An aptamer-aptamer sandwich assay with nanorod-enhanced surface plasmon resonance for attomolar concentration of norovirus capsid protein

A Gold nanorod (NR) enhanced surface sandwich assay utilizing a novel pair of aptamers for the attomolar concentration of norovirus (NoV) capsid protein was developed in conjunction with surface plasmon resonance (SPR). A total of four different DNA aptamer sequences (aptamer I-IV) known to be specific for the NoV protein were examined using SPR for individual binding strength with the NoV protein and for the formation of surface sandwich with the NoV protein, meaning that the chosen aptamer pair possesses different binding epitope towards the NoV protein. One of the aptamer (aptamer II) sequences with the strongest binding constant was covalently tethered onto a chemically modified thin gold chip surface, while the other aptamer I was used for tethering onto the Au NR surface. The surface sandwich complex was formed via the sequential adsorption of NoV capsid protein and Au NR coated aptamer I onto the aptamer II surface. As low as a 70 aM concentration of the NoV protein in buffer solution could be detected, which is 10(5) times better than that of using the aptamer-aptamer sandwich platform without any gold NR particles. As a demonstration, the aptamer-NR coated aptamer sandwich assay was applied to analyze NoV capsid protein concentrations spiked in human serum solutions.