Sensors in vivo

Peterson / Goldstein 1984 fiber optic oxygen in vivo sensor (1 mm i.d.)... 

D.Z. Levine and M. Iacovitti, Real time microelectrode measurement of nitric oxide in kidney tubular fluid in vivo. Sensors 3, 314 (2003). 

Shin JH, Schoenfisch MH. Improving the biocompatibility of in vivo sensors via nitric oxide release. The Analyst 2006, 131, 609-615. 

SWNT-based glucose sensors an enzyme-based sensor and an affinity sensor. These results are a promising beginning however, there is much work left to do before the promise of SWNT in vivo sensors is realized. Investigation of new sensing modalities and optimization of current ones is necessary before the best nanotube-based sensing strategy is discovered. 

Fig. 2. Photograph of a flexible polyimide-based in vivo sensor for glucose, lactate and pH measurements...

The problems that occur with in vivo experiments are not completely solved. The points where the implanted electrodes cause tissue damage are rapidly regenerated and covered by conjunctive tissue or even by antibodies from electrode rejection. The formation and growth of conjunctive tissue is influenced by the form and nature of the electrode material. A material s biocompatibility is defined as its ability to perform with an appropriate host response in a specific application51. Therefore it is important to develop biomaterials for in vivo sensor applications, since neither the conjunctive tissue nor the antibody layer on the electrode is conducting, and a large decrease in electrode response after implantation is observed. 

Relevant issues still to be addressed in constructing amperometric enzyme sensors either using the electrical wiring of enzymes with redox polymers or with flexible polymeric electron mediators are sensor efficiency, accuracy, reproducibility, selectivity, insensitivity to partial pressure of oxygen, detectivity (signal-to-noise ratio) as well as sensor hfetime and biocompatibility [47]. Then we can address manufacturability and the cost of use of either in vitro or in vivo sensors. 

Zhang LR, Xing D,. Wang JS. A non-invasive and real-time monitoring of the regulation of photosynthetic metabolism biosensor based on measurement of delayed fluorescence in vivo. Sensors 2007 7 52-66. 

Sensor temperature coefficient and time response are also variables to be understood. Temperature may shift the pKa of the dye and change the cell thickness, and will certainly affect the actual value of the blood gas variables of the blood that is adjacent to the sensor. For these reasons, a complete blood gas sensor includes a local temperature sensor, particularly if the sensor is to be placed in a peripheral artery where local temperature may not be equal to central body temperature. The chemical sensor temperature coefficient must be well characterized so that it will accurately measure the local blood gas value. Bench analysers usually measure blood samples at 37 °C so the in vivo system must then adjust the measured value to that temperature. The temperature coefficient of the blood gas variables, in blood, may be several percent per degree, and, in the case of Foj, depend very strongly on the actual value. Thus, to make the in vivo sensor agree with bench analysers, local temperature sensing must have an accuracy of better than 1 °C. Size and accuracy requirements can be met by a miniature thermocouple. The system designer has to make sure that the temperature circuit can handle the microvolt signals with adequate accuracy and stability as well as meet patient electrical isolation requirements. 

Two serious problems are encountered in the design, manufacture, and performance of in vivo sensors the lack of biocompatibility of the materials used and the poor long-term stability. The latter, however, plays only a minor role in the case of disposable optodes, which are in use only for the duration of a particular operation or test. Disposable sensor heads for clinical analytes seem to be the most promising candidates for practical use at present. Another problem results from the need for sterilization, which is difficult to solve in the case of biosensors with their thermally labile components such as enzymes. 

In Vivo Sensors for pH, Oxygen, Carbon Dioxide, and Electrolytes... 

In vivo sensors and other sensors for biologically relevant processes ... 

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