Mahesh Uttamlal

Electropolymerised platinum porphyrin polymers for dissolved oxygen sensing

Fast response optical sensors for oxygen, based on luminescent electropolymerised porphyrin polymers, are described. The sensitivity of the electropolymerised polymers for oxygen detection was found to be dependent on the potential at which the polymers were formed. Results are presented for polymers formed at two different oxidation potentials and for two platinum porphyrins: Pt tetraphenylporphyrin (Pt-TPP) and Pt octaethylporphyrin (Pt-OEP). Sensitivities of the poly-Pt-TPP and poly-Pt-OEP films to dissolved oxygen, given by the Stern–Volmer quenching coefficients, were obtained from luminescence lifetime measurements and were 1.12 (mg l–1)–1 and 2.07 (mg l–1)–1, respectively. The response time, which was determined from luminescence intensity measurements, for the poly-Pt-OEP to a step change in oxygen concentration of 4.3 mg l–1 to 38.6 mg l–1 was 8 ms. The limit of detection obtained for the Pt-OEP based sensor was 0.06 mg l–1.

Development of a quasi-distributed optical fibre pH sensor using a covalently bound indicator

A quasi-distributed pH sensing system was developed to utilize information derived from evanescently excited fluorescence signals originating from sensor sites fabricated on an optical fibre. The sensor sites comprise a section of fibre core exposed by polishing upon which is laid down a sensing film. The film comprises a fluorescent indicator dye immobilized covalently within a hydrogel matrix which is then photopolymerized and attached covalently to the exposed fibre core. Position information is determined from the propagation delay of the returning signals. A system comprising eight sensors spaced at 10 m intervals along an optical fibre has been constructed and characterized. The sensors operate in the region pH 6-pH 8 with a response time of 500 s. The properties of the immobilized indicator dye are found to be similar to those of the dye in aqueous solution. Furthermore, the sensing films so created are found to be resistant to dye leaching.

A distributed optical fibre fluorosensor for pH measurement

Abstract A novel distributed optical fibre pH sensor is reported. The principle of operation of the system is based on the detection of time-resolved fluorescence originating at spatially separated sensor sites. Sodium Fluorescein is used as the pH indicator. The fluorophor is immobilised in porous sol-gel films laid over the fibre core. The distributed system has a spatial range of 100 m and a resolution of the order of 1 m. The pH range of the system is observed to be pH 7–11.

Characterization of an electropolymerized Pt(II) diamino phenyl porphyrin polymer suitable for oxygen sensing

The electropolymerization of di-phenyl-di-(4-aminophenyl)-porphyrin-Pt(II) and the application of this polymer to oxygen sensing using spectroscopic measurements is presented. The main advantage of this sensor is that the lumophore forms part of the sensing polymer. The absorption and luminescence spectra of the polymer retain the characteristic shape of the porphyrin monomer spectra indicating that the polymerization process does not perturb the porphyrin molecular orbitals. Images of the polymer surface obtained using atomic force microscopy suggest that a homogeneous polymer is formed and that the polymer structure grows in layers. The luminescence properties of this polymer are exploited for determining oxygen in the concentration range 0 to 0.2 atm (air). The weighted average luminescence lifetime of the polymer was found to vary from 63.7 ?s to 30.9 ?s in nitrogen and air environments respectively. The sensitivity of the polymer was determined from the Stern?Volmer plot which was linear over the concentration range studied giving a Stern?Volmer quenching constant (KSV) of 5.05 ? 0.14 atm?1.

Effect of polymer strengtheners on the local environment of biocompatible glass as probed by fluorescence.

Mixed silica–calcite matrices were prepared by developing a “low” temperature (sol–gel) method in presence of several biocompatible polymers, thus providing samples with adequate porosity for the flow of biological fluids and also mechanically robust. In order to analyse and characterise the sample’s microenvironments, the highly solvatochromic probe Nile red was used, which enabled the role of polymer addition upon local environmental effects in the host media to be elucidated. The polymers used were polyethylene glycol, polymethylmethacrylate and polyethylene. Each matrix was also characterized with respect to microstructure, morphology and pore size via the use of X-ray diffractometry and scanning electron microscopy.The results show that is was possible to obtain, in a controlled way, mixed silica–calcite matrices with a wide range of porosities (important if the material is to be used for scaffold or drug release applications, for example). The spectroscopic behaviour of Nile red when incorporated has confirmed the existence of distinct and specific local polarities within each type of matrix that may determine to a large extent the mechanism of interaction between these matrices and biological molecules.

