Salih Ahmed E, Elsherif Mohamed, Alam Fahad, Chiesa Matteo, Butt Haider
Department of Mechanical Engineering, Khalifa University, Abu Dhabi P.O. Box 127788, United Arab Emirates.
Department of Physics and Technology, UiT The Arctic University of Norway, 9010 Tromsø, Norway.
Nanomaterials (Basel). 2022 Apr 27;12(9):1486. doi: 10.3390/nano12091486.
Surface functionalization of metallic nanoparticles (NPs) with external groups can be engineered to fabricate sensors that are responsive to various stimuli like temperature, pH, and numerous ions. Herein, we report the synthesis of gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (GNPs-MPA) and the doping of these nanoparticles into hydrogel materials using the breathing-in/breathing-out (BI-BO) method. MPA has a carboxyl group that becomes protonated and, thus, ionized at a pH below its pK (4.32); hence, the GNPs-MPA solutions and gels were mostly pH-responsive in the range of 3-5. Optical properties were assessed through ultraviolet-visible (UV-Vis) spectroscopy, namely: transmission and absorption, and the parameters used to quantify the pH changes were the full width at half maximum (FWHM) and position of surface plasmon resonance (SPR). The solutions and gels gradually changed their colors from red to indigo with pH decrementation from 5 to 3, respectively. Furthermore, the solutions' and doped gels' highest FWHM sensitivities towards pH variations were 20 nm and 55 nm, respectively, while the SPR's position sensitivities were 18 nm and 10 nm, respectively. Also, transmission and scanning electron microscopy showed synchronized dispersion and aggregation of NPs with pH change in both solution and gel forms. The gel exhibited excellent repeatability and reversibility properties, and its response time was instantaneous, which makes its deployment as a colorimetric pH-triggered sensor practical. To the best of our knowledge, this is the first study that has incorporated GNPs into hydrogels utilizing the BI-BO method and demonstrated the pH-dependent optical and colorimetric properties of the developed nanocomposites.
通过用外部基团对金属纳米颗粒（NPs）进行表面功能化，可以设计制造出对温度、pH值和多种离子等各种刺激有响应的传感器。在此，我们报告了用3-巯基丙酸功能化的金纳米颗粒（GNPs-MPA）的合成，以及使用呼吸进/呼吸出（BI-BO）方法将这些纳米颗粒掺杂到水凝胶材料中。MPA有一个羧基，在pH值低于其pK（4.32）时会质子化并因此电离；因此，GNPs-MPA溶液和凝胶在3-5的范围内大多对pH值有响应。通过紫外可见（UV-Vis）光谱评估光学性质，即透射和吸收，用于量化pH值变化的参数是半高宽（FWHM）和表面等离子体共振（SPR）的位置。随着pH值分别从5降低到3，溶液和凝胶的颜色逐渐从红色变为靛蓝色。此外，溶液和掺杂凝胶对pH值变化的最高FWHM灵敏度分别为20 nm和55 nm，而SPR的位置灵敏度分别为18 nm和10 nm。而且，透射电子显微镜和扫描电子显微镜显示，在溶液和凝胶形式中，纳米颗粒随着pH值变化同步分散和聚集。该凝胶表现出优异的可重复性和可逆性，其响应时间是即时的，这使得将其用作比色pH触发传感器具有实际可行性。据我们所知，这是第一项利用BI-BO方法将GNPs纳入水凝胶并展示所开发纳米复合材料的pH依赖性光学和比色性质的研究。
