Super‐Resolution Near‐Infrared Fluorescence Microscopy of Single‐Walled Carbon Nanotubes Using Deep Learning

Abstract

Single‐walled carbon nanotubes (SWCNTs) have unique optical and physical properties, with numerous biomedical imaging and sensing applications, owing to their near‐infrared (nIR) fluorescence which overlaps with the biological transparency window. However, their longer emission wavelengths compared to emitters in the visible range result in a lower resolution due to the diffraction limit. Moreover, the elongated high‐aspect‐ratio structure of SWCNTs poses an additional challenge on super‐resolution techniques that assume point emitters. Utilizing the advantages of deep learning and convolutional neural networks, along with the super‐resolution radial fluctuation (SRRF) algorithm for network training, a fast, parameter‐free, computational method is offered for enhancing the spatial resolution of nIR fluorescence images of SWCNTs. An average improvement of 22% in the resolution and 47% in signal‐to‐noise ratio (SNR) compared to the original images is shown, whereas SRRF leads to only 24% SNR improvement. The approach is demonstrated for a variety of SWCNT densities and length distributions, and a wide range of imaging conditions with challenging SNRs, including real‐time videos, without compromising the temporal resolution. The results open the path for accelerated and accessible super‐resolution of nIR fluorescent SWCNTs images, further advancing their applicability as nanoscale optical probes.

High Sensitivity Near‐Infrared Imaging of Fluorescent Nanosensors

“…For example, the maximum resolution for fluorescence microscopy with (6,4)‐SWCNTs using a good 100× oil immersion objective (here λ = 885 nm, NA = 1.45) is about 372 nm, which decreases with increasing wavelength (412 nm for (6,5)‐SWCNTs with λ = 980 nm). Especially for imaging applications, resolution thus plays an important role, and it is not surprising that super‐resolution microscopy, also with SWCNTs, [ 79–81 ] is increasingly used. According to the Nyquist criterion, SWCNTs must therefore be at least 2.3 pixels apart to still be perceived as separate structures.…”

“…Small 2023, 19, 2206856 Especially for imaging applications, resolution thus plays an important role, and it is not surprising that super-resolution microscopy, also with SWCNTs, [79][80][81] is increasingly used. According to the Nyquist criterion, SWCNTs must therefore be at least 2.3 pixels apart to still be perceived as separate structures.…”

Shielding Effects Provide a Dominant Mechanism in J-Aggregation-Induced Photoluminescence Enhancement of Carbon Nanotubes

“…Among those nanomaterials, SWCNTs have attracted tremendous attention as unique nanoscale shortwave infrared (SWIR) light emitters of high photostability, making them promising candidates for optoelectronics, deep-tissue imaging, and sensing applications . Their optical bandgap and distinct electronic properties determined by the quasi-1D structure with a highly delocalized π-electron network result in narrow and diameter-dependent optical bands, allowing for the tuning of absorption and emission by controlling the nanotube diameter and chirality during the synthesis or postsynthetic sorting. − SWCNTs have been successfully utilized as fluorescence probes, including hyperspectral imaging in live mammalian cells, probing cell surface receptors, subcellular localization in plant cells, deep-tissue imaging, , and whole-body small animal imaging. , Although SWCNTs display stable photoluminescence, they typically show low fluorescence quantum yield (QY) in an aqueous suspension (QY varies between 10 –4 and 0.01), ,, significantly limiting their single-particle deep-tissue imaging and tracking applications .…”

Monitoring the Formation of Fibrin Clots as Part of the Coagulation Cascade Using Fluorescent Single-Walled Carbon Nanotubes

“…Single-walled carbon nanotubes (SWCNTs) can be described as graphene sheets rolled up into long, hollow cylinders of 0.7–3 nm diameter, where different rolling orientations of the graphene sheets lead to different chiralities of the nanotubes . Each chirality, described by the ( n , m ) indexes, has a different diameter and physical, chemical, electronic, and optical properties. , Semiconducting SWCNTs fluoresce in the near-infrared (NIR) spectral region, mainly between 900 and 1400 nm, where biological samples are primarily transparent. − Further, SWCNTs do not photobleach or blink upon use, provide spatiotemporal information, are stable at room temperature, and have long term biocompatibility in vivo . − Due to these unique optical properties, SWCNTs become favorable as fluorescent sensors for biomedical applications. − The mechanism of SWCNT-based sensors relies on a heteropolymer that is adsorbed onto the SWCNT surface and mediates the binding of a specific target analyte. Analyte binding then modifies the spectral properties of the NIR-fluorescent emission of the SWCNTs providing optical signal readout in real time. − This approach has been demonstrated to recognize numerous analytes ranging from small molecules − to large proteins and enzymes. − …”