Microfluidic devices emerged in the early 1980s, establishing the feasibility of concepts such as "Lab-on-a-chip" and "Micro Total Analysis System" because on such a small scale, fluids behave differently allowing multiple analytical processes to be integrated into one platform. The idea of constructing portable analytical devices that are accurate, sensitive, cheap, and easy to handle was, and still is, very promising, especially in the area of therapeutic drug monitoring and personalized medicine.

While there is a tendency to think that the use of portable microfluidic devices for therapeutic drug monitoring is quite new, this is in fact incorrect and there are a few devices that have been used for many years. Measuring blood glucose levels is perhaps the oldest and well known example, and this has changed the way in which people with diabetes have been able to live their life. Other commercialized examples include measuring glucose and -hydroxybutyrate and also the very recent electrophoretic microdevice for measuring lithium from whole blood. But these are only the few examples that have made it to commercial reality and there is a long list of therapeutic drugs that need to be monitored. There have been some attempts published for examining parts of the problem, such as sample pretreatment or determination of analytes in pretreated samples, but there are very few examples of a truly integrated sample-in/answer-out device. Moreover, most of the effort is directed to analyze biomarkers for early diagnosis, not monitoring and improving treatment.

In this chapter, we will discuss some of the work in the development of portable lab-on-a-chip devices for the detection of pharmaceuticals in biological fluids, with an emphasis on therapeutic drug monitoring, but it should be realized that there are many other applications for which these devices may also find application. We discuss newly developed materials and how the different technologies can help to fill the gap between proof-of-concept trials and commercialization. Beside the technical challenges, we also discuss the other challenges that need to be faced before realizing the dream of personalized medicine.