Contents lists available at ScienceDirect Progress in Materials Science journal homepage: www.elsevier.com/locate/pmatsci Polymers and organic materials-based pH sensors for healthcare applications Arif Ul Alam a,b , Yiheng Qin a,b,1 , Shruti Nambiar c , John T.W. Yeow c , Matiar M.R. Howlader a, ⁎ , Nan-Xing Hu b , M. Jamal Deen a, ⁎⁎ a Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada b Advanced Materials Laboratory, Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, ON L5K 2L1, Canada c Waterloo Institute of Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada ARTICLE INFO Keywords: Polymers and organic materials Fabrication Electrochemical Electrical field-effect pH sensors Biomedical applications ABSTRACT In this review, we discuss chemical, physical and electrochemical properties of pH-sensitive polymers and organic materials and their sensing mechanisms for healthcare applications. We find that polymers and organic materials, due to their biocompatibility and customizable elec- trical and electrochemical properties, can be used in pH sensors as structural, pH-sensitive, and passivation materials. To do so, we first identify the properties and sensing mechanisms for pH- sensitive polymers and organic materials. Different functional groups in the materials determine their chemical properties and are involved in redox reactions for chemical sensing of pH. The transport of charge carriers in the polymers and organic materials is influenced by pH-induced electrical field change, which is responsible for physical sensing of pH. Some polymers and or- ganic materials also show hybrid sensing properties, where both functional groups and electrical field-effect contribute to their pH response. Next, we review fabrication technologies for poly- mers and organic materials, and identify that engineering the materials and new device struc- tures are two possible approaches to improve the sensitivity and reliability of pH sensing devices. We propose that miniaturized sensors can provide enhanced functionality of the sensing https://doi.org/10.1016/j.pmatsci.2018.03.008 Received 1 August 2017; Received in revised form 22 January 2018; Accepted 28 March 2018 ⁎ Corresponding author. ⁎⁎ Co-corresponding author. 1 Current address: EnviroSen Inc., B26-2660 Speakman Drive, Mississauga, ON L5K 2L1, Canada. E-mail address: mrhowlader@ece.mcmaster.ca (M.M.R. Howlader). Abbreviations: ALD, atomic layer deposition; BCB, divinyltetramethyldisiloxane-bis(benzocyclobutene); BGOFET, back-gated organic field effect transistor; BSD, budesonide; CMOS, complementary metal-oxide semiconductor; CNT, carbon nanotube; CuPc, copper(II) phthalocyanine; CVD, chemical vapor deposition; CYTOP, cyclized perfluoro polymer; DA-BEDA, N,N′-dialkylbenzylethylenediamine; DDFTTF, 5,5′-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2′-bithiophene; DNA, deoxyribonucleic acid; DPV, differential pulse voltammetry; EBL, electron-beam lithography; EDL, electrical double layer; EGFET, electrolyte-gated field-effect transistor; EGOFET, electrolyte-gated organic field-effect transistor; EGOFET, electrolyte-gated organic field-effect transistor; EPPG, edge plane pyrolytic graphite; ExGOFET, extended- gate organic field-effect transistor; FET, field-effect transistor; FGOFET, floating-gate organic field-effect transistor; FITC, fluorescein isothiocyanate; FRET, fluores- cence resonance energy transfer; HDA, 4,4-(hexafluoroisopropylidene)diphthalic anhydride; HEK, human embryonic kidney cells; HeLa, cervical cancer cells; HFCVD, hot filament chemical vapor deposition; HQS, hydroquinone monosulfonate; IJP, ink-jet printing; IS-EGOFET, ion-sensitive electrolyte-gated organic field-effect transistor; ISFET, ion-sensitive field-effect transistor; ISM, ion sensitive membrane; ISOFET, ion-sensitive organic field-effect transistors; LB, Langmuir-Blodgett; LCP, liquid crystal polymer; MWCNT, multi-walled carbon nanotubes; NIL, nano-imprint lithography; OECT, organic electrochemical transistor; OFET, organic field-effect transistor; OTFT, organic thin film transistors; P3CT, poly(3-cyclohexyl thiophene); P3HT, poly(3-hexylthiophene); P3MT, poly(3-methylthiophene); PAA, poly(1- aminoanthracene); PAH, poly-(allylamine hydrochloride); PANI, polyanilline; PB, prussian blue; PBPA, polybisphenol A; PCz, polycarbazole; PDAN, poly-1,5-dia- minonaphthalene; PDAEM, poly(2-dimethylaminoethyl methacrylates); PEAA, polyethylacrylic Acid; PEDOT:PSS, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; PEI, polyethylenimine; PEN, polyethylene naphthalate; PET, polyethylene terephthalate; PGA, polyglycolic acid; PI, polyimide; PLGA, poly(lactic-co-gly- colic); PMMA, poly(methyl methacrylate); PPAA, poly(propyl acrylic acid); PPI, polypropylenimine; PPPD, poly(p-phenylenediamine); PPy, polypyrrole; PTAA, poly (triarylamine); PVA, polyvinyl alcohol; PVC, polyvinyl chloride; PVP, poly(4-vinylphenol); SAM, self-assembled monolayer; SC, suberoyl chloride; SGOFET, solution- gated organic field effect transistor; siRNA, small interfering RNA; SWCNT, single-walled carbon nanotube; TBAP, tetrabutylammonium perchlorate; TPB, tetra- phenylborate; α-6T, α-sexithiophene Progress in Materials Science 96 (2018) 174–216 Available online 11 April 2018 0079-6425/ © 2018 Elsevier Ltd. All rights reserved. T