Self Assembling and Coordination of Water Nano-Layers On Polymer Coated Long Period Gratings: Toward New Perspectives for Cation Detection

Abstract

In this work, polymeric coated Long Period Gratings (LPGs) working in transition mode have\ud been used to monitor the coordination and self assembling of water nano-layers (typical thicknesses\ud range in few tens of nanometers) providing new scenarios in chemical sensing applications.\ud In particular, nano-scale layers (∼320nm) of semicrystalline syndiotactic and amorphous atactic\ud polystyrene (sPS and aPS), have been deposited by dip-coating onto LPGs to tune the devices at the\ud transition point. Experimental results demonstrate the polymers capability to orient water molecules\ud in proximity of their surfaces. The sPS and aPS interactions with water have been continuously\ud monitored and then compared demonstrating the higher capability of the crystalline phase of sPS\ud to orient water nano-layers. Moreover, the high sensitivity of the coated LPGs was used to monitor\ud the effect of disorder induced on the interfacial water molecular arrangement by different cations\ud (sodium, Na+, potassium, K+, and calcium, Ca2+, ions) depending on their size and electrical\ud charge. Experimental results show for the first time that, thanks to the water-polymer interaction,\ud sPS coated LPGs could be successfully employed as high sensitivity cation sensors. In fact, the monitoring\ud of the disorder induced by cations on the coordinated water layer leads to high sensitivities,\ud in terms of detected RI change for unitary variation of concentration (∼7.80 · 10−4RIU · mM−1\ud for Na+ ions, ∼9.00 · 10−4RIU · mM−1 for K+ ions, and ∼1.07 · 10−3RIU · mM−1 for Ca2+\ud ions)

Refractometric Optical Fiber Platforms for Label Free Sensing

“…Long period gratings are the most popular fiber optic sensor for label free sensing, since in 1996 Bhatia et al [21] presented the first LPG based refractometer, many refractive index sensors have been reported along the years, using the refractometric ability to measure parameters such as the concentration of ethylene glycol, sucrose, salt, ethanol among others [33,[41][42][43][44][45][46]. Although this approach is not the most reliable due to the possible interference of other species present in the solution, which are different from the analyte of interest.…”

Lab-on-fiber technology: a new avenue for optical nanosensors

“…Polymeric coated LPGs working in transition mode have also been used as highly sensitive devices for the monitoring of nano-scale phenomena occurring at the polymer/water interface, that have been successfully exploited for cation sensing [52].…”

Etched Fibers of Syndiotactic Polystyrene with Nanoporous-Crystalline Phases

“…Two commercial polymers (syndiotactic polystyrene, s-PS, , and poly­(2,6-dimethyl-1,4-phenylene) oxide, PPO) can be crystallized in nanoporous-crystalline forms. Processes leading to nanoporous-crystalline forms (ultramicroporous according to IUPAC classification) are based on cocrystallization with low-molecular-mass guest molecules followed by suitable guest extraction procedures. − These nanoporous-crystalline polymer phases are able to efficiently absorb guest molecules in their molecular-size cavities and have been proposed for several applications in molecular separation, − sensors, − and catalysis. − For s-PS, two nanoporous crystalline forms with similar density (0.98 g cm –3 , being definitely smaller than for the amorphous phase, 1.05 g cm –3 ), corresponding to different packing of polymer chains in the helical s­(2/1)­2 conformation, have been thoroughly described: the monoclinic δ form, with a = 1.74 nm, b = 1.185 nm, c = 0.77 nm, and γ = 117°, and the orthorhombic ε form, with a = 1.61 nm, b = 2.18 nm, and c = 0.79 nm. The distribution of the empty space is rather different for the two nanoporous-crystalline forms.…”