Surface Functionalization Of Gold Nanoparticles Research Articles

On-demand catalysed n-doping of organic semiconductors.

A new approach to control the n-doping reaction of organic semiconductors is reported using surface-functionalized gold nanoparticles (f-AuNPs) with alkylthiols acting as the catalyst only upon mild thermal activation. To demonstrate the versatility of this methodology, the reaction of the n-type dopant precursor N-DMBI-H with several molecular and polymeric semiconductors at different temperatures with/without f-AuNPs, vis-à-vis the unfunctionalized catalyst AuNPs, was investigated by spectroscopic, morphological, charge transport, and kinetic measurements as well as, computationally, the thermodynamic of catalyst activation. The combined experimental and theoretical data demonstrate that f-AuNPs is inactive at room temperature both in solution and in the solid state, catalyst activation occurs rapidly at mild temperatures (~ 70 °C) and the doping reaction completes in few seconds affording large electrical conductivities (~ 10 - 140 S cm-1). The implementation of this methodology enables the use of semiconductor+dopant+catalyst solutions, will broaden the use of the corresponding n-doped films in opto-electronic devices such as thin-film transistors, electrochemical transistors, solar cells, and thermoelectrics well as guide the design of new catalysts.

Gold and Silver Nanoparticles as Biosensors: Characterization of Surface and Changes in the Adsorption of Leucine Dipeptide under the Influence of Substituent Changes.

Early detection of diseases can increase the chances of successful treatment and survival. Therefore, it is necessary to develop a method for detecting or sensing biomolecules that cause trouble in living organisms. Disease sensors should possess specific properties, such as selectivity, reproducibility, stability, sensitivity, and morphology, for their routine application in medical diagnosis and treatment. This work focuses on biosensors in the form of surface-functionalized gold (AuNPs) and silver nanoparticles (AgNPs) prepared using a less-time-consuming, inexpensive, and efficient synthesis route. This allows for the production of highly pure and stable (non-aggregating without stabilizers) nanoparticles with a well-defined spherical shape, a desired diameter, and a monodisperse distribution in an aqueous environment, as confirmed by transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDS), X-ray diffraction (XRD), photoelectron spectroscopy (XPS), ultraviolet-visible (UV-VIS) spectroscopy, and dynamic light scattering (DLS). Thus, these nanoparticles can be used routinely as biomarker sensors and drug-delivery platforms for precision medicine treatment. The NPs' surface was coated with phosphonate dipeptides of L-leucine (Leu; l-Leu-C(R1)(R2)PO3H2), and their adsorption was monitored using SERS. Reproducible spectra were analyzed to determine the orientation of the dipeptides (coating layers) on the nanoparticles' surface. The appropriate R2 side chain of the dipeptide can be selected to control the arrangement of these dipeptides. This allows for the proper formation of a layer covering the nanoparticles while also simultaneously interacting with the surrounding biological environment, such as cells, tissues, and biological fluids.

Induction of autophagy-dependent and caspase- and microtubule-acetylation-independent cell death by phytochemical-stabilized gold nanopolygons in colorectal adenocarcinoma cells.

Collective functionalization of the phytochemicals of medicinal herbs on nanoparticles is emerging as a potential cancer therapeutic strategy. This study presents the facile synthesis of surface-functionalized gold nanoparticles using Bacopa monnieri (Brahmi; Bm) phytochemicals and their therapeutically relevant mechanism of action in the colorectal cancer cell line, HT29. The nanoparticles were characterized using UV-visible spectroscopy, TEM-EDAX, zeta potential analysis, TGA, FTIR and 1H NMR spectroscopy, and HR-LC-MS. The particles (Bm-GNPs) were of polygonal shape and were stable against aggregation. They entered the target cells and inhibited the viability and clonogenicity of the cells with eight times more antiproliferative efficacy (25 ± 1.5 μg mL-1) than Bm extract (Bm-EX). In vitro studies revealed that Bm-GNPs bind tubulin (a protein crucial in cell division and a target of anticancer drugs) and disrupt its helical structure without grossly altering its tertiary conformation. Like other antitubulin agents, Bm-GNPs induced G2/M arrest and ultimately killed the cells, as confirmed using flow cytometry analyses. ZVAD-FMK-mediated global pan-caspase inhibition and the apparent absence of cleaved caspase-3 in treated cells indicated that the death did not involve the classic apoptosis pathway. Cellular ultrastructure analyses, western immunoblots, and in situ immunofluorescence visualization of cellular microtubules revealed microtubule-acetylation-independent induction of autophagy as the facilitator of cell death. Together, the data indicate strong antiproliferative efficacy and a possible mechanism of action for these designer nanoparticles. Bm-GNPs, therefore, merit further investigations, including preclinical evaluations, for their therapeutic potential as inducers of non-apoptotic cell death.

