Guanidine hydrochloride is often used as an intermediate in medicines, pesticides, dyes and other organic compounds, it is also an important raw material for sulfonamides and folic acid; it can be used as a strong denaturants in the extraction of total RNA from cells, and used for denaturation and complexation of proteins. It can be used as an antistatic agent for synthetic fibers. In this article, we will introduce you another application of guanidine hydrochloride——to improve the property of gold nanoclusters（AuNCs）.

In recent years, metal nanoclusters, especially gold nanoclusters (AuNCs), have attracted much attention as a new class of fluorescent nanomaterials. Since the size of the metal nanoclusters is close to the Fermi wavelength of electrons, the continuous energy state property splits into discrete energy states, and a size-dependent effect of similar molecules occurs. Compared with small molecule organic fluorescent dyes and fluorescent proteins, gold nanocluster materials have the advantages of good photophysical properties, large specific surface area, easy surface modification and adjustable fluorescence properties. Therefore, it has broad application prospects in the fields of compound detection, biosensing and imaging, optoelectronics and nanomedicine.

Although there is a certain research and application of gold nano-cluster materials, there is still a lack of in-depth and systematic research on the relationship between fluorescence and composition/structure. Studies over the past decade have shown that the fluorescent properties of gold nanoclusters cannot be simply attributed to the quantum confinement effect of gold nuclei, which is also closely related to ligands bound to the surface of gold nuclei. By changing the structure of the surface ligand, the fluorescence quantum yield of gold nanoclusters can be significantly improved.

The researchers used 6-aza-2-thiothymidine-gold nanoclusters as precursors, and self-assembly of guanidine hydrochloride/6-aza-2-thiothymidine by adding a rigiding agent guanidine hydrochloride. The obtained gold nanoclusters show strong green fluorescence, and have the characteristics of good water solubility, high fluorescence quantum yield, wide excitation spectrum and narrow emission spectrum. The specific steps are as follows:

(2) Add 2 mL of 40 mmol/L guanidine hydrochloride solution (pH=10) to 18 mL of purified 6-aza-2-thiothymidine-gold nanocluster solution and incubate in a 37°C water bath. After 20 minutes, a solution of guanidine hydrochloride/6-aza-2-thiothymidine-gold nanoclusters was obtained, which was yellow-green, and strong green fluorescence was observed under ultraviolet light.

The fluorescence spectrum of the gold nanoclusters has excitation peaks at 407 nm, 465 nm and 495 nm by adding a rigiding agent guanidine hydrochloride (CAS 50-01-1). The maximum emission peak is at 530 nm and the fluorescence quantum yield is 71%.

There is no need to add any other reducing agent during the reaction process, the preparation process is simple, environmentally friendly, and the excitation spectrum is wide, the emission spectrum is narrow, the stability is high, and the fluorescence quantum yield is high.

Reference

Chen Wei, Deng Haohua, Shi Xiaoqiong, et al. Guanidine hydrochloride/6-aza-2-thiothymidine-gold nanoclusters and preparation method thereof. 2018.6.22, CN105860963B.