Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Abstract

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Figure 1

Carbon nanomaterial (CNM) types and their structures. (A) Pristine carbon nanotubes are cylindrical nanocrystals of sp² hybridized carbon atoms. (B) Carbon dots are quasi-spherical nanoparticles with a mix of sp² and sp³ carbon atoms and contain a variety of functional handles. (C) Carbon nanocones represent sp² carbon atoms rolled into a conical geometry. (D) Carbon nanohoops can be conceptualized as a single slice of a carbon nanotube. (E, F) Pristine graphene is a 2-dimensional material made of sp² carbon atoms in a honeycomb-like arrangement, whereas graphene oxide contains a mix of sp² and sp³ carbon atoms and features various functional moieties.

Figure 2

FTIR and Raman characterization of different preparations of SWCNTs. (A) FTIR spectra for raw SWCNT soot (a), dry oxidized (b), H₂O₂ refluxed (c), purified material via HCl and high-temperature vacuum anneal (HTVA) treatment at 1100 °C (d), and purified material via HNO₃ and HTVA treatment at 1100 °C (e). The top two spectra on purified SWCNTs represent the cleanest material. (B) Raman spectra for the same SWCNT types from (A) showing R-band (100–300 cm^–1) region (left panel) and D- and G-band region (1230–1750 cm^–1) (right panel). Reproduced from ref (138). Copyright 2005 American Chemical Society.

Figure 3

XPS and NMR characterization of CNMs. (A) XPS spectra of (a) unmodified SWCNT C 1s, (b) carboxylated C 1s, (c) amide-functionalized C 1s, (d) amine-functionalized C 1s, (e) amide-functionalized N 1s, (f) amine-functionalized N 1s. Reproduced from ref (150). Copyright 2005 American Chemical Society. (B) (Top panel) ¹H NMR spectrum of Methylene-Bridged [6]CPP. Reproduced from ref (151). Copyright 2020 American Chemical Society. (Bottom panel) Solid-state NMR spectra of polyethylenimine (PEI)-functionalized SWCNTs via ¹³C MAS NMR spectrum with a 12 kHz spinning speed. Reproduced from ref (152). Copyright 2008 American Chemical Society.

Figure 4

SAXS and SANS characterization of CNMs. (A) (Left panel) SAXS patterns of GO aqueous dispersions with maximum mass fraction (f_m’s) of 2.5 × 10^–4, 5 × 10^–3, 1 × 10^–2, 1.5 × 10^–2, 2 × 10^–2, and 2.5 × 10^–2, from 1 to 6. The white arrows indicate the diffuse arc and the scattering peak. (Right panel) SAXS profiles of liquid crystals of GO with high concentrations. The spectra depict the scattering intensity as a function of scattering vector q (q = (4π sin θ)/λ, where 2θ is the scattering angle). Reproduced from ref (157). Copyright 2011 American Chemical Society. (B) (Left panel) SANS patterns of SWCNTs dispersed in Pluronic F127 in 100% D₂O, at four different concentrations of 6, 4, 2, and 1% (%w/w). (Right panel) Schematic of dispersed SWCNTs. Reproduced from ref (158). Copyright 2012 American Chemical Society.

Figure 5

AFM, TEM, SEM, and STM characterization of CNMs. (A) (Top) AFM image of CDs with height profiles of some dots along the highlighted line. (Middle left) Size distribution based on AFM height analyses, (middle right) a high-resolution TEM image of CDs illustrating the carbon core (Bottom) TEM image of the gold-doped CDs. Reproduced from ref (173). Copyright 2014 American Chemical Society. (B) SEM images of GO and rGO nanosheets. Reproduced from ref (174). Copyright 2011 American Chemical Society. (C) (Left) Topographic STM image of a CD in the dashed white box with scale bar of 5 nm and colormap indicating STM height. (Right) PCA and k-means clustering of the tunneling spectroscopy data reveal low (blue) to high (yellow) density of states showing localized defects of about 1–2 nm in diameter. Reproduced from ref (175). Copyright 2020 American Chemical Society.

