A 'one-tube' synthesis of a selective fluorescence 'turn off/on' DNA probe based on a C-phycocyanin-graphene oxide (CPC-GO) bio composite

A naturally fluorescent protein, C-phycocyanin (CPC), was used as a fluorophore to study the effect of graphene oxide (GO) as a quencher. The protein was purified using established procedures and titrated with increasing GO concentrations. UV-visible titration showed a minor effect on the phycocyanobilin absorbance but significant interactions with the amino acid backbone. Fluorescence titration showed notable CPC quenching upon increasing GO concentration to 30 mu g ml(-1); the corresponding fluorescence dropped by similar to 97%. A non-linear Stern Volmer curve showed that the fluorophores did not interact directly with the quencher. Powder X-ray diffraction studies showed that the bio-composite lost the crystalline arrangement of GO and became amorphous, akin to CPC. SEM analysis showed GO sheets enfolding a protein nucleus with an increase in oxygen after the interaction compared to CPC. A 20 min incubation of the bio-composite with various biomolecules including amino acids, sugars, polydispersed exopolysaccharides (EPS), other proteins and DNA showed that only DNA could recover the CPC fluorescence. The `turn on' effect of DNA was distinguishable even when all the other molecules were in the same sample matrix. These results showed that CPC GO could be a fluorescence `turn off/on' DNA probe. (C) 2020 Elsevier B.V. All rights reserved.