Tyrosinase immobilization on aminated magnetic nanoparticles by physical adsorption combined with covalent crosslinking with improved catalytic activity, reusability and storage stability

On-chip structure-switching aptamer-modified magnetic nanobeads for the continuous monitoring of interferon-gamma ex vivo

Cytokines are cell signaling molecules that indicate the health status of the body. In this study, we developed a microfluidic device integrated with structure-switching aptamers capable of continuously tracking the concentration of the cytokine interferon gamma (IFN-γ) in cell culture medium and blood serum. First, a ferrocene (Fc)-labeled structure-switching signaling aptamer with a hairpin structure targeting IFN-γ was immobilized on magnetic nanobeads by the strongest noncovalent interactions between streptavidin and biotin. The aptamer-modified magnetic nanobeads were trapped on a customized microfluidic chip by a magnetic field to form the sensing interface. The binding of IFN-γ could trigger the hairpin structure of the aptamer to unfold, pushing Fc redox molecules away from the sensing interface and consequently switching off the electrochemical signal. The change in the redox current of Fc was quantitatively related to the concentration of IFN-γ in a linear range of 10-500 pg mL^-1 and with the lowest detection limit of 6 pg mL^-1. This microfluidic device was specific to IFN-γ in the presence of overabundant serum proteins and allowed the continuous monitoring of IFN-γ without adding exogenous reagents. It provided a universal point-of-care biosensing platform for the real-time detection of a spectrum of analytes.

Characterization of immobilized tyrosinase - an enzyme that is stable in organic solvent at 100 °C

Tyrosinase is a copper-containing enzyme present in plant and animal tissues, which catalyzes the production of melanin and other pigments. In organic solvent, tyrosinase can convert N-acetyl-l-tyrosine ethyl ester (insoluble in aqueous) to a derivative of l-dopamine (a drug used for the treatment of Parkinson's disease). Thus, the performances of tyrosinase in organic solvent have attracted scientific attention since 1980. In this work, we investigated the stability of immobilized tyrosinase at high temperature in anhydrous organic solvent. Triethylaminoethyl cellulose (TEAE-Cellulose) performed the best out of six immobilization platforms. The dry immobilized tyrosinase became extremely thermostable in organic solvent, and the half-life of the dry immobilized tyrosinase in organic solvent is strongly related to the polarity of the organic solvent than their log P value. The immobilized tyrosinase loses its activity instantaneously in aqueous solution at 100 °C, but it keeps enzymatic activity within 10 min in hydrophilic methanol and over one month in hydrophobic hexane (log P: 4.66, non-polar) even incubating at 100 °C. This research provides valuable information for the design of new biocatalysts.

Immobilized tyrosinase in hexane can withstand 100 °C over one week, and the half-life of the dry immobilized tyrosinase in organic solvent is strongly related to the polarity of the organic solvent.