Colorimetric and visual determination of iodide ions via morphology transition of gold nanobipyramids.

The gold nanobipyramids (Au NBPs) are widely used in the analytical detection of biochemistry due to their unique localized surface plasmon resonance (LSPR) properties. In our developed approach, I- in kelp was detected by etching Au NBPs in the presence of IO3-. Under acidic conditions, IO3- reacted rapidly with I- to form I2, subsequently I2 reacted with I- to form the intermediate I3-. In the presence of CTAB, Au NBPs were etched by I2 derived from I3-, resulting in a decrease in the aspect ratio of Au NBPs, to form a significant blue shift of LSPR longitudinal peak and color variation of colloid which changed from blue-green to magenta and could be employed to quantitatively detect the concentration of I- with the naked eye. A linear relationship can be found between the LSPR peak changes with the I- concentration in a wide range from 4.0 µM to 15.0 µM, and the sensitive limit of detection (LOD) was 0.2 µM for UV-vis spectroscopy and the obvious color changes with a visual LOD was 4.0 µM for the naked eye. Benefiting from the high specificity, the proposed colorimetric detection of I- in kelp samples was achieved, indicating the available potential of the colorimetric detection for the determination of I- in real samples. What's more, this detection procedure was time-saving and could avoid tedious procedures.

Molecular orientation and specificity in the identification of biomolecules via surface enhanced Raman spectroscopy.

The orientation dependence of the Raman spectral features of individual protein/biomolecules is studied using surface-enhanced Raman spectroscopy (SERS). Large variation in spectral features mainly in term of peak intensity is observed from small proteins/peptides. We aim to address the question of whether the spectral features of SERS are uniquely determined by the type of protein/molecules or are influenced prominently by factors more than the identity of the molecules such as orientation of molecules relative to the substrate surface. The standard deviation in the intensity of individual Raman peaks diminishes for protein size larger than 13 amino acids. Secondary structure of protein (such as protein-protein interaction) remains unchanged regardless of protein orientation. Numerical simulation studies corroborate the experimental observation in that the SERS spectral features of biomedically relevant protein (of larger than 13 amino acids in size, which represent all human protein types) are not affected by the orientation of amino acids randomly dispersed on SERS-active surfaces. These findings are instrumental to understanding the exceedingly high (label-free) specificity when SERS is used in identifying proteins/peptides as can be found in numerous publications from different research groups in both in vivo and in vitro analyses. It was noted that the spectral position of all Raman peaks assignable to the various amino acids are independent of molecule orientation even though their intensities do vary.

Crucial Impact of Hydrophilicity on the Self-Assembled 2D Colloidal Crystals Using Langmuir-Blodgett Method.

Large-scale close-packed two-dimensional (2D) colloidal crystal with high coverage is indispensable for various promising applications. The Langmuir-Blodgett (LB) method is a powerful technique to prepare 2D colloidal crystals. However, the self-assembly and movement of microspheres during the whole LB process are less analyzed. In this study, we clarify the crucial impact of hydrophilicity of the microspheres on their self-assembly in the LB process and on the properties of the prepared 2D colloidal crystals. The characteristic surface pressure-area isotherms of the microspheres have been analyzed and adjusted by only counting the quantity of the microspheres on the water surface, which leads to more accurate results. The critical surface pressures for hydrophilic and hydrophobic microspheres are about 61 and 46 mN/m, respectively. The decrease of the surface hydrophilicity of microspheres facilitates their self-assembly on the water surface, which further leads to higher coverage and less defects of the 2D colloidal crystals. A coverage of as high as 97% was obtained using hydrophobic microspheres. Entropy and intersphere capillary forces drive the self-assembly and transportation of the microspheres, respectively. Caused by the diffraction of visible light, opposite contrasts at local adjacent regions on the surface of the 2D colloidal crystals have been observed. The understanding of self-assembly of the microspheres during the LB process paves the way to fabricate the high-quality 2D colloidal crystals for various applications such as photonic papers and inks, stealth materials, biomimetic coatings, and related nanostructures.

Reliable resistive switching of epitaxial single crystalline cubic Y-HfO2 RRAMs with Si as bottom electrodes.

