In this study, a pH responsive carboxymethyl agarose-polydopamine (CMA-PDA) hydrogel carrier was developed. Carboxymethyl agarose (CMA) was synthesized by replacing the hydroxyl groups of agarose with chloroacetic acid and was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA). Then, the CMA-PDA hydrogel was prepared, and its rheological and texture properties were characterized. The results showed that the gel strength, hardness and viscoelasticity of the hydrogel were increased by the addition of PDA. Doxorubicin (DOX) was used as a model to study the release behavior of the hydrogel at pH 2.0, 6.2, 6.8 and 7.4. The results showed that the hydrogel had good pH responsiveness and the release rate was significantly higher at pH 2.0 than at other pH levels. Moreover, the hydrogel had no cytotoxicity on L929 cells. This study proves that CMA-PDA hydrogel has good biocompatibility, pH responsive and slow release properties, and can be used as a potential carrier for bioactive substance delivery.

Sensitive monitoring of the target products during the biosynthesis process is crucial, and facile analytical approaches are urgently needed. Herein, phosphatidylserine (PS) was chosen as the model target, a colorimetric aptasensor was developed for the rapid quantitation in biosynthesis samples. A chimeric aptamer was constructed with two homogeneous original PS aptamers. Specific recognition between the chimeric aptamer and PS results in the desorption of aptamer from the surface of the AuNPs nanozyme, and the peroxidase-like enzymatic activity of the AuNPs nanozyme was weakened in a relationship with the different concentrations. The developed aptasensor performed well when applied for analyzing PS in biosynthesis samples. The aptasensor offers good sensitivity and selectivity, under optimal conditions, achieving monitoring and quantitation of PS in the range of 2.5-80.0 μmol/L, with a limit of detection at 536.2 nmol/L. Moreover, the aptasensor provides good accuracy, with comparison rates of 98.17%-106.40%, when compared with the HPLC-ELSD. This study provides a good reference for monitoring other biosynthesized products and promoting the development of aptamers and aptasensors in real-world applications.

Quorum sensing (QS) system can dynamically control the expression of proteins along with the cell growth. The promoting period of QS system has been little focused on until now. In this study, a self-induced dynamic regulated expression (SIDRE) system was constructed in Escherichia coli. To enable the system suitable for the expression of enzymes, promoter engineering was used to obtain P_luxI mutants. To test the SIDRE system, alginate lyase AL493 and esterase Est7 were used as target protein for expression. The enzyme activity of alginate lyase and esterase reached 96.38% and 106.71% of the control strains containing the T7 promoter. In high-density fermentation, the activity of alginate lyase expressed by the SIDRE system with P_luxI(T-38C) as promoter was 4.34-fold of that expressed by the T7 promoter. Therefore, the P_luxI mutants with different promoting periods and/or different strengths show great potential in both laboratory and industrial scale for protein expression.