle assemblies. The Cys molecules, which are smaller than Hcys by only one CH 2 group, show much less activity. The mechanisms leading to this intriguing disparity in the abilities of these two thioaminoacids to ligand exchange with surfactant- or citrate-capping molecules of the gold nanoparticle shells are proposed on the basis of the experimental evidence, molecular dynamics simulations, and quantum mechanical calculations. For citrate-capped gold nanoparticles, we postulate the formation of surface complexes facilitated by electrostatic attractions and formation of double hydrogen bonds for both Hcys and Cys. The conformational differences between these two kinds of complexes result in marked differences in the distance between –SH groups of the biomarkers to the gold surface and different abilities to induce nanoparticle assembly. Analytical implications of these mechanistic differences are discussed.