Fiber Optic pH Sensor Using Optimized Layer-by-Layer Coating Approach

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. The results obtained from a series of evaluations show that the sensitivity was enhanced by reducing the concentration of the indicator solution used and by designing a U-bend configuration sensor probe with a sharply bent fibre. However, when making an overall comparison, the straight (unbent) fibre probe resulted in a more sensitive probe when compared to the use of a high radius bend. Further, utilizing a small core diameter of the fibre allows a wide pH range to be measured and with high sensitivity. Additionally, the performance was shown to be improved for measurements over a narrower range of pH, by using a fibre with a larger core diameter. Considering the effect of the number of layers, work carried out has shown that probes with 5-6 bilayers presented the best performance. The sensitivity has been shown to diminish when more than 6 layers were used and the sensing range shifts towards higher pH values. When monitored, the value of pKa (the dissociation constant) of the thin film showed the smallest change of any of the design factors considered. In summary, using a larger core diameter, employing a larger curve radius, a higher number of bilayers, a higher concentration of the indicator solution and applying PAH as an outer layer, all cause a higher pKa value and consequently the probe sensitivity moves towards alkaline region. Permanent repository link

Dual-channel fiber surface plasmon resonance biological sensor based on a hybrid interrogation of intensity and wavelength modulation

“…[4][5][6][7][8] Similar to SPR, LSPR is the collective electron oscillations of metal NPs when the incident photon frequency conforms to the oscillation frequency of conductive electrons, but its frequency can be tuned by changing the size, geometry, material, and surrounding dielectrics of the NPs. Currently, most fiber-optic SPR sensors are designed for singlechannel detection, [9][10][11] which cannot detect more than one analyte or eliminate the adverse effect caused by the changes in the refractive index (RI) of the bulk solution. Seldom do sensors have multiple sensing areas fabricated on a short section of optical fiber, which can realize multichannel detection and self-compensation.…”

Optical sensor for pH monitoring using a layer-by-layer deposition technique emphasizing enhanced stability and re-usability

“…Following the approach in previous research reported by the authors [37,38], a glass slide was prepared on which was deposited alternate layers of brilliant yellow (BY) (acting as a pH indicator) and poly (allylamine hydrochloride) [PAH] (acting as a cross-linker of the layers of brilliant yellow), using layer-by-layer coating technique. To determine the stability of thin film, initially neither heat treatment or drying was used in the process of coating of glass slide with a total of 8 bilayers of (PAH/BY); this configuration is denoted by (PAH/BY) 8 , where the subscript indicates the number of bilayers, in this case 8.…”

Layer-by-Layer Nano-assembly: A Powerful Tool for Optical Fiber Sensing Applications

“…Another of the most common strategies for the design of effective optical fiber pH sensors is based on the use of specific pH indicators such as Prussian Blue (PB) [91], Neutral Red (NR) [76,92,93,94] or Brilliant Yellow (BY) [95,96] as well as fluorescent pH indicator such as HPTS [75,97], among others. In several works, the specific pH indicator can be perfectly dissolved in one of the polyelectrolytes, as it can be observed in [91,92,97].…”