Investigation on cellular uptake of gold nanoparticles by multiphoton laser scanning microscopy

Multiphoton absorption induced luminescence (MAIL), as a nonlinear optical feature of noble metallic nanoparticles has shown great advantages in the in situ detection of gold nanoparticles (AuNPs). Selection of excitation wavelengths to yield high efficient MAIL signal from different sized AuNPs is of great significance, but a systematical study of this aspect is still lacking so far. In this chapter, the optimum excitation wavelengths for visualization and discrimination of AuNPs are determined through a systematic investigation into the emission properties of AuNPs in a wide size range (10-80 nm) under multiphoton excitation with various excitation wavelengths between 710 nm and 920 nm. The emission intensity from individual particles showed excitation wavelength dependence and the superior signal to noise (S/N) ratios are obtained at excitation between 780 nm and 840 nm in wavelength. By using two generations of multiphoton microscopy (LSM-510 and LSM-710), the MAIL is confirmed a two photon absorption induced signal, along with second harmonic generation (SHG), being responsible for the visualization of AuNPs. Pure MAIL emission spectra are observed unambiguously at 900 nm excitation excluding the interference from SHG.