Assembling Near-Infrared Dye on the Surface of Near-Infrared Silica-Coated Copper Sulphide Plasmonic Nanoparticles

Abstract

Functionalization of colloidal nanoparticles with organic dyes, which absorb photons in complementary spectral ranges, brings a synergistic effect for harvesting additional light energy. Here, we show functionalization of near-infrared (NIR) plasmonic nanoparticles (NPs) of bare and amino-group functionalized mesoporous silica-coated copper sulphide (Cu2-xS@MSS and Cu2-xS@MSS-NH2) with specific tricarbocyanine NIR dye possessing sulfonate end groups. The role of specific surface chemistry in dye assembling on the surface of NPs is demonstrated, depending on the organic polar liquids or water used as a dispersant solvent. It is shown that dye binding to the NP surfaces occurs with different efficiency, but mostly in the monomer form in polar organic solvents. Conversely, the aqueous medium leads to different scenarios according to the NP surface chemistry. Predominant formation of the disordered dye monomers occurs on the bare surface of mesoporous silica shell (MSS), whereas the amino-group functionalized MSS accepts dye predominantly in the form of dimers. It is found that the dye–NP interaction overcomes the dye–dye interaction, leading to disruption of dye J-aggregates in the presence of the NPs. The different organization of the dye molecules on the surface of silica-coated copper sulphide NPs provides tuning of their specific functional properties, such as hot-band absorption and photoluminescence.

Microscopic Perspective of Synergy between Localized Surface Plasmon Resonance and Disruption of Dye Aggregates in Metal Nanoparticle-Enhanced Fluorescence

“…Generally, the metal NPs charge surface regulates dye aggregation . As a result, the disruption of RB aggregates is observed in the presence of the AgNP surface. , This is reminiscent of an observation with AgNPs and Congo red . At this juncture, we refrain from engaging in a quantitative discussion of the fluorescence decays as a more informative discussion of decays recorded under a microscope is to follow.…”

Plasmon Enhancement of the Hot-Band Absorption-Assisted Anti-Stokes Photoluminescence of Near-Infrared Dyes

“…Second, ethanol dispersions of mesoporous silica-coated Cu 2– x S NPs (Cu 2– x S@MSN) of different sizes and shell thicknesses were synthesized according to the procedure previously reported in ref . Mesoporous silica shell thickness was tuned by varying the volume of the silica precursor, tetraethyl orthosilicate (TEOS), and the growth time, respectively, where the growth time is referred to as the time the reaction mixture was left at room temperature after the heating step (2 h at 40 °C/1 h at 60 °C), which is required for silica precursor hydrolysis and condensation.…”

“…As was observed in our previous studies, plasmonic Cu 2−x S@MSN NPs usually suppress both Stokes and anti-Stokes emission of Dye 1, which is attached by sulfonic groups to the silica surface and which results in distortion of the dye chromophore. 20 Indeed, suppression of the ASPL maximum of Dye 1 when adsorbed on the surface of Cu 2−x S@MSN is observed independent of the silica shell thickness (compare emission intensities in Figures 9a,c,e and S8a), suggesting again that the dye molecule , (e) mixture of Dye 1 and Cu 2−x S@MSN_2 (0.05 g/L), and (f) mixture of Dye 2 and Cu 2−x S@MSN_2 (0.05 g/L). The vertical dashed lines mark conventional spectral borders of the composite solutions.…”