Engineered Glucose Oxidase‐Carbon Nanotube Conjugates for Tissue‐Translatable Glucose Nanosensors

Abstract

Continuous and non‐invasive glucose monitoring and imaging is important for disease diagnosis, treatment, and management. However, glucose monitoring remains a technical challenge owing to the dearth of tissue‐transparent glucose sensors. In this study, we present the development of near‐infrared fluorescent single‐walled carbon nanotube (SWCNT) based nanosensors directly functionalized with glucose oxidase (GOx) capable of immediate and reversible glucose imaging in biological fluids and tissues. We prepared GOx‐SWCNT nanosensors by facile sonication of SWCNT with GOx in a manner that—surprisingly—does not compromise the ability of GOx to detect glucose. Importantly, we find by using denatured GOx that the fluorescence modulation of GOx‐SWCNT is not associated with the catalytic oxidation of glucose but rather triggered by glucose‐GOx binding. Leveraging the unique response mechanism of GOx‐SWCNT nanosensors, we developed catalytically inactive apo‐GOx‐SWCNT that enables both sensitive and reversible glucose imaging, exhibiting a ΔF/F0 of up to 40 % within 1 s of exposure to glucose without consuming the glucose analyte. We finally demonstrate the potential applicability of apo‐GOx‐SWCNT in biomedical applications by glucose quantification in human plasma and glucose imaging in mouse brain slices.

Monitoring Enzyme Activity Using Near-Infrared Fluorescent Single-Walled Carbon Nanotubes

“…Additionally, the Landry research group have successfully developed a biosensor for the reversible monitoring and imaging of glucose in biological fluids and mouse brain slices, utilizing GOx- and apo-GOx-SWCNTs. 87 GOx-SWCNTs, prepared by directly sonicating SWCNTs with GOx, exhibited immediate enhancement of the fluorescence intensity upon incubation with glucose in a buffer, forming the basis for monitoring glucose levels. Notably, other saccharides such as fructose, galactose, fucose, mannose, xylose, maltose, and sucrose did not significantly increase the fluorescence of GOx-SWCNTs under identical conditions, thereby highlighting the selectivity of the sensors.…”

“…Previously, SWCNTs suspended with enzymes have been employed to detect the substrates of the dispersant enzyme, rather than explicitly the activity of enzymes constituting the dispersant of SWCNTs. , Nonetheless, we envision that the approach of enzyme-assisted SWCNT suspension, designed to monitor enzyme activity upon subsequent interaction with relevant substrates, can be further developed based on the existing studies that have utilized a similar strategy for biomarker substrate monitoring.…”

“…Additionally, the Landry research group have successfully developed a biosensor for the reversible monitoring and imaging of glucose in biological fluids and mouse brain slices, utilizing GOx- and apo-GOx-SWCNTs . GOx-SWCNTs, prepared by directly sonicating SWCNTs with GOx, exhibited immediate enhancement of the fluorescence intensity upon incubation with glucose in a buffer, forming the basis for monitoring glucose levels.…”

“…In light of these considerations, the significance of luminescent probes operating in the near-infrared (NIR) region becomes evident. These probes offer real-time and spatiotemporal information, and their utility is particularly notable because biological samples are mostly transparent in the NIR region. − In pursuit of this objective, NIR luminescent single-walled carbon nanotubes (SWCNTs) are advantageous due to their intrinsic physicochemical and optical properties. ,− These include the high surface area and the ease of surface functionalization with molecules of choice that facilitate interaction with a large number of analytes, enabling high-throughput readouts. − Moreover, SWCNTs exhibit remarkable photo and chemical stability, rendering them a compelling choice as sensors for monitoring essential biomarkers, including proteins, − oncometabolites, pathogens, , various small molecules, − hormones, ,, volatiles, , lipids, ,, sugars, − neurotransmitters, ,,− microRNA, , metal ions, lysosomal pH, and enzymatic activity and inhibition. −…”

The Fluorescent Detection of Glucose and Lactic Acid Based on Fluorescent Iron Nanoclusters

“…Enzymatic sensors commonly utilize specific enzymes such as GluOx and LacOx to catalyze the oxidation of glucose or lactic acid. These sensors can measure downstream products such as H 2 O 2 resulting from glucose or lactic acid [ 19 , 20 , 21 , 22 , 23 , 24 ]. For example, Zhang et al developed a visual platform comprising MnO 2 nanosheets, GluOx, and rhodamine B for detecting glucose ranged from 0.25 to 20 μM based on the emission wavelength shift of rhodamine B [ 25 ].…”