Covalent Au Research Articles

In-line RNA-based microreactor direct mass spectrometry for ultrasensitive and rapid assay of terminal deoxynucleotidyl transferase activity

Terminal deoxynucleotidyl transferase (TdT), a unique template-independent DNA polymerase, plays a crucial role in the human adaptive immune system and is considered a promising biomarker for the diagnosis of various forms of acute or chronic leukemia. The accurate and sensitive detection of trace TdT is of pivotal importance to fulfill the significant medical interest in understanding its pathological functions and diagnosing TdT-related diseases. We hereby present an in-line RNA-based microreactor direct mass spectrometry (MS) method and its application for ultrasensitive, accurate, and rapid analysis of trace TdT activity in leukemic cell samples. A specially designed RNA-based microreactor is fabricated by immobilizing short RNA sequence via covalent Au–S bond on the inner surface of a capillary pre-modified with three-dimensional porous layer (PL) and Au nanoparticles (AuNPs). Utilizing this PL@Au@RNA microreactor, the signal of target TdT is conversed into reporter molecules (adenine), which exhibit a strong MS response. This conversion process enables efficient signal amplification and enhances detection sensitivity. The outlet end of the PL@Au@RNA microreactor is deliberately crafted into a porous tip, serving as an electrospray ionization (ESI) interface to directly couple to ESI-MS in-line. This design facilitates the direct transmission of the generated signaling molecules into the MS system, eliminating the need for laborious sample treatment procedures. By implementing this RNA-based microreactor in direct MS analysis, we have achieved remarkable sensitivity in detecting TdT activity with the limit-of-detection of 4 × 10−9 U, surpassing other reported methods in literature by three to four orders of magnitude. Furthermore, each assay requires a minimal sample volume of merely 10 nL. This method has successfully demonstrated its application in accurately and efficiently detecting TdT activity in leukemia cells, and its detection results are consistent with those obtained by ELISA kits.

Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on a “three-in-one” nanohybrid with high oxidase-like activity for AIEgen

A colorimetry/fluorescence dual-mode assay based on the aptamer-functionalized magnetic covalent organic framework-supported CuO and Au NPs (MCOF-CuO/Au@apt) was developed for Salmonella typhimurium (S. typhimurium) biosensing. The nanohybrid combined three functions in one: good magnetic separation characteristic, excellent oxidase-mimic activity for tetrap-aminophenylethylene (TPE-4A), and target recognition capability. The attachment of MCOF-CuO/Au@apt onto the surface of S. typhimurium resulted in a significant reduction in the oxidase-mimicking activity of the nanohybrid, which could generate dual-signal of colorimetry and fluorescence through the catalytic oxidation of TPE-4A. Based on this, S. typhimurium could be specifically detected in the linear ranges of 102– 106 CFU·mL−1 and 101– 106 CFU·mL−1, with LODs of 7.6 and 2.1 CFU·mL−1, respectively in colorimetry/fluorescence modes. Moreover, the smartphone and linear discrimination analysis-based system could be used for on-site and portable testing. In addition, this platform showed applicability in detecting S. typhimurium in milk, egg liquid and chicken samples.

Is there a Covalent Au(I)-Au(I) Bond in the trans-(AuX)2 (X = F, Cl, Br, I) Structure? A Post-Hartree-Fock and Density Functional Theory Study.

We present an exhaustive exploration of the driving forces dominating the interaction between gold atoms in the trans-(AuX)2, where X is a halogen ligand. This work provides insights into the nature of the gold-gold contact in the trans-(AuX)2. The geometries and energies were calculated at the MP2, CCSD(T), and DFT-D3(BJ) (B3LYP, PBE, and TPSS) levels of theory. The results show a short Au-Au distance, typical of a covalent bond, but with a weak interaction energy associated with noncovalent interactions. It is established that the physical contributions from polarization and the electronic correlation forces are the most relevant at the post-Hartree-Fock level of theory. Also, the electrostatic term is attractive but with low contribution. Finally, the Wiberg indices and NBO analysis exposed a small covalent character between the gold atoms, revealing that this contribution is insufficient to explain the stability of the dimers. It is concluded that a sum of contributions makes it possible to establish an attraction between the gold atoms in the dimers studied beyond a classical aurophilic interaction.

