Boosting the Near-Infrared Emission of Ag2S Nanoparticles by a Controllable Surface Treatment for Bioimaging Applications.

Irene Zabala Gutierrez,Erving Ximendes,Daniel Jaque,Yingli Shen,Riccardo Marin,Sonia Melle,Oscar G Calderón,Miguel Manso Silvan,Christoph Gerke,Jorge Rubio-Retama

doi:10.1021/acsami.1c19344

Abstract

Ag2S nanoparticles are the staple for high-resolution preclinical imaging and sensing owing to their photochemical stability, low toxicity, and photoluminescence (PL) in the second near-infrared biological window. Unfortunately, Ag2S nanoparticles exhibit a low PL efficiency attributed to their defective surface chemistry, which curbs their translation into the clinics. To address this shortcoming, we present a simple methodology that allows to improve the PL quantum yield from 2 to 10%, which is accompanied by a PL lifetime lengthening from 0.7 to 3.8 μs. Elemental mapping and X-ray photoelectron spectroscopy indicate that the PL enhancement is related to the partial removal of sulfur atoms from the nanoparticle’s surface, reducing surface traps responsible for nonradiative de-excitation processes. This interpretation is further backed by theoretical modeling. The acquired knowledge about the nanoparticles’ surface chemistry is used to optimize the procedure to transfer the nanoparticles into aqueous media, obtaining water-dispersible Ag2S nanoparticles that maintain excellent PL properties. Finally, we compare the performance of these nanoparticles with other near-infrared luminescent probes in a set of in vitro and in vivo experiments, which demonstrates not only their cytocompatibility but also their superb optical properties when they are used in vivo, affording higher resolution images.

Highlights

Photoluminescence (PL) imaging has gained tremendous relevance in the biomedical field as a noninvasive, fastfeedback, and high-sensitivity visualization technique that can provide valuable information in real time at a relatively low cost.[1−4] At the in vivo level, PL imaging is mainly limited by the tissue-induced extinction that makes the acquisition of high-spatial-resolution fluorescence images of deep tissues and organs challenging.[5]
Therein, tissues are partially transparent to photons and the use of optical probes working in NIR-II has enabled the acquisition of high-resolution, high-signal-to-noise ratio (SNR), and large-penetration images, which constitute a pivotal feature for molecular diagnosis.[8−10]
The error bars are the standard deviation of five different sonication experiments. (D) PL decay curves obtained at different sonication times (0, 6, 12, and 15 min) for NPs dispersed in CHCl3

Summary

Introduction

Photoluminescence (PL) imaging has gained tremendous relevance in the biomedical field as a noninvasive, fastfeedback, and high-sensitivity visualization technique that can provide valuable information in real time at a relatively low cost.[1−4] At the in vivo level, PL imaging is mainly limited by the tissue-induced extinction that makes the acquisition of high-spatial-resolution fluorescence images of deep tissues and organs challenging.[5]. The development of nontoxic, highly luminescent, and NIR-II-active probes is of utmost importance. To this end, Ag2S nanoparticles (NPs) are NIR luminescent materials, which exhibit broad-band PL emission in NIR-II. The extremely low Ksp (1 × 10−49) of Ag2S when compared with those of other materials like PbS (Ksp = 1 × 10−28) or CdSe (Ksp = 1 × 10−27) minimizes the leakage of ions, making them attractive as NIR-II probes for in vivo applications.[11,12] their temperaturedependent optical properties make them suitable for luminescence thermometry, opening the door to several biological applications where these NPs can be used.[13,55] their generally low PL quantum yield (PLQY) is still a downside that should be overcome. These, in turn, have been shown to be the origin of localized

Methods

Results

Conclusion