Surface-modified Gold Nanoparticles Research Articles

Abstract 496: Insights into correlation between nanomechanical properties and cytokines expression during gold nanoparticle endocytosis

Abstract Gold nanoparticles for therapeutic interventions have become a widely popular source due to the ease in surface chemistry available for modification. Several studies undertaken focusses on the size, shape of nanoparticles as well as the signaling mechanisms and yet, knowledge regarding the alteration in membrane dynamics such as nanomechanical properties and cytokines involved during their uptake has not been studies before. To overcome the knowledge deficit, we employed atomic force microscopy and qRT-PCR techniques to acquire nanomechanical attributes and cytokines expressions respectively, in Panc-1 and AsPC-1 cell lines treated with surface modified gold nanoparticles for 1- and 24-hours’ time point. In nanomechanics paradigm, impetus was given on both linear attributes such as membrane stiffness, deformation, and adhesion as well as non-linear attributes such as drained Poisson’s ratio, diffusion coefficient and pore size. On the other hand, qRT-PCR technique yielded alterations in relative mRNA expressions of pro-tumorigenic cytokines such as CCL2, CXCL1, CXCL2, CXCL3, IL8, IL11, IL18 and TGFβ-1. Further, using Pearson’s correlation, we deduced the dependency between nanomechanical properties and cytokines expressions. We evaluated several criteria such as receptor dependent vs independent, PEGylated vs non-PEGylated and 1 hr vs 24hrs, to deduce correlations between cytokines and nanomechanical attributes. In Panc-1 cell line, we observed that PEGylation vs non-PEGylation of gold nanoparticles demonstrated most significant correlations, whereas in AsPC-1 cell line, receptor independent mechanism played a pivotal role in establishing significant correlations. For instance, D_C and P_D were highly correlated with CXCL1, CXCL2 and TGFβ-1 when non-PEGylated gold nanoparticles were up taken by Panc-1 cells. Similarly, D_C and P_D were highly correlated consistently with our cytokine panel except for TGFβ-1. In AsPC-1 cell line, deformation was significantly correlated with CCL2, CXCL2, CXCL3 and IL-8 whereas, D_C and P_D were significantly correlated with CCL2, CXCL1, CXCL3, IL-18 and TGFβ-1 in receptor independent scenario. This study demonstrated that during the uptake of gold nanoparticles, non-linear nanomechanical attributes are detrimental over linear attributes. Moreover, Surface modified gold nanoparticles induce varying levels of alteration in pro-tumorigenic cytokines. Taken together, this study boosts our insights into correlations describing cytokines regulating nanomechanical attributes in endocytosis paradigm. Citation Format: Tanmay Kulkarni, Enfeng Wang, Ramcharan Singh Angom, Debabrata Mukhopadhyay, Santanu Bhattacharya. Insights into correlation between nanomechanical properties and cytokines expression during gold nanoparticle endocytosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 496.

Surface-modified gold nanoparticles: A novel chemical probe for precise fluorescent detection of aluminium (Al3+) ions; investigating DFT insights and molecular logic gate behaviour

