Utility of biodegradable plasmonic nanoclusters in photoacoustic imaging

Abstract

Plasmonic metal nanoparticles are used in photoacoustic imaging as contrast agents because of their resonant optical absorption properties in the visible and near-IR regions. However, the nanoparticles could accumulate and result in long-term toxicity in vivo, because they are generally not biodegradable. Recently, biodegradable plasmonic gold nanoclusters, consisting of sub-5 nm primary gold nanoparticles and biodegradable polymer stabilizer, were introduced. In this Letter, we demonstrate the feasibility of biodegradable nanoclusters as a photoacoustic contrast agent. We performed photoacoustic and ultrasound imaging of a tissue-mimicking phantom with inclusions containing nanoclusters at various concentrations. The results indicate that the biodegradable gold nanoclusters can be used as effective contrast agents in photoacoustic imaging.

Fig. 1

(Color online) Diagram of degradation of gold nanoclusters at different pH levels.

Fig. 2

(Color online) (a) Normalized absorbance spectra and (b) TEM image of biodegradable nanoclusters.

Fig. 3

(Color online) Block diagram of combined ultrasound and photoacoustic (US/PA) imaging system and the gelatin-based tissue-mimicking phantom with biodegradable nanoclusters inclusion.

Fig 4

(Color online) (a) US, PA, and combined US/PA images of the phantom with inclusion containing nanoclusters. The concentration of the nanoclusters was 550 μg/mL. (b) Photoacoustic signal amplitude with respect to fluence rate and (c) dependence of PA signal on nanocluster concentration at 5 and 10:5 mJ/cm². The solid lines represent the linear regression fit of the data.