Terminal Thiol Groups Research Articles

Nanowire Aptasensors for Electrochemical Detection of Cell-Secreted Cytokines.

Cytokines are small proteins secreted by immune cells in response to pathogens/infections; therefore, these proteins can be used in diagnosing infectious diseases. For example, release of a cytokine interferon (IFN)-γ from T-cells is used for blood-based diagnosis of tuberculosis (TB). Our lab has previously developed an atpamer-based electrochemical biosensor for rapid and sensitive detection of IFN-γ. In this study, we explored the use of silicon nanowires (NWs) as a way to create nanostructured electrodes with enhanced sensitivity for IFN-γ. Si NWs were covered with gold and were further functionalized with thiolated aptamers specific for IFN-γ. Aptamer molecules were designed to form a hairpin and in addition to terminal thiol groups contained redox reporter molecules methylene blue. Binding of analyte to aptamer-modified NWs (termed here nanowire aptasensors) inhibited electron transfer from redox reporters to the electrode and caused electrochemical redox signal to decrease. In a series of experiments we demonstrate that NW aptasensors responded 3× faster and were 2× more sensitive to IFN-γ compared to standard flat electrodes. Most significantly, NW aptasensors allowed detection of IFN-γ from as few as 150 T-cells/mL while ELISA did not pick up signal from the same number of cells. One of the challenges faced by ELISA-based TB diagnostics is poor performance in patients whose T-cell numbers are low, typically HIV patients. Therefore, NW aptasensors developed here may be used in the future for more sensitive monitoring of IFN-γ responses in patients coinfected with HIV/TB.

Voltammetric determination of tumor necrosis factor-α based on the use of an aptamer and magnetic nanoparticles loaded with gold nanoparticles

The authors are presenting an electrochemical aptasensor for tumor necrosis factor-alpha (TNF-α) detection that is aided by the use of magnetic nanoparticles (NPs) and two DNA probes. Firstly, magnetic NPs coated with gold NPs (Fe3O4@AuNP) are synthesized. Then, DNA probe 1 with a terminal thiol group is immobilized on the surface of Fe3O4@AuNP via gold-thiol chemistry. DNA probe 1 is then hybridized with DNA probe 2, which is labeled with Methylene Blue (MB). The composite of Fe3O4@AuNP-DNA duplex is formed as a result, which can be easily absorbed on a magnetized glassy carbon electrode. The electrochemical signal is obtained after reductant-mediated amplification. Since MB-labeled DNA probe 2 is the aptamer against TNF-α, it will be released in the presence of TNF-α. This process leaves Fe3O4@AuNP-DNA probe 1 on the surface of the electrode. Thus, the recorded electrochemical response decreases dramatically. The assay, best operated at a working voltage of −0.39 V (vs. SCE), has a linear response in the 10 pg mL−1 to 100 ng·mL−1 TNF-α concentration range, and the limit of detection is 10 pg mL−1. The sensing strategy is highly sensitive and selective, and has been successfully applied to real samples.

Multifunctional Peptide-Amphiphile End-Capped Mesoporous Silica Nanoparticles for Tumor Targeting Drug Delivery.

A tumor targeting redox-responsive drug delivery system (DDS) with bioactive surface was constructed by immobilizing peptide-based amphiphile C12-CGRKKRRQRRRPPQRGDS (defined as ADDA-TCPP) onto the mesoporous silica nanoparticles (MSNs) as an end-capping nanovalve, which consists of two main segments: a hydrophobic alkyl chain ADDA and a hydrophilic amino acid sequence containing a Tat48-60 peptide sequence with a thiol terminal group and an RGDS targeting ligand, via a disulfide linkage for redox-triggered intracellular drug delivery. A series of characterizations confirmed that the nanosystem had been successfully fabricated. The antitumor drug doxorubicin (DOX) was selected as a model drug and efficiently trapped in the pores of MSNs, and an in vitro release experiment demonstrated that the mesopores of the resulting DOX-loaded MSNs (DOX@MSN-ss-ADDA-TCPP) could be sealed tightly with ADDA-TCPP self-assemblies through hydrophobic interactions between the alkyl chains; the resulting DDS exhibited "zero premature release" of DOX in the physical environment. However, a burst drug release was triggered by a high concentration of glutathione (GSH) in simulated cellular cytosol. Moreover, detailed investigations confirmed that incorporation of RGDS peptide facilitated the active targeting delivery of DOX to αvβ3 integrin overexpressed tumor cells, and Tat48-60 modification on MSNs could enhance intracellular drug delivery, exhibiting an obvious toxicity to tumor cells. The multifunctional nanosystem constructed here can realize the controlled drug release and serve as a platform for designing multifunctional nanocarriers using diversified bioactive peptide-based amphiphile.

