Single-Atom Site SERS Chip for Rapid, Ultrasensitive, and Reproducible Direct-Monitoring of RNA Binding

Ribonucleic acids (RNA) play active roles within cells or viruses by catalyzing biological reactions, controlling gene expression, and communicating responses to cellular signals. Rapid monitoring RNA variation has become extremely important for appropriate clinical decisions and frontier biological research. However, the most widely used method for RNA detection, nucleic acid amplification, is restricted by a mandatory temperature cycling period of ≈1 h required to reach target detection criteria. Herein, a direct detection approach via single-atom site integrated surface-enhanced Raman scattering (SERS) monitoring nucleic acid pairing reaction, can be completed within 3 min and reaches high sensitivity and extreme reproducibility for COVID-19 and two other influenza viruses' detection. The mechanism is that a single-atom site on SERS chip, enabled by positioning a single-atom oxide coordinated with a specific complementary RNA probe on chip nanostructure hotspots, can effectively bind target RNA analytes to enrich them at designed sites so that the binding reaction can be detected through Raman signal variation. This ultrafast, sensitive, and reproducible single-atom site SERS chip approach paves the route for an alternative technique of immediate RNA detection. Moreover, single-atom site SERS is a novel surface enrichment strategy for SERS active sites for other analytes at ultralow concentrations.

Atomically Dispersed Ce Sites Augmenting Activity and Durability of Fe-Based Oxygen Reduction Catalyst in PEMFC

In the cathode of proton exchange membrane fuel cells (PEMFCs), Fe and N co-doped carbon (Fe-N-C) materials with atomically dispersed active sites are one of the satisfactory candidates to replace Pt-based catalysts. However, Fe-N-C catalysts are vulnerable to attack from reactive oxygen species, resulting in inferior durability, and current strategies failing to balance the activity and stability. Here, this study reports Fe and Ce single atoms coupled catalysts anchored on ZIF-8-derived nitrogen-doped carbon (Fe/Ce-N-C) as an efficient ORR electrocatalyst for PEMFCs. In PEMFC tests, the maximum power density of Fe/Ce-N-C catalyst reached up to 0.82 W cm-2 , which is 41% larger than that of Fe-N-C. More importantly, the activity of Fe/Ce-N-C catalyst only decreased by 21% after 30 000 cycles under H2 /air condition. Density functional theory reveals that the strong coupling between the Fe and Ce sites result in the redistribution of electrons in the active sites, which optimizes the adsorption of OH* intermediates on the catalyst and increases the intrinsic activity. Additionally, the admirable radical scavenging ability of the Ce sites ensured that the catalysts gained long-term stability. Therefore, the addition of Ce single atoms provides a new strategy for improving the activity and durability of oxygen reduction catalysts.

WCx-Supported RuNi Single Atoms for Electrocatalytic Oxygen Evolution

Single-atom catalysts anchored to oxide or carbonaceous substances are typically tightly coordinated by oxygen or heteroatoms, which certainly impact their electronic structure and coordination environment, thereby affecting their catalytic activity. In this study, we prepared a stable oxygen evolution reaction (OER) catalyst on tungsten carbide using a simple pyrolysis method. The unique structure of tungsten carbide allows the atomic RuNi catalytic site to weakly bond to the surface W and C atoms. XRD patterns and HRTEM images of the WCx-RuNi showed the characteristics of phase-pure WC and W2C, and the absence of nanoparticles. Combined with XPS, the atomic dispersion of Ru/Ni in the catalyst was confirmed. The catalyst exhibits excellent catalytic ability, with a low overpotential of 330 mV at 50 mA/cm2 in 1 m KOH solutions, and demonstrates high long-term stability. This high OER activity is ascribed to the synergistic action of metal Ru/Ni atoms with double monomers. The addition of Ni increases the state density of WCx-RuNi near the Fermi level, promoting the adsorption of oxygen-containing intermediates and enhancing electron exchange. The larger proximity of the d band center to the Fermi level suggests a strong interaction between the d electrons and the valence or conduction band, facilitating charge transfer. Our research offers a promising avenue for reasonable utilization of inexpensive and durable WCx carrier-supported metal single-atom catalysts for electrochemical catalysis.

