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Photonic calcium and humidity array sensor prepared with reactive cholesteric liquid crystal mesogens

Dan-bi Myung,S. Hussain,Soo-young Park

Published 2019 in Sensors and Actuators B: Chemical

ABSTRACT

Abstract Ion and humidity sensor array films have been developed using an interpenetrating polymeric network (IPN) of photonic networked cholesteric liquid crystals (CLCs) intertwined with network-structured poly(acrylic acid). Selective curing of a photonic CLC network film infiltrated with an acrylic acid/tri(propylene glycol) diacrylate mixture produced an array film of dots with photonic IPN structures on a simple photonic CLC background. Water isolation by individual hydrophilic dots against a hydrophobic background allowed testing of small sample amounts. Subsequent acetone/KOH treatments of the IPN film (IPNacetone/KOH film) prevented hydrogen bonding between carboxylic groups, maximized swelling of the film with water, and increased the speed of photonic color change. A full range of reflected colors, i.e., blue (dry) to red (humid), allows this film to act as an optical humidity sensor. The replacement of K+ with divalent ions that bridge the carboxylic groups prevented film swelling. Given that the photonic band gap wavelength is inversely proportional to the CaCl2 concentration, the amount of Ca2+ can be determined from the reflected color by the naked eye. This cost-effective, convenient IPNacetone/KOH film has been successfully applied as a biosensor for detecting Ca2+ in human blood serum and saliva and as an anti-counterfeiting label that reveals a colorful image under humid conditions.

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