Application of Nanomaterials in Photoacoustic Imaging
Photoacoustic imaging technology is a new imaging technology developed in recent years. It is a hybrid mode of bio/medical imaging methods based on the photoacoustic effect. In photoacoustic imaging, pulsed laser light is usually required to illuminate the imaging site. The absorbed light energy is converted into heat energy, causing thermal expansion of nearby tissue, creating broadband (megahertz) ultrasound. This ultrasonic wave can be detected by an ultrasonic transducer. Compared with traditional fluorescence imaging, magnetic resonance imaging, ultrasound imaging, and positron emission tomography (PET) imaging technologies have the advantages of real-time performance, high spatial resolution, and no use of harmful radiation. Photoacoustic imaging can be used for imaging of endogenous contrast agents (such as hemoglobin, oxyhemoglobin, melanin, and fluorescent proteins); however, some diseases (such as breast cancer, glioma, etc.) do not produce endogenous contrast agents, so they cannot diagnosis of these diseases. In order to be able to detect these diseases, exogenous contrast agents are increasingly favored by researchers and medical practitioners. In recent years, with the development of nanotechnology, more and more nanomaterials can be used as exogenous contrast agents in photoacoustic imaging.
Figure 1: Photoacoustic Imaging Setup and Sample Configuration
Carbon-Based Nanomaterials
Due to their unique optical properties and ease of preparation, carbon-based nanomaterials have attracted extensive attention in the biological field. Carbon nanomaterials have been used as optical reagents in the field of biological imaging such as Raman detection, fluorescence imaging, and in vivo photoacoustic imaging. Carbon nanomaterials are mainly divided into two categories: graphene and single-walled carbon nanotubes, both of which can be used as contrast agents for photoacoustic imaging.
Gold Nanomaterials
Gold nanomaterials, such as gold vesicles, gold nanocages, gold nanoparticles, etc., have attracted everyone's attention in diagnostic medicine. Gold nanomaterials rely on tunable scattering and absorption in the near-infrared range (700–900 nm), and thus, are good contrast agents for photoacoustic imaging. At the same time, gold-based nanomaterials can absorb light energy and efficiently convert light energy into heat energy through the Landau damping effect. These materials have attracted great interest in the field of photothermal therapy (PTT). Based on these unique properties of gold nanomaterials, they can be further used to control the release of hydrophilic drugs under near-infrared excitation. The gold nanomaterials can be monitored by photoacoustic imaging when the drug is released at the targeted location in the targeted direction. The possibility of loading therapeutic drugs with gold nanomaterials offers great benefits for their therapeutic applications.
Conjugated Polymer Nanomaterials
In recent years, polymer nanomaterials are mainly used as nanocarriers for drug delivery research. These polymer nanomaterials have good biocompatibility and can effectively deliver drugs to tumor sites through targeting. However, recent studies have found that conjugated polymer nanomaterials also possess unique optical properties (such as near-infrared absorption), which allow them to be used as contrast agents for photoacoustic imaging.
Photoacoustic Enhanced Composite Nanomaterials
Photoacoustic-enhanced composite nanomaterials are composite materials that combine different types of nanomaterials through different methods to achieve the purpose of enhancing photoacoustic signals and reducing the amount of contrast agents. For example, if we first adsorb near-infrared dyes on single-walled carbon nanotubes by adsorption technology, then modify the PEG on the surface of carbon nanotubes to enhance their biocompatibility, and then perform further research on the target polypeptide (RGD) in PEG. modification, we will find that the final composite nanomaterial can effectively enhance the photoacoustic signal.
In conclusion, the application of nanoparticles in photoacoustic imaging has greatly promoted the development of photoacoustic imaging technology. The key to photoacoustic imaging technology is a photoacoustic imaging contrast agent. At present, the research on photoacoustic imaging contrast agents mainly focuses on two aspects. On the one hand, researchers seek to improve existing photoacoustic imaging materials through chemical modification or combination with other functional materials to form new multifunctional functions. On the other hand, they are also constantly developing new and efficient photoacoustic imaging contrast agents, which can achieve higher photoacoustic imaging efficiency while overcoming the shortcomings of traditional contrast agents.
References
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