Thiol-capped Gold Nanoparticles Research Articles

Probing the Influence of Hydrophobicity of Modified Gold Nanoparticles in Modulating the Lipid Surface Behavior Using Vibrational Sum Frequency Generation Spectroscopy.

A deep understanding of how the surface modifications of nanoparticles impact their interactions with cell membranes is vital for advancing safe and effective biomedical applications. Among the pivotal factors governing these interactions, the hydrophobicity of nanoparticles plays a crucial role, predominantly driven by the hydrophobic interactions with the cell membrane. Herein, we study the influence of the hydrophobic alkyl chain length of thiol-capped gold nanoparticles (GNPs) on lipid surfaces with the help of vibrational sum frequency generation spectroscopy. We have utilized the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid monolayer as a representative model of cell membranes on the water surface. Our findings revealed that GNPs capped with the thiol ligand having a shorter alkyl chain such as heptanethiol (HT, C7) show minimal changes in the C-H stretching vibrations while interacting with the lipid monolayer. These observations could be attributed to the perturbation of the lipid chain due to hydrophobic-hydrophobic interactions between the alkyl chain of thiol-capped GNPs and the hydrophobic group of the lipid membrane or simply by the adsorption of GNPs at the interface without disrupting the monolayer structure. However, with increasing the chain length of thiol-capped GNPs from decanethiol (DDT, C10) to octadecanethiol (ODT, C18), the extent of spectral change in the C-H stretching vibration is increased. The controlled experiment performed with the deuterated lipids conforms that the changes observed in the C-H stretching vibration after adding HT (C7) GNPs are only because of their presence in the surface without altering the monolayer structure. However, in the case of DT (C10) and DDT (C12) GNPs, the strong hydrophobic interactions between the monolayer and the alkyl chain of the thiol-capped GNPs result in the increased orientational order of the monolayer. Moreover, in the case of ODT (C18) GNPs, the very long alkyl chain induces pronounced perturbations in the monolayer structure with net disordering of the monolayer. These observations are further supported by the spectral changes observed in the O-H vibration of the interfacial water molecules. Our findings reveal the crucial role of the hydrophobic nature of GNPs in influencing the interface. Understanding these effects is crucial for drug delivery applications and improving the stability and effectiveness of lipid-based systems.

Quantifying Bound Proteins on Pegylated Gold Nanoparticles Using Infrared Spectroscopy.

Protein-nanoparticle (NP) complexes are nanomaterials that have numerous potential uses ranging from biosensing to biomedical applications such as drug delivery and nanomedicine. Despite their extensive use quantifying the number of bound proteins per NP remains a challenging characterization step that is crucial for further developments of the conjugate, particularly for metal NPs that often interfere with standard protein quantification techniques. In this work, we present a method for quantifying the number of proteins bound to pegylated thiol-capped gold nanoparticles (AuNPs) using an infrared (IR) spectrometer, a readily available instrument. This method takes advantage of the strong IR bands present in proteins and the capping ligands to quantify protein-NP ratios and circumvents the need to degrade the NPs prior to analysis. We show that this method is generalizable where calibration curves made using inexpensive and commercially available proteins such as bovine serum albumin (BSA) can be used to quantify protein-NP ratios for proteins of different sizes and structures.

Gold nanoparticles spectral CT imaging and limit of detectability in a new materials contrast-detail phantom

This study involves the synthesis, characterization, and spectral photon counting CT (SPCCT) imaging of gold nanoparticles tailored for enhancing the contrast of small cancer lesions. We used the modified Turkevich method to produce thiol-capped gold nanoparticles (AuNPs) at different concentrations (20, 15, 10, 5, 2.5, 1.25, 0.6 mg/ml). We thoroughly characterized the AuNPs using Transmission Electron Microscopy (TEM), X-ray diffraction spectroscopy (XRD), Dynamic Light Scattering (DLS), and UV–visible absorption spectroscopy. To assess the AuNPs contrast enhancing performance, we designed and built a new material contrast detail phantom for CT imaging and determined the minimum detectable concentrations of AuNPs in simulated lesions of small diameters (1, 2, 3, and 5 mm). The synthesized AuNPs are spherical with an average size of approximately 20 ± 4 nm, with maximum UV absorption occurring at 527 nm wavelength, and exhibit a face-centered cubic structure of gold according to XRD analysis. The synthesized gold nanoparticles demonstrated high contrast in SPCCT, suggesting their potential as contrast agents for imaging cancer tissues. The AuNPs image contrast was directly proportional to the AuNPs concentration. We are the first to determine that the lowest visually distinguishable contrast was achieved at a gold concentration of 5 mg/ml for a 2 mm simulated lesion. For 1 mm size lesion the smallest visible concentration was 10 mg/ml. This newly developed phantom can be used for determining the minimal concentration required for various high-Z nanoparticles to produce detectable contrast in X-ray imaging for small-size simulated lesions.

