Electrochemical impedance spectroscopy (EIS) measurement, performed in the presence of a redox agent, is a convenient method to measure molecular interactions of electrochemically inactive compounds taking place on the electrode surface. High sensitivity of the method, being highly advantageous, can be also associated with nonspecific impedance changes that could be easily mistaken for specific interactions. Therefore, it is necessary to be aware of all possible causes and perform parallel control experiments to rule them out. We present the results obtained during the early stages of aptamer-based sensor development, utilizing a model system of human alpha thrombin interacting with a thiolated DNA aptamer, immobilized on gold electrodes. EIS measurements took place in the presence of iron ferrocyanides. In addition to known method limitations, that is, inability to discriminate between specific and nonspecific binding (both causing impedance increase), we have found other factors leading to nonspecific impedance changes, such as: (i) initial electrode contamination; (ii) repetitive measurements; (iii) additional cyclic voltammetry (CV) or differential pulse voltammetry (DPV) measurements; and (iv) additional incubations in the buffer between measurements, which have never been discussed before. We suggest ways to overcome the method limitations.

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Poly(methyl methacrylate)/single‐walled carbon nanotube (PMMA/SWNT) composites were prepared via in situ polymerization induced either by heat, ultraviolet (UV) light, or ionizing (gamma) radiation. The composites dissolved in methylene chloride and then cast into films exhibited enhanced transparency as compared with the melt‐blended composite material. UV/visible spectroscopy was used to quantitatively analyze the transparency of the composites. The dielectric constant (ε′) was measured via dielectric analysis (DEA) and correlated to the refractive‐index values using Maxwell's relationship. The dielectric constant increased in the composite samples as compared with the neat PMMA samples prepared by the same methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) provided images of the polymer–nanotube composites and single‐walled CNTs, respectively.

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Poly(4-methyl-1-pentene), PMP, a high melting polymer composed of hydrogen and carbon, has the potential to become an alternative to polyethylene (PE) as shielding material against Galactic Cosmic Radiation (GCR). PMP exhibits higher thermal stability than PE and is transparent in the UV/visible region of the electromagnetic spectrum. Single walled carbon nanotubes (SWNTs) were pretreated with a polar solvent, N, N-Dimethylformimide (DMF), and then dispersed in a halogenated hydrocarbon, cyclohexyl chloride, which also dissolved the non polar polymer, PMP. The composites were characterized via differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), microhardness measurements, and optical microscopy. DMA data revealed that the carbon nanotubes contributed to the enhancement of the high temperature alpha(c) relaxation which is thought to arise from motion around crystalline regions in the matrix. The storage modulus (60 Hz) increased from 2409 MPa in the neat PMP to 3716 MPa at -50 degrees C. The magnitude of the increase diminished near and above the glass transition region; the glassy matrix restricted motion of the crystalline regions. DSC data showed an increase in the percent crystallinity of the composite (75%) as compared to the neat polymer (68%). Low concentrations of nanotubes, when well dispersed, produced nanocomposites with varying degrees of transparency.