Photoacoustic imaging and photothermal therapy in the second near-infrared window

Abstract

This review summarizes the recent progress of PA imaging and PTT agents in the second NIR window.

Deep-Tissue Photothermal Therapy Using Laser Illumination at NIR-IIa Window

“…Compared to traditional therapeutic modalities, PTT displays excellent performance in tumor treatment owing to not only high specificity but also precise spatial and temporal selectivity [1]. The crucial factors that determine the PTT outcomes of solid tumors are mainly the absorption of photothermal transduction agents (PTAs) and the penetration depth of irradiation into tumor tissue [2][3][4]. Though great efforts have been devoted to increase the photothermal conversion efficiencies of PTAs, current PTT applications are still only suited for superficial tumors because of the limited penetration depth of light illumination [4][5][6].…”

“…The crucial factors that determine the PTT outcomes of solid tumors are mainly the absorption of photothermal transduction agents (PTAs) and the penetration depth of irradiation into tumor tissue [2][3][4]. Though great efforts have been devoted to increase the photothermal conversion efficiencies of PTAs, current PTT applications are still only suited for superficial tumors because of the limited penetration depth of light illumination [4][5][6]. To promote the application of PTT in the clinic, especially PTT for the treatment of deep-seated tumor, the penetration depth of the irradiation laser is expected to be improved.…”

Indocyanine Green–Coated Gold Nanoclusters for Photoacoustic Imaging and Photothermal Therapy

“…In particular, near infrared light (NIR, 650-1350 nm) is a highly attractive radiation source, primarily due to its relatively deep tissue penetration-up to several centimeters-compared to lower-wavelength light. [10,11] NIR photomedicine has been broadly applied in cancer treatment and imaging through numerous modalities, [8] including photodynamic therapy, or PDT (light excites a photoactive agent to a triplet excited state, which then directly or indirectly generates free radicals and/or reactive oxygen species); photothermal therapy, or PTT (absorbed energy is emitted as vibrational energy, i.e., heat); fluorescence imaging (energy is emitted radiatively as a photon); and photoacoustic imaging, or PA (energy is emitted as heat, which generates a detectable acoustic wave). PA imaging has become increasingly popular due to its deep signal penetration (ࣘ5-6 cm), high resolution (ࣙ5 µm), and decreasing instrument costs.…”

Prototypic Heptamethine Cyanine Incorporating Nanomaterials for Cancer Phototheragnostic

“…Furthermore, the practical use of nanomaterials incorporating prototypic NIR heptamethine cyanines for cancer phototheragnostics is strongly circumscribed to superficial cancers (e.g., melanoma, breast cancer) due to the limits imposed by the penetration depth of the NIR radiation. In this context, phototheragnostics in the second‐NIR window (1000–1350 nm) can achieve a higher penetration depth (due to reduced light scattering) and higher maximal permissible exposure (due to the lower energy of longer wavelength photons) . Among the different heptamethine cyanines, only FD‐1080 has optical properties that enable its efficient use in the second‐NIR window.…”

“…In this context, phototheragnostics in the second-NIR window (1000-1350 nm) can achieve a higher penetration depth (due to reduced light scattering) and higher maximal permissible exposure (due to the lower energy of longer wavelength photons). [73] Among the different heptamethine cyanines, only FD-1080 has optical properties that enable its efficient use in the second-NIR window. To surpass this bottleneck, endoscopes coupled with fiber-type NIR lasers (e.g., 808 nm) are promising devices that may enable the use of nanomaterials incorporating prototypic NIR heptamethine cyanines for the imaging and PTT/PDT of nonsuperficial tumors.…”