Photo-controllable antifouling hydrogels embedded with AgNPs coated spiropyran functionalized mesoporous silica for long-term antibacterial activity

Silver nanoparticles (AgNPs) are widely used in antimicrobial applications. However, its easy aggregation and rapid loss hinder the effective antifouling. To address this issue, a novel stimuli-responsive antibacterial nanocomposite (Ag@SP-MSN) was developed based on spiropyran covalently conjugated mesoporous silica nanoparticles (284.6 nm) and AgNPs (27.1 nm) via strong electrostatic attraction. Both transmission electron microscopy (TEM) and atomic force microscopy (AFM) images proved the successful modification of AgNPs onto SP-MSN. The light-induced maximum loading amount towards AgNPs was calculated to be 95.0 wt.% after ultraviolet irradiation, while the amount of AgNPs released from Ag@SP-MSN was 94.4 wt.% under visible light in the aid of ammonia (0.1%, v/v). Upon cycled light irradiation, Ag@SP-MSN could recover 84.5 wt.% of AgNPs even after four cycles. The proposed Ag@SP-MSN exhibited better antibacterial activity against both E. coli and S. aureus than Ag@MSN under visible light illumination, indicating the efficient photo-responsive isomerization of spiropyran. Furthermore, the Ag@SP-MSN embedded gel demonstrated outstanding antifouling ability even after 21 days when compared to AgNPs gel. The long-term photo-controllable antifouling property proved the excellent reversible absorption and release of Ag@SP-MSN towards AgNPs. This work provides new insights into the safe utilization of nanomaterials, offering promising advancements to meet clinical antibacterial requirements.