Figure 6

UV–vis-IR, zeta potential, and size characterization of CNMs. (A) UV–vis absorption spectroscopy of CDs with increasing number of oxygen-containing defects (blue to red CDs). (B) Fluorescence emission spectra of the four fractionated CD samples. (C) Zeta potential measurements of four CDs. (D) Hydrodynamic diameter measurements by DLS indicate no size trend of blue to red CDs. Reproduced from ref (175). Copyright 2020 American Chemical Society.

Figure 7

SWCNT photophysical properties. (A) CNTs can be conceptualized as graphene sheets rolled according to unique rollup vectors that determine their optoelectronic properties and give rise to a diversity of species. The direction and magnitude of the rollup vector is often denoted by a pair of indices, (n, m), which can be thought of as scalar multipliers of the unit basis vectors into which the roll up vector can be decomposed. (B) CNT species can fall within three categories depending on the “twist” of the graphitic lattice. (C) An electronic density of states for a nanotube species of the semiconducting (chiral) type, with a small but nonzero bandgap between the valence and conduction bands. Note the sharp peaks in the density of states, which gives rise to “feature-rich” spectra depicted in (D). Excitation is typically carried out using E₂₂-lasers, and fluorescence emission is detected with Stokes shift of >100 nm from the E₁₁ state (equivalent to the first excited stated in molecular spectroscopy). (D) Absorption (top) and fluorescence emission (bottom) spectra from a multichiral (polydisperse) dispersion of single wall carbon nanotubes synthesized by the HiPco method. λ_ext = 785 nm is typically used for broad resonant and off-resonance excitation of nanotubes for most imaging applications. Peak assignments for some of the prominent chiralities observed in HiPco samples are shown in red text. For a thorough treatment of optical spectroscopy of SWCNTs, the reader is invited to review Weissman et al.

Figure 8

SWCNT photoluminescence in the NIR/SWIR window is coincident with reduced absorption, scattering, and autofluorescence from biological samples. (A) Effective attenuation coefficients of skin and blood in the 1^st and 2^nd NIR windows. (B) Absorption by water from 400–1800 nm. (C) Reduced scattering coefficients of various biological matrices exhibit monotonic decrease into the NIR/SWIR window. (D) Autofluorescence spectra of ex vivo mouse tissues at 808 nm excitation. Reproduced from ref (251). Copyright 2018 American Chemical Society.

Figure 9

Engineered covalent adducts on SWCNTs allow for tunable fluorescence emission. Note the emergence of a brighter, red-shifted emission peak (E₁₁^–) after functionalization with covalent color centers.

Figure 10

Electronic density of states for graphene, GO , and RGO. Conduction band (CB) is shown in blue and valence band (VB) is shown in orange. Notice the absence of bandgap in graphene vs graphene oxide. Adapted with permission from ref (385). Copyright 2018 Springer Nature under CC BY. http://tinyurl.com/yuh4xfa4.

Figure 11

Various carbon nanomaterials have been used in microorganisms, plants, and animals for diverse applications in imaging, biosensing, biomacromolecule and drug delivery, and combined therapy. Figure prepared using BioRender.com.

Figure 12

(A) NIR-II SWCNT fluorescence and micro-CT images of a mouse thigh (same area imaged in both modalities) and the cross-sectional intensity profiles measured along the green dashed lines fitted with a Gaussian distribution function (scale bar = 2 mm). (B) Time course NIR-II fluorescence images of a hind limb blood flow in a healthy vs ischemic mouse. Principal component analysis (PCA) revealed arteries and veins, color-coded in red and blue, respectively (scale bar = 2 mm). Reproduced with permission from ref (901). Copyright 2012 Springer Nature.

Figure 13

(A) Images of a head-shaved mouse and fluorescence images of the same mouse in the NIR-I, NIR-II, and NIR-IIa windows after a tail vein injection of SWCNTs. Inferior cerebral vein, superior sagittal sinus, and transverse sinus are labeled as 1, 2, and 3. (B) Time course NIR-IIa images (top rows) of a control (healthy) vs MCAO (stroke model) mouse treated with SWCNTs. PCA overlaid images (bottom rows) showing arterial (red) and venous (blue) vessels. Adapted with permission from ref (904). Copyright 2014 Springer Nature.

