title: 'Rough guide' evanescent wave optrode for colorimetric metalloporphyrine sensors.
abstract: When films of zinc 5-(4-carboxyphenyl),10,15,20-triphenyl porphyrin (ZnTPP) are exposed to waterborne amine in pH- neutral or alkaline media, both Q- band and Soret band respond with a change of absorbance due to the donation of amine 'lone pair' electrons to the metalloprophyrin π orbital. However, this is difficult to reveal with a conventional spectrometer even under high amine concentration. We therefore introduce optical fibres coated with ZnTPP into a bespoke 'light balance' evanescent wave absorbance meter [doi:10.1016/j.snb.2016.05.065]. The light balance makes absorbance changes clearly visible under only 5μM aqueous amine, making PVC membranes redundant. We find sensitivity is higher, and limit- of- detection lower, in the Soret band rather than the Q- band, reflecting the stronger Soret band absorbance. Also, we find that sensitivity is higher, and limit- of- detection approximately two times lower, when rough rather than smooth fibres are used. We believe the rough fibre surface leads to enhanced evanescence, and therefore better overlap of the wave propagating in the fibre with the ZnTPP fibre cladding. We find a limit of detection to waterborne amines below 1μM, which compares well to other sensors for waterborne amines [Korent, S.M. et.al. Anal. Bioanal. Chem. 387 (2007) 2863-2870; Algarni, S. A. et.al. Talanta 153 (2016) 107-110]. We therefore recommend 'rough guide' evanescent wave optrodes, in combination with sensitive 'light balance' detector, to succeed membrane- embedding of colorimetric sensitisers such as metalloporphyrines.
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, S3 7RH Sheffield, United Kingdom; Department of Physical Sciences, Chuka University, P.O. Box 109, 60400 Chuka, Kenya. Electronic address: atkirwa1@sheffield.ac.uk.
authors.forename: Abraham Kirwa
authors.initials: AK
authors.lastname: Tuwei
authors.affiliation: Centre for Chemical Biology, Department of Chemistry, University of Sheffield, S3 7HF Sheffield, United Kingdom.
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: Williams
authors.affiliation: Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Roma, Italy.
authors.forename: Mohammad Yusuf
authors.initials: MY
authors.lastname: Mulla
authors.affiliation: Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Roma, Italy.
authors.forename: Corrado
authors.initials: C
authors.lastname: Di Natale
authors.affiliation: Department of Chemical Science and Technology, University of Rome Tor Vergata, Via della Ricerca Scientifica, Roma 00133, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Paolesse
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, S3 7RH Sheffield, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Grell
keywords: Amine; Evanescent wave; Lock-in; Metalloporphyrin; Optrode