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Coatings
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Thin Films and Structures for Optical Sensing
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Thin Films and Structures for Optical Sensing

A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Thin Films".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 10966

Special Issue Editor

Prof. Dr. Tsvetanka Babeva

E-Mail Website
Guest Editor
Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Interests: thin films optics; multilayered structures; sensors with optical read-out; porous thin films and structures; zeolite nanocomposites
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

You are cordially invited to submit your original work to this Special Issue devoted on “Thin Films and Structure for Optical Sensing”. In recent years, sensors with optical read-out, so-called “optical sensors”, have gained an increasing amount of interest because they operate at room temperature, which is very important considering energy-saving issues; they also offer safety when working with easily inflammable and explosive substances, cannot be influenced by electromagnetic disturbances, and have relatively simple principles of operation and low price. The main disadvantage is the lower sensitivity of optical sensors compared to that of electrical ones. Two approaches are implemented for enhancing sensing performance—developing sensitive and selective materials and optimizing the structure of the sensor.

This Special Issue will cover the recent progress and new developments in the area of synthesis, deposition, structuring, immobilization, and characterization of thin films for optical sensing of humidity, temperature, vapors, gases, heavy metal ions, bio-materials, etc.

In particular, the topics of interest include but are not limited to:

  • Synthesis of porous, sensitive, and selective materials;
  • Deposition approaches for responsive thin films and structures, including wet and dry methods;
  • Characterization of optical and sensing properties;
  • Strategies for selectivity improvement;
  • Optical sensing of humidity and temperature;
  • Color sensing of vapors and gases;
  • Monitoring of water and air quality;
  • Biosensing;
  • Transducing elements, including but not limited to 1D, 2D, and 3D photonic crystals, diffraction gratings, plasmonic structures, optical fibers, etc.

Prof. Dr. Tsvetanka Babeva
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Further information on MDPI's Special Issue polices can be found here.

Published Papers (2 papers)

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Research

10 pages, 1662 KiB  
Article
Influence of Al Doping on the Morphological, Structural and Gas Sensing Properties of Electrochemically Deposited ZnO Films on Quartz Resonators
by Gergana Alexieva, Konstantin Lovchinov, Miroslav Petrov, Rositsa Gergova and Nikolay Tyutyundzhiev
Coatings 2022, 12(1), 81; https://doi.org/10.3390/coatings12010081 - 12 Jan 2022
Cited by 9 | Viewed by 1987
Abstract
The detection of hazardous gases at different concentration levels at low and room temperature is still an actual and challenging task. In this paper, Al-doped ZnO thin films are synthesized by the electrochemical deposition method on the gold electrodes of AT-cut quartz resonators, [...] Read more.
The detection of hazardous gases at different concentration levels at low and room temperature is still an actual and challenging task. In this paper, Al-doped ZnO thin films are synthesized by the electrochemical deposition method on the gold electrodes of AT-cut quartz resonators, vibrating at 10 MHz. The average roughness, surface morphology and gas sensing properties are investigated. The average roughness of Al-doped ZnO layers strongly depends on the amount of the doping agent Al2(SO4)3 added to the solution. The structural dependence of these films with varying Al concentrations is evident from the scanning electron microscopy images. The sensing properties to ethanol and ammonia analytes were tested in the range of 0–12,800 ppm. In the analysis of the sensitivity to ammonia, a dependence on the concentration of the added Al2(SO4)3 in the electrochemically deposited layers is also observed, as the most sensitive layer is at 3 × 10−5 M. The sensitivity and the detection limit in case of ammonia are, respectively, 0.03 Hz/ppm and 100 ppm for the optimal doping concentration. The sensitivity depends on the active surface area of the layers, with those with a more developed surface being more sensitive. Al-doped ZnO layers showed a good long-term stability and reproducibility towards ammonia and ethanol gases. In the case of ethanol, the sensitivity is an order lower than that for ammonia, as those deposited with Al2(SO4)3 do not practically react to ethanol. Full article
(This article belongs to the Special Issue Thin Films and Structures for Optical Sensing)
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19 pages, 6683 KiB  
Article
Novel Rapid Protein Coating Technique for Silicon Photonic Biosensor to Improve Surface Morphology and Increase Bioreceptor Density
by Suruk Udomsom, Ukrit Mankong, Pathinan Paengnakorn and Nipon Theera-Umpon
Coatings 2021, 11(5), 595; https://doi.org/10.3390/coatings11050595 - 18 May 2021
Cited by 16 | Viewed by 8270
Abstract
Silicon photonic devices with either silicon or silicon nitride waveguides have increasingly been used in many applications besides communications, especially as sensors in label-free biosensing, where guided light signals are affected by biorecognition molecules immobilized on the surface. The coating of protein (i.e., [...] Read more.
Silicon photonic devices with either silicon or silicon nitride waveguides have increasingly been used in many applications besides communications, especially as sensors in label-free biosensing, where guided light signals are affected by biorecognition molecules immobilized on the surface. The coating of protein (i.e., bioreceptors) by biochemical process on the waveguide surface is a crucial step in creating a functionalized device that can be used for biosensing. As a conventional method that uses 3-aminopropryltriethoxysilane (APTES) and glutaraldehyde (GA), the APTES-GA method has the limitation of using a GA crosslink, of which the two functional groups can bind to nonspecific proteins, causing irregular binding. In this study, we proposed a new coating technique to avoid such problem by applying APTES silanization with 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (EDC)-N-hydroxysuccinimide (NHS) protein crosslink, denoted by the APTES-(EDC/NHS) method. The EDC/NHS reaction was shown to be able to immobilize protein in ordered orientation due to consistent arrangement between a carboxylic group of protein molecules and an amine group of covalent-linked APTES on surface. By applying APTES silanization, we circumvented the use of hazardous cleaning agent in the conventional EDC/NHS technique. Several surface characterization techniques were carried out to assess and compare the two biocoating techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), spectroscopic ellipsometry (SE), and atomic force microscopy (AFM). On silicon, the results of antihuman TNF-alpha antibody coating showed that the proposed APTES-(EDC/NHS) technique has better repeatability in terms of less roughness of the coated protein at 1.5 nm compared with 6.3 nm, due to the ordered arrangement of coated antibody molecules. On a silicon nitride waveguide device, the proposed APTES-(EDC/NHS) technique exhibits dense antibody immobilization on a waveguide in SEM images due to stable amide bond formation via EDC/NHS crosslink mechanism. The specificity of the immobilized antibodies was confirmed by enzyme-linked immunosorbent assays (ELISA), with an average optical density at 450 nm of 0.175 ± 0.01 compared with 0.064 ± 0.009 of negative control. The proposed technique also reduced the overall process time since proteins are crosslinked to the silanized waveguide surface in a single step. Full article
(This article belongs to the Special Issue Thin Films and Structures for Optical Sensing)
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