Methoxy Polyethylene Glycol Thiol Research Articles

Ratiometric electrochemical aptasensor with strand displacement for insulin detection in blood samples

BackgroundDiabetes patients suffer either from insulin deficiency or resistance with a high risk of severe long-term complications, thus the quantitative assessment of insulin level is highly desired for diabetes surveillance and management. Utilizing insulin-capturing aptamers may facilitate the development of affordable biosensors however, their rigid G-quadruplex structures impair conformational changes of the aptamers and diminish the sensor signals. ResultsHere we report on a ratiometric, electrochemical insulin aptasensor which is achieved by hybridization of an insulin-capturing aptamer and a partially complementary ssDNA to break the rigid G-quadruplex structures. To improve the durability of the aptasensor, the capturing aptamer was immobilized on gold electrodes via two dithiol-phosphoramidite functional groups while methoxy-polyethylene glycol thiol was used as a blocking molecule. The exposure of the sensor to insulin-containing solutions induced the dissociation of the hybridized DNA accompanied by a conformational rearrangement of the capturing aptamer back into a G-quadruplex structure. The reliability of sensor readout was improved by the adoption of an AND logic gate utilizing anthraquinone and methylene blue redox probes associated to the aptamer and complementary strand, respectively. Our aptasensor possessed an improved detection limit of 0.15 nM in comparison to aptasensors without strand displacement. SignificanceThe sensor was adapted for detection in real blood and is ready for future PoC diagnostics. The capability of monitoring the insulin level in an affordably manner can improve the treatment for an increasing number of patients in developed and developing nations. The utilization of low-cost and versatile aptamer receptors together with the engineering of ratiometric electrochemical signal recording has the potential to considerably advance the current insulin detection technology toward multi-analyte diabetes sensors.

The Effect of Different Stabilisers on Stability and Photothermal Profiling of Gold Nanorods

AbstractThe photothermal application of gold nanorods (AuNRs) as a photothermal agent has gained popularity due to their optical, photothermal and biological properties. However, AuNRs are synthesised using a biotoxic surfactant (cetyl trimethyl ammonium bromide) which limits their biological applications. Though different techniques have been established to address this challenge using different stabilizers or passivating agents, the effect of these stabilizers on AuNRs' colloidal stability, thermal stability, and photothermal conversion efficiency still need to be investigated. In this study, we evaluated the effect of different polymers or stabilisers; two synthetic polymers [methoxy polyethylene glycol thiol (mPEG-SH) and polyvinylpyrrolidone (PVP)] and one biopolymer (gelatin) on the stability and photothermal properties of AuNRs. AuNRs absorbing around 800 nm were synthesised and coated with these three stabilisers. The colloidal stability of the as-synthesised material was evaluated in Dulbecco's phosphate-buffered saline (PBS) and Roswell Park Memorial Institute (RPMI-1640) using Ultraviolet–Visible–Near-Infrared (UV–Vis–NIR). The results show that PEG@AuNRs was more stable in both media due to fewer functional groups on its structure to bond with ions and protein. PVP@AuNRs showed good thermal stability under heat incubation (at 37, 50 and 70 °C) for 24 h because of its high thermal decomposition properties, while PEG@AuNRs proved superior in improving the AuNRs heat generation. In addition, coating with different polymers did not affect the photothermal ability of AuNRs. This study demonstrated that it is crucial to choose polymers with less functional groups when coating nanoparticles for biological application.

Biological Impact of the Interaction of Functionalized and Bioconjugated Gold Nanoparticles of Different Sizes on HeLa and SH‐SY5Y Human Cell Lines

Nanotechnology opens new perspectives in many science and technology fields through new materials, such as metal nanoparticles. The biomedical field is one of these areas where nanoparticles offer promising application in the diagnosis and therapy of disease, generating biosensors for disease detection, bioimaging, and drug delivery. However, the controversy about whether nanoparticles are inert or exhibit different degrees of toxicity related to their physicochemical properties remains a subject of study and debate. This work shows how gold nanoparticles and nanorods were simultaneously functionalized with 4‐aminothiophenol (4‐ATP) and methoxypolyethylene glycol thiol (mPEG‐SH). Then, folic acid (FA) gold nanoparticle bioconjugates caused diverse biological effects on HeLa and SH‐SY5Y cell cultures after 24 h of incubation, when they were evaluated in the range of gold concentrations from 0.17 to 350 μM. We found notable changes in cell metabolic activity, viability, and biomass. 16 nm nanoparticles produced the most enhanced damage for functionalized (AuNPs) and bioconjugated (AuNPs‐FA) nanoparticles, which we expected to be more biocompatible when coated with FA. Besides, epifluorescence images showed damage to F‐actin microfilaments, adhesion and cell attachment loss, morphology changes (cells became round and detached), presence of blebs, and rupture of cell membrane. These results suggested that both AuNPs and AuNPs‐FA have significant biological impact on HeLa and SH‐SY5Y cell cultures, whereas gold nanorods showed significant changes only in the metabolic activity of SH‐SY5Y cells when they were exposed to gold nanorods of 23 and 27 nm in length with a diameter of 5 nm, and crystal violet did not show evidence of toxicity.

