Solvatochromic indicators for fiber optic chemical sensors

The goal of this thesis was to develop and evaluate solvatochromic indicators for fiber optic chemical sensors. Interaction with analyte modifies the polarity of the immobilized indicator environment leading to a shift in their fluorescence spectra. Three systems were studied. In the first study a cationic fluorescent probe, 5-dimethylaminonaphthalene-1-sulfonamidoethyltrimethylammonium ion (DA\sp+), was equilibrated with unmodified- and hydrocarbon bonded-silicas. In solution and unmodified silica, maximum DA\sp+ fluorescence shifts to longer wavelengths with increasing percentages of methanol, tetrahydrofuran and acetonitrile in water. On hydrocarbon bonded silicas, however, DA\sp+ emission maxima in water occur at shorter wavelengths indicating a very nonpolar environment. This indicates chat the organic fluorophor is excluded from the solvent and experiences primarily a surface environment. Added organic solvent competes with DA+ for the hydrocarbon surface, causing it to interact more strongly with the solvent. In the second study, 5-Dimethylaminonaphthalene-1-sulfonamidoethyltrimethylammonium ion (AEANS) immobilized on controlled pore glass, cellulose and poly(vinyl alcohol) (PVOH), was shown to respond to cationic surfactants including Dodecyl-, Tetradecyl- and Cetyl-trimethyl ammonium ions. The emission spectrum shifts to shorter wavelengths and increases in intensity with increasing surfactant concentration because surfactant forms an ion pair with AEANS causing its environment to be less polar. Both in solution and immobilized on solid substrates, AEANS responds more sensitively to cationic surfactant with longer hydrocarbon chain lengths. There is no significant response to anionic and nonionic surfactants. AEANS covalently bound to PVOH membranes was coupled to a fiber optic system for reversible in-situ determination of cationic surfactants. The third system involved a betaine dye, 2,6-diphenyl-4-(3,4,6-triphenyl-N-pyridinio) phenolate (ET30), immobilized in a silicone rubber membrane. At low concentrations immobilized ET(30) fluoresces strongly. Fluorescence intensity decreases and spectra shift to longer wavelengths when the membrane is exposed to increasing percentages of methanol in water. Response is reversible with a response time of several minutes. All systems studied undergo spectral shifts as a function of analyte concentration. This allows analyte to be related to an intensity ratio measurement at two wavelengths which compensates for changes in variables other than analyte concentration that affect the magnitude of the analytical intensity

Variation in the optical sensing properties of dithiocarbamate polymer microspheres as function of surface morphology

Three polymers with N-ethanolamino-, N-benzylamino-, and N-t-butylamino-dithiocarbamate groups were synthesized from polyvinylbenzylchloride. Each of the three polymers was incorporated in a hydrogel membrane (PVA) cross-linked with glutaraldehyde to form a sensing element. The latter was, then, evaluated for its optical sensing behavior by subjecting it to varying concentrations (1.0x10-5 up to 0.1 M) of metal ions (Zn2+, Cd2+, Pb2+, Hg2+,Ca2+, Mg2+, K+, Na+, Cr3+, Ni2+, Cu2+). Significant response was observed for the Hg2+ ions while the others showed negligible or no response. The turbidity absorbance increased consecutively from the dithiocarbamate polymer derived from N-t-butylamine towards that from ethanolamine as the concentration of the Hg2+ solution increased. The response time measured for the three polymer microspheres ranged between 2 and 30 minutes. The aminodithiocarbamate polymers were stable at normal temperatures (25ο - 40 ο C) and as pH was changed between 2 and 7. In addition, the polymers demonstrated excellent stability with time and a capacity of 3.967, 3.787, 3.355 mmol Hg2+ ions per gram of polymer for the N-ethanolamino-, N-benzylamino-, and N-t-butylamino-dithiocarbamate respectively. SEM and Eds analyses showed an increase in size of about 25% in the case of complexation with N-ethanolamino-, no size change with N-benzylamino-, and a 16.6% decrease in size with N-t-butylamino-dithiocarbamate.We are grateful to professor W.R.Seitz and his research group, of the University of New Hampshire (USA) for supplying us with the polymer polyvinylbenzylchloride.We are also grateful to professor M.Khamis of Al-Quds University for financial support for the SEM analyses

An Optical Sensor Based on Polyvinyl Benzyl Malonate Cross-Linked with Divinyl Benzene Dispersed in a Hydrogel Membrane for Detection of Some Heavy Metals