Surface Functionalization of Gold Nanoparticles for Targeting the Tumor Microenvironment to Improve Antitumor Efficiency.

Gold nanoparticles (AuNPs) have undergone significant research for their use in the treatment of cancer. Numerous researchers have established their potent antitumor properties, which have greatly impacted the treatment of cancer. AuNPs have been used in four primary anticancer treatment modalities, namely radiation, photothermal therapy, photodynamic therapy, and chemotherapy. However, the ability of AuNPs to destroy cancer is lacking and can even harm healthy cells without the right direction to transport them to the tumor microenvironment. Consequently, a suitable targeting technique is needed. Based on the distinct features of the human tumor microenvironment, this review discusses four different targeting strategies that target the four key features of the tumor microenvironment, including abnormal vasculature, overexpression of specific receptors, an acidic microenvironment, and a hypoxic microenvironment, to direct surface-functionalized AuNPs to the tumor microenvironment and increase antitumor efficacies. In addition, some current completed or ongoing clinical trials of AuNPs will also be discussed below to further reinforce the concept of using AuNPs in anticancer therapy.

Development of a coarse-grained model for surface-functionalized gold nanoparticles: towards an accurate description of their aggregation behavior.

Understanding the dispersion stability and aggregation propensity of self-assembled monolayer gold NPs at a molecular level is crucial to guide their rational design and to inform about the optimal surface functionalization for specific applications. To reach this goal, in silico modeling via coarse-grained (CG) molecular dynamics (MD) simulations is a fundamental tool to complement the information acquired from experimental studies since CG modeling allows to get a deep knowledge of the molecular interactions that take place at the nanoscale in this kind of systems. Unfortunately, current CG models of monolayer-protected AuNPs present several drawbacks that limit their accuracy in certain scenarios. We here develop a CG model that is fully compatible and extends the SPICA/SDK (Shinoda-DeVane-Klein) force field. Our model allows reproducing the behavior of AuNPs functionalized with hydrophobic as well as charged and more hydrophilic ligands. This model improves upon results obtained with previously derived CG force fields and successfully describes NPs aggregation and self-assembly in aqueous solution.

Aqueous Synthesis of the Tiopronin-Capped Gold Nanoclusters/Nanoparticles with Precise Size Control via Deprotonation of the Ligand

Gold nanoparticles have led to numerous advances in nanomaterial-based sensors and biomedical technologies owing to their chemical inertness and outstanding physiochemical and optical properties. Gold nanoparticles are still considered one of the most promising types of nanomaterials in various biomedical fields, including drug delivery, cancer therapy, biomolecule detection, and high-accuracy diagnosis. Surface functionalization of gold nanoparticles with various ligands modifies the physicochemical properties of the surface, thereby improving the biocompatibility and uptake efficiency of a living system. Tiopronin, one of the most commonly used ligands for gold nanoparticles, has both thiol and carboxyl functional groups that can be easily attached to various biomolecules. However, the conventional method of synthesizing tiopronin-capped gold nanoclusters using methanol and acetic acid as a solvent requires a laborious and time-consuming dialysis process to remove methanol and acetic acid. In this study, we demonstrate a novel and simple aqueous synthesis method to obtain tiopronin-capped gold nanoclusters/nanoparticles with precise size control in the sub-nanometer to nanometer range. The main advantage of our synthesis method is that it does not require a dialysis process because it uses water as a solvent. The boron byproduct produced during the synthesis can be removed with a simple volatilization process. Moreover, we characterized the physical morphologies, photoelectronic properties, hydrodynamic size, and crystal structure of the tiopronin-capped gold nanoclusters/nanoparticles using transmission electron microscopy, spectrophotometry, fluorescence spectrometry, dynamic light scattering, zeta potential, and X-ray diffraction.

