Colorimetric and fluorescence “turn-on” methods for the sensitive detection of bromelain using carbon dots functionalized gold nanoparticles as a dual probe

Abstract

Bromelain is a group of sulfhydryl-containing proteolytic enzymes, which exhibit antiedematous, anti-inflammatory, antithrombotic and fibrinolytic activity. Herein, we report a dual-mode nanosensor with both colorimetric and fluorescence detection of bromelain using carbon dots capped gold nanoparticles (CDs-Au NPs) as a dual probe. Upon the addition of bromelain to the CDs-Au NPs dispersed in an aqueous solution, the probe shows a dramatic color change from red to blue and a remarkable ratiometric fluorescence enhancement, which are based on two distance-dependent phenomena: the color change of CDs-Au NPs and the displacement of the CDs from the surface of the Au NPs. A red-shift in the surface plasmon resonance (SPR) peak from 523 to 576 nm and an enrichment of the fluorescence emission at 425 nm was observed, which resulted in good linear relationships between A₅₇₆/A₅₂₃ and I/I₀, and at concentrations of 1.0–260 μM (R² = 0.991) and 1.0–100 nM (R² = 0.993), the limits of detection for bromelain at a signal-to-noise ratio of 3 were 18.9 nM and 0.52 nM using UV-visible and fluorescence spectroscopy, respectively. This dual probe allows for the quantification and detection of bromelain in real samples such as pineapple extracts and biological samples.