Au NPs-aptamer conjugates as a powerful competitive reagent for ultrasensitive detection of small molecules by surface plasmon resonance spectroscopy

Features of Au NPs-aptamer conjugates as a powerful competitive reagent to substitute antibody in enhancing surface plasmon resonance spectroscopy (SPR) signal for the detection of small molecule are explored for the first time. In order to evaluate the sensing ability of Au NPs-aptamer conjugates as a competitive reagent, a novel SPR sensor based on indirect competitive inhibition assay (ICIA) for the detection of adenosine is constructed by employing the competitive reaction between antiadenosine aptamer with adenosine and antiadenosine aptamer with its partial complementary ss-DNA. The partial complementary ss-DNA of antiadenosine aptamer is firstly immobilized on SPR gold film as sensing surface. When the Au NPs-antiadenosine aptamer conjugates solution is added to SPR cell in the absence of adenosine, Au NPs-antiadenosine aptamer conjugates is adsorbed to SPR sensor by the DNA hybridization reaction, and results in a large change of SPR signal. However, the change of SPR signal is decreased when the mixing solution of adenosine with Au NPs-antiadenosine aptamer conjugates is added. This is because adenosine reacts with antiadenosine aptamer in Au NPs-antiadenosine aptamer conjugates and changes its structure from ss-DNA to tertiary structure, which cannot hybridize with its partial complementary ss-DNA immobilized on SPR gold surface. Based on this principle, a SPR sensor for indirect detection of adenosine can be developed. The experimental results confirm that the SPR sensor possesses a good sensitivity and a high selectivity for adenosine, which indirectly confirms that Au NPs-aptamer conjugates is a powerful competitive reagent. More significantly, it can be used to develop other SPR sensors based on ICIA to detect different targets by changing the corresponding type of aptamer in Au NPs-aptamer conjugates.