Trivalent metal cation fluorescence chemosensors are one of the most important areas of research because of their rarity. The necessity for easy-to-synthesize molecular chemosensors and to immobilize them on materials platform are enhancing continually. In this paper, we report the rapid sensing of Al3+ ion recognition by naphthalene derivative (N1) and tethered with gold nanoparticles (N1-AuNps). The cysteine-carrying naphthalene derivative is synthesized (Receptor-N1) and it forms a self-assembled monolayer on gold nanoparticles through the thiol moiety (N1-AuNPs). The structure of the synthesized receptor and the chemosensor assembled with AuNPs are characterized using spectroscopic and imaging techniques. On the gold nanoparticles, the surface-assembled compound highly selectively binds with Al3+ ion in the aqueous medium compared with a free receptor (N1). We present an improved colorimetric method that offers both high sensitivity and rapid detection for transition metal ions, specifically Al3+ ions. The determination of the binding stoichiometry and binding ratio between N1 / N1-AuNPs and Al3+ ion was achieved through the utilization of Jobs' plot and B-H plot which confirmed a 1:1 ratio. The binding phenomenon between N1-AuNPs and Al3+ ion has been ascertained to be predominantly according to the limited PET with CHEF impact technique. The N1-AuNPs chemosensor responds to H+ and Al3+ ions by demonstrating XOR molecular logic gate functionality and operating across a wide pH range. The nanoparticle-tethered chemosensor presents an effective system that can be employed in Al3+ ion sensing. The addition of Na2EDTA to the [N1-AuNPs - Al3+] complex solution caused a quenching of the fluorescence emission, which provides evidence of the reversible nature of the chemosensor. To gain further insights into the binding mode of Al3+ with N1-AuNPs, quantum mechanical investigations using density functional theory (TDDFT) have been conducted. We evaluated the effectiveness of our methodology for quantifying Al3+ ions in the water waste produced by significant industrial reactions.

Single-electron transfer reactions on surface-modified gold plasmons

Photoredox catalysis's relevance in organic synthesis research and innovation will increase in the coming decades. However, the processes rely almost exclusively on expensive noble metal complexes, most notably iridium complexes, to absorb light and transfer a single charge to a substrate or a catalyst to initiate cascade transformations. Light-triggered plasmon resonances generate a non-Fermi-Dirac energy distribution with many hot carriers that decay in ∼1 ps. Their ultrafast relaxation makes performing single electron transfer (SET) transformations challenging. Herein, a novel photosystem is proposed based on surface-modified gold nanoparticles (aka plasmon "molecularization"), which improved charge separation and, more importantly, enabled SET reactions, expanding the portfolio of photocatalysts available for photoredox catalysis. The photosystem was made into an electrode, permitting its use in photoelectrochemical arrangements that leverage electro- and photo-chemical approaches' benefits and chemical engineering solutions, helping the synthetic chemistry efforts towards greener synthesis and synthesis of more complex structures on a scale.

An application of carbohydrate polymers-based surface-modified gold nanoparticles for improved target delivery to liver cancer therapy - A systemic review

Gold nanoparticles have been broadly investigated as cancer diagnostic and therapeutic agents. Gold nanoparticles are a favorable drug delivery vehicle with their unique subcellular size and good biocompatibility. Chitosan, agarose, fucoidan, porphyran, carrageenan, ulvan and alginate are all examples of biologically active macromolecules. Since they are biocompatible, biodegradable, and irritant-free, they find extensive application in biomedical and macromolecules. The versatility of these compounds is enhanced because they are amenable to modification by functional groups like sulfation, acetylation, and carboxylation. In an eco-friendly preparation process, the biocompatibility and targeting of GNPs can be improved by functionalizing them with polysaccharides. This article provides an update on using carbohydrate-based GNPs in liver cancer treatment, imaging, and drug administration. Selective surface modification of several carbohydrate types and further biological uses of GNPs are focused on.

Astatine-211-Labeled Gold Nanoparticles for Targeted Alpha-Particle Therapy via Intravenous Injection.

Alpha-particle radiotherapy has gained considerable attention owing to its potent anti-cancer effect. 211At, with a relatively short half-life of 7.2 h, emits an alpha particle within a few cell diameters with high kinetic energy, which damages cancer cells with high biological effectiveness. In this study, we investigated the intravenous injection of 211At-labeled gold nanoparticles (AuNPs) for targeted alpha-particle therapy (TAT). Different kinds of surface-modified gold nanoparticles can be labeled with 211At in high radiochemical yield in 5 min, and no purification is necessary. The in vivo biodistribution results showed the accumulation of 5 nm 211At-AuNPs@mPEG at 2.25% injection dose per gram (% ID/g) in tumors within 3 h via the enhanced permeability and retention (EPR) effect. Additionally, we observed a long retention time in tumor tissues within 24 h. This is the first study to demonstrate the anti-tumor efficacy of 5 nm 211At-AuNPs@mPEG that can significantly suppress tumor growth in a pancreatic cancer model via intravenous administration. AuNPs are satisfactory carriers for 211At delivery, due to simple and efficient synthesis processes and high stability. The intravenous administration of 5 nm 211At-AuNPs@mPEG has a significant anti-tumor effect. This study provides a new framework for designing nanoparticles suitable for targeted alpha-particle therapy via intravenous injection.