Cost effective synthesis approach for green food packaging coating by gallic acid conjugated gold nanoparticles from Caesalpinia pulcherrima extract

Reactive oxygen species (ROS) are the most threatening element for shelf life of packaged food. Mainly increase ROS is related to enzymatic, photochemical and pathogen action in the packaged food. In this study the cascade in ROS is observed in the presence of gold nanoparticles (AuNPs) conjugated with gallic acid. This is an efficient and promising approach for decreasing oxidative damage and physiological deterioration of packaged food. Firstly, the amine stabilized AuNPs were synthesized to meet the demand of high stability and long shelf-life. The surface functionalization of gold nanoparticles with gallic acid from extract of Caesalpinia pulcherrima to get gallic acid conjugated AuNPs (GA-AuNPs) reduces the toxicity of chemically stabilized AuNPs. Characterization techniques like dynamic light scattering, SEM, UV–vis spectroscopy evaluated morphology and electrochemical technique such as cyclic voltammetry (CV) estimated free radical scavenging by GA-AuNPs. The antimicrobial and antioxidant properties for GA-AuNPs were also investigated for pure gallic acid (GA) and its derivatives. The excellency of GA-AuNPs for free radical scavenging was proved by remarkable shift in peak potential and decrease in peak current with high binding constant (Kb) value of 1.99 M−1. Moreover, a lower IC50 value 4 × 10−9 g/mL synergistically contributes to higher antioxidant coefficient (Ka) against superoxide radical (O2-∙). The potential free radical scavenging ability and green catalytic action against microbes attributes GA-AuNPs the most suitable food packaging lining in food industry without any side effect.

Monovalent ion-mediated charge-charge interactions drive aggregation of surface-functionalized gold nanoparticles.

Monolayer-protected metal nanoparticles (NPs) are not only promising materials with a wide range of potential industrial and biological applications, but they are also a powerful tool to investigate the behaviour of matter at nanoscopic scales, including the stability of dispersions and colloidal systems. This stability is dependent on a delicate balance between attractive and repulsive interactions that occur in the solution, and it is described in quantitative terms by the classic Derjaguin-Landau-Vewey-Overbeek (DLVO) theory, that posits that aggregation between NPs is driven by van der Waals interactions and opposed by electrostatic interactions. To investigate the limits of this theory at the nanoscale, where the continuum assumptions required by the DLVO theory break down, here we investigate NP dimerization by computing the Potential of Mean Force (PMF) of this process using fully atomistic MD simulations. Serendipitously, we find that electrostatic interactions can lead to the formation of metastable NP dimers at physiological ion concentrations. These dimers are stabilized by complexes formed by negatively charged ligands belonging to distinct NPs that are bridged by positively charged monovalent ions present in solution. We validate our findings by collecting tomographic EM images of NPs in solution and by quantifying their radial distribution function, that shows a marked peak at interparticle distance comparable with that of MD simulations. Taken together, our results suggest that not only van der Waals interactions, but also electrostatic interactions mediated by monovalent ions at physiological concentrations, contribute to attraction between nano-sized charged objects at very short length scales.

Mimosine functionalized gold nanoparticles (Mimo-AuNPs) suppress β-amyloid aggregation and neuronal toxicity

Evidence suggests that increased level/aggregation of beta-amyloid (Aβ) peptides initiate neurodegeneration and subsequent development of Alzheimer's disease (AD). At present, there is no effective treatment for AD. In this study, we reported the effects of gold nanoparticles surface-functionalized with a plant-based amino acid mimosine (Mimo-AuNPs), which is found to cross the blood-brain barrier, on the Aβ fibrillization process and toxicity. Thioflavin T kinetic assays, fluorescence imaging and electron microscopy data showed that Mimo-AuNPs were able to suppress the spontaneous and seed-induced Aβ1-42 aggregation. Spectroscopic studies, molecular docking and biochemical analyses further revealed that Mimo-AuNPs stabilize Aβ1-42 to remain in its monomeric state by interacting with the hydrophobic domain of Aβ1-42 (i.e., Lys16 to Ala21) there by preventing a conformational shift towards the β-sheet structure. Additionally, Mimo-AuNPs were found to trigger the disassembly of matured Aβ1-42 fibers and increased neuronal viability by reducing phosphorylation of tau protein and the production of oxyradicals. Collectively, these results reveal that the surface-functionalization of gold nanoparticles with mimosine can attenuate Aβ fibrillization and neuronal toxicity. Thus, we propose Mimo-AuNPs may be used as a potential treatment strategy towards AD-related pathologies.

