Analytical Sciences

Thermal-induced Immuno-nephelometry Using Gold Nanoparticles Conjugated with a Thermoresponsive Polymer for the Detection of Avidin

Nobuo UEHARA,* Yoshikuni NUMANAMI,* Toru OBA,* Noriyuki ONISHI,** and Xiaomao XIE**

*Department of Applied Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, Japan
**JNC Petrochemical Corporation, Goi Research Center, 5-1 Goi-kaigan, Ichihara, Chiba 290-8551, Japan

Thermoresponsive immunonephelometry was achieved with biotinylated poly(acrylate) and thermoresponsive gold nanocomposites composed of 13-nm gold nanoparticles and thermoresponsive polymers containing triethylenetetramine and biotin groups. The avidin–biotin interaction was used to model an immunoreaction in order to demonstrate thermoresponsive immunonephelometry. In the absence of avidin, positively charged gold nanocomposites electrostatically interacted with biotinylated poly(acrylate) to form binary complexes, in which the charges canceled each other out. The charge cancelation resulted in the binary complexes precipitating when the solution was heated above the phase-transition temperature. However, adding avidin formed ternary sandwich complexes through the avidin–biotin interaction. The ternary complexes remained sufficiently soluble above the phase-transition temperature because of the spatial isolation of the positive and negative charges. The transmittance of the solution containing the thermoresponsive gold nanocomposites and biotinylated poly(acrylate) at 37°C increased as the avidin concentration increased. A sigmoidal profile was observed from 10^−6.5 to 10^−5.5 mol/L. The concentration of avidin spiked in bovine serum was determined by our method.

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