Optical fiber pH sensors based on layer-by-layer electrostatic self-assembled Neutral Red

Wavelength dependent pH optical sensor using the layer-by-layer technique

“…The sensitivity of a pH sensor is, of course, a measure of the degree of change in the sensor output with change in the solution pH. In optical sensors this transduction effect (that can then be related to the measurand) typically can be absorbance [12,35,36], reflected optical power [20,34], transmitted power [37] or the wavelength at maximum absorbance [22], for example, and indeed other effects can be used. Therefore, the sensitivity of the device will depend on the optimum choice of this transduction mechanism -where for example, a cross-comparison of Fig.…”

“…16. The PAH film is individually applied as a pH indicator [12,22,33] for which the value of pK a is reported to be between 8.0 to 8.8 [33,[38][39][40][41], where the pK a value for BY is 7. observed that the pK a value for both the odd and even number of layers decreases with an increase in the thickness of the thin film from 5.5 to 6 bilayers, whilst beyond this the pK a value starts to go up with an increasing number of bilayers. This means that the peak sensitivity of the probes slightly shifts for the alkaline region when more layers are deposited onto the fibre.…”

“…glass, ceramics, metals, wood, plastics and so on [1][2][3][4] of any size and topology [5,6]. In essence, the process is based on the electrostatic attraction of opposite charges and can be used with various reagents such as polymers [7], nanoparticles [8,9], metals [10], dyes [11,12], quantum dots [13], nanotubes [14], biomolecules like enzymes [15], proteins [16], etc. The technique is based simply on the alternate dipping of a charged substrate into cationic and anionic solutions.…”

Fluorescence based fibre optic pH sensor for the pH 10–13 range suitable for corrosion monitoring in concrete structures

“…Prior work has shown that poor immobilization results in dye leaching and consequently a drifting of the calibration of the probe, which leads to the gradual breakdown of its useful sensing ability [17]. Among several widely used immobilization methods are included absorption or entrapment [45][46][47], layer-by-layer (LbL) electrostatic self-assembly [48,49] and covalent binding [18,[50][51][52][53]. The first two approaches are generally easier and simpler but not suitable for this type of application as they suffer from numerous disadvantages such as cracking, dye leaching and inhomogeneity of the material (in case of absorption or entrapment in a sol-gel matrix) or irreversible damage at extreme pH values and issue related to effect of ionic strength (in case of electrostatic attachment).…”

Nanostructured Materials in Optical Fiber Sensing

“…This, configuration is usually referred as cladding removed (CR) followed by the optical fiber type such as multi-mode fiber (MMF) or plastic optical fiber (POF) and have been largely exploited in literature for the development of optical fiber sensors for ammonia [86,87], humidity [88,89], toluene [90], H 2 S [91,92], aerosol [93] or pH [94][95][96][97][98][99][100][101][102][103][104] detection.…”