Controlled Synthesis of Ag₂Te@Ag₂S Core–Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near‐Infrared Window

Abstract

much-depressed photon absorption and scattering by tissues, which offers deeper tissue penetration and higher spatial and temporal resolution compared with the first NIR window (NIR-I) with wavelengths from 650 to 900 nm. [1][2][3][4][5][6][7][8] To achieve the optimum performance of in vivo imaging, NIR-II fluorophores with high quantum yield (QY) and excellent biocompatibility are necessary. Up to now, various NIR-II nanoprobes have been widely studied, including organic dyes, [1,[9][10][11][12][13][14][15][16][17] single-wall carbon nanotubes, [18][19][20] rare earth luminescent materials [21] and inorganic semiconductor quantum dots (QDs). [2,3,[22][23][24] Among these nanoprobes, QDs have stimulated extensive researches due to their small size, high QY, and facile surface functionalization. Therefore, NIR-II QDs has been a prominent fluorescent probe for bioimaging and has stimulated great attention. To date, some NIR-II QDs, such as Ag 2 S and Ag 2 Se, different from CdHgTe, [25,26] PbS, [27][28][29] and PbSe, [30,31] were reported for their good optical properties and excellent biocompatibility. [22,32] Silver telluride (Ag 2 Te) has a narrower direct bandgap of 0.06 eV [33] than that of Ag 2 S or Ag 2 Se and does not contain highly toxic heavy metal ions, promising it as an ideal nanoprobes to have a broader emissive spectrum in the NIR-II window for bioimaging. However, the poor fluorescence brightness and stability prevent its potential applications. Consequently, it is of great significance to develop Ag 2 Te-based nanoprobes with high QYs and stability in NIR-II window along with high biocompatibility.The dangling bond on the QDs surface is one of the crucial factors responsible for its low QY. An effective strategy to improve QY is to passivate the QDs surface by overgrowing a shell of a second semiconductor to construct a core-shell structure. [34] In this manner, the fluorescence intensity and stability of the QDs will gain vast enhancement. [35,36] Considering the crystalline structure, lattice parameters and the bandgap, as well as the biocompatibility of the shell materials, herein, Ag 2 S is selected as the shell to passivate Ag 2 Te QDs. The as-obtained Ag 2 Te@Ag 2 S QDs show superior photoluminescence properties in comparison with Ag 2 Te QDs itself.Ag 2 Te@Ag 2 S QDs were synthesized via a facile two-step method as shown in Figure 1a. First, Ag 2 Te QDs was prepared Fluorescence in the second near-infrared window (NIR-II, 900-1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR-II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag-rich Ag 2 Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag 2 S shell to passivate the Ag 2 Te core via a facile colloidal route, which greatly enhances the PLQY of Ag 2 Te QDs and significantly improves the stability of Ag 2 Te ...

NIR-quantum dots in biomedical imaging and their future

“…Although the QDs obtained show excellent properties and NIR emission, toxicity problems due to the leaching of heavy metals have been a major drawback for their application in biological systems (Allocca et al, 2019;Brunetti et al, 2013). iScience 24, 102189, March 19, 2021 In recent years, the synthesis of NIR QDs has evolved toward the integration of new materials such as Ag(I), Cu(I), and more recently carbon dots (Li and Wu, 2019a;Li et al, 2019c;Zhang et al, 2020). These present safer alternatives to the classical QDs, while even improving upon some of the photophysical properties.…”

“…Zhang and co-workers demonstrated the hot-injection synthesis of Ag 2 Te QDs (Zhang et al, 2020); starting from a mixture of Ag(OAc) and 1-dodecanethiol at 120 C, injection of tributylphosphine-Te rapidly yielded Ag 2 Te QDs within minutes. These were subsequently coated with an Ag 2 S shell by addition of further .…”

Application of Nanotechnology in Cancer Diagnosis and Therapy - A Mini-Review

“…A second near-infrared (NIR) window (NIR-ii, 900-1700 nm) with higher tissue penetration depth, higher spatial and temporal resolution has also been developed to aid cancer imaging. Also, the development of a silver-rich Ag2Te quantum dots (QDs) containing a sulfur source has been reported to allow visualization of better spatial resolution images over a wide infrared range 25 .…”

Perfecting and extending the near-infrared biological window

“…The definition of NIR-II window has been always limited to 1000-1700 nm, prompting the launch of various NIR emitters with the peak emission wavelength beyond 1000 nm [13][14][15] and even beyond 1500 nm (NIR-IIb region, 1500-1700 nm) [16][17][18] . Some existing and developing fluorophores with peak emission below 1000/1500 nm but bright emission tail beyond 1000/1500 nm, meanwhile, are also well suited for NIR-II/NIR-IIb fluorescence imaging.…”