Inkjet-printed gold nanoparticle electrochemical arrays on plastic. Application to immunodetection of a cancer biomarker protein

Electrochemical detection combined with nanostructured sensor surfaces offers potentially low-cost, high-throughput solutions for detection of clinically significant proteins. Inkjet printing offers an inexpensive non-contact fabrication method for microelectronics that is easily adapted for incorporating into protein immunosensor devices. Herein we report the first direct fabrication of inkjet-printed gold nanoparticle arrays, and apply them to electrochemical detection of the cancer biomarker interleukin-6 (IL-6) in serum. The gold nanoparticle ink was printed on a flexible, heat resistant polyimide Kapton substrate and subsequently sintered to create eight-electrode arrays costing <0.2 euro per array. The inkjet-printed working electrodes had reproducible surface areas with RSD <3%. Capture antibodies for IL-6 were linked onto the eight-electrode array, and used in sandwich immunoassays. A biotinylated secondary antibody with 16-18 horseradish peroxidase labels was used, and detection was achieved by hydroquinone-mediated amperometry. The arrays provided a clinically relevant detection limit of 20 pg mL(-1) in calf serum, sensitivity of 11.4 nA pg(-1) cm(-2), and a linear dynamic range of 20-400 pg mL(-1).     

Synthesis and characterization of a hydrogel with controllable electroosmosis: a potential brain tissue surrogate for electrokinetic transport

Electroosmosis is the bulk fluid flow initiated by application of an electric field to an electrolyte solution in contact with immobile objects with a nonzero ζ-potential such as the surface of a porous medium. Electroosmosis may be used to assist analytical separations. Several gel-based systems with varying electroosmotic mobilities have been made in this context. A method was recently developed to determine the ζ-potential of organotypic hippocampal slice cultures (OHSC) as a representative model for normal brain tissue. The ζ-potential of the tissue is significant. However, determining the role of the ζ-potential in solute transport in tissue in an electric field is difficult because the tissue's ζ-potential cannot be altered. We hypothesized that mass transport properties, namely the ζ-potential and tortuosity, could be modulated by controlling the composition of a set of hydrogels. Thus, poly(acrylamide-co-acrylic acid) gels were prepared with three compositions (by monomer weight percent): acrylamide/acrylic acid 100/0, 90/10, and 75/25. The ζ-potentials of these gels at pH 7.4 are distinctly different, and in fact vary approximately linearly with the weight percent of acrylic acid. We discovered that the 25% acrylic acid gel is a respectable model for brain tissue, as its ζ-potential is comparable to the OHSC. This series of gels permits the experimental determination of the importance of electrokinetic properties in a particular experiment or protocol. Additionally, tortuosities were measured electrokinetically and by evaluating diffusion coefficients. Hydrogels with well-defined ζ-potential and tortuosity may find utility in biomaterials and analytical separations, and as a surrogate model for OHSC and living biological tissues.     

Oxidation of Plasmalogen,Low‐Density Lipoprotein and RAW 264.7 Cells by Photoactivatable Atomic Oxygen Precursors

The oxidation of lipids by endogenous or environmental reactive oxygen species (ROS) generates a myriad of different lipid oxidation products that have important roles in disease pathology. The lipid oxidation products obtained in these reactions are dependent upon the identity of the reacting ROS. The photoinduced deoxygenation of various aromatic heterocyclic oxides has been suggested to generate ground state atomic oxygen (O[³P]) as an oxidant; however, very little is known about reactions between lipids and O(³P). To identify lipid oxidation products arising from the reaction of lipids with O(³P), photoactivatable precursors of O(³P) were irradiated in the presence of lysoplasmenylcholine, low‐density lipoprotein and RAW 264.7 cells under aerobic and anaerobic conditions. Four different aldehyde products consistent with the oxidation of plasmalogens were observed. The four aldehydes were: tetradecanal, pentadecanal, 2‐hexadecenal and hexadecanal. Depending upon the conditions, either pentadecanal or 2‐hexadecenal was the major product. Increased amounts of the aldehyde products were observed in aerobic conditions.     

Metal clusters that freeze into high energy geometries

Heat capacities measured for isolated aluminum clusters show peaks due to melting. For some clusters with around 60 and 80 atoms there is a dip in the heat capacities at a slightly lower temperature than the peak. The dips have been attributed to structural transitions. Here we report studies where the clusters are annealed before the heat capacity is measured. The dips disappear for some clusters, but in many cases they persist, even when the clusters are annealed to well above their melting temperature. This indicates that the dips do not result from badly formed clusters generated during cluster growth, as originally suggested. We develop a simple kinetic model of melting and freezing in a system consisting of one liquidlike and two solidlike states with different melting temperatures and latent heats. Using this model we are able to reproduce the experimental results including the dependence on the annealing conditions. The dips result from freezing into a high energy geometry and then annealing into the thermodynamically preferred solid. The thermodynamically preferred solid has the higher freezing temperature. However, the liquid can bypass freezing into the thermodynamically preferred solid (at high cooling rates) if the higher energy geometry has a larger freezing rate.     

