| Chirality, describing an object which is non-superimposable with its mirror image, has been extensively studied since the first reported observation of optical activity in quartz by F. J. D. Arago in 1811.O ver the past two centuries, however, most of the investigated chiral materials are organic compounds, inorganic salts and biological molecules, and although chirality at the molecular level is exclusively understood, the investigation of nanoscale chirality is scarce. In 2000, Schaaff and Whetten did the first observation of the intense optical activity in giant gold–glutathione nanocluster compounds, which indicated that chiral effects are present in matter at the nanoscale.Triggered by potential applications in the fields of heterogeneous enantioselective catalysis, chiral separation, chiral recognition and sensing, and nonlinear optics, chirality in nanostructures has become an emerging field of research in recent years. Here, we used different chiral materials to synthesize chiral metal nanoclusters with different optical activity characteristics and applied them in cell imaging and colorimetric chiral recognition. The detail research contents are as followings:(1) Histidine- mediated synthesis of chiral fluorescencegold nanoclusters: insight into the origin ofnanoscale chirality Despite a significant surge in the number of investigations into chirality at the nanoscale, there is currently only limited knowledge about the chirality origin and potential applications. Here, we have succeeded in preparing a pair of gold nanocluster enantiomers, in which the histidine(His) enantiomers serve as both the reducing agent and the stabilizing ligand. Origins of the optical activity are discussed from the viewpoint of the intrinsically chiral core model and the dissymmetric field effect. The former is proposed to be responsible for the chirality origin of the as-prepared chiral gold nanoclusters(Au NCs), and both of them act concurrently for the chiroptical response observed in the ligand exchange reactions, which are per formed on the His enantiomer-based clusters with enantiopure thiol Pen and C ys ligands,respectively. In addition, the clusters display potential toward biological labelling due to the highphotoluminescence(PL) quantum yield and remarkable cellular uptake, in spite of the fact that nochirality-dependent effects in autophagy and subcellular localization are observed in the followingfluorescence imaging.(2) Facile synthesis of chiral ultrafine Au-Ag alloy nanoparticles and colorimetric chiral recognition of enantiomers So far most of efforts towards the development of optically active nanostructures have been focused on single-component systems, especially thiolated chiral molecules capping gold clusters, however, compared with single-component systems, alloy metal nanoparticles often demonstrate unique characteristics. Interactions between the constituent atoms can modify the electronic structure and surface composition of the alloy nanoparticles, leading to enhanced chemical, catalytic and optical properties. Thus in this study, as a test case for chiral bimetallic nanoparticle synthesis, chiral ultrafine Au-Ag alloy nanoparticles were synthesized viareduction of varying mole fractions of HAu C l4 and Ag NO3 by sodium borohydride in the presence D/L-penicillamine(D/L-Pen) because of their convenient optical properties to distinguish core-shell growth from alloy growth.To the best of our knowledge, few successful cases as to the efforts towards the development of colorimetric enantiosensing have been made, and therefore the approach described here would open new opportunities for design of more novel enantiosening strategies. |
