Synthesis and characterization of polyaniline crystalline nanocellulose composite for cholesterol biosensor application

A cholesterol biosensor was developed by the modification of Screen-Printed Electrode (SPE) with a polyaniline/crystalline nanocellulose (PANi/CNC) A thin layer of ionic liquid (IL) was used to enhance the electron transfer and cholesterol oxidase (ChOx) was immobilized on the substrate for biological recognition. Crystalline nanocellulose was prepared from Semantan bamboo (Gigantochloa scortechinii) via acid hydrolysis which was then used to synthesize the polyaniline/ crystalline nanocellulose (PANi/CNC) nanocomposite via in situ oxidative polymerization of aniline in the presence of crystalline nanocellulose. The electrochemical properties of the nanocomposite were studied using a modified PANi/CNC electrode via cyclic voltammetry (CV), and a higher current response was observed for the PANi/CNC-modified electrode compared to that for the modified electrode with PANi. The data obtained from EIS showed lower charge transfer resistance (Rct) values for the PANi/CNC-modified electrode, indicating that the incorporation of CNC into the PANi structure enhanced the electron transfer rate. The FTIR spectra of the nanocomposite revealed the characteristic peaks of PANi and CNC, however, an overlapping of some of the characteristic peaks of pure PANi and CNC resulted in a broad band at 3263 cm-1 that could be due to the interaction between the NH group of PANi and the OH group of CNC inside the nanocomposite structure. The XRD diffraction spectra indicated lowered crystallinity which was observed at 2-theta values of 22.6 and 16.1 for PANi/CNC nanocomposite compared to the corresponding values in CNC. The FESEM images showed no phase separation in the nanostructure composite, revealing the homogenous polymerization of the monomer on the surface of the crystalline cellulose. Aggregation of PANi particles was observed with increasing aniline concentration. Research surface methodology (RSM) was applied to optimize the parameters and conditions in order to maximise the performance and sensitivity of the biosensor. Differential Pulse Voltammetry (DPV) as a powerful electroanalytical technique was used for all electrochemical measurements. The PANi/CNC/IL/GAL/ChOx-modified electrode showed a comparable sensitivity value of 35.19 μA mM /cm-2 towards H2O2 and cholesterol. The biosensor also exhibited a high dynamic response ranging from 1 μM to 12 mM cholesterol with a low Limit of Detection (LOD) of 0.48 μM. The biosensor displayed an acceptable reproducibility and repeatability with low relative standard deviations (RSD) of 3.76 % and 3.31 %, respectively. The biosensor showed high selectivity by excluding the interfering species and current response was maintained at over 84% of the initial value after 19 days.

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