The bacteriostatic performance of a chitosan film is closely related to its ionic and physical properties, which are significantly influenced by the mode of cross-linking. In the current work, chitosan with or without bacterial cellulose was cross-linked with borate, tripolyphosphate, or the mixture of borate and tripolyphosphate, and the composite films were obtained by a casting of dispersion. Mechanical measurements indicated that different modes of cross-linking led to varying degrees of film strength and elongation increases, while the films treated with the borate and tripolyphosphate mixture showed the best performance. Meanwhile, changes in the fractured sectional images showed a densified texture induced by cross-linkers, especially for the borate and tripolyphosphate mixture. Measurements of Fourier transform infrared showed the enhanced interaction between the matrix polymers treated by borate, confirmed by a slight increase in the glass transitional temperature and a higher surface hydrophobicity. However, the reduced antimicrobial efficiency of composite films against E. coli, B. cinerea, and S. cerevisiae was obtained in cross-linked films compared with chitosan/bacterial cellulose films, indicating that the impact on the antimicrobial function of chitosan is a noteworthy issue for cross-linking.

Bisphenol A (BPA) has emerged as a contaminant of concern because long-term exposure may affect the human endocrine system. Herein, a novel aptamer sensor based on magnetic separation and surface-enhanced Raman scattering (SERS) is proposed for the extremely sensitive and specific detection of trace BPA. Moreover, the capture unit was prepared by immobilizing thiolated (SH)-BPA aptamer complementary DNA on AuNP-coated magnetic halloysite nanotubes (MNTs@AuNPs), and SH-BPA aptamer-modified Au@4-MBA@Ag core–shell SERS nanotags acted as signal units. By the complementary pairing of the BPA aptamer and the corresponding DNA, MNTs@AuNPs and Au@4-MBA@AgCS were linked together through hybridization-ligation, which acted as the SERS substrate. In the absence of BPA, the constructed aptamer sensor generated electromagnetic enhancement and plasmon coupling to improve the sensitivity of SERS substrates. Owing to the high affinity between BPA and the aptamer, the aptamer probe bound to BPA was separated from the capture unit by an externally-induced magnetic field. Thus, the Raman intensity of the MNTs@AuNP-Ag@AuCS core–satellite assemblies was negatively correlated with the BPA concentration. High sensitivity measurements of BPA might be performed by determining the decline in SERS signal strength together with concentration variations. The proposed aptasensor is a promising biosensing platform for BPA detection.