Printed two-dimensional micro-zone plates for chemical analysis and ELISA

In this study we report a new concept of printing low-cost two-dimensional micro-zone plates for chemical and biochemical assays and ELISA. It is different from the concept of forming multi-zone micro-zones on paper by hydrophobic barriers first reported by Yagoda. Instead, the desired multi-zone micro-zone pattern was first printed using a UV-curable varnish onto a polymer film; then fine powders of cellulose or other materials were applied onto the uncured varnish, allowing the powder to stick to the varnish layer. After UV-curing, the powder particles were fixed by the cured varnish, leading to the formation of porous, water absorbing micro-zones on the polymer film. This type of micro-zone plate has the required liquid handling capacity for a variety of low-volume and portable two-dimensional plates for chemical, biochemical assays and ELISA. By suitably spacing porous micro-zones on a non-porous substrate, this type of plate eliminates inter-zone sample leaking. Rapid colorimetric analysis of the results can be performed using a portable battery-powered colour densitometer or a desktop scanner. By introducing a refractive-index-matching liquid into the microzones, the plate can be easily analyzed using transmission instruments. A major advantage of this plate fabrication method is that it enables the printing of different powders or functionalized powders to form micro-zones on a same plate, potentially allowing certain more difficult functionalization of materials to be performed before printing. We demonstrate the assaying performance of the plates using an analytical system that aims to clarify the analytical interference between NO2- and uric acid (UA) in the analysis of samples where both chemical species are present. We also show that ELISA assays can be performed using this type of plates.