Marc Garland

DNA detection using nanostructured SERS substrates with Rhodamine B as Raman label

A technique is demonstrated to detect DNA hybridization at low concentrations, based on Surface-Enhanced Raman Scattering (SERS) using silicon nanostructures coated with gold-silver as substrate. Standard silicon process technologies were employed to fabricate the SERS substrates featuring nanogaps with a characteristic distance of 15+/-10nm. Target DNA was hybridized with cysteine-modified Peptide Nucleic Acids (PNA), which was previously fixed into the nanogaps as the capture sites. After hybridization, the introduced phosphate groups from the backbone of the target DNA showed strong affinity to an inorganic linker, Zr(4+), so that resulting in the assembly substrate-PNA-DNA-Zr. Since PNA does not possess phosphate groups, the linker is avoided when there is no hybridization from the complimentary DNA. Subsequently, the assembly of substrate-PNA-DNA-Zr was incubated with a Raman label, Rhodamine B (RB). The carboxylic acid group in RB reacted with the linker Zr(4+) allowing this Raman Label to be attached to the assembly substrate-PNA-DNA-Zr. The Raman peaks corresponding to RB were selected to detect the target DNA, with a detection limit of 1 x 10(-12)M.

A new modified parachor model for predicting surface compositions of binary liquid mixtures. On the importance of surface volume representation

Differences in composition between the surface region and the bulk region for binary liquids can occur due to preferential adsorption, and such surface enrichment can influence mass and heat transport across the interface. In order to investigate surface enrichment, reliable methods for predicting surface compositions are required. In this study, an approach based on a modified parachor model is developed in order to provide a generally more accurate prediction for the surface composition. In contrast to other predictive models, a more realistic surface volume representation is considered. This model is subsequently utilized to predict the surface compositions of several binary systems, involving organic-aqueous, organic-organic and aneotropic mixtures. The surface compositions obtained are compared to those directly determined from experimental measurements, if any, and to those calculated using other predictive models. The results show that the present modified parachor model provides surface composition predictions which are equal to, and in some cases are better than (particularly for aneotropic mixtures), those provided by other models. In general, the results demonstrate the usefulness of including a real surface volume approximation in the surface enrichment calculations.

Transmembrane exchange of hyperpolarized 13C-urea in human erythrocytes: subminute timescale kinetic analysis.

The rate of exchange of urea across the membranes of human erythrocytes (red blood cells) was quantified on the 1-s to 2-min timescale. (13)C-urea was hyperpolarized and subjected to rapid dissolution and the previously reported (partial) resolution of (13)C NMR resonances from the molecules inside and outside red blood cells in suspensions was observed. This enabled a stopped-flow type of experiment to measure the (initially) zero-trans transport of urea with sequential single-pulse (13)C NMR spectra, every second for up to ~2 min. Data were analyzed using Bayesian reasoning and a Markov chain Monte Carlo method with a set of simultaneous nonlinear differential equations that described nuclear magnetic relaxation combined with transmembrane exchange. Our results contribute to quantitative understanding of urea-exchange kinetics in the whole body; and the methodological approach is likely to be applicable to other cellular systems and tissues in vivo.

New insights into the relationship between structure and photocatalytic properties of TiO2 catalysts

This work systematically investigated the relationship between structure, morphology, photoelectrochemical (PEC) and photocatalytic (PC) properties of TiO2 catalysts. A series of TiO2 catalysts with various phase compositions (anatase-, brookite- and finally rutile-rich samples) and morphologies (1D morphology, rhomboid nanoparticles (NPs) and flower-like assemblies of nanorods) were prepared by an acidic hydrothermal treatment of hydrogen titanate nanofibres (H-TNFs). The structures of the samples, such as crystal phase composition and their spatial distribution, were extensively characterised, and the samples were tested for photocatalytic degradation of ethanol. A strong correlation is found between PEC and PC properties. PEC measurements revealed that the brookite-rich samples generated high but unstable photocurrents. The anatase and rutile-rich samples showed good stability, but for the rutile-rich samples low photocurrents were detected due to the poor conductivity of this polymorph. In contrast, the sample containing 93.2% anatase and 6.8% brookite with elongated morphology not only showed the ability to generate high photocurrents but also maintained a stable photoresponse upon an extended period of time, because of its well-balanced bi-crystalline structure and elongated morphology. Therefore, the abilities to generate high photocurrents and to maintain a stable photoresponse are equally important and probably a prerequisite for a good photocatalyst.

Detection of bio-constituents in complex biological tissue using Raman microscopy. Application to human nail clippings.

Raman spectra of human nail clippings from various sources were collected and then deconvoluted to obtain the pure component spectra of the underlying constituents present. This blind-deconvolution was performed using a self-modeling curve resolution technique, namely band-target entropy minimization (BTEM). The aim was to simplify the complexity of the Raman spectra and hence to identify the underlying biological molecules in more detail. BTEM analysis could recover 13 pure component Raman spectral estimates from the collected 438 spectra measured from 113 nail samples. Six recovered pure component spectral estimates correspond to proteins or polypeptides that contain various amino acids such as phenylalanine, tyrosine, tryptophan, and cysteine. Two are associated with the secondary structures of proteins, and five are associated with two carotenoid species, lipid, ferulic acid, and calcium phosphate. Subsequently, the relative concentrations of these bio-constituents were calculated from the measured mixture spectra and the pure component BTEM estimates. These profiles indicated that the concentrations of some bio-constituents are correlated while others are not. A further analysis using target transformation factor analysis (TTFA) revealed the possible presence of curcumin in the human nails. Since the present approach and analysis is rather general, it might be extended to many other biological tissues in a rather straightforward and similar manner, thus revealing more detailed underlying biochemical information such as biomarkers that may be useful for diagnostic purposes.

