Impedimetry and potentiometry for the design of paper-based biosensors

Monitoring water quality is of paramount importance, as demonstrated in the 2015 publication of the United Nations’ 17 Sustainable Development Goals (SDGs). Access to safe drinking water for all was placed sixth among the 17 goals to be achieved by 2030 [1]. The project that led to this master thesis aims at designing a Point-of-Care paper-based biosensors for bacteria detection. The Point-of-Care aspect is important because it allows water quality assessment at the place where it is consumed. This biosensor is designed to meet the ASSURED criteria (Affordable, Sensitive, Specific, User friendly, Rapid and robust, Equipment free and Deliverable to end users). This biosensor combines two main elements, the LFA and the detection method. Detection methods are colorimetric and electrochemical. Colorimetric detection is done by simple optical reading of the LFA. Within the framework of electrochemical detection, several options are available. This is where this master thesis comes in. Indeed, a comparison between two interesting electrochemical detections is carried out: the non-faradaic impedimetric detection and the potentiometric detection. These methods have the advantage of being cheap and easy to miniaturize. The comparison seeks to determine which detection should be encouraged in the future development of the biosensor. These detection methods are compared in three cases of variations of the sample characteristics. The sample may vary in conductivity, permittivity or permeability. The comparative analysis is also done in the case where the LFA has two kind of detection pad. One is constructed with a nitrocellulose membrane combined with a layer of polyester on one of its faces and the other without any polyester layer. The analyses are carried out on simplified systems. The LFA is simply represented by a nitrocellulose membrane alone. The conductivity and permittivity variations are simulated by model fluids such as Phosphate-Buffered Saline (PBS) and deionized (DI) water. Permeability variation is simulated by a variable spiral planar inductance. Simplified equivalent circuits are developed for each system. They are used to analyse the underlying physical charactesristics behind each observations.