Surface NMR using quantum sensors in diamond.

NMR is a noninvasive, molecular-level spectroscopic technique widely used for chemical characterization. However, it lacks the sensitivity to probe the small number of spins at surfaces and interfaces. Here, we use nitrogen vacancy (NV) centers in diamond as quantum sensors to optically detect NMR signals from chemically modified thin films. To demonstrate the method's capabilities, aluminum oxide layers, common supports in catalysis and materials science, are prepared by atomic layer deposition and are subsequently functionalized by phosphonate chemistry to form self-assembled monolayers. The surface NV-NMR technique detects spatially resolved NMR signals from the monolayer, indicates chemical binding, and quantifies molecular coverage. In addition, it can monitor in real time the formation kinetics at the solid-liquid interface. With our approach, we show that NV quantum sensors are a surface-sensitive NMR tool with femtomole sensitivity for in situ analysis in catalysis, materials, and biological research.

The role of mediators for the pretesting effect.

Taking a pretest (e.g., smoke - ?) before material is studied (smoke - fog) can improve later recall of that material, compared to material which was initially only studied. The goal of the present study was to evaluate for this pretesting effect the potential role of semantic mediators, i.e., of unstudied information that is semantically related to the study material. In all three experiments, subjects studied weakly associated word pairs (e.g., smoke - fog), half of which received a pretest. Subjects then either completed a recognition test (Experiment 1) or a cued-recall test (Experiments 2 and 3), during which they were presented with both the original study material and never-before-seen semantic mediators that were strongly related to the cue item of a pair (e.g., cigarette). Strikingly, presenting semantic mediators as lures led to higher false alarm rates for mediators following initial pretesting than study only (Experiment 1), and presenting semantic mediators as retrieval cues led to better recall of target items following pretesting than study only (Experiments 2 and 3). We argue that these findings support the elaboration account of the pretesting effect but are difficult to reconcile with other prominent accounts of the effect.

The pretesting effect thrives in the presence of competing information.

Taking a pretest (e.g., blanket - ?) before some target material (blanket - sheet) is studied can promote recall of that material on a subsequent final test compared to material which was initially only studied. Here, we examine whether such pretesting can shield the tested material from interference-induced forgetting, which often occurs when before final testing, related material is encountered. We applied a typical pretesting task but asked subjects, between acquisition and final testing of the target list (list 1), to study two additional lists of items with either completely new and unique pairs (e.g., atom - cell) or overlapping - and thus potentially interfering - pairs (e.g., blanket - sleep). Target-list recall on the final test showed a typical pretesting effect for unique pairs, but the size of the effect even increased for overlapping pairs, as recall of study-only pairs was impaired, whereas recall of pretest pairs was left largely unaffected. This held regardless of whether a low (Experiment 1) or high (Experiment 2) degree of learning was induced for the interfering material, suggesting that pretesting can indeed protect the tested material from interference. These findings indicate that pretesting could play a significant role in educational settings where information often needs to be retained in the presence of competing information.

Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon.

Hybrid inorganic/organic heterointerfaces are promising systems for next-generation photocatalytic, photovoltaic, and chemical-sensing applications. Their performance relies strongly on the development of robust and reliable surface passivation and functionalization protocols with (sub)molecular control. The structure, stability, and chemistry of the semiconductor surface determine the functionality of the hybrid assembly. Generally, these modification schemes have to be laboriously developed to satisfy the specific chemical demands of the semiconductor surface. The implementation of a chemically independent, yet highly selective, standardized surface functionalization scheme, compatible with nanoelectronic device fabrication, is of utmost technological relevance. Here, we introduce a modular surface assembly (MSA) approach that allows the covalent anchoring of molecular transition-metal complexes with sub-nanometer precision on any solid material by combining atomic layer deposition (ALD) and selectively self-assembled monolayers of phosphonic acids. ALD, as an essential tool in semiconductor device fabrication, is used to grow conformal aluminum oxide activation coatings, down to sub-nanometer thicknesses, on silicon surfaces to enable a selective step-by-step layer assembly of rhenium(I) bipyridine tricarbonyl molecular complexes. The modular surface assembly of molecular complexes generates precisely structured spatial ensembles with strong intermolecular vibrational and electronic coupling, as demonstrated by infrared spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy analysis. The structure of the MSA can be chosen to avoid electronic interactions with the semiconductor substrate to exclusively investigate the electronic interactions between the surface-immobilized molecular complexes.

Role of Different Receptor-Surface Binding Modes in the Morphological and Electrochemical Properties of Peptide-Nucleic-Acid-Based Sensing Platforms.

Label-free detection of charged biomolecules, such as DNA, has experienced an increase in research activity in recent years, mainly to obviate the need for elaborate and expensive pretreatments for labeling target biomolecules. A promising label-free approach is based on the detection of changes in the electrical surface potential on biofunctionalized silicon field-effect devices. These devices require a reliable and selective immobilization of charged biomolecules on the device surface. In this work, self-assembled monolayers of phosphonic acids are used to prepare organic interfaces with a high density of peptide nucleic acid (PNA) bioreceptors, which are a synthetic analogue to DNA, covalently bound either in a multidentate (∥PNA) or monodentate (⊥PNA) fashion to the underlying silicon native oxide surface. The impact of the PNA bioreceptor orientation on the sensing platform's surface properties is characterized in detail by water contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Our results suggest that the multidentate binding of the bioreceptor via attachment groups at the γ-points along the PNA backbone leads to the formation of an extended, protruding, and netlike three-dimensional metastructure. Typical "mesh" sizes are on the order of 8 ± 2.5 nm in diameter, with no preferential spatial orientation relative to the underlying surface. Contrarily, the monodentate binding provides a spatially more oriented metastructure comprising cylindrical features, of a typical size of 62 ± 23 × 12 ± 2 nm2. Additional cyclic voltammetry measurements in a redox buffer solution containing a small and highly mobile Ru-based complex reveal strikingly different insulating properties (ion diffusion kinetics) of these two PNA systems. Investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA layers represented by detectable changes of the conductance and capacitance of the underlying silicon substrate in the range of 30-50% depending on the surface organization of the bioreceptors in different bias potential regimes.

