Silver-based quantum dots (QDs) such as Ag₂S, Ag₂Se, and Ag₂Te, which emit in the second near-infrared window (NIR-II, 900–1700 nm), have attracted great research interest due to their prominent optical properties and eco-friendly compositions. Over the past decade, the controllable synthesis, bandgap modulation, and fluorescence improvement of NIR-II Ag-based QDs have greatly promoted their practical applications. In this review, we summarize the development process and latest achievements of NIR-II Ag-based QDs, covering major synthesis techniques for fabricating NIR-II Ag-based QDs, general methods for improving their fluorescence properties and recent advances in the applications of NIR-II Ag-based QDs from bioimaging to optoelectronic devices. Finally, we discuss the challenges and prospects of NIR-II Ag-based QDs in their optical properties and applications. This review aims to present synthesis and modification strategies and future application prospects for NIR-II Ag-based QDs, providing guidance for the design and integration of fluorescent probes in NIR-II window.

Cation exchange (CE) has been emerged as a promising post-synthesis strategy of colloidal nanocrystals. However, it is unclear how the cation precursor affects the CE process and the final colloidal nanocrystals. Herein, we utilized two Zn-B Lewis acid-base adduct complexes (B = oleylamine (OAM) and methanol (MeOH)) as Zn precursors for CE with Ag₂S quantum dots (QDs). Our study revealed that the steric hindrance and complexing capabilities of Zn precursor significantly affect the CE kinetics. As a result, the Zn-doped Ag₂S (Zn:Ag₂S) and Ag₂S@ZnS core–shell QDs were successfully obtained with enormous enhancement of their photoluminescence (PL) intensities. Theoretical simulation showed that the Zn-OAM with higher desolvation energy and spatial hindrance tended to form doped Zn:Ag₂S QDs due to the inefficient cation exchange. Whereas the Zn-MeOH with lower exchange barrier promoted the conversion of Ag-S to Zn-S, thus forming Ag₂S@ZnS core–shell QDs. We anticipate that this finding will enrich the regulatory approaches of post-synthesis of colloidal nanocrystals with desirable properties.

Surface ligands of colloidal quantum dots (QDs) have a profound influence on their surface states, which has been verified in the studies of the effect of ligand head groups on the photoluminescence (PL) properties of QDs. However, the investigation of the ligand chain length is limited. Here, we systematically explored the effect of chain length on the Ag₂Se QDs by selecting three ligands, 1-octanethiol (OTT), 1-dodecanethiol (DDT), and 1-hexadecanethiol (HDT), with diverse chain lengths. We found that the PL intensity of Ag₂Se QDs increased with the decrease of the ligand chain length due to the enhanced passivation of surface defects emerging from the robust QD-ligand interface binding affinity and the weaker hydrophobic chain–chain interaction. Subsequently, AgAuSe QDs terminated with OTT were obtained by alloying parent OTT-Ag₂Se QDs with Au precursor with a record absolute PL quantum yield (PLQY) of 87.2% at 970 nm, facilitating ultrasensitive in vivo angiography imaging in a nude mouse model. We expect that our finding of the important role of the ligand chain length on the optical properties of QDs will be suggestive to the design and synthesis of high-quality QDs, and also look forward to the clinical applications of the ultra-bright AgAuSe QDs.

The plasma membrane of cells is a crucial biological membrane that involved in a variety of cellular processes including cell signaling transduction through membrane electrical activity. Recently, monitoring membrane electrical activity using fluorescence imaging has attracted numerous attentions for its potential applications in evaluating how the nervous system works. However, the development of ideal fluorescent voltage-sensitive probes with both high membrane labeling efficiency and voltage sensitivity is still retain a big challenge. Herein, glutathione- capped CdSe@ZnS quantum dots (CdSe@ZnS-GSH QDs) with a size of 2.5 nm and an emission peak at 520 nm are synthesized using a facile ligand exchange method for plasma membrane labeling and membrane potential imaging. The as-synthesized CdSe@ZnS-GSH QDs can effectively label cell membrane at neutral pH within 30 min and exhibit excellent optical stability in continuous imaging for up to 60 min. With the test concentration up to 200 nM, CdSe@ZnS-GSH QDs show high biocompatibility to cells and do not affect cell proliferation, disturb cell membrane integrity or cause apoptosis and necrosis of cells. Then, a two-component voltage sensor strategy based on fluorescence resonance energy transfer (FRET) between CdSe@ZnS-GSH QDs and the dipicrylamine (DPA) is successfully developed to monitor the membrane potential by the fluorescence of CdSe@ZnS-GSH QDs. This study offers a facile strategy for labeling plasma membrane and monitoring the membrane potential of cells and will hold great potential in the research of signaling within intact neuronal circuits.

