Chemistry Reference
In-Depth Information
Fig. 6.1 Mobile-cellular
subscriptions in the emerging
economies, developing world
and worldwide from 2004 to
2014
6.2 A Smartphone Algorithm for the Quanti
cation
of Colorimetric Assays
6.2.1 Calibration of the Application
The smartphone app measured the electromagnetic radiation from the colorimetric
test zones with the complementary metal-oxide-semiconductor (CMOS) sensor
present in the smartphone camera. The algorithm processed the colorimetric data as
concentrations of the analytes in each test zone, and then the app displayed the
corresponding value on the smartphone screen. The sensitivity of the measurement
was based on the accuracy of the CMOS sensor, the colour uniformity of the
reactions, and the number of calibration points. In testing a colorimetric urine test
strip (Fig.
6.2
a), the app stored a calibration curve for the assay and the ambient
light condition. The user inputted (i) the sensor type, (ii) target analytes, (iii) units
of the concentration, (iv) number of reference data points, and (v) the images of the
calibration points were captured. The smartphone was perpendicularly positioned
over the assay at 5 cm, which was kept constant to match the colorimetric zones
with the evaluation area de
ned by the software (Fig.
6.2
b). The measurements
were carried out at
room temperature (24
°
C). Calibration was performed
within
1 min, and it was stored in the smartphone memory.
The app was calibrated for pH, glucose and protein measurements based on 5, 4
and 5 data points, respectively. The app located the reference colours (100 pixels),
transformed and averaged the CMOS data into non-linear red, green, blue (RGB)
values (R
c
, G
c
, B
c
) for each pixel. Subsequently, the app linearised the RGB values
(R
l
, G
l
, B
l
)[
22
]:
*