Phenol-Boronic surface functionalization of gold nanoparticles; to induce ROS damage while inhibiting the survival mechanisms of cancer cells

The natural phenolic molecule caffeic acid, show promising effects on biological systems as an anti/pro-oxidant, anti-cancer, and anti-inflammatory agent. In nanoparticle functionalization designs, most organic nanoparticle coatings are utilized only for their ability to carry chemotherapeutics and targeting ligand. In this study, UV-light and auto-oxidation polymerization of caffeic acid on top of as-prepared gold nanoparticles was utilized to bring about a 5 nm multifunctional coating. The resulting polycaffeic acid (PCA) coating was used to conjugate both boronic acid containing compounds, chemotherapeutic bortezomib (BTZ) and cancer targeting ligand folate, while inducing mitochondrial reactive oxygen species that can damage intracellular proteins and DNA. This complements the drug payload, bortezomib’s cell survival inhibition properties. The drug, targeting ligand, and coating complexation are all pH cleavable under acidic pH condition (<5.0) which can be found in a tumor and endosomal microenvironment. The in vitro and in vivo experiments demonstrated cancer cytotoxicity and tumor inhibiting properties of the developed nanomedicine.

The interplay between surface-functionalized gold nanoparticles and negatively charged lipid vesicles.

The comprehensive understanding of the interactions between gold nanoparticles (AuNPs) and phospholipid vesicles has important implications in various biomedical applications; however, this is not yet well understood. Here, coarse-grained molecular dynamics (CGMD) simulations were performed to study the interactions between functionalized AuNPs and negatively charged lipid vesicles, and the effects of the surface chemistry and surface charge density (SCD) of AuNPs were analyzed. It is revealed that AuNPs with different surface ligands adhere to the membrane surface (anionic AuNPs) or get into the vesicle bilayer (hydrophobic and cationic AuNPs). Due to the loose arrangement of lipid molecules, AuNPs penetrate curved vesicle membranes more easily than planar lipid bilayers. Cationic AuNPs present three different interaction modes with the vesicle, namely insertion, partial penetration and complete penetration, which are decided by the SCD difference. Both hydrophobic interaction and electrostatic interaction play crucial roles in the interplay between cationic AuNPs and lipid vesicles. For the cationic AuNP with a low SCD, it gets into the lipid bilayer without membrane damage through the hydrophobic interaction, and it is finally stabilized in the hydrophobic interior of the vesicle membrane in a thermodynamically stable "snorkeling" configuration. For the cationic AuNP with a high SCD, it crosses the vesicle membrane and gets into the vesicle core through a membrane pore induced by strong electrostatic interaction. In this process, the membrane structure is destroyed. These findings provide a molecular-level understanding of the interplay between AuNPs and lipid vesicles, which may further expand the application of functional AuNPs in modern biomedicine.

Calcium based siRNA coating: a novel approach for knockdown of HER2 gene in MCF-7 cells using gold nanoparticles

Surface functionalization of nanoparticles (NPs) for therapeutic siRNA delivery into cancer cells has gained interest. The present study was designed for surface functionalization of gold nanoparticles (AuNPs) for efficient siRNA delivery and knockdown in cancer cells. In order to achieve this objective, AuNPs were coated with HER2-siRNA in the presence of 11-mercaptoundecanoic acid (11-MUA), calcium chloride (CaCl2) and polyethyleneimine (PEI) in alternate charge bearing successive layers. MCF-7 cells were cultured and transfected with fabricated assembly of AuNPs. Cytotoxicity analysis revealed that the half inhibitory concentration (IC50) for the formulation was 45.35 nM . Total RNA was isolated from transfected cells, reverse transcribed into complementary DNA (cDNA) and real-time polymerase chain reaction (RT-PCR) was performed. The RT-PCR based delta-delta Ct analysis in treated cells revealed a significant 18.94 times decrease (p&lt;0.001) in the expression of HER2 gene standardized with ACTB housekeeping gene as compared to untreated cells, which makes this formulation a potent approach for siRNA delivery and gene knockout.

Design, Synthesis, Computational and Biological Evaluation of 4-Amino-3,5-dimercapto-1,2,4-triazole Surface Functionalized Gold Nanoparticles

