Despite many benefits of nanotechnology, some studies indicate that certain nanoparticle (NPs) may cause adverse effects because of their small size and unique properties. The aim of the present study was to elucidate the period effects of intraperitonealy administration of different gold nanoparticle sizes on rat heart tissue in vivo using fluorescence spectroscopy. The experimental rats were divided into control and six groups (G1A, G1B, G2A, G2B, G3A and G3B; G1: 20 nm; G2: 10 nm; G3: 50 nm; A: infusion of GNPs for 3 days; B: infusion of GNPs for 7 days). To investigate the period effects of gold nanoparticles (GNPs) 10, 20 and 50 nm on the heart tissue of rats, 50 µl dose of GNPs (of concentration 0.1% Au) were intraperitonealy injected into rats for periods of  3 and 7 days to identify the toxicity and tissue distribution of GNPs in vivo using fluorescence measurements. The high electron densities of GNPs as well as the homogeneity of the particles shape and size make them highly conspicuous under the transmission electron microscope (TEM). The peak fluorescence intensity increased for G1B compared with G1A, increased for G2B compared with G2A and sharply decreased for G3A and G3B compared with the control. The peaks of G1A, G1B, G2A, G2B, G3A and G3B shifted towards the UV-Visible wavelength compared with the control. The peak fluorescence intensity for G1A was higher than G2A, G3A and G3B while G2A was higher than G3A. The peak fluorescence intensity for G2B was higher than G1B and G3B while G1B was higher than G3B. GNPs of sizes 10 and 20 nm have spherical shape while GNPs of size 50 nm have hexagonal shape. Fluorescence intensity of GNPs was size, shape and infusion period dependent. The decrease in peak fluorescence intensity induced in large 50 nm GNPs may be attributed to occurrence of quenching, decrease number and surface area of GNPs in addition to high clearance of GNPs via urine and bile. Moreover, decreasing size may lead to an exponential increase in surface area relative to volume, thus making the GNPs surface more reactive on itself (aggregation) and to its surrounding environment (biological components). Size, shape, surface area, number and clearance of GNPs play a key role in toxicity, and alterations of accumulation of GNPs in the heart tissue which may be mediated by dynamic protein binding and exchange. A better understanding of these mechanisms will improve drug delivery.

Key words: Gold nanoparticles, sizes, administration period, heart tissue, fluorescence spectroscopy.