Epidermal growth factor (EGF) fragment-guided anticancer theranostic particles for pH-responsive release of doxorubicin

EGF fragment (EGFfr) and doxorubicin were chemically co-decorated on single magnetic nanoparticles (MNPs) for concomitant cancer targeting and treatment. Magnetic nanoparticles were prepared by the precipitation of ferric chloride hydrates in an ammonia solution and subsequent surface-functionalization with amines. The terminal thiol group of the EGF fragment was first conjugated to surface amines of the MNPs using a heterofunctional crosslinker, and doxorubicin was sequentially conjugated to the MNPs via a hydrazone linker, where the degree of subsitution of the surface amines to EGFfr was varied from 1% to 40%. The decorated doxorubicin showed clear pH-dependency in the release profile, and doxorubicin showed fast release at pH 5.0 in comparison to pH 7.4. The EGF-decorated MNPs were tested for differential cellular uptakes against EGF overexpressing cells (A549), and the uptake levels gradually increased to 10% and saturated, which was quantified by ICP-OES. Internalized doxorubicin was also visualized by confocal microscopy, and A549 cells with EGF-decorated MNPs with EGF decoration showed higher fluorescence intensity of doxorubicin than those with non-decorated MNPs. Anti-cancer activity of the MNPs was compared at various concentrations of doxorubicin and EGFfr. Decoration of EGFfr significantly increased the anti-cancer activity of doxorubicin-incorporated MNPs in A549 cells; however, EGFfr alone did not affect the viability of the cells. Thus, we concluded that MNPs with optimized EGFfr and doxorubicin ratios showed higher targeting and drug payload against EGF receptor overexpressing cancer cells.

Composites based on liquid-crystalline polymers with terminal functional groups and inorganic nanoparticles

A method of controlled radical polymerization via the reversible addition fragmentation chain transfer mechanism is used to synthesize LC polymers with functional terminal thiol groups. These polymers are used to create composites containing gold nanoparticles at a concentration of up to 40 wt % and capable of LC ordering. The structural, thermodynamic, and optical properties of the composites are studied. It is shown that the spatial separation of mesogenic groups and groups responsible for the binding of a macromolecule with nanoparticles makes it possible to considerably widen the concentration range of nanoparticles while preserving the LC state of the composites.

Visible light‐induced thiol‐ene reaction: A new strategy to prepare Α,ω‐dithiol and Α,ω‐divinyl telechelic polythiolether oligomers

ABSTRACTA new strategy is developed to prepare both α,ω‐dithiol and α,ω‐divinyl linear telechelic polythiolether oligomers by visible light induced thiol‐ene chemistry in the presence of a fac‐Ir(ppy)3 photoredox catalyst. Polythiolether oligomers of well‐defined end groups and controlled molecular weights have been successfully synthesized at varying monomer molar ratios of 1,4‐benzenedimethanethiol (BDMT) to diethylene glycol divinyl ether (DEGVE). 1H NMR and MALDI‐TOF MS analyses demonstrate that as‐prepared polythiolethers possess high end‐group fidelity, which is further supported by the successful polyaddition of polythiolethers bearing α,ω‐dithiol and α,ω‐divinyl groups. For example, with the α,ω‐dithiol‐ (Mn = 1900 g mol−1, PDI = 1.25) and α,ω‐divinyl‐terminated (Mn = 2000 g mol−1, PDI = 1.29) polythiolethers as macromonomers, the molecular weight of resulting polythiolether is up to 7700 g mol−1 with PDI as 1.67. The reactivity of the terminal thiol group is further confirmed by the addition reaction with N‐(1‐pyrenyl)maleimide. UV‐vis spectra and fluorescene measurements suggest that fac‐Ir(ppy)3 undergo a redox quenching process reacted with BDMT to generate thiyl free radicals. With these results, the mechanism of the thiol‐ene reaction catalyzed by photoredox catalyst is proposed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 740–749

