Long-period grating fiber-optic sensors exploiting molecularly imprinted TiO 2 nanothin films with photocatalytic self-c
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ORIGINAL PAPER
Long-period grating fiber-optic sensors exploiting molecularly imprinted TiO2 nanothin films with photocatalytic self-cleaning ability Tao Wang 1 & Sergiy Korposh 2 & Stephen James 3 & Seung-Woo Lee 1 Received: 5 May 2020 / Accepted: 20 October 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Highly sensitive and selective long-period grating (LPG) fiber-optic sensors modified with molecularly imprinted TiO2 nanothin films were fabricated. The films were deposited onto the surface of the optical fiber via liquid-phase deposition (LPD), using tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) as a template. Three LPG resonance bands were monitored during film deposition, which was of duration 4.5 h. Prior to template removal, heat treatment at 60 °C under high-humidity conditions led to an increase in refractive index of the TiO2 film, evidenced by changes in the central wavelengths of the attenuation bands. After template removal using HCl solution (0.01 M), the TMPyP-imprinted film-modified LPG sensor showed higher sensitivity to the template molecule than to structurally related guest molecules. This was measured at the 1st and 2nd resonance bands, with wavelengths ranging from 690 to 738 nm and 815 to 905 nm, respectively. No selective binding of the template was observed with a non-imprinted TiO2 film prepared in the same manner. Furthermore, the heat-treated imprinted films exhibited a substantial enhancement of photocatalytic activity for template irradiation. In particular, the self-cleaning property of the imprinted filmmodified LPG sensor under ultraviolet irradiation led to highly efficient and selective binding to the template. The mechanism of the interaction between the template and the TiO2 matrix was investigated by UV–vis and Fourier-transform infrared (FTIR) spectroscopies. Additionally, morphological studies using scanning electron microscopy (SEM) were conducted. Keywords Long-period grating (LPG) . Molecular imprinting . Liquid-phase deposition (LPD) . TiO2 nanothin film . Photocatalyst . Fiber-optic sensor
Introduction Recent applications of imprinted nanomaterials in bio and chemical sensors have received tremendous attention from the viewpoints of materials chemistry and surface chemistry because the molecular imprinting technique is considered to be an alternative tool for artificially realizing the molecular recognition in the biological system [1–5]. In particular,
* Seung-Woo Lee [email protected] 1
Graduate School of Environmental Engineering, The University of Kitakyushu, 1-1 Hibikino, Kitakyushu 808-0135, Japan
2
Optics and Photonics Group, Department of Electrical and Electronic Engineering, University of Nottingham, Nottingham NG7 2RD, UK
3
Engineering Photonics, School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, Bedford MK43 0AL, UK
molecularly imprinted thin films have many advantages, including a quick response time and high sensitivity and selectivity [6]. Different methodologies have been empl
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