Three approaches to total quantitative phase analysis of organic mixtures using an external standard

Three different approaches for a total quantitative phase analysis of organic mixture data were presented and subsequently tested on a set of ten ternary powder mixtures consisting of α-glycine, α-lactose monohydrate and paracetamol form I. In each of these methods, an external standard was used (in the present study, diamond) to determine the diffractometer constant, which was employed to place the crystalline intensities of all other samples on an absolute scale. In Method A, pure component diffractograms were also measured. In Methods B and C, no pure component diffractograms were used. Using Methods A–C, both the absolute crystalline compositions and all the amorphous compositions of the samples were determined. These methods outperform the quantitative phase analysis provided by conventional Rietveld analysis. An average error of less than 0.5u2005wt% was achieved with the present approaches, whereas the average error from conventional Rietveld analysis was ca 1.3u2005wt%.

Determination of the individual specific heat capacities of solids from multi-component powder mixtures and polymorphic mixtures

This study describes a method to determine the specific heat capacities of individual solids from multi-component solid mixtures. To achieve this end, powder X-ray diffraction measurements are used to provide information on the number and identity of constituents as well as their compositions while calorimetry measurements give the specific heat capacities of the bulk solid mixtures. The method is applied to investigate three different solid mixture systems, namely (i) ternary organic mixtures containing α-glycine, α-lactose monohydrate, and paracetamol; (ii) ternary inorganic mixtures containing calcium fluoride, titanium nitride, and tungsten carbide; and (iii) polymorphic mixtures of α- and γ-glycine. All systems are investigated at 298.15xa0K and at atmospheric pressure. The results show that the specific heat capacities of individual solids determined from multi-component solid mixtures are in good agreement with those directly determined from pure solid compounds.

Characterizing Diffusion and Transport in Microfluidics Channels: A Combined Raman Microscopy and Band-Target Entropy Minimization Study

With the increasing use of microfluidics, there is a need for a rather general experimental approach in order to monitor and characterize transport effects. Indeed, micro-fabrication methods have allowed the inclusion of numerous new structures and devices within microfluidics channels, and such alterations in flow patterns should impact solute transport characteristics. In the present contribution, Raman microscopy is combined with band-target entropy minimization analysis (BTEM) in order to rapidly assess and map concentration profiles in various regions of a microfluidics device. Two isotopomers, CHCl3 and CDCl3, are contacted under laminar conditions. Special consideration is given to the point of contact between the two liquids, transport in straight sections, transport in curved sections, and wall effects. Break-through curves confirmed that stagnation of fluid at the wall is not occurring, despite substantial wall roughness. Since the methods used in the present study are quite general, they should be useful in rapidly accessing transport effects when fluids (also in conjunction with colloids, suspensions, and solids) are contacted in the presence of both simple as well as complex geometries.

Reverse engineering of multi-layer films

This contribution introduces the combined application of Raman microscopy and band-target entropy minimization (BTEM) in order to successfully reverse-engineer a multi-layer packaging material. Three layers are identified, namely, polyethylene, a paper and talc layer (with two distinct cellulose forms), and a poly-styrene co-polymer composite containing anatase and calcite. This rapid and non-destructive approach provides a unique opportunity for the assessment of multi-layer composites, including the constitution of the additives present.

Combined on-line transmission FTIR measurements and BTEM analysis for the kinetic study of a consecutive reaction in aqueous–organic phase medium

Combined on-line transmission FTIR spectroscopy and band-target entropy minimization (BTEM) analysis were employed in order to monitor and analyze the kinetics of the alkaline hydrolysis reaction of diethyl phthalate (DEP) in aqueous-ethanol solvent mixture. This reaction is irreversible and involves two consecutive steps with the formation of the observable mono-ion intermediate species. The pure component mid-FTIR spectra of the reactive species involved in this reaction, namely DEP, mono-ion intermediate and di-ion product were successfully reconstructed using BTEM. Their corresponding concentrations were also calculated and subsequently employed to derive the kinetic rate parameters. The effect of temperature and the solvent mixture compositions on these two consecutive reaction steps were also discussed. The temperature variation study showed that both reaction rate coefficients increased with temperature. Both rate coefficients were also affected by the solvent mixture compositions and reached minimum values at certain water-ethanol solvent composition (circa 60% (v/v)). This study shows the utility of combined on-line transmission FTIR spectroscopy and chemometric techniques for the present, rather complex, consecutive organic reaction. Moreover, the present type of approach could facilitate better understanding of a wide variety of organic reactions that are performed in aqueous and mixed aqueous-organic solvents.