Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc Label-free liquid crystal-based detection of As(III) ions using ssDNA as a recognition probe Duy Khiem Nguyen, Chang-Hyun Jang ⁎ Department of Chemistry, Gachon University, Seongnam-daero 1342, Sujeong-gu, Seongnam-si, Gyeonggi-do 13120, Republic of Korea ARTICLEINFO Keywords: Liquid crystals LC-based biosensor Arsenic Ars-3 aptamer As3+ detection ABSTRACT We report a label-free liquid crystal (LC)-based biosensor for sensitive detection of arsenic (III) ions (As3+) in aqueoussolutions,usinganarsenic-bindingaptamer(Ars-3aptamer)asamolecularrecognitionelement.Inthis sensing system, the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was employed to induce a homeotropicorientationoftheLCsattheaqueous/LCinterface,aresultoftheself-assemblyofCTABmolecules. In the absence of As3+, the addition of Ars-3 aptamers disturbed the self-assembly of CTAB at the aqueous/LC interface, due to interactions between CTAB and the Ars-3 aptamers, causing an orientational transition of LCs from homeotropic to planar. In the presence of As3+, the specific binding of the Ars-3 aptamers with As3+ led totheformationofanaptamer-As3+complex,resultinginaconformationalchangeoftheaptamer.Thischange weakened the interaction between CTAB and the aptamer at the interface, causing the orientation of the LCs to remain unchanged in a homeotropic state. The changes in the orientation of the LCs caused by the interactions between the Ars-3 aptamer, As3+, and CTAB were simply converted and observed under a polarized light microscope as a shift between a bright and a dark image. A low detection limit of 50 nM (~3.7 ppb) was obtained,whichiswellbelowthemaximumpermissiblelevelofAs3+indrinkingwater(133nM)setbytheUS EnvironmentalProtectionAgencyandtheWorldHealthOrganization.Otherchemicalspecies(heavymetalions) did not induce these changes, and thus, the biosensor was highly specific for As3+ ion sensing. The potential application of the developed sensor for As3+ detection in tap water was also demonstrated. Therefore, this LC- based biosensor is a promising platform for simple, rapid, label-free determination of As3+ concentration in aqueous samples with high selectivity and sensitivity. 1. Introduction Arsenic is one of the most toxic heavy metals present in water, soil, rain, vegetables, and cereals [1]. It is a known carcinogen and is be- comingamajorhazardtothehealthofhumansandecosystemsglobally [2,3]. In the natural environment, arsenic exists in two forms, as tri- valent arsenite (As3+) and pentavalent arsenate (As5+) [4]. Both As3+andAs5+compoundsarerapidlyandextensivelyabsorbedfrom the gastrointestinal tract; however, As3+ compounds are more water soluble and 60 times more toxic than As5+ compounds [3–5]. Pro- longed consumption of arsenic-contaminated water or plants grown in an arsenic-contaminated area may lead to various health problems, such as skin lesions, diabetes, circulatory and cardiovascular disorders, neurological complications, many types of cancer, or even death [6–8]. Due to its high toxicity, the US Environmental Protection Agency and theWorldHealthOrganizationhavesetthemaximumpermissiblelevel forarsenicindrinkingwateraslowas10 ppb(10µg L −1 or133nmol L −1 ) [9]. Various conventional methods, such as high-performance liquid chromatography (HPLC) [10]. atomic fluorescence spectroscopy [11]. atomic absorption spectroscopy [12]. inductively coupled plasma mass spectrometry[13, 14].andinductivelycoupledplasmaatomicemission spectrometry [15]. have been used for the detection of As3+ in water. Although these techniques can sensitively and accurately measure As3+ levels below 10 ppb (133 nmol L −1 ), they have some draw- backs, such as the need for expensive and bulky equipment, chemicals, labeling of samples, and highly trained personnel [16,17]. Therefore, thedevelopmentofsimpleandrobustmethodsfortheprecisedetection of As3+ levels, with high sensitivity and selectivity, is highly neces- sary. Aptamers are artificial, single-stranded DNA or RNA oligonucleo- tides (ssDNA or ssRNA) that possess the ability to recognize a broad rangeoftargetmolecules,includingdrugs [18].proteins [19–21].small molecules [22]. and even cancer cells with high affinity and specificity https://doi.org/10.1016/j.microc.2020.104834 Received 14 February 2020; Received in revised form 12 March 2020; Accepted 12 March 2020 ⁎ Corresponding author. E-mail address: chjang4u@gachon.ac.kr (C.-H. Jang). Microchemical Journal 156 (2020) 104834 Available online 13 March 2020 0026-265X/ © 2020 Published by Elsevier B.V. T