Strong Photoacoustic Signal Enhancement by Coating Gold Nanoparticles with Melanin for Biomedical Imaging

Abstract

Photoacoustics is a powerful biomedical imaging and detection technique, because it is a noninvasive, nonionizing, and low‐cost method facilitating deep tissue penetration. However, suitable contrast agents need to be developed to increase the contrast for in vivo imaging. Gold nanoparticles are often discussed as potential sonophores due to their large absorption cross‐section and their tunable plasmon resonance. However, disadvantages such as toxicity and low photoacoustic efficiency in the tissue transparency window prevail, preventing their clinical application. As a result, there remains a strong need to develop colloidal photoacoustic contrast agents which absorb in the tissue transparency window, exhibit high photoacoustic signal, and are biocompatible. Here, a facile synthetic approach is presented to produce melanin shells around various gold nanoparticle geometries, from spheres to stars and rods. These hybrid particles show excellent dispersability, better biocompatibility, and augmented photoacoustic responses over the pure melanin or pristine gold particles, with a rod‐shape geometry leading to the highest performance. These experimental results are corroborated using numerical calculations and explain the improved photoacoustic performance with a thermal confinement effect. The applicability of melanin coated gold nanorods as gastrointestinal imaging probes in mouse intestine is showcased.

Enhanced endosomal escape by photothermal activation for improved small interfering RNA delivery and antitumor effect

“…9,[13][14][15][16][17] Herein, melanin, a naturally distributed and biocompatible pigment, was used as an efficient photothermal sensitizer. [18][19][20] Melanin could generate heat under NIR light due to its strong absorption in both far-infrared and NIR band. 21,22 Inspired by its excellent photothermal conversion efficiency, we first attempt to involve melanin in the siRNA delivery system.…”

Role of gold nanoparticles in advanced biomedical applications

“…The excellent optical properties of GNPs combined with easy surface modication capability make GNPs suitable for in vivo and in vitro bio-imaging applications. 6,46,67,212,213 Recently, the biomedical imaging applications of GNPs have drawn tremendous interest owing to their desirable size and tunable optical properties. The use of GNPs in biomedical imaging techniques such as X-ray computed tomography, photo-acoustic imaging, dark eld microscopic imaging, magnetic resonance imaging, and uorescence imaging is very popular.…”

A literature review on multimodality molecular imaging nanoprobes for cancer detection

“…They have shown this probe could assess the cell nucleus and provide significant information in living cells which employed (surface-enhanced Raman scattering) SERS for the research of drug delivery and cancer therapy. In addition, the applicability of melanin coated gold nanorods as a photoacoustic contrast agent was evaluated by Repenko et al [98]. They have indicated photoacoustic contrast produced by nanoprobe in mouse intestine greatly improved over the pure melanin or pristine gold particles.…”