An Ionophore‐Based Anion‐Selective Optode Printed on Cellulose Paper

Abstract

Ag eneral anion-sensing platform is reported based on ap ortable and cost-effective ion-selective optode and as martphone detector equipped with ac olor analysis app.I n contrast to traditional anion-selective optodes using ah ydrophobic polymer and/or plasticizer to dissolve hydrophobic sensing elements,the new optode relies on hydrophilic cellulose paper.The anion ionophore and alipophilic pH indicator are inkjet-printed and adsorbed on paper and form a" dry" hydrophobic sensing layer.P orous cellulose sheets also allow the sensing site to be modified with dried buffer that prevents any sample pH dependence of the observed color change.A highly selective fluoride optode using an Al III -porphyrin ionophore is examined as an initial example of this new anion sensing platform for measurements of fluoride levels in drinking water samples.A part from Lewis acid-base recognition, hydrogen bonding recognition is also compatible with this sensing platform.

Digital printing of selective and reversible ion optodes on fabrics: toward smart clothes for epidermal chemical sensing

“…Since digital printing has been widely used in the textile industry for dyeing purposes, the simple replacement of traditional dye inks with optode inks will create sensors onto clothing. In contrast to previously reported Na + -and F − -selective optodes on cellulose paper for disposable applications, 12,13 the fabric-based pH, Na + , and K + optodes are characterized with a focus on their reversibility and response time. More hydrophobic ionophores are necessitated to attain robust chemical adsorption on the fabric and therefore acceptable reversibility in multiple measurements.…”

“…We recently discovered that these hydrophobic sensing chemicals readily adsorb on hydrophilic substrates such as cellulose paper, enabling ion sensing in the absence of a plasticized polymer matrix. [12][13][14][15] The optode cocktail without the plasticized polymer becomes inkjet-printable because of its ideal viscosity and surface tension. As a result, ISOs can be fabricated in an unprecedentedly precise and reproducible fashion, making batch calibration possible.…”

“…As a result, ISOs can be fabricated in an unprecedentedly precise and reproducible fashion, making batch calibration possible. 13 The elimination of the plasticized polymer (typically PVC) also dramatically reduces the hydrophobicity of the sensor and facilitates spreading of the aqueous sample. 14 These features make the inkjet-printed plasticizer-free optodes highly suited for wearable sensing applications compared to traditional ion optodes.…”

“…This is why the zeta potential of the polyester fabric is much lower than that of the filter paper (−60 vs. −35 mV at pH 6). 13,19 The anionic sites possessed by polyester serve as cation exchangers to attract protons to the sensing layer, thereby requiring more basic solutions to deprotonate the Chromoionophore III and leading to a dynamic range at higher pH.…”

Equipment-Free Detection of K+ on Microfluidic Paper-Based Analytical Devices Based on Exhaustive Replacement with Ionic Dye in Ion-selective Capillary Sensors

“…More recently, neutral carrier-based ion-selective optodes (ISOs), 26,27 which can detect ion concentration based on a chemically selective twophase ion exchange reaction, have been applied to μPADs for the detection of Na + , 28,29 K + , 30 and the anionic species Cl − , F − , and polyanions. 31 Thus, the application of optode principles to μPADs aims to achieve point-of-care testing of biologically important ionic species, especially alkali metal ions. Until now, the need for external equipment is still indispensable for colorimetric quantification and reduces the practicability of those devices.…”