Mediatorless, Reversible Optical Nanosensor Enabled through Enzymatic Pocket Doping

Abstract

Single-walled carbon nanotubes (SWCNTs) exhibit intrinsic near-infrared fluorescence that benefits from indefinite photostability and tissue transparency, offering a promising basis for in vivo biosensing. Existing SWCNT optical sensors that rely on charge transfer for signal transduction often require exogenous mediators that compromise the stability and biocompatibility of the sensors. This study presents a reversible, mediatorless, near-infrared glucose sensor based on glucose oxidase-wrapped SWCNTs (GOx-SWCNTs). GOx-SWCNTs undergo a selective fluorescence increase in the presence of aldohexoses, with the strongest response toward glucose. When incorporated into a custom-built membrane device, the sensor demonstrates a monotonic increase in initial response rates with increasing glucose concentrations between 3 × 10 and 30 × 10 m and an apparent Michaelis-Menten constant of K (app) ≈ 13.9 × 10 m. A combination of fluorescence, absorption, and Raman spectroscopy measurements suggests a fluorescence enhancement mechanism based on localized enzymatic doping of SWCNT defect sites that does not rely on added mediators. Removal of glucose reverses the doping effects, resulting in full recovery of the fluorescence intensity. The cyclic addition and removal of glucose is shown to successively enhance and recover fluorescence, demonstrating reversibility that serves as a prerequisite for continuous glucose monitoring.

Carbon Nanotubes Encapsulated in Coiled‐Coil Peptide Barrels

“…The key challenge is to tailor their surface and thus render them stable in aqueous solution but also to control interactions with their environment . To preserve their nIR fluorescence, mainly non‐covalent functionalization schemes including amphiphilic (bio)polymers, modified polyethyleneglycols, proteins and especially single‐stranded DNA (ssDNA) have been used . Covalent conjugation strategies of SWCNTs are highly promising but they alter the nanotube's conjugated sp 2 system and thus their excitonic fluorescence .…”

“…[8] To preserve their nIR fluorescence, mainly noncovalentf unctionalization schemes including amphiphilic (bio)polymers, modified polyethyleneglycols,p roteinsa nd especially single-stranded DNA (ssDNA) have been used. [9][10][11][12][13][14][15][16] Covalent conjugation strategies of SWCNTsa re highly promising but they alter the nanotube's conjugated sp 2 system and thus their excitonic fluorescence. [17][18][19] Therefore, these approaches are less used if unchanged optoelectronic properties such as the nIR fluorescence are important.…”

Nanoröhren‐Nanobody‐Konjugate als zielgerichtete Sonden und Marker für die In‐vivo‐Nahinfrarot‐Bildgebung

“…SWCNTs sind jedoch nicht nur statische Fluorophore, sondern sind auch bereits erfolgreich als Sonden für die Detektion von kleinen Molekülen, mRNAs, Zuckern und Proteinen verwendet worden . Insbesondere SWCNT/DNA‐Hybride konnten in der Vergangenheit als optische Sonden in der orts‐ sowie zeitaufgelösten Detektion des Neurotransmitters Dopamin eingesetzt werden .…”

Exfoliated near infrared fluorescent CaCuSi4O10 nanosheets with ultra-high photostability and brightness for biological imaging

“…nIR fluorescent nanomaterials include InAs quantum dots, lanthanide doped nanoparticles or semiconducting single-walled carbon nanotubes (SWCNTs) [8][9][10][11][12] . For example, SWCNTs have been used as building blocks for nIR imaging and as fluorescent sensors that detect small signaling molecules, proteins or lipids [13][14][15][16][17][18][19] . They can be chemically tailored and have been used to reveal spatiotemporal release patterns of neurotransmitters from single cells 2,15,[20][21][22] .…”