Gold Nanocage Assemblies for Selective Second Harmonic Generation Imaging of Cancer Cell

Abstract

Second harmonic generation (SHG) imaging using near infrared laser light is the key to improving penetration depths, leading to biological understanding. Unfortunately, currently SHG imaging techniques have limited capability due to the poor signal-to-noise ratio, resulting from the low SHG efficiency of available dyes. Targeted tumor imaging over nontargeted tissues is also a challenge that needs to be overcome. Driven by this need, in this study, the development of two-photon SHG imaging of live cancer cell lines selectively by enhancement of the nonlinear optical response of gold nanocage assemblies is reported. Experimental results show that two-photon scattering intensity can be increased by few orders of magnitude by just developing nanoparticle self-assembly. Theoretical modeling indicates that the field enhancement values for the nanocage assemblies can explain, in part, the enhanced nonlinear optical properties. Our experimental data also show that A9 RNA aptamer conjugated gold nanocage assemblies can be used for targeted SHG imaging of the LNCaP prostate cancer cell line. Experimental results with the HaCaT normal skin cell lines show that bioconjugated nanocage-based assemblies demonstrate SHG imaging that is highly selective and will be able to distinguish targeted cancer cell lines from other nontargeted cell types. After optimization, this reported SHG imaging assay could have considerable application for biology.

Nanovaccines for malaria using Plasmodium falciparum antigen Pfs25 attached gold nanoparticles

“…To synthesize spherical GN-particles (GNP, Figure 1A) (53, 55), aqueous solutions of HAuCl4.3H 2 O (1.8 mL, 0.01 M) and sodium citrate (0.5 mL, 0.01M) were added to 40 mL of deionized H 2 O with continuous stirring. Next, freshly prepared NaBH 4 (0.12 mL, 0.1M) was added and when the solution changed from colorless to light pink / orange (approximately 30 minutes), stirring was stopped and the solution was left undisturbed for 2 h. Star shape GN-particles (GNS, Figure 1B) were synthesized using a two-step procedure as reported (51).…”

“…Next, freshly prepared NaBH 4 (0.12 mL, 0.1M) was added and when the solution changed from colorless to light pink / orange (approximately 30 minutes), stirring was stopped and the solution was left undisturbed for 2 h. Star shape GN-particles (GNS, Figure 1B) were synthesized using a two-step procedure as reported (51). The first step involved synthesis of small size spherical GN-particle seed as described above for GNP, followed by the addition of shape-templating surfactant cetyltrimethylammonium bromide (46.88 mL, 0.59 mM) and 0.3 mL, 0.01 M AgNO 3 and incubation for 24 hours to synthesize GNS (53, 55). Cage shape GN-particles (GNC, Figure 1C) were prepared by galvanic replacement reaction (53, 55).…”

“…The first step involved synthesis of small size spherical GN-particle seed as described above for GNP, followed by the addition of shape-templating surfactant cetyltrimethylammonium bromide (46.88 mL, 0.59 mM) and 0.3 mL, 0.01 M AgNO 3 and incubation for 24 hours to synthesize GNS (53, 55). Cage shape GN-particles (GNC, Figure 1C) were prepared by galvanic replacement reaction (53, 55). Initially silver nanocubes were synthesized followed by the addition of HAuCl 4 .3H 2 O (5 mL, 0.01M) to 5 mL of concentrated silver nanocubes (0.01mM).…”

“…Covalent immobilization of the CHrPfs25 antigen onto the GN-particles was performed using 4-amino-thio phenol (4-ATP) and a glutaraldehyde spacer method (51–53). In brief, 10 mM 4-ATP added to 20 mL of GN-particles and the solution was kept at 55°C for 6 hours under constant sonication and excess ATP was removed by centrifugation at 8,000 rpm for 30 minutes.…”

Multimodal Nonlinear Optical Imaging of Live Cells Using Plasmon-Coupled DNA-Mediated Gold Nanoprism Assembly

“…Multiphoton microscopy via coupling of nonlinear optics (NLO) and scanning microscopy has opened up the possibility of new discovery for breakthrough in biology 1–10 . NLO imaging using second harmonic generation (SHG) and two-photon luminescence (TPL) are the emerging techniques to watch the biological world due its ability to penetrate deep into living tissue 11–20 .…”