Photomicrographs of virtual well successes and failures. Slides were printed and photographed as stated in Figure 4 with the following modifications. (a) Virtual reaction wells are each formed by printing a droplet of phosphoramidite solution followed by a droplet of tetrazole solution using the standard 1:1 3MP:MGN. (b) Tetrazole droplets were printed before phosphoramidite droplets. Discrete virtual reaction wells fail to form. (c) Wells formed by printing two droplets of phosphoramidite solution. (d) Two droplets of tetrazole solution printed with no phosphoramidite. Virtual wells fail to form. (e) Phosphoramidite and tetrazole dissolved in 1:3 3MP:MGN and phosphoramidite printed first. Virtual wells form well. (f) Two droplets of tetrazole in 1:3 3MP:MGN solvent. Although not perfectly round, virtual wells do form.