Intermediates-induced CO2 Reduction Reaction Activity at Single-Atom M-N2 (M=Fe, Co, Ni) Sites

Single-atom M-N2 (M=Fe, Co, Ni) catalysts exhibit high activity for CO2 reduction reaction (CO2 RR). However, the CO2 RR mechanism and the origin of activity at the single-atom sites remain unclear, which hinders the development of single-atom M-N2 catalysts. Here, using density functional theory calculations, we reveal intermediates-induced CO2 RR activity at the single-atom M-N2 sites. At the M-N2 sites, the asymmetric *O*CO configuration tends to split into *CO and *OH intermediates. Intermediates become part of the active moiety to form M-(CO)N2 or M-(OH)N2 sites, which optimizes the adsorption of intermediates on the M sites. The maximum free energy differences along the optimal CO2 RR pathway are 0.30, 0.54, and 0.28 eV for Fe-(OH)N2 , Co-(CO)N2 , and Ni-(OH)N2 sites respectively, which is lower than those of Fe-N2 (1.03 eV), Co-N2 (1.24 eV) and Ni-N2 (0.73 eV) sites. The intermediate modification can shift the d-band center of the spin-up (minority) state downward by regulating the charge distribution at the M sites, leading to less charge being accepted by the intermediates from the M sites. This work provides new insights into the understanding of the activity of single-atom M-N2 sites.

Atomically Local Electric Field Induced Interface Water Reorientation for Alkaline Hydrogen Evolution Reaction

The slow water dissociation process in alkaline electrolyte severely limits the kinetics of HER. The orientation of H2O is well known to affect the dissociation process, but H2O orientation is hard to control because of its random distribution. Herein, an atomically asymmetric local electric field was designed by IrRu dizygotic single-atom sites (IrRu DSACs) to tune the H2O adsorption configuration and orientation, thus optimizing its dissociation process. The electric field intensity of IrRu DSACs is over 4.00 ×1010 N/C. The ab initio molecular dynamics simulations combined with in-situ Raman spectroscopy analysis on the adsorption behavior of H2O show that the M-H bond length (M = active site) is shortened at the interface due to the strong local electric field gradient and the optimized water orientation promotes the dissociation process of interfacial water. This work provides a new way to explore the role of single atomic sites in alkaline hydrogen evolution reaction.

Synergetic Function of the Single-Atom Ru-N4 Site and Ru Nanoparticles for Hydrogen Production in a Wide pH Range and Seawater Electrolysis

Hydrogen production by water splitting and seawater electrolysis is a promising alternative to develop clean hydrogen energy. The construction of high-efficiency and durable electrocatalysts for the hydrogen evolution reaction (HER) in a wide pH range and seawater is critical to overcoming the sluggish kinetic process. Herein, we develop an efficient catalytic material composed of a single-atom Ru-N₄ site and Ru nanoparticles anchored on nitrogen-doped carbon (Ru_1+NPs/N-C) through the coordination-pyrolysis strategy of the melamine formaldehyde resin. The Ru_1+NPs/N-C catalyst shows outstanding HER activity with the smallest overpotentials, the lowest Tafel slopes, the highest mass activity and turnover frequency, as well as excellent stability in both acidic and alkaline media. Moreover, Ru_1+NPs/N-C shows comparable hydrogen production performance and a higher faradic efficiency to 20% Pt/C in natural seawater and artificial simulated seawater. Theoretical calculations demonstrate that the strong synergistic effects between the Ru-N₄ site and Ru nanoparticles modify the electronic structure to accelerate the HER kinetics. Ru nanoparticles can effectively realize dissociation of H₂O to generate adsorbed hydrogen and also promote the single-atom Ru-N₄ site to combine adsorbed hydrogen to H₂ and desorption. This work provides a new perspective for designing high-efficiency hydrogen production electrocatalysts for large-scale seawater electrolysis.

Single-atom sites on perovskite chips for record-high sensitivity and quantification in SERS

Surface enhanced Raman scattering (SERS) is a rapid and nondestructive technique that is capable of detecting and identifying chemical or biological compounds. Sensitive SERS quantification is vital for practical applications, particularly for portable detection of biomolecules such as amino acids and nucleotides. However, few approaches can achieve sensitive and quantitative Raman detection of these most fundamental components in biology. Herein, a noble-metal-free single-atom site on a chip strategy was applied to modify single tungsten atom oxide on a lead halide perovskite, which provides sensitive SERS quantification for various analytes, including rhodamine, tyrosine and cytosine. The single-atom site on a chip can enable quantitative linear SERS responses of rhodamine (10^-6-1 mmol L^-1), tyrosine (0.06-1 mmol L^-1) and cytosine (0.2-45 mmol L^-1), respectively, which all achieve record-high enhancement factors among plasmonic-free semiconductors. The experimental test and theoretical simulation both reveal that the enhanced mechanism can be ascribed to the controllable single-atom site, which can not only trap photoinduced electrons from the perovskite substrate but also enhance the highly efficient and quantitative charge transfer to analytes. Furthermore, the label-free strategy of single-atom sites on a chip can be applied in a portable Raman platform to obtain a sensitivity similar to that on a benchtop instrument, which can be readily extended to various biomolecules for low-cost, widely demanded and more precise point-of-care testing or in-vitro detection.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available for this article at 10.1007/s40843-022-1968-5 and is accessible for authorized users.