ABSTRACT
In this study, multilayered films of polyethylenimine/poly (sodium-p-styrene sulfonate) (PEI)/(PSS) and type I collagen/heparin sodium (COL)/(HEP) were fabricated using the layer-by-layer technique, and fully characterized using Infrared Variable Angle Spectroscopic Ellipsometry (IRVASE) to simultaneously analyze the chemistry, thickness, and roughness of the multilayers with respect to changes in pH of the washing solution, and changes in temperature. Film topography and Young's modulus were obtained by atomic force microscopy (AFM) and nanoindentation. Our results show that with IRVASE it is possible to analyze the thickness of the multilayers prepared using a washing solution of pH 5, obtaining values of 71.7 nm and 40.3 nm for three bilayers of PEI/PSS and COL/HEP, respectively. Film roughness varies between multilayer systems, obtaining values of 37.76 nm for three bilayers of PEI/PSS and 33.58 nm for three bilayers of COL/HEP. Increasing the pH of the washing solution for PEI/PSS yielded thinner films that were less susceptible to thermal induced changes in film chemistry in the range of 25 - 150 °C. PEI/PSS films decreased in thickness with increasing temperature up to 75 °C, whereas above 75 °C film thickness increased. Through IRVASE, a transition temperature for the PEI/PSS multilayers was observed at 75 °C. Temperatures above 37 °C drastically alter the chemistry and the thickness of the COL/HEP multilayers indicating a possible degradation of the polymers. We obtained, through nanoindentation, a Young's modulus of 15000 kPa and 9000 kPa for 12 bilayers of PEI/PSS and COL/HEP, respectively. These results demonstrate that, using IRVASE, we can simultaneously evaluate the physical, chemical, and thermal properties of synthetic and natural multilayered polymeric films.
ABSTRACT
In this work, we explore the use of electrochemical methods (i.e., impedance) along with the arsenic-specific aptamer (ArsSApt) to fabricate and study the interfacial properties of an arsenic (As(III)) sensor. The ArsSApt layer was self-assembled on a gold substrate, and upon binding of As(III), a detectable change in the impedimetric signal was recorded because of conformational changes at the interfacial layer. These interfacial changes are linearly correlated with the concentration of arsenic present in the system. This target-induced signal was utilized for the selective detection of As(III) with a linear dynamic range of 0.05-10 ppm and minimum detectable concentrations of ca. 0.8 µM. The proposed system proved to be successful mainly because of the combination of a highly sensitive electrochemical platform and the recognized specificity of the ArsSApt toward its target molecule. Also, the interaction between the ArsSApt and the target molecule (i.e., arsenic) was explored in depth. The obtained results in this work are aimed at proving the development of a simple and environmentally benign sensor for the detection of As(III) as well as in elucidating the possible interactions between the ArsSApt and arsenic molecules.