Quantum dots assisted in vivo two-photon microscopy with NIR-II emission

Abstract

With the advantages of high resolution and deep penetration depth, two-photon excited NIR-II (900–1880 nm) fluorescence (2PF) microscopic bioimaging is promising. However, due to the lack of imaging systems and suitable probes, few such works, to our best knowledge, were demonstrated utilizing NIR-II excitation and NIR-II fluorescence simultaneously. Herein, we used aqueously dispersible PbS/CdS quantum dots with bright NIR-II fluorescence as the contrast agents. Under the excitation of a 1550 nm femtosecond (fs) laser, they emitted bright 2PF in the NIR-II region. Moreover, a 2PF lifetime imaging microscopic (2PFLIM) system was implemented, and in vivo 2PFLIM images of mouse brain blood vessels were obtained for the first time to our best knowledge. To improve imaging speed, an in vivo two-photon fluorescence microscopy (2PFM) system based on an InGaAs camera was implemented, and in vivo 2PFM images of QDs-stained mouse brain blood vessels were obtained.

Two-Photon Absorption: An Open Door to the NIR-II Biological Window?

“…Pioneering work combining 2P fluorescence and 2PFLIM using PbS/CdS QDs (84) as water-dispersible contrast agents was recently reported (Ni et al, 2022). These QDs allowed "NIR-to-NIR" imaging under 2PE at 1550 nm with a σ 2 of 530 GM in water.…”

“…However, although difficult, methods for expanding the tunability range of fibre lasers are being explored by implementing nonlinear effects as well as temperature and magnetic field control (Wei et al, 2021) So far only a limited number of biological 2P NIR-II studies have been reported with fibre lasers despite their portability, easeof-use, access to longer wavelengths, and high power features, possibly due to the lack of commercially available microscopes that integrates such lasers. However, in vivo studies using in-house built fibre lasers have demonstrated their high potential, both by performing 2P NIR-II imaging at 1550 nm-the longest wavelength so far reported (Berezin et al, 2011;Ni et al, 2022), and by reaching the deepest in vivo penetration (1040 nm) (Alifu et al, 2017) (Section 3.2, Table 3). In addition, the components of fibre lasers are much cheaper than OPO sources, as evidenced by Perillo et al who developed a 2P NIR-II microscope using a modelocked Yb-doped fibre laser for ~$13000 and applied it to image FPs at 1060 nm with penetration depths of up to 900 μm (Perillo et al, 2016).…”

“…The authors also showed the distinct resolution improvement using NIR-II light for 2P imaging when imaging at depths, when compared to light of shorter wavelengths (Figure 8, m). Among other classes of luminescent materials, in vivo 2P NIR-II imaging was shown for the first time using QDs as a contrast agent by Ni et al with the PbS/CdS QDs 84 (Ni et al, 2022). Imaging depths of 220 µm were achieved in the mouse brain vasculature with a fibre laser operating at 1550 nm.…”

Ultra‐Broadband Photoluminescent Carbon Dots Synthesized by Laser‐Induced Thermal Shock

“…[40][41][42] Emission in NIR-II window (1100-1600 nm) is commonly covered by semiconductor quantum dots, such as PbS, or silver-based QDs such as AgTe or AgSe. [43][44][45][46][47] The CDs reported in this paper cover the whole spectrum from 400 to 1600 nm. The summarizing diagram is presented in Figure 4b.…”

Confocal Laser Scanning Microscopy Based on a Silicon Photomultiplier for Multicolor In Vivo Imaging in Near‐Infrared Regions I and II

“…[13][14][15][16] Although confocal and twophoton fluo rescence lifetime imaging show enhanced imaging capability in the NIRII region, [17,18] the used Indium gallium arsenide (InGaAs) photomultiplier tubes (PMTs) significantly increase the cost to around tens of thousands of US dollars. [18][19][20] In addition, InGaAs PMT needs deep cooling during the imaging operation, whose quantum efficiency is only 1-3%. Meanwhile, InGaAs PMT has the disadvantage of being irreversibly dam aged by excess incident photons in a brightfield environment.…”