Stephen P. Wren

Silver@graphene oxide nanocomposite-based optical sensor platform for biomolecules

In this report, a silver@graphene oxide (Ag@GO) nanocomposite-based optical sensor was developed for the detection of biomolecules such as dopamine (DA), ascorbic acid (AA), and uric acid (UA). An aqueous solution of Ag@GO was prepared using a simple chemical reduction method, and it showed a characteristic surface plasmon resonance (SPR) band at 402 nm. The SPR features of the Ag@GO nanocomposite were used for the detection of DA, AA, and UA. The SPR intensity-based limits of detection (LODs) of DA, AA, and UA were 49 nM, 634 nM, and 927 nM, respectively. The SPR band position-based LODs of DA, AA, and UA were 30 nM, 1.64 μM, and 2.15 μM, respectively. The present optical sensor was more sensitive to DA than to UA and AA. The interactions of the biomolecules with Ag@GO were studied based on density functional theory (DFT), and it was found that DA had more interaction than AA and UA. This novel Ag@GO nanocomposite is simple to prepare and showed excellent stability and sensitivity toward the detection of biomolecules.

Computational Design and Fabrication of Optical Fibre Fluorescent Chemical Probes for the Detection of Cocaine

A rationally designed fluorophore has been developed and has been incorporated into molecularly imprinted polymers, as the basis of the design of a sensor. Its use has allowed the fabrication of two different designs of fibre-optic chemical probes using an approach based on the change of the emitted fluorescence being related to the concentration of the desired species that was present. A high sensitivity to the drug Cocaine was achieved with each of the probes, showing positive changes in the fluorescence signal achieved in response to 1-100 μM solutions of the drug, in solution in aqueous acetonitrile. High sensitivity for Cocaine over a range of compounds was demonstrated for one of the probes (probe X) and detection of the drug is possible even in the presence of strong fluorescence interference. The work has also shown that probes of this type do not need to be discarded when used: re-use of probe X is possible using a straightforward washing procedure and the calibration performance was maintained.

Design and synthesis of a fluorescent molecular imprinted polymer for use in an optical fibre-based cocaine sensor

Previously, we have developed chemical sensors using fibre optic-based techniques for the detection of Cocaine, utilising molecularly imprinted polymers (MIPs) containing fluorescein moieties as the signalling groups. Here, we report the computational design of a fluorophore which was incorporated into a MIP for the generation of a novel sensor that offers improved sensitivity for Cocaine with a detection range of 1-100μM. High selectivity for Cocaine over a suite of known Cocaine interferants (25μM) was also demonstrated by measuring changes in the intensity of fluorescence signals received from the sensor.

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.

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.

A suite of optical fibre-based chemical sensors for environmental monitoring

This paper is to review the research activities at City University London in the development of a suite of optical fibre-based chemical sensors, including pH, humidity and heavy metal sensors, for environmental monitoring.

Glucose optical fibre sensor based on a luminescent molecularly imprinted polymer

An optrode able to detect glucose dissolved in water has been implemented. The device is based on the luminescence emission of a Molecularly Imprinted Polymer synthesized specifically for glucose detection, therefore its intensity changes in presence of glucose. This sensing material is attached onto a cleaved ended polymer-clad optical fibre and it is excited by light via 1x2 fibre coupler. The reflected fluorescence signal increases when it is immersed into glucose solutions and recovers to the baseline when it is dipped in ultrapure water. This reversible behaviour indicates the measurement repeatability of using such a glucose sensor.

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).