Enzyme-Assisted Metabolically Coated Bimetallic Thalassiosira pseudonana Nanosilica as a Surface-Enhanced Raman Scattering Substrate for Specific Screening of Prostate Cancer Individuals

Multicomponent heteronanostructures offering catalytic and optical properties have applications across various fields. Photonic crystals (diatom frustules) coated with Au and copper chalcogenide domains represent a unique nanosystem that integrates multiple plasmon resonances from guided-mode resonance, conduction electrons, and valence holes in a single nanoscale system. In this work, we fabricate an enzyme-assisted photonic crystal-enhanced plasmonic nanosystem using a live diatom (Thalassiosira pseudonana) for surface-enhanced Raman scattering (SERS) quantification of sarcosine, an early stage prostate cancer (PCa) biomarker. The biosynthesized heteronanostructure was constructed by coating bimetallic nanoparticles (Au/CuX) on the diatom frustule via a two-stage cultivation process. A silaffin peptide-tagged sarcosine oxidase (SoX) was designed for specific substrate recognition and oriented conjunction. The components were coupled into a single entity (SoX-immobilized Au/CuX-coated frustule, BioNPS) to overcome the interenzyme distance and analyte trade-offs between mass transport. The sarcosine detection by BioNPS outperforms suspended bimetallic nanoparticles and single NP-coated diatom frustules. The improvement is attributed to the coupling of photonic frustule guided-mode resonance to the localized surface plasmonic resonance of bimetallic NPs via both electromagnetic and CT mechanisms. The cascade reaction in close proximity greatly enhances the catalytic efficiency by 5.47-fold compared to the solution-phase assay. The biochem nanosystem precisely detects tiny sarcosine concentration changes in the urine samples of PCa patients and healthy individuals. As a proof of concept, the in vivo fabrication of photonic/plasmonic heterostructures with tunable properties holds great promise for noninvasive biomarker screening.