Nano Gold Colorimetric Determination Of Heparin And Nuclease Activity

Gold nanoparticles (AuNPs) have aroused attention because of their many advantages, such as special small size effect, surface effect and quantum size effect. AuNPs, as colorimetric probes, are widely used in the bioanalysis fields, in which sophisticated equipments are not required. In this paper, we developed the AuNPs-based colorimetric approach for detection of heparin and nuclease.1. Simple and Sensitive Detection of Heparin Using Positively-charged Gold Nanoparticles as Colorimetric ProbesAn operational simple colorimetric method for measuring heparin is developed using positively-charged gold nanoparticles ((+)AuNPs). The negatively-charged heparin interacts with positive-charged AuNPs through electrostatic interaction, which leads to aggregation of AuNPs and color change from red to blue in solution. The concentration of heparin can be determined by monitoring with the naked eye or a UV-vis spectrometer. Under the optimized conditions, the assay shows a linear response toward heparin concentration in the range of 0.09-3.12μg/mL. In addition, addition of hyaluronic acid, an analogue of heparin, leads to less change in solution color due to the lower charge density as compared to that of heparin. This simple, sensitive, inexpensive and visual method provides a potentially useful tool for the heparin detection.2. Sensitive and visual method for label-free nuclease assay using positively-charged gold nanoparticles as colorimetric probeswe described a simple, rapid and general colorimetric method to measure nuclease activity using cysteamine-stabilized AuNPs as probes. By taking advantage of our interesting finding that the AuNPs solution showed a color change from red to blue when ssDNA or dsDNA is directly added into the cysteamine-stabilized AuNPs solution, whereas fragmented DNA can not induce the color change of the cysteamine-stabilized AuNPs solution. S1 nuclease, which exhibits endo- and exolytic hydrolytic activity for the phosphodiester bonds of ssDNA or RNA and produces mono- or oligonucleotide fragments, is taken as the model enzyme to provide the "proof-of-principle" verification of this method. The ssDNA-6 (5'-GAGTTAGCACCCGCATAGTCAAGAT-3') is used as the nuclease substrate. The cysteamine-stabilized AuNPs are positively charged. In absence of nuclease, the electrostatic attraction between the positively-charged AuNPs ((+)AuNPs) and polyanionic DNA leads to the aggregation of AuNPs, and this causes a rapid red-to-blue color change. In the presence of nuclease, ssDNA is hydrolyzed into small fragments, and the AuNPs solution remains red. Thus, nuclease activity can be facilely measured with the naked eye or a simple colorimetric reader.