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WIREs Nanomed Nanobiotechnol
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Structural control and biomedical applications of plasmonic hollow gold nanospheres: A mini review

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Abstract Hollow gold nanospheres (HGNs) are core/shell structures with a dielectric material core, usually composed of solvent, and a gold metal shell. Such structures have two metal/dielectric interfaces to allow interaction between the gold metal with the interior and external dielectric environment. Upon illumination by light, HGNs exhibit unique surface plasmon resonance (SPR) properties compared to solid gold nanoparticles. Their SPR absorption/scattering can be tuned by changing their diameter, shell thicknesses, and surface morphologies. In addition to the low toxicity, easy functionalization, resistance to photobleaching, and sensitivity to changes in surrounding medium of gold, the enhanced surface‐to‐volume ratio and tunable SPR of HGNs make them highly attractive for different applications in the fields of sensing, therapy, and theranostics. In this article, we review recent progress on the synthesis and structural control of HGNs and applications of their SPR properties in biomedical sensing and theranostics. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > in vitro Nanoparticle‐Based Sensing Diagnostic Tools > in vivo Nanodiagnostics and Imaging
Galvanic exchange protocols for HGN synthesis. Anaerobic protocol: galvanic exchange and oxygenation steps are separated, and the gold salt is deaerated so that galvanic exchange may be carried out in the absence of environmental oxygen. A representative SEM image is provided for the cobalt nanoparticle (Co2B NP) formed in step I and representative HRTEM images are provided for the Co2B NP/Au core/shell structures and resultant HGNs formed in steps II and III, respectively (Lindley et al., 2018)
In vivo biodistribution and photothermal effects of HGNs and siRNA conjugated HGNs (HGN‐siHsp70). (a) Fluorescence imaging of HGN‐siHsp70 and HGN at 15 min, 2 h, 6 h, 12 h, and 24 h after intravenous injection. (b) Tumor to normal tissue ratios of glioma tumor bearing mice at different time points after injection. (c) Infrared thermal images of glioma tumor bearing mice i.v. injected with HGN and HGN‐siHsp70 within 8 min under 765 nm laser irradiation. (d) Temperature changes on tumor sites according to the imaging in (c) (Z. Wang et al., 2017)
Noninvasive PAT imaging of a mouse brain in vivo employing PEG‐HGN and NIR light at a wavelength of 800 nm. Photoacoustic image acquired (a) before injection, (b) 5 min after injection, and (c) 2 h after the intravenous injection of PEG‐HGN. (d,e) Differential images that were obtained by subtracting the pre‐injection image from the post‐injection images. (f) Open‐skull photograph of the mouse brain cortex obtained after the data acquisition for PAT. Bar = 2 mm
(a–d) SEM and TEM images of bumpy hollow gold nanospheres made using template directed method and increasing concentrations of OH from left to right. (e) SEM and TEM image of bumpy hollow gold nanospheres with maximum addition of NaOH and 60‐min wait time before injection of NaOH. SEM scale bars are 100 nm. TEM scale bars are 50 nm (Lindley & Zhang, 2019). (f) UV–Vis spectra of corresponding bumpy HGNs (Lindley & Zhang, 2019). (g–j) SEM images of spiky HGNs synthesized using the surfactant‐assisted seed‐mediated method through change of surfactant: (g) CTAC, (h) CTAB, (i and j) CTACBr. (k) UV–Vis spectra of corresponding spiky HGNs (Sanchez‐Gaytan et al., 2013)
Aerobic protocol: cobalt nanoparticles (Co2B NP) are prepared by wet‐chemical reaction between cobalt ions and sodium borohydride, galvanic exchange is carried out by the introduction of Co2B NP to aqueous gold ions, and the Co2B NP core is simultaneously oxidized out of the shell by interaction with environmental oxygen resulting in bumpy surface morphology (Lindley et al., 2018)
Demonstration of twofold tunability. (a) Relationship between SPR, size, and aspect ratio. (b) Normalized extinction for HGNs with the same outer diameter but different SPR: 48 nm HGNs with 635, 700, and 765 nm SPR. (c) Corresponding HRTEM images with average diameter (d), shell thickness (t), and aspect ratio (AR) as indicated; scale bar 10 nm. (d) Normalized extinction for HGNs with a different outer diameter but the same SPR: 73 ± 6, 48 ± 6, and 37 ± 4 nm HGNs with 700 nm SPR. After normalization, the 48 ± 6 and 73 ± 6 nm extinctions were offset on the y‐axis by 0.25 and 0.50 OD, respectively. (e) Corresponding HRTEM images with d, t, and AR as indicated; scale bar 10 nm (Lindley et al., 2018)

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Diagnostic Tools > In Vivo Nanodiagnostics and Imaging
Diagnostic Tools > In Vitro Nanoparticle-Based Sensing
Diagnostic Tools > Biosensing

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