Low-Cost Optical pH Sensor with a Polyaniline (PANI)-Sensitive Layer Based on Commercial Off-the-Shelf (COTS) Components

Abstract

In this paper, we presented a novel, compact, conceptually simple, and fully functional low-cost prototype of a pH sensor with a PANI thin film as a sensing layer. The PANI deposition process is truly low-cost; it performs from the liquid phase, does not required any specialized equipment, and comprises few processing steps. The resulting PANI layer has excellent stability, resistance to solvents, and bio- and chemical compatibility. The pH sensor’s sensing part includes only a few components such as a red-light-emitting diode (LED) as a light source, and a corresponding photodiode (PD) as a detector. Unlike other PANI-based sensors, it requires no sophisticated and expensive techniques and components such lasers to excite the PANI or spectrometry to identify the PANI color change induced by pH variation. The pH sensor is sensitive in the broad pH range of 3 to 9, which is useful for numerous practical applications. The sensor requires a tiny volume of the test specimen, as little as 55 µL. We developed a fully integrated packaging solution for the pH sensor that comprises a limited number of components. The pH sensor comprises exclusively commercial off-the-shelf (COTS) components and standard printed circuit boards. The pH sensor is assembled using standard surface mounting technology (SMT).

Design Aspects for Portable LED-Based Colorimetric Characterisation Systems Targeting Liquid Analytes

“…A white LED is used to illuminate the sample, and the three channels of an RGB sensor are used to obtain a quantitative evaluation of the analyte’s pH. This enables pH measurement over the whole pH range, compared to colorimetric pH measurement systems based on a single reagent and a single photodiode [ 9 ].…”