Conventional flow injection systems for aquatic environmental analysis typically comprise large laboratory benchscale equipment, which place considerable constraints for portable field use. Here, we demonstrate the use of an integrated acoustically driven microfluidic mixing scheme to enhance detection of a chemiluminescent species tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate--a common chemiluminescent reagent widely used for the analysis of a wide range of compounds such as illicit drugs, pharmaceuticals, and pesticides--such that rapid in-line quantification can be carried out with sufficient on-chip sensitivity. Specifically, we employ surface acoustic waves (SAWs) to drive intense chaotic streaming within a 100 μL chamber cast in polydimethoxylsiloxane (PDMS) atop a microfluidic chip consisting of a single crystal piezoelectric material. By optimizing the power, duration, and orientation of the SAW input, we show that the mixing intensity of the sample and reagent fed into the chamber can be increased by one to two orders of magnitude, leading to a similar enhancement in the detection sensitivity of the chemiluminescent species and thus achieving a theoretical limit of detection of 0.02 ppb (0.2 nM) of l-proline--a decade improvement over the industry gold-standard and two orders of magnitude more sensitive than that achievable with conventional systems--simply using a portable photodetector and without requiring sample preconcentration. This on-chip microfluidic mixing strategy, together with the integrated miniature photodetector and the possibility for chip-scale microfluidic actuation, then alludes to the attractive possibility of a completely miniaturized platform for portable field-use microanalytical systems.
Gracioso Martins, Ana M., Nick R. Glass, Sally Harrison, Amgad R. Rezk, Nichola A. Porter, Peter D. Carpenter, Johan Du Plessis, James R. Friend, Leslie Y. Yeo