Previous studies have mainly focused on the resistive switching (RS) of amorphous or polycrystalline HfO2-RRAM. The RS of single crystalline HfO2 films has been rarely reported. Yttrium doped HfO2 (YDH) thin films were fabricated and successful Y incorporation into HfO2 was confirmed by x-ray photoemission spectroscopy. A pure cubic phase of YDH and an abrupt YDH/Si interface were obtained and verified by x-ray diffraction, Raman spectroscopy and transmission electron microscopy. A Pt/YDH/n++-Si heterostructure using Si as the bottom electrode was fabricated, which shows stable RS with an ON/OFF ratio of 100 and a reliable data retention (104 s). The electron transport mechanism was investigated in detail. It indicates that hopping conduction is dominating when the device is at a high resistance state, while space charge limited conduction acts as the dominant factor at a low resistance state. Such behavior, which is different from devices using TiN or Ti as electrodes, was attributed to the Y doping and specific YDH/Si interface. Our results demonstrate a proof of concept study to use highly doped Si as bottom electrodes along with single crystalline YDH as insulator layer for such RRAM applications as wireless sensors and synaptic simulation.

Interfacial States and Fano-Feshbach Resonance in Graphene-Silicon Vertical Junction.

Interfacial quantum states are drawing tremendous attention recently because of their importance in design of low-dimensional quantum heterostructures with desired charge, spin, or topological properties. Although most studies of the interfacial exchange interactions were mainly performed across the interface vertically, the lateral transport nowadays is still a major experimental method to probe these interactions indirectly. In this Letter, we fabricated a graphene and hydrogen passivated silicon interface to study the interfacial exchange processes. For the first time we found and confirmed a novel interfacial quantum state, which is specific to the 2D-3D interface. The vertically propagating electrons from silicon to graphene result in electron oscillation states at the 2D-3D interface. A harmonic oscillator model is used to explain this interfacial state. In addition, the interaction between this interfacial state (discrete energy spectrum) and the lateral band structure of graphene (continuous energy spectrum) results in Fano-Feshbach resonance. Our results show that the conventional description of the interfacial interaction in low-dimensional systems is valid only in considering the lateral band structure and its density-of-states and is incomplete for the ease of vertical transport. Our experimental observation and theoretical explanation provide more insightful understanding of various interfacial effects in low-dimensional materials, such as proximity effect, quantum tunneling, etc. More important, the Fano-Feshbach resonance may be used to realize all solid-state and scalable quantum interferometers.

Sculpting Extreme Electromagnetic Field Enhancement in Free Space for Molecule Sensing.

A strongly confined and enhanced electromagnetic (EM) field due to gap-plasmon resonance offers a promising pathway for ultrasensitive molecular detections. However, the maximum enhanced portion of the EM field is commonly concentrated within the dielectric gap medium that is inaccessible to external substances, making it extremely challenging for achieving single-molecular level detection sensitivity. Here, a new family of plasmonic nanostructure created through a unique process using nanoimprint lithography is introduced, which enables the precise tailoring of the gap plasmons to realize the enhanced field spilling to free space. The nanostructure features arrays of physically contacted nanofinger-pairs with a 2 nm tetrahedral amorphous carbon (ta-C) film as an ultrasmall dielectric gap. The high tunneling barrier offered by ta-C film due to its low electron affinity makes an ultranarrow gap and high enhancement factor possible at the same time. Additionally, its high electric permittivity leads to field redistribution and an abrupt increase across the ta-C/air boundary and thus extensive spill-out of the coupled EM field from the gap region with field enhancement in free space of over 103 . The multitude of benefits deriving from the unique nanostructure hence allows extremely high detection sensitivity at the single-molecular level to be realized as demonstrated through bianalyte surface-enhanced Raman scattering measurement.

Hierarchical Hybrids Integrated by Dual Polypyrrole-Based Porous Carbons for Enhanced Capacitive Performance.

