Gold chloride trihydrate (, cat. no. 520918), ammonium hydroxide solution (30% as assay, cat. no. 221228), ethanol (cat. no. 459828), tetraethyl orthosilicate (TEOS, cat. no. 333859), sodium hydroxide (NaOH, cat. no. 306576), tetrakis (hydroxymethyl)phosphonium chloride solution (THPC, 80% aqueous solution, cat. no. 404861), (3-aminopropyl)trimethoxysilane (APTMS, cat. no. 281778), potassium carbonate (cat. no. 367877), and formaldehyde solution (cat. no. F8775) were purchased from Sigma-Aldrich (Milwaukee, Wisconsin). Ultrapure water from a Direct-Q3 system (, Millipore, Billerica, Massachusetts) was used in this work. A Cary 5000 ultraviolet-visible-NIR (UV-vis-NIR) spectrophotometer was used to measure the extinction of the nanoparticles.