Design of a Ratiometric Plasmonic Biosensor for Herceptin Detection in HER2-Positive Breast Cancer.

Breast cancer is the most common cause of cancer death in women; therefore, its early detection and treatment are crucial. To achieve this goal, we designed an optical sensor based on direct interaction of trastuzumab [Herceptin (HER)], a monoclonal antibody used to treat HER2-positive breast cancer, with plasmonic nanoparticles. Surface-modified gold nanoparticles (AuNPs) have gained considerable attention in biosensing techniques over the last years, which actuated these nanoparticles to the heart of various biosensing notions. We have exploited the localized surface plasmon resonance (LSPR) of gold nanoparticles to determine HER in human serum. AuNPs were decorated with negatively charged citrate ions, yielding enhanced direct-surface interaction with HER antibodies. The AuNPs are mixed with silver nanoparticles (AgNPs) in an optimized ratio to increase selectivity and sensitivity further. AuNPs detect the HER antibodies using LSPR, whereas AgNPs help monitor interferences' effect on the sensing media. The three effective factors in HER sensing, including the nanoparticle ratio, temperature, and pH were optimized via response surface methodology (RSM) based on the central composite design (CCD). The sensor's response toward HER was achieved in the linear range of 0.5 × 10-7 to 40 × 10-7 M with the detection limit of 3.7 × 10-9 M and relative standard deviation (RSD) less than 5%. The selectivity of the LSPR sensor was assessed by monitoring its response toward HER in the presence of other biological molecules with similar physicochemical properties. Rapid response time (less than 1 min), selectivity, and the simplicity of the developed LSPR-based sensor are the key advantages of the developed sensor.

Cinnamomum verum-derived bioactives-functionalized gold nanoparticles for prevention of obesity through gut microbiota reshaping.

Existing drugs have limited success in managing obesity in human due to their low efficacy and severe side-effects. Surface-modified gold nanoparticles have now received considerable attention of researchers for efficient biomedical applications owing to their superior uptake by cells, biocompatibility, hydrophilicity and non-immunogenicity. Here we prepared Cinnamomum verum derived bioactives-functionalized gold nanoparticles (Au@P-NPs) and assessed their impact on obesity and related immune-metabolic complications in high-fat diet (HFD)-induced obese mice using metabolic experiments along with 16S RNA gene-based gut microbial profiling and faecal microbiota transplantation (FMT). Au@P-NPs treatment prevented weight gain, decreased fat deposition, reduced metabolic inflammation and endotoxaemia in HFD-fed mice. Au@P-NPs-treated group exhibited better glucose tolerance and insulin sensitivity than HFD-fed control mice, and got completely protected against hepatic steatosis. These impacts were related to increased energy expenditure and enhanced Ucp1 expression in the brown adipose tissues of Au@P-NPs-administered animals, which strongly linked with the mRNA expression of the membrane bile acid receptor TGR5. Treatment of HFD-fed animals with Au@P-NPs altered plasma bile acid profile, and increased Akkermansia muciniphila and decreased Lactobacillus populations in the faeces. Au@P-NPs-treated animals revealed altered plasma bile acid profile, and increased Akkermansia muciniphila and decreased Lactobacillus populations in the faeces. FMT experiments showed lesser weight gain and greater energy expenditure in the mice fed with faecal suspension from Au@P-NPs-treated animals than that from HFD-fed mice. These results clearly establish that gold nanoparticles functionalized with bioactive compounds of C. verum have high potential to be an anti-obesity drug.

