Photoluminescence Response in Carbon Nanomaterials to Enzymatic Degradation

Abstract

Myeloperoxidase (MPO), a key enzyme released by neutrophils during inflammation, has been shown to catalyze the biodegradation of carbon nanomaterials. In this work, we perform photoluminescence studies on the MPO-catalyzed oxidation of graphene oxide (GO) and surfactant-coated pristine (6,5) singlewalled carbon nanotubes (SWCNTs). The enzymatic degradation mechanism involves the introduction of defects, which promotes further degradation. Interestingly, the photoluminescence responses of GO and SWCNTs to enzymatic degradation are counterposed. Although the near-infrared (NIR) fluorescence intensity of SWCNTs at 998 nm is either unchanged or decreases depending on the surfactant identity, the blue fluorescence intensity of GO at 440 nm increases with the progression of oxidation by MPO/H 2 O 2 /Cl − due to the formation of graphene quantum dots (GQDs). Turn-on GO fluorescence is also observed with neutrophil-like HL-60 cells, indicative of potential applications of GO for imaging MPO activity in live cells. Based on these results, we further construct two ratiometric sensors using SWCNT/GO nanoscrolls by incorporating surfactant-wrapped pristine SWCNTs as the internal either turn-off (with sodium cholate (SC)) or reference (with carboxymethylcellulose (CMC)) sensor. The ratiometric approach enables the sensors to be more stable to external noise by providing response invariant to the absolute intensity emitted from the sensors. Our sensors show linear response to MPO oxidative machinery and hold the promise to be used as self-calibrating carbon nanomaterial-based MPO activity indicators.

Biosensing with Fluorescent Carbon Nanotubes

“…used aratiometric system based on graphene oxide (GO) wrapped SC-SWCNT sensors and GO-wrapped carboxymethylcellulose (CMC)-SWCNTs as ar eference. [169] GO and SC-SWCNTs showed an opposed fluorescence signal in response to enzymatic degradation. Whereas the blue fluorescence intensity of GO was increased due to oxidation and degradation of GO leading to the formation of graphene quantum dots,t he NIR emission of SWCNTs decreased due to the generation of defects on the SWCNT surface.Incontrast, the CMC-SWCNT reference was almost stable as ar esult of the better surface protection of the CMC-wrapping.…”

Composition and Structure of Fluorescent Graphene Quantum Dots Generated by Enzymatic Degradation of Graphene Oxide

“…Here, hypochlorite (ClO − ) and reactive radical intermediates of MPO are the two oxidants involved in biodegradation of GO. 9,13,45 These two strong oxidants could play a similar role as hydroxyl radicals. 14 They start attacking defect sites in GO, namely, those sp 3 carbon atoms connected with hydroxyl and epoxide groups on the basal planes to break the C−C/CC bonds apart (Scheme 1).…”

“…Similar to the reported MPO-catalyzed oxidation of CNMs, , MPO enzymatic degradation of GO was conducted as described previously . Samples were prepared by adding 446 μL of 1× phosphate buffer saline (PBS) (Sigma-Aldrich, 0.01 M phosphate buffer, 0.0027 M potassium chloride, and 0.137 M sodium chloride, pH 7.4, at 25 °C) and 50 μL of 1 mg/mL GO.…”

“…We have recently reported the observation of gradually increased photoluminescence (PL) of GO during MPOcatalyzed enzymatic degradation. 13 We attributed the observed fluorescence to the formation of the fluorescent degradation products, graphene quantum dots (GQDs) 14,15 or carbon quantum dots, 16 which are presumably PAHs with specific molecular structures. Similar blue-luminescent GQDs have also been previously generated through a photo-Fenton oxidation reaction of GO.…”

Biosensing with Fluorescent Carbon Nanotubes

“…To study the enzyme myeloperoxidase, which is involved in the regulation of inflammation processes, He et al. used a ratiometric system based on graphene oxide (GO) wrapped SC‐SWCNT sensors and GO‐wrapped carboxymethylcellulose (CMC)‐SWCNTs as a reference [169] . GO and SC‐SWCNTs showed an opposed fluorescence signal in response to enzymatic degradation.…”