In vivo monitoring of calcium ions in rat cerebrospinal fluid using an all-solid-state acupuncture needle based potentiometric microelectrode.

Acupuncture needles are regarded as ideal materiel for the development of microelectrodes for in vivo sensing. In this work, an all-solid-state ion-selective microelectrode (ISμE) has been developed by coating a calcium ion-selective membrane on an acupuncture needle tip with a diameter of less than 80 μm, which is modified with poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) as solid contact. The proposed Ca2+-ISμE shows a Nernstian response toward Ca2+ in the range from 1.0 × 10-6 to 3.1 × 10-3 M with a slope of 30.8 ± 0.9 mV/decade (R2 = 0.999), and the detection limit is 1.2 × 10-7 M. The Ca2+-ISμE has been used for in vivo monitoring of the calcium changes in rat cerebrospinal fluid (CSF) under the injury of spinal cord transection. The results demonstrate that the calcium concentration in CSF increases sharply from the normal level of 20.6 ± 1.72 μM (n = 3) to 133.2 ± 7.63 μM (n = 3) with a severe fluctuation after spinal cord damage. Thus, the proposed Ca2+-ISμE is available for in vivo monitoring of calcium ions with high temporal resolution and flexibility. The detection system can be extended to measure other ions in CSF by changing different ion-selective membranes.