To date, single-walled carbon nanotubes (SWNTs) were fully investigated for photoacoustic imaging [30]. For example, for cell imaging, Avti et al. adopted photoacoustic microscopy to detect, map, and quantify the trace amount of SWNTs in different histological XL184 order tissue specimens. The results showed that noise-equivalent detection sensitivity was as low as about 7 pg [31]. For in vivo PA imaging, Wu et al. adopted RGD-conjugated SWNTs as a PA contrast agent, and strong PA signals could be observed from the tumor in the SWNT-RGD-injected group [32]. With

the aim of enhancing the sensitivity of the PA signal of SWNTs, Kim et al. developed one kind of gold nanoparticle-coated SWNT by depositing a thin layer of gold nanoparticles around JQEZ5 mouse the SWNTs for photoacoustic imaging in vivo and obtained enhanced NIR PA imaging contrast (approximately 102-fold) [33–35]. RG7420 However, to date, few reports are closely associated with the use of multiwalled carbon nanotubes (MWNTs) as a PA contrast agent. Therefore, it is very necessary to investigate the feasibility and effects of the use of MWNTs and gold nanorod-coated MWNTs as PA contrast agents. In addition, CNT-based in vivo applications have to consider their toxicity [36]. How to decrease

or eliminate their cytotoxicity has become a great challenge. How to develop one kind of safe and effective NIR absorption enhancer MWNT has become our concern. Gold nanorods (GNRs), because of their small size, strong light-enhanced absorption in the NIR, and plasmon resonance-enhanced properties, have become attractive noble nanomaterials for their potential in applications such as photothermal therapy [37], biosensing [38], PA imaging [39], and gene delivery [40] for cancer treatment. However, the toxicity derived from a large amount of the surfactant cetyltrimethylammonium bromide (CTAB) during GNR synthesis severely Janus kinase (JAK) limits their biomedical applications. Therefore,

removal of CTAB molecules on the surface of GNRs is an important step to avoid irreversible aggregation of GNRs and enhance their biocompatibility. In our previous work, we used a dendrimer to replace the CTAB on the surface of GNRs, markedly decreasing the toxicity of GNRs, and realized the targeted imaging and photothermal therapy [41]. We also used folic acid-conjugated silica-modified GNRs to realize X-ray/CT imaging-guided dual-mode radiation and photothermal therapy. Silica-modified GNRs can markedly enhance the biocompatibility of GNRs [42–44]. In recent years, molecular imaging has made great advancement. Especially, the system molecular imaging concept has emerged [45], which can exhibit the complexity, diversity, and in vivo biological behavior and the development and progress of disease in an organism qualitatively and quantitatively at a system level.