Probing of PNA-DNA Hybrid Duplex Stability with AFM Force Spectroscopy

Peptide nucleic acids (PNA) are synthetic polymers the neutral peptide backbone of which provides elevated stability to PNA-PNA and hybrid PNA-DNA duplex. It was demonstrated recently (J.Org.Chem.2011, 76, 5614-5627) that additional modification of the backbone such as incorporation of diethylene glycol (miniPEG) further increases the duplex thermal stability, so the hybrid duplex with 10 miniPEG units (γ-PNA) has the melting temperature 23°C higher compared to the regular PNA-DNA duplex. Here we applied AFM force spectroscopy to probe the strength of the γ-PNA-DNA duplex (5′GAGTAG GTAG-3’) containing ten miniPEG-modified units. Single-stranded PNA and DNA oligonucleotides containing terminal thiol groups were immobilized on amino-functionalized AFM tip and mica substrate, respectively via bifunctional PEG tethers and the interaction between the DNA and γ-PNA polymers was analyzed by multiple approach retraction cycles over various locations on the mica substrate. Such single molecule probing experiments produced force curves with well-defined rupture events corresponding to the dissociation of the duplex formed during the approach step. The experiments were performed at various pulling rates (300-3000 nm/sec) enabled us to characterize the hybrid duplex stability using dynamic force spectroscopy (DFS) approach. The DFS measurements yielded rupture forces varying in the range 60-70 pN. The data analyzed in the framework of the Bell-Evans approach yielded a dissociation constant, koff ∼ 10−9 sec−1 and rupture distance x-1∼ 1.7 nm. Similar published DFS measurements of DNA duplex are characterized by koff with ∼ 108 times less values, which is in line with elevated stabilities of the γ-PNA-DNA duplexes compared with the DNA duplexes.The work was supported by NIH grants 5P01 GM091743-03 and 5R01 GM096039-04 to YLL. γ-PNA was synthesized at PNA innovation.

Preparation of Highly Dispersed Gold Nanoparticles on Organosilane Modified Graphene Nanosheets

In this study, we present a novel strategy for the immobilization of gold nanoparticles (AuNPs) on the surfaces of modified graphene oxide (MGO/Au) using (3-mercaptopropyl) trimethoxysilane as a bridging agent. In the fabrication process, the hydroxyl functionalized GO was covalently functionalized with (3-mercaptopropyl) trimethoxysilane through C‒O‒Si linkage and the terminal thiol groups were further used to fabricate MGO/Au hybrids via the specific interaction between ‒SH and Au. The degree of covalent functionalization and fabrication of MGO/Au hybrid materials were confirmed with Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermal gravimetric analysis and high resolution transmission electron microscopy (HRTEM) analyses. HRTEM images demonstrated that the AuNPs were homogeneously distributed on the surfaces of GO. The MGO/Au hybrid showed enhanced thermal stability due to the intrinsic properties of graphene and gold nanoparticles.

Triblock Terpolymers Bearing a Redox-Cleavable Junction and a Photo-Cross-Linkable Block

