Abstract

In the present study, colloidal gold nanoparticles (AuNPs) were synthesized by the citrate reduction method. The physical properties and their stability were studied in the various buffer systems at different pH and time intervals. Monodisperse AuNPs were used to assess their stability and aggregation in 0.1 M of buffers. We analyzed the stability of the colloidal gold nanoparticles in borate, phosphate, Tris–citrate and Tris–HCl buffers with variable pH and time-dependent manner. For understanding the stability and aggregation of AuNPs in different buffers, AuNPs and buffer mixture was incubated at 4 °C for different time-periods. The surface plasmon resonance (SPR) spectra and colorimetric changes were recorded at time interval. Absorbance spectra revealed that different ratios of AuNPs in borate buffer were stable at pH 7.5 to 9.3. Wine red colour with maximum absorbance at 520 nm was obtained due to lack of the aggregation. The phosphate buffer was not suitable for monodisperse gold nanoparticles and got aggregated. In Tris–citrate buffer, the absorbance A₅₂₀ (*P < 0. 05 and ***P < 0. 001) and correlation coefficient changed with incubation time and λ_max shifts to longer wavelengths at pH 8.5. Tris–HCl buffer revealed significant changes A₅₂₀ with incubation period and did not correlate with time. There were changes in A₅₂₀ with incubation time and λ_max shifts towards longer wavelength at pH 4.0 while AuNPs was stable at pH 10.5. The phosphate buffer, Tris–citrate buffer and Tris–HCl buffer made complexes and got aggregated colorimetric response was shifted wine red color to blue –black color.

Graphical Abstract

中文翻译：

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不同缓冲液体系中金纳米颗粒（AuNPs）的合成，表征和稳定性

摘要

在本研究中，胶体金纳米粒子（AuNPs）通过柠檬酸盐还原法合成。在各种缓冲液系统中，在不同的pH和时间间隔下研究了物理性质及其稳定性。单分散AuNP用于评估其在0.1 M缓冲液中的稳定性和聚集。我们分析了胶体金纳米颗粒在硼酸盐，磷酸盐，Tris-柠檬酸盐和Tris-HCl缓冲液中的稳定性，其pH和时间依赖于可变方式。为了理解AuNPs在不同缓冲液中的稳定性和聚集，将AuNPs和缓冲液混合物在4°C下孵育不同的时间。以时间间隔记录表面等离子体共振（SPR）光谱和比色变化。吸收光谱表明，硼酸盐缓冲液中不同比例的AuNPs在pH 7.5至9.3时稳定。由于没有聚集，获得了在520nm处具有最大吸光度的酒红色。磷酸盐缓冲液不适用于单分散金纳米颗粒，并且会发生聚集。在Tris–柠檬酸盐缓冲液中，吸光度A₅₂₀（* P  <0. 05和*** P  <0. 001），相关系数随孵育时间而变化，_λmax在pH 8.5时移至更长的波长。Tris-HCl缓冲液在孵育期间显示出A _520的显着变化，并且与时间无关。A ₅₂₀随孵育时间的变化而变化，_λmax在pH 4.0时移向更长的波长，而AuNP在pH 10.5时稳定。磷酸盐缓冲液，Tris-柠檬酸盐缓冲液和Tris-HCl缓冲液形成复合物，并获得了比色响应，从而使酒红色变为蓝黑色。

图形概要