Synergistic Effect in Hybrid Plasmonic Conjugates for Photothermal Applications

Abstract

Photothermal conversion efficiency (η) plays a crucial role in selecting suitable gold nanoparticles for photothermal therapeutic applications. The photothermal efficiency depends on the material used for the nanoparticles as well as their various parameters, such as size and shape. By maximizing the light-to-heat conversion efficiency (η), one can reduce the concentration of nanoparticle drugs for photothermal cancer treatment and apply lower laser power to irradiate the tumor. In our study, we explored a new hybrid plasmonic conjugate for theranostic (therapy + diagnostic) applications. We conjugated PEG-functionalized 20 nm gold nanospheres with cyanine IR dyes via a PEG linker. The resulting conjugates exhibited significantly enhanced photothermal properties compared with bare nanoparticles. We experimentally showed that a proposed new hybrid plasmonic conjugate can achieve almost four times larger conversion efficiency (47.7%) than 20 nm gold nanospheres (12%). The enhanced photothermal properties of these gold conjugates can provide the required temperature for the photothermal treatment of cancer cells with lower concentrations of gold nanoparticles injected in the body as well as with lower applied incident laser power density. Moreover, the improved photothermal properties of the conjugates can be explained by a synergistic effect that has not been observed in the past. This effect results from the coupling between the metal nanosphere and the organic dye.

Figure 1

(a) Absorbance spectrum of 20 nm Gold Nanosphere (20 nm AuNP) and AuNPCs in UPW. (b) Schematic representation of AuNPCs with a cyanine dye absorbance spectrum. (c) Sketch of the experimental setup for measuring the temperature profiles of different solutions.

Figure 2

Temperature profiles for AuNPCs and 20 nm AuNPs in UPW for different laser powers: (a) 1 W, (b) 1.5 W, and (c) 2 W.

Figure 3

(a) ΔT vs (P₀ – P_tr) graph for AuNPCs. (b) ΔT vs (P₀ – P_tr) graph for 20 nm AuNPs. The error bars represent the range of the absolute value for ΔT for each solution based on measured triplicate (Figure 2).

Figure 4

(a) Absorbance spectra of AuNPCs in UPW and cyanine IR dyes in methanol. (b) Temperature profile for cyanine IR dyes in methanol at laser’s power of 1 W.

Figure 5

Temperature profile for AuNPCs in UPW, 20 nm AuNPs in UPW, IR cyanine dyes in methanol, and for 20 nm AuNPs + IR cyanine dye mixture at laser’s power of 1 W.