Figure 14

(A) Optical micrographs and NIR fluorescence images of three SWCNT preparations at equal concentrations. Emission was collected using excitation at 808 nm. (B) NIR fluorescence images (1000–1700 nm) of nude mice treated with exchange or direct-SWCNTs at 30 min and 24 h post tail vein injections. Reproduced with permission from ref (910). Copyright 2009 Springer Nature.

Figure 15

(A) Frames of video-rate imaging of a mouse following a tail vein injection with SWCNTs (scale bar = 1 cm). (B) Dynamic contrast-enhancing imaging via PCA analysis. Adapted with permission from ref (911). Copyright 2011 Proceedings of the National Academy of Sciences.

Figure 16

Time course NIR-II fluorescence images of a 4T1 tumor bearing mouse after injection of SWCNTs decorated with octadecene appended PEG chains. Reproduced from ref (924). Copyright 2012 American Chemical Society.

Figure 17

(A) Bright-field and merged fluorescence images of mice subcutaneously injected with CDs (top) and C_ZnS-Dots (bottom). Emission at 525 and 620 nm were collected by 470 and 545 nm excitations, respectively. Adapted with permission from ref (937). Copyright 2009 American Chemical Society. (B) Fluorescence and bright-field merged images of a zebrafish incubated with CQDs at 488 nm excitation. Adapted with permission from ref (942). Copyright 2020 Dove Medical Press Limited.

Figure 18

(A) Dependence of subcellular localization and cellular penetration on the type and length of the CNMs. The diameters of MWCNTs were 10–30 nm and SWCNTs were 1–3 nm. Length distributions for long MWCNT, short MWCNT, long SWCNT, and short SWCNT were 1–2 μm, 0.5–1 μm, 100–200 nm, and 50–100 nm, respectively. Nanotubes were conjugated to Alexa Fluor 488, and merged images of bright-field and fluorescence are presented. Scale bar is 20 μm. Adapted with permission from ref (960). Copyright 2010 Wiley-VCH. (B) Transmitted light and broadband NIR fluorescence (950–1350 nm) time lapse images of human umbilical vein endothelial (HUVEC) cells stained with 1 mg L^–1 (GT)₃₀-SWCNTs for 1 h. Scale bars for transmitted and NIR fluorescence images are 20 and 10 μm, respectively. Reproduced from ref (961). Copyright 2021 American Chemical Society. (C) Subcellular localization of HeLa cells costained with guanidinium- or ammonium-polymer coated SWCNTs and Hoechst 33258. Scale bar is 10 μm. Reproduced from ref (962). Copyright 2017 American Chemical Society.

Figure 19

(A) Schematic of kif5c and HaloTag (HT) protein fusion. (B) SWCNTs are bound to the kinesin via their HT ligand surface motifs. (C) Movement of kinesin labeled with SWCNTs is tracked in a COS-7 cell line. Nucleus and periphery are outlined in red dashed and dotted lines, respectively. The red diamond marks beginning and end of the 500 s trajectory over 40 μm. Adapted with permission from ref (963). Copyright 1979 American Association for the Advancement of Science. (D) Super resolved image of an ECS obtained from 20,000 localizations of a diffusing SWCNT. (E) Characteristic length scales of ECS microdomains pooled from many tracking experiments. (F) Diffusion coefficients and viscosity of the ECS computed from single particle tracking experiments. Adapted with permission from ref (966). Copyright 2017 Springer Nature.

Figure 20

HeLa cells stained with functionalized fluorescent CDs with tunable emission profiles. Cells were imaged under fluorescence (top) and bright-field (bottom) modes. Adapted with permission from ref (983). Copyright 2013 Springer Nature. FCN stands for fluorescent carbon nanoparticles, which we collectively refer to as CDs in this review.

Figure 21

Live cell imaging using carbon nanohoops. (A) CPPs can be conceptualized as the smallest macrocyclic slices of an armchair nanotube. Notice the counter-intuitive red shifting of fluorescence as ring size decreases. Right: structure of cell permeable disulfonate [8]CPP, used for live cell imaging depicted in panel B. (B) Bright-field, nuclear (NucRed, red) and cytoplasmic (disulfonate [8]CPP, green) images of HeLa cells, and overlay between red and green channels. Top row: imaged in the absence of disulfonate [8]CPP. Reproduced from ref (1011). Copyright 2018 American Chemical Society. (C) Structure of meta[6]CPP with PEG chains to enhance aqueous solubility, capped with subcellular targeting ligands (R). (D) Top row: Lysosome-targeting motif enables localization of meta[6]CPP punctate signal to lysosome (good overlap with LysoTracker). Middle row: Nanohoop without lysosome-targeting motif exhibits diffuse labeling and poor overlap with LysoTracker. Bottom row: lysosome-targetted nanohoops show poor overlap with MitoTracker, a mitochondrial marker. Reproduced from ref (1013). Copyright 2021 American Chemical Society.

