60-nt DNA Direct Detection without Pretreatment by Surface-Enhanced Raman Scattering with Polycationic Modified Ag Microcrystal Derived from AgCl Cube

Direct detection of long-strand DNA by surface-enhanced Raman scattering (SERS) is a valuable method for diagnosis of hereditary diseases, but it is currently limited to less than 25-nt DNA strand in pure water, which makes this approach unsuitable for many real-life applications. Here, we report a 60-nt DNA label-free detection strategy without pretreatment by SERS with polyquaternium-modified Ag microcrystals derived from an AgCl cube. Through the reduction-induced decomposition, the size of the about 3 × 3 × 3 μm3 AgCl cube is reduced to Ag, and the surface is distributed with the uniform size of 63 nm silver nanoparticles, providing a large area of a robust and highly electromagnetic enhancement region. The modified polycationic molecule enhances the non-specific electrostatic interaction with the phosphate group, thereby anchoring DNA strands firmly to the SERS enhanced region intactly. As a result, the single-base recognition ability of this strategy reaches 60-nt and is successfully applied to detect thalassemia-related mutation genes.

Unveiling the Changes in the Molecular Groups of Tight Sandstones in Response to an Electric Field

The electric field method proved in the lab and oil fields is an effective and fast way to significantly improve oil recovery, which can be applied to greatly realize the urgent-need requirements for energy, especially in tight sandstones. Generally, the changed molecular groups treated with an electric field modulate the wettability of reservoirs, affecting the final oil recovery. Herein, the investigation of the impact of the electric field on the molecular groups of reservoirs is imperative and meaningful. In this paper, tight sandstones were placed into a particular instrument and subjected to various strengths of the electric field. Nine treated powders and one untreated powder of tight sandstones were processed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) experiments. FTIR results show that the electric field decreases aromatic groups, C-O groups, COOH groups, and aliphatic groups, whereas it increases C=C groups, C=O groups, and OH groups. Interestingly, the changes in C-O groups, C=O groups, COOH groups, and OH groups are all the competitive results of production and consumption during the treatment process. With regard to C-O groups and COOH groups, the consumption has an advantage over the production on the content of functional groups, and the situations for C==O groups and OH groups exhibit a contrary trend. The fitted result of XPS proves the fact that the electric field improves C=O groups, OH groups, and COOR groups, whereas it reduces C-O groups, supporting that the molecular groups can be mutually transformed during the electric field treatment. The obtained knowledge is beneficial to the study of electric field-related technologies on the molecular groups of reservoirs.

Spontaneous Polarity Flipping in a 2D Heterobilayer Induced by Fluctuating Interfacial Carrier Flows

Polarity often refers to the charge carrier type of a semiconductor or the charging state of a functional group, generally dominating their functionality and performance. Herein we uncover a spontaneous and stochastic polarity-flipping phenomenon in monolayer WSe₂, which randomly switches between the n-type and p-type states and is essentially triggered by fluctuating carrier flows from or to the adjacent WS₂ monolayer. We have traced such fluctuating carrier flows by interfacial photocurrent measurements in a zero-bias two-terminal device. Such polarity flipping results in switching between the negative and positive correlations between the emission intensities of WS₂ and WSe₂ in the heterobilayer, which is further well-controlled by the electrostatic gate-tuning experiments in a capacitor-structure device. Our work not only demonstrates giant and intermittent carrier flows through long-range coupling in 2D heterostructures and a consequent spontaneous polarity flipping phenomenon but also provides a two-emitter system with a switchable correlation sign that could project future applications in optical logic devices.

Ionic Liquid Electrolyte-Based Switchable Mirror with Fast Response and Improved Durability

Electrochemically tunable devices based on reversible metal electrodeposition have attracted extensive attention for energy-saving smart windows, information displays, digital signage, and variable reflectance mirrors, owing to their excellent optical modulation characteristics, low operation voltage, and superb electrochemical stability. Here, we study the effects of ionic liquid (IL)-based electrolytes on electrodeposition of the reversible electrochemical mirrors (REMs) by changing the organic cations of the ILs to obtain devices with the desired spectroelectrochemical and electrodeposited properties. Spectroelectrochemical measurements and scanning electron microscopy images show that organic cations drastically affect the switching speed and cycling durability, which we proposed on the basis of the difference in the absorption energies between cations and Ag(111) surfaces. Higher adsorption energy indicates strong adhesion between organic cations and Ag(111) surfaces, and this strong adsorption would prevent aggregation and agglomeration during the nucleation of Ag nanoparticles (AgNPs), leading to a denser and more compact electrodeposited Ag film and faster switching speeds (3.3 s for coloring and 14.3 s for bleaching). These findings allow us to fabricate dynamic devices that exhibit reversibly switchable light modulation at fast switching speeds and excellent cycling stability over thousands of cycles without attenuation. The combination of rapid switching and durable cycling stability enables tunable windows, which are based on reversible electrodeposition of metal Ag and IL-based electrolytes, make REM devices a competitive and promising alternative to traditional intelligent response materials.