Gold(I)···Lanthanide(III) Bonds in Discrete Heterobimetallic Compounds: A Combined Computational and Topological Study.

The chemical nature of the ligand-unsupported gold(I)-lanthanide(III) bond in the proposed [LnIII(η5-Cp)2][AuIPh2] (Ln-Au; LnIII = LaIII, EuIII, or LuIII; Cp = cyclopentadienide; Ph = phenyl) models is examined from a theoretical viewpoint. The covalent bond-like Au-Ln distances (Au-La, 2.95 Å; Au-Eu, 2.85 Å; Au-Lu, 2.78 Å) result from a strong interaction between the oppositely charged fragments (ΔEintMP2 > 600 kJ mol-1), including the aforementioned metal-metal bond and additional LnIII-Cipso and C-H···π interactions. The Au-Ln bond has been characterized as a chemical bond rather than a strong metallophilic interaction with the aid of energy decomposition analysis, interaction region indicator, and quantum theory of atoms in molecules topological tools. The chemical nature of the Au-Ln bond cannot be fully ascribed to a covalent or an ionic model; an intermediate situation or a charge shift bond is proposed. The [AuIPh2]- anion has also been identified as a suitable lanthanide(III) emission sensitizer for La-Au and Lu-Au.

DNA Nanostructure-Guided Plasmon Coupling Architectures

DNA Nanostructure-Guided Plasmon Coupling Architectures

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

Photocatalytic hydrogen generation using colloidal covalent organic polymers decorated bimetallic Au-Pd nanoalloy (COPs/Pd-Au)

Photocatalytic H2 generation has been considered as an effective method for H2 generation, in which the cocatalysts play a critical role. Here, we report highly reactive nanocomposites composed of two-dimensional triazine-based covalent organic Polymers (COPs), Pd and Au nanocomponents which is designed to benefit from the alloying and visible light illumination effects as well as LSPR effect. Photocatalytic hydrogen production was achieved under low-cost visible light-driven. The COP/Pd-Au exhibited higher photocatalytic outstanding turnover frequency of 260.5 h − 1, which was 1.47 times of that under no light (177.3 h − 1). Additionally, it exhibits much advanced catalytic performance, which is 2.83-fold that of COP/Pd (91.98 h − 1) and 434.17-fold that of COP/Au (0.60 h − 1), under the similar reaction conditions. The great photocatalytic activity for COP/Pd-Au was also ascribed to the strong interface between Pd-Au NPs and COPs, and the preparation of single hollow construction of Pd-Au alloy with porous nature that presented active sites for hydrogen production.

Promotion and suppression of single-molecule conductance by quantum interference in macrocyclic circuits

Promotion and suppression of single-molecule conductance by quantum interference in macrocyclic circuits

Adsorption/Desorption Behaviors and SERS Chemical Enhancement of 6-Mercaptopurine on a Nanostructured Gold Surface: The Au20 Cluster Model.

Computational approaches are employed to elucidate the binding mechanism and the SERS phenomenon of 6-mercaptopurine (6MP) adsorbed on the tetrahedral Au20 cluster as a simple model for a nanostructured gold surface. Computations are carried out in both vacuum and aqueous environments using a continuum model. In the gaseous phase and neutral conditions, interaction of 6MP with the gold cluster is mostly dominated by a covalent Au−S bond and partially stabilized by the Au⋅⋅⋅H−N coupling. However, in acidic solution, the nonconventional Au⋅⋅⋅H−S hydrogen-bond becomes the most favorable binding mode. The 6MP affinity for gold clusters decreases in the order of vacuum > neutral solution > acidic medium. During the adsorption, the energy gap of Au20 substantially declines, leading to an increase in its electrical conductivity, which can be converted to an electrical noise. Moreover, such interaction is likely a reversible process and triggered by either the low pH in sick tissues or the presence of cysteine residues in protein matrices. While N−H bending and stretching vibrations play major roles in the SERS phenomenon of 6MP on gold surfaces in neutral solution, the strongest enhancement in acidic environment is mostly due to an Au⋅⋅⋅H−S coupling, rather than an aromatic ring-gold surface π overlap as previously proposed.

