Controlled Au–Polymer Nanostructures for Multiphoton Imaging, Prodrug Delivery, and Chemo–Photothermal Therapy Platforms

We have successfully introduced a proton-induced controlled reaction of HAuCl₄ and poly­(styrene-<i>alt</i>-maleic acid) (PSMA) sodium salt to prepare triangular and multicore Au@polymer nanoparticles (NPs). The interparticle interactions in the core gave rise to an absorption band at the near-infrared wavelength. The near-infrared optical properties of the resulting Au–polymer nanostructures are highly stable in a physiological environment, which offered strong photo-to-thermal conversion by a moderate continuous-wave 808 nm laser and exhibited multiphoton fluorescence for imaging using a 1230 nm light excitation (femtosecond laser). Exposure of the carboxylate groups at the polymer shell made the surface structure of the Au multicore @polymer NPs directly conjugate Pt­(II)-/Pt­(IV)-based drugs, which possessed the elimination of the immediate toxicity over the short time and resulted in an anticancer effect after 3 days. A synergistic effect of the chemo–photothermal therapy showed a moderate hyperthermia assistance (<1 W/cm²) and better anticancer performance over time compared with the individual treatments. We demonstrated that such PSMA-based methodology not only enables a broad range of chemical material synthesis in the kinetic control to form Au nano-octahedrons and nanotriangles using Br^–/I^– ions additives but also could be extended to form Au/Fe₃O₄@polymer nanocomposites via proton-assisted PSMA self-assembly

Images of a lacuna and canaliculi in the calvarial bone of a transgenic 2.3ColGFP mouse.

<p>THG (a) and 3PF of SR101 dye (b) were imaged with 1700 nm excitation while 2PF from GFP (c) was imaged with 850 nm excitation. A structural image cross-correlation analysis [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186846#pone.0186846.ref031" target="_blank">31</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186846#pone.0186846.ref032" target="_blank">32</a>] between 3PF, 2PF, and THG was performed (d).</p

LCN parameters for WT and HDAC4/5 DKO mice.

<p>Measurement of the number of osteocytes in a volume consisting of 100 × 100 × 10 μm³ (a), lacunar surface area (b) and lacunar volume (d) per osteocyte as well as the number of canaliculi per lacunar surface area (e) in WT and HDAC4/5 DKO mice. Data are represented as the mean ± standard deviation (error bar). A statistically significant difference was not found in the lacunar surface area and volume measurements. The lacunar surface area, lacunar volume and number of canaliculi were determined from 3D renderings generated with Imaris software where an example osteocyte in WT (c) and HDAC4/5 DKO (f) mice is shown.</p

A schematic of the laser microscope for three-photon imaging using 1550 nm and 1700 nm.

<p>Second and third harmonic generation (SHG and THG) as well as three photon excitation fluorescence (3PF) are collected while the laser is scanned with a polygonal and galvanometric mirror pair. HWP represents half-wave plates, PCF represents a polarization maintaining large mode area single mode photonic crystal fiber for generation of 1700 nm, while BiBO represents a bismuth borate crystal for frequency doubling of 1700 nm.</p

THG signal intensity from canaliculi oriented at a number of angles to the optical axis.

<p>From optical sections of epi-THG collected signal from a WT mouse <i>in vivo</i>, a summed image of 6 consecutive XY slices which are 2 μm apart in Z were colored in such a way that the top slice is white, second slice is red, third slice is yellow, fourth slice is green, fifth slice is blue and the bottom slice is purple (a). A summed image of 6 consecutive XZ slices of the area of the canaliculus outlined in a white box is shown in the inset of (a) demonstrating that the canaliculus is parallel to laser propagation which is along Z. The tilt angle between bright areas within a canaliculus was calculated and the corresponding average THG intensities were plotted (b).</p

THG power dependency plot.

<p>THG images of osteocytes obtained at 1550 nm (a) and 1700 nm (b) excitation <i>in vivo</i> as well as a logarithmic plot (c) of the THG intensity of an osteocyte with fundamental laser power for both 1550 nm and 1700 nm excitation. The data was fit with a line corresponding to a slope of 2.8 ± 0.2 for 1550 nm excitation and 2.9 ± 0.2 for 1700 nm excitation.</p

Forward-THG versus epi-THG from the LCN.

<p>Forward-THG (F-THG) (a) and epi-THG (epi-THG) (b) images of lacunae and canaliculi in thinned calvarial bone from a WT mouse taken with 1550 nm excitation and compared to an epi-THG image of the calvarial bone of WT mouse <i>in vivo</i> without bone thinning (c). The results are summarized in (d) showing that epi-collected THG is a combination of backwards-directed and backscattered forward-generated signals.</p

Imaging Endogenous Bilirubins with Two-Photon Fluorescence of Bilirubin Dimers

On the basis of an infrared femtosecond Cr:forsterite laser, we developed a semiquantitative method to analyze the microscopic distribution of bilirubins. Using 1230 nm femtosecond pulses, we selectively excited the two-photon red fluorescence of bilirubin dimers around 660 nm. Autofluorescences from other endogenous fluorophores were greatly suppressed. Using this distinct fluorescence measure, we found that poorly differentiated hepatocellular carcinoma (HCC) tissues on average showed 3.7 times lower concentration of bilirubins than the corresponding nontumor parts. The corresponding fluorescence lifetime measurements indicated that HCC tissues exhibited a longer lifetime (500 ps) than that of nontumor parts (300 ps). Similarly, oral cancer cell lines had longer lifetimes (>330 ps) than those of nontumor ones (250 ps). We anticipate the developed methods of bilirubin molecular imaging to be useful in diagnosing cancers or studying the dynamics of bilirubin metabolisms in live cells