A sensitive dual mode turn-on fluorescence and colorimetric nanosensor for ultrasensitive detection of trace amount of gluten proteins in bread products based on crystalline nano cellulose and gold nanoparticles.

In this work, Gold nanoparticles (AuNPs) encapsulated in the surface of crystalline nano cellulose grafted poly citric acid (CNC-g-PCA) and CNC-g-PCA/Au nanocomposite were synthesized successfully that exhibited stable and intense fluorescence property in aqueous buffer. A dual-mode nanosensor is reported with both colorimetric and fluorimetric readout based on citrate-protected AuNPs for discriminative detection of gluten proteins. The proposed sensing system consists of AuNPs and fluorescent CNCs, where CNCs function as a fluorimetric reporter and AuNPs serve a dual function as a colorimetric reporter and fluorescence quencher. The mechanism of the reported dual-mode nanosensor is based on two distance-dependent phenomena, the color change of AuNPs and FRET. The presence of gluten proteins can reverse the process by enlarging the inter-particle distance between AuNPs and CNCs and recovering the fluorescence emission of CNC. The linear range was 0.05 to 0.40 μgmL for UV-vis spectroscopy and 0.017 to 0.298 μgmL for fluorescence spectroscopy, The limit of detection was 4.43 ± 0.019 ngmL for UV-vis spectroscopy and 3.13 ± 0.033 ngmL for fluorescence spectroscopy (n = 6). The fabricated nanosensor was applied to the gluten analysis in gluten-free bread successfully.