2 research outputs found
Simplified Nitrate-Reductase-Based Nitrate Detection by a Hybrid Thin-Layer Controlled Potential Coulometry/Spectroscopy Technique
A novel method for the detection
of nitrate was developed using
simplified nitrate reductase (SNaR) that was produced by genetic recombination
techniques. The SNaR consists of the fragments of the Mo–molybdopterin
(MO–MPT) binding site and nitrate reduction active site and
has high activity for nitrate reduction. The method is based on a
unique combination of the enzyme-catalyzed reduction of nitrate to
nitrite by thin-layer coulometry followed by spectroscopic measurement
of the colored product generated from the reaction of nitrite with
Griess reagents. Coulometric reduction of nitrate to nitrite used
methyl viologen (MV<sup>2+</sup>) as the electron transfer mediator
for SNaR and controlled potential coulometry in an indium tin oxide
(ITO) thin-layer electrochemical cell. Absorbance at 540 nm was proportional
to the concentration of nitrate in the sample with a linear range
of 1–160 μM and a sensitivity of 8000 AU M<sup>–1</sup>. The method required less than 60 μL of sample. Detection
of nitrate could also be performed by measuring the charge associated
with coulometry. However, the spectroscopic procedure gave superior
performance because of interference from the large background charge
associated with coulometry. Results for the determination of nitrate
concentration in several natural water samples using this device with
spectroscopic detection are in good agreement with analysis done with
a standard method
Carbon Nanotube-Loaded Nafion Film Electrochemical Sensor for Metal Ions: Europium
A Nafion film loaded with novel catalyst-free
multiwalled carbon
nanotubes (MWCNTs) was used to modify a glassy carbon (GC) electrode
to detect trace concentrations of metal ions, with europium ion (Eu<sup>3+</sup>) as a model. The interaction between the sidewalls of MWCNTs
and the hydrophobic backbone of Nafion allows the MWCNTs to be dispersed
in Nafion, which was then coated as a thin film on the GC electrode
surface. The electrochemical response to Eu<sup>3+</sup> was found
to be ∼10 times improved by MWCNT concentrations between 0.5
and 2 mg/mL, which effectively expanded the electrode surface into
the Nafion film and thereby reduced the diffusion distance of Eu<sup>3+</sup> to the electrode surface. At low MWCNT concentrations of
0.25 and 0.5 mg/mL, no significant improvement in signal was obtained
compared with Nafion alone. Scanning electron microscopy and electrochemical
impedance spectroscopy were used to characterize the structure of
the MWCNT–Nafion film, followed by electrochemical characterization
with Eu<sup>3+</sup> via cyclic voltammetry and preconcentration voltammetry.
Under the optimized conditions, a linear range of 1–100 nM
with a calculated detection limit of 0.37 nM (signal/noise = 3) was
obtained for determination of Eu<sup>3+</sup> by Osteryoung square-wave
voltammetry after a preconcentration time of 480 s