Repeated guessing attempts during acquisition can promote subsequent recall performance.

Taking a pretest before to-be-learned material is studied can improve long-term retention of the material relative to material that was initially only studied. Using weakly associated word pairs (Experiments 1 and 3), Swahili-German word pairs (Experiment 2), and prose passages (Experiment 4) as study material, the present study examined whether this pretesting effect is modulated in size when pretests are repeatedly administered during acquisition. All four experiments consistently showed the typical pretesting effect, with enhanced recall after a single guessing attempt relative to the study-only baseline. Critically, the pretesting effect increased in size when multiple guessing attempts were made during acquisition, regardless of whether the duration of the pretesting phase increased with the number of guesses (Experiments 1, 2, and 4) or was held constant (Experiment 3). The results of Experiment 4 also indicate that neither a single guessing attempt nor multiple guessing attempts easily induce the transfer of learning to previously studied but untested information. Together, the findings demonstrate that additional guesses can promote access to the pretested target material on the final test, suggesting that in educational contexts, extensive pretesting during acquisition may serve as an effective learning strategy. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Viscoelastic properties of suspended cells measured with shear flow deformation cytometry.

Numerous cell functions are accompanied by phenotypic changes in viscoelastic properties, and measuring them can help elucidate higher level cellular functions in health and disease. We present a high-throughput, simple and low-cost microfluidic method for quantitatively measuring the elastic (storage) and viscous (loss) modulus of individual cells. Cells are suspended in a high-viscosity fluid and are pumped with high pressure through a 5.8 cm long and 200 µm wide microfluidic channel. The fluid shear stress induces large, ear ellipsoidal cell deformations. In addition, the flow profile in the channel causes the cells to rotate in a tank-treading manner. From the cell deformation and tank treading frequency, we extract the frequency-dependent viscoelastic cell properties based on a theoretical framework developed by R. Roscoe [1] that describes the deformation of a viscoelastic sphere in a viscous fluid under steady laminar flow. We confirm the accuracy of the method using atomic force microscopy-calibrated polyacrylamide beads and cells. Our measurements demonstrate that suspended cells exhibit power-law, soft glassy rheological behavior that is cell-cycle-dependent and mediated by the physical interplay between the actin filament and intermediate filament networks.

Cells in the human body are viscoelastic: they have some of the properties of an elastic solid, like rubber, as well as properties of a viscous fluid, like oil. To carry out mechanical tasks ­ such as, migrating through tissues to heal a wound or to fight inflammation ­ cells need the right balance of viscosity and elasticity. Measuring these two properties can therefore help researchers to understand important cell tasks and how they are impacted by disease. However, quantifying these viscous and elastic properties is tricky, as both depend on the time-scale they are measured: when pressed slowly, cells appear soft and liquid, but they turn hard and thick when rapidly pressed. Here, Gerum et al. have developed a new system for measuring the viscosity and elasticity of individual cells that is fast, simple, and inexpensive. In this new method, cells are suspended in a specialized solution with a consistency similar to machine oil which is then pushed with high pressure through channels less than half a millimeter wide. The resulting flow of fluid shears the cells, causing them to elongate and rotate, which is captured using a fast camera that takes 500 images per second. Gerum et al. then used artificial intelligence to extract each cell's shape and rotation speed from these images, and calculated their viscosity and elasticity based on existing theories of how viscoelastic objects behave in fluids. Gerum et al. also investigated how the elasticity and viscosity of cells changed with higher rotation frequencies, which corresponds to shorter time-scales. This revealed that while higher frequencies made the cells appear more viscous and elastic, the ratio between these two properties remained the same. This means that researchers can compare results obtained from different experimental techniques, even if the measurements were carried out at completely different frequencies or time-scales. The method developed by Gerum et al. provides a fast an inexpensive way for analyzing the viscosity and elasticity of cells. It could also be a useful tool for screening the effects of drugs, or as a diagnostic tool to detect diseases that affect the mechanical properties of cells.

Functionalization of small platinum nanoparticles with amines and phosphines: Ligand binding modes and particle stability.

We report the binding mode of amines and phosphines on platinum nanoparticles. Protective ligands comprising different functional groups are systematically studied for the elucidation of ligand binding at different functionalization conditions. From the functionalization conditions it is concluded that the binding of amines to the nanoparticles occurs via the formation of a PtHN moiety or electrostatic interaction, which is supported by spectroscopic evidences. In particular from complex chemistry such a binding mode is surprising, as amines are expected to bind via their electron pair to the metal. Similar results from functionalization are observed for phosphine-protected nanoparticles, which suggest similar binding modes in these systems. In contrast to the strong covalent bond of the protection with thiols, considerable weakly binding systems result. The characteristics of the binding mode are reflected by the stability of the colloids and their catalytic properties. In the selective hydrogenation of 3-hexyne to 3-hexene thiolate-stabilized Pt particles are highly stable, but exhibit the lowest activity. On the other hand, amine- and phosphine-capped platinum nanoparticles show a significantly higher activity, but rapidly agglomerate.