On-chip processing of droplets for surface plasmon resonance analysis

Solutions in the form of liquid droplets were processed and analyte molecule sensing was performed, based on surface plasmon resonance (SPR). Two types of devices with different microfluidic functions were used. Procedures such as measurement of solution volume, mixing of solutions, and sequential analyses were conducted, followed by SPR sensing. A distinct difference in the variation of reflectivity was observed with solutions of different concentrations prepared by diluting 100 and 1000 mM glucose solutions on the chip. A linear relationship was observed between the change in reflectivity and glucose concentration. The functionality of this device was also tested by detecting the DNA that was tagged with a quantum dot (Q-dot) (QD-DNA complex) accompanying the DNA hybridization with thiol-terminated single-stranded DNA immobilized on the gold surface of the sensing region. Sequential analysis of plugs including those containing glucose and the QD-DNA complex in a single flow channel was carried out. Reflectivity changed rapidly when a water plug was replaced with a glucose plug, whereas the binding of the QD-DNA complex showed a gradual increase in reflectivity.