Microchip-based immunomagnetic detection of circulating tumor cells

Screening for circulating tumor cells (CTCs) in blood has been an object of interest for evidence of progressive disease, status of disease activity, recognition of clonal evolution of molecular changes and for possible early diagnosis of cancer. We describe a new method of microchip-based immunomagnetic CTC detection, in which the benefits of both immunomagnetic assay and the microfluidic device are combined. As the blood sample flows through the microchannel closely above arrayed magnets, cancer cells labeled with magnetic nanoparticles are separated from blood flow and deposited at the bottom wall of the glass coverslip, which allows direct observation of captured cells with a fluorescence microscope. A polydimethylsiloxane (PDMS)-based microchannel fixed on a glass coverslip was used to screen blood samples. The thin, flat dimensions of the microchannel, combined with the sharp magnetic field gradient in the vicinity of arrayed magnets with alternate polarities, lead to an effective capture of labeled cells. Compared to the commercially available CellSearch? system, fewer (25%) magnetic particles are required to achieve a comparable capture rate, while the screening speed (at an optimal blood flow rate of 10 mL h(-1)) is more than five times faster than those reported previously with a microchannel-based assay. For the screening experiment, blood drawn from healthy subjects into CellSave? tubes was spiked with cultured cancer cell lines of COLO205 and SKBR3. The blood was then kept at room temperature for 48 hours before the screening, emulating the actual clinical cases of blood screening. Customized Fe(3)O(4) magnetic nanoparticles (Veridex Ferrofluid?) conjugated to anti-epithelial cell adhesion molecule (EpCAM) antibodies were introduced into the blood samples to label cancer cells, and the blood was then run through the microchip device to capture the labelled cells. After capture, the cells were stained with fluorescent labelled anti-cytokeratin, DAPI and anti-CD45. Subsequent immunofluorescence images were taken for the captured cells, followed by comprehensive computer aided analysis based on fluorescence intensities and cell morphology. Rare cancer cells (from ～1000 cells down to ～5 cells per mL) with very low tumor cell to blood cell ratios (about 1?:?10(7) to 10(9), including red blood cells) were successfully detected. Cancer cell capture rates of 90% and 86% were demonstrated for COLO205 and SKBR3 cells, respectively.     

Parylene insulated probes for scanning electrochemical-atomic force microscopy

Scanning electrochemical-atomic force microscopy (SECM-AFM) is a powerful technique that can be used to obtain in situ information related to electrochemical phenomena at interfaces. Fabrication of probes to perform SECM-AFM experiments remains a challenge. Herein, we describe a method for formation of microelectrodes at the tip of commercial conductive AFM probes and demonstrate application of these probes to SECM-AFM. Probes were first insulated with a thin parylene layer, followed by subsequent exposure of active electrodes at the probe tips by mechanical abrasion of the insulating layer. Characterization of probes was performed by electron microscopy and cyclic voltammetry. In situ measurement of localized electrochemical activity with parylene-coated probes was demonstrated through measurement of the diffusion of Ru(NH)(6)(3+) across a porous membrane.     

Development of botanical and fish oil standard reference materials for fatty acids

As part of a collaboration with the National Institutes of Health’s Office of Dietary Supplements and the Food and Drug Administration’s Center for Drug Evaluation and Research, the National Institute of Standards and Technology has developed Standard Reference Material (SRM) 3274 Botanical Oils Containing Omega-3 and Omega-6 Fatty Acids and SRM 3275 Omega-3 and Omega-6 Fatty Acids in Fish Oil. SRM 3274 consists of one ampoule of each of four seed oils (3274-1 Borage (Borago officinalis), 3274-2 Evening Primrose (Oenothera biennis), 3274-3 Flax (Linium usitatissimum), and 3274-4 Perilla (Perilla frutescens)), and SRM 3275 consists of two ampoules of each of three fish oils (3275-1 a concentrate high in docosahexaenoic acid, 3275-2 an anchovy oil high in docosahexaenoic acid and eicosapentaenoic acid, and 3275-3 a concentrate containing 60 % long-chain omega-3 fatty acids). Each oil has certified and reference mass fraction values for up to 20 fatty acids. The fatty acid mass fraction values are based on results from analyses using gas chromatography with flame ionization detection (GC-FID) and mass spectrometry (GC/MS). These SRMs will complement other reference materials currently available with mass fractions for similar analytes and are part of a series of SRMs being developed for dietary supplements.

Professional Development Strategically Connecting Mathematics and Science: The Impact on Teachers' Confidence and Practice

The press to integrate mathematics and science comes from researchers, business leaders, and educators, yet research that examines ways to support teachers in relating these disciplines is scant. Using research on science and mathematics professional development, we designed a professional development project to help elementary teachers improve their teaching of mathematics and science by strategically connecting these disciplines. The purposes of this study are: (a) to identify changes in teachers' confidence and practice after participating in the professional development and (b) to identify different ways to connect mathematics and science during the professional development. We use a Likert‐scale survey to assess changes in teachers' confidence related to teaching mathematics and science. In addition, we report on a thematic analysis of teachers' written responses to open‐ended questions that probed teachers' perceived changes in practice. We analyze field notes from observations of project workshops to document different types of opportunities for connecting mathematics and science. We conclude with implications for future professional development that connects mathematics and science in meaningful ways, as well as suggestions for future research.     

