A New Clark-Type Layered Double Hydroxides-Enzyme Biosensor for H2O2 Determination in Highly Diluted Real Matrices: Milk and Cosmetics

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.

Peroxidase-Like Metal-Based Nanozymes: Synthesis, Catalytic Properties, and Analytical Application

Nanozymes (NZs) are nanostructured artificial enzymes that mimic catalytic properties of natural enzymes. The NZs have essential advantages over natural enzymes, namely low preparation costs, stability, high surface area, self-assembling capability, size and composition-dependent activities, broad possibility for modification, and biocompatibility. NZs have wide potential practical applications as catalysts in biosensorics, fuel-cell technology, environmental biotechnology, and medicine. Most known NZs are mimetics of oxidoreductases or hydrolases. The present work aimed to obtain effective artificial peroxidase (PO)-like NZs (nanoPOs), to characterize them, and to estimate the prospects of their analytical application. NanoPOs were synthesized using a number of nanoparticles (NPs) of transition and noble metals and were screened for their catalytic activity in solution and on electrodes. The most effective nanoPOs were chosen as NZs and characterized by their catalytic activity. Kinetic parameters, size, and structure of the best nanoPOs (Cu/CeS) were determined. Cu/CeS-based sensor for H2O2 determination showed high sensitivity (1890 A·M−1·m−2) and broad linear range (1.5–20,000 µM). The possibility to apply Cu/CeS-NZ as a selective layer in an amperometric sensor for hydrogen-peroxide analysis of commercial disinfectant samples was demonstrated.

ITO ELECTRODES MODIFIED WITH MnO2/SiO2 FOR THE DETERMINATION OF HYDROGEN PEROXIDE

Nanostructured transition metal oxide nanoparticles possess a catalytic activity to hydrogen peroxide. Manganese dioxide particles are one of the promising and available modificators of the electrode surface. Nanostructured MnO2 deposited onto the surface of the electrode enhances the electron transport from the H2O2 molecule to the surface. Thus selectivity and sensitivity of H2O2 detection can be improved. There are a lot of different methods of the impregnation of manganese dioxide particles onto electrode surface. An electrophoretic deposition is one of the most simple and rapid. By adjusting the electrodeposition parameters, particles of different sizes or films can be obtained. A simple and novel hydrogen peroxide sensor based on layer-by-layer assembly of MnO2 nanoparticles and SiO2 film on the ITO electrode was developed. For this purpose MnO2 nanoparticles were electrodeposited on the surface of ITO electrode from MnSO4/CH3COOK solution. The electrochemical characteristics of the modified electrodes were investigated by cyclic voltammetry.The presence of MnO2 on the surface of modified electrode was indicated by the appearance of clear oxidation-reduction peaks of Mn(IV)/Mn(III,II) at E=0.65 V in the electrolyte solution in contrast to unmodified electrode. Optimization of measurement parameters such as the amount of MnO2, applied potential and pH value were studied in details. Under the optimum conditions, the calibration curve for H2O2 determination using modified electrode was linear in the range from 1×10−4 to 1×10−3 mol/dm3 with a detection limit of 0.09×10−4 mol/dm3 (S/N = 3). The linear rang for non-modified electrode was from 1×10−3 to 1×10−2 mol/dm3 with a detection limit of 1.8×10−4 mol/dm3 (S/N = 3). The modified ITO electrode was characterized by higher current than non modified ITO as a result of increasing of electroactive surface area and catalytic effect of electrodeposited MnO2.For the stabilization of MnO2 particles and protection of the electrode surface from impurities, the ITO/MnO2 was covered by thin silica film. The selectivity of H2O2 determination at ITO modified with MnO2/SiO2 was better than at ITO especially in the presence of ascorbic acid which is oxidized at the same potential as H2O2. The oxidation current of ascorbic acid was much higher than H2O2 at nonmodified ITO in contrast to ITO modified with MnO2/SiO2. The developed ITO electrode modified with MnO2/SiO2 is a perspective element of amperometric sensor for the detection of hydrogen peroxide.