Color analytical reader for procalcitonin colloidal gold test strips
(2.Beijing Zhongketonghe Information Technology Limited Company, Beijing, China 100088)
【Abstract】The semi-quantitative method of colloidal gold strip detection by colorimetric principle is widely used in biomedical diagnosis. To achieve quantitative measurement of procalcitonin concentration, a CMOS color analytical reader based on raspberry Pi was designed for the acquisition of color characteristics of chromogenic reaction by taking a picture of colloidal gold strip. According to the color characteristics of procalcitonin colloidal gold test strips, the CMOS sensor was corrected by proper white balance parameter adjustment, which enabled the CMOS image sensor had a better color restoration property. In order to eliminate the difference of color management between different devices, the mathematical model of the sensor from RGB space to XYZ space was established via polynomial regression by taking pictures of NCS standard color cards. Thus the instrument was adjusted in color characteristics. Then, the mathematical model of XYZ values and concentration values of the samples was derived from the representative gray value pixel areas of the processed images. In this way the color uniformity problem was solved and the concentration was accurately measured. The experiment results show that the measuring precision can be as high as 93.8%, the repeated measurement error is less than 1.5% and the effective measurement range is from 0.1 ng/mL to 35 ng/mL. With the virtues of cost effective and high measurement speed, the analyzer has a promising application prospect.
【Keywords】 chrominance analysis; colloidal gold; color space; polynomial regression; procalcitonin; concentration measurement;
 WANG SH, ZHENG D ZH, FANG SH CH. Detecting method of quantitative colloidal gold test strip concentration [J]. Journal of Beijing University of Aeronautics and Astronautics, 2009, 35 (8): 942–945 (in Chinese).
 WANG Y, BAI Y J, ZHANG Y CH, et al. Design and reasearch of a photoelectrical apparatus for laterflow based on CCD [J]. Chinese Journal of Sensors and Actuators, 2008, 21 (8): 1370–1373 (in Chinese).
 KIM S, PARK J. Development of a test strip reader for a lateral flow membrane-based immunochromatographic assay [J]. Biotechnology and Bioprocess Engineering, 2004, 9 (2): 127–131.
 HONG G W. LUO M R, RHODES P A. A study of digital camera colorimetric characterization based on polynomial modeling [J]. Color Res. Appl., 2001, 26 (1): 76–84.
 WANG Y. Design of a Colloidal-gold Strip reader with High Accuracy[D]. Hangzhou: Zhejiang University, 2013 (in Chinese).
 XU Y F, LIU W Y, ZUO K L, et al. Reasearch on hierarchical color correction method [J]. Opt. Precision Eng., 2004, 12 (1): 15–20 (in Chinese).
 ZHAO Z Q, WANG R G, ZHENG X F, et al. Measurement of chroma of LED display with color CCD camera [J]. Opt. Precision Eng., 2013, 21 (3): 575–582 (in Chinese).
 ZHAO P, WANG W J, CHEN W. Research on hierarchical colour correction method [J]. Engineering and Applications, 2015, 51 (6): 158–162 (in Chinese).
 QIU X B, LIU CH CH, MAUK M G. A portable analyzer for pouch-actuated, immunoassay cassettes [J]. Sensors and Actuators B: Chemical, 2011, 160 (1): 1529–1535.
 BARNARD, FUNT B. Camera characterization for color research [J]. Color Res. Appl., 2002, 27 (3): 152–163.
 CHEUNG T L V, WESTLAND S. Color camera characterisation using artificial neural networks [C]. IS&T/SID Tenth Color Imaging Conference, 2002: 117–120.
 SUN H C, TIAN R, DING N N, et al. Automatic white balance algorithm based histogram equalization and its FPGA implementation [J]. Chinese Journal of Scientific Instrument, 2015, 36 (12): 222–226 (in Chinese).
 LI B, XU D, XIONG W H, et al. Color constancy using achromatic surface [J]. Color Res. Appl., 2010, 35 (4): 304–312.
 KAWAKAMI R, ZHAO H X, TAN R T, et al. Camera spectral sensitivity and white balance estimation from sky images [J]. International Journal of Computer Vision, 2013, 105 (3): 187–204.
 XU M F, WANG L Q, YUAN B. Auto white balance algorithm of high definition electronic endoscope [J]. Infrared and Laser Engineering, 2014, 43 (9): 3110–3115 (in Chinese).
 YAO H T, TIAN Q Q, SU W, et al. Reasearch on automatic white balance algorithm based on color histogram equalization [J]. Journal of Changchun University of Science and Technology: Natural Science Edition, 2014, 37 (4) :104–107 (in Chinese).