Architectural design of nitrogenous polymer-based carbons represents a facile and efficient strategy to improve performance because of their morphological diversity, tailorability, and N-containing structure. In this research, 0D and 1D forms of polypyrrole-derived porous carbons (A-PCS and A-PCT, respectively) are first integrated into nitrogen-doped hierarchically porous A-PCS/PCT hybrids by applying an easy multistep method. This integration, along with chemical activation, prevents serious agglomeration of carbon particles or tubes and creates a connected porous network structure, leading to improved textural properties (high surface area of 1684 m2 g-1 , high pore volume of 1.57 cm3 g-1 , and hierarchical porosity). Thus, A-PCS/PCT hybrids in a three-electrode setup reach high specific capacitances of 224 and 206 F g-1 at 1 and 20 A g-1 , respectively, with high rate capability (92 % capacitance retention). A symmetrical supercapacitor with A-PCS/PCT electrodes presents the highest power and energy densities of 12.6 kW kg-1 and 8.58 Wh kg-1 , respectively, and exceptional cycling life and stability with 92.4 % retention for up to 20 000 cycles. This study on conductive polymer-based hybrid materials may guide the design of architectures with new structures for applications in energy storage and conversion technologies.

Copper Ion Binding Site in ß-Amyloid Peptide.

ß-Amyloid aggregates in the brain play critical roles in Alzheimer's disease, a chronic neurodegenerative condition. Amyloid-associated metal ions, particularly zinc and copper ions, have been implicated in disease pathogenesis. Despite the importance of such ions, the binding sites on the ß-amyloid peptide remain poorly understood. In this study, we use scanning tunneling microscopy, circular dichroism, and surface-enhanced Raman spectroscopy to probe the interactions between Cu2+ ions and a key ß-amyloid peptide fragment, consisting of the first 16 amino acids, and define the copper-peptide binding site. We observe that in the presence of Cu2+, this peptide fragment forms ß-sheets, not seen without the metal ion. By imaging with scanning tunneling microscopy, we are able to identify the binding site, which involves two histidine residues, His13 and His14. We conclude that the binding of copper to these residues creates an interstrand histidine brace, which enables the formation of ß-sheets.

Label-Free SERS Selective Detection of Dopamine and Serotonin Using Graphene-Au Nanopyramid Heterostructure.

Ultrasensitive detection and spatially resolved mapping of neurotransmitters, dopamine and serotonin, are critical to facilitate understanding brain functions and investigate the information processing in neural networks. In this work, we demonstrated single molecule detection of dopamine and serotonin using a graphene-Au nanopyramid heterostructure platform. The quasi-periodic Au structure boosts high-density and high-homogeneity hotspots resulting in ultrahigh sensitivity with a surface enhanced Raman spectroscopic (SERS) enhancement factor ∼10(10). A single layer graphene superimposed on a Au structure not only can locate SERS hot spots but also modify the surface chemistry to realize selective enhancement Raman yield. Dopamine and serotonin could be detected and distinguished from each other at 10(-10) M level in 1 s data acquisition time without any pretreatment and labeling process. Moreover, the heterostructure realized nanomolar detection of neurotransmitters in the presence of simulated body fluids. These findings represent a step forward in enabling in-depth studies of neurological processes including those closely related to brain activity mapping (BAM).

Controlled direct growth of Al2O3-doped HfO2 films on graphene by H2O-based atomic layer deposition.

Graphene has been drawing worldwide attention since its discovery in 2004. In order to realize graphene-based devices, thin, uniform-coverage and pinhole-free dielectric films with high permittivity on top of graphene are required. Here we report the direct growth of Al2O3-doped HfO2 films onto graphene by H2O-based atom layer deposition (ALD). Al2O3-onto-HfO2 stacks benefited the doping of Al2O3 into HfO2 matrices more than HfO2-onto-Al2O3 stacks did due to the micro-molecular property of Al2O3 and the high chemical activity of trimethylaluminum (TMA). Al2O3 acted as a network modifier, maintained the amorphous structure of the film even to 800 °C, and made the film smooth with a root mean square (RMS) roughness of 0.8 nm, comparable to the surface of pristine graphene. The capacitance and the relative permittivity of Al2O3-onto-HfO2 stacks were up to 1.18 µF cm(-2) and 12, respectively, indicating the high quality of Al2O3-doped HfO2 films on graphene. Moreover, the growth process of Al2O3-doped HfO2 films introduced no detective defects into graphene confirmed by Raman measurements.

Stimulated emission in GaN-based laser diodes far below the threshold region.

