Au nanostar nanoparticle as a bio-imaging agent and its detection and visualization in biosystems

Abstract

In the present work, we report the imaging of Au nanostars nanoparticles (AuNSt) and their multifunctional applications in biomedical research and theranostics applications. Their optical and spectroscopic properties are considered for the multimodal imaging purpose. The AuNSt are prepared by the seed-meditated method and characterized for use as an agent for bio-imaging. To demonstrate imaging with AuNSt, penetration and localization in different biological models such as cancer cell culture (A549 lung carcinoma cell), 3D tissue model (multicellular tumor spheroid on the base of human oral squamous carcinoma cell, SAS) and murine skin tissue are studied. AuNSt were visualized using fluorescence lifetime imaging (FLIM) at two-photon excitation with a pulse duration 140 fs, repetition rate 80 MHz and 780 nm wavelength femtosecond laser. Strong emission of AuNSt at two-photon excitation in the near infrared range and fluorescence lifetime less than 0.5 ns were observed. It allows using AuNSt as a fluorescent marker at two-photon fluorescence microscopy and lifetime imaging (FLIM). It was shown that AuNSt can be observed inside a thick sample (tissue and its model). This is the first demonstration using AuNSt as an imaging agent for FLIM at two-photon excitation in biosystems. Increased scattering of near-infrared light upon excitation of AuNSt surface plasmon oscillation was also observed and rendered using a possible contrast agent for optical coherence tomography (OCT). AuNSt detection in a biological system using FLIM is compared with OCT on the model of AuNSt penetrating into animal skin. The AuNSt application for multimodal imaging is discussed.

Multimodal bioimaging using nanodiamond and gold hybrid nanoparticles

“…For ND@Au the lifetime is estimated about 0.1 ns, comparable to the instrument response function (IRF). As such short lifetime was previously found characteristic for nanogold at two-photon excitation 43 , and Au emission is strong enough so we can suppose the observed lifetime of ND@Au is determined by Au shell. ND has two components of lifetime equal to 2.25 ns and 0.321 ns with close weights.…”

Multifunctional plasmonic gold nanostars for cancer diagnostic and therapeutic applications

“…AuNSts are clearly observable at two‐photon excitation due to high intensity of the fluorescence, which is described as a sequential process of absorption of photons resulting in the recombination of electrons and holes and the following emission [17]. For AuNSts, the fluorescence lifetime is very short [39]; significantly shorter than lifetimes of most cellular endogenous fluorophores [55]. This allows distinguishing AuNSt's signal from autofluorescence of the biological object and the visualization of its interaction with the bio‐objects via fluorescence lifetime imaging.…”

“…Fluorescence lifetime of AuNP depends on their size, shape and the excitation power. TP‐FLIM of AuNPs [33–39] was demonstrated for Au nanospheres [33–35], Au nanotriangles [35], Au nanorods [36, 37] and Au nanoshells [37]. Fluorescence lifetime of gold nanorods is found to be in the order of 100 ps and the corresponding lifetime was easily distinguished from the endogenous fluorophores [36].…”

“…TP‐FLIM of AuNSts was only mentioned as a potential opportunity for bioimaging [40, 41]. Recently, our group has reported on using gold nanostar for bioimaging using FLIM [39]. Gold nanostars were visualized using two‐photon excitation of femtosecond laser of 780 nm wavelength.…”

Probing the Intracellular Bio-Nano Interface in Different Cell Lines with Gold Nanostars

“…The plasmon resonances of these anisotropic nanostructures can be tuned in the visible and near-infrared wavelength range by modifying their size and spike morphology [ 1 , 2 ]. Their optical properties are specifically suited for imaging [ 3 , 4 ], biosensing [ 5 , 6 , 7 ], and photothermal applications [ 8 , 9 , 10 ]. The unique geometry of plasmonic nanostars enables versatile field enhancement [ 11 , 12 ], that allows for efficient metal-enhanced fluorescence [ 13 ] and a high electromagnetic contribution to surface-enhanced Raman scattering (SERS) [ 1 , 14 ].…”