Nanoparticles 100 nm in diameter containing indocyanine green (ICG) have been developed as a contrast agent for photoacoustic (PA) imaging based on (photonic explorers for biomedical use by biologically localized embedding PEBBLE) technology using organically modified silicate (ormosil) as a matrix. ICG is an FDA-approved dye with strong optical absorption in the near-infrared (NIR) region, where light can penetrate deepest into biological tissue. A photoacoustic imaging system was used to study image contrast as a function of PEBBLE concentration in phantom objects. ICG-embedded ormosil PEBBLEs showed improved stability in aqueous solution compared with free ICG dye. The particles were conjugated with HER-2 antibody for breast cancer and prostate cancer cell targeting. Initial in vitro characterization shows high contrast and high efficiency for binding to prostate cancer cells. ICG can also be used as a photosensitizer (generating toxic oxygen by illumination) for photodynamic therapy. We have measured the photosensitization capability of ICG-embedded ormosil nanoparticles. This feature can be utilized to combine detection and therapeutic functions in a single agent.
We describe here a nontoxic two-photon photodynamic nanoparticle platform and its cellular application. We demonstrate that the dye's potential toxicity can be circumvented by its permanent encapsulation into a biocompatible nanoparticle polymer matrix; this was examined by dye leaching experiments and confirmed by cell uptake experiments. Infrared two-photon nanoplatform phototoxicity was demonstrated for rat C6 glioma cells, while the controls showed no dark toxicity for these living cells.
Expressions for radiation-induced forces are presented for the case of a Rayleigh particle near the focus of a Gaussian laser beam at near-resonant conditions. Classical electromagnetic theory was used to obtain the dependence of the scattering and gradient forces on the incident laser frequency, the beam convergence angle, and the spatial position of the particle with respect to the focus. Approximative numerical analysis performed for particles with a single resonant absorption peak demonstrates the occurrence of up to 50-fold enhanced trapping forces at near-resonant frequencies. The use of this technique of gradient force enhancement may provide optical tweezers with enhanced trapping strengths and a degree of specificity.
Shifts in the nonlinear rotational frequency of magnetic microspheres, driven by an external magnetic field, offer a dynamic approach for the detection of single bacterial cells. We demonstrate this capability by optically measuring such frequency shifts when an Escherichia coli attaches to the surface of a 2.0μm magnetic microsphere, thereby affecting the drag of the system. From this change in drag, the nonlinear rotation rate was reduced, on average, by a factor of 3.8. Sequential bacterial cell attachments were also monitored.
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