Colorimetric Tubes

Low Cost Manufacturing of optical system to detect E. coli 0157 on the basis of
4-methyl-umbelliferyl ß-D-galactoside - Reaction ß-galactosidase.

Joseph Michael D. Racho, Erba V. Del Rosario, C. Karlen Dawala,
Dan R. Lawrence, and Raymond J. Sucgang * 1,
In cooperation with the
Chemists and educators' Support
Promoting science education relevant, Inc., CESARSED, Inc.
1R.J. Sucgang Center for Natural Science Research
NAPT, Batan, Aklan
Keywords: sensor, optical sensing, E. coli
This paper presents the manufacture of a handheld, easy to use sensor that detects contamination by deadly strains of E. coli in drinking water. E. coli 0157, especially 0157: H7, was identified as the causative agent of hemolytic uremic syndrome and ulcerative colitis. The sensor works based on irreversible color changes that occur after the hydrolysis of a chromogenic substrate by the enzyme beta-galactosidase of E. coli. Recognition materials, umbelliferyl 4-methyl-ß-D-galactoside has two components: a fluorescent dye and a quencher that is sensitive to cleavage by ß-galactosidase. In the absence of E. coli, the quencher binds to the dye and prevents fluorescence, while the interaction of ß-galactosidase with the results extinguisher dissociation of the complex ,7-hydroxy-4-methylcoumarin, which boasts a blue fluorescence.

The sensor uses an LED light source is shining on a photodetector. When the color reaction took place, the light passes through a beaker containing the sample, and a meter sensitive to light. A tube of clear water or other clear solution is white and has a zero absorbance. A fraction of incident light that is blocked by the sample can be used for the quantitative determination of the bacterial population in water. Population E. coli is related to the absorbance reading after Beer's law. The amount of incident light is transmitted and expressed in units of footcandles, with a light meter LX 104. The sensor has outstanding response throughout the range of 0.8 to 1.35 x107 x108 concentration E. coli CFU. The number of bacteria in each test solution was confirmed using the standard method germs. Excellent sensitivity and linearity (R2 = 0.984) was performed using the sensor, together with 6 repeated measurements by a particular concentration. The specificity of the detection system of E. coli, was tested by spiking the other bacterial strains (Staphylococcus aureus) during the fourth to sixth determination. The sensor is very selective and specific in its responses to E. coli. The cost of the sensor is very low, unlike the cost of acquiring a laboratory spectrophotometer.

This work has shown that the assembly of a sensitive, portable devices at low cost from an ordinary light meter, an LED light source, and traditional biochemical chromogenic reagents for the detection and quantification of bacterial populations is practical.