Iodide-doped precious metal nanoparticles: measuring oxidative stress in vivo via photoacoustic imaging.

Accumulation of reactive oxygen and nitrogen species (RONS) can induce cell damage and even cell death. RONS are short-lived species, which makes direct, precise, and real-time measurement difficult. Biologically-relevant RONS levels are in the nM-µM scale; hence, there is a need for highly sensitive RONS probes. We previously used hybrid gold-core silver-shell nanoparticles with mM sensitivity to H2O2. These particles reported the presence of RONS via spectral shifts which could easily be quantified via photoacoustic imaging. Here, we used halide doping to tune the electrochemical properties of these materials to better match the oxidation potential of RONS. This work describes the synthesis, characterization, and application of these AgI-coated gold nanorods (AgI/AuNR). The I : Ag molar ratio, pH, and initial Ag shell thickness were optimized for good RONS detection limits. Halide doping lowers the reduction potential of Ag from to resulting in a 1000-fold increase in H2O2 and 100 000-fold increase in ONOO- sensitivity. The AgI/AuNR system also etches 45-times faster than undoped Ag/AuNR. The AgI/AuNR easily reported the endogenously produced RONS in established cells lines as well as murine models.

Photoacoustic Imaging Quantifies Drug Release from Nanocarriers via Redox Chemistry of Dye-Labeled Cargo.

We report a new approach to monitor drug release from nanocarriers via a paclitaxel-methylene blue conjugate (PTX-MB) with redox activity. This construct is in a photoacoustically silent reduced state inside poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PTX-MB@PLGA NPs). During release, PTX-MB is spontaneously oxidized to produce a concentration-dependent photoacoustic signal. An in vitro drug-release study showed an initial burst release (25 %) between 0-24 h and a sustained release between 24-120 h with a cumulative release of 40.6 % and a 670-fold increase in photoacoustic signal. An in vivo murine drug release showed a photoacoustic signal enhancement of up to 649 % after 10 hours. PTX-MB@PLGA NPs showed an IC50 of 78 µg mL-1 and 44.7±4.8 % decrease of tumor burden in an orthotopic model of colon cancer via luciferase-positive CT26 cells.

Increasing the Efficacy of Stem Cell Therapy via Triple-Function Inorganic Nanoparticles.

Stem cell therapy in heart disease is challenged by mis-injection, poor survival, and low cell retention. Here, we describe a biocompatible multifunctional silica-iron oxide nanoparticle to help solve these issues. The nanoparticles were made via an in situ growth of Fe3O4 nanoparticles on both the external surfaces and pore walls of mesocellular foam silica nanoparticles. In contrast to previous work, this approach builds a magnetic moiety inside the pores of a porous silica structure. These materials serve three roles: drug delivery, magnetic manipulation, and imaging. The addition of Fe3O4 to the silica nanoparticles increased their colloidal stability, T2-based magnetic resonance imaging contrast, and superparamagnetism. We then used the hybrid materials as a sustained release vehicle of insulin-like growth factor-a pro-survival agent that can increase cell viability. In vivo rodent studies show that labeling stem cells with this nanoparticle increased the efficacy of stem cell therapy in a ligation/reperfusion model. The nanoparticle-labeled cells increase the mean left ventricular ejection fraction by 11 and 21% and the global longitudinal strain by 24 and 34% on days 30 and 60, respectively. In summary, this multifunctional nanomedicine improves stem cell survival via the sustained release of pro-survival agents.

Gadolinium Doping Enhances the Photoacoustic Signal of Synthetic Melanin Nanoparticles: A Dual Modality Contrast Agent for Stem Cell Imaging.

