Nanoparticle-based analytical-bioanalytical probes: Investigation of interactions and reactivities between gold nanoparticles and homocysteine

This work is aimed at exploring nanoparticles (1--100 nm) as bioanalytical probes for the development of rapid detection methods. Gold nanoparticles (Aunm) are studied as a model probe for the detection of homocysteine (Hcys). Hcys is of interest because of the potential link to cardiovascular disease. The unique optical properties of citrate- or Hcys-capped gold nanoparticles and their reactivity with Hcys are studied as a colorimetric detection means. The mechanism and kinetics of this reaction were probed by various techniques. The viability of immobilizing Hcys-capped gold nanoparticles onto Hcys-monolayer assembled gold surfaces via interactions at the amino acid functional groups was investigated to assess the interparticle reactivity. The reactivity involved in the surface assembly is discussed in terms of the capping structure of the nanoparticles, the surface structure of the self-assembled monolayer, and their interfacial interactions. Implications to the understanding of the interactions of Hcys-Aunm and potential applications are discussed.