Binding of metal ions to the curcumin mediated methoxy polyethylene glycol thiol conjugated greenly synthesized gold nanoparticles: A fluorescence spectroscopic study

Curcumin, a nontoxic molecule obtained from plant extract, was used to reduce gold salt to produce gold nanoparticles (AuNPs). First time the particles were functionalized with methoxy polyethylene glycol thiol (mPEGT), which acts as a stabilizing agent in such a manner that the methoxy group is pointed toward the aqueous solution to serve as anchor point to many metal ions. The greenly synthesized gold nanoparticles have a size between ∼40 and ∼83 nm. The prepared material was characterized in detail by SEM, XRD, TGA and FT-IR spectroscopy. These AuNPs were found to be fluorescence active similar to free curcumin suggesting that curcumin is conjugated at the surface of AuNPs. Exposure of the mPEGT functionalized AuNPs to different concentrations of metal cations in the range between 0 and 100 μM resulted in the decrease in the fluorescence intensity of the AuNPs unlike free curcumin in aqueous solution. Excited state lifetime measurements further validated quenching mechanism to be static in nature. The binding constant and number of binding sites for such interaction were evaluated. Based on observed bimolecular quenching rate constants, kQ values, the order of association of the metals studied is Pb (II) > Hg (II) >Hg (I) > Cd (II)>Al (III) >Ni (II) >Cu (II) >Na2HAsO4. These interactions between the mPEGT conjugated AuNPs and the metal ions in solution contribute a proof-of-concept that mPEGT functionalized curcumin mediated AuNPs can be used as a simple, cheap and straightforward, on-site detection system for toxic and even essential metal ions in solution.

The stimuli-responsive properties of doxorubicin adsorbed onto bimetallic Au@Pd nanodendrites and its potential application as drug delivery platform

Bimetallic nanoparticles have continued to attract interest as drug delivery systems in cancer therapy even though their nature of interaction with small molecules is limited. Currently, many delivery systems based on monometallic nanoparticles are being fabricated for loading of drugs, thus prompting the need to explore and get more understanding of dendritic bimetallic nanostructure-drug interaction. The bimetallic gold-core palladium-dendritic shell nanoparticles (Au@PdNDs) were synthesized by hot injection method and stabilized with methoxy polyethylene glycol thiol (mPEG-SH). An anti-cancer drug, doxorubicin (DOX) was conjugated to the bimetallic nanodendrites leading to the formation of DOX/Au@PdNDs.PEG complex. We used TEM, FTIR, and zeta-potential to study the drug-nanodendrites interaction. The effect of DOX binding and release capacity with regards to pH, adsorption kinetics, solvent polarity, isotherms and temperature on Au@PdNDs.PEG were investigated. The results showed a spontaneous heterogeneous binding of DOX on the Au@PdNDs.PEG surfaces and time-dependent loading capacity of ~90% maximum adsorption within 24h. Moreover, the experimental results showed that the adsorption isotherm data fitted well with the Freundlich model and a pseudo-second order adsorption kinetics. The desorption of DOX was triggered under simulated tumor microenvironmental conditions and should open new opportunities for potential multi stimuli-responsive drug delivery applications.

PH optimization for high-efficiency PEGylation of gold nanorods

The use of methoxy polyethylene glycol thiol (mPEG-SH), in conjunction with additives, is one of the most straightforward, versatile, and widely used methods for modifying gold nanorods (GNRs), especially for applications in the field of biomedicines. The decreased toxicity of PEGylated GNRs is critical for investigating cell-nanomaterial interactions. Most techniques suffer from low PEGylation efficiency. Several investigations of the PEGylation process have been conducted to determine its mechanism. Herein, we systematically investigated the qualitative and quantitative effects of the pH value on GNR PEGylation efficiency. The PEGylation process was applied to modify the GNRs at pH 0.3–14. PEGylation of GNRs at pH 2.3 and 9.9 resulted in better modification efficiency than under other pH conditions, achieving average PEGylation efficiencies of 95.5% and 83.6%, respectively. In both cases, the resulting GNRs could survive centrifugation after surface modification as demonstrated by measuring their longitudinal surface plasmon resonance (LSPR) UV-Vis absorption peaks. The aggregation index correlated to the PEGylation efficiency at the various pH levels. The origin of the differences observed at different pH values was also elucidated. These findings significantly expand the potential use of the aggregation index, as well as the understanding of processes used to modify gold nanoparticles.

