Monitoring the Photocleaving Dynamics of Colloidal MicroRNA-Functionalized Gold Nanoparticles Using Second Harmonic Generation

Abstract

Photoactivated drug delivery systems using gold nanoparticles provide the promise of spatiotemporal control of delivery that is crucial for applications ranging from regenerative medicine to cancer therapy. In this study, we use second harmonic generation (SHG) spectroscopy to monitor the light-activated controlled release of oligonucleotides from the surface of colloidal gold nanoparticles. MicroRNA is functionalized to spherical gold nanoparticles using a nitrobenzyl linker that undergoes photocleaving upon ultraviolet irradiation. The SHG signal generated from the colloidal nanoparticle sample is shown to be a sensitive probe for monitoring the photocleaving dynamics in real time. The photocleaving irradiation wavelength is scanned to show maximum efficiency on resonance at 365 nm, and the kinetics are investigated at varying irradiation powers to demonstrate that the nitrobenzyl photocleaving is a one-photon process. Additional characterization methods including electrophoretic mobility measurements, extinction spectroscopy, and fluorimetry are used to verify the SHG results, leading to a better understanding of the photocleaving dynamics for this model oligonucleotide therapeutic delivery system.

Plasmon-Enhanced Photocleaving Dynamics in Colloidal MicroRNA-Functionalized Silver Nanoparticles Monitored with Second Harmonic Generation

“…The obtained results are compared with our previous studies on miRNA-functionalized gold nanoparticles. 33 Representative SHG spectra of SNPs and miRNA-functionalized SNPs are shown in Figure 4a. The SHG peak from the 800 nm probe laser is located at 400 nm, as expected, with full width half-maximum of 4.5 nm.…”

“…This interpretation is consistent with previous work and with our earlier results on miRNA-functionalized GNPs. 10,33,58,62 The 6-TAMRA fluorophore has negligible contribution to the SHG signal because it has negligible absorption near the 800 nm probe and 400 nm SHG wavelengths. Figure 4b shows representative SHG spectra from the miRNA-functionalized SNPs at different UV-irradiation times of 0, 90, and 800 s using 365 nm irradiation with a 20 mW average power.…”

“…33 The SHG electric field can be described by the equation E SHG = A + B [ C ], where A is an offset, B is a proportionality constant, and [ C ] is the cumulative concentration of miRNA attached to the surface of nanoparticles. As noted earlier, the change in E SHG as a function of attached miRNA at the nanoparticle surface is attributed mainly to the surface charge density and the resulting χ (3) term.…”

“…The error bars are included in Figure 8a,b but are mostly smaller than the data points. The previously obtained GNP data 33 are included for direct comparison. The linear variation of the rate constants as a function of the UV laser power is consistent with a pseudo-first-order kinetics model, indicating that the photocleaving is a one-photon process for all nanoparticle samples investigated.…”

“…29–32 Previously, we have investigated the kinetics of photoactivated controlled-release of miRNA from the surface of colloidal gold nanoparticles using time-resolved second harmonic generation (SHG). 33 …”