Black Mesoporous Silicon as a Contrast Agent for LED-Based 3D Photoacoustic Tomography

Assembly of fluorophore J-aggregates with nanospacer onto mesoporous nanoparticles for enhanced photoacoustic imaging

Many fluorophores, such as indocyanine green (ICG), have poor photostability and low photothermal efficiency hindering their wide application in photoacoustic (PA) tomography. In the present study, a supramolecular assembly approach was used to develop the hybrid nanoparticles (Hy NPs) of ICG and porous silicon (PSi) as a novel contrast agent for PA tomography. ICG was assembled on the PSi NPs to form J-aggregates within 30 min. The Hy NPs presented a red-shifted absorption, improved photothermal stability, and enhanced PA performance. Furthermore, 1-dodecene (DOC) was assembled into the NPs as a 'nanospacer', which enhanced non-radiative decay for increased thermal release. Compared to the Hy NPs, adding DOC into the Hy NPs (DOC-Hy) increased the PA signal by 83%. Finally, the DOC-Hy was detectable in PA tomography at 1.5 cm depth in tissue phantom even though its concentration was as low as 6.25 µg/mL, indicating the potential for deep tissue PA imaging.

A Spiky Silver-Iron Oxide Nanoparticle for Highly Efficient Targeted Photothermal Therapy and Multimodal Imaging of Thrombosis

Thrombosis and its complications are responsible for 30% of annual deaths. Limitations of methods for diagnosing and treating thrombosis highlight the need for improvements. Agents that provide simultaneous diagnostic and therapeutic activities (theranostics) are paramount for an accurate diagnosis and rapid treatment. In this study, silver-iron oxide nanoparticles (AgIONPs) are developed for highly efficient targeted photothermal therapy and imaging of thrombosis. Small iron oxide nanoparticles are employed as seeding agents for the generation of a new class of spiky silver nanoparticles with strong absorbance in the near-infrared range. The AgIONPs are biofunctionalized with binding ligands for targeting thrombi. Photoacoustic and fluorescence imaging demonstrate the highly specific binding of AgIONPs to the thrombus when functionalized with a single chain antibody targeting activated platelets. Photothermal thrombolysis in vivo shows an increase in the temperature of thrombi and a full restoration of blood flow for targeted group but not in the non-targeted group. Thrombolysis from targeted groups is significantly improved (p < 0.0001) in comparison to the standard thrombolytic used in the clinic. Assays show no apparent side effects of AgIONPs. Altogether, this work suggests that AgIONPs are potential theranostic agents for thrombosis.

Black porous silicon as a photothermal agent and immunoadjuvant for efficient antitumor immunotherapy

Photothermal therapy (PTT) in combination with other treatment modalities has shown great potential to activate immunotherapy against tumor metastasis. However, the nanoparticles (NPs) that generate PTT have served as the photothermal agent only. Moreover, researchers have widely utilized highly immunogenic tumor models to evaluate the immune response of these NPs thus giving over-optimistic results. In the present study black porous silicon (BPSi) NPs were developed to serve as both the photothermal agent and the adjuvant for PTT-based antitumor immunotherapy. We found that the poorly immunogenic tumor models such as B16 are more valid to evaluate NP-based immunotherapy than the widely used immunogenic models such as CT26. Based on the B16 cancer model, a cocktail regimen was developed that combined BPSi-based PTT with doxorubicin (DOX) and cytosine-phosphate-guanosine (CpG). BPSi-based PTT was an important trigger to activate the specific immunotherapy to inhibit tumor growth by featuring the selective upregulation of TNF-α. Either by adding a low dose DOX or by prolonging the laser heating time, a similar efficacy of immunotherapy was evoked to inhibit tumor growth. Moreover, BPSi acted as a co-adjuvant for CpG to significantly boost the immunotherapy. The present study demonstrates that the BPSi-based regimen is a potent and safe antitumor immunotherapy modality. Moreover, our study highlighted that tuning the laser heating parameters of PTT is an alternative to the toxic cytostatic to evoke immunotherapy, paving the way to optimize the PTT-based combination therapy for enhanced efficacy and decreased side effects. STATEMENT OF SIGNIFICANCE: Tumor metastasis causes directly or indirectly more than 90% of cancer deaths. Combination of photothermal therapy (PTT), chemotherapy and immunotherapy based on nanoparticles (NPs) has shown great potential to inhibit distant and metastatic tumors. However, these NPs typically act only as photothermal agents and many of them have been evaluated with immunogenic tumor models. The present study developed black porous silicon working as both the photothermal conversion agent and the immunoadjuvant to inhibit distant tumor. It was recognized that the poorly immunogenic tumor model B16 is more appropriate to evaluate immunotherapy than the widely used immunogenic model CT26. The coordination mechanism of the PTT-based combination therapy regimen was discovered in detail, paving the way to optimize cancer immunotherapy for enhanced efficacy and decreased side effects.

Experimental Evaluation of Radiation Response and Thermal Properties of NPs-Loaded Tissues-Mimicking Phantoms

Many efforts have recently concentrated on constructing and developing nanoparticles (NPs) as promising thermal agent for optical hyperthermia and photothermal therapy. However, thermal energy transfer in biological tissue is a complex process involving different mechanisms such as conduction, convection, radiation. Therefore, having information about thermal properties of tissue especially when NPs are embedded in is a necessity for predicting the heat transfer during hyperthermia. In this work, the thermal properties of solid phantom based on agar in the presence of three different nanoparticles (BPSi, tNAs, GNRs) and alone were measured and reported as a function of temperature (ranging from 22 to 62 °C). The thermal response of these NPs to an 808 nm laser beam with three different powers were studied in the water comparatively. Agar and tNAs have almost constant thermal properties in the considered range. Among the three NPs, gold has the highest conductivity and diffusivity. At 62 °C BPSi NPs have the similar amount of increase for the diffusivity. The thermal parameters reported in this paper can be useful for the mathematical modeling. Irradiation of the NPs-loaded water phantom displayed the highest radiosensitivity of gold among the three mentioned NPs. However, for the higher power of irradiation, BPSi and tNAs NPs showed the increased absorption of heat during shorter time and the increased temperature gradient slope for the initial 15 s after the irradiation started. The three NPs showed different thermal and irradiation response behavior; however, this comparison study notes the worth of having information about thermal parameters of NPs-loaded tissue for pre-clinical planning.