In this paper, we show that gadolinium-loaded synthetic melanin nanoparticles (Gd(III)-SMNPs) exhibit up to a 40-fold enhanced photoacoustic signal intensity relative to synthetic melanin alone and higher than other metal-chelated SMNPs. This property makes these materials useful as dual labeling agents because Gd(III)-SMNPs also behave as magnetic resonance imaging (MRI) contrast agents. As a proof-of-concept, we used these nanoparticles to label human mesenchymal stem cells. Cellular uptake was confirmed with bright-field optical and transmission electron microscopy. The Gd(III)-SMNP-labeled stem cells continued to express the stem cell surface markers CD73, CD90, and CD105 and proliferate. The labeled stem cells were subsequently injected intramyocardially in mice, and the tissue was observed by photoacoustic and MR imaging. We found that the photoacoustic signal increased as the cell number increased (R 2 = 0.96), indicating that such an approach could be employed to discriminate between stem cell populations with a limit of detection of 2.3 × 104 cells in in vitro tests. This multimodal photoacoustic/MRI approach combines the excellent temporal resolution of photoacoustics with the anatomic resolution of MRI.

Synthesis of Ultrasmall Synthetic Melanin Nanoparticles by UV Irradiation in Acidic and Neutral Conditions.

Synthetic melanin nanoparticles have value in metal chelation, photoprotection, and biocompatibility. Applications of these materials have been reported in optics, biomedicine, and electronics. However, precise size control has remained relatively difficult-especially for materials below 1000 nm. In this paper we describe the synthesis of ultrasmall synthetic nanoparticles with size of 9.4-31.4 nm in weakly acidic and neutral conditions via UV-irradiation. Size control of these particles was possible by varying the pH from 6.4-10.0. We then used UV-vis, FTIR, and nuclear magnetic resonance to investigate the mechanism of UV-induced polymerization. The data show that reactive oxygen species from UV irradiation oxidizes intermediates of the reaction and accelerates the formation of these synthetic melanin structures.

Cellular toxicity of silicon carbide nanomaterials as a function of morphology.

Silicon carbide has been shown to be biocompatible and is used as a coating material for implanted medical devices to prevent biofilms. Silicon carbide nanomaterials are also promising in cell tracking due to their stable and strong luminescence, but more comprehensive studies of this material on the nanoscale are needed. Here, we studied the toxicity of silicon carbide nanomaterials on human mesenchymal stem cells in terms of metabolism, viability, adhesion, proliferation, migration, oxidative stress, and differentiation ability. We compared two different shapes and found that silicon carbide nanowires are toxic to human mesenchymal stem cells but not to cancer cell lines at the concentration of 0.1 mg/mL. Control silicon carbide nanoparticles were biocompatible to human mesenchymal stem cells at 0.1 mg/mL. We studied the potential mechanistic effect of silicon carbide nanowires on human mesenchymal stem cells' phenotype, cytokine secretion, and gene expression. These findings suggest that the toxic effect of silicon carbide nanomaterials to human mesenchymal stem cells are dependent on morphology.

Development of a Trimodal Contrast Agent for Acoustic and Magnetic Particle Imaging of Stem Cells.

Stem cell therapy has the potential to improve tissue remodeling and repair. For cardiac stem cell therapy, methods to improve the injection and tracking of stem cells may help to increase patient outcomes. Here we describe a multimodal approach that combines ultrasound imaging, photoacoustic imaging, and magnetic particle imaging (MPI). Ultrasound imaging offers real-time guidance, photoacoustic imaging offers enhanced contrast, and MPI offers high-contrast, deep-tissue imaging. This work was facilitated by a poly(lactic-co-glycolic acid) (PLGA)-based iron oxide nanobubble labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide (DiR) as a trimodal contrast agent. The PLGA coating facilitated the ultrasound signal, the DiR increased the photoacoustic signal, and the iron oxide facilitated the MPI signal. We confirmed that cell metabolism, proliferation, differentiation, and migration were not adversely affected by cell treatment with nanobubbles. The nanobubble-labeled cells were injected intramyocardially into live mice for real-time imaging. Ultrasound imaging showed a 3.8-fold increase in the imaging intensity of labeled cells postinjection compared to the baseline; photoacoustic imaging showed a 10.2-fold increase in the cardiac tissue signal postinjection. The MPI intensity of the nanobubble-treated human mesenchymal stem cells injected into the hearts of mice was approximately 20-fold greater than the negative control.

