Search

There have been remarkable advances in imaging drug nanocarriers, but there are few real-time imaging strategies to determine if the cargo has been released from the carrier. This is important because the pharmacokinetics and pharmacodynamics of the carrier can often be dramatically decoupled from that of the cargo. Thus, new tools are clearly needed to image the timing and quantity of drug release from nanocarriers. Here, we describe a simple strategy for photoacoustic monitoring of drug release based on the redox chemistry of methylene blue, which offers predictable redox chemistry: It can transition from the oxidized state with a bright blue color and robust photoacoustic signal to the reduced state that the transparent with no photoacoustic signal. We locked this drug-dye conjugate into a reduced state inside of a nanoparticle with no photoacoustic signal. As the drug is released from the carrier, the dye is oxidized for quantification with photoacoustic imaging. We first prepared paclitaxel-methylene blue conjugate (PTX-MB) with strong absorbance at 640 nm and photoacoustic intensity proportional to its concentration. This cargo was co-encapsulated in a poly(lactic-co-glycolic acid) nanoparticle with a dithiothreitol reducing agent. The IC(50) of PTX-MB-loaded NPs (PTX-MB @ PLGA NPs) was 78 μg mL(−1). We then used the redox reaction of PTX-MB to monitor its release from poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs). In vitro drug-release in phosphate buffer saline with 20% v/v normal mice serum showed a 670-fold increase in photoacoustic signal. The particles showed an initial burst release (25%) during the first 24 hours. After 24 hours, a sustained release was observed through 120 hours leading to cumulative release of 40.6% of PTX-MB. In vivo drug release study in mice for a duration of 12 hours showed a photoacoustic signal enhancement of up to 649% after 10 hours. We then used this system to treat an orthotopic model of colon cancer via luciferase-positive CT26 cells. Our data showed that tumor burden decreased by 44.7% ± 4.8% when treated with the PTX-MB @ PLGA NPs versus the empty PLGA carrier. This work presents a direct strategy to simultaneously monitor drug release biodistribution.

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 H(2)O(2). 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 E(0)(Ag) = 0.80 V to E(0)(AgI) = − 0.15 V resulting in a 1000-fold increase in H(2)O(2) 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.

This study details a polydopamine-coated gold nanorod synthesis for photoacoustic imaging. The most important finding is that the photoacoustic intensity and spectrum shifted upon coating with polydopamine. We used this photoacoustic signal change to identify samples in a phantom. Additionally, the polydopamine-coated gold nanorods exhibited an increase in stability over bare nanorods under photoacoustic irradiation. Future studies will study drug release and will monitor from the polydopamine coating and monitor the fate of the gold nanorods over time in vivo.

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 × 10(4) cells in in vitro tests. This multimodal photoacoustic/MRI approach combines the excellent temporal resolution of photoacoustics with the anatomic resolution of MRI.

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.

Graphical abstract, Highlights • We characterized a commercially available LED-based photoacoustic imaging system. • The LED beam profile, spatial/temporal resolution, and penetration depth were measured. • Indocyanine green and methylene blue were utilized as exogenous contrast agent, and their detection limits were calculated. • The capability for in vivo experiments was demonstrated using human mesenchymal stem cells labeled with a near-infrared dye (DiR) in living mice., Photoacoustic imaging (PAI) is a non-invasive, high-resolution hybrid imaging modality that combines optical excitation and ultrasound detection. PAI can image endogenous chromophores (melanin, hemoglobin, etc.) and exogenous contrast agents in different medical applications. However, most current equipment uses sophisticated and complicated OPO lasers with tuning and stability features inconsistent with broad clinical deployment. As the number of applications of PAI in medicine increases, there is an urgent need to make the imaging equipment more compact, portable, and affordable. Here, portable light emitting diode – based photoacoustic imaging (PLED-PAI) was introduced and characterized in terms of system specifications, light source characterizations, photoacoustic spatial/temporal resolution, and penetration. The system uses two LED arrays attached to the sides of a conventional ultrasound transducer. The LED pulse repetition rate is tunable between 1 K Hz, 2 K Hz, 3 K Hz, and 4 K Hz. The axial resolution was 0.268 mm, and the lateral resolution was between 0.55 and 0.59 mm. The system could detect optical absorber (pencil lead) at a depth of 3.2 cm and the detection limits of indocyanine green (ICG) and methylene blue (MB) were 9 μM and 0.78 mM. In vivo imaging of labeled human mesenchymal stem cells was achieved to confirm compatibility with small animal imaging. The characterization we report here may have value to other groups evaluating commercially available photoacoustic imaging equipment.

