A Simple Optical Reader for Upconverting Phosphor Particles Captured on Lateral Flow Strip

A simple optical reader was developed for rapid and sensitive quantification of lateral flow (LF) strip with upconverting phosphor (UCP) particles as reporters. The excitation beam from a 980 nm laser diode (LD) was focused to a 4 mm (length) $,times,$0.02 mm (width) rectangular spot on LF strip. A rectangular slit with 4 mm $,times,$0.02 mm before the photomultiplier tube (PMT) which was selected as receiver was introduced as field diaphragm to prevent stray light from entering the PMT. The scanning resolution was 20 $mu$m, and the scanning speed was 0.75 mm/s, and the scanning range was 10 mm. With the above optical reader, serial dilutions of Yersinia pestis F1 antigen were detected to achieve the test sensitivity was 5 ng/ml, and the dynamic range reached 150 ng/ml. The algorithms of the low-pass filter and the first derivative were used to search the boundaries of T line and C line from the original data acquired by the reader. A four-parameter logistic mathematical model was used to deduce the quantitative equation for determination of unknown F1 antigen concentration. Our 1-D optical reader possessed the following characteristics: high 1-D testing resolution, high sensitivity, simple structure, simple data processing method, high testing efficiency, and small total volume.