Photoluminescence Brightening of Isolated Single-Walled Carbon Nanotubes

Advances and Challenges of Fluorescent Nanomaterials for Synthesis and Biomedical Applications

With the rapid development of nanotechnology, new types of fluorescent nanomaterials (FNMs) have been springing up in the past two decades. The nanometer scale endows FNMs with unique optical properties which play a critical role in their applications in bioimaging and fluorescence-dependent detections. However, since low selectivity as well as low photoluminescence efficiency of fluorescent nanomaterials hinders their applications in imaging and detection to some extent, scientists are still in search of synthesizing new FNMs with better properties. In this review, a variety of fluorescent nanoparticles are summarized including semiconductor quantum dots, carbon dots, carbon nanoparticles, carbon nanotubes, graphene-based nanomaterials, noble metal nanoparticles, silica nanoparticles, phosphors and organic frameworks. We highlight the recent advances of the latest developments in the synthesis of FNMs and their applications in the biomedical field in recent years. Furthermore, the main theories, methods, and limitations of the synthesis and applications of FNMs have been reviewed and discussed. In addition, challenges in synthesis and biomedical applications are systematically summarized as well. The future directions and perspectives of FNMs in clinical applications are also presented.

Quantitative Detection of the Disappearance of the Antioxidant Ability of Catechin by Near-Infrared Absorption and Near-Infrared Photoluminescence Spectra of Single-Walled Carbon Nanotubes

We succeeded in quantitatively detecting the disappearance of catechin antioxidant ability as a function of time using near-infrared (NIR) absorbance and NIR photoluminescence (PL) spectra of single-walled carbon nanotubes (SWNTs) wrapped with DNA molecules (DNA-SWNT hybrids). When 15 μg/mL of catechin was added to the oxidized hybrid suspension, the absorbance of SWNTs increased, according to the antioxidant ability of catechin, and the effect was maintained at least for 30 min. When catechin concentrations were less than 0.3 μg/mL, SWNT absorbance gradually decreased, although it increased when catechin is added. The results revealed that disappearance of the catechin effects could be quantitatively detected by NIR absorbance spectra. When NIR PL was employed, the disappearance of PL intensity was also observed in the case of low catechin concentrations. However, time-lapse measurement of the disappearance was difficult because the PL intensity was rapidly quenched. In addition, the optical responses were different due to different chirality of SWNTs. Our results suggested that both NIR absorbance and PL can detect disappearance of catechin antioxidant effects; in particular, slow response of NIR absorbance was effective to detect time dependence of the disappearance of the catechin effects. Contrarily, PL revealed huge and rapid responses in contrast to NIR absorbance. PL might be effective for reversible use of DNA-SWNT hybrids as a nanobiosensor.

Influence of Encapsulated Water on Luminescence Energy, Line Width, and Lifetime of Carbon Nanotubes: Time Domain Ab Initio Analysis

In a broad range of applications, carbon nanotubes (CNTs) are in direct contact with a condensed-phase environment that perturbs CNT properties. Experiments show that water molecules encapsulated inside of semiconducting CNTs reduce the electronic energy gap, enhance elastic and inelastic electron-phonon scattering, and shorten the excited-state lifetime. We rationalize the observed effects at the atomistic level using real-time time-dependent density functional theory combined with nonadiabatic molecular dynamics. Encapsulated water makes the nanotube more rigid, suppressing radial breathing modes while enhancing and slightly shifting the optical G-mode. Water screens Coulomb interactions and shifts charge carrier energies and wave functions. The screening, together with distortion of the CNT geometry and lifting of orbital degeneracy, produces a luminescence red shift. Enhanced elastic and inelastic electron-phonon scattering explains line width broadening and shortening of the excited-state lifetime. The influence of water on the CNT properties is similar to that of defects; however, in contrast to defects, water creates no new phonon modes or electronic states in the CNTs. The atomistic understanding of the influence of the condensed-phase environment on CNT optical, electronic, and vibrational properties, and electron-vibrational dynamics guides design of novel CNT-based materials.