We identify that the stimulated emission of GaN laser diodes (LDs) emerges far below the traditionally recognized threshold from both optical and electrical experiments. Below the threshold, the linear-polarized stimulated emission has been the dominating part of overall emission and closely related to resonant cavity. Its intensity increases super linearly with current while that of spontaneous emission increases almost linearly. Moreover, the separation of quasi-Fermi levels of electrons and holes across the active region has already exceeded the photon emission energy, namely, realized the population-inversion.

AI-Driven Spectral Decomposition: Predicting the Most Probable Protein Compositions from Surface Enhanced Raman Spectroscopy Spectra of Amino Acids.

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for elucidating the molecular makeup of materials. It possesses the unique characteristics of single-molecule sensitivity and extremely high specificity. However, the true potential of SERS, particularly in capturing the biochemical content of particles, remains underexplored. In this study, we harnessed transformer neural networks to interpret SERS spectra, aiming to discern the amino acid profiles within proteins. By training the network on the SERS profiles of 20 amino acids of human proteins, we explore the feasibility of predicting the predominant proteins within the µL-scale detection volume of SERS. Our results highlight a consistent alignment between the model's predictions and the protein's known amino acid compositions, deepening our understanding of the inherent information contained within SERS spectra. For instance, the model achieved low root mean square error (RMSE) scores and minimal deviation in the prediction of amino acid compositions for proteins such as Bovine Serum Albumin (BSA), ACE2 protein, and CD63 antigen. This novel methodology offers a robust avenue not only for protein analytics but also sets a precedent for the broader realm of spectral analyses across diverse material categories. It represents a solid step forward to establishing SERS-based proteomics.

Enhancing Efficiency and Stability in Carbon-Based Perovskite Solar Cells by Double Passivation with Ultralow-Cost Coal-Derived Graphene and Its Derivatives.

Coal-derived carbon nanomaterials possess numerous superior features compared to other classic carbon, such as readily accessible surfaces, tunable pore structure, and facile and precise surface functionalization. Therefore, the controllable preparation of coal-derived carbon nanomaterials is anticipated to be of great significance for the performance improvement and commercialization process of carbon-based perovskite solar cells (C-PSCs). In this study, we successfully synthesized highly stable and commercially valuable graphene oxide (GO) and reduced graphene oxide (rGO) utilizing coal. Compared to traditional methods and commercial graphene, the chemical oxidation and pyrolysis process used in this study is mild and simple, offering the advantages of controlled composition and the absence of other impurities. GO or rGO was incorporated into the top of the SnO2 electron transport layer (ETL) of C-PSCs. Under optimized conditions and ultraviolet-ozone (UVO) irradiation, the ultimate power conversion efficiency (PCE) increased from the unmodified 12.4 to 14.04% (based on rGO) and 15.18% (based on GO), representing improvements of 22 and 31%, respectively. The improved photovoltaic performance is mainly owing to enhanced charge transport capabilities, denser interfacial contacts, improved carrier separation properties, increased conductivity, and abundance of hydrophilic functional groups in GO, which can form more stable hydrogen bonds with SnO2. After being stored at room temperature and ambient humidity for 30 days, the modified, unpacked devices retained 87% of the highest power conversion efficiency (PCE). This study introduces a practical and manageable method to enhance the performance of C-PSCs by using functional carbon nanomaterials derived from coal.

The cellulose nanocrystal jammed interfaces induced by CO2-assisted self-assembly for enhancing oil recovery.

Stability of displacement front is of great importance in the immiscible fluid displacement for enhancing oil recovery. Here, a CO2-strenghened assembly approach is demonstrated for the fabrication of highly jammed CNSs (cellulose nanocrystal surfactants) with EPD (N'-ethylpropane-1,3-diamine) and TOCNC (TEMPO oxidized cellulose nanocrystal), which produce a structured film at the oil-water interface to counteract the capillary force, and thus governing the local displacing pattern. In this approach, EPD molecules can be deeply protonated in the presence of CO2, favoring their binding forces with TOCNC at the interface to produce more CNSs. Meanwhile, the strong intermolecular attractions among CO2-bearing CNSs promote to form a striped interfacial film with both the close-packed rod-like arrays in horizontal and the multi-layer in lateral. Further, the CNSs-based film confers with a high strength and elasticity can reduce the capillary force by 87 % in micro-channels, yielding a smooth water-to-oil displacement front, which markedly enhances the oil recovery by 20.6 % compared to the surfactant-only flooding. This self-assembly strategy has a great implication in eco-friendly and cost-effective applications, such as enhanced oil recovery, CO2 geo-sequestration, and water infiltration.

