Page 417 - Handbook of Biomechatronics

412 Graham Brooker

Fig. 2 Basic functions of the individual layers of a reflectance-based test strip. (Based on
Bronzino, J. (Ed.), 2006. Medical Devices and Systems, CRC Press.)

swellable films or semipermeable membranes and commonly use glass-fiber
wool to separate the plasma from the whole blood.
Once the reaction product is formed, the percentage of diffuse light
reflected from the analytical layer of the strip, R % , decreases in accordance
with the following equations.

I u
R % ¼ R s (1)
I s

where I u is the reflected light intensity from the sample, I s is the reflected
light intensity from a standard reference, and R s is the percentage reflectivity
of the standard.
A more usual way of representing this relationship is to use the Kubelka-
Munk (K-M) equation.

2
K ð 1 R Þ
C∝ ¼ (2)
S 2R
where C is the concentration, K is the absorption coefficient, S is the scat-
tering coefficient, and R¼R % /100 (the percentage reflectance from the strip
divided by 100).
The K-M transform of the measured reflectance is approximately pro-
portional to the absorption coefficient and hence is approximately propor-
tional to the concentration, assuming that the scattering coefficient is