Photoacoustic Imaging of Human Mesenchymal Stem Cells Labeled with Prussian Blue-Poly(l-lysine) Nanocomplexes.

Acoustic imaging is affordable and accessible without ionizing radiation. Photoacoustic imaging increases the contrast of traditional ultrasound and can offer good spatial resolution when used at high frequencies with excellent temporal resolution. Prussian blue nanoparticles (PBNPs) are an emerging photoacoustic contrast agent with strong optical absorption in the near-infrared region. In this study, we developed a simple and efficient method to label human mesenchymal stem cells (hMSCs) with PBNPs and imaged them with photoacoustic imaging. First, PBNPs were synthesized by the reaction of FeCl3 with K4[Fe(CN)6] in the presence of citric acid and complexed with the cationic transfection agent poly-l-lysine (PLL). The PLL-coated PBNPs (PB-PLL nanocomplexes) have a maximum absorption peak at 715 nm and could efficiently label hMSCs. Cellular uptake of these nanocomplexes was studied using bright field, fluorescence, and transmission electron microscopy. The labeled stem cells were successfully differentiated into two downstream lineages of adipocytes and osteocytes, and they showed positive expression for surface markers of CD73, CD90, and CD105. No changes in viability or proliferation of the labeled cells were observed, and the secretome cytokine analysis indicated that the expression levels of 12 different proteins were not dysregulated by PBNP labeling. The optical properties of PBNPs were preserved postlabeling, suitable for the sensitive and quantitative detection of implanted cells. Labeled hMSCs exhibited strong photoacoustic contrast in vitro and in vivo when imaged at 730 nm, and the detection limit was 200 cells/µL in vivo. The photoacoustic signal increased as a function of cell concentration, indicating that the number of labeled cells can be quantified during and after cell transplantations. In hybrid ultrasound/photoacoustic imaging, this approach offers real-time and image-guided cellular injection even through an intact skull for brain intraparenchymal injections. Our labeling and imaging technique allowed the detection and monitoring of 5 × 104 mesenchymal stem cells in living mice over a period of 14 days.

The development and characterization of a novel yet simple 3D printed tool to facilitate phantom imaging of photoacoustic contrast agents.

We report a new approach to preparing phantoms using 3D printing. This device supports plastic tubing containing the contrast agent and is immersed in a solution with absorption or scattering properties that mimic tissue. Up to 12 tubing samples could be placed in the device with sample-to-sample spacing as low as 0.3 mm and at a constant distance from the transducer (±0.16 mm), which is critical in validating photoacoustic contrast agents. We also studied different types of tubing and found that tubing with a larger outside diameter has more inherent signal. Both 40% India Ink and lipids in the immersion media modulated the signal. Finally, we created a depth phantom and found that signal decayed following a linear relationship (R2 = 0.997) with respect to distance from the focal point. We include computer-assisted drafting code the community can use to print this phantom or customized versions of this phantom.

What is new in nanoparticle-based photoacoustic imaging?

Photoacoustic imaging combines the high temporal and spatial resolution of ultrasound with the good contrast and spectral tuning of optical imaging. Contrast agents are used in photoacoustic imaging to further increase the contrast and specificity of imaging or to image a specific molecular process, e.g., cell-surface proteins or small molecule biomarkers. Nanoparticle-based contrast agents are important tools in photoacoustic imaging because they offer intense and stable signal and can be targeted to specific molecular processes. In this review, we describe some of the most interesting and recent advances in nanoparticle-based photoacoustic imaging including inorganic nanoparticles, organic/polymeric nanoparticles, nanoparticle coatings, multimodality imaging, as well as emerging topics in the field. WIREs Nanomed Nanobiotechnol 2017, 9:e1404. doi: 10.1002/wnan.1404 For further resources related to this article, please visit the WIREs website.