Gold nanoparticles doped organic liquid crystalline material for fast charge migration in nano-devices

ABSTRACT With the ever-growing need for low-cost, easily processable multifunctional materials and increasing miniaturisation in devices, we have landed in the era of nanodevices. Discotic liquid crystals are multifaceted materials that have shown their applicability as photonic devices, nanowires, optical switches, memory storage devices and many more. These materials show 1D conductivity which can be boosted upon doping with a suitable doping agent in appropriate concentrations. In this work, we present nanocomposite materials composed of a triphenylene discotic liquid crystal material, doped with thiol capped gold nanoparticles, and propose to apply it as a charge transportation layer in nanodevices for faster charge migration. Various techniques have been used to analyse the effect of doping on the different electrical, optical and lattice parameters of these nanocomposite systems. An increase in the value of the conductivity is obtained at higher temperatures, and it is successfully preserved till room temperature due to the presence of thiol capped gold nanoparticles in the columnar matrix. Thus, an increase in conductivity, lowering of the optical band gap, broadening of UV-Visible absorbance peak and decrease in core-to-core distance infers the increase in stability and optical and conduction properties of the host material after doping.

Nanocomposite system of a discotic liquid crystal doped with thiol capped gold nanoparticles

In the pursuit of novel charge transporting materials, composite systems have always proved to be a promising option. While it seems cumbersome and ponderous to molecularly engineer a material, combining and customizing two exclusive systems to obtain a new material, with desired properties appears far simpler and more yielding. One such developing field of research is the study of discotic liquid crystal (DLC) – nanocomposite systems for applicability as a charge transport material in the form of one-dimensional nanowires or two-dimensional conducting matrix layers. In this work, we present a detailed study of composite systems of gold nanoparticles doped in Hexa-hexylthiotriphenylene DLC. In addition to an appreciable increase in conductivity, we also observe a decrease in lattice parameters by using small-angle X-ray scattering (SAXS). An increase in the enthalpy of transition observed by using thermodynamic study and formation of dendritic textures observed by using polarized light microscopy (PLM) study signifies the formation of perfect hexagonal structures despite doping. Overall, the different studies suggest that the doped nanoparticles have very well settled in between host molecules without disturbing the molecular ordering of the hosts. Such results are encouraging and indicative of the potential applicability of the nanocomposite systems in portable electronic devices as a charge transport layer.

Electrochemical sensing of limonene using thiol capped gold nanoparticles and its detection in the real breath sample of a cirrhotic patient

• Molar ratio of gold salt to thiol compound (2:1) synthesised best performing AuNPs. • Hexanethiolated capped AuNPs electrochemically detected limonene (LOD= 0.2 mmol L −1 ). • Limonene was detecteded in a cirrhotic patient breath sample using Hexanethiolated capped AuNPs. • Quantitative electrochemical detection of limonene was confirmed vusing GCMSto be 800 ppm. Volatile organic compounds (VOCs) are a major constituent of human breath which is being investigated as potential targets to be sensed in e-nose biosensors. Limonene is found in the breath of cirrhotic liver patients and can be used for early diagnosis using electrochemical biosensors. In the current study, electrochemical detection of limonene was performed using monolayer thiolated gold nanoparticles. Three different types of monolayer thiol capped AuNPs were synthesized by the modified biphasic method with the different molar ratios (2:1 and 1:1) of hydrogen tetrachloroaurate (III) (HAuCl 4 ·2H 2 O) and thiol groups: dodecanethiol, decanethiol, and hexanethiol. Thiol capped AuNPs were characterized physiochemically and for electrochemical sensing at different factors such as pHs, scan rate, current stability. Based on the best presented electrochemical results, hexanethiol AuNPs were selected as a sensor for analyzing the electrochemical detection of limonene as an analyte. Hexanethiol capped AuNPs based biosensing platform showed high sensitivity with a LOD of 0.2 mmol L −1 as observed via its DPV, and high specificity when was used against another VOC standard. The sensor was also used to detect limonene in the real breath sample of the clinical patient, besides testing the lab standard of limonene. The breath sample of cirrhotic patients was collected and tested for the presence of limonene by using GC–MS. The quantity of limonene measured via GC–MS was 800 ppm in cirrhotic patients and electrochemical sensor measurements of limonene were almost the same providing confidence over quantitative detection of the synthesized hexanethiol capped AuNPs based biosensing platform in this study.

