Review paper :
Nitric Oxide Electrochemical Sensor in Biomedical Research

OUT LINE

Nitric Oxide

Electrochemical Sensor

Principles of Detection

Commercial

Nitric Oxide

Nitric oxide or Nitrogen monoxide
is a chemical compound with chemical formula NO. This gas is an important signaling molecule in the body of mammals

NITRIC OXIDE

Molecular formula : NOMolar mass : 30.0061Appearance : colourless gasShape : Linear Melting point : 163.6C Boiling point : 151.7C

The nitric oxide molecule is a free radical, high reactivity

NO is a fundamental player in the fields of neuroscience, physiology, and immunology, and was proclaimed Molecule of the Year in 1992

NITRIC OXIDE

NO is messenger molecule involved in many physiological processes

Levels of NO production are important in protecting an organ such as the liver from ischemic damage.

Levels of NO production result in direct tissue toxicity to the vascular collapse associated with septic shock.

Chronic expression of NO is associated with various carcinomas and inflammatory conditions including juvenile diabetes, multiple sclerosis, arthritis and ulcerative colitis.

Technical applications

Although NO has relatively few direct uses, it is produced on a massive scale as an intermediate in the Ostwald process for the synthesis of nitric acid from ammonia. In 2005, the US alone produced 6M metric tons of nitric acid

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)2NO(g) + O2(g) 2NO2(g)3NO2(g) + H2O(l) 2HNO3(aq) + NO(g)4NO2(g) + O2(g) + 2H2O(l) 4HNO3(aq)

Biological functions

NO is signaling molecules in biological processes

Nitric oxide, known as the 'endothelium-derived relaxing factor', or 'EDRF', is biosynthesised endogenously from arginine and oxygen by various nitric oxide synthase (NOS) enzymes

Biological functions

NO is signaling molecules in biological processes

Nitric oxide, known as the 'endothelium-derived relaxing factor', or 'EDRF', is biosynthesised endogenously from arginine and oxygen by various nitric oxide synthase (NOS) enzymes

Endothelium-derived relaxing factor(EDRF)

Figure 1. L-arginine - nitric oxide system. B 2 , bradykinin B 2 receptor; cGMP, cyclic guanosine 3',5'-monophosphate; eNOS, endothelial nitric oxide synthase; GC, guanylate cyclase; GTP, guanosine 5'-triphosphate; M, muscarinic receptor; NO, nitric oxide; .OH, hydroxyl radical; ONOO - , peroxynitrite.

The Nobel Prize in Physiology or Medicine 1998

Robert F Furchgott Louis J Ignarro Ferid Murad

Discoveries concerning "the nitric oxide as a signalling molecule in the cardiovascular system".

Effects include blood vessel dilatation, neurotransmission modulation of the hair cycle, and penile erections. Nitroglycerin and amyl nitrite serve as vasodilators because they are converted to nitric oxide in the body

Popularly known by the trade name Viagra

Immune response

Nitric oxide is also generated by macrophages and neutrophils as part of the human immune response.

Nitric oxide is toxic to bacteria and other human pathogens.

Reactions

When exposed to oxygen, NO is converted into nitrogen dioxide.
2NO + O2 2NO2

NO react with oxygen and water to form HNO2 or nitrous acid.
4 NO + O2 + 2 H2O 4 HNO2

Preparation

nitric oxide is produced industrially by the direct reaction of O2 and N2 at high temperatures.

In the laboratory, it is conveniently generated by reduction of nitric acid:
8HNO3 + 3Cu 3Cu(NO3)2 + 4H2O + 2NO

or by the reduction of nitrous acid:

2 NaNO2 + 2 NaI + 2 H2SO4 I2 + 4 NaHSO4 + 2 NO
2 NaNO2 + 2 FeSO4 + 3 H2SO4 Fe2(SO4)3 + 2 NaHSO4 + 2 H2O + 2 NO
3 KNO2(l) + KNO3 (l) + Cr2O3(s) 2 K2CrO4(s) + 4 NO (g)

Some of the methods commonly used for
the determination of NO include

Chemiluminescence

Electron paramagnetic

Resonance (EPR) spectrometry

The Griess method

Spectrophotometric assays

They can not be used for continuous monitoring

or local measurement of NO concentrations in

real time.

Electrochemical techniques

i = nFCAke-(E-E0)(-nF/RT)

NO-electrochemical microsensors

Structure

Printed Screen

Nedle

Electrode

Carbon fiber

Pt

Glassy Carbon

Gold

NO-electrochemical microsensors

Modifier(s) Layer

Nafion

Cellulose

O-PD

NiTHMP

NiTMPyP

Neoprene

CytC-PITO

PolyCoTAPc

etc..

Problematic interfering

Nitrite

ascorbate

dopamine

Nafion

NO-electrochemical microsensors

Detection limit 0.5 nM

Carbon (fiber; o=30-40m;length=200-250 m)

NiTHMP1/Nafion3/AAO4/polylysine4

0.65V /Ag;AgCl

(aerated PBS, pH=7.4)

Activator for WPI nitric oxide sensors

NSA SPECIFICATIONS

Battery 1.5 V AAA

Applied Potential 860 mV

Battery Useful Life One year

1 mM

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