Analysis of Samples of Clinical and Alimentary Interest with Paper-based Devices

Paper has been present in our culture for more than two thousand years, traditionally used to represent value, store information, for communication, sanitary use, packaging and many more. Recently, this material was rediscovered as a valuable substrate for electronic applications, sensors and microfluidic platforms. In this chapter we will take a closer look at the chemical composition of paper, its structure, and how they influence analytical performence of paper-based devices. Short history of paper-based analytics will also be presented, going back as far as to the beginings of the Current Era. In the end more focus will be given to up-to-date applications of paper in analytical systems including novel possiblities in the areas of both architecture and detection.

This chapter describes the devices destined to quantify glucose, uric acid and cholesterol in biological samples with both colorimetric and electrochemical detection which were proposed in the course of this work. Glucose is one of the most critical for life compounds found in nature; clinically it is used to evaluate diabetes. The World Health Organization estimates that 347 million people suffer from this disease worldwide. High levels of uric acid are related to conditions such as gout,  Lesch-Nyan disease, obesity, diabetes, hypertension and renal dysfunction. Cholesterol can aggravate medical conditions through its toxic derivatives or by depositing in arteries leading to plaque formation (atherosclerosis). Literature review spans from importance of those three compounds, their methods of quantifications, later passing to enzyme immobilization methods and as some of the proposed devices work in flow conditions a short description of laws governing flow in the paper matrix is also included. This chapter contains detailed descriptions of systems with both colorimetric and electrochemical detection including architectures such as spot test, lateral flow assay and a tangential flow device. A thorough study of enzyme immobilization methods on paper is also presented. 

Desire to model, replace and improve human olfactory and taste systems drove scientists to develop new sensor arrays for gaseous and liquid samples. Design of those devices resembles biological recognition systems in which arrays of non-specific sensors present in the tongue or nose are used to gather information. This complex data is later processed and analyzed in the brain which provides decision about the sample (recognition, identification or quantification). Instead of brain, arrays of chemical sensors use methods of artificial intelligence and chemometry. In this study potentiometric sensors were chosen, as this technique is simple, low cost and does not require sophisticated equipment thus being consistent with the ideology of paper-based sensors. Development of an integrated system, with miniaturized reference electrode and using a minimum amount of sample was divided in three steps, each of them ending with a proof of concept application of proposed advances. First, individual, potentiometric, paper-based sensors were developed and used to discriminate forged water samples. In the next step an integrated Ag/AgCl reference electrode was introduced in the system which was used to classify 34 different beers. Last but not least, efforts were made to minimize sample volume and the final device was applied to discriminate 11 wine types.