Study of the interaction mechanism between hydrophilic thiol capped gold nanoparticles and melamine in aqueous medium

In the last years, intense efforts have been made in order to obtain colloidal-based systems capable of pointing out the presence of melamine in food samples. In this work, we reported about the recognition of melamine in aqueous solution, using gold nanoparticles stabilized with 3-mercapto-1-propanesulfonate (AuNPs-3MPS), with the aim of deepening how the recognition process works. AuNPs were synthesized using a wet chemical reduction method. The synthesized AuNPs-3MPS probe was fully characterized, before and after the recognition process, by both physicochemical (UV–vis, FT-IR, 1H-NMR, DLS and ζ-potential) and morphostructural techniques (AFM, HR-TEM). The chemical and electronic structure was also investigated by SR-XPS. The sensing method is based on the melamine-induced aggregation of AuNPs; the presence of melamine was successfully detected in the range of 2.5−500 ppm. The results achieved also demonstrate that negatively charged AuNPs-3MPS are potentially useful for determining melamine contents in aqueous solution. SR-XPS measurements allowed to understand interaction mechanism between the probe and the analyte. The presence of sulfonate groups allows a mutual interaction mediated by electrostatic bonds between nanoparticles surface thiols and positively charged amino groups of melamine molecules.

Nanoparticle Induced Morphology Modulation in Spin Coated PS/PMMA Blend Thin Films.

The influence of adding nanoparticles on the ascast morphology of spin coated immiscible polystyrene/poly(methyl methacrylate) (PS/PMMA) thin films of different thickness (hE) and composition (RB, volume ratio of PS to PMMA) has been explored in this article. To understand the precise effect of nanoparticle addition, the morphology of PS/PMMA thin blend films spin cast from toluene on a native oxide covered silicon wafer substrate was first investigated. It is seen that in particle free films, the generic morphology of the films remains nearly unaltered with increase in hE, for RB = 3:1 and 1:3. In contrast, strong hE dependent morphology transformation is observed in films with RB = 1:1. Subsequently, thiol-capped gold nanoparticles (AuNP) containing films with different particle concentrations (CNP) were cast from the same solvent along with the polymer mixture. We observe that addition of AuNPs barely alters the generic morphology of the films with RB = 3:1. In contrast, the presence of the particles significantly influences the morphology of the films with RB = 1:1 and 1:3, particularly at higher CNP (≈10.0%). X-ray photoelectron spectroscopy and X-ray reflectivity of some samples reveal that the AuNPs tend to migrate to the free surface through the PS phase, thereby stabilizing this layer partially or fully (depending on CNP) against dewetting over a surface of adsorbed PMMA layer and influencing the ascast morphology as a function of CNP. The work is fundamentally important in understanding largely overlooked implications of nanoparticle addition on the morphology of PS/PMMA blend thin films which forms the fundamental basis for future interesting studies involving dynamics of nanoparticles within the blend thin films.

Construction of thiol-capped ultrasmall Au–Bi bimetallic nanoparticles for X-ray CT imaging and enhanced antitumor therapy efficiency

Thiol capped gold nanoparticles with small size, high dispersity, and broad light absorption covering ultraviolet (UV) to near infrared (NIR) region have been developed for catalysis, fluorescence imaging and photodynamic therapy (PDT). The constitution of the metal core in such nanoparticles can strongly influence the luminescence, catalysis, and stability properties. However, to date, a corresponding investigation of the influence of the metallic core on the generation of reaction oxygen species (ROS) and its therapeutic efficiency towards tumor cells remains to be lacking. Herein, we fabricated bimetallic nanoparticles by introducing bismuth into captopril capped gold nanoparticles. Surprisingly, the introduction of the Bi was found enhance the photothermal effect of the nanoparticles to a great extent, and the variation trends for the thermal effect, ROS generation rate, and tumor cell inhibition effect were found to disparate with the changes in the Au and Bi composition. The origin of the photothermal effect was deduced through density functional theory calculations based on microscopic construction. Combined with the intrinsic photodynamic effect, the bimetallic nanoparticles showed an outstanding tumor cell inhibition effect. Furthermore, due to the excellent CT imaging property, our designed nanoparticles provide the exciting possibility to realize CT imaging guided and light-mediated tumor therapy.