Figure 22

Confocal images after a 2-h treatment with CDs@MR-1, showcasing two Gram-positive bacterial strains (S. aureus and B. subtilis) and two Gram-negative bacterial strains (E. coli and P. aeruginosa). Adapted with permission from ref (1031). Copyright 2022 Elsevier.

Figure 23

(Left) Schematics of Gram-negative and Gram-positive bacteria cell walls. (Right) Competition assay using T-SCQDs at a concentration of 500 μg/mL with peptidoglycan, lipoteichoic acid, and lipopolysaccharide to assess their binding affinity toward peptidoglycan and lipoteichoic acid. Adapted from ref (1032). Copyright 2021 American Chemical Society.

Figure 24

(A) Fluorescence emission spectra of Fe₃O₄/CD aptasensor after incubation with different concentrations of S. aureus in vitro. (B) An investigation into the aptasensor’s specificity for the detection of S. aureus, E. coli, A. hydrophila, P. aeruginosa, P. fluorescens, Y. enterocolitica, and S. typhimurium, each at a concentration of 10⁵ CFU·mL^–1. Adapted from ref (1035). Copyright 2019 American Chemical Society.

Figure 25

Ratiometric fluorescent nanoprobe, which utilizes both vancomycin and aptamer dual-recognition elements, offers an extensive Stokes shift. Adapted from ref (1036). Copyright 2020 American Chemical Society.

Figure 26

(A) Bright-field, autofluorescence, and NIR fluorescence (both under wide field and confocal modes) of Synechocystis cells incubated with ssDNA- or LSZ-wrapped SWCNTs. Note LSZ-coated SWCNTs efficiently label bacterial cells, while ssDNA-coated SWCNTs do not (scale bar = 3 μm). (B) AFM images of short and long SWCNTs (scale bar = 1 μm) and NIR fluorescence images of Synechocystis cells incubated with short and long SWCNTs (scale bar = 10 μm). Adapted with permission from ref (1037). Copyright 2022 Springer Nature.

Figure 27

Interactions between carbon dots and the cell walls of native plants and algae. (A) Confocal images showing the cell walls isolated from Arabidopsis plant leaves and live green algae (Coleochaete). The scale bar in the images is 100 μm. (B) Comparative analysis of CD fluorescence intensity, which was normalized by the imaging area, for the cell walls of native plants and algae based on multiple confocal images (n = 3–9). Different letters in the graph represent statistically significant differences, as determined by one-way ANOVA and Tukey test (** p < 0.01, **** p < 0.0001). (C) The z-stack images depict the binding of PEI-CDs to the cell wall and membrane of algae, with chloroplasts shown in magenta. Adapted from ref (1056). Copyright 2023 American Chemical Society.

Figure 28

(A) Evaluation of the adsorption efficiency of PEI-CNDs on bilayers containing 0–10% SQDG. The adsorption efficiency was determined as zero for the 0% SQDG bilayer since the exposure to PEI-CNDs did not result in detectable frequency changes. (B) Adsorption efficiencies of PEI-CNDs on 0–10% SQDG containing bilayers under 0–100 mM KCl, showing effects of increasing ionic conditions. Adapted from ref (1061). Copyright 2022 American Chemical Society.

Figure 29

(Left) Schematics of CNM targeting to plant chloroplasts. (Right) The analysis of colocalization in nanostructures revealed a notably increased proportion of chloroplasts containing targeted nanomaterials, in contrast to the control group lacking TPs. Statistical evaluation was performed using one-way ANOVA and post hoc Tukey’s test, with a sample size of 7 to 12, yielding a highly significant result with p < 0.0001. Adapted from ref (1066) Copyright 2022 American Chemical Society.

