Mechanistic Pathways for the Molecular Step Growth of Calcium Oxalate Monohydrate Crystal Revealed by In Situ Liquid-Phase Atomic Force Microscopy.

Calcium oxalate monohydrate (COM) crystal is the most common crystalline component of human kidney stones. The molecular-scale inhibitory mechanisms of COM crystal growth by urinary biomolecules such as citrate and osteopontin adsorbed onto the crystal surface are now well understood. However, the pathways by which dissolved calcium and oxalate ions are incorporated into the molecular step of the COM crystal surface, leading to COM crystal growth-a prerequisite to be elucidated for developing effective therapeutics to inhibit COM stones-remain unknown. Here, using in situ liquid-phase atomic microscopy along with a step kinetic model, we reveal the pathways of the calcium and oxalate ions into the COM molecular step via the growth speed analysis of the molecular steps with respect to their step width at the nanoscale. Our results show that, primarily, the ions are adsorbed onto the terrace of the crystal surface from the solution-the rate-controlling stage for the molecular step growth, i.e., COM crystal growth-and then diffuse over it and are eventually incorporated into the steps. This primary pathway of the ions is unaffected by the model peptide D-Asp6 adsorbed on the COM crystal surface, suggesting that urinary biomolecules will not alter the pathway. These new findings rendering an essential understanding of the fundamental growth mechanism of COM crystal at the nanoscale provide crucial insights beneficial to the development of effective therapeutics for COM kidney stones.

Ultra-Permeable Single-Walled Carbon Nanotube Membranes with Exceptional Performance at Scale.

Enhanced fluid transport in single-walled carbon nanotubes (SWCNTs) promises to enable major advancements in many membrane applications, from efficient water purification to next-generation protective garments. Practical realization of these advancements is hampered by the challenges of fabricating large-area, defect-free membranes containing a high density of open, small diameter SWCNT pores. Here, large-scale (≈60 cm2) nanocomposite membranes comprising of an ultrahigh density (1.89 × 1012 tubes cm-2) of 1.7 nm SWCNTs as sole transport pathways are demonstrated. Complete opening of all conducting nanotubes in the composite enables unprecedented accuracy in quantifying the enhancement of pressure-driven transport for both gases (>290× Knudsen prediction) and liquids (6100× no-slip Hagen-Poiseuille prediction). Achieved water permeances (>200 L m-2 h-1 bar-1) greatly exceed those of state-of-the-art commercial nano- and ultrafiltration membranes of similar pore size. Fabricated membranes reject nanometer-sized molecules, permit fractionation of dyes from concentrated salt solutions, and exhibit excellent chemical resistance. Altogether, these SWCNT membranes offer new opportunities for energy-efficient nano- and ultrafiltration processes in chemically demanding environments.

Quantifying the Hierarchical Order in Self-Aligned Carbon Nanotubes from Atomic to Micrometer Scale.

Fundamental understanding of structure-property relationships in hierarchically organized nanostructures is crucial for the development of new functionality, yet quantifying structure across multiple length scales is challenging. In this work, we used nondestructive X-ray scattering to quantitatively map the multiscale structure of hierarchically self-organized carbon nanotube (CNT) "forests" across 4 orders of magnitude in length scale, from 2.0 Å to 1.5 µm. Fully resolved structural features include the graphitic honeycomb lattice and interlayer walls (atomic), CNT diameter (nano), as well as the greater CNT ensemble (meso) and large corrugations (micro). Correlating orientational order across hierarchical levels revealed a cascading decrease as we probed finer structural feature sizes with enhanced sensitivity to small-scale disorder. Furthermore, we established qualitative relationships for single-, few-, and multiwall CNT forest characteristics, showing that multiscale orientational order is directly correlated with number density spanning 109-1012 cm-2, yet order is inversely proportional to CNT diameter, number of walls, and atomic defects. Lastly, we captured and quantified ultralow-q meridional scattering features and built a phenomenological model of the large-scale CNT forest morphology, which predicted and confirmed that these features arise due to microscale corrugations along the vertical forest direction. Providing detailed structural information at multiple length scales is important for design and synthesis of CNT materials as well as other hierarchically organized nanostructures.

Deterministic control over high-Z doping of polydicyclopentadiene-based aerogel coatings.

We report on simple and efficient routes to dope polydicyclopentadiene (PDCPD)-based aerogels and their coatings with high-Z tracer elements. Initially, direct halogenation of PDCPD wet gels and aerogels with elemental iodine or bromine was studied. Although several pathways were identified that allowed doping of PDCPD aerogels by direct addition of bromine or iodine to the unsaturated polymer backbone, they all provided limited control over the amount and uniformity of doping, especially at very low dopant concentrations. Deterministic control over the doping level in polymeric aerogels and aerogel coatings was then achieved by developing a copolymerization approach with iodine and tin containing comonomers. Our results highlight the versatility of the ring-opening metathesis polymerization (ROMP)-based copolymerization approach in terms of functionalization and doping of low density polymeric aerogels and their coatings.