An Organometallic Strategy for Assembling Atomically Precise Hybrid Nanomaterials.

For decades, chemists have strived to mimic the intricate design and diverse functions of naturally occurring systems through the bioinspired synthesis of programmable inorganic nanomaterials. The development of thiol-capped gold nanoparticles (AuNPs) has driven advancement in this area; however, although versatile and readily accessible, hybrid AuNPs are rarely atomically precise, which limits control over their surface topology and therefore the study of complex structure-function relationships. Here, we present a bottom-up approach to the systematic assembly of atomically precise hybrid nanoclusters employing a strategy that mimics the synthetic ease with which thiol-capped AuNPs are normally constructed, while producing well-defined covalent nanoscale assemblies with diverse surface topologies. For the first time, using a structurally characterized cluster-based organometallic building block, we demonstrate the systematic synthesis of nanoclusters with multivalent binding capabilities to complex protein targets.

Two Growth Mechanisms of Thiol-Capped Gold Nanoparticles Controlled by Ligand Chemistry.

Thiols play an important role in the synthesis of well-defined nanoparticles (NPs) with tailored properties, but their effects on the formation kinetics of NPs are still under investigation. Here, we used in situ small-angle X-ray scattering (SAXS)/UV-vis spectroscopy and time-dependent transmission electron microscopy (TEM) to elucidate the role of thiols in the formation process of gold NPs (AuNPs) by changing the adding sequence between thiol ligand and reducing agent. Through quantitative analysis of in situ SAXS/UV-vis and TEM, detailed information on size, size distribution, the number of particles, optical properties, and the size evolution was obtained. Two different growth mechanisms of monodisperse AuNPs controlled by thiol ligand are exhibited: (i) thiol plays a dual role as a digestive ripening etchant and as a stabilizing ligand in the presence of a weak phosphine ligand. The digestive ripening mechanism involving the dissolution of bigger particles and subsequent deposition of monomers onto existing small NPs is responsible for producing narrowly dispersed NPs. (ii) Thiol acts as a strong stabilizing agent; in this case, the formation rate constant is quite slow, thus limiting the growth rate of NPs. Therefore, diffusion-limited growth mechanism is proposed for obtaining narrowly dispersed NPs with a diameter of 5.6 nm (12%). Our findings demonstrate that the formation of nearly monodisperse AuNPs with controllable size distribution could be realized by different growth mechanisms in the presence of thiol ligand.

Thiol-Capped Gold Nanoparticle Biosensors for Rapid and Sensitive Visual Colorimetric Detection of Klebsiella pneumoniae.

In the last few years, gold nanoparticle biosensors have been developed for rapid, precise, easy and inexpensive with high specificity and sensitivity detection of human, plant and animal pathogens. Klebsiella pneumoniae serotype K2 is one of the common gram-negative pathogens with high prevalence. Therefore, it is essential to provide the effective and exclusive method to detect the bacteria. Klebsiella pneumoniae serotype K2 strain ATCC9997 genomic DNA was applied to establish the detection protocol either with thiol-capped oligonucleotide probes and gold nanoparticles or polymerase chain reaction based on K2A gene sequence. In the presence of the genomic DNA and oligonucleotide probes, a change in the color of gold nanoparticles and maximum changes in wavelength at 550-650nm was achieved. In addition, the result showed specificity of 15 × 105CFU/mL and 9pg/μL by gold nanoparticles probes. The lower limit of detection obtained by PCR method was 1pg/μL. Moreover, results demonstrated a great specificity of the designed primers and probes for colorimetric detection assay and PCR. Colorimetric detection using gold nanoparticle probe with advantages such as the lower time required for detection and no need for expensive detection instrumentation compared to the biochemical and molecular methods could be introduced for rapid, accurate detection of the bacteria.

The Role of Onium Salts in the Pro-Oxidant Effect of Gold Nanoparticles in Lipophilic Environments.