Electrorheological Effect of Gold Nanoparticles Coated with Fluorescent Mesogenic Groups Dispersed in Nematic Liquid Crystal

The electrorheological (ER) properties of composite materials consisting of a nematic liquid crystal (LC) and gold nanoparticles (GNPs) coated with bistolane-based mesogenic groups were studied. The GNPs were coated by normal alkyl chains and the fluorescent LC compounds, of which the molecular structure was similar to that of the LC matrix. The dispersity of the GNPs in the nematic LC was investigated by polarizing optical microscopy (POM). In order to improve the ER effect of the composite, a simple strategy was investigated from the viewpoint of a material design in surface-modified GNPs by lateral substitution of the mesogenic groups. The presence of the GNPs in the nematic LC led to a slightly enhanced ER effect compared to that observed for only the nematic LC. This study demonstrates the potential of a hybrid system consisting of LCs and GNPs to yield a larger ER effect.

Biocompatibility of surface-modified gold nanoparticles towards red blood cells and haemoglobin

Studies related to corona formation have been carried out largely for proteins and nanomaterials, however specific studies about the synthesis of nano-systems with bio-benign surface designing and their biological effect on red blood cells (RBCs) lysis is still inadequate. Therefore, it is prime requisite to synthesize gold nanoparticles (AuNPs) which are free from harmful stabilizers to mitigate their biological nano-toxicology. In present work, we evaluate the absolute task, starting from the synthesis of surface designed AuNPs to in vitro physiochemical study of their concentration gradient effect on RBCs toxicity and thermal and structural stability of haemoglobin (Hb). Five-fold and multiple folds twinned AuNPs of different shapes, sizes and zeta-potential are prepared using two novel tryptophan based ionic liquids possessing tryptophan (Trp) group as reducing agent. From the results, it can be determined that both AuNPs are having negative charge fabrication with face centred cubic lattice. Subsequently, the hemolysis percentage results reveal the exceedingly biocompatible nature of AuNPs providing less than 3% hemolysis of cholinium tryptophan-based AuNPs ([CHO][Trp]AuNPs). Moreover, the secondary structure of Hb remains unaltered with no significant change in its thermal stability was observed even for higher concentration of AuNPs.

Electrostatically controlled plasmonic effects of gold nanoparticles with indigo-carmine functionation for rapid and straightforward colorimetric detection of Cu2+ ions.

A colorimetric sensor is fabricated for effective on-site monitoring of Cu2+ ions content based on the distance-dependent optical properties of gold nanoparticles-polyvinyl alcohol-citrate (Au-NPs-PVA-Cy) which plasmonic effect electrostatically was controlled by PVA-Cy stabilizing indigo-carmine (IC) functionalizing. The surface-modified gold nanoparticles were extremely stable with a strong affinity toward Cu2+ ions. Citrate ion was employed as a cross-linking agent for pairs of Au-NPs-PVA-Cy and IC for stabilizing coordination between Cu2+ ion and IC. The active materials were characterized by UV-Vis, SEM, DLS, XRD, FT-IR, and EDS analyses. The sensor response toward Cu2+ ion was found to be linear in the range of 0.0974 to 3.27μM with the limit of detection and quantification values of 0.021 and 0.07μM, respectively. The sensor represents good sensitivity and stability, promisingly suggesting this device for the accurate and repeatable determination of Cu2+ in real water samples. The effect of different foreign ions on the selectivity of the sensor was checked. The sensor has a long shelf life in comparison to other similar colorimetric sensors. Also, it shows a repeatable response with RSD% of 2.02%. Thus, the sensing of Cu2+ ions based on the electrostatically control plasmonic of Au-NPs-PVA-Cy was developed with proper signaling based on the color change from dark blue to light blue as readily seen by the naked eye. Furthermore, the efficient environmental applicability of this simple and rapid determination of the Cu2+ sensor is proved.