The Formation and Conducting Mechanism of Imidazole‐Gold Molecular Junctions

AbstractThe formation mechanism and electronic transport properties of imidazole sandwiched between gold electrodes are investigated using the non‐equilibrium Green's function formalism combined with density functional theory. Our calculations show that the imidazole radical bridges the gold electrodes and the covalent Au−N bonds formed at the molecule‐electrode interfaces enhance the junction stability. In contrast, adding one more electron to the junction, which corresponds to the imidazole radical anion, will increase the antibonding orbital population and thus weaken the junction stability. The calculated low‐bias conductance values of junctions with a single imidazole radical and two imidazole radicals linked in series through one gold atom are in excellent agreement with the experimental measurements, which are mainly contributed by the σ‐type Au−N bonds. These findings deepen our understanding of the structure‐property relationship of imidazole‐gold molecular junctions and facilitate the design of future imidazole‐based molecular electronic devices.

Revealing the Active Site of Gold Nanoparticles for the Peroxidase-Like Activity: The Determination of Surface Accessibility

Despite the fact that the enzyme-like activities of nanozymes (i.e., nanomaterial-based artificial enzymes) are highly associated with their surface properties, little is known about the catalytic active sites. Here, we used the sulfide ion (S2−)-induced inhibition of peroxidase-like activity to explore active sites of gold nanoparticles (AuNPs). The inhibition mechanism was based on the interaction with Au(I) to form Au2S, implying that the Au(I) might be the active site of AuNPs for the peroxidase-like activity. X-ray photoelectron spectroscopy (XPS) analysis showed that the content of Au(I) on the surface of AuNPs significantly decreased after the addition of S2−, which might be contributed to the more covalent Au–S bond in the formation of Au2S. Importantly, the variations of Au(I) with and without the addition of S2− for different surface-capped AuNPs were in good accordance with their corresponding peroxidase-like activities. These results confirmed that the accessible Au(I) on the surface was the main requisite for the peroxidase-like activity of AuNPs for the first time. In addition, the use of S2− could assist to determine available active sites for different surface modified AuNPs. This work not only provides a new method to evaluate the surface accessibility of colloidal AuNPs but also gains insight on the design of efficient AuNP-based peroxidase mimics.

Confined organometallic Au1Nx single-site as an efficient bifunctional oxygen electrocatalyst

The development of organometallic complexes with abundant stable single-atom active sites is highly desirable for cost-effective and commercial electrocatalysis towards renewable energy conversion and storage. Here, we report an atomic-level design and construction of a new type of organometallic Au1Nx single-site confined on organic carbon-nitride support as a promising bifunctional electrocatalyst for efficient and durable oxygen reduction (ORR) and evolution reaction (OER) performance. The combination of atomic characterizations and theoretical calculations confirm that the atomically dispersed Au1+ atoms are grafted onto carbon-nitride support by covalent Au–N bonds via an amine-induced-reduction strategy, forming atomic Au1Nx single-sites with potential oxygen-related catalytic activity. Hence, this developed Au1Nx single-site electrocatalyst could exhibit excellent electrocatalytic activity and durability with extraordinarily large mass activities of ~9000 A•gAu−1 for ORR at the half-wave potential 0.76 V, and of ~1500 A•gAu−1 for OER at overpotential 0.45 V, 20–26 times higher than those of benchmarking Pt/C and RuO2 electrocatalysts.

