Study on system parameters of gold nanoparticle aggregation-based visible detection system

Abstract

There has been a lot of research pursuing an easy, rapid and sensitive detection method for pathogenic microorganisms, proteins and chemicals. However, many methods have their own problems such as complicated sample preparation, low sensitivity, and complex procedure often demanding trained experts or sophisticated instruments. In the preceding studies, a rapid and simple detection method using gold nanoparticle (AuNP) was developed. This method has two steps for detection. First, the target reacts with switchable linker (SL). Second, After SL reacting with the target, add streptavidin coated AuNP (stAuNP) to the mixture. By biotin-streptavidin binding force, biotins on the SL connect with the streptavidin on the stAuNPs. The aspect of aggregation is observed differently by the concentration of SL. In the low concentration of SL, the number of SL is not enough for forming aggregation after reacting with the targets. In the high concentration, the number of remaining SL after reacting with target is too many. These many SL covers the stAuNPs, so they cannot exhibit their bridging ability for making aggregation. If this quantitative relationship is appropriate for making aggregation, we can observed with naked eye. At this time, the key factors of the former detection system were studied for giving background information on further improvement of the system. The effect of the size of AuNPs on the range exhibiting a visible color change (REVC) and reaction time was investigated. The bigger the size of AuNPs REVC region moved to high concentration of SL and took more time for making enough aggregation. Furthermore, how the number of biotins on the SL and activity of antibody affect the REVC and aggregation appearance was studied. The more biotins binds on the single SL, the less SL is needed for making same amount of aggregation. Lastly, the impact of the environment (pH and salts existence) on the stability of the system was evaluated. 1M NaCl doesnt affect the stability of the system. In the pH 6-8, the detection system works well. However, in the pH 5 and pH 9, the time for making enough aggregation took much longer than the control. In the real application, the conditions are very different according to what kinds of foods or ingredients make use of. Thus, the result of this study could be used as valuable references for improving and applying this detection system.