<title>Design and manufacture of capillary wicks for ultrasensitive detection of antigenic and nucleic acid analytes</title>

Abstract

Using upconverting phosphor reporter probes to detect antigenic and nucleic acid analytes in environmental samples required the design and manufacture of a novel sampling and assay device that exploits the unique characteristics of the upconverting phosphors. The absence of natural materials that upconvert energy make single particle detection possible with these reporters. Ultrasensitive detection and quantitation of analytes is governed by the area of the capture surface, the density of the capture probe,s as well as the specific upconversion efficiency of the phosphor label. The optimization of a flow channel and capture surface for single phosphor particle detection is a complex function of the volume of sample that is drawn through the channel, the probability that this sample volume contains an analyte particle, the fraction of analytes contained in the sampled volume that bind to the capture site, and the optical dimensions of the capture site. The result of this optimization using theoretical diffusion models for submicron upconverting phosphor particles was a rectangular flow channel with a 200 X 300 micrometers capture surface. Capture surfaces of this size have been prepared using photo-directed synthesis methods inside glass capillary wicks that have been subsequently used for the phosphor- based assays.