Nanoprobes for Biomedical Imaging with Tunable Near‐Infrared Optical Properties Obtained via Green Synthesis

Abstract

Ideally, any material used should be nontoxic and produced with safe, inexpensive, and energy‐effective processes. In the case of optically active nanoparticles, this is often not the case, as they are frequently composed of hazardous heavy metals and/or produced with methods far from being environmentally friendly. Herein, the preparation of Ag2S‐based nanoparticles via a simple green synthesis route is explored. Aqueous extracts of roasted coffee are used as sources of coordinating molecules. Optimization of the reaction conditions yields dimeric Ag−Ag2S nanoparticles, whose near‐infrared photoluminescence can be switched on via H2O2‐mediated oxidation. This oxidation transforms suitable photoacoustic contrast agents into fluorescence imaging probes. Theoretical calculations further clarify the role of metallic silver in determining the optical properties of Ag2S. Overall, it is demonstrated that nanomaterials with tangible applicative potential can be prepared via cost‐ and energy‐effective synthesis strategies that entail benign, renewable chemicals.

Ion-induced bias in Ag2S luminescent nanothermometers

“…1A). The behavior is the one expected from the literature: 22,23 a linear decrease in intensity (quenching) is accompanied by a linear red-shift of the peak maximum when increasing the temperature (Fig. 1B).…”

Semiconductor Nanocrystals Emitting in the Second Near‐Infrared Window: Optical Properties and Application in Biomedical Imaging

“…[166] In addition, plasmonic-fluorescent Janus nanoparticles (Ag/Ag 2 S) were used for in situ activating the NIR-II PL of Ag 2 S SNCs by controlled oxidation of Ag with H 2 O 2 through decreasing the electron-transfer effect. [167,168] A surface etching strategy for improving NIR-II emission of Ag 2 S SNCs was proposed by Gutierrez et al, where partial removal of surface sulfur atoms reduced surface traps responsible for nonradiative recombination. [169] In the following, we will consider the commonly used approaches mentioned above in more detail.…”

Prospects of NIR fluorescent nanosensors for green detection of SARS-CoV-2

“…For example, Ag-Ag 2 S-based NPs can be prepared by a simple green synthetic route. [53] The coordinating molecules are produced from aqueous extracts of roasted coffee and the Ag-Ag 2 S are obtained from aqueous solutions at room temperatures. Notwithstanding, the optimized reaction conditions only produce weak fluorescent Ag-Ag 2 S NPs (Emission:1250 nm; Excitation: 784 nm) with a QY of 0.1%.…”

“…Some NIR fluorescent nanosensors show potential from raw material production to waste recycling. NIR fluorescent nanosensors can be designed through green methods and low-toxic NIR fluorescent nanomaterials; [53] It can also be fabricated based on the loading of NIR organic dyes on low-toxic but non-fluorescent nanomaterials ( Table 1 ). In combination with a bioreceptor (or biological recognition element), the analytes could be detected by reading the NIR emissions with an appropriate excitation.…”