Reversible intercalation of iodine monolayers between on-surface synthesised covalent polyphenylene networks and Au(111).

We report on post-synthetic decoupling of covalent polyphenylene networks from Au(111) by intercalation of a chemisorbed iodine monolayer. The covalent networks were synthesised by on-surface Ullmann polymerization of 1,3-bis(p-bromophenyl)-5-(p-iodophenyl)benzene precursors on Au(111) under ultra-high vacuum conditions. The present study relates to previous work, where successful detachment was demonstrated on Ag(111) by a combination of microscopic and spectroscopic techniques. On the more reactive Ag(111) surfaces, intercalation was readily accomplished by exposing the samples to iodine vapour at room temperature. On more noble Au(111), however, STM, XPS and NEXAFS consistently indicate that the same protocol merely results in co-adsorption of iodine on uncovered surface areas, whereas the covalent networks remain adsorbed on the metal. Yet, performing the iodine exposure at elevated surface temperatures similarly results in detachment of the organic networks via intercalation of an iodine monolayer also on Au(111) as evidenced by characteristic changes in STM. In addition, owing to the high thermal stability of the covalent networks and the comparatively low iodine desorption temperature, the reversibility of the process is demonstrated: sample annealing at 400 °C results in complete desorption of the iodine monolayer, whereby the covalent networks re-adsorb directly on Au(111).

Gold-Organic Hybrids: On-Surface Synthesis and Perspectives.

Gold-organic hybrids can be prepared on gold substrates by on-surface dehalogenation of molecular precursors with multiple halogen substituents. Various contact geometries of covalent arylAu bonds are achieved by changing the halogen substituents in the bay or peri regions. Scanning tunneling microscopy/spectroscopy (STM/STS) investigations allow a better understanding of the structure/property relationships in various gold-aryl contacts. Recent progress on the synthesis, large-scale alignment, and STS measurement of gold-organic hybrids is described, ending with an emphasis on potential future applications, e.g., as precursors (intermediates) for the synthesis of graphene nanoribbons (GNRs) on insulating surfaces, and as a model system to investigate the role of covalent arylAu bonds in electron transport through gold-GNR contacts.

Visualization and quantification of Hg2+ based on anti-aggregation of label-free gold nanoparticles in the presence of 2-mercaptobenzothiazole

A highly sensitive and simple colorimetric strategy for Hg2+ detection is introduced based on anti-aggregation of gold nanoparticles (AuNPs). 2-Mercaptobenzothiazole (MBT) can cause the aggregation of AuNPs due to strong covalent Au–S bond formation resulting in color change from red to blue. However, the presence of Hg2+ led the AuNPs to remain in the dispersed state because MBT prefers to interact with Hg2+ rather than AuNPs. Based on the anti-aggregation mechanism, Hg2+ can be detected by observing the color change of AuNPs solution containing MBT. The minimum detectable quantity is 0.1μM by the naked eyes, and the limit of the detection (LOD) is 6.0nM by UV–vis spectroscopy with the linear range from 0.05 to 1.0μM. Furthermore, the developed detection system is also environmental-friendly and inexpensive, which has been successfully used in lake water and milk powder samples detection.

Surface Organization of Polyoxometalate Hybrids Steered by a 2D Supramolecular PTCDI/Melamine Network

A 2D supramolecular honeycomb network built on hydrogen bonding of perylene-3,4,9,10-tetracarboxylic acid diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (Melamine) has been self-assembled on Au(111) by a solution processed method. The ability of the porous network to host functional molecular oxides or polyoxometalates (POMs) has been investigated using a functionalized species [PW11O39Ge{p-C6H4-C≡C–C6H4-NHC(O) (CH2)4{-CH(CH2)2S-S-}}]4– (KWGe[S-S]): this inorganic/organic hybrid built on a Keggin-type POM core and an organic tether incorporating a thioctic acid function has been designed to enhance the host–guest interaction by the formation of covalent Au–S bonds. XPS analysis confirmed the presence of the POMs that are covalently held onto the surface. Probed by STM operating under ambient conditions, the spatial organization of the POMs display some reminiscence of the organic template, while monitoring the POM deposition at various immersion times by PM-IRRAS showed that the POM raising at the subs...

