Yejin Ha

Measurements of Location-Dependent Nitric Oxide Levels on Skin Surface in relation to Acupuncture Point.

Location-dependent skin surfaces partial nitric oxide pressure (pNO) is studied using highly sensitive amperometric NO microsensor with a small sensing area (diameter  = 76 μm). The pNO level of LI4 (Hegu) acupuncture point is measured and compared with the pNO level of nonacupuncture point. In addition, the mapping of pNO is carried out over the left wrist skin area one- as well as two-dimensionally. Statistically higher pNO levels near the position of acupuncture points than non-acupuncture points are observed consistently, implying tight relationship between the level of NO release of skin and acupuncture points. The amperometric planar NO microsensor successfully monitors the heterogeneity of skin pNO distribution in high spatial resolution due to its advantageous features such as high sensitivity and small sensing dimension. The current study suggests the direct connection between NO and acupuncture points and possibly provides beneficial information to understand physiological roles and basis of the acupuncture points.

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.

Heterogeneity of Skin Surface Oxygen Level of Wrist in Relation to Acupuncture Point

The distribution of partial oxygen pressure (pO2) is analyzed for the anterior aspect of the left wrist with an amperometric oxygen microsensor composed of a small planar Pt disk-sensing area (diameter = 25 μm). The pO2 levels vary depending on the measurement location over the wrist skin, and they are systematically monitored in the analysis for both one-dimensional single line (along the wrist transverse crease) and two-dimensional square area of the wrist region. Relatively higher pO2 values are observed at certain area in close proximity to the position of acupuncture points with statistical significance, indicating strong relationship between oxygen and acupuncture point. The used oxygen microsensor is sensitive enough to detect the pO2 variation depending on the location. This study may provide information helpful to understand possible physiological roles of the acupuncture points.

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(+) sensors 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.

Selectivity Enhancement of Amperometric Nitric Oxide Detection via Shape-Controlled Electrodeposition of Platinum Nanostructures

Nitric oxide (NO) is a biologically multifunctional gaseous signaling molecule. For electrochemical NO detections, complex membranes are commonly adopted to acquire the selectivity for NO over other oxidizable biological species. In this study, we demonstrate the improved selectivity in amperometric NO measurements at nanostructured Pt. The Pt layers were electrodeposited on Au substrate electrodes at a constant potential (-0.2 V vs. Ag/AgCl) with a constant deposition charge (0.08 C). The various distinctive nanostructures of Pt deposits were obtained via either changing the precursor concentrations (from 5 to 75 mM K2PtCl4) or using a different precursor (75 mM H2PtCl6). With a higher K2PtCl4 concentration, the Pt deposition became less sharp and the smoothest Pt was deposited with 75 mM H2PtCl6. The most greatly sharp-pointed nanostructures were generated with the lowest precursor concentration (5 mM K2PtCl4) and exhibited the highest sensitivity, which was attributed to the hydrophobic property of sharply nanostructured Pt. A hydrophobic neutral gas molecule, NO, possibly has a more favorable access to the inner surface of more hydrophobic Pt deposition and eventually increases the oxidation current. NO current sensitivity was enhanced at the more hydrophobic Pt surface, whereas the oxidation currents of acetaminophen, l-ascorbic acid, nitrite and hydrogen peroxide, four oxidizable biological interfering species, were independent of the Pt nanostructure. Conclusively, the enhanced amperometric selectivity to NO was achieved by the simple electrodeposition method without any additional membranes.

Insertable NO/CO Microsensors Recording Gaseous Vasomodulators Reflecting Differential Neuronal Activation Level with Respect to Seizure Focus

Nitric oxide (NO) and carbon monoxide (CO) are important signaling molecules shaping vasomodulation. This paper reports simultaneous in vivo monitoring of NO, CO and dendritic summation of action potential at three different cortical regions: seizure focus and two additional places, vertically and horizontally separated by 1.2 mm from the seizure focus, during epileptic seizure induced by 4-aminopyrindine injection. An amperometric dual microsensor having a high spatiotemporal resolution monitored fast and dynamic changes of NO and CO, and neural changes were recorded with a glass pipet electrode for local field potential (LFP). At all three locations, onsets and offsets of NO and CO changes well synchronized with fast LFP changes, while the patterns and concentrations of NO and CO changes were varied depending on the sensing locations. The insertable NO/CO dual microsensor was successful to measure intimately linked NO and CO in acute seizure events with high sensitivity, selectivity, and spatiotemporal resolution.