In previous work we have developed a dicarboxylate functionalized polymer that demonstrated chemical sensing. It showed good response to pH changes as well as to varying concentrations of copper and calcium ions. Our recent investi- gations showed interesting results upon testing the functionalized sensing polymer on heavy metals. This sensor is composed of microspheres of polyvinyl benzyl malonate lightly-cross-linked with divinyl benzene dispersed in a hy- drogel membrane. The response of the optical sensor is based on the interaction between the metal cations with the de-protonated functional group. The polymer, thus, undergoes shrinking as a result of neutralization of adjacent negative charges on the back-bone of the polymer. This causes significant changes in the optical properties of the sensing ele- ment. The optical changes were measured as absorbance vs. wavelength as the sensing membrane is exposed to solu- tions of varying concentrations of heavy metal ions. The sensor showed significant increase in absorbance up to a con- centration of 5 × 10–3 M to the following metal ions: Ni2+, Zn2+, and Cd2+. Furthermore, the studied capacity of the deri- vatized microspheres showed close values to Ni2+, Zn2+, Cd2+ (1.20, 1.09, 1.08 mmol/g respectively). These kinds of properly functionalized polymers appear to be suitable, versatile sensing elements for the detection of low concentra- tions of heavy metal ions. In addition, all of the tested heavy metals showed a similar value of the equilibrium formation constant, (log Kf1 is 2.63). In contrast, the sensor showed no significant response to varying concentrations of K+ and Mg2+ metal ions.The authors are indebted to the faculty of Science and Technology at Alquds University for financial support, and to George Mwangi, Necati Kaval and Huqun Liu at the University of New Hampshire for providing poly (vinylbenzyl chloride) microspheres

Polyvinylbenzyl Tris-Aminodicarboxylate Microspheres for the Optical Sensing of Cu2+ Ions

In this work, a tris(2-aminoethyl)aminodicaboxylate functionality was substituted for the chloride of polyvinyl- benzyl chloride (PVBC) which was lightly cross-linked (2%) with divinyl benzene. The resulting derivatized po- lymer microspheres were embedded in a hydrogel matrix of poly vinyl alcohol cross-linked with glutaraldehyde to produce a sensing membrane. The latter responded selectively to Cu2+ solutions of different concentration ranges (1 × 10−4 M to 1 × 10−6 M). The response is based on the interaction between the metal cations and the negatively charged deprotonated dicarboxylate functional group, which led to neutralization of the charges. As a result, an increase in the turbidity of the sensing membrane occurred which is attributed to a change in the re- fractive index of the derivatized polymer microspheres relative to that of the hydrogel. The change in the turbid- ity of the sensing membrane was measured as absorbance using a conventional spectrophotometer. It was found that Cu2+ ions bind to the aminodicarboxylated-polymer with a formation constant, Kf, of 1 × 105 M−1. SEM, Eds and IR analyses were performed on the aminodicarboxylated microspheres and their Cu2+ complex.We are grateful to Professor W. R. Seitz and his research group, at the University of New Hampshire (USA) for their fruitful comments and for supplying us with the polyvinylbenzyl chloride microspheres. We are also grateful to the staff at the department of chemistry of An-Najah National University (PA), for their technical assistance

Hexavalent Chromium Removal and Reduction to Cr (III) by Polystyrene Tris(2-aminoethyl)amine

A commercially available chelating polymer, polystyrene tris(2-aminoethyl)amine, was used for the removal of chromium from aqueous solution. The influence of pH, contact time, adsorbent dosage and initial Cr (VI) concentration on adsorption was studied. The optimum pH for the removal of Cr (VI) was at pH 5, while optimum contact time and adsorbent dosage were 120 minutes and 10 g/L, respectively. Total chromium and Cr (VI) concentrations were analyzed by ICP-MS and UVVisible. Adsorption isotherms using Langmuir and Freundlich isotherm models revealed that the data fitted Langmuir isotherm model better than Freundlich with a maximum adsorption capacity of 312.27 mg/g. FTIR spectroscopy, Scanning electron microscopy (SEM) and Energy Dispersive Spectrometry (EDS) analyses were performed on the adsorbent before and after binding Cr (VI). All analyses confirmed the complexation of Cr (VI) to the adsorbent. Desorption experiments using KCl solution indicated 89.3% release of chromium, rendering this method of high potential for adsorbent regeneration.We wish to thank Professor Dr. Z. Abdeen for his valuable financial support which made this work possible. We also wish to thank the Aquatic and Aquaculture Research Laboratory at Al-Quds University for performing the ICP-MS analysis

Optical Sensing Properties of Dithiocarbamate-Functionalized Microspheres, Using a Polyvinylpyridine-Polyvinylbenzyl Chloride Copolymer

