Self-Standing Thin Films of Cellulose Nanocrystals and Graphene Quantum Dots for Detection of Trace Iron(III)

Cellulose nanocrystal (CNC) thin films have gained attentionforapplication in green optoelectronics devices. However, the dependenceon plasticizers, external cross-linkers, or auxiliary polymers canimpair the full exploration of the nanomaterials' properties.Herein, we report on the evaluation of a surface-oxidized CNCs ultrathinfilm, made from a formulation that excludes the use of auxiliary compounds,to be used as a sensing platform. The physicochemical characterizationsusing UV-vis, Fourier transform infrared , and Raman spectroscopies,nuclear magnetic resonance, zeta potential, transmission electronand field emission scanning electron microscopies, X-ray diffraction,thermogravimetric analysis, and contact angle measurement showed thatthe adopted procedure led to (i) the modification of the CNC surfaceand (ii) the formation of smaller CNCs. The production of castingfilms from highly diluted CNC-modified aqueous suspensions showedthat a very thin, transparent, self-supporting, and manipulable filmcould be obtained, which was not the case for diluted unmodified CNCsuspension. Additionally, the CNC thin film has been demonstratedto be a suitable platform for hosting graphene quantum dots, basedon which an optochemical sensor was successfully employed to detectiron(III) in a dynamic range from 1 fM to 2 pM, yielding a limit ofdetection of 0.8 fM.