A study of the relationship between molecular biomarkers of joint degeneration and the magnetic resonance-measured characteristics of cartilage in 16 symptomatic knees

We used quantitative magnetic resonance (MR) imaging to determine if relationships exist between proposed molecular biomarkers for degenerative joint disease (DJD) and structural characteristics of articular cartilage. Subjects were eight male and eight female volunteers diagnosed with osteoarthritis. Magnetic resonance images of the symptomatic knee were taken and blood samples were drawn. Concentrations of serum cartilage oligomeric matrix protein (COMP) and cleaved collagen neoepitope were compared to cartilage volume and cartilage T2, respectively, in four compartments of the tibiofemoral joint. A significant, negative correlation was found between serum COMP and medial tibia volume in the male subject group (rho=-.738, P=.037). A significant, positive correlation (rho=.881, P=.0039) was found between serum COMP and lateral femur volume in the female subject group. In both groups, positive correlations were found between serum C2C and cartilage T2, which were significant in two compartments of the male group (rho=.714, P=.047; rho=.738, P=.037) and similarly strong, but not statistically significant (rho=.750, P=.052), in one compartment of the female group. We identify strong and biologically relevant correlations between two proposed molecular biomarkers for DJD and MR measures of symptomatic knees of a small number of arthritic patients. Our findings support the hypothesis that cartilage molecular biomarkers reflect the molecular processes of cartilage degeneration and loss.     

Time-domain ab initio simulation of electron and hole relaxation dynamics in a single-wall semiconducting carbon nanotube

The electron and hole relaxation in the (7, 0) zigzag carbon nanotube is simulated in time domain using a surface-hopping Kohn-Sham density functional theory. Following a photoexcitation between the second van Hove singularities, the electrons and holes decay to the Fermi level on characteristic subpicosecond time scales. Surprisingly, despite a lower density of states, the electrons relax faster than the holes. The relaxation is primarily mediated by the high-frequency longitudinal optical (LO) phonons. Hole dynamics are more complex than the electron dynamics: in addition to the LO phonons, holes couple to lower frequency breathing modes and decay over multiple time scales.     

Dynamic processes in [16]annulene: Möbius bond-shifting routes to configuration change

Density functional and ab initio methods have been used to study the mechanisms for key dynamic processes of the experimentally known S4-symmetric [16]annulene (1a). Using BH&HLYP/6-311+G** and B3LYP/6-311+G**, we located two viable stepwise pathways with computed energy barriers (Ea = 8-10 kcal/mol) for conformational automerization of 1a, in agreement with experimental data. The transition states connecting these conformational minima have M?bius topology and serve as starting points for non-degenerate pi-bond shifting (configuration change) via M?bius aromatic transition states. The key transition state, TS1-2, that connects the two isomers of [16]annulene (CTCTCTCT, 1 --> CTCTTCTT, 2) has an energy, relative to the S4 isomer, that ranged from 6.9 kcal/mol (B3LYP/6-311+G**) to 16.7 kcal/mol (BH&HLYP/6-311+G**), bracketing the experimental barrier. At our best level of theory, CCSD(T)/cc-pVDZ(est), this barrier is 13.7 kcal/mol. Several other M?bius bond-shifting transition states, as well as M?bius topology conformational minima, were found with BH&HLYP energies within 22 kcal/mol of 1a, indicating that many possibilities exist for facile thermal configuration change in [16]annulene. This bond-shifting mechanism and the corresponding low barriers contrast sharply with those observed for cis/trans isomerization in acyclic polyenes, which occurs via singlet diradical transition states. All M?bius bond-shifting transition states located in [16]- and [12]annulene were found to have RHF --> UHF instabilities with the BH&HLYP method but not with B3LYP. This result appears to be an artifact of the BH&HLYP method. These findings support the idea that facile thermal configuration change in [4n]annulenes can be accounted for by mechanisms involving twist-coupled bond shifting.     

Ultrasensitive Hydrogen Peroxide Biosensor Based on Enzyme Bound to Layered Nonoriented Multiwall Carbon Nanotubes/Polyelectrolyte Electrodes

A sensitive hydrogen peroxide sensor based on horseradish peroxidase covalently attached to layered nonoriented MWNTs modified electrode is presented. Cyclic voltammetry results gave quasi‐reversible Fe^III/Fe^II voltammetry. The electron transfer rate constant (k_s) and Michaelis–Menten constant (K_M) in pH 7 is 48.8±0.9 s^?1 and 0.13±0.05 mM respectively. A linear calibration curve for hydrogen peroxide was obtained up to 120 nM under the optimized conditions with a remarkable detection limit of (S/N=3) 1.5 nM. Results suggest that the nonoriented nanotubes act as electrical conductors and may also provide large surface area facilitating facile electron transfer and excellent electrochemical catalysis.