Regulating interparticle proximity in plasmonic nanosphere aggregates to enhance photoacoustic response and photothermal stability.

Designing plasmonic nanoparticles for biomedical photoacoustic (PA) imaging involves tailoring material properties at the nanometer scale. A key in developing plasmonic PA contrast nanoagents is to engineer their enhanced optical responses in the near-infrared wavelength range, as well as heat transfer properties and photostability. This study introduces anisotropic plasmonic nanosphere aggregates with close interparticle proximity as photostable and efficient contrast agent for PA imaging. Silver (Ag), among plasmonic metals, is particularly attractive due to its strongest optical response and highest heat conductivity. Our results demonstrate that close interparticle proximity in silver nanoaggregates (AgNAs), spatially confined within a polymer shell layer, leads to blackbody-like optical absorption, resulting in robust PA signals through efficient pulsed heat generation and transfer. Additionally, our AgNAs exhibit a high photodamage threshold highlighting their potential to outperform conventional plasmonic contrast agents for high-contrast PA imaging over multiple imaging sessions. Furthermore, we demonstrate the capability of the AgNAs for molecular PA cancer imaging in vivo by incorporating a tumor-targeting peptide moiety.

Preventing Metastasis Using Gold Nanorod-Assisted Plasmonic Photothermal Therapy in Xenograft Mice.

Despite significant research regarding metastasis, there has been limited success in preventing it. However, gold nanoparticle (AuNP) technology has shown the potential to inhibit metastasis. Our earlier studies of gold nanorod-assisted plasmonic photothermal therapy (AuNRs-PPTT), where gold nanorods (AuNRs) were irradiated with near-infrared (NIR) light to induce heat, were utilized in slowing cancer cell migration in vitro. Herein, we have expanded the in vitro studies of the AuNRs-PPTT to xenograft mice to inhibit metastasis of mammary gland tumors. The study duration was 32 days from 4T1 cancer cell injections in four treatment groups: control (PBS), NIR Only, AuNRs, and AuNRs + NIR. Multiple AuNRs-PPTT treatment sessions with intratumoral AuNRs injections were conducted every 7 days on average on the mice. Photoacoustic spectroscopy has been utilized to study the distribution and aggregation of AuNRs within the tumors and the drainage of particles to the sentinel right subiliac lymph node. The photoacoustic results revealed that the AuNRs' shapes are still stable regardless of their heterogeneous distributions inside the mammalian tumor and lymph nodes. Bioluminescence imaging was used to monitor metastasis using luciferin labeling techniques and has shown that AuNRs-PPTT inhibited metastasis completely within the first 21 days. Moreover, proteomics was run to determine the most pivotal inhibitory pathways: NETosis, cell growth, cell proliferation, inflammation, and extracellular matrix (ECM) degradation. These five mechanisms are interdependent within related networks, which synergistically explains the molecular mechanism of metastasis inhibition by AuNRs-PPTT. The current in vivo data ensures the viability of PPTT applications in inhibiting metastasis in humans.

pH-responsive ratiometric photoacoustic imaging of polyaniline nanoparticle-coated needle for targeted cancer biopsy.

Cancer microenvironment exhibits lower pH compared to healthy tissues, a characteristic which can be exploited using a pH-responsive needle to increase the accuracy of cancer biopsy. A needle, coated with pH-responsive polyaniline (PANI) nanoparticles (PANI-needle), is developed for the minimally invasive and quantitative pH analysis of tissue based on ratiometric photoacoustic (PA) imaging. The ratiometric PA signal from the PANI-needle within the 850-700 nm wavelength range shows a linear response as pH changes from 7.5 to 6.5. Owing to the high surface area of nanostructured PANI, the PA signal of PANI-needle exhibits a fast and reversible response of less than a few seconds. In a tissue-mimicking hydrogel phantom composed of two regions with different pH, PA ratios of PANI-needle successfully differentiate the local pH. The PANI-needle coupled with ultrasound-guided PA imaging is a promising technology for detection of malignant tissue through quantitative pH analysis during needle biopsy.

Characterizing a photoacoustic and fluorescence imaging platform for preclinical murine longitudinal studies.

Significance: To effectively study preclinical animal models, medical imaging technology must be developed with a high enough resolution and sensitivity to perform anatomical, functional, and molecular assessments. Photoacoustic (PA) tomography provides high resolution and specificity, and fluorescence (FL) molecular tomography provides high sensitivity; the combination of these imaging modes will enable a wide range of research applications to be studied in small animals. Aim: We introduce and characterize a dual-modality PA and FL imaging platform using in vivo and phantom experiments. Approach: The imaging platform's detection limits were characterized through phantom studies that determined the PA spatial resolution, PA sensitivity, optical spatial resolution, and FL sensitivity. Results: The system characterization yielded a PA spatial resolution of 173 ± 17 µ m in the transverse plane and 640 ± 120 µ m in the longitudinal axis, a PA sensitivity detection limit not less than that of a sample with absorption coefficient µ a = 0.258 cm - 1 , an optical spatial resolution of 70 µ m in the vertical axis and 112 µ m in the horizontal axis, and a FL sensitivity detection limit not < 0.9 µ M concentration of IR-800. The scanned animals displayed in three-dimensional renders showed high-resolution anatomical detail of organs. Conclusions: The combined PA and FL imaging system has been characterized and has demonstrated its ability to image mice in vivo, proving its suitability for biomedical imaging research applications.

Gold nanoparticles conjugated with DNA aptamer for photoacoustic detection of human matrix metalloproteinase-9.

Matrix metalloproteinase-9 (MMP-9) plays major roles in extracellular matrix (ECM) remodeling and membrane protein cleavage, suggesting a high correlation with cancer cell invasion and tumor metastasis. Here, we present a contrast agent based on a DNA aptamer that can selectively target human MMP-9 in the tumor microenvironment (TME) with high affinity and sensitivity. Surface modification of plasmonic gold nanospheres with the MMP-9 aptamer and its complementary sequences allows the nanospheres to aggregate in the presence of human MMP-9 through DNA displacement and hybridization. Aggregation of gold nanospheres enhances the optical absorption in the first near-infrared window (NIR-I) due to the plasmon coupling effect, thereby allowing us to detect the aggregated gold nanospheres within the TME via ultrasound-guided photoacoustic (US/PA) imaging. Selective and sensitive detection of human MMP-9 via US/PA imaging is demonstrated in solution of nanosensors with the pre-treatment of human MMP-9, in vitro in cell culture, and in vivo in a xenograft murine model of human breast cancer.