In this study, a new modified optical chemical sensor based on swellable polymer microspheres is developed using a 5% copolymer of polyvinylpyridine-polyvinyl -benzyl chloride microspheres functionalized as the corresponding dithiocarbamate. This sensor demonstrated significant enhancements in sensitivity, dynamic range and response time. These improvements are related to the presence of pyridine in the polymer backbone, which is believed to increase the space between the groups, thus decreasing steric hindrance, and hence increasing substitution of the dithiocarbamate group. The hydrophilicity of pyridine also allows free movement of the solvent and analyte to and from the inside of the microspheres. These dithiocarbamate-derivatized polymer microspheres were embedded in a hydrogel matrix of polyvinylalcohol cross-linked with glutaraldehyde. This sensor responded selectively to Hg2+ solutions of different concentrations (1 × 10−5 M to 0.1 M). The observed turbidity measured as absorbance varied between 1.05 and 1.75 units at a wavelength of 700 nm. The response is based on the interaction between the metal cations with the negative charges of the deprotonated dithiocarbamate functional group, which led to neutratization of the charges and thus to polymer shrinking. As a result, an increase in the turbidity of the sensing element due to a change in the refractive index between the hydrogel and the polymer microspheres occured. The changes in the turbidity of the sensing element were measured as absorbance using a conventional spectrophotometer.We are grateful to W.R. Seitz and his research group at the University of New Hampshire (USA) for their fruitful comments and for supplying us with the copolymer polyvinylpyridinepolyvinylbenzylchloride. We are also grateful to the Palestinian Ministry of Higher Education and to A.E.D. (USA) for financial support

An Optical Chemical Sensor Based on Polymer Swelling and Shrinking using Dithiocarbamate-Polymer Microspheres

In this work, an optical chemical sensor based on a swelling and shrinking polymer has been developed. A dithiocarbamate functional group was attached chemically to the backbone of poly vinyl benzyl chloride which was lightly crosslinked with divinyl benzene. The derivatized polymer microspheres were dispersed in a hydrogel membrane to produce a sensing element. This modified membrane was used for sensing specific heavy metal ions, such as Hg2+. The response is based on the interaction between the metal cations with the negative charges of the deprotonated dithiocarbamate functional group, whereby the swellable polymer undergoes shrinking as a result of neutralization of the negative charges of this functional group. This complex formation of a metal cation with a dithiocarbamate functionality causes significant changes in the optical properties of the sensing element. Shrinking of the polymer microspheres resulted in a decrease in the optical transmission through the sensing membrane. This is due to the increasing difference in refractive indices between the microspheres and the dispersing hydrogel membrane. This sensor showed a good response particularly to mercury ion. There was insignificant response to H+ in the pH range 2 -13. In addition, there was no detectable response towards alkali, alkaline earth metals and other heavy metal ions such as Pb2+, Zn2+, and Cd2+.Acknowledgment We are grateful to professor W.R.Seitz and his research group, of the University of New Hampshire (USA) for their fruitful comments and for supplying us with P(VBC) polymer microspheres. We are also grateful to the Palestinian Ministry of Higher Education and to A.E.D. (USA) for financial support

Hexavalent Chromium Removal and Reduction to Cr (III) by Polystyrene Tris(2-aminoethyl)amine

A commercially available chelating polymer, polystyrene tris(2-aminoethyl)amine, was used for the removal of chromium from aqueous solution. The influence of pH, contact time, adsorbent dosage and initial Cr (VI) concentration on adsorption was studied. The optimum pH for the removal of Cr (VI) was at pH 5, while optimum contact time and adsorbent dosage were 120 minutes and 10 g/L, respectively. Total chromium and Cr (VI) concentrations were analyzed by ICP-MS and UVVisible. Adsorption isotherms using Langmuir and Freundlich isotherm models revealed that the data fitted Langmuir isotherm model better than Freundlich with a maximum adsorption capacity of 312.27 mg/g. FTIR spectroscopy, Scanning electron microscopy (SEM) and Energy Dispersive Spectrometry (EDS) analyses were performed on the adsorbent before and after binding Cr (VI). All analyses confirmed the complexation of Cr (VI) to the adsorbent. Desorption experiments using KCl solution indicated 89.3% release of chromium, rendering this method of high potential for adsorbent regeneration.Acknowledgements We wish to thank Professor Dr. Z. Abdeen for his valuable financial support which made this work possible. We also wish to thank the Aquatic and Aquaculture Research Laboratory at Al-Quds University for performing the ICP-MS analysis

Photonic hydrogel sensors

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified