Amplification of fluorescence with packed beads to enhance the sensitivity of miniaturized detection in microfluidic chip

This paper reports the pre-concentration of C-reactive protein (CRP) antigen with packed beads in a microfluidic chamber to enhance the sensitivity of the miniaturized fluorescence detection system for portable point-of-care testing devices. Although integrated optical systems in microfluidic chips have been demonstrated by many groups to replace bulky optical systems, the problem of low sensitivity is a hurdle for on-site clinical applications. Hence we integrated the pre-concentration module with miniaturized detection in microfluidic chips (MDMC) to improve analytical sensitivity. Cheap silicon-based photodiodes with optical filter were packaged in PDMS microfluidic chips and beads were packed by a frit structure for pre-concentration. The beads were coated with CRP antibodies to capture antigens and the concentrated antigens were eluted by an acid buffer. The pre-concentration amplified the fluorescence intensity by about 20-fold and the fluorescence signal was linearly proportional to the concentration of antigens. Then the CRP antigen was analyzed by competitive immunoassay with an MDMC. The experimental result demonstrated that the analytical sensitivity was enhanced up to 1.4 nM owing to the higher signal-to-noise ratio. The amplification of fluorescence by pre-concentration of bead-based immunoassay is expected to be one of the methods for portable fluorescence detection system.