In the field of biological science, heterogeneous-phase biochemical assays, including both immunoassays and nucleic acid hybridization assays, have been among the most powerful analytical techniques. Traditionally, the assays in this type, such as the enzyme-linked immunosorbent assay (ELISA) are carried out without sample replenishment in containers having milliliter scale volumes. Having such high sample consumption for rare samples presents a limitation. Moreover, ELISA relies on an enzyme-conjugated secondary antibody to couple with the immunocomplex for generating signals for measurement. Until the end of an ELISA, no information can be obtained from the assay. When analyzing samples in low quantity, ELISA often takes hours to complete.
To develop a system for running heterogeneous-phase biological assays with higher rapidity and lower sample consumption, we combine a microfluidic device, made of polydimethylsiloxane (PDMS) and an array of thin gold spots, with surface plasmon resonance (SPR) imaging. The combined system offers significant advantages: (1) the microfluidic device provides flow channels with nanoliter volumes, by which the heterogeneous-phase reactions are accelerated because the reagents are quickly replenished by the liquid flow; (2) the use of microfluidics allows an immunoassay to be carried out with less sample consumption; and (3) SPR imaging gives real-time monitoring of the formation of an immunocomplex or a hybridized complex by sensing the refractive index change of binding molecules to the surfaces of gold spots giving kinetic data on the process. Moreover, signal amplification is available for SPR imaging by applying an additional gold-nanoparticle-linked reagent. The results below show the excellent performance of the combined system and indicate the potential clinical applications.
For more information on how we make microfluidic devices in the Zarelab, please see our guide (PPT or PDF).
Figure 1. Layout and photograph of the microfluidic chip designed for coupling with SPR imaging system.
Figure 2. (a) Background corrected end-point SPR image of the microfluidic chip obtained after anti-biotin antibody binding to biotinylated BSA covered gold spots. (b) Kinetic curves of anti-biotin antibody binding to pure biotinylated BSA covered gold spots. (c) End-point calibration curves of the density of bound anti-biotin antibody versus its working concentration.