Constructing a novel type-â ¡ ZnO/BiOCOOH heterojunction microspheres for the degradation of tetracycline and bacterial inactivation.

A novel ZnO/BiOCOOH microsphere photocatalyst with a type-Ⅱ mechanism was developed for the first time. This strategy was accomplished by immobilizing ZnO onto 3D BiOCOOH microspheres via a single-step hydrothermal synthesis method. The ability to degrade tetracycline (TC) in water under visible light and inactivate bacteria of as-catalyst were analyzed. Among the prepared samples, the ZnO/BiOCOOH composite, with a mass ratio of 40%(Zn/Bi), exhibited the highest photocatalytic activity, which was able to degrade 98.22% of TC in just 90 min and completely eradicated Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in 48 h, and had potential application in solving water resource environmental pollution. The photoelectric characteristics of the photocatalysts were examined by means of electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) spectroscopy. The findings indicated that the superior photocatalytic performance could be credited to the dissociation of electrons (e-) and holes (h+) in heterojunction composites. Finally, electron paramagnetic resonance (EPR) and capture experiments were conducted to confirm the photocatalytic mechanism of the type-Ⅱ heterojunction. This work provides a new Bi-base photocatalyst for aqueous environmental control.

Label-free single-vesicle based surface enhanced Raman spectroscopy: A robust approach for investigating the biomolecular composition of small extracellular vesicles.

Small extracellular vesicles (sEVs) are cell-released vesicles ranging from 30-150nm in size. They have garnered increasing attention because of their potential for both the diagnosis and treatment of disease. The diversity of sEVs derives from their biological composition and cargo content. Currently, the isolation of sEV subpopulations is primarily based on bio-physical and affinity-based approaches. Since a standardized definition for sEV subpopulations is yet to be fully established, it is important to further investigate the correlation between the biomolecular composition of sEVs and their physical properties. In this study, we employed a platform combining single-vesicle surface-enhanced Raman spectroscopy (SERS) and machine learning to examine individual sEVs isolated by size-exclusion chromatography (SEC). The biomolecular composition of each vesicle examined was reflected by its corresponding SERS spectral features (biomolecular "fingerprints"), with their roots in the composition of their collective Raman-active bonds. Origins of the SERS spectral features were validated through a comparative analysis between SERS and mass spectrometry (MS). SERS fingerprinting of individual vesicles was effective in overcoming the challenges posed by EV population averaging, allowing for the possibility of analyzing the variations in biomolecular composition between the vesicles of similar and/or different sizes. Using this approach, we uncovered that each of the size-based fractions of sEVs contained particles with predominantly similar SERS spectral features. Indeed, more than 84% of the vesicles residing within a particular group were clearly distinguishable from that of the other EV sub-populations, despite some spectral variations within each sub-population. Our results suggest the possibility that size-based EV fractionation methods produce samples where similarly eluted sEVs are correlated with their respective biochemical contents, as reflected by their SERS spectra. Our findings therefore highlight the possibility that the biogenesis and respective biological functionalities of the various sEV fractions may be inherently different.

High stretchable and self-healing nanocellulose-poly(acrylic acid) composite hydrogels for sustainable CO2 shutoff.

The injection of CO2 into oil reservoirs to enhance oil recovery (EOR) has become a widely accepted and effective technical method, which, however, remains subject to the gas channeling caused by the reservoir fractures. Herein, this work developed a novel plugging gel combining excellent mechanical properties, fatigue resistance, elastic and self-healing properties for the CO2 shutoff purpose. This gel consisting of grafted nanocellulose and polymer network was synthesized via a free-radical polymerization, and reinforced by using Fe3+ to cross-link the two networks. The as-prepared PAA-TOCNF-Fe3+ gel has a stress of 1.03 MPa and a high strain of 1491 %, and self-heals to its original 98 % in stress and 96 % in strain after rupture, respectively. The introduce of TOCNF/Fe3+ improves the excellent energy dissipation and self-healing via the synergy effect of dynamical coordination bonds and hydrogen bonds. Further, the PAA-TOCNF-Fe3+ gel is both flexible and high-strength in plugging the multi-round CO2 injection, during which the CO2 breakthrough pressure is above 9.9 MPa/m, the plugging efficiency exceeds 96 %, and the self-healing rate is larger than 90 %. Given that above, this gel shows a great potential to plug the high-pressure CO2 flow, which could offer a new method for CO2-EOR and carbon storage.

