Investigation of dopamine immobilized on gold by surface plasmon resonance

Dopamine (DA) existed as small-molecules can serve as a versatile platform for secondary surface modified reactions in biomedical engineering and biosensors especially a surface plasmon resonance (SPR) sensor. For sensing modification purposes, the environment of DA polymerization may be varied. This study involved using DA for the modification of a gold film under different conditions. It was anticipated that the change of environmental conditions would have an influence on the immobilization reaction of DA onto the gold film, and hence the impact on the SPR phenomenon. These conditions included varying pH, using different kinds of buffers, varying DA concentrations in buffer solutions as well as the DA immobilization time which reflected the length of time that the gold film was being exposed to DA. It was found that both neutral and mildly alkaline conditions offered favorable immobilization environments with 2 mg/mL dopamine in pH 8.6 Tris buffer, producing the optimum reactive result on gold. It was observed that the SPR phenomenon became non-existence at pH 9.5 for 2-hour DA immobilization time. Under the optimum environmental condition, the critical DA immobilization time for the disappearance of SPR phenomenon was estimated to be 277 min (approx. 4.6 hours). The results from this work have produced a series of valuable data served as a good foundation for surface modification using DA.