Applying imaging ToF-SIMS and PCA in differentiation of tissue types.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has proven to be an extremely powerful tool for characterizing chemical distributions within biological cells and tissues. However, differentiating biological samples, e.g., cancerous cells from their normal counterparts or benign tissues from malignant tissues, presents unique challenges to ToF-SIMS. Repeatable differentiation of such samples, especially formalin-fixed paraffin-embedded (FFPE) histological specimens, could be used to improve tissue-based diagnosis and aid in prognosis decisions. In this chapter, we describe a strategy for characterizing and differentiating FFPE tissues. ToF-SIMS was used to image deparaffinized FFPE mouse embryos and differentiate tissue types. The robustness and repeatability of the method was determined by analyzing ten tissue slices from three different embryos over a period of 1 month. Using principal component analysis (PCA) to reduce the spectral data generated by ToF-SIMS, histopathologically identified tissue types of the mouse embryos can be differentiated based on the characteristic differences in their mass spectra.

Preparation of single cells for imaging/profiling mass spectrometry.

Characterizing chemical changes within individual cells is important for determining fundamental mechanisms of biological processes that will lead to new biological insights and improved disease understanding. Analyzing biological systems with imaging and profiling mass spectrometry (MS) has gained popularity in recent years as a method for creating chemical maps of biological samples. To obtain mass spectra that provide relevant molecular information about individual cells, samples must be prepared so that salts and other cell culture components are removed from the cell surface and that the cell contents are rendered accessible to the desorption beam. We have designed a cellular preparation protocol for imaging/profiling MS that removes the majority of the interfering species derived from the cellular growth medium, preserves the basic morphology of the cells, and allows chemical profiling of the diffusible elements of the cytosol. Using this method, we are able to reproducibly analyze cells from three diverse cell types: MCF7 human breast cancer cells, Madin-Darby canine kidney (MDCK) cells, and NIH/3T3 mouse fibroblasts. This preparation technique makes possible routine imaging/profiling MS analysis of individual cultured cells, allowing for understanding of molecular processes within individual cells.

Porphyrin-based photocatalytic lithography.

Photocatalytic lithography couples light with photoreactive coated mask materials to pattern surface chemistry. We excite porphyrins to create radical species that photocatalytically oxidize, and thereby pattern, chemistries in the local vicinity. The technique advantageously is suited for use with a wide variety of substrates. It is fast and robust, and the wavelength of light does not limit the resolution of patterned features. We have patterned proteins and cells to demonstrate the utility of photocatalytic lithography in life science applications.

Steady-state asymmetric nanospray dual ion source for accurate mass determination within a chromatographic separation.

Here we report the design, implementation, and initial use of an asymmetric steady-state continuous dual-nanospray ion source. This new source design consists of two independently controlled and continuously operating nanospray interfaces with funnel shaped counter electrodes. A steady-state ion mixing region combines the ions from the two sources into a single ion beam in the intermediate region after ion extraction from the nanospray sources but before the bulk of the pressure gradient of the vacuum interface. With this design we have achieved robust mixing of ions with no loss of duty cycle and remarkable ionization characteristics that appear entirely noncompetitive and potentially beneficial. This allows continuous introduction of internal mass calibration ions during a liquid chromatography-mass spectrometric analysis. This in turn allows for recalibration of individual spectra yielding sub part per million mass accuracy throughout the run. The steady-state approach presented here has several advantages over previous approaches. Since neither the voltage nor positions of the sprayers are changed, the nanospray has greater spray stability. The ions produced by the analyte sprayer are continuously sampled, as opposed to time-sharing which necessitates that the analyte ion stream be interrupted for some part of the duty cycle. There are no moving parts, no rapid changes to high voltages requiring additional control electronics, and no need for completely separate vacuum interfaces and the associated complexity. The sprayers are independently controlled and do not exhibit competition or mutual ionization suppression. This novel source has been implemented with a Bruker Apex II 9.4 T FTICR with a modified Apollo electrospray ion source as part of a nanoflow liquid chromatography-Fourier transform ion cyclotron resonance mass spectrometry analysis platform. Because of the low cost of implementation, the new source could potentially be applied to other forms of mass spectrometry, such as electrospray ionization-time-of-flight (ESI-TOF), which can benefit from internal mass calibration.