Paper-Based Device for Sweat Chloride Testing Based on the Photochemical Response of Silver Halide Nanocrystals

Dimosthenis L Giokas,Christina Matiaki,Afroditi Sfakianaki,Tatiana G Choleva,Athanasios G Vlessidis

doi:10.3390/chemosensors9100286

Dimosthenis L Giokas, Christina Matiaki + Show 3 more

Open Access

https://doi.org/10.3390/chemosensors9100286

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Journal: Chemosensors	Publication Date: Oct 8, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: University of Ioannina

Abstract

A new method for the determination of chloride anions in sweat is described. The novelty of the method relies on the different photochemical response of silver ions and silver chloride crystals when exposed to UV light. Silver ions undergo an intense colorimetric transition from colorless to dark grey-brown due to the formation of nanosized Ag while AgCl exhibits a less intense color change from white to slightly grey. The analytical signal is obtained as mean grey value of color intensity on the paper surface and is expressed as the absolute difference between the signal of the blank (i.e., in absence of chloride) and the sample (i.e., in the presence of chloride). The method is simple to perform (addition of sample, incubation in the absence of light, irradiation, and offline measurement in a flatbed scanner), does not require any special signal processing steps (the color intensity is directly measured from a constant window on the paper surface without any imager processing) and is performed with minimum sample volume (2 μL). The method operates within a large chloride concentration range (10–140 mM) with good detection limits (2.7 mM chloride), satisfactory recoveries (95.2–108.7%), and reproducibility (<9%). Based on these data the method could serve as a potential tool for the diagnosis of cystic fibrosis through the determination of chloride in human sweat.

Highlights

Cystic fibrosis (CF) is one of the most common and severe inherited genetic disorders, especially among Caucasian populations, with an estimated incidence between 1 to 2500 and 1 to 7000 births in Europe [1]
For over 60 years the gold standard method to diagnose CF and monitor the response of patients to therapeutic treatment is sweat testing which is based on the determination of abnormally elevated sweat chloride concentrations (i.e., >60 mM) or total sweat conductivity (i.e., >90 mM) [2,3]
The principle of chloride sensing on the developed paper devices is based on the principles of early photography and it uses the photosensitivity of silver halides to control the photoreduction of silver

Summary

Introduction

Cystic fibrosis (CF) is one of the most common and severe inherited genetic disorders, especially among Caucasian populations, with an estimated incidence between 1 to 2500 and 1 to 7000 births in Europe [1]. Timely diagnosis is important to ensure early treatment that can ease symptoms and reduce complications, improving in the quality of life and the median life expectancy of CF patients. For over 60 years the gold standard method to diagnose CF and monitor the response of patients to therapeutic treatment is sweat testing which is based on the determination of abnormally elevated sweat chloride concentrations (i.e., >60 mM) or total sweat conductivity (i.e., >90 mM) [2,3]. The standard sweat chloride test consists of three steps: (a) the cholinergic stimulation of sweating with pilocarpine iontophoresis; (b) the collection of sweat with filter paper, gauze, or plastic capillary tubing (e.g., Macroduct coils) and (c) the determination of chloride concentration [4].

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