Metal nanoparticles are reported to be toxic due to the generation of free radicals at their surface. Relatively inert thiol-capped gold nanoparticles (AuNPs) have been reported to induce radical formation in the presence of hydroperoxides, which would conflict with their potential use as inert scaffolds for the design of novel nano-antioxidants. With the aim of clarifying this aspect, we investigated the pro-oxidant activity of dodecanethiol-capped AuNPs (∼5 nm diameter), prepared through the Brust-Schiffrin synthesis, by oxygen-uptake kinetic studies. The pro-oxidant activity was found to be proportional to the impurities of the transfer agent tetraoctylammonium bromide (TOAB) left from the synthesis and decreased on repeated washing of the nanoparticles. Under identical settings similar batches of AuNP (∼9 nm diameter) prepared through the Ulman method without onium salts showed no pro-oxidant behavior. The alternative onium phase-transfer agents Oct4 NBF4 (Oct=octyl), Hex4 NBF4 (Hex=hexyl), and Hex4 NPF6 were comparatively investigated and showed lower pro-oxidant activity depending on the counterion (Br- >PF6- >BF4- ).

Nature of magnetism in thiol-capped gold nanoparticles investigated with Muon spin rotation

Muon spin rotation/relaxation measurements show clear evidence for magnetism in 2.2 nm gold nanoparticles capped with butanethiol. At low temperatures (1.8 K), there is significant spin relaxation which decreases as a function of both the applied longitudinal magnetic field and increasing temperature. The results indicate that there are spatially inhomogeneous electronic moments that fluctuate with a wide distribution of correlation times. Possible explanations are discussed.

Sensing of low concentration of ammonia at room temperature by decorated multi-walled carbon nanotube: fabrication and characteristics

A chemical sensor based on multi-walled carbon nanotube (MWCNT) decorated with densely populated thiol-capped gold nanoparticles (AuNPs) with sizes smaller than 3 nm for sensing low concentrations of ammonia gas is reported. The functionalized MWCNTs, subsequently decorated with AuNPs following an easy fabrication route were exposed to NH3 gas at the room temperature and the electrical resistance of the sensor changed upon exposure. The sensor also partially recovered the initial state after sensing in the normal air environment (without any dry air or N2 gas purge). The gold nanoparticles decoration is found to enhance the sensitivity and selectivity of MWCNT towards NH3 gas under ambient conditions with a reduced response and recovery time. The material was structurally characterized by Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. Thermal stability of the sensor till 574 °C was demonstrated by TGA analysis. This papers describes how thiol-capped AuNPs are uniformly decorated on the outer walls of the MWCNTs with a separation of 2–3 nm making use of the ionic nature of Au and how this uniform distribution of AuNPs increases the active sites for absorption of NH3 gas molecules leading to sensing its low concentrations.

X-ray Reflectivity Studies on the Mixed Langmuir-Blodgett Monolayers of Thiol-Capped Gold Nanoparticles, Dipalmitoylphosphatidylcholine, and Sodium Dodecyl Sulfate.

Langmuir-Blodgett monolayers of thiolated gold nanoparticles mixed with dipalmitoylphosphatidylcholine/sodium dodecyl sulfate (DPPC/SDS) were investigated by combining the X-ray reflectivity, grazing-incident scattering, and TEM analyses to reveal the in-depth and in-plane organization and the 2D morphology of such mixed monolayers. It was found that the addition of a charged single-tail surfactant to the thiolated Au nanoparticle monolayer helps to stabilize the Au nanoparticle monolayer and to strengthen the mechanical property of the mixed monolayer film. For mixing with lipids, it was found that the thiolated gold nanoparticles could be pushed on top of the lipid monolayer when the mixed monolayer is compressed. At a typical comparable total surface area ratio of gold nanoparticle to lipid, the thiolated gold nanoparticles could form a uniform domain on top of the DPPC monolayer. When there are more thiolated gold nanoparticles than that could be supported by the lipid monolayer, domain overlapping could occur to form bilayer gold nanoparticle domains at some regions. At low total surface area ratio of thiolated gold nanoparticle to lipid, the thiolated gold nanoparticles tend to form a connected threadlike aggregation structure. Evidently, the morphology of the thiolated gold nanoparticle monolayer is highly depending on the total surface area ratio of the thiolated gold nanoparticle to lipid. SDS is found to have a dispersion power capable of dispersing the originally uniform Au-8C nanoparticle domain of the mixed Au-8C/DPPC monolayer into a foamlike structure for the mixed Au-8C/SDS/DPPC monolayer. It is evident that not only the concentration ratio but also the size and shape of the template formed by the amphiphilic molecules and their interaction with the thiolated gold nanoparticles can all have great effects on the organizational structure as well as morphology of the thiolated gold nanoparticle monolayer.

