Pregnancy Test Color Sensor

Background

Home self-diagnostic assays are becoming a popular point-of-care tool due to their accessibility and low costs. Quantifying these assays have been shown using desktop scanners, cameras and smartphones which allows the user readily available and, in some cases, portable modes of diagnosis. These assays are quantified using a colorimetric strip reader that instead of using color intensity from an image, uses specific chromaticity values to construct a calibration curves of a concentration of a certain molecule present. Specifically, in pregnancy tests, the presence of a hormone called human chorionic gonadotropin (HCG) indicates that the user is pregnant.
The goal of this project is to develop a colorimetric strip reader that is integrated within a user interface in order to engage users with their test results. The test in this case would be based on a pregnancy test.

Project Aims

Aim 1: Develop A colorimetric strip reader

Use pH strips as a proxy
TCS3200 and Arduino color sensor
Requires mode of calibration
Account for ambient light
Resolution and error limits

Aim 2: Create a user interface

Engage user with Celebrated results

Long term aim: Develop a point-of-care app for smartphone

Increase accessibility to Diagnostics

Our project utilized a TCS3200 color sensor and an Arduino to read color from a sample strip. Due to our limitations for the project we utilized pH test strips to test the mechanism of color identification. If we had more time we would have liked to utilize hCG, a hormone released during pregnancy. We have been able to utilize the system to recognize the color of differing test strips and had the color code output into the serial terminal. The Arduino recognizes three ranges of color based on a color code, of a 0-0-0 pattern. Based on the colors and calibration set due to the ranges we can obtain 3 possibilities from our device. An inconclusive result comes from a too central color, the color neither being acidic or basic enough. And the two other possibilities are a positive (indicated by a red light) and a negative (indicated by a green light).

The Code

Our software was designed to take the analog output from the array of photodiodes, and analyze the result to determine results. By writing to specific pins on the photo TCS3200 chip, we can record output from the red, green, and blue photodiodes. This output is arbitrarily valued, based on scaling of the frequencies, however, it can be mapped to the appropriate RGB color model using the arduino’s map() function. Through trial and error, we were able to determine the ranges of RGB values for each specific color that we provided. Finally, using system logic, we can determine the color of the paper being tested in real time from the sensor. In the context of our project, the “pH” of the test sample can be analyzed instantly, with pregnancy results shown to the users in seconds.