In an effort of developing clinical LANTCET (laser-activated nano-thermolysis as cell elimination technology) we
achieved selective destruction of individual tumor cells through laser generation of vapor microbubbles around clusters
of light absorbing gold nanorods (GNR) selectively formed in target tumor cells. Among all gold nanoparticles,
nanorods offer the highest optical absorption in the near-infrared. We applied covalent conjugates of gold nanorods with
targeting vectors such as monoclonal antibodies CD33 (specific for Acute Myeloid Leukemia), while GNR conjugates
with polyethylene-glycol (PEG) were used as nonspecific targeting control. GNR clusters were formed inside the tumor
cells at 37 °C due to endocytosis of large concentration of nanorods accumulated on the surface of tumor cells targeted at
4 °C. Formation of GNR clusters significantly reduces the threshold of tumor cell damage making LANTCET safe for
normal cells. Appearance of GNR clusters was verified directly with optical resonance scattering microscopy.
LANTCET was performed in vitro with living cells of (1) model myeloid K562 cells (CD33 positive), (2) primary
human bone marrow CD33-positive blast cells from patients diagnosed with acute myeloid leukemia. Laser-induced
microbubbles were generated and detected with a photothermal microscope equipped with a tunable Ti-Sa pulsed laser.
GNT cluster formation caused a 100-fold decrease in the threshold optical fluence for laser microbubble generation in
tumor cells compared with that in normal cells under the same targeting and irradiation conditions. Combining imaging
based on resonance optical scattering with photothermal imaging of microbubbles, we developed a method for detection,
image-guided treatment and monitoring of LANTCET. Pilot experiments were performed in flow mode bringing
LANTCET closer to reality of clinical procedure of purging tumor cells from bone marrow grafts.
Here we describe the application of single star-shaped gold nanoparticles (nanostars) for localized surface plasmon resonant (LSPR) sensing. The gold nanostars were fabricated by a modified seed-mediated, surfactant-directed nanoparticle synthesis which is known to produce gold nanorods in high yield. Due to the sample heterogeneity, single nanostars were studied by dark-field microspectroscopy. The single particle spectra demonstrate that the plasmon resonances of single gold nanostars are extremely sensitive to the local dielectric environment, yielding sensitivities as high as 1.41 eV photon energy shift per refractive index unit. To test their properties as molecular sensors, single nanostar spectra were monitored upon exposure to alkane thiols (mercaptohexadecanoic acid) and a proteins (bovine serum albumin) known to bind gold surfaces. The observed shifts are consistent with the effects of these molecular layers on the surface plasmon resonances in continuous gold films. The results suggest that LSPR sensing with single nanoparticles is analogous to the well developed field surface plasmon resonance (SPR) sensors, and will push the limits of sensitivity.
A contrast agent for optoacoustic imaging and laser therapy of early tumors is being developed based on gold
nanocolloids strongly absorbing visible and near-infrared light. The optoacoustic signals obtained from gold nanospheres
and gold nanorods solutions are studied. In the case of 100 nm nanospheres as an example, a sharp increase in the total
area under the curve of the optoacoustic signal is observed when the laser fluence is increased beyond a threshold value
of about 0.1 J/cm<sup>2</sup>. The change in the optoacoustic signal profile is attributed to the formation of water vapor bubbles
around heated nanoparticles, as evidenced via thermoacoustic microscopy experiments. It has been determined that,
surprisingly, gold nanoparticles fail to generate detectable nanobubbles upon irradiation at the laser fluence of ~2
mJ/cm2, which heats the nanoparticles up to 374°C, the critical temperature of water. Only when the estimated
temperature of the particle reaches about 10,000°C, a marked increase of the optoacoustic pressure amplitude and a
changed profile of the optoacoustic signals indicate nanobubble formation. A nanoparticle based contrast agent is the
most effective if it can be activate by laser pulses with low fluence attainable in the depth of tissue. With this goal in
mind, we develop targeting protocols that form clusters of gold nanocolloid in the target cells in order to lower the
bubble formation threshold below the level of optical fluence allowed for safe laser illumination of skin. Experiments
and modeling suggest that formation of clusters of nanocolloids may improve the sensitivity of optoacoustic imaging in
the detection of early stage tumors.