Simulation studies on structural and thermal properties of alkane thiol capped gold nanoparticles

The structural and thermal properties of the passivated gold nanoparticles were explored employing molecular dynamics simulation for the different surface coverage densities of the self-assembled monolayer (SAM) of alkane thiol. The structural properties of the monolayer protected gold nanoparticles such us overall shape, organization and conformation of the capping alkane thiol chains were found to be influenced by the capping density. The structural order of the thiol capped gold nanoparticles enhances with the increase in the surface coverage density. The specific heat capacity of the alkane thiol capped gold nanoparticles was found to increase linearly with the thiol coverage density. This may be attributed to the enhancement in the lattice vibrational energy. The present simulation results suggest, that the structural and thermal properties of the alkane thiol capped gold nanoparticles may be modified by the suitable selection of the SAM coverage density.

Magnetic Gold Confined in Ordered Mesoporous Titania Thin Films: A Noble Approach for Magnetic Devices.

In the past decade, the surprising magnetic behavior of gold nanoparticles has been reported. This unexpected property is mainly attributed both to size and surface effects. Mesoporous thin films are ideal matrices for metallic nanoparticles inclusion, because of their highly accessible and tailorable pore systems that lead to completely tunable chemical environments. Exploiting these features, we synthesized Au nanoparticles within mesoporous titania thin films (film thickness of ∼150 nm and pore diameter of ∼5 nm), and we studied their magnetic properties under confinement. Here, we present the results of the magnetization as a function of temperature and magnetic field for this system, which are consistent with the previously reported for free (unconfined) thiol-capped gold nanoparticles. The successful inclusion of stable magnetic Au nanoparticles within transparent mesoporous thin films opens the gates for the application of these nanocomposites in two-dimensional (2D) microdevices technology and magneto-optical devices.

Thiol-Capped Gold Nanoparticles Swell-Encapsulated into Polyurethane as Powerful Antibacterial Surfaces Under Dark and Light Conditions.

A simple procedure to develop antibacterial surfaces using thiol-capped gold nanoparticles (AuNPs) is shown, which effectively kill bacteria under dark and light conditions. The effect of AuNP size and concentration on photo-activated antibacterial surfaces is reported and we show significant size effects, as well as bactericidal activity with crystal violet (CV) coated polyurethane. These materials have been proven to be powerful antibacterial surfaces against both Gram-positive and Gram-negative bacteria. AuNPs of 2, 3 or 5 nm diameter were swell-encapsulated into PU before a coating of CV was applied (known as PU-AuNPs-CV). The antibacterial activity of PU-AuNPs-CV samples was tested against Staphylococcus aureus and Escherichia coli as representative Gram-positive and Gram-negative bacteria under dark and light conditions. All light conditions in this study simulated a typical white-light hospital environment. This work demonstrates that the antibacterial activity of PU-AuNPs-CV samples and the synergistic enhancement of photoactivity of triarylmethane type dyes is highly dependent on nanoparticle size and concentration. The most powerful PU-AuNPs-CV antibacterial surfaces were achieved using 1.0 mg mL−1 swell encapsulation concentrations of 2 nm AuNPs. After two hours, Gram-positive and Gram-negative bacteria were reduced to below the detection limit (>4 log) under dark and light conditions.

Charge Transfer at Hybrid Interfaces: Plasmonics of Aromatic Thiol-Capped Gold Nanoparticles.

Although gold nanoparticles stabilized by organic thiols are the building blocks in a wide range of applications, the role of the ligands on the plasmon resonance of the metal core has been mostly ignored until now. Herein, a methodology based on the combination of spectroscopic ellipsometry and UV-vis spectroscopy is applied to extract dielectric functions of the different components. It is shown that aromatic thiols allow a significant charge transfer at the hybrid interface with the s and d bands of the gold core that yields "giant" red shifts of the plasmon band, up to 40 nm for spherical particles in the size range of 3-5 nm. These results suggest that hybrid nanoplasmonic devices may be designed through the suitable choice of metal core and organic components for optimized charge exchange.