Dr. Aleksandar Radu Profile

Dr. Aleksandar Radu

at Dublin City Univ

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Proceedings Article | 29 October 2007 Paper

Photo-switchable surfaces: a new approach to chemical sensing

Aleksandar Radu, Silvia Scarmagnani, Robert Byrne, Conor Slater, Nameer Alhashimy, Dermot Diamond

Proceedings Volume 6749, 67491Z (2007) https://doi.org/10.1117/12.737098

KEYWORDS: Surface plasmons, Metals, Ions, Light emitting diodes, Sensors, Absorbance, Ultraviolet radiation, Copper, Polymers, Cobalt

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Here, we discuss an interesting concept that brings an added flexibility in chemo/bio sensing. We present system that can be switched photonically between two states, only one of which exhibits ion-binding behaviour. The system is based on molecular photoswitch spiropyran, which is probably the most studied compound exhibiting above characteristics. Upon irradiation with UV light the passive spiropyran (SP) molecule undergoes a heterocyclic ring cleavage that results with the formation of the merocyanine (MC) which is zwitterionic form capable of ion binding. In contrast to the uncharged and colourless spiropyran form, the merocyanine form is highly charged and can be utilized as ligand for other charged species. Moreover, it is strongly coloured, and the colour tells us which form is present. In addition it provides interesting information about the immediate environment of the merocyanine binding site (e.g. polarity, presence of certain ions etc.). In this work, we present a SP-based system in which SP is immobilized and protected within a polymeric matrix. Such system may be used for detection of metal ions in highly polar solvents, e.g. water. The response characteristics and kinetics of MC-Cr³⁺ complex formation and SP-MC switching within the polymer matrix have been determined. Simple light emitting diodes (LEDs) have been employed for photoswitching and colorimetric measurement of SP-MC switching and MC-Cr³⁺ complex formation as light sources and detectors.

Proceedings Article | 29 October 2007 Paper

Ion-selective electrodes with polypyrrole- and poly(3-octylthiophene)-mediated internal solid contact in soil analysis

Tanja Radu, Aleksandar Radu, Dermot Diamond

Proceedings Volume 6749, 674922 (2007) https://doi.org/10.1117/12.737333

KEYWORDS: Electrodes, Lead, Soil science, Ions, Sensors, Polymers, Sensor networks, Solids, Diamond, Ion exchange

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The integration of chemo/bio sensors in large wireless sensing networks (WSN) is currently limited, largely due to the issues related with power consumption and data handling. Also, there are very few low cost chemo/bio sensors that combine sensitive, low limit of detection capabilities with simple experimental setup. However, with recent advances, ion-selective electrodes (ISEs) may become an excellent candidate for deployment in WSNs. In this paper, we describe a solid-contact electrode based on poly(3-octylthiophene) (POT) as an internal contact. We report its characteristics and its application to the for measurement of Pb²⁺ in 16 soil samples, with a ultimate goal of producing a small, simple and sensitive sensor that can be integrated into WSNs. The electrode had a detection in the soil digestion matrix (1×10^-3 M HNO₃) of 1×10^-7 M (20 ppb). The electrodes results were compared with atomic absorbtion spectrometry (AAS) as a common instrumental technique used in soil analysis. We also report on the performance of solid-contact ISEs based on polypyrrole (PPy) and POT. A superior detection limit of POT- relative to PPy-based ISEs was observed. Furthermore, a good correlation has been observed between POT-based ISEs and AAS and between the two types of ISEs.

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