Bottom-up microwave-assisted seed-mediated synthesis of gold nanoparticles onto nanocellulose to boost stability and high performance for SERS applications

The development of accurate, reliable, inexpensive and fully recyclable analytical platforms is of utmost relevance to several fields from medical diagnosis to environmental screening. Surface-enhanced Raman spectroscopy (SERS) is a compelling detection method with high specificity and sensitivity. In this work, a microwave-assisted synthesis method was used for fast and uniform in situ growth of gold nanoparticles (AuNPs) onto nanocellulose (NC) membranes, through a seed-mediated process. The as-prepared membranes were fully optimized and its application as SERS platforms was demonstrated. A direct comparison with other cellulose-based substrates showed the superior characteristics of NC such as high mechanical strength, high surface area and lower porous content. An Enhancement Factor (EF) up to ~10⁶ was obtained using rhodamine 6G (R6G) 10⁻⁶ M as probe molecule and a remarkable shelf life of at least 7 months was achieved, with no special storage requirements. Preliminary results on the label-free detection of spike protein from SARS-CoV-2 virus are shown, through direct measurements on the optimized SERS membrane. We believe that this work evidences the effectiveness of in situ seed-mediated microwave-assisted synthesis as a fabrication method, the high stability of AuNPs and the superior characteristics of NC substrates to be used as SERS platforms.