Efficient Ag+ adsorption of in-vivo thiol-functionalized diatoms and its application for sensitive surface-enhanced Raman scattering

Abstract

Diatom silica frustules are recognized as a valuable biomaterial with hierarchically porous silica structures and can be used for many applications. To obtain targeted functional diatom-based materials, many strategies have been explored, mainly focusing on diatomite (fossilized diatoms) but rarely on living diatom silica frustules. In this work, the frustules of living diatoms (T. weissflogii) were in-vivo functionalized with thiol (-SH) groups by using (3-mercaptopropyl) trimethoxysilane (MPTMS) as silicon source, through living biomineralization process. The -SH groups were homogeneously distributed in diatom biosilica structures, as revealed by FIB-TEM-EDS result. Two applications of thiol-functionalized frustules were demonstrated. The first was for Ag+ adsorption, showing significantly enhanced adsorption capacity (87.59 mg·g−1) compared with unmodified frustules (33.21 mg·g−1). The adsorption data and the spectroscopic and microscopic analyses revealed that the inner-sphere complexation of -SH with Ag+ was the primary mechanism. The second application showed that Ag+-loaded diatom frustules exhibited a significant surface-enhanced Raman scattering (SERS), which can be used for detecting methylene blue and rhodamine 6G. The charge transfer resonance between Ag2S and probe molecules makes the primary contribution to the distinct enhancement of Raman signals. These findings demonstrate that these in-vivo functionalized -SH groups on diatom silica frustules can still maintain their excellent chemical reactivities, suggesting that this modification strategy could be extended to modify living diatom silica frustules with other functional groups. This study is of great significance for developing functional materials from living diatoms and their applications in the fields of environmental remediation, biosensing, and drug delivery, etc.