Well‐Defined Nanoclusters as Fluorescent Nanosensors: A Case Study on Au₂₅(SG)₁₈

Abstract

The fluorescence of nanoparticles has attracted much attention in recent research, but in many cases the underlying mechanisms are difficult to evaluate due to the polydispersity of nanoparticles and their unknown structures, in particular the surface structures. Recent breakthroughs in the syntheses and structure determinations of well-defined gold nanoclusters provide opportunities to conduct in-depth investigations. Devising well-defined nanocluster sensors based on fluorescence change is of particular interest not only for scientific studies but also for practical applications. Herein, the potential of the glutathionate (SG)-capped Au(25) nanocluster as a silver ion sensor is evaluated. The Ag(+) detection limit of approximately 200 nM, based on the fluorescence enhancement and good linear fluorescence response in the silver ion concentration range from 20 nM to 11 μM, in combination with the good selectivity among 20 types of metal cations, makes Au(25) (SG)(18) a good candidate for fluorescent sensors for silver ions. Further experiments reveal three important factors responsible for the unique fluorescence enhancement caused by silver ions: 1) the oxidation state change of Au(25) (SG)(18) ; 2) the interaction of neutral silver species (Ag(0) , reduced by Au(25) (SG)(18) (-) ) with Au(25) (SG)(18) ; and 3) the interaction of Ag(+) with Au(25) (SG)(18.) Experiments demonstrate the very different chemistry of hydrophobic Au(25) (SC(2) H(4) Ph)(18) and hydrophilic Au(25) (SG)(18) in the reaction with silver ions. This work indicates another potential application of gold nanoclusters, offers new strategies for nanocluster-based chemical sensing, and reveals a new way to influence nanocluster chemistry for potential applications.

Ultrasmall Palladium Nanoclusters as Effective Catalyst for Oxygen Reduction Reaction

“…Thiolate-protected palladium nanoclusters with a mass of approximately 5 kDa are synthesized by using a one-phase method, and the chemical formula is estimated to be Pd [13][14][15][16][17] (SR) [18][19][20][21][22] . The ultrasmall palladium nanoclusters exhibit excellent performance for the ORR in alkaline solutions.…”

Exclusive synthesis of Au11(PPh3)8Br3 against the Cl Analogue and the Electronic Interaction between Cluster Metal Core and Surface Ligands

“…It has been revealed in our previous work that the surface can greatly influence the properties of gold nanoclusters. [24] To address these questions, we herein start from HAuCl 4 and have developed a two-phase protocol (tetraoctylammonium bromide (TOAB) as the phase transfer reagent) to synthesize Au 11 clusters. Our experiments confirmed the applicability of two-phase synthesis for Au 11 , and revealed that bromo-substituted Au 11 is the exclusive product even if the Br/Cl ratio was 1:4 at the start, due to the thermodynamic stability difference.…”

Cytidine-stabilized gold nanocluster as a fluorescence turn-on and turn-off probe for dual functional detection of Ag+ and Hg2+

“…Compared with PL Au NPs, gold nanoclusters (Au NCs) have smaller particle size and higher PL quantum yield [8,[34][35][36]. Thus, Au NCs have attracted an increasing interest due to their simplicity and low detection limit in both fundamental research and research toward practical applications [37][38][39][40][41]. Advances in synthesis and application of Au NCs as fluorescence probes have drawn wide attention due to their ultrasmall size, large Stokes shift, low toxicity, strong fluorescence, and long term stability.…”

“…A number of methods have been reported to synthesize Au NCs by using specific capping agents such as thiol ligands [42], or using templates such as DNA [7,43] and polymers [44]. These Au NCs have been used in the determination of various heavy metals such as Hg 2+ [8,34,35,45,46], Ag + [14,15,38], Cu 2+ [30], Fe 3+ [47], As 3+ [48], and Pb 2+ [49] with advances of being simple, rapid, and economical. Thus it is possible to utilize Au NCs as a fluorescent probe for selective determination of Ag + and Hg 2+ , which is valuable for monitoring the relevant environment and human health [10,50].…”