A new catalase amperometric biosensor for hydroperoxides detection has been built as part of research aimed at the development of biosensors based on layered double hydroxides (LDH) used as support for enzyme immobilization. The fabricated device differs from those developed so far, usually based on an LDH enzyme nanocomposite adsorbed on a glassy carbon (GC) electrode and cross-linked by glutaraldehyde, since it is based on an amperometric gas diffusion electrode (Clark type) instead of a GC electrode. The new biosensor, which still uses LDH synthesized by us and catalase enzyme, is robust and compact, shows a lower LOD (limit of detection) value and a linearity range shifted at lower concentrations than direct amperometric GC biosensor, but above all, it is not affected by turbidity or emulsions, or by the presence of possible soluble species, which are reduced to the cathode at the same redox potential. This made it possible to carry out accurate and efficient determination of H2O2 even in complex or cloudy real matrices, also containing very low concentrations of hydrogen peroxide, such as milk and cosmetic products, i.e., matrices that would have been impossible to analyze otherwise, using conventional biosensors based on a GC–LDH enzyme. An inaccuracy ≤7.7% for cosmetic samples and ≤8.0% for milk samples and a precision between 0.7 and 1.5 (as RSD%), according to cosmetic or milk samples analyzed, were achieved.
A combination of X‐ray diffraction and Raman scattering is employed to investigate (GeTe)m(Sb2Te3)n alloys crystallized by thermal annealing from the amorphous (a‐) phase. The films are deposited by molecular beam epitaxy on Si(111) substrates. First, a series of a‐GeSbTe (GST) films of different composition is deposited and studied by Raman spectroscopy to identify the Ge‐rich features of the alloys. Second, the crystallization properties of Ge10Sb2Te13 are studied upon different annealing conditions. The aim of this work is to develop a procedure to avoid segregation of Ge and GeTe at the GST crystallization onset (Tx). This is here achieved by means of an incubation step at temperature lower than Tx. The crystallization onset Tx increased to 270 °C, which is about 160 °C higher compared to a reference GeTe sample, while the alloy always crystallizes in the stable Ge1Sb2Te4 composition. The increase of Tx is observed for all annealing conditions, regardless the amount of crystalline Ge segregated. For the optimized annealing treatment, the presence of Ge nanocrystals along with crystalline GeSbTe is unveiled by Raman measurements, paving the way for the control of the microstructure and electrical/thermal properties of Ge‐rich alloys.
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