T. V. Nguyen, C. D. Vu, T. B. Pham, V. H. Pham, H. Bui, T. H. H. Vu and V. H. Pham, Detection of Ultra-Low Concentration of Methylene Blue by Porous Silicon Photonic Crystals Covered With Siver Nanoparticles as Efficient Sers Substrate, Comm. Phys. 31 (2021) 381. DOI: https://doi.org/10.15625/0868-3166/15927.