A novel method for fabrication of horseradish peroxidase biosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl)-trimethoxysilane (MPS) sol-gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol-gel network. Finally, horseradish peroxidase (HRP) was adsorbed onto the surface of the gold nanoparticles. The distribution of gold nanoparticles and HRP was examined by atomic force microscopy (AFM). The immobilized horseradish peroxidase exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide. The performance and factors influencing the performance of the resulting biosensor were studied in detail. The resulting biosensor exhibited fast amperometric response (2.5 s) to H2O2. The detection limit of the biosensor was 2.0 micromol L(-1), and the linear range was from 5.0 micromol L(-1) to 10.0 mmol L(-1). Moreover, the studied biosensor exhibited high sensitivity, good reproducibility, and long-term stability.

The rare case of changing-look (CL) AGNs, with the appearance or disappearance of broad Balmer emission lines within a few years, challenges our understanding of the AGN unified model. We present a sample of 21 new CL AGNs at 0.08 < z < 0.58, which doubles the number of such objects known to date. These new CL AGNs were discovered by several ways, from (1) repeat spectra in the SDSS, (2) repeat spectra in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and SDSS, and (3) photometric variability and new spectroscopic observations. We use the photometric data from surveys, including the SDSS imaging survey, the Pan-STARRS1, the DESI Legacy imaging survey, the Wide-field Infrared Survey Explorer (WISE), the Catalina Real-time Transient Survey, and the Palomar Transient Factory. The estimated upper limits of transition timescale of the CL AGNs in this sample spans from 0.9 to 13 years in the rest frame. The continuum flux in the optical and mid-infrared becomes brighter when the CL AGNs turn on, or vice versa. Variations of more than 0.2 mag in W 1 band were detected in 15 CL AGNs during the transition. The optical and mid-infrared variability is not consistent with the scenario of variable obscuration in 10 CL AGNs at more than 3σ confidence level. We confirm a bluer-when-brighter trend in the optical. However, the mid-infrared WISE colors W 1 − W 2 become redder when the objects become brighter in the W 1 band, possibly due to a stronger hot dust contribution in the W 2 band when the AGN activity becomes stronger. The physical mechanism of type transition is important for understanding the evolution of AGNs.

A new type of sol-gel organic-inorganic hybrid material was developed and used for the production of biosensors. This material is composed of silica sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. It prevents the cracking of conventional sol-gel-derived glasses and eliminates the swelling of the hydrogel. The optimum composition of the hybrid material was first examined, and then glucose oxidase was immobilized in this matrix to demonstrate its application. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The biosensor exhibited a series of good properties: high sensitivity (600 nA mmol-1 L-1), short response time (11 s) and remarkable long-term stability in storage (at least 5 months). In addition, the characteristics of the second-generation biosensor with the use of tetrathiafulvalene as a mediator were discussed.

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An acid-stable soybean-peroxidase biosensor was developed by immobilizing the enzyme in a sol-gel thin film. Methylene blue was used as a mediator because of its high electron-transfer efficiency. The sol-gel thin film and enzyme membrane were characterized by FT-IR, and the effects of pH, operating potential, and temperature were explored for optimum analytical performance by using the amperometric method. The H2O2 sensor exhibited a fast response (5 s), high sensitivity (27.5 microA/mM), as well as good thermostability and long-term stability. In addition, the performance of the biosensor was investigated using flow-injection analysis (FIA).

Films containing presynthesized [Ru(bpy)2poly(4-vinylpyridine)10Cl)]Cl and ds-DNA grown layer by layer by alternate electrostatic assembly were used to detect DNA damage from an epoxide metabolite and methylating agents on a reaction time scale of minutes. The redox polymer [Ru(bpy)2poly(4-vinylpyridine)10Cl)]Cl was used as an inner layer in films 14-25 nm thick to catalyze the voltammetric oxidation of guanine bases of ds-DNA in the outer layers. This film architecture provides a self-contained, reagentless sensor for toxicity screening based on detection of DNA damage. Films were incubated with reactants and washed, and then DNA damage was analyzed by square wave voltammetry (SWV). Bioactivation of styrene to its metabolite styrene oxide was accomplished by incorporating the protein myoglobin into the films to catalyze the conversion. DNA damage caused the catalytic SWV peaks at approximately 0.75 V vs SCE to increase nearly linearly over the first 10-20 min of reaction, depending on the damage agent employed. Such prototype toxicity biosensors hold promise for in vitro screening of new agricultural chemicals and drugs for potential genotoxicity.

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