A polyaniline/platinum coated fiber optic surface plasmon resonance sensor for picomolar detection of 4-nitrophenol

Abstract

The paper reports for the first time an innovative polyaniline (PANI)/platinum (Pt)-coated fiber optic-surface plasmon resonance (FO-SPR) sensor used for highly-sensitive 4-nitrophenol (4-NP) pollutant detection. The Pt thin film was coated over an unclad core of an optical fiber (FO) using a DC magnetron sputtering technique, while the 4-NP responsive PANI layer was synthetized using a cost-effective electroless polymerization method. The presence of the electrolessly-grown PANI on the Pt-coated FO was observed by field-emission scanning electron microscopy and subsequently evidenced by energy dispersive X-ray analysis. These FO-SPR sensors with a demonstrated bulk sensitivity of 1515 nm/RIU were then employed for 4-NP sensing, exhibiting an excellent limit-of-detection (LOD) in the low picomolar range (0.34 pM). The proposed sensor’s configuration has many other advantages, such as low-cost production, small size, immunity to electromagnetic interferences, remote sensing capability, and moreover, can be operated as a “stand-alone device”, making it thus well-suited for applications such as “on-site” screening of extremely low-level trace pollutants.

Sensitive pH Monitoring Using a Polyaniline-Functionalized Fiber Optic—Surface Plasmon Resonance Detector

“…The FO-SPR sensing platform and its working principle (see Figure 1 ) were presented in more details elsewhere [ 14 , 22 ]. Briefly, herein, a sensitive SPR zone of cm was created at one side of a multimode optical fiber (with a total length of cm and a diameter of 400 μm) by removing the jacket and subsequently uncladding the optical fiber in acetone ( Figure 1 A).…”

“…The bulk sensitivity of the Pt-coated FO-SPR sensors was determined by refractive index (RI) measurements in a serial set of sucrose dilutions (0, 2, 4, 8, w / w ). The Brix values of these sucrose dilutions were verified with a digital refractometer (Atago Palette PR-32, Japan) and the corresponding RI units were reported elsewhere [ 14 , 22 ]. The interchangeable FO-SPR sensor was inserted into the connector and fixed on the computer-controlled SPR sensing platform (see Section 2.2 ).…”

“…The prepared Pt-coated FO-SPR sensors were further used as catalysts in the electroless polymerization of aniline. The rudimentary steps of PANI electroless deposition approach were selected from literature [ 18 , 28 ] and optimized to the micrometer-sized optical fiber geometry [ 22 ]. Briefly, the Pt-coated substrates were immersed in an aqueous solution of aniline ( M) and H SO ( M) for 6 h. This solution was kept under oxygen saturation and at a constant temperature of C by means of a thermostatic circulating water bath model TC120 from Grant Instruments, for reproducibility reasons.…”

“…PANI is a well-known electro-conductive polymer with excellent stability and physico-chemical properties, featuring rapid and reversible adsorption and desorption RedOx kinetics [ 19 , 20 ]. In these circumstances, PANI can be successfully employed as a functional sensitive layer in energy storage applications [ 21 ], pollutants detection [ 19 , 22 ], gas sensing [ 23 ], and pH monitoring [ 24 , 25 ]. To the best of our knowledge, few theoretical studies were reported with Pt-coated transmission-type FO-SPR sensors [ 26 , 27 ].…”

“…To the best of our knowledge, few theoretical studies were reported with Pt-coated transmission-type FO-SPR sensors [ 26 , 27 ]. Only in our recent work, a Pt-coated reflection-type FO-SPR sensor has been proposed for the first time, wherein the thin Pt plasmonic film has been used in conjunction with a functional PANI film to demonstrate highly-sensitive detection capabilities of the 4-nitrophenol pollutant [ 22 ]. Herein, we continued the optimization studies of the novel Pt/PANI bilayer reflection-type FO-SPR sensor, aiming to maximize its bulk sensitivity and to expand its applicative range towards pH monitoring.…”