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This article presents a device incorporating surface plasmon resonance (SPR) sensing and surface acoustic wave (SAW) actuation integrated onto a common LiNbO(3) piezoelectric substrate. The device uses Rayleigh-type SAW to provide active microfluidic mixing in the fluid above the SPR sensor. Validation experiments show that SAW-induced microfluidic mixing results in accelerated binding kinetics of an avidin-biotin assay. Results also show that, though SAW action causes a parasitic SPR response due to heat injection into the fluid, a relatively brief relaxation time following the SAW pulses allows the effect to dissipate, without affecting the overall assay response. Since both SPR sensors and SAW transducers can be fabricated simultaneously using low-cost microfabrication methods on a single substrate, the proposed design is well-suited to lab-on-chip applications.

Real-size assimilation systems basically rely on estimation theory in which two sources of information, background and observations, are combined in an optimal way. However, the optimality of such large problems is not guaranteed, since they rely on different approximations. The observed values of the subparts of the cost function measuring the distance between the analysis and the two sources of information can be compared to their theoretical statistical expectations. Such a posteriori diagnostics can be used to optimize the statistics of observation and also background errors. Moreover, the expectations of the subparts of the cost function associated with observations are related to the weights of the different sources of observations in the analysis. It is shown that those theoretical statistical expectations are direct by-products of an ensemble of perturbed assimilations.