Functionalized gold nanostructures: promising gene delivery vehicles in cancer treatment.

Surface-modified gold nanoparticles are recognized as promising gene delivery vehicles in the treatment of cancer owing to their excellent biocompatibility with biomolecules (like DNA or RNA) and their unique optical and structural properties. In this context, this review article focuses on the diverse transfection abilities of the gene to the targeted cell on the basis of different shapes and sizes of gold nanoparticles in order to promote its effective expression for cancer treatment. In addition, recent trends in gold nanoparticle mediated gene silencing, gene delivery, detection and combinatory therapies are highlighted considering their cytotoxic effects on healthy human cells.

Alteration of MicroRNA Expression Profiles by Surface-Modified Gold Nanoparticles in Human Lung Adenocarcinoma Cells.

MicroRNAs that bind to mRNA are important post-transcriptional regulators that control gene expression by degradation or suppressing translation of target mRNAs. Several studies indicate that nanoparticles (NPs) induce alterations in microRNA expression relating to cell processes including cell development and progressive diseases. However, the alteration of microRNA expression by surface-modified gold nanoparticles (AuNPs) in A549 cells has not been reported. In order to investigate the patterns of microRNA expression, we analyzed data from microRNA arrays using cells treated with citrate- or chitosan-AuNPs. The results demonstrate that the expression of microRNA (hsa-miR-198) in cells treated with citrate-AuNPs significantly differed from non-treated cells, and the expression of 16 microRNAs in cells treated with chitosan-AuNPs significantly differed from non-treated cells. Furthermore, the predicted target genes of microRNAs were related to proliferation, apoptosis, migration, and cell differentiation, including the mitogen-activated protein kinase, ErbB, and Wnt signaling pathway. Thus, the alteration of microRNA expression profiles by citrate- and chitosan-AuNPs would mediate the regulation of the cell processes including cell survival, migration, and differentiation.

Papain-functionalized gold nanoparticles as heterogeneous biocatalyst for bioanalysis and biopharmaceuticals analysis

Surface-modified gold nanoparticles (GNPs) were synthesized via layer-by-layer process with alternating cationic polyallylamine and anionic poly(acrylic acid) polyelectrolyte layers leading to a highly hydrophilic biocompatible shell supporting colloidal stability. Afterwards, papain was covalently immobilized on the modified GNPs via amide coupling between the amino groups on papain and the terminal carboxylic groups of the modified GNPs by using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide and N-hydroxysulfosuccinimide sodium as coupling agents. The resultant papain-functionalized gold nanoparticles were characterized by surface plasmon resonance, dynamic light scattering and zeta potential measurements. The new technology resonant mass measurement was applied for determining the average number of papain molecules immobilized per GNP by measurement of the single nanoparticle buoyant mass in the range of femtograms. The activity of the immobilized enzyme was estimated by determination of the kinetic parameters (Km, Vmax and kcat) with the standard chromogenic substrate Nα-benzoyl-dl-arginine-4-nitroanilide hydrochloride. It was found that Km of immobilized and free enzyme are in the same order of magnitude. On contrary, turnover numbers kcat were significantly higher for GNP-conjugated papain. Further, the gold nanobiocatalyst was applied for digestion of polyclonal human immunoglobulin G to yield protein fragments. The resultant fragment mixture was further analyzed by high-performance liquid chromatography-microelectrospray ionization-quadrupole-time-of-flight mass spectrometry, which demonstrated the applicability of the bioreactor based on papain functionalized GNPs. The immobilized papain not only has higher catalytic activity and better stability, but also can be easily isolated from the reaction medium by straightforward centrifugation steps for reuse.

Electrically Modulated Localized Surface Plasmon around Self-Assembled-Monolayer-Covered Nanoparticles.