Two linear triblock terpolymers were synthesized and used to coat cotton textiles. These copolymers consist in sequence of a water-soluble poly(ethylene glycol) (PEG) block, a highly water- and oil-repellant poly[2-(perfluorooctyl)ethyl methacrylate] (PFOEMA) block, and a photo-cross-linkable poly(2-cinnamoyloxyethyl methacrylate) (PCEMA) block. The PEG block bonds to PFOEMA via a redox-cleavable disulfide junction (-S2-). To prepare the copolymers, monomethoxy PEG (PEG-OH) was derivatized to yield a PEG chain bearing one terminal thiol group (PEG-SH). Atom transfer radical polymerization and deprotection chemistry were used to prepare Py-S2-PFOEMA-b-PHEMA, where PHEMA and Py-S2- denote poly(2-hydroxyethyl methacrylate) and a terminal pyridin-2-yldisulfanyl group, respectively. Reacting PEG-SH with Py-S2-PFOEMA-b-PHEMA via a thiol–disulfide exchange reaction yielded PEG-S2-PFOEMA-b-PHEMA, and the cinnamation of the PHEMA block produced PEG-S2-PFOEMA-b-PCEMA. PEG-S2-PFOEMA-b-PCEMA dispersed in water and plasticized by a trace amount of dimethyl phthalate was then used to coat cotton textiles, and this coating was secured by photo-cross-linking the PCEMA domains. Treating the coating with dithiothreitol cleft the disulfide junction and thus the PEG block, revealing the hidden PFOEMA block and its water- and oil-repellant properties. Aqueous solutions of these copolymers could thus be applied onto a substrate to provide amphiphobic coatings.

Diamond surface functionalization with biomimicry – Amine surface tether and thiol moiety for electrochemical sensors

The surface of conducting diamond was functionalized with a terminal thiol group that is capable of binding and detecting nitrogen–oxygen species. The functionalization process employed multiple steps starting with doped diamond films grown by plasma enhanced chemical vapor deposition followed by hydrogen termination and photochemical attachment of a chemically protected amine alkene. The surface tether was deprotected to reveal the amine functionality, which enabled the tether to be extended with surface chemistry to add a terminal thiol moiety for electrochemical sensing applications. Each step of the process was validated using X-ray photoelectron spectroscopy analysis.

Aggregation of thiol coated gold nanoparticles: A simulation study on the effect of polymer coverage density and solvent

Molecular dynamics simulations have been carried out to investigate the effect of alkane thiol coverage density, terminal group and water solvent on the aggregation of thiol coated gold nanoparticles. The increase in polymer coverage density enhances the size of the aggregate as the van der Waals force of attraction dominates with the increase in the number of thiol chains. The change in the terminal group from methyl (hydrophobic) to hydroxy (hydrophilic) group modifies the size of the aggregate as the extent of interdigitation between thiol chains is reduced due to the hydrogen bond interactions between the hydroxy terminal groups. The water solvent does not much alter the aggregation of methyl terminated gold nanoparticles. It weakens the aggregation of hydroxy terminated gold nanoparticles due to the hydrophilic interaction between the water molecules and the hydroxy terminal groups.

Construction of a metal–organic monolayer–semiconductor junction on a hydrogen-terminated Si(111) surface via Si–C covalent linkage and its electrical properties

A metal-organic monolayer-semiconductor junction, exhibiting a diode behaviour, was constructed on a hydrogen-terminated n-type Si(111) by sequential surface reactions of (1) formation of an organic monolayer with a thiol terminal group, (2) platinum deposition onto the thiol group via adsorption of a platinum complex followed by chemical reduction, and finally (3) continuous Ag layer formation by electroless deposition. Rectifying behaviour was observed at this interface.

Development of nonfouling polypeptides with uniform alternating charges by polycondensation of the covalently bonded dimer of glutamic acid and lysine.

