Electrochemical Sensing of Idarubicin—DNA Interaction Using Electropolymerized Azure B and Methylene Blue Mediation

A highly sensitive electrochemical DNA sensor for detection of the chemotherapeutic drug idarubicin mediated by Methylene blue (MB) has been developed. DNA from fish sperm has been immobilized at the electropolymerized layers of Azure B. The incorporation of MB into the DNA layers substantially increased the sensor sensitivity. The concentration range for idarubicin determination by cyclic voltammetry was from 1 fM to 0.1 nM, with a limit of detection (LOD) of 0.3 fM. Electrochemical impedance spectroscopy (EIS) in the presence of a redox probe ([Fe(CN)6]3−/4−) allowed for the widening of a linear range of idarubicin detection from 1 fM to 100 nM, retaining LOD 0.3 fM. The DNA sensor has been tested in various real and artificial biological fluids with good recovery ranging between 90–110%. The sensor has been successfully used for impedimetric idarubicin detection in medical preparation Zavedos®. The developed DNA biosensor could be useful for the control of the level of idarubicin during cancer therapy as well as for pharmacokinetics studies.

Isolation and Characterization of Bacillus Sp. Capable of Degradating Alkali Lignin

Alkali lignin-degrading Bacillus were isolated from forest soils in China and were identified as Bacillus subtilis TR-03 and Bacillus cereus TR-25 by 16S rDNA sequence analysis. Wherein TR-03 displayed optimal 26.72% alkali lignin (2 g/L) degradation at 7 days and 71.23% of Azure-B (0.01%) decolorization at 36 h of cultivation at 37°C. Ligninolytic enzyme analysis revealed that TR-03 was capable of depolymerizing alkali lignin effectively by the producing of lignin peroxidase and laccase, wherein higher laccase activity was cell-associated. At last, the physical and chemical changes of lignin via SEM and FTIR analysis was further observed to prove the lignin degradation by Bacillus subtilis TR-03.

Determination of Methylene Blue and Its Metabolite Residues in Aquatic Products by High-Performance Liquid Chromatography–Tandem Mass Spectrometry

A sensitive and reliable method was developed to determine methylene blue (MB) and its metabolite residues, including azure A (AZA), azure B (AZB), and azure C (AZC) in aquatic products by HPLC–MS/MS. The samples were extracted by acetonitrile and cleaned up by alumina-neutral (ALN) cartridges. The analytes were separated on a Sunfire C18 column (150 mm × 2.1 mm, 5 µm). The method was validated according to the European criteria of Commission Decision 2002/657/CE. Good linearity between 1–500 µg/L was obtained with correlation coefficients (R2) greater than 0.99. The limit of quantification (LOQ) was 1.0 µg/kg. The average recoveries at three levels of each compound (1, 5, and 10 µg/kg) were demonstrated to be in the range of 71.8–97.5%, with relative standard deviations (RSDs) from 1.05% to 8.63%. This method was suitable for the detection of methylene blue and its metabolite residues in aquatic products.

Electrochemical DNA Sensor Based on the Copolymer of Proflavine and Azure B for Doxorubicin Determination

A DNA sensor has been developed for the determination of doxorubicin by consecutive electropolymerization of an equimolar mixture of Azure B and proflavine and adsorption of native DNA from salmon sperm on a polymer film. Electrochemical investigation showed a difference in the behavior of individual drugs polymerized and their mixture. The use of the copolymer offered some advantages, i.e., a higher roughness of the surface, a wider range of the pH sensitivity of the response, a denser and more robust film, etc. The formation of the polymer film and its redox properties were studied using scanning electron microscopy and electrochemical impedance spectroscopy. For the doxorubicin determination, its solution was mixed with DNA and applied on the polymer surface. After that, charge transfer resistance was assessed in the presence of [Fe(CN)6]3−/4− as the redox probe. Its value regularly grew with the doxorubicin concentration in the range from 0.03 to 10 nM (limit of detection 0.01 nM). The DNA sensor was tested on the doxorubicin preparations and spiked samples mimicking blood serum. The recovery was found to be 98–106%. The DNA sensor developed can find application for the determination of drug residues in blood and for the pharmacokinetics studies.