This article reports the observation of electrical modulation of localized surface plasmon around self-assembled monolayer (SAM)-modified gold nanoparticles and the establishment of a new spectroscopy technique, that is, dynamic electro-optical spectroscopy (DEOS). The gold nanoparticles are deposited onto a transparent conductive substrate, and an electrical bias applied on the conductive substrate can cause shift of resonance plasmon response, where the direction of peak shift is related to the polarity of applied bias. The peak shift observed at 2.4 V is approximately ten times larger than those reported in previous work. It is postulated that significant peak shift is the result of reorientation of adsorbed water on electrode, which can change local dielectric environment of nanoparticles. An energy barrier is identified when adsorbed water molecules are turned from oxygen-down to oxygen-up. Frequency-dependent peak shifts on surface-modified gold nanoparticles show that reorientation is a fast reversible process with rich dynamics.

Development of Sialic Acid-coated Nanoparticles for Targeting Cancer and Efficient Evasion of the Immune System.

Evading the reticuloendothelial system (RES) remains a critical challenge in the development of efficient delivery and diagnostic systems for cancer. Sialic acid (N-acetylneuraminic acid, Neu5Ac) is recognized as a “self” marker by major serum protein complement factor H and shows reduced interaction with the innate immune system via sialic acid-binding immunoglobulin-like lectin (Siglec), which is known as one of the significant regulators of phagocytic evasion. Accordingly, we prepared different surface-modified gold nanoparticles (AuNPs) and investigated the effects of sialic acid on cellular and immune responses of nanoparticles in vitro and in vivo. Sialic acid modification not only facilitates evasion of the RES by suppressing the immune response, but also enhances tumor accumulation via its active targeting ability. Therefore, sialic acid modification presents a promising strategy to advance nanotechnology towards the prospect of clinical translation.

Two-Photon Luminescent Bone Imaging Using Europium Nanoagents

Summary An accumulation of fatigue-induced microdamage can often result in an overall thinning and weakening of the bone's structure through a reduction in its mass, which increases its fragility and makes an individual more susceptible to fractures. Consequently, it is vitally important to detect and quantify microdamage early in order to diagnose skeletal diseases and combat their progression. Herein, we present the synthesis and study of europium [Eu(III)]-emitting surface-modified gold nanoparticles as contrast agents for imaging microdamaged bone structure at low concentrations. These nanostructures can be utilized to generate three-dimensional maps (z stacking) of microcracks formed within bone. Using two-photon excitation fluorescence microscopy, we were able to visualize and understand the manner in which these nanoagents bind to damaged bone, as well as demonstrate their selectivity toward exposed Ca(II) within microcracks. Such systems are therefore ideal for biological application as targeted contrast agents for both optical imaging and MRI.

Investigation of the influence of protein corona composition on gold nanoparticle bioactivity using machine learning approaches

The understanding of the mechanisms and interactions that occur when nanomaterials enter biological systems is important to improve their future use. The adsorption of proteins from biological fluids in a physiological environment to form a corona on the surface of nanoparticles represents a key step that influences nanoparticle behaviour. In this study, the quantitative description of the composition of the protein corona was used to study the effect on cell association induced by 84 surface-modified gold nanoparticles of different sizes. Quantitative relationships between the protein corona and the activity of the gold nanoparticles were modelled by using several machine learning-based linear and non-linear approaches. Models based on a selection of only six serum proteins had robust and predictive results. The Projection Pursuit Regression method had the best performances (r2 = 0.91; Q2loo = 0.81; r2ext = 0.79). The present study confirmed the utility of protein corona composition to predict the bioactivity of gold nanoparticles and identified the main proteins that act as promoters or inhibitors of cell association. In addition, the comparison of several techniques showed which strategies offer the best results in prediction and could be used to support new toxicological studies on gold-based nanomaterials.

