T. Hien Nguyen

Development of intrinsic optical fiber pH sensors for industrial applications

The development of intrinsic optical fiber pH sensors based on fluorescence from novel coumarin dyes which are covalently immobilized onto the distal end of the fiber is described. The sensors provide response in the pH range of 0.5–6 with good stability over 24 h. The response time of the sensors is approximately 25 s. The sensors show no sensitivity to ionic strength (IS) and have excellent photostability.

A fibre-optic chemical sensor for the detection of cocaine

A fibre-optic chemical sensor for the detection of cocaine has been developed, based on a molecularly imprinted polymer (MIP) containing a fluorescein moiety as the signalling group. The fluorescent MIP was formed and covalently attached to the distal end of an optical fibre. The sensor exhibited an increase in fluorescence intensity in response to cocaine in the concentration range of 0 - 500 μM in aqueous acetonitrile mixtures with good reproducibility over 24 h. Selectivity for cocaine over others drugs has also been demonstrated.

Preparation of a novel drug sensor using a molecular imprinted polymer approach

A chemical sensor for the detection of cocaine has been developed, based on a molecularly imprinted polymer (MIP) containing a fluorescein moiety as the signalling group. The fluorescent MIP was formed and covalently attached to the distal end of an optical fibre. The sensor exhibited an increase in fluorescence intensity in response to cocaine in an aqueous acetonitrile mixture. Selectivity for cocaine over codeine has been demonstrated.

Development of a fiber-optic chemical sensor for the detection of cadmium

The detection of cadmium in the environment is very important and in this work the development of an optical fiber chemical sensor for the detection of Cd2+ is described. To achieve this, an optical fiber-based technique has been developed using a sensing layer containing a coumarin fluorophore and dipicolylamine receptor. This was covalently attached to the distal end of an optical fiber and exhibited a significant increase in fluorescence intensity in response to Cd2+ in the μM concentration range via a photoinduced electron transfer (PET) mechanism. Selectivity for Cd2+ over other metal ions has also been demonstrated showing the value of the approach for environmental measurements.

Surface plasmon resonance based fibre optic chemical sensor for the detection of cocaine

A surface plasmon based fibre-optic chemical sensor for the detection of cocaine has been developed using a molecularly imprinted polymer (MIP) film with embedded gold nanoparticles as the recognition element. The MIP was formed on the layer of gold thin film which was deposited on the surface of a fibre core. The sensing was based on swelling of the MIP film induced by analyte binding that shifted the resonance spectrum toward a shorter wavelength. The sensor exhibited a response to cocaine in the concentration range of 0 - 400 μM in aqueous acetonitrile mixtures. Selectivity for cocaine over other drugs has also been demonstrated.

Fluorescent optical fibre chemosensor for the detection of mercury

This work aims to develop a stable, compact and portable fibre optic sensing system which is capable of real time detection of the mercury ion (II), Hg2+. A novel fluorescent polymeric material for Hg2+ detection, based on a coumarin derivative (acting as the fluorophore) and an azathia crown ether moiety (acting as the mercury ion receptor), has been designed and synthesized. The material was covalently attached to the distal end of an optical fibre and exhibited a significant increase in fluorescence intensity in response to Hg2+ in the μM concentration range via a photoinduced electron transfer (PET) mechanism. The sensor has also demonstrated a high selectivity for Hg2+ over other metal ions. A washing protocol was identified for sensor regeneration, allowing the probe to be re-used. The approach developed in this work can also be used for the preparation of sensors for other heavy metals.

Application of a fluorescence intensity ratio technique for the intrinsic determination of pH using an optical fiber sensor

An intensity ratio technique has been used for characterizing fluorescence spectra from novel coumarin dyes for pH sensing, in the range of 0.5 – 6, providing results that are independent of possible fluctuations in the intensity of the excitation source, deterioration of the indicator and changes in optical coupling. The arrangement was determined to have a sensitivity of 25% per unit pH change (at a pH of 4).

P2.3.16 yFibre optic pH sensor for Corrosion Monitoring in Concrete Structures

The development of a fluorescence-based optical fibre pH sensor designed specifically for monitoring the high pH condition of concrete utilizing a novel pH sensitive fluorescent polymer is discussed in this paper. The sensor provides a response over the required pH range for concrete monitoring of 10.0 ‐ 13.2, having shown a very good stability over a period of longer than 20 months thus far. The sensor has also demonstrated little cross-sensitivity to ionic strength (IS) and excellent photostability in a series of laboratory tests carried out. These features make this type of sensor potentially well suited for the conditions required for long term in-situ monitoring of pH in concrete structures.

An optical fibre salinity sensor based on fluorescence quenching mechanism

Salinity measurement is very important for many industrial applications and in this work an intrinsic optical fibre-based salinity sensor is developed specifically for the detection of the salt water concentrations. The sensing principle was based on the fluorescence quenching as a result of the interaction between the sensing material incorporated into the tip of an optical fibre and target chloride ions in salt solutions. The peak intensity of the fluorescent signal generated has shown to change with the change of the salinity of the solutions measured. The experimental data obtained are in good agreement with a modified theoretical model when the hydrophobicity of the silicone supporting material is taken into account, thus demonstrating a clear feasibility of the developed sensor system of this type.