DNA–gold nanoparticles network based electrochemical biosensors for DNA MTase activity

In this work, a highly sensitive electrochemical DNA methyltransferase (MTase) activity assay was fabricated with DNA–gold nanoparticles (Au NPs) network as signal amplification unit and an easy assembly method by the linkage of benzenedithiol bridge. By two complementary AuNPs modified single-stranded DNA, DNA–gold nanoparticles network was self-assembled. With the linkage of benzenedithiol bridge, the DNA network structure was immobilized on the surface of gold electrode through the covalent Au–S bond. In the presence of Dam MTase, the special sites of DNA–AuNPs network were methylated and could not be digested by restriction endonuclease Mbo I. Thus the loaded electrochemical indicator Methylene blue (MB) was MB molecules still remained on the DNA–Au NPs network. The electrochemical response depended on the methylated degree, which could be used to detect MTase activity. By the differential pulse voltammetry (DPV), it was demonstrated that a linear relationship between the DPV response and logarithm of Dam concentration ranged from 0.075 to 30U/mL, achieving a low detection limit of 0.02U/mL. The use of benzenedithiol avoided the direct incubation of the solid electrode with the capture DNA probe under complex and harsh conditions. Therefore the immobilization of DNA–AuNPs network was easy to be carried out, which is favorable for the specially high stability and reproducibility of the electrochemical biosensor.

Synthesis of 3,4-diaminobenzenethiol and its application in gold nanoparticle-based colorimetric determination of copper ions

3,4-Diaminobenzenethiol can react with AuNPs via a strong covalent Au–S bond. The exposed amino functional groups on the benzene ring from neighboring AuNPs could bind to copper ions, resulting in AuNP aggregation.

(Au/PANA/PVAc) nanofibers as a novel composite matrix for albumin and streptavidin immobilization

A novel electrospun nanofiber mat (Au/PANA/PVAc) consists of (Gold/Poly Anthranilic acid) (Au/PANA) core/shell nanostructures as a support material for protein immobilization that was developed and characterized by electrochemical impedance spectroscopy. In the core/shells, PANA served carboxyl groups (−COOH) for covalent protein immobilization and Au enhanced the electrochemical properties by acting as tiny conduction centers to facilitate electron transfer. Covalent immobilization of albumin and streptavidin as model proteins onto the (Au/PANA/PVAc) nanofibers was carried out by using 1-ethyl-3-(dimethyl-aminopropyl) carbodiimide hydrochloride (EDC)/N-hydroxyl succinimide (NHS) activation. PVAc nanofibers were compared with Au/PANA/PVAc nanofibers before and after protein immobilization. The successful covalent binding of both albumin and streptavidin onto (Au/PANA/PVAc) nanofibers was confirmed by FTIR-ATR, Electron Microscopy/Energy-Dispersive X-ray Spectroscopy SEM/EDX and Electrochemical impedance spectroscopy (EIS). The nanofibers became resistive due to protein immobilization and the higher charge transfer resistance was observed after higher amount of protein was immobilized.

Preparation and properties of organo-soluble tetraphenylethylene monolayer-protected gold nanorods

Organo-soluble tetraphenylethylene derived monolayer-protected gold nanorods were prepared and characterized. The prepared gold nanorods covered with tetraphenylethylene thiol via the strong covalent Au–S linkage were found to be soluble and stable in organic solvents. The successful thiol exchange and modification of tetraphenylethylene derivative molecules on gold nanorods were confirmed from UV–Vis, Raman and FT-IR spectra. The gold nanorods were found to have a quenching effect on the aggregation-induced emission of the tetraphenylethylene thiol molecule modified on their surfaces.