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(1025-A) A passively addressable electrochemical sensor for the detection of chloride ion levels in ultralow volumes of perspired human sweat


Authors:

Antra Ganguly – Doctoral Student, University of Texas At Dallas

Abstract:

Sweat chloride is used as the biomarker for gold standard diagnosis of Cystic Fibrosis (CF), a lethal progressive, genetic disorder of childhood. Quantification of chloride concentration in human sweat can also be used to reliably monitor and control hydration levels in an individual within homeostatic limits. The conventional CF sweat tests, based on coulometric titration, involve the steps of iontophoretic sweat induction, collection and subsequent laboratory analysis which generally are associated with the risks of evaporation and/or contamination of the collected sweat samples. We have developed a biosensor that is passively addressable and conveniently eliminates these steps, allowing reliable measurement of chloride ion concentration in ultra-low volumes (1-3 mL) of perspired human sweat. The proposed sensor consists of gold working and counter/ reference electrodes deposited in nanoscale thickness onto nanoporous polyamide substrate.  Highly specific affinity-based assay allows the label free detection of chloride ions which is achieved by using Chloride Ionophore IV, 4,5-Bis-[N′-(butyl)thioureido]-2,7-di-tert-butyl-9,9-dimethylxanthene, as the capture probe. The ionophore, by its highly preorganized bis-thiourea receptors based on a xanthene spacer, captures the sweat chloride ions by way of multitopic hydrogen bonding forming stable complexes.  The ionophore is anchored to the gold electrodes by using DSP (dithiobis (succinimidyl propionate) as a crosslinker. Binding of chloride ions to the capture probe modulates the charge transfer within the Electrical Double Layer (EDL) at the electrode/ human sweat interface and, also changes the overall solution resistance. Changes in these parameters are probed by the sensor using frequency specific (100 Hz) Non-Faradaic Electrochemical Impedance Spectroscopy and Chronoamperometry. Linear calibration dose response plots were obtained, and the proposed electrochemical sensor shows potential of precisely quantifying chloride concentration for varying chloride doses from 10-100mM with a detection limit of 1mM over the entire physiological pH range of human sweat (pH 2 to 8). Thus, this work proposes a novel, flexible and robust sweat chloride sensor, capable of detecting abnormal levels of chloride in human sweat. This impedance-based chloride sensing mechanism, when rendered as a point-of-care device, can be used at home to reliably detect, monitor and track the efficacy of CF treatments and to plan visits to the doctor’s clinic. The performance of the developed sensor is unaffected by bending and ambulation, thus it can be potentially developed as a wearable device for dynamically tracking the hydration levels of athletes or sportspersons while on the field by monitoring their sweat chloride concentrations.

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