In this work, nonfouling polypeptides with homogenous alternating charges were synthesized by polycondensation of the covalently bonded dimer of glutamic acid (E) and lysine (K) (EK dimer) with benzyloxycarbonyl (Z)-protected side chains. This facile method successfully solved the uniformity problem of nonfouling peptides caused by the copolymerization of two different monomers and enabled the incorporation of various terminal functional groups for future applications. The molecular weights (MWs) of the nonfouling peptides can be easily controlled by the ratio of the terminal group, lipoic acid, to the EK dimer. The nonfouling peptides can form self-assembling monolayers (SAMs) on a gold surface through two terminal thiol groups, which were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and ellipsometry (ELL). The resistance to nonspecific protein adsorption, cell attachment and bacterial adhesion of these nonfouling peptide SAMs and the in vitro cytotoxicity and haemolytic activity of these peptides were also evaluated. The results show that the lowest relative protein adsorptions of antibody (anti-IgG) and fibrinogen (Fg) on the SAMs are 5.1 ± 1.6% and 7.3 ± 1.8%, respectively, determined by enzyme-linked immunosorbent assay (ELISA), where the protein adsorption on a tissue culture polystyrene (TCPS) surface was set to 100%. Almost no obvious cell attachment and bacterial adhesion were observed, and no cytotoxicity and no haemolytic activity in vitro were detected. With the advantages of biocompatibility, biodegradability and the abundance of moieties for ligand immobilization, these nonfouling peptides developed by the facile method can be used in a wide range of biomedical applications.

Labeling of islet cells with iron oxide nanoparticles through DNA hybridization for highly sensitive detection by MRI

A labeling method for islet cells with superparamagnetic iron oxide nanoparticles (SPIOs) based on DNA hybridization is proposed for monitoring of transplanted islets by magnetic resonance imaging (MRI). The surfaces of SPIOs were modified by via Michael reaction by reacting oligo-(deoxyadenylic acid)-bearing a terminal thiol group at the 5′-end ((dA)20-SH) with maleic acid functional groups on the SPIOs. The SPIOs were immobilized on islet cells which had been pretreated with oligo-(thymidylic acid)–poly(ethylene glycol)–phospholipid conjugates ((dT)20–PEG–DPPE) through DNA hybridization. Transmission electron microscopy observations revealed that SPIOs were initially anchored on the islet cell surfaces and subsequently transferred to endosomes or exfoliated with time. The SPIO-labeled islet cells could be clearly detected as dark spots by T2∗-weighted MR image, whereas non-labeled islet cells could not be detected.

Ultrasound‒Mediated Synthesis of High‒Molecular Weight Polystyrene‒Grafted Silver Nanoparticles by Facile Ligand Exchange Reactions in Suspension

Ultrasound mediated facile ligand exchange method in suspension for the formation of polystyrene-grafted silver nanoparticles is reported. Amazingly, this method allows even grafting of very high molecular weight polystyrenes (up to 217 200 g mol(-1) ) having a single terminal thiol group at the chain end. Detailed studies are carried out to gain insights in the role of molecular weight of the ligands and the mechanism of the ligand exchange reactions. Key factors are determined to be the droplet formation by ultrasonification and low silver content, which enhances the availability of the terminal thiol end group significantly. The extraordinary compatibility of the ligand exchange method in particular regarding high molecular weights is attributed to hydrophilic orientation of the terminal thiol groups at the liquid-liquid interphase. This is proved conclusively by using an in situ method as a reference approach in which agglomeration occurs at considerably lower molecular weights due to the absence of preferred end group orientation within the polymer coil. In homogeneous phase only the chain length is found to be the crucial factor in stabilization of silver nanoparticles.

Preparation and tribological properties of novel carbon nanotube self-assembled composite films

Carbon nanotube (CNT) composite thin films were prepared on a single-crystal silicon substrate by a self-assembling process from a specially formulated solution. Rare earth solution (RES) surface modification and appropriate acid-treatment methods were used to functionalise carbon nanotubes (CNTs). Silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared first. The terminal thiol groups (–SH) in the film was oxidised to sulphonic acid groups (–SO3H) in situ to enhance the film with good chemisorption ability. Treated Caron nanotubes were deposited on the oxidised MPTS–SAM by means of chemisorption with the SO3H group. The surface energy, chemical composition, phase transformation and surface morphology of the films were analysed using contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy. As a result, a conclusion could be made that some lanthanum elements react with –SO3H groups on the surface of the substrate by a chemical bond, which will improve the bonding strength between the films and the CNTs. Since the CNT thin films were well adhered to the silicon substrate, it might find promising application in the surface-modification of single-crystal Si and SiC in microelectromechanical systems (MEMS).

