DOI: 10.1002/tcr.201600014 Personal Account THE CHEMICAL RECORD Synthesis, Optical Properties, and Sensing Applications of Gold Nanodots Rini Ravindranath, [a,b] Prathik Roy, [a] and Huan-Tsung Chang* [a] ABSTRACT: In this Personal Account, we briefly address our journey in developing photoluminescent nanomaterials for sensing purposes, with a focus on gold nanodots (Au NDs). Their synthetic strategies, optical properties, and sensing applications are emphasized. The Au NDs can be simply prepared from the etching of small-sized Au nanoparticles (<3 nm in diameter) by thiol compounds such as 11-mercaptoundecanoic acid under alkaline conditions. This simple approach allows the preparation of various functional Au NDs by choosing different thiol compounds as etching agents. Since the optical properties of Au NDs are highly dependent on the core and shell of each Au ND, the selection of etching reagents is important. Over the years we have developed various sensing systems using Au NDs for the detection of metal ions, anions, and proteins, based on analyte-induced photoluminescence quenching/enhancement of Au NDs as a result of changes in their oxidation state, shell composition, and structure. Keywords: gold, luminescence, nanostructures, proteins, sensors 1. Introduction Photoluminescent gold nanoparticles (Au NPs) with sizes smaller than 2 nm are known as gold nanodots (NDs) or nano- clusters (NCs). [1] In this manuscript, both terms are used, sim- ply based on those used in the original papers. Their molecular-like photoluminescence (PL) properties are strongly related to the size and composition of the core and metal– ligand complexes on the surface of each core. [2,3] Unlike larger Au NPs (e.g., >13 nm) that have been widely used for the detection of various analytes because of their strong surface plasmon resonance (SPR) in the visible region, [4] Au NDs do not exhibit SPR in the visible region. PL probes based on Au NDs function through analyte-induced PL quenching or enhancement, which are different from the colorimetric/ absorption changes due to aggregation or de-aggregation of Au NPs of larger size. [5] Au NDs can be prepared through various routes, includ- ing chemical reduction, etching, and photoreduction. [1a,6] We developed a different strategy for the preparation of Au NDs from Au NPs (3 nm in diameter) through chemical etching under alkaline conditions. [1a] Our chemical etching approach allows simple preparation of high-quality Au NDs. It is easy to tune the PL properties of Au NDs by using various etching reagents. For example, using 6-mercaptohexanol (6-MH) and 11-mercaptoundecanoic acid (11-MUA), yellow- and green- colored Au NDs were prepared separately. [1a] Their corre- sponding emission wavelengths are 538 and 520 nm when excited at 365 nm, with quantum yields (QYs) of 1.5% and 3.1%, respectively. Having the advantages of large Stokes shift, long lifetime, and biocompatibility, Au NDs have been demonstrated as [a] R. Ravindranath, P. Roy, H.-T. Chang Department of Chemistry National Taiwan University No. 1, Section 4 Roosevelt Road Taipei 10617 (Taiwan) E-mail: changht@ntu.edu.tw [b] R. Ravindranath Nanoscience and Technology Program Taiwan International Graduate Program Academia Sinica Taipei 11529 (Taiwan) Chem. Rec. 2016, 16, 1664–1675 V C 2016 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Wiley Online Library 1664