Significant Sensitivity Improvement for Camera-Based Lateral Flow Immunoassay Readers

Abstract

Recent developments in smartphone-based strip readers have further improved the performances of lateral flow test kits. Most smartphone cameras encode an unaltered and nonlinear power-law transfer function that maps the light intensity to a pixel value; this poses some limitations for camera-based strip readers. For faint-color test lines which are almost as white such as with nitrocellulose pads, the slope of the transfer function is low. Therefore, it is difficult to differentiate between the faint test lines and the white background. We show that by manually setting the camera exposure time—instead of using the automatic settings—to the high-slope region of the transfer function, the reader’s sensitivity can be improved. We found that the sensitivity and the limit of detection of the Acidovorax avenae subsp. citrulli (Aac) test kit were enhanced up to 3-fold and 5-fold, respectively, when using the readers at the optimal camera settings, compared to the automatic mode settings. This simple technique can be readily applied to any existing camera-based colorimetric strip reader to significantly improve its performance.

Six decades of lateral flow immunoassay: from determining metabolic markers to diagnosing COVID-19

“…Thus, in the last decade, commercial models of open and closed detectors have appeared, based on optical data processing, which allow reading not only color stripes, but also fluorescent labels [6] , [76] , [79] ( Table 3 ). In addition, the advent of related software products for smartphones allows these individual mobile devices to be used to obtain rapid quantitative results without the use of additional equipment [75] , [80] . The use of mobile device platforms in quantitative LFIA formats to accurately record test results increases the efficiency of the clinic, epidemiological surveillance and disease control at the system level, and ultimately reduces the time it takes to initiate specialized treatment.…”

“…In recent years, with the emergence advent of related software products for smartphones allows these personal mobile devices to be used to obtain rapid quantitative results without the use of additional equipment [75] , [80] . The use of mobile device in quantitative LFIA formats to accurately record test results increases the efficiency of the clinic, epidemiological surveillance and disease control at the system level, and ultimately reduces the time it takes to initiate specialized treatment.…”

“…Before the emergence in the XXI century of epidemic outbreaks of infections (SARS in 2002–2004 and MERS in 2012 caused by β-coronaviruses MERS-CoV [80] , [81] , [84] and SARS-CoV [86] , [87] , these pathogens were not considered highly pathogenic to humans. They circulated in the human population, causing only sporadic cases of diseases that occur, as a rule, in a mild form [85] , [88] .…”

“…The main disadvantages of this method in the diagnosis of infections are derived from the principle of the RT-PCR method, which provides for the detection of coronavirus RNA of only a specific type (SARS-CoV-2) and at a certain period of the disease [80] , [87] , [92] . Therefore, the results may be negative when examining convalescing patients cleared of the pathogen, as well as in patients with other infections [88] , [98] .…”

“…This diagnostic technology involves the use of simple-to-operate equipment with the ability to visually evaluate the result [69] , [82] . This diagnostic method was proposed in 2000 and managed to prove itself in epidemics of SARS and MERS infections [69] , [79] , [80] , as well as during the COVID-19 pandemic as a screening tool for remote regions and rural hospitals [86] , [88] .…”