| Fabrication of Low Cost Optical Detection | | | | to the dissociation of the complex |
| System For E. coli 0157 Based On | | | | ,7-hydroxy-4-methylcoumarin, giving off a |
| | | | blue fluorescence. |
| 4-Methyl Umbelliferyl- ß -D-Galactoside-- | | | | |
| ß-Galactosidase Reaction. | | | | The sensor uses an LED light source shining |
| | | | on a photodetector. When the colorimetric |
| Joseph Michael D. Racho, Erba V. Del Rosario, | | | | reaction has taken place, light shines |
| Karlen C. Dawal, | | | | through a beaker containing the sample, and |
| | | | onto a light-sensitive meter. A clear tube of |
| Dan R. Laurente, and Raymond J. Sucgang*1, | | | | water or other clear solution is the BLANK |
| | | | and has zero absorbance. A fraction of the |
| In cooperation with the | | | | incident light that is blocked by the sample, |
| | | | can be used for quantitative determination of |
| Chemists' & Educators' Support for the | | | | the bacterial population in the water. The |
| | | | E. coli population is related to the |
| Advancement of Relevant Science Education, | | | | absorbance reading, following Beer's law. The |
| Inc., CESARSED, Inc. | | | | amount of incident and transmitted light is |
| | | | expressed in foot candle units, by a LX 104 |
| 1R.J. Sucgang Center for Research in the | | | | light meter. The sensor shows outstanding |
| Natural Sciences | | | | response over the range of 0.8 x107 to 1.35 |
| | | | x108 CFUs E. coli concentration. The |
| Napti, Batan, Aklan | | | | bacterial numbers in each test solution has |
| | | | been confirmed using standard plate count |
| Keywords: Sensor, Optical detection, E.coli | | | | method. Excellent sensitivity and linearity |
| | | | (R2=0.984) has been achieved using the |
| This paper reports the fabrication of a | | | | sensor, working with 6 replicate measurements |
| handheld, simple to use sensor which detects | | | | per particular concentration. The specificity |
| contamination by deadly strains of E coli in | | | | of the sensing system to E. coli, was tested |
| drinking water. E. coli 0157, predominately | | | | by spiking other bacterial strains, ( |
| 0157:H7, has been implicated as the causative | | | | Staphyloccus aureus) during the 4th to 6th |
| organism of hemolytic uremic syndrome and | | | | determination. The sensor is highly selective |
| hemorrhagic colitis. The sensor works based | | | | and specific in its responses to E. coli. The |
| on irreversible color changes that occur | | | | cost of the sensor is very low in contrast to |
| subsequent to hydrolysis of a chromogenic | | | | the cost of acquiring a laboratory |
| substrate by a ß-galactosidase enzyme of | | | | spectrophotometer. |
| E.coli. The recognition material, 4-methyl | | | | |
| umbelliferyl- ß -D-galactoside has two | | | | This work demonstrated that assembly of a |
| components: a fluorescent dye and a | | | | sensitive, portable, low cost devices from an |
| "quencher" which is sensitive to cleavage by | | | | ordinary light meter, an LED light source, |
| ß-galactosidase. In the absence of E.coli, | | | | and traditional biochemical chromogenic |
| the quencher binds to the dye and prevents | | | | reagents for the detection and quantization |
| fluorescence, while the interaction of | | | | of bacterial populations is practical. |
| ß-galactosidase with the quencher results | | | | |