Printed two-dimensional micro-ring film plate for spot assays and its functionalization by immobilized enzymes

In this paper, we present a simple printable two-dimensional micro-ring plate for spot assays in low-resource settings. Each micro-zone on the overhead transparency contains a hydrophilic center restricted by a superhydrophobic ring. The zone can be fully wetted by a small amount of aqueous sample (0.5 mu l) and can also hold a large volume up to 100 mu l, offering the flexibility to handle different amount of samples. Bio-analysis capacity of the micro-ring plate was demonstrated by the Pierce 660 nm protein assay and blood typing assay. We further functionalized the plate by depositing enzymes-immobilized nanorods into micro-zones. This functionalization, for the first time, enables multi-diagnostic functions in one micro-ring as demonstrated by analysis of individual substrate of the two enzymes. The functionalized plates show a high stability under varied temperatures that mimic the changes of environment during transport. Importantly, all the assays were carried out using non-laboratory devices such as mobile phone, ensuring its low-cost application under limited resources.