Hydrophobically Modified Silica-Coated Gold Nanorods for Generating Nonlinear Photoacoustic Signals

Area of Science:

• Nanotechnology
• Biomedical Optics
• Materials Science

Background:

• Gold nanorods (AuNRs) are utilized in photoacoustic imaging due to their strong optical absorption.
• Mesoporous silica shells are employed to functionalize nanoparticles, but their impact on photoacoustic signal generation requires further investigation.

Purpose of the Study:

• To investigate the photoacoustic (PA) signal enhancement and response linearity of gold nanorods coated with hydrophobically-modified mesoporous silica shells.
• To elucidate the underlying mechanisms responsible for enhanced PA signal generation and nonlinear behavior.

Main Methods:

• Synthesis of gold nanorods with near-infrared absorption.
• Growth of ~14 nm thick mesoporous silica shells with ~3 nm pores on AuNRs.
• Hydrophobization of silica shells using dodecyltrichlorosilane and re-suspension in aqueous media with a lipid monolayer.
• Analysis of photoacoustic signal amplitude in relation to varying laser fluences.

Main Results:

• Hydrophobically modified mesoporous silica shells enhanced photoacoustic signal compared to unmodified shells.
• A strong nonlinear relationship was observed between PA signal amplitude and input laser fluence, even at low fluences (5 mJ cm⁻²).
• PA enhancement exceeded 12-fold at the highest tested laser fluence (21 mJ cm⁻²).

Conclusions:

• The entrapment of solvent vapor within the mesopores of the hydrophobic shells is responsible for enhanced PA signal generation and nonlinear response.
• The hydrophobic surface promotes phase transitions, leading to increased acoustic energy conversion.
• These modified nanorods show potential for improved sensitivity and performance in photoacoustic applications.