Label-free imaging of gold nanoparticles uptake by cancer cells and tissues using multimodal nonlinear optical microscopy

Session

LSA.1 - Label-free life science imaging

Authors

Dr. Chun-Chin Wang (2), Dr. Priyanka Dey (2), Dr. Alexandra Vaideanu (1), Dr. Tanveer A. Tabish (2), Mr. Ryan Mellor (1), Dr. Jessica C. Mansfield (2), Professor Andreas G. Schätzlein (1), Professor Ijeoma F. Uchegbu (1), Professor Nicholas Stone (2), Professor Julian Moger (2)

Affiliations

1. UCL
2. University of Exeter

Keywords

stimulated Raman scattering, Label-free, gold nanoparticles, two-photon, cancer, microscopy

Abstract text

　Gold nanoparticles (AuNPs) have shown great potential as biocompatible imaging probes which can be used as effective surface-enhanced Raman spectroscopy (SERS) substrates in various biomedical applications. Major applications include such fields as biosensing, bioimaging, surface-enhanced spectroscopies, and photothermal therapy for cancer treatment. Probing AuNPs in living systems is essential to reveal the interaction between AuNPs and biological tissues. Compared to conventional microscopy, nonlinear processes offer many advantages: the near-IR excitation extends the depth of penetration into tissues with minimal photodamage and the nonlinear signal dependence provides intrinsic 3D optical sectioning. Moreover, utilizing techniques such as transient absorption (TA) and stimulated Raman scattering (SRS) it is possible to derive label-free biochemical contrast of AuNPs and cellular structures. Visualising AuNPs without the use of extrinsic labels is vital since any chemical perturbation of the nanoparticles will modify their physical properties and hence uptake. In this study, we apply second harmonic generation (SHG), two-photon excited fluorescence (TPEF), transient absorption (TA), and stimulated Raman scattering (SRS) microscopy to perform label-free chemically specific imaging of AuNPs in cancer cells and tissues.

　Multimodal imaging was carried by using ultrafast lasers and OPO to provide the pump and probe beams. Both femtosecond laser beams where chirped to picosecond pulses and spatially overlapped in the Spectral Focusing Timing and Recombination Unit (SF-TRU), which allowed us to rapidly select which Raman vibration was probed, and acquire other nonlinear optical signals. The AuNPs-dosed samples (human breast cancer cell line and murine breast tumour tissues) were mounted between two coverslips. The laser power at the sample was attenuated to below 10 mW in total.

Figure 1. In situ selective imaging of intrinsic molecules and gold nanoparticles (AuNPs) in cancer cells and tissues. (a) In vivo chemically specific mapping of lipid and protein molecules in cancer cells (breast cancer cell line MCF7) using stimulated Raman scattering (SRS) microscopy. (b) In vivo imaging of AuNPs uptake by cancer cells using transient absorption (TA) microscopy. (c) Ex vivo label-free multimodal mapping of the lipids, AuNPs, FAD and NADH, and collagen fibrils distribution in murine tumour microenvironment.

　In summary, we have demonstrated the in situ mapping of AuNPs uptake in cancer cells and cancerous tissues using multimodal nonlinear optical microscopy in a label free manner. We also showed that the combination of SHG, TPEF, TA, and SRS microscopy is an excellent imaging platform to study AuNPs and intrinsic biomolecules with submicron resolution, high detection sensitivity, and fast imaging speed. This capability offers a new tool for designing more efficient functionalised AuNPs and determining whether they are within vasculatures surrounding the tumour, pericellular, or cellular spaces.  

Acknowledgements
This research was supported by EPSRC Programme Grants "RaNT" (EP/R020965/1) and "CONTRAST facility" (EP/S009957/1).