Two-photon excited photoluminescence lifetime imaging studies on individual gelatin-coated gold nanorods

Abstract

• Intrinsic TPE photoluminescence of different-sized gelatin-coated gold nanorods. • Combined fluorescence spectroscopy and FLIM assays on individual nanorods. • Single gold nanorod TPE photoluminescence overlaps the transverse LSPR band. • Effect of laser excitation power and wavelength on the TPE photoluminescence. The intriguing intrinsic photoluminescence (PL) properties of gold nanorods (AuNRs) have been intensively studied over the last years, not only in the linear but also in the non-linear optics regime, boosting their applicability in various fields of nanobiotechnology. In the present work, we investigate the two-photon excited (TPE) intrinsic PL of different-aspect ratio (AR) synthesized AuNRs, coated with gelatin (g@AuNRs), by performing innovative fluorescence spectroscopy - fluorescence lifetime imaging microscopy (FLIM) combined studies on individual g@AuNRs. In the first step, we employ Finite-difference time-domain (FDTD) simulations to confirm the optical response of AuNRs before and after coating with gelatin. While TPE FLIM assays performed under 800 nm excitation expose some interesting aspect regarding the AR-dependent TPE PL emission generated by individual g@AuNRs, spectroscopic measurements reveal that the TPE PL has a lifetime of around 100 ps and overlaps the corresponding transverse plasmonic band. Finally, we evaluate the effect of laser excitation power and wavelength on the TPE PL, pointing towards the important correlation between these parameters and the TPE PL performance of g@AuNR, as possible contrast agents for label-free TPE fluorescence imaging applications.