Figure 30

Neurons receive input through dendrites, integrate this input at the cell body, and send information out to neighboring neurons through their axons. Communication occurs via interfaces known as chemical synapses that convert electrical signals in axons to chemical signals that are released via vesicular exocytosis (inset).

Figure 31

SWCNT-based sensors for the catecholamine dopamine. (A) Pristine nanotubes surface functionalized with a short, 12-mer oligonucleotide sequence (GT)₆ exhibits a strong turn-on sensitivity to dopamine. The ssDNA coat affords colloidal stability and tiles the surface of nanotubes, creating binding pockets for dopamine molecular recognition. Ligand binding is transduced via modulation of the nanotube’s fluorescence emission. To the right: current model of how the sensor is thought to work. Dispersions of ssDNA@SWCNT exhibit quenched fluorescence, which is partially rescued by the addition of dopamine (+DA). (B) Top: Fluorescence spectra of a polydisperse nanotube colloid before (black) and after (red) addition of 10 μM dopamine (+DA) in solution. Bottom: Dose response curve for surface immobilized nanotubes show half maximal response (EC₅₀) of ∼250 nM.

Figure 32

Imaging of dopamine release from brain slice tissue. (A) Brain slices are incubated in solutions that contain dopamine nanosensors. This process delivers the nanosensors into the brain slice through passive diffusion. (B) Electrical stimulation derives dopamine release, which are detected as hotspots by dopamine nanosensors. Application of nomifensine (bottom row) delays the clearance kinetics of dopamine and increases spatial extent of dopamine diffusion relative to standard imaging buffer (ACSF) (scale bar = 10 μm). (C) Spatially averaged traces of nanosensor fluorescence transients under various stimulation paradigms (top) and pharmacological perturbations (bottom with nomifensine, +NOMF). Reproduced with permission from ref (1088). Copyright 2019 American Association for the Advancement of Science.

Figure 33

(A) Composite nanofilm strategy for culturing primary dopaminergic neurons. Dopamine neurons are cultured on fluorescent and dopamine sensitive substrate produced from drop casting a solution of ssDNA@SWCNT conjugates on glass surfaces. (B) Dopamine release evoked by field stimulation modulates the fluorescence of the nanosensor layer, which is recorded as a “hotspot” of activity (a cluster of pixels that exhibit highly correlated temporal behavior). Images show temporal evolution of signal. Reproduced with permission from ref (1090). Copyright 2022 Elife under CC BY 4.0.

Figure 34

Fluorescence spectra that compare the original spectrum of SWCNTs (black), the spectrum after adding 50 mM boronic acid (blue), and the spectrum after adding 50 mM glucose (red). (A) The BA-SWCNT complexes were prepared with 4-chlorophenylboronic acid and (B) 4-cyanophenylboronic acid. Adapted from ref (1125). Copyright 2011 American Chemical Society.

Figure 35

(A) Schematic illustration of a-GQDs synthesis and its glucose sensing mechanism. (B) Fluorescence spectra of a-GQDs/PBA with different glucose concentrations showing the turn-on sensor response. (C) Portable paper-based printed sensor and a wearable composite thin-film sensor responding to patient glucose levels. Adapted with permission from ref (1128). Copyright 2021 Elsevier.

Figure 36

Detection of endolysosomal lipid accumulation in live cells. (A) Schematics of the ss(GT)₆-(8,6) SWCNTs in macrophages treated with compounds that accumulate lipids in cells (U18666A or Lalistat 3a2). (B) Overlay of brightfield and hyperspectral images of macrophages incubated with sensors under the specified treatments. Color legend maps to nanotube emission peak wavelength. Scale bar = 50 μm. Adapted from ref (1132). Copyright 2017 American Chemical Society.

Figure 37

(A) Schematic of the ss(GT)₁₅-SWCNT sensors encapsulated in PCL polymers. (B) The fluorescence spectra of the microfibrous samples exposed to various H₂O₂ concentrations ranging from 0 to 5 mM. (C) Optical fibrous samples that are integrated into a commercial wound bandage still responds to exogenously applied H₂O₂. Adapted with permission from ref (1140). Copyright 2021 Wiley.