Cytocompatibility and antibacterial activity of titania nanotubes incorporated with gold nanoparticles

TiO2 nanotubes prepared by electrochemical anodization have received considerable attention in the biomedical field. In this work, different amounts of gold nanoparticles were immobilized onto TiO2 nanotubes using 3-aminopropyltrimethoxysilane as coupling agent. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to investigate the surface morphology and composition. Photoluminescence spectra and surface zeta potential were also measured. The obtained results indicate that the surface modified gold nanoparticles can significantly enhance the electron storage capability and reduce the surface zeta potential compared to pristine TiO2 nanotubes. Moreover, the surface modified gold nanoparticles can stimulate initial adhesion and spreading of rat bone mesenchymal stem cells as well as proliferation, while the osteogenous performance of TiO2 nanotubes will not be reduced. The gold-modified surface presents moderate antibacterial effect on both Staphylococcus aureus and Escherichia coli. It should be noted that the surface modified fewer gold nanoparticles has better antibacterial effect compared to the surface of substantial modification of gold nanoparticles. Our study illustrates a composite surface with favorable cytocompatibility and antibacterial effect and provides a promising candidate for orthopedic and dental implant.

Cytotoxicity, intracellular localization and exocytosis of citrate capped and PEG functionalized gold nanoparticles in human hepatocyte and kidney cells.

Surface-modified gold nanoparticles (AuNPs) are nanomaterials that hold promise in drug delivery applications. In this study, the cytotoxicity, uptake, intracellular localization, and the exocytosis of citrate-stabilized (Cit-AuNP) and polyethylene glycol (PEG)-modified gold nanoparticles with the carboxyl (COOH) terminal functional group were assessed in human embryonic kidney (HEK 293) and the human caucasian hepatocytes carcinoma (Hep G2) cell systems, representing two major accumulation sites for AuNPs. The zeta (ζ)-potential measurements confirmed the negative surface charge of the AuNPs in water and in cell growth medium. The transmission electron microscopy confirmed the size and morphology of the AuNPs. Both types of AuNPs were shown to induce cytotoxic effects in cells. The Hep G2 cells were more sensitive cell type, with the COOH-PEG-AuNPs inducing the highest toxicity at higher concentrations. Dark field microscopy and TEM images revealed that the AuNPs were internalized in cells, mostly as agglomerates. TEM micrographs further revealed that the AuNPs were confined as agglomerates inside vesicle-like compartments, likely to be endosomal and lysosomal structures as well as in the cytosol, mostly as individual particles. The AuNPs were shown to remain in cellular compartments for up to 3weeks, but thereafter, clearance of the gold nanoparticles from the cells by exocytosis was evident. The results presented in this study may therefore give an indication on the fate of AuNPs on long-term exposure to cells and may also assist in safety evaluation of AuNPs.

In vitro cytotoxicity and phototoxicity of surface-modified gold nanoparticles associated with neutral red as a potential drug delivery system in phototherapy

The surface of gold nanoparticles (AuNP) was modified, improving their interaction with neutral red (NR), by using sodium thioglycolate (TGA) as a covering agent. The resulting NR-AuNPTGA system was evaluated as a potential drug delivery system for photodynamic therapy (PDT). The associations of NR with the gold nanoparticles were evaluated using UV-vis spectrometry and measurement of their zeta potential and size distribution. The toxicity and phototoxicity of NR, AuNPTGA and NR-AuNPTGA were evaluated in NIH-3T3 fibroblast and 4T1 tumor cell lines. The compounds NR and NR-AuNPTGA induced toxicity in 4T1 tumor cells and NIH-3T3 fibroblasts under visible light irradiation. Modification of the surface of AuNP with TGA prevented nanoparticle aggregation and allowed greater association with NR molecules than for naked AuNP. The photosensitizer (PS) characteristics were not affected by its association with the modified surface of the gold nanoparticles, leading to a reduction of cell viability in both cell lines assayed. This NR-AuNPTGA system is a promising drug delivery system for photodynamic cancer therapy.