Nanocellulose- based biosensor for colorimetric detection of glucose

This work reports for the first time a colorimetric based biosensor using nanocellulose (NC) based supports drop-deposited onto a cellulose paper substrate for glucose detection in point-of-care. For this purpose, microcrystalline cellulose (MCC) samples were oxidized with 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO), sodium hypochlorite, and potassium bromide, to produce carboxylated NC. For the characterization, we used several methods: TEM, FTIR and conductometric titration. In all samples, the primary alcohol groups were selectively oxidized into carboxyl groups, provided the sodium hypochlorite is added dropwise and the reaction is performed at constant pH 10. Carboxyl- NC was further casted on a cellulose substrate and used as support for glucose oxidase (GOx), horseradish peroxidase (HRP) and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) reactions, aiming to yield a coloured detection system for glucose. The sensing system was generated by integrating GOx on the carboxyl- NC /cellulose substrate. Upon reaction with glucose, the enzyme produced hydrogen peroxide, which was converted into a blue-coloured product by reaction with HRP and the chromogenic reagent ABTS. The test-strip was calibrated by incubating it in different concentrations of glucose. The colours obtained were further analysed by a suitable image analysis software. Linear response for glucose ranged from 1.5 to 13.0 mM. Overall, this new test-strip used renewable material for glucose determination, which is an advantage when compared to other systems that require more complex technological approaches. Moreover, it was found that carboxyl- NC improved the colour homogeneity of the test-strip and the intrinsic linear response of concentration range.The Portuguese Science and Technology Foundation, I.P. (FCT), is acknowledged for the financial support through the project reference P2020-PTDC/AAG-TEC/5400/2014 (also POCI-01-0145-FEDER-016637, FEDER, COMPETE, POCI) and POCTEP/INTERREG is also acknowledged through the project 2QBioneuro, Impulso de una red de I+i en química biológica para diagnóstico y tratamiento de enfermedades neurológicas. MCCGC acknowledges FCT for the PhD grant SFRH/BD/131959/2017. The Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte.