A miniaturized chemiluminescence detection system for a microfluidic paper-based analytical device and its application to the determination of chromium(III)

A miniaturized detection system for chemiluminescence that is generated on a microfluidic paper-based analytical device (mu PAD) was developed using optical fibers and was applied to the determination of Cr(III). The mPAD was fabricated by wax printing and consisted of 6 separate channels in a parallel alignment. Each channel was composed of an injection zone for a reagent solution, a reaction zone, and a waste zone. The mu PAD was placed on a plastic holder equipped with 6 optical fibers to collect chemiluminescence (CL). The other ends of the optical fibers were bundled and introduced into a small photomultiplier tube module to obtain the CL signals. The CL reaction was based on luminol oxidation by hydrogen peroxide in the presence of Cr(III), which catalyzed the reaction in an alkaline medium. The reaction conditions, including the use of an enhancer and a masking agent, were optimized to obtain high sensitivity and selectivity. Under the optimal conditions, a linear range was obtained at 0.05 to 1.00 ppm with a detection limit of 0.02 ppm. The analysis time was less than 1 min per one mu PAD in order to obtain 6 measurements of differing concentrations with a precision of < 6.5%. This method was successfully applied to the determination of Cr(III) spiked into natural water samples at the sub-ppm range.