Insertable Fast-Response Amperometric NO/CO Dual Microsensor: Study of Neurovascular Coupling During Acutely Induced Seizures of Rat Brain Cortex

This paper reports the fabrication of an insertable amperometric dual microsensor and its application for the simultaneous and fast sensing of NO and CO during acutely induced seizures of living rat brain cortex. NO and CO are important signaling mediators, controlling cerebrovascular tone. The dual NO/CO sensor is prepared based on a dual microelectrode having Au-deposited Pt microdisk (WE1, 76 μm diameter) and Pt black-deposited Pt disk (WE2, 50 μm diameter). The different deposited metals for WE1 and WE2 allow the selective anodic detection of CO at WE1 (+0.2 V vs Ag/AgCl) and that of NO at WE2 (+0.75 V vs Ag/AgCl) with sufficient sensitivity. Fluorinated xerogel coating on this dual electrode provides exclusive selectivity over common biological interferents, along with fast response time. The miniaturized size (end plane diameter < 300 μm) and tapered needle-like sensor geometry make the sensor become insertable into biological tissues. The sensor is applied to simultaneously monitor dynamic changes of NO and CO levels in a living rat brain under acute seizure condition induced by 4-aminopyridine in cortical tissue near the area of seizure induction. In-tissue measurement shows clearly defined patterns of NO/CO changes, directly correlated with observed LFP signal. Current study verifies the feasibility of a newly developed NO/CO dual sensor for real-time fast monitoring of intimately connected NO and CO dynamics

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, <i>n</i> = 10, at +0.85 V applied vs Ag/AgCl) and for potentiometric sensing of K⁺ (51.6 ± 1.9 mV pK^–1, <i>n</i> = 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, <i>n</i> = 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