||Surface plasmon resonance (SPR) biosensor has several advantages such as lable-free, high sensitivity, specificity and real-time detection, so it has been used for a large number of biomolecular detection. The fiber-optic SPR biosensor is low cost and has small size due to its small sensing area, it makes the sensor ideal for studying small volumes of samples. The applications are more and more than before.
In this study, we used the fiber-optic SPR sensor to determine the small biomolecules. Using SPR detect system needs to make a good modification layer on the sensing surface to improve the detecting sensitivity and stability. Mercapto-undecanoic acid (MUA) mixed molecules with different length of carbon chains, β-mercaptoethanol (2-MEOH) and 6-mercapto-1-hexanol (6-MHOH), in different ratio to deposit as self-assembled monolayer (SAM) on the sensing surface, and then biotin-albumin bovine serum (biotin-BSA) was immobilized on SAM surface of fiber-optic SPR as a detection platform for small molecular analytes.
The results show that SAM layers by single 6-MHOH or MUA mixed with 6-MHOH could immobilize more biotin-BSA than one by single MUA in silicon wafer system. In fiber-optic SPR sensing system, however, excess biotin-BSA could cause unstable in the SPR signal. In the contrast, the immobilized biotin-BSA was less for MUA SAM layer, but the stability in fiber SPR sensing system is the best.
In the test for SPR signal amplification, we select enzyme precipitation method and nanogold method that common used in other studies. And then, the enzyme precipitation method that use 3,3’-diaminobenzidine tetrahydrochloride (DAB) as substrate is better in this fiber-optic SPR system. Therefore, using MUA as the SAM layer and amplifying the signal by DAB precipitation are the better conditions to the fiber-optic SPR system.