Amperometric detection of salivary α-amylase on screen-printed carbon electrodes as a simple and inexpensive alternative for point-of-care testing

Abstract

This study describes the amperometric detection of salivary α-amylase (sAA) in human saliva samples using screen-printed carbon electrodes (SPCE). The proposed method was based on the indirect determination of sAA in a sequence of two chemical reactions. Basically, the first reaction is the hydrolysis of starch by sAA to produce maltose. Then, the generated reducing sugar promotes the conversion of [Fe(CN)6]3− into [Fe(CN)6]4− in a second reaction. Different parameters, such as pH, reaction time, sAA volume and starch concentration were thoroughly optimised. The best electrochemical response was found using 5 mmol L−1 NaOH (pH = 12), reaction time of 20 min, sAA volume of 15 μL and 0.5% (w/v) starch. The analytical performance revealed good linear correlation for sAA concentration levels between 100 and 1200 U mL−1. The achieved limit of detection (LOD) and sensitivity values were 1.1 U mL−1 and 10.7 μA/(log U mL−1), respectively. The proposed electrochemical sensor exhibited great selectivity. The amperometric response for sAA was recorded in the presence of different glucose levels (0.01—0.10 mmol L−1) and no noticeable change was observed. The feasibility of the proposed method was investigated through the determination of sAA levels in five human saliva samples. The concentration levels found ranged between 182.8 and 1117.1 U mL−1 and presented accuracy between 90 and 97%. The method reported herein emerges as a simple, inexpensive, portable, reliable and powerful tool for rapid point-of-care testing (POCT).