Cost-effective electrocatalysts for the hydrogen evolution reaction (HER) play a key role in the field of renewable energy. Although tremendous efforts have been devoted to the search of alternative materials, Pt/C is still the most efficient electrocatalyst for the HER. Nevertheless, decreasing the loading of Pt in the designed eletrocatalysts is of significance. However, with low Pt loading, it is challenging to maintain excellent catalytic performance. Herein, a new catalyst (Pt/NPC) was prepared by dispersing Pt nanoparticles (PtNPs) with an average diameter of 1.8 nm over a three-dimensional (3D) carbon network co-doped with N and P. Because of the high electronegativity of the N and P dopants, PtNPs were uniformly dispersed on the carbon network via high electronic affinity between Pt and carbon, affording a Pt/NPC catalyst; Pt/NPC exhibited superior HER activity, attributed to the down-shift of the Pt d-band caused by the donation of charge from N and P to Pt. The results show that Pt/NPC with an ultralow Pt loading of 1.82 wt.% exhibits excellent HER performance, which corresponds to a HER mass activity 20.6-fold greater than that observed for commercial 20% Pt/C at an overpotential of 20 mV vs. RHE.

In this article, we report a facile precursor pyrolysis method to prepare porous spinel-type cobalt manganese oxides (Co_xMn_3-xO₄) with controllable morphologies and crystalline structures. The capping agent in the reaction was found to be crucial on the formation of the porous spinel cobalt manganese oxides from cubic Co₂MnO₄ nanorods to tetragonal Co₂Mn₄ microspheres and tetragonal Co₂Mn₄ cubes, respectively. All of the prepared spinel materials exhibit brilliant oxygen reduction reaction (ORR) electrocatalysis along with high stability. In particular, the cubic Co₂MnO₄ nanorods show the best performance with an onset potential of 0.9 V and a half-wave potential of 0.72 V which are very close to the commercial Pt/C. Meanwhile, the cubic Co₂MnO₄ nanorods present superior stability with negligible degradation of their electrocatalytic activity after a continuous operation time of 10, 000 seconds, which is much better than the commercial Pt/C electrocatalyst.

Real-time and objective feedback of therapeutic efficacies would be of great value for tumor treatment. Here, we report a smart Ag₂S QD-based theranostic nanoplatform (DOX@PEG-Ag₂S) obtained by loading the anti-cancer drug doxorubicin (DOX) into polyethylene glycol-coated silver sulfide quantum dots (PEG-Ag₂S QDs) through hydrophobic-hydrophobic interactions, which exhibited high drug loading capability (93 wt.% of DOX to Ag₂S QDs), long circulation in blood (t_1/2 = 10.3 h), and high passive tumor-targeting efficiency (8.9% ID/gram) in living mice where % ID/gram reflects the probe concentration in terms of the percentage of the injected dose (ID) per gram of tissue. After targeting the tumor tissue, DOX from PEG-Ag₂S cargoes was selectively and rapidly released into cancer cells, giving rise to a significant tumor inhibition. Owing to the deep tissue penetration and high spatio-temporal resolution of Ag₂S QDs fluorescence in the second near-infrared window (NIR-Ⅱ), the DOX@PEG-Ag₂S enabled real-time in vivo reading of the drug targeting process and therapeutic efficacy. We expect that such a novel theranostic nanoplatform, DOX@PEG-Ag₂S, with integrated drug delivery, therapy and assessment functionalities, will be highly useful for personalized treatments of tumors.

A facile colloidal route to synthesize MoSe₂ porous microspheres with diameters of 400–600 nm made up of MoSe₂ monolayer flakes (~0.7 nm in thickness) is reported. The solvents trioctylamine (TOA) and oleylamine (OAM) are found to play important roles in the formation of MoSe₂ microspheres, whereby TOA determines the three-dimensional (3D) microspherical morphology and OAM directs the formation of MoSe₂ monolayer flakes. The robust 3D MoSe₂ microspheres exhibit remarkable activity and durability for the electrocatalytic hydrogen evolution reaction (HER) in acid, maintaining a small onset overpotential of ~77 mV and keeping a small overpotential of 100 mV for a current density of 5 mA/cm² after 1, 000 cycles. In addition, similar 3D WSe₂ microspheres can also be prepared by using this method. We expect this facile colloidal route could further be expanded to synthesize other porous structures which will find applications in fields such as in energy storage, catalysis, and sensing.

We report a novel method for rapid, colorimetric detection of a specific deoxyribonucleic acid (DNA) sequence by carrying out a polymerase chain reaction in the presence of gold nanoparticles functionalized with two primers. Extension of the primers when the target DNA is present as a template during the polymerase chain reaction process affords the complementary sequences on the gold nanoparticle surfaces and results in the formation of gold nanoparticle aggregates with a concomitant color change from red to pinkish/purple. This method provides a convenient and straightforward solution for ultrasensitive DNA detection without any further post-treatment of the polymerase chain reaction products being necessary, and is a promising tool for rapid disease diagnostics and gene sequencing.