N-terminal site-specific PEGylation enhances the circulation half-life of Thymosin alpha 1

Covalent attachment of polyethylene glycol (PEG) to peptides and proteins has been used to increase the clinical efficacy and circulation half-life of biopharmaceuticals. The purpose of this study was to enhance the half-life of an important immune-modulating agent, Thymosin alpha 1 (Tα1), using site-specific PEGylation. A novel N-terminal modified Tα1 (Mal-Tα1) was constituted by condensing the N-terminal amino group of Tα1 with 3-maleimidopropionic acid (Mal). Then, Mal-Tα1 was site-specifically conjugated with methoxy polyethylene glycol thiol (mPEG-SH) under mild conditions to form mPEG-Mal-Tα1. The conjugation efficiency was greater than 95%. mPEG-Mal-Tα1 was stable in the presence of 2-mercaptoethanol and exhibited significantly increased immunoactivity compared to Tα1 in mice. The terminal half-life (t1/2β) of mPEG-Mal-Tα1 was 2.5 times longer than that of mPEG-Cys-Tα1 (PEGylation product of mPEG-Mal conjugated with Cysteine-Tα1) in rats. These results demonstrate that site-specific PEGylation of N-terminal Mal-Tα1 is a promising strategy for enhancing the circulation t1/2β of Tα1 compared to Cysteine-Tα1.

Transferrin Adsorbed on PEGylated Gold Nanoparticles and Its Relevance to Targeting Specificity.

Polyethylene glycol (PEG) has been frequently used for surface modification of nanoparticles (NPs) to reduce non-specific binding of proteins on NPs. The investigation of protein absorption on PEGylated nanoparticles is necessary. In the work, the conjugation of transferrin (Tf) to PEGylated AuNPs via adsorption or bonding was studied. The 13 nm AuNPs were coated with various molecular weight (300, 2000, 5000) carboxyl and methoxy PEG thiol. The presence of Tf on PEGylated AuNP was characterized by dynamic light scattering (DLS) and infrared spectroscopy (IR). The data of IR confirmed the presence of Tf on PEGylated AuNPs. The diameter decrease of PEGylated AuNPs after Tf adsorption was observed by DLS measurement, which is attributed to competitive adsorption between Tf and PEG molecules. These phenomena may be important to the preservation of Tf targeting specificity on PEGylated AuNPs.

Disposable Plasmonic Plastic SERS Sensor Using Gold Nanoparticles Arrays

Our ultimate goal of this study is to form a monolayer of plasmonic anisotropic gold nanoparticles on the surface of disposable plastics via chemical processes to use LSPR sensor. The process creates hydroxyl group by method of plasma cleaning or piranha treatment, subsequently substitute hydroxyl groups for Amine functions by using amino silane solution. Then, the surface is coated with the gold nanoparticles. For the plasmonic gold nanoparticles, gold bipyramids (Au BPs) and gold nanorods (Au NRs) with a surfactant, cetyltrimethylammonium bromide (CTAB) bilayer were employed. Then, their surfaces were modified with methoxy polyethylene glycol thiol (mPEG-SH). Based on these plasmonic gold nanoparticle substrates, we have investigated adsorption sensitivity and kinetics of self-assembly of thiolated organic molecules.

Xanthan gum stabilized PEGylated gold nanoparticles for improved delivery of curcumin in cancer

In recent years, gold nanoparticles (AuNPs) have received immense interest in various biomedical applications including drug delivery, photothermal ablation of cancer and imaging agent for cancer diagnosis. However, the synthesis of AuNPs poses challenges due to the poor reproducibility and stability of the colloidal system. In the present work, we developed a one step, facile procedure for the synthesis of AuNPs from hydrogen tetrachloroaurate (III) hydrate (HAuCl4. 3H2O) by using ascorbic acid and xanthan gum (XG) as reducing agent and stabilizer, respectively. The effect of concentrations of HAuCl4, 3H2O, ascorbic acid and methoxy polyethylene glycol-thiol (mPEG800-SH) were optimized and it was observed that stable AuNPs were formed at concentrations of 0.25 mM, 50 μM and 1 mM for HAuCl4.3H2O, ascorbic acid, and mPEG800-SH, respectively. The XG stabilized, deep red wine colored AuNPs (XG-AuNPs) were obtained by drop-wise addition of aqueous solution of ascorbic acid (50 mM) and XG (1.5 mg ml−1). Synthesized XG-AuNPs showed λmax at 540 nm and a mean hydrodynamic diameter of 80 ± 3 nm. PEGylation was performed with mPEG800-SH to obtain PEGylated XG-AuNPs (PX-AuNPs) and confirmed by Ellman’s assay. No significant shift observed in λmax and hydrodynamic diameter between XG-AuNPs and PX-AuNPs. Colloidal stability of PX-AuNPs was studied in normal saline, buffers within a pH range of 1.2–7.4, DMEM complete medium and in normal storage condition at 4 ˚C. Further, water soluble curcumin was prepared using PVP-K30 as solid dispersion and loaded on to PX-AuNPs (CPX-AuNPs), and evaluated for cellular uptake and cytotoxicity in Murine melanoma (B16F10) cells. Time and concentration dependent studies using CPX-AuNPs showed efficient uptake and decreased cell viability compared to free curcumin.