Figure 38

A method for creating cell-based CDs-microspheres utilizing S. aureus cells as carriers to encapsulate CDs particles. These inactivated cells can subsequently bind to antibody molecules via SPA proteins present on their surfaces. The development of the CDs-microsphere immunoassay involves the integration of immunomagnetic separation and CDs-microsphere fluorescence detection for pathogen detection. Adapted with permission from ref (1160). Copyright 2021 Elsevier.

Figure 39

(A) The use of SWCNT-based fluorescent sensors integrated into the agar culture medium. A soybean seedling (G. max) grows through the agar, and when the plant encounters a pathogenic elicitor, its response in terms of polyphenol secretion is monitored through NIR fluorescence imaging from a distance of more than 20 cm. (B) Genistein and THP, which are significant components of soybean (G. max) polyphenols, reduce the fluorescence of PEG-PL-SWCNTs in the agar (mean ± SD, n = 3). (C) Visible and NIR images of the soybean seedling with a scale bar of 1 cm. (D) The NIR fluorescence of the sensors (I/I₀) in the plant’s environment (rhizosphere) decreases over time near the challenged root area (where root tissue is indicated by black overlay; the white triangle represents the position for elicitor induction, and the red line shows the line profile position, with a scale bar of 1 cm). Adapted with permission from ref (1159). Copyright 2022 Wiley.

Figure 40

Spatial and temporal patterns of NAA and 2,4-D in spinach leaves. (A) Bright-field and false-color fluorescent images of a spinach leaf from a whole plant, showing infiltration with reference (red) and 1 mM NAA (blue) sensors under 785 nm laser light after 5 and 30 min. (B) Bright-field and false-color fluorescent images of a spinach leaf with reference (red) and 100 μM 2,4-D (blue) sensors under 785 nm laser light after 30 and 90 min. Adapted from ref (1248). Copyright 2021 American Chemical Society.

Figure 41

(A) The integrated fluorescence intensity was quantified for both Ler and GA20ox1 seedlings, and then standardized against the fluorescence intensity of Ler seedlings. The resulting graphs display the average standardized fluorescence intensities along with their standard deviations, with each data point represented by dots. (B) Biochemical determination of GA₃ levels in wild-type (Ler) and 35S::GA20ox1 overexpression lines was conducted. Gibberellins were extracted from seedlings aged 10 days and their concentrations were measured using LC-MS/MS analysis. (C) Normalized fluorescence intensity of GA₃-SWNT in the roots of lettuce for various NaCl treatments, based on 21–25 data points gathered from six seedlings across two independent experiments. (D) Lettuces at the age of 10 days, treated with either no NaCl or with 100 or 125 mM NaCl for an additional 10 days. Adapted from ref (1251). Copyright 2023 American Chemical Society.

Figure 42

(A) Plant health is monitored real-time using optical techniques by employing H₂O₂ nanosensors. The changes in NIR fluorescence intensity of HeAptDNA-SWCNT sensors in leaves (as shown in color map insets) provide information about the initiation of various environmental stresses, such as UV-B radiation, intense light exposure, and stress caused by pathogen-associated peptides like flg22. Adapted from ref (1225) with permission. Copyright 2020 American Chemical Society. (B) The response of a ratiometric sensor to H₂O₂ inside leaves is observed in vivo. Leaf sections are infiltrated with a ratiometric sensor consisting of a 6,5 ss(AT)₁₅ strand and a 7,6 ss(GT)₁₅ strand, each with different chiralities. These chiralities are independently imaged using a 785 nm excitation source. The internal standard and H₂O₂ detection are represented in maps based on the change in NIR intensity within the leaf section. Adapted from ref (1228). Copyright 2020 American Chemical Society.

Figure 43

(A) Ratiometric fluorescence responses of N-CDs@SiO₂@BSA-AuNCs with Cu²⁺ in response to glyphosate and seven other pesticides at a concentration of 100 ng/mL, and (B) the linear correlation between the I₄₃₆/I₆₅₁ intensity ratio and glyphosate concentrations ranging from 5 to 100 ng/mL. Adapted from ref (1258). Copyright 2023 American Chemical Society.

