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 mum, 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.