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.

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 Fe(3)O(4) 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 Fe(3)O(4) to the silica nanoparticles increased their colloidal stability, T(2)-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.

LED-based photoacoustic imaging has practical value in that it is affordable and rugged; however, this technology has largely been confined to anatomic imaging with limited applications into functional or molecular imaging. Here, we report molecular imaging reactive oxygen and nitrogen species (RONS) with a near-infrared (NIR) absorbing small molecule (CyBA) and LED-based photoacoustic imaging equipment. CyBA produces increasing photoacoustic signal in response to peroxynitrite (ONOO−) and hydrogen peroxide (H2O2) with photoacoustic signal increases of 3.54 and 4.23-fold at 50 µM of RONS at 700 nm, respectively. CyBA is insensitive to OCl−, ˙NO, NO2−, NO3−, tBuOOH, O2−, C4H9O˙, HNO, and ˙OH, but can detect ONOO− in whole blood and plasma. CyBA was then used to detect endogenous RONS in macrophage RAW 246.7 cells as well as a rodent model; these results were confirmed with fluorescence microscopy. Importantly, CyB suffers photobleaching under a Nd:YAG laser but the signal decrease is

We characterized a commercially available LED-based photoacoustic system (Prexion Inc. Japan) that offered a tunable LED pulse repetition rate (1K Hz, 2K Hz, 3K Hz, and 4K Hz) and found that the temporal resolution of the scanner is dependent on the choice of repetition rate. The LED system have lower power, and averaging is used to minimize the noise. The power from the LED arrays at 690 nm and 850 nm with 70 ns pulse width was measured to be 9.85 mW/cm2 and 31.55 mW/cm2. Beam profiling showed that the average intensity at the center of the transducer was ~ 18% higher than the power on the edges of the transducer. The system had axial and lateral resolution of 268 μm and 590 μm, respectively. This system has frame rates of 30 Hz and 0.15 Hz. Pencil lead inside chicken breast could be detected up to 3.2 cm deep with a frame rate of 15 Hz. Indocyanine green (ICG), methylene blue (MB), and DiR were used as exogenous contrasts to measure the limit of detection using PLED-PAI. The limit of detection values for ICG, MB, and DiR are 9 μM, 0.75 mM, and 68 μM, respectively. For in vivo experiments, DiR (positive control), 400,000 stem cells labeled with DiR, and bare stem cells (negative control) were subcutaneously injected on the spinal cord of male mice. Results shows difference between labeled and unlabeled cells in photoacoustic intensity using PLED-PAI. This experiment shows the capability of this LED-based system to perform molecular imaging at a price point and device footprint nearly a log order smaller than systems based on an optical parametric oscillator laser.

We report a novel yet simple 3D-printed tubing holder for characterizing photoacoustic contrast agents. This device supports up to 12 plastic tubing with sample-to-sample spacing as low as 0.3 mm and provides a consistent distance (± 0.12 mm) between the tubing and the transducer, which is critical for validating photoacoustic contrast agents. An immersion media containing both 40% India ink and lipid that mimics tissue scattered the incident irradiation. We further studied different types of tubing and distance between tubing and transducer. Statistical analysis shows that tubing with a larger outside diameter has more inherent signal, and the signal decayed following a linear relationship (R2=0.997) with respect to distance from the laser focal point. We finally provide a computer-assisted drafting code for the community to customize and print their own phantoms.

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.

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.

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.

The personal ultraviolet (UV) dosimeter is a useful measurement tool to prevent UV induced dermal damages; however, conventional digital dosimeters are either bulky or require external power sources. Here, a wearable, colorimetric UV film dosimeter that provides color transition, from purple to transparent, is reported to indicate the UV dose. The film dosimeter is made of a purple photodegradable dye ((2Z,6Z)-2,6-bis(2-(2,6-diphenyl-4H-thiopyran-4-ylidene)ethylidene)cyclohexanone or DTEC) blended in low density polyethylene film. The DTEC film discolored 3.3 times more under the exposure of UV light (302 nm) than visible light (543 nm), and a UV bandpass filter is developed to increase this selectivity to UV light. The DTEC film completely discolors to transparency in 2 h under an AM 1.5 solar simulator, suggesting the potential as an indicator for individuals with types I-VI skin to predict interventions to avoid sunburn. Finally, the DTEC film is integrated with the UV bandpass filter on a wristband to function as a wearable dosimeter for low cost and convenient monitoring of sunlight exposure.