Images were captured at 4´ and 10´ magnifications. Stability testing involved imaging under the same parameters after 30 mins of immersed water wash at 220 RPM. Food overlay imaging was done under the same parameters, but with 10 mm thick food samples placed on the printed arrays. fNAP synthesis. A substrate strand possessing a fluorophore-quencher separated by a riboadenosine base was enzymatically ligated to the 5' terminal of a probe fragment with a 3` amino modification. This was templated by a splint strand. In preparation for ligation, 4 nmol of the probe strand was first phosphorylated using excess adenosine triphosphate, 1× T4 polynucleotide kinase buffer A and 40 U T4 polynucleotide kinase in a 50 µl reaction at 37 °C for 30 minutes. Following phosphorylation, 4 nmol of the substrate strand and 4 nmol of the split strand were added to the reaction, then heated at 90 °C for 1 minute and cooled at room temperature for 5 minutes to anneal the fragments. The cooled ligation reaction was then diluted to 400 µl by addition of T4 DNA ligase buffer to 1×, 20 U T4 DNA ligase, and water. The ligation reaction was then incubated at room temperature for 1 hour and ethanol precipitated using 2.5 volumes of chilled ethanol, followed by centrifugation at 4 °C, 20000 × g for 20 minutes. The ligated product was purified on a 10%, 8 M urea polyacrylamide gel. The band corresponding to the ligated product was excised from the gel, crushed, and eluted in buffer (200 mM NaCl, 10 mM Tris pH 7.5, 1 mM EDTA). The elution supernatant containing the nucleic acid probe was then ethanol precipitated as described above, followed by a final wash with 70% ethanol. The pellet was then air dried and resuspended in water.