Colorimetric-Luminance Readout for Quantitative Analysis of Fluorescence Signals with a Smartphone CMOS Sensor

Abstract

Smartphones have shown promise as an enabling technology for portable and distributed point-of-care diagnostic tests. The CMOS camera sensor can be used for detecting optical signals, including fluorescence for applications such as isothermal nucleic acid amplification tests. However, such analysis is typically limited mostly to endpoint detection of single targets. Here we present a smartphone-phone based image analysis pipeline that utilizes the CIE xyY (chromaticity-luminance) color space to measure the luminance (in lieu of RGB intensities) of fluorescent signals arising from nucleic acid amplification targets, with a discrimination sensitivity (ratio between the positive to negative signals) which is an order of magnitude more than traditional RGB intensity based analysis. Furthermore, the chromaticity part of the analysis enables reliable multiplexed detection of different targets labeled with spectrally separated fluorophores. We apply this chromaticity-luminance formulation to simultaneously detect Zika and chikungunya viral RNA via endpoint RT-LAMP (Reverse transcription Loop-Mediated isothermal amplification). We also show real time LAMP detection of Neisseria gonorrhoeae samples down to a copy number of 3.5 copies per 10 μL of reaction volume in our smartphone-operated portable LAMP box. Furthermore, the chromaticity-luminance analysis is readily adaptable to other types of multiplexed fluorescence measurements using a smartphone camera.

Loop-mediated isothermal amplification (LAMP) – review and classification of methods for sequence-specific detection

“…73 Technical applications of QUASR on a chip and with smartphone readout are described elsewhere. [74][75][76] The analytical sensitivity for detection of cell-cultured zika virus by QUASR RT-LAMP was 44 copies per reaction. Furthermore, the assay showed high analytical specicity when tested against other aviviruses and alphaviruses.…”

“…Platforms designed specically to meet the demands for use at the PON 182,183 have mainly been presented for uorescence-based detection. Simple readout via smartphone, replacing bulky and expensive optical components, has been implemented by a portable LAMP box 74,75 or combined with lter-based sample preparation. 85,86 The integration of small smartphones into diagnostic platforms can reduce costs considerably.…”

“…The latest trends in research show that bulky optical components can be replaced by smartphones. 74,75,85,86 Further developments could lead to various heterogeneous detection methods being combined with simple smartphone readout, making expensive and sophisticated devices redundant and thus increasing userfriendliness. An exciting and stimulating demonstration of the smartphone approach is the detection of SPR, with a smartphone as the transducing element.…”

Sandwich-Type DNA Micro-Optode Based on Gold–Latex Spheres Label for Reflectance Dengue Virus Detection

“…The developed optical reflectance DNA biosensor shows high promise for smartphone-based image analysis with complementary metal-oxide-semiconductor/charge-coupled device (CMOS/CCD) sensors and camera systems for discrimination of color change of the DNA biosensor upon DNA sandwich hybridization detection. The novel approach of quantifying the colors of colorimetric diagnostic assays allows the high accuracy and portability of point-of-care diagnostic tests of dengue infection to be carried in resource-limited settings [28][29][30].…”

Smartphone Coupled with a Paper-Based Colorimetric Device for Sensitive and Portable Mercury Ion Sensing

“…Recently, digital image-based colorimetry is receiving more attention as an alternative to the conventional methods, owing to its green, low-cost, portable and simple analytical procedure to analyze chemical compounds including metals [8][9][10][11], anions [12,13], organics [14,15], biochemical compounds [16,17] and medical applications [18][19][20]. The dynamic range of the digital image represented by red-green-blue or RGB color space (i.e., from 0 to 255), is much broader than conventional colorimetry or spectrophotometry methods (i.e., from 0 to 2.0 absorbance) providing the opportunity to improve the sensitivity of detection [8,18].…”