Abstract
Gold nanoparticles (AuNPs) have been attracted much attention over the past decades because they have a wild variety of applications in biological sensing. Depending on their size, shape, composition, structure, and local environment, AuNPs can show different characteristics especially the surface plasmon resonance (SPR) property. SPR can observe the color changed that reflect the underlying coherent oscillations of conduction band electrons of particle under the irradiation with the light of fitting wavelengths. These electrons (plasmons) bring the different intensities of absorption and scattering of light, and from the basis to design many biological sensing applications of AuNPs. In this study, Au nanorods was synthesized using a simple and low cost method and then were used for biosensing applications because the morphology of Au nanarods have the wide SPR absorption range which can be adjust by aspect ratio. We have successfully developed one-step growth method to improve the efficiency of Au nanorods by comparison with traditional two-step growth method. The average diameter of gold nanorods was 50 nm in length and 15 nm in wide, which was confirmed by TEM images, and the SPR absorption position was located 800 nm. Without the seed solution synthesis step, we can more efficiently and greenly to prepare gold nanorods solution. In addition, several parameters were selected to optimize the growth of Au nanorods. We found that silver nitrate (AgNO3) of 100~120 M could fabricate good morphology for gold nanorods growth solution. The Au seed concentration of growth solution is related to the overgrowth process and the short axis of Au nanorods increased with the increase in gold precursor to seed ratio from 208 to 13333. In contrast to the two-step growth method which the gold nanorods appeared just after the addition of Au seed solution, one-step growth method needed to wait 15 minutes for nuclei formation. In addition, high concentration of ascorbic acid can inhibit blue-shift of Au nanorods. After the optimization, Au nanorods were surface modified with several organics for Tau protein detection. Results of FT-IR, XPS and Zeta potential identified that 11-Mercaptoundecanoic acid, cystamine, and dithiobis[succinimidylpropionate] ( DSP) can be used as the modifiers for Tau protein detection. Later, we used linker to modify anti-Tau antibody for Tau protein sensing and the influence of end-to-end and side-by-side aggression of Au nanorods on how the sensitivity of Tau protein detection was evaluated.