Fabrication of a GUMBOS-based acid-base indicator: smart probe for sensing acids and bases in any solvent Prabal Pramanik a , Rajkumar Sahoo a , Sudhir Kumar Das b , and Mintu Halder a * a Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. b Department of Chemistry, University of North Bengal, Darjeeling,734013, India. Email: mintu@chem.iitkgp.ac.in Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics. This journal is © the Owner Societies 2020