Altering the substituents of salicylic acid to improve Berthelot reaction for ultrasensitive colorimetric detection of ammonium and atmospheric ammonia

The Berthelot reaction is a classic method for detection of ammonium (NH₄⁺) and atmospheric ammonia (NH₃) by using salicylic acid (SA) as the chromogenic substrate. However, there lacks a method for improving the activity of the Berthelot reaction to enhance the analytical performance for detection of NH₄⁺ and NH₃. Here, five SA analogues with electron-withdrawing groups (-F) and electron-donating groups (-CH₃ and -OCH₃) at different positions of the aromatic ring have been chosen as the alternative to SA for Berthelot reaction. Among these analogues, 4-methoxysalicylic acid (4-OCH₃-SA) shows the best colorimetric response and color change at a NH₄⁺ concentration of 30 μM, and the sensitivity of 4-OCH₃-SA-based colorimetric assay for NH₄⁺ increases 1.75-fold compared with that of SA-based colorimetric method. This enhancement effect is attributed to the strong electron-donating property of 4-OCH₃ group, activating the two-step electrophilic aromatic substitution reaction in the Berthelot reaction. Additionally, visual and sensitive detection of NH₃ is realized, along with a low limit of detection down to 0.037 ppm. Furthermore, we demonstrate that this assay is reliable and practical for detection of NH₄⁺ and NH₃ in real water and air samples with good accuracy.

Vibrational Stark shift spectroscopy of catalysts under the influence of electric fields at electrode-solution interfaces

External control of chemical processes is a subject of widespread interest in chemical research, including control of electrocatalytic processes with significant promise in energy research. The electrochemical double-layer is the nanoscale region next to the electrode/electrolyte interface where chemical reactions typically occur. Understanding the effects of electric fields within the electrochemical double layer requires a combination of synthesis, electrochemistry, spectroscopy, and theory. In particular, vibrational sum frequency generation (VSFG) spectroscopy is a powerful technique to probe the response of molecular catalysts at the electrode interface under bias. Fundamental understanding can be obtained via synthetic tuning of the adsorbed molecular catalysts on the electrode surface and by combining experimental VSFG data with theoretical modelling of the Stark shift response. The resulting insights at the molecular level are particularly valuable for the development of new methodologies to control and characterize catalysts confined to electrode surfaces. This Perspective article is focused on how systematic modifications of molecules anchored to surfaces report information concerning the geometric, energetic, and electronic parameters of catalysts under bias attached to electrode surfaces.

Heterogeneous electrocatalysis: characterization of interfacial electric field within the electrochemical double layer.

Direct Observation of Amide Bond Formation in a Plasmonic Nanocavity Triggered by Single Nanoparticle Collisions

The real-time observation of chemical bond formation at the single-molecule level is one of the great challenges in the fields of organic and biomolecular chemistry. Valuable information can be gleaned that is not accessible using ensemble-average measurements. Although remarkably sophisticated techniques for monitoring chemical reactions have been developed, the ability to detect the specific formation of a chemical bond in situ at the single-molecule level has remained an elusive goal. Amide bonds are routinely formed from the aminolysis of N-hydroxysuccinimide (NHS) esters by primary amines, and the protocol is widely used for the synthesis, cross-linking, and labeling of peptides and proteins. Herein, a plasmonic nanocavity was applied to study aminolysis reaction for amide bond formation, which was initiated by single nanoparticle collision events between suitably functionalized free-moving gold nanoparticles and a gold nanoelectrode in an aqueous buffer. By means of simultaneous surface enhanced Raman spectroscopy (SERS) and single-entity electrochemistry (EC) measurements, we have probed the dynamic evolution of amide bond formation in the aminolysis reaction with 10 s of millisecond time resolution. Hence, we demonstrate that single-entity EC-SERS is a valuable and sensitive technique by which chemical reactions can be studied at the single-molecule level.

Design of robust 2,2'-bipyridine ligand linkers for the stable immobilization of molecular catalysts on silicon(111) surfaces

The attachment of the 2,2'-bipyridine (bpy) moieties to the surface of planar silicon(111) (photo)electrodes was investigated using ab initio simulations performed on a new cluster model for methyl-terminated silicon. Density functional theory (B3LYP) with implicit solvation techniques indicated that adventitious chlorine atoms, when present in the organic linker backbone, led to instability at very negative potentials of the surface-modified electrode. In prior experimental work, chlorine atoms were present as a trace surface impurity due to required surface processing chemistry, and thus could plausibly result in the observed surface instability of the linker. Free energy calculations for the Cl-atom release process with model silyl-linker constructs revealed a modest barrier (14.9 kcal mol-1) that decreased as the electrode potential became more negative. A small library of new bpy-derived structures has additionally been explored computationally to identify strategies that could minimize chlorine-induced linker instability. Structures with fluorine substituents are predicted to be more stable than their chlorine analogues, whereas fully non-halogenated structures are predicted to exhibit the highest stability. The behavior of a hydrogen-evolving molecular catalyst Cp*Rh(bpy) (Cp* = pentamethylcyclopentadienyl) immobilized on a silicon(111) cluster was explored theoretically to evaluate differences between the homogeneous and surface-attached behavior of this species in a tautomerization reaction observed under reductive conditions for catalytic H2 evolution. The calculated free energy difference between the tautomers is small, hence the results suggest that use of reductively stable linkers can enable robust attachment of catalysts while maintaining chemical behavior on the electrode similar to that exhibited in homogeneous solution.

Electro-inductive effect: Electrodes as functional groups with tunable electronic properties

In place of functional groups that impose different inductive effects, we immobilize molecules carrying thiol groups on a gold electrode. By applying different voltages, the properties of the immobilized molecules can be tuned. The base-catalyzed saponification of benzoic esters is fully inhibited by applying a mildly negative voltage of –0.25 volt versus open circuit potential. Furthermore, the rate of a Suzuki-Miyaura cross-coupling reaction can be changed by applying a voltage when the arylhalide substrate is immobilized on a gold electrode. Finally, a two-step carboxylic acid amidation is shown to benefit from a switch in applied voltage between addition of a carbodiimide coupling reagent and introduction of the amine.