Dual Electrochemical Microsensor for Real-Time Simultaneous Monitoring of Nitric Oxide and Potassium Ion Changes in a Rat Brain during Spontaneous Neocortical Epileptic Seizure

In this work, we developed a dual amperometric/potentiometric microsensor for sensing nitric oxide (NO) and potassium ion (K+). The dual NO/K+ sensor was prepared :based on a dual recessed electrode possessing Pt (diameter, 50 mu m) and Ag (diameter, 76.2 mu m) microdisks. The Pt disk surface (WE1) was modified with electroplatinization and the following coating with fluorinated xerogel; and the Ag disk surface (WE2) was oxidized to AgCl on which K+ ion selective membrane was loaded-subsequent to the silanization. WE1 and WE2 of a dual microsensor were used for amperometric sensing of NO (106 +/- 28 pA mu M(-1)n = 10, at +0.85 V applied vs Ag/AgCl) and for potentiometric sensing of K+ (51.6 +/- 1.9 mV pK(-1), n = 10), respectively, with high sensitivity. In addition, the sensor showed good selectivity over common biological interferents, sufficiently fast response time and relevant stability (within 6 h in vivo experiment). The sensor had a small dimension (end plane diameter, 428 +/- 97 mu m, n = 20) and needle-like sharp geometry which allowed the sensor to be inserted in biological tissues. Taking advantage of this insertability, the sensor was applied for the simultaneous monitoring of NO and K+ changes in a living rat brain cortex at a depth of 1.19 +/- 0.039 mm and near the spontaneous epileptic seizure focus. The seizures were induced with 4-aminopyridine injection onto the rat brain cortex. NO and K+ levels were dynamically changed in clear correlation with the electrophysiological recording of seizures. This indicates that the dual NO/K+ sensor's measurements well reflect membrane potential changes of neurons and associated cellular components of neurovascular coupling. The newly developed NO/K+ dual microsensor showed the feasibility of real-time fast monitoring of dynamic changes of closely linked NO and K+ in vivo.