Comparison of Different Unmodified and Nano-Material Modified Sensors for the Ultrasensitive Determination of Serotonin

Abstract

A comparison of response of different unmodified and polymer nanocomposite modified sensors has been monitored for the sensitive determination of serotonin (5-hydroxytryptamine; 5-HT). For the modification of sensors, polymer nanocomposite of poly-bromocresol green (p-BG) with single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and graphene (GRA) were prepared by electro polymerization at the surface of edge plane pyrolytic graphite (EPPG). Surface morphology of the different unmodified and modified sensor surfaces was studied by using Electrochemical Impedance Spectroscopy, Field Emission Scanning Electron Microscopy, cyclic voltammetry and square wave voltammetry (SWV). The calibration curves for 5-HT were recorded using SWV and linear relations between peak current and concentration were found in the wide concentration range. For unmodified electrode surfaces, limit of detection were found as 1.339, 0.850, 0.737, 0.405 and 0.104 μM for gold, palladium, glassy carbon, basal plane pyrolytic graphite and EPPG surfaces, respectively. The limit of quantification was found as 4.462, 2.835, 2.456¸ 1.349 and 0.348 μM respectively. Among unmodified sensors, EPPG sensor exhibited lowest detection limit. The modified sensors p-BG/SWCNTs/EPPG, p-BG/MWCNTs/EPPG and p-BG/GRA/EPPG electrocatalyzed the oxidation of 5-HT and a well-defined oxidation peak with enhanced peak current was observed. The detection limit was observed as 5.9, 4.3 and 2.4 nM with quantification limit of 19.66, 14.33 and 8 nM, respectively. The lowest detection limit was found for p-BG/GRA/EPPG sensor in comparison to all unmodified and other modified surfaces. An excellent electrocatalytic activity of p-BG/GRA/EPPG surface towards the sensitive determination of 5-HT was noticed, which exhibited much lower L.O.D in comparison to the ones reported in recent years.