Water-Induced Cellulose Nanofibers/Poly(vinyl alcohol) Hydrogels Regulated by Hydrogen Bonding for In Situ Water Shutoff.

Hydrogels have been widely applied to the water shutoff in oilfields due to their excellent three-dimensional network and thermal and physicochemical stability, and it is still a huge challenge to develop new hydrogels with simple preparation, low cost, and high mechanical performance that can meet the requirements of practical applications. Herein, we devised a simple and universal manufacturing method for regulating the hydrogen bonds between poly(vinyl alcohol) (PVA) and cellulose nanofibers (CNF) via the water-diffusion action, thus fabricating a physically tough PVA-CNF hydrogel for the in situ water shutoff. This method allowed the polymer chains to strengthen the molecular interactions between polymers upon replacing with water (a poor solvent) to regulate the cross-linking structure, characterizing by the nano-crystallinity domains and fibrillar segments, which also accounted for the thermal stability, extraordinary elasticity, high stretchability, and toughness of PVA-CNF hydrogel. Further, the obtained PVA-CNF hydrogel exhibited superb plugging performance, that is, the breakthrough pressure gradient could reach 71.56 MPa·m-1, surpassing all currently reported gelling water shutoff agents. This water-induced in situ hydrogelation made it well suited as a water shutoff agent in oilfields and may provide a promising strategy to fabricate mechanically robust smart materials for the water shutoff projects with low cost, simple processing, and high efficiency.

Controlling the Nucleation and Growth of Salt from Bodily Fluid for Enhanced Biosensing Applications.

Surface-enhanced Raman spectroscopy (SERS) represents a transformative tool in medical diagnostics, particularly for the early detection of key biomarkers such as small extracellular vesicles (sEVs). Its unparalleled sensitivity and compatibility with intricate biological samples make it an ideal candidate for revolutionizing noninvasive diagnostic methods. However, a significant challenge that mars its efficacy is the throughput limitation, primarily anchored in the prerequisite of hotspot and sEV colocalization within a minuscule range. This paper delves deep into this issue, introducing a never-attempted-before approach which harnesses the principles of crystallization-nucleation and growth. By synergistically coupling lasers with plasmonic resonances, we navigate the challenges associated with the analyte droplet drying method and the notorious coffee ring effect. Our method, rooted in a profound understanding of crystallization's materials science, exhibits the potential to significantly increase the areal density of accessible plasmonic hotspots and efficiently guide exosomes to defined regions. In doing so, we not only overcome the throughput challenge but also promise a paradigm shift in the arena of minimally invasive biosensing, ushering in advanced diagnostic capabilities for life-threatening diseases.

Analyzing bronchoalveolar fluid derived small extracellular vesicles using single-vesicle SERS for non-small cell lung cancer detection.

An emerging body of research by biologists and clinicians has demonstrated the clinical application of small extracellular vesicles (sEVs, also commonly referred to as exosomes) as biomarkers for cancer detections. sEVs isolated from various body fluids such as blood, saliva, urine, and cerebrospinal fluid have been used for biomarker discoveries with highly encouraging outcomes. Among the biomarkers discovered are those responsible for multiple cancer types and immune responses. These biomarkers are recapitulated from the tumor microenvironments. Yet, despite numerous discussions of sEVs in scientific literature, sEV-based biomarkers have so far played only a minor role for cancer diagnostics in the clinical setting, notably less so than other techniques such as imaging and biopsy. In this paper, we report the results of a pilot study (n = 10 from each of the patient and the control group) using bronchoalveolar lavage fluid to determine the presence of sEVs related to non-small cell lung cancer in twenty clinical samples examined using surface enhanced Raman spectroscopy (SERS).