In this chapter, we deal mainly with the aspects of biosensor development related to specific areas of their application. It is definitely clear that biosensors that perform well in the laboratory can be utterly inappropriate outside the university walls. The gap between the laboratory pattern and a commercial product is intuitively understandable. The end-users want to receive a device that is robust, costeffective, simple to operate, and as sensitive as required for its purpose. As regards biosensors, the following aspects are imperative for the various stages of commercialization:• Stability of the biological component. The satisfactory working period estimated from the stability of the calibration parameters begins after six months. This is a rather mild estimate accepted by the medical services that are used to maintaining the unstable biochemicals that are necessary for conventional bioassays. In other areas, e.g., industry or environmental monitoring, the requirements can be stricter.• Operation/functioning convenience. To some extent, this is implied from the previous statements. A limited period of operation simply means the replacement of the sensing elements performed by an unqualified staff or an inexperienced buyer. In addition, mass production is hardly compatible with a complicated, multi-stage protocol of measurement. The simpler (faster, cheaper), the better. The producer should take into account that the customer might not be familiar with the specific conditions of biochemical reactions and will make very simple mistakes that a biochemist can't possibly make (buffers, order of reagents addition, temperature regime, etc.).• Analytical characteristics and metrology. The more complicated the sensor, the more difficult to establish the expected accuracy of the measurement. Concerning real samples assay, the main problems are focused on selectivity and signal drift. The biochemical recognition is sensitive enough to compete with most of the conventional instrumentation techniques, and this is one of the undisputable benefits always mentioned in research related to biosensor development. However, in real sample testing, the selectivity of the transducer can seriously limit the prospects of biochemical recognition. Careful consideration G. Evtugyn, Biosensors: Essentials, Lecture Notes in Chemistry 84,