Thread-based microfluidic sensor for lithium monitoring in saliva

Lithium administration is a commonly prescribed treatment for some mental disorders, e.g. bipolar disorder. However, Li+ level must be regularly monitored to maintain therapeutical effect and avoid adverse side effects. Currently, it is determined in blood, using complex instrumentation, which excludes self-monitoring of lithium concentration by patients themselves. That creates a need for simple, reliable and fast sensors for Li monitoring in biological fluids. In this paper, we introduced a microfluidic thread-based analytical device for optical determination of lithium in saliva. Lithium ion recognition was achieved by incorporating of chromoionophore-ionophore chemistry onto thread. To ensure appropriate selectivity over other alkaline metal ions, it was necessary to include an efficient lithium extractant in the sensing cocktail, alongside its usual components. After optimization of cocktail composition, the developed sensors allowed for lithium determination in a range from 8.8 center dot 10(-4) to 0.95 mol L-1 with remarkable precision of 0.3% (at 10(-2) mol L-1) and within a very short time of ca. 10 s. The analytical usefulness of the developed sensors was tested with saliva samples, which were analyzed without any prior processing. A comparison of the obtained results with a reference method revealed high accuracy (relative error < +/- 20% in most cases).