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 μm) and Ag (diameter, 76.2 μm) 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 μM^-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 μm, 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.