Short single-stranded DNA (ssDNA) has emerged as the natural polymer of choice for non-covalently functionalizing photoluminescent single-walled carbon nanotubes. In addition, specific empirically identified DNA sequences can be used to separate single species (chiralities) of nanotubes with exceptionally high purity. Currently, only limited general principles exist for designing DNA-nanotube hybrids amenable to separation processes, due in part to an incomplete understanding of the fundamental interactions between a DNA sequence and a specific nanotube structure, while even less is known in the design of nanotube-based sensors with determined optical properties. We therefore developed a combined experimental and analysis platform, based on time-resolved near-infrared fluorescence spectroscopy, to extract the complete set of photoluminescence parameters that characterize DNA-nanotube hybrids. Here, we systematically investigated the affinity of the d(GT)n oligonucleotide family for structurally-defined carbon nanotubes by measuring photoluminescence response of the nanotube upon oligonucleotide displacement. We found, surprisingly, that the rate of displacement of oligonucleotides is independent of the coverage on the nanotube, as inferred through intrinsic optical properties of the hybrid. The kinetics of intensity modulation are essentially single exponentials, and the time constants, which quantify the stability of DNA binding, span an order of magnitude. Surprisingly, these time constants do not depend on the intrinsic optical parameters within the hybrids, suggesting that DNA-nanotube stability is not due to increased nanotube surface coverage by DNA. Further, a principal component analysis of the excitation and emission shifts, along with intensity enhancement at equilibrium accurately identified the (8,6) nanotube as the partner chirality to (GT)6 ssDNA. Combined, the chirality-resolved equilibrium and kinetics data can guide the development of DNA-nanotube pairs with tunable stability and optical modulation. Additionally, this high-throughput optical platform could function as a primary screen for mapping the DNA-chirality recognition phase space.
The ongoing SARS-CoV-2 pandemic has highlighted the importance of the rapid development of vaccines and antivirals. However, the potential for the emergence of antibiotic resistances due to the increased use of antibacterial cleaning products and therapeutics presents an additional, underreported threat. Most antibacterial cleaners contain simple quaternary ammonium compounds (QACs), however these compounds are steadily becoming less effective as antibacterial agents. QACs are extensively used in SARS-CoV-2 related sanitization in clinical and household settings. Similarly, due to the danger of secondary infections, antibiotic therapeutics are increasingly used as a component of COVID-19 treatment regimens, even in the absence of a bacterial infection diagnosis. The increased use of antibacterial agents as cleaners and therapeutics is anticipated to lead to novel resistances in the coming years.
Noncovalent hybrids of single-stranded DNA and single-walled carbon nanotubes (SWCNTs) have demonstrated applications in biomedical imaging and sensing due to their enhanced biocompatibility and photostable, environmentally responsive near-infrared (NIR) fluorescence. The fundamental properties of such DNA-SWCNTs have been studied to determine the correlative relationships between oligonucleotide sequence and length, SWCNT species, and the physical attributes of the resultant hybrids. However, intracellular environments introduce harsh conditions that can change the physical identities of the hybrid nanomaterials, thus altering their intrinsic optical properties. Here, through visible and NIR fluorescence imaging in addition to confocal Raman microscopy, we show that the oligonucleotide length controls the relative uptake, intracellular optical stability, and retention of DNA-SWCNTs in mammalian cells. Although the absolute NIR fluorescence intensity of DNA-SWCNTs in murine macrophages increases with increasing oligonucleotide length (from 12 to 60 nucleotides), we found that shorter oligonucleotide DNA-SWCNTs undergo a greater magnitude of spectral shift and are more rapidly internalized and expelled from the cell after 24 h. Furthermore, by labeling the DNA with a fluorophore that dequenches upon removal from the SWCNT surface, we found that shorter oligonucleotide strands are displaced from the SWCNT within the cell, altering the physical identity and changing the fate of the internalized nanomaterial. Finally, through a pharmacological inhibition study, we identified the mechanism of SWCNT expulsion from the cells as lysosomal exocytosis. These findings provide a fundamental understanding of the interactions between SWCNTs and live cells as well as evidence suggesting the ability to control the biological fate of the nanomaterials merely by varying the type of DNA wrapping.
In an effort to facilitate personalized medical approaches, the continuous and noninvasive monitoring of biochemical information using wearable technologies can enable a detailed understanding of an individual's physiology. Reactive oxygen species (ROS) are a class of oxygen‐containing free radicals that function in a wide range of biological processes. In wound healing applications, the continuous monitoring of ROS through a wearable diagnostics platform is essential for the prevention of chronicity and pathogenic infection. Here, a versatile one‐step procedure is utilized to fabricate optical core‐shell microfibrous textiles incorporating single‐walled carbon nanotubes (SWCNTs) for the real‐time optical monitoring of hydrogen peroxide concentrations in in vitro wounds. The environmentally sensitive and non‐photobleachable fluorescence of SWCNTs enables continuous analyte monitoring without decay in signal over time. The existence of multiple chiralities of SWCNTs emitting near‐infrared fluorescence with narrow bandwidths allows a ratiometric signal readout invariant to the excitation source distance and exposure time. The individual fibers encapsulate the SWCNT nanosensors for at least 21 days without apparent loss in structural integrity. Moreover, the microfibrous textiles are utilized to spatially resolve peroxide concentrations using a camera and further integrated into commercial wound bandages without significant degradation in their optical properties.
Single-walled carbon nanotubes (SWCNTs) functionalized with short single-stranded DNA have been extensively studied within the last decade for biomedical applications due to the high dispersion efficiency and intrinsic biocompatibility of DNA as well as the photostable and tunable fluorescence of SWCNTs. Characterization of their physical properties, particularly their length distribution, is of great importance regarding their application as a bioengineered research tool and clinical diagnostic agent. Conventionally, atomic force microscopy (AFM) has been used to quantify the length of DNA-SWCNTs by depositing the hybrids onto an electrostatically charged flat surface. Here, we demonstrate that hybrids of DNA-SWCNTs with different oligomeric DNA sequences ((GT)6 and (GT)30) differentially deposit on the AFM substrate, resulting in significant inaccuracies in the reported length distributions of the parent solutions. Using a solution-based surfactant exchange technique, we placed both samples into a common surfactant wrapping and found identical SWCNT length distributions upon surface deposition. Additionally, by spincoating the surfactant wrapped SWCNTs onto a substrate, thus mitigating effects of electrostatic interactions, we found length distributions that did not depend on DNA sequence but were significantly longer than electrostatic deposition methods, illuminating the inherent bias of the surface deposition method. Quantifying the coverage of DNA molecules on each SWCNT through both absorbance spectroscopy and direct observation, we found that the density of DNA per SWCNT was significantly higher in short (GT)6-SWCNTs (length < 100 nm) compared to long (GT)6-SWCNTs (length > 100 nm). In contrast, we found no dependence of the DNA density on SWCNT length in (GT)30-SWCNT hybrids. Thus, we attribute differences in the observed length distributions of DNA-SWCNTs to variations in electrostatic repulsion induced by sequencedependent DNA density.
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