# POC device for rapid oral pH determination based on a smartphone platform

## TL;DR

A smartphone-based POC device was developed to quickly and accurately measure oral pH using a colorimetric sensor, eliminating the need for traditional lab equipment.

## Contribution

The novel contribution is a portable, smartphone-integrated POC device for in situ oral pH measurement using a chitosan-based colorimetric sensor.

## Key findings

- The device measures pH in the range of 5.4 to 8.1 with 0.6% precision.
- The sensor has a stability of 50 days and provides results in just 1 minute.
- Validation against a pH-meter showed an average error of 2.4%.

## Abstract

Salivary pH serves as a valuable and useful diagnostic marker for periodontal disease, as it not only plays a critical role in disease prevention but also in its development. Typically, saliva sampling is collected by draining and spitting it into collection tubes or using swabs. In this study, we have developed a Point-of-Care (POC) device for in situ determination of oral pH without the need for complex instruments, relying solely on a smartphone as the detection device. Our system utilizes a non-toxic vegetable colourimetric indicator, immobilized on a chitosan membrane located on a disposable stick, enabling direct sampling within the buccal cavity. An ad hoc designed 3D-printed attachment is used to ensure accurate positioning and alignment of the stick, as well as isolation from external lighting conditions. A custom-developed smartphone application captures and automatically processes the image of the sensing membrane, providing the salivary pH results. After optimizing the cocktail composition, the developed sensors demonstrated the capacity to determine pH within a range of 5.4 to 8.1 with a remarkable precision of 0.6%, achieving a very short analysis time of just 1 min. A stability study conducted on the sensing membranes revealed a lifetime of 50 days. To validate the performance of our analytical device, we compared its results against those obtained from a calibrated pH-meter, using a group of individuals. The device exhibited an average error of 2.4% when compared with the pH-meter results, confirming its reliability and accuracy.

The online version contains supplementary material available at 10.1007/s00604-024-06227-1.