Concentration clinical diagnostic analytes

In clinical diagnostics, one of the most commonly used analytical techniques for chemical analysis of body fluid samples is spectrophotometric analysis (the study of the interaction of electromagnetic radiation with chemical compounds). Biological molecules interact in some way with many different parts of the electromagnetic spectrum. Spectrophotometry is a very popular technique and can be used to determine the concentration and/or amount of a particular analyte, determine the structure of a new compound, identify a specific compound, and determine the activity of a specific enzyme, among others. The spectrophotometric detection methods are briefly reviewed in the following paragraphs. More detailed information can be found in books such as [3]. 

Similar to quantitative methods, qualitative tests should also undergo a method validation. The measuring system of a qualitative test usually transforms a quantitative result into a negative or positive report or in some cases a semi-quantitative outcome however, the absolute numerical concentration of the analyte itself is not reported. Qualitative tests can be validated by using a series of samples with known concentrations of analyte that fall either side of the positive-negative cut-off. These known values may be assigned by an alternative method, or may be reference material. It is particularly important to assess reproducibility of results around a concentration of the analyte of interest that is clinically important such as around a diagnostic cut-off. A method comparison study can also be undertaken with a comparator. The new method can usually be implemented when predefined criteria are fulfilled. 

In contrast to other analytical methods, ion-selective electrodes respond to an ion activity, not concentration, which makes them especially attractive for clinical applications as health disorders are usually correlated to ion activity. While most ISEs are used in vitro, the possibility to perform measurements in vivo and continuously with implanted sensors could arm a physician with a valuable diagnostic tool. In-vivo detection is still a challenge, as sensors must meet two strict requirements first, minimally perturb the in-vivo environment, which could be problematic due to injuries and inflammation often created by an implanted sensor and also due to leaching of sensing materials second, the sensor must not be susceptible to this environment, and effects of protein adsorption, cell adhesion, and extraction of lipophilic species on a sensor response must be diminished [13], Nevertheless, direct electrolyte measurements in situ in rabbit muscles and in a porcine beating heart were successfully performed with microfabricated sensor arrays [18],... 

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