Autofluoresence of Intralipid Phantoms at Lipid Concentration for Embedding Gold Nanoparticles

V. N. Du Le 1* , Zhaojun Nie 2 , Joseph E. Hayward 1 , Thomas J. Farrell 1 and Qiyin Fang 2 1 Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada 2 School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada *ledvn@mcmaster.ca Introduction Intralipid with lipid concentration of 1% to 10% v/v has been widely used to simulate background scattering which enables mapping of gold nanoparticle inclusions in spectroscopy [1], ultrasound imaging [2], and photoacoustic tomography [3]. These studies have shown that gold nanoparticles embedded in Intralipid are potential tools for cancer delineation. While optical properties and fluorescence of gold nanoparticles (GNS) were well established [1,3,4], the fluorescence characteristics of Intralipid at the lipid concentration 1% to 10% v/v has not been a subject of extensive study and remain controversy. In the present study, we construct Intralipid phantoms at concentrations that mimic tissue scattering, and measure their autoflouresence in broadband spectral region 350-650 nm using laser excitation at 355 nm with power of 2.8 µ J. Methods Two Intralipid phantoms with lipid concentrations of 1.5% and 2% v/v were created for fluorescence measurements. These phantoms were prepared by diluting the concentrated Intralipid 20% v/v solution in de-ionized water. The selected lipid concentrations produce best simulations for scattering of stromal layer in mucosal tissue which was reported previously [5]. Fluorescence measurements of Intralipid phantoms were performed using an excitation pulsed laser at 355 nm, a single optical fiber with core diameter of 600 µ m, and a calibrated spectrometer to record fluorescence at a broadband wavelength range 350-650 nm. Results The µ s values of Intralipid 10% v/v was extrapolated from the transmission measurement of low lipid concentration using linear regression method and was compared to previous data. As shown in Fig. 1, an agreement (within 10% error) in µ s values between current extrapolated data and van Staveren et al.’s data was obtained [6]. Therefore, we apply similar anisotropy expression to back-calculate reduced scattering coefficients ( µ s ′) values for Intralipid phantoms. We demonstrated that phantoms with lipid concentration of 1.5% and 2% were best simulations for scattering of stromal layer in the mucosa (Fig. 2). The µ s ′ value of lipid 1.5% and 2% at wavelength 355 nm is approximately 28.4 cm -1 and 37.