Figure 44

(A) Bright-field visualization of Pteris cretica leaf with (GT)₅-SWCNT and C₁₀-SWCNT, excited at 785 nm. Scale bar = 0.5 mm. (B) Sequential images depicting intensity variation in nanosensors following arsenite exposure, with timestamps postarsenite application via roots. (C) Comparison of fluorescence intensity shifts in SWCNT nanosensors within spinach, rice, and Pteris cretica under 10 μM arsenite-treated root medium. (D) Arsenite levels in Pteris cretica leaves subjected to varying arsenite concentrations (10, 5, 1, 0.1 μM) and deionized water in the root medium. (E) Contour plot of sensor’s detection limit after 7 days. Cross indicates the detection limit of 4.7 nM (0.6 ppb). (f) Contour plot of sensor’s detection limit after 14 days. Cross indicates the detection limit of 1.6 nM (0.2 ppb). Adapted with permission from ref (1261). Copyright 2021 Wiley.

Figure 45

(A) Confocal laser scanning microscopy is utilized to determine GFP expression 18 h postinfiltration of two different plasmid constructs pDONR-35S-GFP with a 35S (nuclear) promoter and pDONR-Cox2-GFP with a cox2 (mitochondrial) promoter delivered with SWCNT-PM-CytKH9. (B, C) Quantification of protein expression via SWCNT-cytKH9 in plants by Western blotting shows GFP protein presence in both the cytosol (b) and mitochondria (c) 18 h postinfiltration. Adapted with permission from ref (1293). Copyright 2022 Nature.

Figure 46

(A–C) The tracking of CQD-PP (A), Lipo2000 (B), and CQD-P (C) through fluorescence microscopy. (D–F) Insertion/deletion of nucleotides utilizing CQD-PP/pX459-sgRNA, Lipo2000/pX459-sgRNA, and CQD-P/pX459-sgR, respectively. (G–I) The quantification of gene editing efficiencies for CQD-PP/pX459-sgRNA (34.2%), Lipo2000/pX459-sgRNA (18.4%), and CQD-P/pX459-sgR(0%) of EFHD1 gene in HeLa cells. Adapted with permission from ref (1296). Copyright 2022 Royal Society of Chemistry.

Figure 47

A 3D reconstruction of the rabbit calvarial defects conferred to measure the regeneration of bone for chemically distinct (neat, −COOH, −NH₂,–OH, dopamine) MWCNTs (red) and graphene (yellow) particles decorated with BMP2 and/or OGP peptides at 4 and 8 weeks. The reconstruction is utilized to measure the growth of new bone as demonstrated by all the CNM conjugate implantations. Adapted with permission from ref (1297). Copyright 2022 Elsevier.

Figure 48

(A) Confocal images of cells after nanocarbon incubations. Intracellular nanocarbons were detected by laser reflection (LR) technology and shown with pseudo green color showing less cell entry of SNHs. Scale bar = 10 μm. (B) Cellular viability comparisons of different nanocarbons detected by a MTT assay (left) and LDH release investigations (right) (n = 5). Adapted with permission from ref (1304). Copyright 2018 Nature.

Figure 49

(A–C) Relative cell viability of three cell types (HeLa [a], HepG2 [b], HEK-293 [c]) at 24 h postincubation with 5 samples (n-CD, i_0.5-CD, i₁-CD, i₄-CD, i₈-CD) individually at different concentrations (0, 10, 30, 100, and 300 mg carbon/L), where n-CD is the nonirradiated CDs and n in i_n-CD indicates the number of days the CDs were irradiated with 60 μmol photons/m²/s. Trends depict decreased cell viability with longer irradiation times. (D–F) The relative cell viability of three cell types (HeLa [d], HepG2 [e], HEK-293 [f]) at 24 h postincubation of three CD samples (i₈-CD, i₈-CD_>3kD, i₈-CD_<3kD). Similarly, i8-CD demonstrates CDs irradiated with 60 μmol photons/m2/s for 8 days and where i8-CD_>3kD and i₈-CD_<3kD indicate the molecular size of the fraction tested from an original i₈-CD sample. Trends depict the increase cytotoxicity with i₈-CD_<3kD and i8-CD indicative of increased cytotoxicity with photolyzed carbon dot products which have a size of <3kD. Adapted with permission from ref (1309). Copyright 2021 Nature.

Figure 50

Accumulation and fate of CNMs in aquatic and terrestrial environments. Figure prepared using BioRender.com.