Gold nanoparticles (AuNPs) are an obvious choice for rapid advance in nanotechnology due to their amenability of synthesis, functionalization and less toxicity. Functionalization of AuNP surface with 4-amino-3,5-dimercapto-1,2,4-triazole (ADMT) ligand as ADMT-AuNPs was investigated with the aim to probe the suitability of innovative product to develop new antibacterial and anticancer strategies. Various characterization studies like UV-spectra, Zeta size, Zeta potential, XRD, SEM, TEM and FTIR results of AuNPs and ADMT-AuNPs have been performed to study the structural and electronic properties. The studies revealed that the functionalized nanoparticles are highly crystalline in nature with the sizes ranging between 20-22 and 50-55 nm for AuNPs and ADMT-AuNPs, respectively with FCC structures. The characterization data reveals that the synthesized nanoparticles are stable and presence of strong interactions between the metallic surface and the organic ligand. Further, ADMT-AuNPs showed good antibacterial activity against Gram-positive and Gram-negative bacteria. MTT assay exhibited the cell viability with an IC50 value of 45.32 % v/v for ADMT-AuNPs against breast adenocarcinoma (MCF-7) cell lines. Molecular characterization i.e., in silico docking analysis helped in identifying and organizing the structural similarity/diversity at the molecular level. The in silico study indicated that the structure S1a has good glide score and glide energy for H-bonding among the possible conformations against bacterial and breast cancer protein. Molecular docking studies confirmed the introduction of conformational changes that are essential to surpass the potential energy barriers of ADMT-AuNPs for biocompatibility and proved that they hold a promising future in the medical field.

Green synthesis of multifunctional PEG-carboxylate π back-bonded gold nanoconjugates for breast cancer treatment.

BackgroundSurface functionalization of gold nanoparticles (AuNPs) has emerged as a promising field of research with enormous biomedical applications. The folate (FA)-attached polymer-gold nanoconjugates play vital role in targeting the cancer cells.MethodsAuNPs were synthesized by using di- or tri-carboxylate-polyethylene glycol (PEG) polymers, including citrate-PEG (CPEG), malate-PEG (MAP), and tartrate-PEG (TAP), as a reducing and stabilizing agent. After synthesis of polymer-AuNPs, the freely available hydroxyl and carboxylate groups of CPEG, MAP, and TAP were used to attach a cancer cell-targeting agent, FA, via a 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxy succinimide coupling reaction to obtain FA-CPEG-AuNP, FA-MAP-AuNP, and FA-TAP-AuNP nanocon-jugates, respectively. The 5-fluorouracil (5FU) was attached to π back-bonded carbonyl oxygens of the nanoconjugates, and the in vitro drug release profile was studied by high pressure liquid chromatography. Biocompatibility profiles of the FA-CPEG-AuNP, FA-MAP-AuNP, and FA-TAP-AuNP nanoconjugates were investigated using adult human dermal fibroblasts. Anti-breast cancer activity of 5FU-loaded nanoconjugates was investigated using MCF-7 breast cancer cells.ResultsX-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy analyses confirmed that AuNPs attached to CPEG, MAP, or TAP via the formation of π back bonding between AuNPs and the ester carbonyl group. The π back-bonded nanoconjugates exhibited sustained release of 5FU up to 27 days. FA-MAP-AuNPs exhibited an IC50 at 5 µg/mL, while FA-CPEG-AuNPs and FA-TAP-AuNPs showed the IC50 at 100 µg/mL toward MCF-7 cancer cells.ConclusionThe developed polymer π back-bonded multifunctional gold nanoconjugates could be used as a potential drug delivery system for targeting MCF-7 cancer cells.

Curvature-driven adsorption of cationic nanoparticles to phase boundaries in multicomponent lipid bilayers.

Understanding the interactions between surface-functionalized gold nanoparticles (NPs) and lipid bilayers is necessary to guide the design of NPs for biomedical applications. Recent experiments found that cationic NPs adsorb more strongly to phase-separated multicomponent lipid bilayers than single-component liquid-disordered bilayers, suggesting that phase separation affects NP-bilayer interactions. In this work, we use coarse-grained molecular dynamics simulations to investigate the effect of lipid phase behavior on the adsorption of small cationic NPs. We first determined the free energy change for adsorbing a NP to one-phase liquid-disordered and one-phase liquid-ordered bilayers. The simulations indicate that NP adsorption depends on a competition between favorable NP-lipid interactions and the unfavorable curvature deformation of the bilayer, resulting in stronger interactions with the liquid-disordered bilayer due to its lower bending modulus. We then measured the free energy change associated with moving a NP across the surface of a phase-separated bilayer and identified a free energy minimum at the phase boundary. The free energy minimum is attributed to the thickness gradient between the two phases that enables favorable NP-lipid interactions without necessitating large curvature deformations. The simulation results thus indicate that the intrinsic curvature present at phase boundaries drives preferential interactions with surface-adsorbed NPs, providing new insight into the forces that drive NP behavior at multicomponent, phase-separated lipid bilayers.

Role of Citrate and NaBr at the Surface of Colloidal Gold Nanoparticles during Functionalization

A molecular understanding of the ligand shell and the functionalization process is essential for the development of surface-functionalized gold nanoparticles (AuNPs). Obviously, the initial ligand ...

