The investigation of the behavior of a long period grating sensor with a copper sensitive coating fabricated by layer-by-layer electrostatic adsorption

Sensors based on changes of refractive index in response to sorption of an analyte on the coating or film of a long period grating fiber (LPG) fiber have recently been reported. In most prior work the coating or film swelled during interaction with the analyte. The swelling mechanism produced a kinetic response that slowed both the sensorʹs time for steady-state measurement and the reversibility of the sensor. Here, the analytical utility of fabricating these nanometer thin films using the layer-by-layer (LBL) electrostatic assembly method is evaluated using CuII as the test analyte and Cibacron Blue as the reagent immobilized in the LBL assembly; a generation-4 poly(amidoamine) dendrimer served as the spacer in the assembly. Detection of 1.3 mg CuII L−1 was observed when six bilayers comprised the coating. The stable response was achieved with 0.6 mg L−1 in less than 1 min. When 0.1 M HCl was used as the rinsing solution, this LPG sensor was reversible and the signal to similar concentrations of CuII reproducible.