Abstract
Porous gold nanoparticles (PGNs) are usually prepared in an immobilized form on a solid substrate, which is not practical in many applications. In this work, a simple method is reported for the preparation and stabilization of mesoporous gold particles of a few hundred nanometers in size in aqueous suspension. Nanoparticles of Ag-Au alloy were fabricated on CaF and Si/SiO substrates by the solid-state dewetting method. Silver was selectively dissolved (dealloyed), and the resulting porous gold nanoparticles were chemically removed from the substrate either in a concerted step with dealloying, or in a subsequent step. Nitric acid was used for the one-step dealloying and detachment of the particles from CaF substrate. The consecutive use of HNO and HF resulted in the dealloying and the subsequent detachment of the particles from Si/SiO substrate. The PGNs were recovered from the aqueous suspensions by centrifugation. The Au content of the suspensions was monitored by using elemental analysis (ICP-OES), and recovery was optimized. The morphology and the optical characteristics of the support-free PGNs were analyzed by scanning electron microscopy (SEM), dynamic light scattering spectroscopy (DLS), and near-infrared spectrophotometry (NIR). The obtained PGNs are spherical disk-shaped with a mean particle size of 765 ± 149 nm. The suspended, support-free PGNs display an ideally narrow dipole plasmon peak at around 1450 nm in the NIR spectral region. Thus, the new colloidal PGNs are ideal candidates for biomedical applications, for instance photothermal therapy.
Highlights
Porous noble metal nanoparticles and thin layers are highly attractive for applications in catalysis, sensing, plasmonics, biochemistry, medical diagnosis, and therapy owing to their unique chemical and optical characteristics. [1,2,3,4,5,6,7,8,9,10]
The amount of material in the particles detached from the CaF2 support perfectly matches the amount of material deposited by sputtering, which shows the excellent efficiency of the detachment method. (SEM images of spent supports recorded after the detachment confirm the complete removal of the nanoparticles.) The Au contents of the suspensions were determined after each centrifugation step and compared to that of the initial acidic suspension. 6.26 ± 0.72 μg Au was recovered after the first centrifugation step, and the second round of centrifugation decreased the yield to 5.11 ± 0.58 μg Au
A simple method is presented for the synthesis and stabilization of porous gold nanoparticles (PGNs) in water
Summary
Porous noble metal nanoparticles and thin layers are highly attractive for applications in catalysis, sensing, plasmonics, biochemistry, medical diagnosis, and therapy owing to their unique chemical and optical characteristics. [1,2,3,4,5,6,7,8,9,10]. Porous noble metal nanoparticles and thin layers are highly attractive for applications in catalysis, sensing, plasmonics, biochemistry, medical diagnosis, and therapy owing to their unique chemical and optical characteristics. The high surface/volume ratios and the advantageous optical properties of the porous gold nanoparticles (PGNs) are attractive and interesting. Even a well-defined porous particle can yield multiple, infrared-shifted plasmon peaks due to the fragmentation of the bulk metal phase. It is an additional tool for tuning the optical properties of PGNs and shifting the wavelengths of the dipole plasmon peaks [14,15,16,17]. The presence of a substrate naturally limits the utilization of porous nanoparticles
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