A Spectral Probe for Detection of Aluminum (III) Ions Using Surface Functionalized Gold Nanoparticles.

A simple green route has been developed for the synthesis of casein peptide functionalized gold nanoparticles (AuNPs), in which casein peptide acts as a reducing as well as the stabilizing agent. In this report, AuNPs have been characterized on the basis of spectroscopic and microscopic results; which showed selective and sensitive response toward Al3+ in aqueous media, and Al3+ induces aggregation of AuNPs. The sensing study performed for Al3+ revealed that the color change from red to blue was due to a red-shift in the surface plasmon resonance (SPR) band and the formation of aggregated species of AuNPs. The calibration curve determines the detection limit (LOD) for Al3+ about 20 ppb (0.067 μM) is presented using both decrease and increase in absorbance at 530 and 700 nm, respectively. This value is considerably lower than the higher limit allowed for Al3+ in drinking water by the world health organization (WHO) (7.41 μM), representing enough sensitivity to protect water quality. The intensity of the red-shifted band increases with linear pattern upon the interaction with different concentrations of Al3+, thus the possibility of producing unstable AuNPs aggregates. The method is successfully used for the detection of Al3+ in water samples collected from various sources, human urine and ionic drink. The actual response time required for AuNPs is about 1 min, this probe also have several advantages, such as ease of synthesis, functionalization and its use, high sensitivity, and enabling on-site monitoring.

Gum ghatti mediated, one pot green synthesis of optimized gold nanoparticles: Investigation of process-variables impact using Box-Behnken based statistical design

Due to unique inherent catalytic characteristics of different size, shape and surface functionalized gold nanoparticles, their potential applications, are being explored in various fields such as drug delivery, biosensor, diagnosis and theranostics. However conventional process for synthesis of these metallic nanoparticles utilizes toxic reagents as reducing agents, additional capping agent for stability as well as surface functionalization for drug delivery purposes. Hence, in this work suitability of gum Ghatti for reducing, capping and surface functionalization during the synthesis of stable Gold nanoparticles were duly explored. Role and impact of key process variables i.e. volume of chloroauric acid solution, gum solution and temperature at their respective three different levels, as well as mechanism of formation of optimized gold nanoparticles were also investigated using Box- Behnken design. These novel synthesized optimized Gold nanoparticles were further characterized by UV spectrophotometer for its surface plasmon resonance (SPR) at around ∼530nm, dynamic light scattering (DLS) for its hydrodynamic size (112.5nm), PDI (0.222) and zeta potential (−21.3mV) while, transmission electron microscopy (TEM) further revealed surface geometry of these nanoparticles being spherical in shape.

Non-Gaussian Resistance Fluctuations in Gold-Nanoparticle-Based Gas Sensors: An Appraisal of Different Evaluation Techniques.

Volatile organic compounds, such as formaldehyde, can be used as biomarkers in human exhaled breath in order to non-invasively detect various diseases, and the same compounds are of much interest also in the context of environmental monitoring and protection. Here, we report on a recently-developed gas sensor, based on surface-functionalized gold nanoparticles, which is able to generate voltage noise with a distinctly non-Gaussian component upon exposure to formaldehyde with concentrations on the ppm level, whereas this component is absent, or at least much weaker, when the sensor is exposed to ethanol or to pure air. We survey four different statistical methods to elucidate a non-Gaussian component and assess their pros and cons with regard to efficient gas detection. Specifically, the non-Gaussian component was clearly exposed in analysis using level-crossing parameters, which require nothing but a modest computational effort and simple electronic circuitry, and analogous results could be reached through the bispectrum function, albeit with more intense computation. Useful information could be obtained also via the Lévy-stable distribution and, possibly, the second spectrum.

3D Time-lapse Imaging and Quantification of Mitochondrial Dynamics

We present a 3D time-lapse imaging method for monitoring mitochondrial dynamics in living HeLa cells based on photothermal optical coherence microscopy and using novel surface functionalization of gold nanoparticles. The biocompatible protein-based biopolymer coating contains multiple functional groups which impart better cellular uptake and mitochondria targeting efficiency. The high stability of the gold nanoparticles allows continuous imaging over an extended time up to 3000 seconds without significant cell damage. By combining temporal autocorrelation analysis with a classical diffusion model, we quantify mitochondrial dynamics and cast these results into 3D maps showing the heterogeneity of diffusion parameters across the whole cell volume.