Quasi-distributed pH sensor

A Quasi-distributed pH sensing system based on Optical Time Domain Reflectometry (OTDR) was developed to determine the spatial and intensity information from fluorescence signals coupled back into a single fiber. The evanescent wave due to a 488 nm light pulse from a N2 pumped dye laser was used to excite a pH sensitive fluorophore and the emission around 515 nm was detected. A 3dB Y-coupler was used to convey excitation light to the sensing sites and to deliver emission signals from these sites back to a filtered photomultiplier tube. Data collection was performed using a HP 54540A 500 MHz digital scope and analysis was carried out using a dedicated Pentium 166 MHz PC. A reproducible laboratory fabrication process was developed to produce sensing sites at discrete intervals along the length of the fiber. A polishing process carefully removed the cladding at each sensing site and photo- polymerization was then used to covalently bind the fluorophore fluorescein with a co-polymer directly onto the site. The results show the sensors performance over a range of pH4-pH10 with a pKa value of 6.3. The present system was chosen to have sites 10 m apart, however, based on the propagation rate of 5 ns m-1 for light in the fiber and 10 ns for the fluorescence lifetime, a resolution of approximately 1 m is possible.

Characterization of a quasi-distributed optical fiber chemical sensor

A distributed optical fiber pH sensor based on time resolved fluorescence is investigated. Fluorescein sodium was chosen as a pH indicator for this work because of its well known properties and high fluorescent intensity. A low temperature sol-gel glass manufacturing process was utilized to immobilize the indicator onto the optical fiber core. Thin (approximately 1 micrometer) porus glass films were deposited on the surface of the optical fiber core with indicator molecules entrapped in the matrix. An OTDR technique was employed to obtain the signal at specific positions along the fiber. A dye laser, pumped by a N2 laser, produced 1 ns light pulses at 490 nm which were launched into a 1 by 2 optical fiber coupler. A 100 meter fiber with eight sensor sites was spliced to the coupler. The indicator molecules were excited via the evanescent wave. Part of the fluorescent emission from the indicator molecules was coupled back into the fiber and transmitted back to the coupler. A fast PMT tube was attached to the other arm of the 1 by 2 coupler to detect the fluorescent light. Results were obtained for solutions of various pH value in the range 6 - 12. The system appears to have potential for applications in environmental and safety monitoring.

The use of nanotechnology in the development of a distributed fibre-optic temperature sensor for subsea applications

Monitoring temperature in subsea pipelines and processing plants is paramount to ensuring the efficient extraction of oil and gas. Preliminary results from studies of an alternative optical temperature sensing methodology based on the fluorescence spectroscopy of quantum dots (QDs) immobilised in a sol-gel thin film are presented. A discussion of the potential for this approach to oil and gas industry applications is given.

Scanning electron microscopy analysis of sol-gel derived biocompatible glass

Bioactive silica gels/polymer systems have been produced using a sol-gel route and their bio-compatibility has been investigated by immersing them in simulated body fluid (SBF). The porous monoliths have been characterised by SEM and EDX analysis where images obtained show pores on the surface of 10–200 μm. The silica gels are not homogeneous and distinct regions of silicon and calcium are observed. The growth of an apatite layer on the surface of the gels was evident after steeping in SBF.

Immobilization of a calcein derivative onto optical fibers for calcium ion sensing

This paper describes a new fiber-optic calcium ion sensor using the calcein derivative, calcein acrylamide. Calcein acrylamide (CA) is a fluorescent indicator with a sensitivity for calcium ions at pH greater than 10. Ca2+ binds with CA with a binding ratio of 2:1 ratio therefore the concentration range for Ca2+ sensing depends on the amount of indicator present. Typically, calcium can be detected in the range 0 to 20 micrometers ol 1-1. The indicator can be covalently immobilized within a polymer matrix which itself is covalently immobilized onto a chemically modified optical fiber using photo-initiated polymerization. Three Ca2+ sensitive polymers are presented; CA in (1) poly-hydroxyethyl methacrylate (poly- HEMA), (2) poly-acrylamide and (3) poly-N-vinyl-pyrrolidinone (n-VP). The sensitivity of the immobilized CA are similar to that of CA in free solution.