LED and Laser Illumination for Gold Nanorod-Based Photoacoustic Imaging

Gold nanorods (AuNRs) are promising theranostic agents for photoacoustic imaging (PAI) due to their anisotropic geometry and tunable localized surface plasmon resonance (LSPR). However, their performance and structural stability depend strongly on the excitation source. This study compared high-power LED and pulsed-laser excitation for PAI using AuNRs with different longitudinal dimensions. Quantitative analysis shows that the photoacoustic (PA) response is governed by LSPR alignment and nanoparticle concentration, with signal-to-noise ratio (SNR) values of 22.7 dB (LED) and 20.7 dB (laser), indicating comparable image quality under the tested conditions. Despite the intrinsically higher instantaneous PA intensity under laser excitation, experiments conducted at a frame rate of 1 Hz enabled temporal averaging under LED illumination, resulting in comparable image quality between both modalities. In contrast, significant differences were observed in AuNR stability. TEM analysis reveals that laser irradiation induces pronounced morphological changes, with dimensional variations of 15–30 nm, whereas LED exposure results in minimal changes 1–3 nm. These results indicate that similar PA image quality can be achieved under both excitation regimes, but with markedly different impacts on AuNR integrity. Overall, laser excitation provides a higher instantaneous signal and deeper penetration but increases susceptibility to irradiation-induced reshaping and reduces stability. LED excitation, operating at lower pulse energies and higher repetition rates, preserves AuNR stability while achieving comparable SNR through signal averaging. These findings highlight a clear balance between performance and stability and provide critical guidance for optimizing AuNR-based contrast agents for safe and effective clinical theranostic applications.