Tailoring highly conductive graphene nanoribbons from small polycyclic aromatic hydrocarbons: a computational study

Pyrene, the smallest two-dimensional mesh of aromatic rings, with various terminal thiol substitutions, has been considered as a potential molecular interconnect. Charge transport through two terminal devices has been modeled using density functional theory (with and without self interaction correction) and the non-equilibrium Green’s function method. A tetra-substituted pyrene, with dual thiol terminal groups at opposite ends, has been identified as an excellent candidate, owing to its high conductance, virtually independent of bias voltage. The two possible extensions of its motif generate two series of graphene nanoribbons, with zigzag and armchair edges and with semimetallic and semiconducting electron band structure, respectively. The effects related to the wire length and the bias voltage on the charge transport have been investigated for both sets. The conductance of the nanoribbons with a zigzag edge does not show either length or voltage dependence, owing to an almost perfect electron transmission with a continuum of conducting channels. In contrast, for the armchair nanoribbons a slow exponential attenuation of the conductance with the length has been found, due to their semiconducting nature.

Synthesis and photochromic properties of a novel thiol-terminated 1,3-diazabicyclo[3.1.0]hex-3-ene on silver nanoparticles

Inorganic nanoparticles functionalized with organic photochromes have been used for a much wider variety of applications. In this work, we have designed and synthesized a novel photochromic 1,3-diazabicyclo[3.1.0]hex-3-ene with a thiol-terminal group to form a self-assembled monolayer on the silver nanoparticles (AgNPs). The prepared photochromic material was characterized using X-ray diffraction, scanning electron microscopy, UV–Vis, NMR and IR methods. Analysis of the results showed that there is a chemical interaction between the AgNPs and terminal-thiol group of the photochromic. The photochromic structure behavior relationship (PSBR) of photochromic ligand and photochromic/AgNPs assemblies has been analyzed.

A bioreducible polypeptide for efficient gene transfection both in vitro and in vivo

A disulfide bond containing polypeptide, PolyK6-R8, was designed and prepared by oxidative polymerization between terminal cysteinyl thiol groups of CHK6HC and CR8C. The molar ratio between CHK6HC and CR8C within obtained PolyK6-R8 was 9:1, and PolyK6-R8 could combine DNA compactly when weight ratio reached 5. Through in vitro investigation, it was found that PolyK6-R8 was an efficient gene vector with low cytotoxicity for delivering DNA in both COS-7 and HeLa cells. Cellular uptake of DNA mediated by PolyK6-R8/DNA complexes was promoted after incubation for 4 h. Moreover, by examining the histological sections of hindlimb ischemia rats through immunohistochemistry, PolyK6-R8/VEGF complexes were proved to be effective in both VEGF protein expression and succeeding vessel formation. The results indicated that polypeptide-based PolyK6-R8 is a promising gene vector for the limb ischemia treatment.

Preparation and photolithography of self-assembled monolayers of 10-mercaptodecanylphosphonic acid on glass mediated by zirconium for protein patterning

Self-assembled monolayers (SAMs) formed by adsorption of octadecylphosphonic acid (ODPA) on zirconium mediated glass substrates were prepared. In this sandwich structure, Zr4+ was used as a bi-linker to bind phosphonic acid head group in ODPA to glass substrates. The contact angle of the as-prepared SAMs was measured to be around 104°. X-ray photoelectron spectroscopy (XPS) characterization indicated the modification of Zr4+ on glass substrates was critical for the formation of reasonably dense, well-ordered SAMs similar in quality to those typically formed on other metal oxide surfaces. Bifunctional molecule, 10-mercaptodecanylphosphonic acid (MDPA), bearing thiol terminal groups for various chemical reactions, was synthesized and formed SAMs on glass using the same approach, which allowed us to control the surface chemistry and functionality through photooxidation of the thiol terminal group. Photopatterning of proteins was performed first by exposing the SAMs to UV light through a mask, followed by protein immobilization to the masked regions through a heterobifunctional linker, while the exposed areas prohibit nonspecific protein absorption. The present strategy, which combined the SAMs assembly and photolithography, offered a facile approach for the fabrication of biomolecule patterning and could be applied to construction of biochips and other applications.