Specific synthetic 5 0 amine-C12 modified 70-mer probes for influenza A were designed and solid-phase coupled to xMAP carboxylated color-coded microspheres (Luminex Corp., Austin TX, USA), according to the protocol of the Luminex corporation (Austin TX, USA). Briefly, 2.5 Â 10 6 stock microspheres were collected by centrifugation and resuspended in 25 ml of 0.1 M MES, pH 4.5 (2N-morpholino-ethanesulfonic acid, Sigma). Subsequently, 0.2 nmol of the probe and freshly made 2 ml 10 mg/ml EDC [1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (water-soluble carbodiimide; Pierce; sold by Nordic Biolabs AB, Sweden)] in H 2 O were added to the microspheres and the suspension was incubated in the dark for 30 min at room temperature. Care was taken to store the EDC in a dry condition, in aliquots. After addition of another 2 ml (10 mg/ml) EDC in H 2 O and repeated incubation, the microspheres were washed with 0.5 ml of 0.02% Tween-20. The coupled microspheres were pelleted by centrifugation at 8000 Â g for 2 min and resuspended in 0.5 ml of 0.1% SDS. After a second spin at 8000 Â g for 2 min, the final pellet was resuspended in 50 ml of TE, pH 8.0.