Method of Detection of Volatile Organic Compounds Using Liquid Crystals that Form a Blue Phase; and Device for Stabilization and Thickness Control of Liquid Crystal Films

Abstract

Methods and compositions for detecting a targeted analyte, such as volatile organic compound (VOCs), are disclosed. Specifically, a cholesteric liquid crystal composition comprising a nematic liquid crystal and a chiral dopant transitions to a liquid crystal blue phase or undergoes other optical changes when in contact with a sample containing the analyte. The phase transition can be readily detected with the naked eye. The disclosed methods and compositions may be used in, for example, dosimeters for detecting analyte (e.g., VOC) exposure. Methods and compositions for producing arrays of liquid crystal thin films are also disclosed. The surface between the microwells in a microwell array is coated with a liquid-crystal-phobic material, such as a fluorinated polymer or a fluorinated silane, creating isolated microwell domains that are preferentially wetted by liquid crystal. Liquid crystal can be added to the microwell domains by simple techniques such as spin coating.

What is claimed is: 
     
         1 . A device for detecting a target analyte in a in a gaseous or liquid sample, comprising a blue phase-forming liquid crystal film that undergoes an irreversible optical change upon exposure to the sample containing the target analyte. 
     
     
         2 . The device of  claim 1 , wherein the blue phase-forming liquid crystal film comprises a nematic liquid crystal and a chiral dopant. 
     
     
         3 . The device of  claim 1 , wherein at least a portion of the blue phase-forming liquid crystal film has transitioned into a liquid crystal blue phase. 
     
     
         4 . The device of  claim 1 , wherein the sample comprises ambient air, a gas carrier that does not trigger a response in the blue phase-forming liquid crystal film, a liquid mixture, or an aqueous solution. 
     
     
         5 . The device of  claim 2 , wherein the chiral dopant makes up about 30-50% by weight of the blue phase-forming liquid crystal film. 
     
     
         6 . The device of  claim 2 , wherein the chiral dopant is selected from the group consisting of S-811 ((S)-Octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy)benzoate), R-811 ((R)-Octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy)benzoate), C15 
       
         
           
           
               
               
           
         
       
       CB15 ((S)-4-(2-methylbutyl)-4-cyanobiphenyl), S-1011, R-1011, S-2011, and R-2011. 
     
     
         7 . The device of  claim 1 , wherein the blue phase-forming liquid crystal film further comprises a non-volatile organic compound that increases the sensitivity of response of the blue phase-forming liquid crystal film to the target analyte. 
     
     
         8 . The device of  claim 7 , wherein the non-volatile organic compound is a polymer or a polycyclic aromatic compound. 
     
     
         9 . The device of  claim 7 , wherein the non-volatile organic compound is selected from the group consisting of pyrene, phenanthrene, polystyrene, benzoic acid, biphenyl, a halogenated biphenyl, and benzopyrene. 
     
     
         10 . A method for detecting a target analyte in a sample, comprising:
 (a) contacting the blue phase-forming liquid crystal film of the device of  claim 1  with the sample; and   (b) observing one or more optical properties of the blue phase-forming liquid crystal film;   wherein an irreversible change in the optical properties of the blue phase-forming liquid crystal film indicates the presence of the target analyte in the sample.   
     
     
         11 . The method of  claim 10 , wherein the target analyte is a volatile organic compound (VOC). 
     
     
         12 . The method of  claim 10 , wherein the concentration of the target analyte in the sample is less than 500 ppm. 
     
     
         13 . The method of  claim 10 , wherein the concentration of the target analyte in the sample is less than 200 ppm.