Abstract:
The sensitivity of the detection techniques used in biological analysis primarily depends on
the fluorescence labelling agent. A new generation of fluorophores such as Europium
doped hydroxyapatite nanoparticle (Eu-HAPnps) has the ability to emit near infrared
radiations which are of low absorptivity by tissue chromophores and especially suitable
for biological system imaging.
Eu-HAP luminescent nanoparticles were prepared by co-precipitation method with the
aim of seeking a compromise proposal for achieving high luminescence and nano-scale
particles. Hence, the effect of reaction temperature and Eu3+ doping content on
luminescence property as well as phase composition, crystal size and crystallinity of EuHAPnps were investigated. The 2% Eu doping content and reaction temperature of 1210C
were preferred for preparing Eu-HAPnps with strong luminescence.
We synthesised two sets of well stable Eu-HAPnps in the presence of different
concentration of a low molecular weight capping agent, Polyacrylic acid (PAA) and
different concentration of sodium heparin to investigate the best stabiliser and its
productive concentration. Results of this characterization study showed that 0.3 PAA was
an effective stabiliser concentration.
Furthermore, we also investigated on the modifications made by pluronic F 127 and
targeting conjugation of folic acid on Eu-HAPnps. Thereafter, a tumour specific targeting
ligand, folic acid is conjugated onto PF127-PAA-Eu-HAPnps to produce a multifunctional
hydroxyapatite nanoparticle. According to characterization observations of synthesised
nanoparticles, PF127 and its derivatives were grafted onto PAA-Eu-HAPnps by the
chemical conjugation to yield more stable and smaller HAP clusters which could be stored
in lyophilized form and rapidly re-suspended in double distilled water. Moreover, the
surface coating polymer on PAA-Eu-HAPnps was also the determining factor for the
efficiency of cellular uptake. FA-PF127-PAA-Eu-HAP having the FA moiety showed a better
cellular internalisation in the folic receptor overexpressing cells. The biocompatibility of
Eu-HAPnps was studied by hemolysis test and cytotoxicity experiment. Results showed
that Eu-HAPnps has no hemolysis and cytotoxicity to L02 human normal liver cells.
Therefore, the targeting experiment in vitro demonstrates that folic acid targeting EuHAPnps shows much higher cell uptake than non-folic acid conjugated Eu-HAPnps.
