Controlled etching and tapering of Au nanorods using cysteamine

Abstract

While gold nanorods (AuNRs) have found many applications due to their unique optical properties, a few challenges persist in their synthesis. Namely, it is often difficult to reproducibly synthesize AuNRs with specific and monodisperse sizes, especially at shorter aspect ratios. Here, we report a method of post-synthesis precise tailoring of AuNRs by etching with cysteamine. Cysteamine selectively etches AuNRs from their ends while preserving the initial rod shape and monodispersity, making this a viable means of obtaining highly monodisperse short AuNRs down to aspect ratio 2.3. Further, we explore the effect of this etching method on two types of silica-coated AuNRs: silica side-coated and silica end-coated AuNRs. We find that the etching process is cysteamine concentration-dependent and can lead to different degrees of sharpening of the silica-coated AuNRs, forming elongated tips. We also find that cysteamine behaves only as a ligand at concentrations above 200 mM, as no etching of the AuNRs is observed in this condition. Simulations show that excitation of plasmon resonances in these sharpened AuNRs produces local electric fields twice as strong as those produced by conventional AuNRs. Thus, cysteamine etching of AuNRs is shown to be an effective means of tailoring both the size and shape of AuNRs along with their corresponding optical properties. At the same time, the resulting cysteamine coating on the etched AuNRs displays terminal amino groups that allow for further functionalization of the nanorods.

Studies on Thiol Etching of Gold by Using QCM‐D Sensor as the Sacrificial Probe

“…First, sodium borohydride (NaBH 4 ) or higher temperatures were often utilized in the previous reports. [5][6]13,24] Second and more importantly, the Au atoms on the small particle surfaces (including nanoparticles and nanoclusters) are more active than those on the flat surface of QCM-D sensor. [9b] Depositing one layer of gold nanoparticles or nanoclusters on the QCM-D sensor can simulate the etching situations of gold particles.…”

“…Clearly, throughout the entire history of gold particle chemistry, thiols have played an indispensable role both in preparing and in stabilizing nano‐ or subnano‐particles of gold. Among all the used thiol agents for the etching of gold nanoparticles or nanoclusters, cysteamine (CS), glutathione and cysteine are the most used types of water soluble biothiols, due to their security, strong etching abilities and mild conditions of etching reaction [4d,5,9a,10–11,12c,d] …”

Improvement of Gold Nanorods in Photothermal Therapy: Recent Progress and Perspective

“…GNRs with LSPR bands ranging from 600 to 1270 nm are accessible by this method without significantly affecting their dispersion in size and shape, which simultaneously optimize the symmetry breaking and the seeded growth process (Gonzalez-Rubio et al, 2019). Besides, postsynthesis modification, including the secondary growth (Ratto et al, 2010;Khlebtsov et al, 2014a; and controlled etching (Szychowski et al, 2018) of GNRs, serves as an effective strategy to improve the reproducibility and precisely control the shape of GNRs.…”

Heterostructures Built through Site‐Selective Deposition on Anisotropic Plasmonic Metal Nanocrystals and Their Applications

“…This approach has previously been successfully explored for etching noble metals, where mild oxidation of noble metals is realized by use of cysteamine, Au(III) complex ions, O 2 , and H 2 O 2 . [10,[107][108][109] In general, etching preferentially is initiated from the sharp tips of noble metal NCs. [109] By varying the oxidation condition, the etching site can be well controlled.…”