Multiple peptide conformations give rise to similar binding affinities: molecular simulations of p53-MDM2

Molecular dynamics simulations, guided by experimental information (Zondlo et al. Biochemistry 2006, 45, 11945-11957) have been used successfully to reproduce experimental trends in binding affinities of variant p53 peptides with MDM2. Simulations reveal how the conformations of the peptides and the receptor modulate each other to optimize interactions. The conformations of the uncomplexed peptides are governed by a combination of helix and intrinsic disorder (in agreement with experiments), while in the complexed state two very different conformations can coexist. This yields very similar binding affinities, driven by either enthalpy or entropy.     

Coordination polymers based on aluminum(III) porphyrins

Aluminum(III) porphyrin carboxylate complexes have shown an affinity for a sixth nitrogenous ligand. The use of isonicotinic or nicotinic acid, which offers both a carboxylate and a nitrogen donor in the same molecule, resulted in the formation of one-dimensional (1-D) coordination polymers. The complexes and their linear oligomers have been characterized by (1)H NMR spectroscopy and nanoelectrospray ionization spectrometry. X-ray analyses confirmed the formation of the 1-D polymers in the solid state.     

Particle detection and non-detection in a quantum time of arrival measurement

The standard time-of-arrival distribution cannot reproduce both the temporal and the spatial profile of the modulus squared of the time-evolved wave function for an arbitrary initial state. In particular, the time-of-arrival distribution gives a non-vanishing probability even if the wave function is zero at a given point for all values of time. This poses a problem in the standard formulation of quantum mechanics where one quantizes a classical observable and uses its spectral resolution to calculate the corresponding distribution. In this work, we show that the modulus squared of the time-evolved wave function is in fact contained in one of the degenerate eigenfunctions of the quantized time-of-arrival operator. This generalizes our understanding of quantum arrival phenomenon where particle detection is not a necessary requirement, thereby providing a direct link between time-of-arrival quantization and the outcomes of the two-slit experiment.     

Poly(dG) spacers lead to increased surface coverage of DNA probes: an XPS study of oligonucleotide binding to zirconium phosphonate modified surfaces

A spacer is often employed between the surface linking group and the probe sequence to improve the performance of DNA microarrays. Previous work demonstrated that a consecutive stretch of guanines as a spacer increased target capture during hybridization relative to probes with either no spacer or a similar stretch of one of the other nucleotides. Using zirconium phosphonate modified surfaces with 5'-phosphorylated ssDNA probes, the present study compares the surface coverage of ssDNA probes containing either a poly(dG) spacer or a poly(dA) spacer. Surface coverages are quantified by XPS using a modified overlayer model. The results show that after treatment to mimic conditions of the passivation and hybridization steps the probe with the poly(dG) spacer has about twice the surface coverage as the probe with the poly(dA) spacer, indicating that increased target capture is due to higher probe coverage. When monitoring the surface coverage after each rinsing step, it is observed that the probe with the poly(dA) spacer is more susceptible to rinsing, suggesting the interaction with the surface is different for the two probes. It is suggested that the formation of G quadruplexes causes an increased avidity of the probe for the zirconium phosphonate surface.     

The exponent in the general Randić index

We determine conditions for the parameters n and δ, for which the general Randić index R _δ is not an acceptable index of branching of n-vertex trees, i.e., for which the n-vertex star and the n-vertex path have not extremal R _δ-values among all n-vertex trees. Analogous results are established also in the case of n-vertex chemical trees. Numerous other results for the general Randić index of trees and chemical trees are obtained.      

Rate coefficients for the reaction of OH with a series of unsaturated alcohols between 263 and 371 K

Rate coefficients for the gas-phase reactions of OH radicals with four unsaturated alcohols, 3-methyl-3-buten-1-ol (k1), 2-buten-1-ol (k2), 2-methyl-2-propen-1-ol (k3) and 3-buten-1-ol (k4), were measured using two different techniques, a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The Arrhenius rate coefficients (in units of cm(3) molecule(-1) s(-1)) over the temperature range 263-371 K were determined from the kinetic data obtained as k1 = (5.5 +/- 1.0) x 10(-12) exp [(836 +/- 54)/T]; k2 = (6.9 +/- 0.9) x 10(-12) exp [(744 +/- 40)/T]; k3 = (10 +/- 1) x 10(-12) exp [(652 +/- 27)/T]; and k4 = (4.0 +/- 0.4) x 10(-12) exp [(783 +/- 32)/T]. At 298 K, the rate coefficients obtained by the two methods for each of the alcohols studied were in good agreement. The results are presented and compared with those obtained previously for the same and related reactions of OH radicals. Reactivity factors for substituent groups containing the hydroxyl group are determined. The atmospheric implications for the studied alcohols are considered briefly.