Single-photon and two-photon cellular imagings of gold nanorods and dyes

A method to obtain the expressions of gold nanorods (GNRs) and dye molecules simultaneously is proposed for the single-photon and two-photon cellular imagings by using laser scanning confocal microscopy. For our experiment, GNRs with an average aspect ratio of 2.14 were synthesized using electrochemical method, and the peak of absorption spectrum of GNRs is at 600 nm. The human breast cancer cell lines (MDA-MB-435) were studied by incubating them with GNRs for 20 hours and then staining their nuclei with dye molecules-Prodium Iodide (PI). For the single-photon imaging, different CW lasers (458, 488, 514, 561, and 633 nm) were used individually to irradiate the samples. By adjusting the ranges of two bandpass filters for the detection, the scattered light from the GNRs due to surface plasmon resonance (SPR) and the fluorescence from PI can be induced simultaneously but be detected separately without crosstalk. Furthermore, the two cellular images can be merged together to become a composited cellular image. The TEM image shows that several clusters of GNRs internalized by the vesicles are distributed sparsely inside the cytoplasm, due to the endocytosis of the cells. The aggregation of GNRs causes SPR band broadened. Therefore strong scattered light from GNRs can almost be induced by different-wavelength lasers irradiating. However, the expression of PI can only be detected by the exciting lasers with a wavelength shorter than 600 nm. For the two-photon imaging of these cells internalizing GNRs, an ultrafast Ti:Sapphire IR-laser (800 nm) was used for irradiating the sample, and two bandpass filters were also adjusted to distinguish the photoluminescence of GNRs from the fluorescence of PI.