Photography by Cameras Integrated in Smartphones as a Tool for Analytical Chemistry Represented by an Butyrylcholinesterase Activity Assay

Abstract

Smartphones are popular devices frequently equipped with sensitive sensors and great computational ability. Despite the widespread availability of smartphones, practical uses in analytical chemistry are limited, though some papers have proposed promising applications. In the present paper, a smartphone is used as a tool for the determination of cholinesterasemia i.e., the determination of a biochemical marker butyrylcholinesterase (BChE). The work should demonstrate suitability of a smartphone-integrated camera for analytical purposes. Paper strips soaked with indoxylacetate were used for the determination of BChE activity, while the standard Ellman's assay was used as a reference measurement. In the smartphone-based assay, BChE converted indoxylacetate to indigo blue and coloration was photographed using the phone's integrated camera. A RGB color model was analyzed and color values for the individual color channels were determined. The assay was verified using plasma samples and samples containing pure BChE, and validated using Ellmans's assay. The smartphone assay was proved to be reliable and applicable for routine diagnoses where BChE serves as a marker (liver function tests; some poisonings, etc.). It can be concluded that the assay is expected to be of practical applicability because of the results' relevance.

Keywords: CMYK; RGB; acetylcholinesterase; butyrylcholinesterase; colorimetry; diagnosis; digital photography; imagination; mobile phone; naked eye detection; photography; photometry.

Scheme 1

Principle of the indoxylacetate-based assay used for the determination of BChE activity.

Figure 1

Photos of gear used for the assay. (A) Smartphone beside distance tube and paper soaked with indoxylacetate. The camera and LED light source are visible in the photo; (B) Setup used for photographing the paper.

Figure 2

Performance of the smartphone for R, G and B channel color intensity change measurements with time. Rs, Gs and Bs were acquired by assay of plasma samples on filter paper treated with indoxylacetate while Rc, Gc and Bc were determined by assay of plasma samples on papers without any treatment. Error bars indicate standard deviations for n = 5.

Figure 3

An example based on calibration using two-fold serial dilutions of plasma. Undiluted plasma is the left drop; the right drop is 32 times diluted plasma. The photograph was taken in the dark (in a black distance tube) using the smartphone chosen for the experiments and integrated LED flash as a sole source of light.

Figure 4

Calibration of the smartphone-based assay using diluted plasma samples. Differences of color intensity for the R, G and B channels are given. These were acquired by processing photographs taken at the beginning (0 min) of the assay and after 30 min. Points in brackets was taken by assay of pure PBS. Error bars indicate standard deviations for n = 5.

Figure 5

Validation of the smartphone-based assay using plasma samples spiked with carbofuran. Standard Ellman’s assay was used as a reference. The concentration of carbofuran in the plasma sample is written beside the experimental point. Error bars indicate standard deviations for n = 5.