Department of Industrial Chemistry "Toso Montanari", University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy.
Biomater Sci. 2019 Apr 23;7(5):1746-1775. doi: 10.1039/c8bm01444b.
Photoacoustic (PA) imaging is indeed one of the most promising bioimaging techniques for theranostics applications in humans, allowing for the visualization of blood vessels and melanomas with high spatial resolution. However, in order to overcome the endogenous contrast arising from interfering endogenous species such as haemoglobin and melanin, specific contrast agents need to be developed, allowing PAI to successfully identify targeted contrast in the range of wavelengths in which interference from the biomatrix is minimized. This has been first performed by small molecule dyes, which, however, suffer from some important limitations such as low hydrophilicity and short circulation times. For this reason, scientific research has recently directed its efforts towards the development of nanostructured contrast agents capable of providing efficient PA contrast at low concentrations with low toxicity and high biocompatibility. The principal nanostructures are based on (1) metal and semiconducting nanoparticles, amongst which variously shaped nano-gold plays the main role, (2) carbon nanomaterials, such as carbon nanotubes and graphene, and (3) conjugated polymer nanoparticles. In this review, the principal characteristics of this class of materials are reported and greater focus is directed towards in vivo studies. A detailed analysis is performed on various physical-chemical parameters that define the PA response of reported contrast agents, like absorption coefficients and photoacoustic efficiencies. By comparing the experimental data, this review provides a comprehensive tool for the evaluation of new nanostructured contrast agents for PA imaging.
光声（PA）成像是一种非常有前途的用于人类治疗诊断应用的生物成像技术，能够以高空间分辨率可视化血管和黑色素瘤。然而，为了克服由血红蛋白和黑色素等内源性物质引起的内源性对比，需要开发特定的对比剂，使 PAI 能够成功地识别生物基质干扰最小的波长范围内的靶向对比。这首先是通过小分子染料来实现的，然而，它们存在一些重要的局限性，如低亲水性和短循环时间。出于这个原因，科学研究最近致力于开发纳米结构的对比剂，这些对比剂能够以低浓度提供有效的 PA 对比，具有低毒性和高生物相容性。主要的纳米结构基于（1）金属和半导体纳米粒子，其中各种形状的纳米金起着主要作用，（2）碳纳米材料，如碳纳米管和石墨烯，以及（3）共轭聚合物纳米粒子。在这篇综述中，报道了这类材料的主要特性，并更侧重于体内研究。对定义报道的对比剂的 PA 响应的各种物理化学参数（如吸收系数和光声效率）进行了详细分析。通过比较实验数据，本综述为 PA 成像用新型纳米结构对比剂的评估提供了一个全面的工具。