Superparamagnetic iron oxide nanocargoes for combined cancer thermotherapy and MRI applications.

Nanoparticle-based cancer diagnosis-therapy integrative systems (cancer theranostics) represent an emerging approach in oncology. To address this issue in the present work iron oxide (γ-Fe2O3-maghemite) nanoparticles (IONPs) were encapsulated within the matrix of (bis(p-sulfonatophenyl)phenylphosphine)-methoxypolyethylene glycol-thiol (mPEG) polymer vesicles using a two-step process for active chemotherapeutic cargo loading in cancer theranostics. This formation method gives simple access to highly reactive surface groups present on IONPs together with good control over the vesicle size (50-100 nm). The simultaneous loading of a chemotherapeutic drug cargo (doxorubicin) and its in vitro release in cancer cells was achieved. The feasibility of controlled drug release under different pH conditions was demonstrated in the case of encapsulated doxorubicin molecules, showing the viability of the concept of stimulated drug delivery for magneto-chemotherapy. These polymer-magnetic nanocargoes (PMNCs) exhibit enhanced contrast properties that open potential applications for magnetic resonance imaging. These self-assembled magnetic polymersomes can be used as efficient multifunctional nanocarriers for combined therapy and imaging.

Photochemical transformations of thiolated polyethylene glycol coatings on gold nanoparticles.

Photochemical reactions can cause significant transformations of manufactured nanomaterials in sunlit environments. While transformations of inorganic nanoparticles (NPs) have been investigated extensively, less attention has been focused on the direct impact of aqueous photochemical reactions on adsorbed organic macromolecules that form the NP corona and strongly influence the surface interactions and reactivity that affect NP transport, fate, and toxicity. Here, we assess the transformations of methoxy polyethylene glycol thiol (mPEGSH) coatings on gold NPs (AuNPs) under controlled UV irradiation. A decrease in the adsorbed layer thickness of polymer was observed within 24 h of UV irradiation, resulting in increased susceptibility of the transformed NPs to aggregation. Surface chemistry analyses, including X-ray photoelectron spectroscopy (XPS), showed loss of the ether groups but persistence of reduced S on the AuNP surface, indicative of a chain scission mechanism yielding different NP surface properties from that of either the initial PEGylated AuNP or the citrate-stabilized AuNP prior to coating with mPEGSH. The transformation of the chemisorbed polymer was compared to that of dissolved mPEGSH in the presence and absence of the Au NPs, as evaluated by liquid chromatography - mass spectrometry (LC-MS). In contrast to the NP-adsorbed coating, the primary observed transformation of the dissolved mPEGSH was thiol oxidation to disulfides without extensive chain scission. This study demonstrates that transformations of adsorbed macromolecular coatings must be considered to accurately predict NP attachment behavior, and hence transport, in environmental systems. Because the corona transformation was not predictable from that of the dissolved polymer, direct NP surface characterization is required to discern the fundamental reactions involved in the photochemical transformation of coatings after sorption to the NP surface.

Surface-modified gold nanorods for specific cell targeting

Gold nanoparticles (GNPs) have unique properties that make them highly attractive materials for developing functional reagents for various biomedical applications including photothermal therapy, targeted drug delivery, and molecular imaging. For in vivo applications, GNPs need to be prepared with very little or negligible cytotoxicitiy. Most GNPs are, however, prepared using growth-directing surfactants such as cetyl trimethylammonium bromide (CTAB), which are known to have considerable cytotoxicity. In this paper, we describe an approach to remove CTAB to a non-toxic concentration. We optimized the conditions for surface modification with methoxypolyethylene glycol thiol (mPEG), which replaced CTAB and formed a protective layer on the surface of gold nanorods (GNRs). The cytotoxicities of pristine and surface-modified GNRs were measured in primary human umbilical vein endothelial cells and human cell lines derived from hepatic carcinoma cells, embryonic kidney cells, and thyroid papillary carcinoma cells. Cytotoxicity assays revealed that treating cells with GNRs did not significantly affect cell viability except for thyroid papillary carcinoma cells. Thyroid cancer cells were more susceptible to residual CTAB, so CTAB had to be further removed by dialysis in order to use GNRs for thyroid cell targeting. PEGylated GNRs are further modified to present monoclonal antibodies that recognize a specific surface marker, Na-I symporter, for thyroid cells. Antibody-conjugated GNRs specifically targeted human thyroid cells in vitro.