Recent developments of porous silicon nanovectors with various imaging modalities in the framework of theranostics

The number of in vitro, ex vivo, and in vivo studies on porous silicon (PSi) nanoparticles for biomedical applications has increased extensively over the last decade. The focus of the reports has been on the carrier properties of PSi concerning the therapeutic aspect due to several beneficial nanovector characteristics including high payload capacity, biocompatibility, and versatile surface chemistry. Recently, increasing attention has been paid to the diagnostic aspects of PSi, which is typically attributed to the biotraceability of the nanovector. Also, PSi has been studied as a contrast agent. When both these aspects, therapy and diagnosis, are integrated into one nanovector, we can discuss a real nanotheranostics approach. Herein, we review the recent progress developing PSi for various imaging modalities, specifically focusing on optical imaging, magnetic resonance imaging, and nuclear medicine imaging. Furthermore, we summarized the knowledge gaps that must be covered before applying PSi in clinical imaging, highlighting future research trends.

Study of Cryogenic Unmasked Etching of "Black Silicon" with Ar Gas Additives

The influence of Ar gas additives on ≪black silicon≫ formation is shown in this work. The way to achieve the conical shape of Si texture using low Ar dilution is demonstrated. Also, a possibility of silicon nanowire width reduction keeping a high density of array is shown. No damage to the Si structure caused by Ar plasma was detected. The introduction of Ar into the plasma also does not affect electrical properties. The lifetime value after cryogenic etching with 5 sccm Ar flow remains at the same level of 0.7 ms. The resulting black silicon has a low total reflectance of 1 ± 0.5% in the range of 450-1000 nm in the overall 100 mm Si wafer surface.

Comparison between Fluorescence Imaging and Elemental Analysis to Determine Biodistribution of Inorganic Nanoparticles with Strong Light Absorption

Black porous silicon nanoparticles (BPSi NPs) are known as highly efficient infrared light absorbers that are well-suitable for photothermal therapy (PTT) and photoacoustic imaging (PAI). PTT and PAI require a sufficient number of effectively light-absorbing NPs to be accumulated in tumor after intravenous administration. Herein, biodistribution of PEGylated BPSi NPs with different sizes (i.e., 140, 200, and 300 nm in diameter) is investigated after intravenous administration in mice. BPSi NPs were conjugated with fluorescent dyes Cy5.5 and Cy7.5 to track them in vitro and in vivo, respectively. Optical imaging with an in vivo imaging system (IVIS) was found to be an inadequate technique to assess the biodistribution of the dye-labeled BPSi NPs in vivo because the intrinsic strong absorbance of the BPSi NPs interfered fluorescence detection. This challenge was resolved via the use of inductively coupled plasma optical emission spectrometry to analyze ex vivo the silicon content in different tissues and tumors. The results indicated that most of the polyethylene glycol-coated BPSi NPs were found to accumulate in the liver and spleen after intravenous injection. The smallest 140 nm particles accumulated the most in tumors at an amount of 9.5 ± 3.4% of the injected dose (concentration of 0.18 ± 0.08 mg/mL), the amount known to produce sufficient heat for cancer PTT. Furthermore, the findings from the present study also suggest that techniques other than optical imaging should be considered to study the organ biodistribution of NPs with strong light absorbance properties.

Another decade of photoacoustic imaging

Photoacoustic imaging - a hybrid biomedical imaging modality finding its way to clinical practices. Although the photoacoustic phenomenon was known more than a century back, only in the last two decades it has been widely researched and used for biomedical imaging applications. In this review we focus on the development and progress of the technology in the last decade (2010-2020). From becoming more and more user friendly, cheaper in cost, portable in size, photoacoustic imaging promises a wide range of applications, if translated to clinic. The growth of photoacoustic community is steady, and with several new directions researchers are exploring, it is inevitable that photoacoustic imaging will one day establish itself as a regular imaging system in the clinical practices.

Engineering Plasmonic Nanoparticles for Enhanced Photoacoustic Imaging

Photoacoustic (PA) imaging is an emerging imaging modality whereby pulsed laser illumination generates pressure transients that are detectable using conventional ultrasound. Plasmonic nanoparticles such as gold nanorods and nanostars are often used as PA contrast agents. The thermoelastic expansion model best describes the PA response from plasmonic nanoparticles: Light absorption causes a small increase in temperature leading to thermoelastic expansion. The conversion of optical energy into pressure waves (po) is dependent on several features: (i) the absorption coefficient (μa), (ii) the thermal expansion coefficient (β), (iii) specific heat capacity (Cp) of the absorbing material, (iv) speed of sound in the medium (c), and (v) the illumination fluence (F). Controlling the geometry, composition, coatings, and solvents around plasmonic nanostructures can help tune these variables to generate the optimum PA signal. The thermoelastic expansion model is not limited to plasmonic structures and holds true for all absorbing molecules. Here, we focus on ways to engineer these variables to enhance the PA response from plasmonic nanoparticles.