Chitosan/polyacrylic acid film based on a tapered fiber structure for the ultrasensitive detection of Cu2+ concentration

Abstract

A tapered fiber with a total length of 7.680 mm and a taper waist diameter of 11.8 μm is fabricated, and encapsulated with a V-type quartz groove to enhance the mechanical strength of the sensor. Chitosan (CS) and polyacrylic acid (PAA) solution through the layer-by-layer self-assembly are deposited on the surface of the tapered fiber to detect the concentration of copper ions (Cu2+) in deionized water (DIW). Due to diffusion and chemisorption of Cu2+ in the functional films, the optimal adsorption effect of Cu2+ is achieved when the CS and PAA film are assembled with 4 layers each. The dip wavelength of interference spectra exhibits different nonlinear responses to different ranges of Cu2+ concentration due to the coordination effect (CS/PAA)4 with Cu2+ and hydrolysis of the (CS/PAA)4. After functionalizing the surface of the fiber with (CS/PAA)4, the wavelength sensitivity and detection limit (DL) for Cu2+ concentration in the DIW are 46.87 nm/μΜ and 0.31 μM in the range of 0.16 ∼ 2.4 μM. Additionally, the sensor designed possesses the advantages of wide detection range, temperature insensitivity, and excellent stability. It indicates that the proposed sensor has a promising potential for application in Cu2+ concentration detection.