Single-Walled Carbon Nanotubes as Optical Transducers for Nanobiosensors In Vivo

Abstract

Semiconducting single-walled carbon nanotubes (SWCNTs) may serve as signal transducers for nanobiosensors. Recent studies have developed innovative methods of engineering molecularly specific sensors, while others have devised methods of deploying such sensors within live animals and plants. These advances may potentiate the use of implantable, noninvasive biosensors for continuous drug, disease, and contaminant monitoring based on the optical properties of single-walled carbon nanotubes (SWCNTs). Such tools have substantial potential to improve disease diagnostics, prognosis, drug safety, therapeutic response, and patient compliance. Outside of clinical applications, such sensors also have substantial potential in environmental monitoring or as research tools in the lab. However, substantial work remains to be done to realize these goals through further advances in materials science and engineering. Here, we review the current landscape of quantitative SWCNT-based optical biosensors that have been deployed in living plants and animals. Specifically, we focused this review on methods that have been developed to deploy SWCNT-based sensors in vivo as well as analytes that have been detected by SWCNTs in vivo. Finally, we evaluated potential future directions to take advantage of the promise outlined here toward field-deployable or implantable use in patients.

Keywords: SWCNT; biosensor; implants; in planta; in vivo; mice; nanosensor; near-infrared fluorescence; point-of-care.

Figure 1

Response of a SWCNT-based fluorescence sensor. Interaction of the analyte with the SWCNT transducer modulates fluorescence upon excitation. In the above example, analyte binding to the sensor induces an SWCNT increase in intensity and red-shifting in center wavelength (to the right). However, the magnitude and change in energy of fluorescence modulation is specifically dependent on the interactions of the analyte, binding element, and SWCNT transducer, as well as local environment, and thus may manifest as any combination of a modulation of intensity (ΔI) or modulation of center wavelength (Δλ).

Figure 2

Common SWCNT functionalization methods with demonstrated functionality in vivo. In each panel, the gray tube represents a SWCNT transducer, the blue elements represent SWCNT functionalization methods, and the orange elements represent various analytes of interest. A) A method for complementary nucleic acid base pair detection. Dark blue ssDNA stabilizes SWCNTs in solution and light blue is complementary to the sequence of interest (orange). B) A method for protein antigen detection. Dark blue ssDNA stabilizes SWCNTs in solution and a light blue antibody is conjugated to it, which detects the analyte of interest (orange). C) A method of small molecule (orange) detection based on its interaction with dark blue ssDNA used to stabilize SWCNTs. The ssDNA may have some intrinsic or screened affinity for the analyte of interest. D) CoPhMoRe-based detection of a small molecule analyte (orange), wherein dark blue represents a screened polymer or ssDNA that has creates binding pockets for the analyte. This may be enhanced by target templating, using conjugated target (purple). E) Integration of sp³ carbon functionalization, termed organic color centers (OCCs) or quantum defects, which may impart selectivity for an analyte itself or, in this example, after conjugation with an antibody fragment.

Figure 3

Examples of direct SWCNT sensor application. A) A fluorescent SWCNT sensor was injected intravenously, exhibited liver accumulation and imaged with a near-infrared hyperspectral microscope, where it detected lipid accumulation. Reprinted in part with permission from Galassi et al. 2018 Sci. Trans. Med. copyright AAAS. B) A SWCNT sensor designed to detect pH was injected intratumorally into mice with an ovarian cancer xenograft. Reproduced in part with permission from Kim et al. 2023 Nat. Chem. Biol. copyright Springer Nature. C) A fluorescent SWCNT sensor designed to detect the Alzheimer’s disease protein amyloid-beta was injected via a stereotactic device intracranially into the hippocampus of a mouse disease model. Reproduced in part with permission from Antman-Passig et al. 2022 ACS Nano copyright American Chemical Society. D) A SWCNT-based sensor designed to detect synthetic plant hormones auxins was added to plant leaves and was imaged in the near-infrared region. Reproduced in part with permission from Ang et al. 2021 ACS Sensors copyright American Chemical Society.

Figure 4

Examples of encapsulated SWCNT application. A) A SWCNT sensor for the ovarian cancer protein biomarker HE4 was encapsulated inside a semipermeable dialysis membrane surgically implanted into mice with orthotopic ovarian cancer xenografts. Reproduced in part with permission from Williams et al. 2018 Sci. Adv. copyright AAAS. B) A SWCNT sensor was used to detect doxorubicin in mice after embedding it within semipermeable dialysis membranes and implantation into the peritoneal cavity or subcutaneously in mice. Reproduced in part with permission from Harvey et al. 2019 Nano Lett. copyright American Chemical Society. C) A preformed hydrogel composed of alginate and embedded with SWCNT sensors for nitric oxide were implanted into mice (not shown) and the ears of sheep. Reprinted in part with permission from Hofferber et al. 2022 Nanomed.: Nanotech., Bio., Med. copyright Elsevier. D) A polyethylene glycol diacrylate (PEGDA) hydrogel array with riboflavin-responsive SWCNT sensors was embedded beneath the scales of several species of fishes. Reproduced in part with permission from Lee et al. 2019 ACS Sensors copyright American Chemical Society.

Figure 5

Schematic encompassing common in vivo applications of SWCNT-based sensors. Top represents common methods of in vivo deployment. The middle section represents several different species in which SWCNT sensors have been used, with mice being the most prominent. Bottom demonstrates several various analytes that have been detected in vivo by SWCNT-based sensors.