Highly Sensitive MoS2-Indocyanine Green Hybrid for Photoacoustic Imaging of Orthotopic Brain Glioma at Deep Site

Abstract

Photoacoustic technology in combination with molecular imaging is a highly effective method for accurately diagnosing brain glioma. For glioma detection at a deeper site, contrast agents with higher photoacoustic imaging sensitivity are needed. Herein, we report a MoS₂-ICG hybrid with indocyanine green (ICG) conjugated to the surface of MoS₂ nanosheets. The hybrid significantly enhanced photoacoustic imaging sensitivity compared to MoS₂ nanosheets. This conjugation results in remarkably high optical absorbance across a broad near-infrared spectrum, redshifting of the ICG absorption peak and photothermal/photoacoustic conversion efficiency enhancement of ICG. A tumor mass of 3.5 mm beneath the mouse scalp was clearly visualized by using MoS₂-ICG as a contrast agent for the in vivo photoacoustic imaging of orthotopic glioma, which is nearly twofold deeper than the tumors imaged in our previous report using MoS₂ nanosheet. Thus, combined with its good stability and high biocompatibility, the MoS₂-ICG hybrid developed in this study has a great potential for high-efficiency tumor molecular imaging in translational medicine.

Keywords: MoS2–ICG hybrid; Molecular imaging; Orthotopic brain glioma; Photoacoustic imaging.

Scheme 1

Schematic of MoS₂–ICG hybrid synthesis and its application in photoacoustic (PA) imaging of orthotopic brain glioma

Fig. 1

a, b AFM images and c, d thickness profiles of MoS₂ (a, c) and MoS₂–ICG (b, d). e Absorbance spectra of MoS₂ and MoS₂–ICG at the same concentration of MoS₂. f Fluorescence spectra of free ICG and MoS₂–ICG at the same concentration of ICG

Fig. 2

a Photoacoustic (PA) signal comparison of MoS₂ and MoS₂–ICG at the same concentration of MoS₂. Photoacoustic signals of b MoS₂–ICG at different concentrations and c MoS₂–ICG illuminated with 5000 laser pulses

Fig. 3

a Attenuation rate of 675- and 800-nm pulsed laser after penetrating the mouse skull. b Photoacoustic cross-sectional B-scan images of MoS₂–ICG covered with mouse skull under 675- and 800-nm laser excitation. Yellow dashed line delineates the outline of the skull. Red circle indicates the MoS₂–ICG sample. c Photoacoustic MAP images of mouse back post-subcutaneous injection of MoS₂–ICG under 675- and 800-nm laser excitation. The enclosed area by the yellow dashed line indicates the injected region. d Photoacoustic signal intensity plot corresponding to the two red dashed lines in c. e SNR of photoacoustic images under 675- and 800-nm laser excitation in c

Fig. 4

a Confocal fluorescence images of U87 glioma cells incubated with free ICG and MoS₂–ICG for 1, 3, and 8 h. Blue shows fluorescence of DAPI and red shows fluorescence of ICG. b Viability of U87 glioma cells incubated with different concentrations of MoS₂–ICG for 24 h. c Hemolysis percentage of RBCs after treatment with different concentrations of MoS₂–ICG for 3 h. (+) and (−) each indicates distilled water and PBS as positive and negative controls. The inset photograph shows the direct observation of hemolysis

Fig. 5

a B-scan ultrasound (US), photoacoustic (PA), and their merged images of the brain tumor region before and at 1, 3, and 5 h after intravenous injection of MoS₂–ICG. The ultrasound images were used to delineate the scalp and skull of the mouse. The photoacoustic signals in the red circles show the accumulation and distribution of MoS₂–ICG within the brain glioma. b Quantification results of photoacoustic signals in the tumor region at different time points before and after MoS₂–ICG injection

Fig. 6

a Representative H&E-stained images of the major organs including the heart, liver, spleen, lung, and kidney collected from control group mice and mice treated with MoS₂–ICG. b, c Blood analysis of MoS₂–ICG-treated group mice. WBC number of white blood cells; RBC number of red blood cells; MPV mean platelet volume; MCH mean corpuscular hemoglobin; HGB concentration of hemoglobin; HCT hematocrit; MCV mean corpuscular volume; MCHC mean corpuscular hemoglobin concentration; PLT platelets