A novel fast response fiber-optic pH sensor based on nanoporous self-assembled multilayer films

Three-component multilayer films were prepared by consecutively depositing a polycation blend of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC) and poly(diallyldimethylammonium) (PDDA) with poly(acrylic acid) (PAA). The self-assembly and disintegration behavior of the multilayer films were investigated in details by UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that nanoporous PDDA/PAA multilayer films can be obtained conveniently by partly disintegrating (PVPMC + PDDA)/PAA multilayer films in a 0.15 M NaCl solution. A novel fast response fiber-optic pH sensor was successfully prepared by constructing nanoporous self-assembly multilayer films on the thin-core fiber interferometer (TCFMI) surface. The response time of a fiber-optic pH sensor deposited with nanoporous PDDA/PAA multilayer film (20 s rise time (t(r)) and 15 s fall time (t(f))) was only one-tenth of that with the nonporous PDDA/PAA multilayer film (240 s and 160 s for t(r) and t(f)).