Improved Planar Amperometric Nitric Oxide Sensor Based on Platinized Platinum Anode. 1. Experimental Results and Theory When Applied for Monitoring NO Release from Diazeniumdiolate-Doped Polymeric Films

Abstract

An improved miniature amperometric nitric oxide sensor design with a planar sensing tip (ranging from 150 microm to 2 mm in diameter) is reported. The sensor is fabricated using a platinized platinum anode and a Ag/AgCl cathode housed behind a microporous poly(tetrafluoroethylene) (PTFE; Gore-tex) gas-permeable membrane. Platinization of the working platinum electrode surface dramatically improves the analytical performance of the sensor by providing approximately 10-fold higher sensitivity (0.8-1.3 pA/nM), approximately 10-fold lower detection limit (< or =1 nM), and extended (at least 3-fold) stability (>3 d) compared to sensors prepared with bare Pt electrodes. These improvements in performance arise from increasing the kinetics and lowering the required potential for the 3-electron oxidation of NO to nitrate, relative to that observed using a nonplatinized working electrode. The outer porous PTFE membrane provides complete selectivity for NO over nitrite ions (up to 10 mM nitrite). The new sensor is applied for surface measurements of NO released from diazeniumdiolate-loaded silicone rubber films (SR-DACA-6/N(2)O(2)). The effects of sensor size (for sensor dimensions of 0.15-, 1-, and 2-mm o.d.) and the distance of the sensor from the surface of the NO-emitting polymer film are investigated via experiments as well as theoretical calculations. A significant analyte trapping effect is demonstrated, the degree of which depends on the sensor size and its distance from the surface. It is further demonstrated that surface NO concentrations for fresh SR-DACA-6/N(2)O(2) loaded films are also influenced by the polymer film thickness, with thicker films generating higher surface concentrations of NO.

Real-time electrical detection of nitric oxide in biological systems with sub-nanomolar sensitivity

“…S7). The sensitivity of the sensor is 54 mS per 1,000 nM originally, and became 53 mS per 1,000 nM (98%) after 1 week and 47 mS per 1,000 nM (89%) after 3 weeks, which are comparable to the electrochemical sensors 7,12 . This signal drift is probably because of nonspecific surface adsorptions, and the stability of the device may be further improved through storage in a controlled environment.…”

“…Electrochemical NO-sensing electrodes allow for real-time detection of NO with high sensitivity and selectivity [11][12][13][14] . However, as the signal amplitude and sensitivity of electrochemical sensors are generally proportional to the electroactive surface area of the electrodes 13 , it is often difficult to simultaneously achieve high sensitivity and high-spatial resolution.…”

Real-Time Monitoring of Nitric Oxide Dynamics in the Myocardium: Biomedical Application of Nitric Oxide Sensor

“…Therefore, further surface modification with permselective membranes is required to achieve the desired selectivity for NO via size exclusion or electrostatic repulsion [4]. Indeed, several polymeric materials have been evaluated as gaspermeable or permselective membranes including nafion, collodion, polycarbazole, o-and m-phenylenediamine, poly(tetrafluoroethylene), cellulose acetate, and multilayer hybrids of these polymers [27,[30][31][32][33][34][35][36]. In particular, Shin et al reported that sol-gel-derived electrochemical sensors showed good sensitivity and selectivity for NO detection [17,27].…”

Electrochemical Sensors

“…100 The porous membrane effectively discriminated against potentially interfering nitrite ions, and the platinization was responsible for a 10-fold lower detection limit down to 1 nM), higher sensitivity and improved stability compared to bare platinum electrodes. This type of sensor was later modified with a thin hydrophilic polyurethane film containing catalytic copper sites that mediated the decomposition of S-nitrosothiols to NO for the fabrication of an electrochemical sensor for S-nitrosothiols.…”