Surface conformations of anti-ricin aptamer and its affinity to ricin determined by atomic force microscopy and surface plasmon resonance

Authors: WANG, BIN - University Of Georgia; ZHICHAO, LOU - Nanjing Agricultural University; Park, Bosoon; KWON, YONGKUK - Animal, Plant And Fisheries Quarantine And Inspection Agency (QIA); XU, BINGQIAN - University Of Georgia

Submitted to: Physical Chemistry Chemical Physics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2014
Publication Date: 8/11/2014
Publication URL: http://www.rsc.org/pccp
Citation: Wang, B., Zhichao, L., Park, B., Kwon, Y., Xu, B. 2014. Surface conformations of anti-ricin aptamer and its affinity to ricin determined by atomic force microscopy and surface plasmon resonance. Physical Chemistry Chemical Physics. 17:307-14. doi: 10.1039/c4cp03190c.

Interpretive Summary: Nucleic acid aptamers have been widely used as binding reagents for the label free detections of biomolecules. Compared to antibodies, aptamers demonstrated advantages such as easy synthesis, low cost and better stability. Thus, aptamers can be integrated into various detection platforms and provide versatile applications in the fast detection and analysis related to biosafety and biosecurity such as the detection of toxins in forensic samples, food products and public environments. Among various detection platforms, nanotechnologies have been widely used in recent years to improve the sensitivity and specificity of detections. By integrating aptamers with various nanotechnologies, the aptamer based biosensors will provide more versatile methods and devices for the high throughput and label-free detection. In this study, two nanotechnology platforms, atomic force microscopy and surface plasmon resonance, were examined to apply for food toxin detection by measuring specific interactions between ricin and anti-ricin aptamer.

Technical Abstract: The specific interactions between ricin and anti-ricin aptamer were measured with atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectrometry and the results were compared. In AFM, a single-molecule experiment with ricin functionalized AFM tip was used for scanning the aptamer molecules immobilized on Au(111) surface. The AFM topography images showed resolution high enough to distinguish different aptamer conformations on Au (111) surface. The specific binding site on the aptamer molecule was clearly recognized by the AFM recognition images. These high resolution images of single aptamer molecules and aptamer aggregations were consistent with the conformations and binding sites predicted by molecular simulations. The SPR with aptamer modified gold substrates was used to conduct repeatable detections of ricin samples in the range from 1.7 nM to 166.7 nM. The off rate values of ricin aptamer interactions were estimated by both single-molecule dynamic force microscopy (DFS) and SPR as (6.8±0.9)×10-4 s-1 and (1.4±8.3)×10-4 s-1, respectively. The subtle differences between the off rate values of SPR and AFM came from the various conformations and aggregations of aptamer immobilized on gold surface, which determine the availability of the specific binding site to the ricin molecules. The SPR bulk solution measurements resulted in the averaged signals from both specific and non-specific interactions. While the single-molecule AFM images and DFS measurements provide more specific information for the interactions between individual aptamer and ricin molecules.