Development of Lateral Flow Immunochromatographic Strips for Micropollutant Screening Using Colorants of Aptamer-Functionalized Nanogold Particles, Part II: Experimental Verification with Aflatoxin B1 and Chloramphenicol

Lateral flow immunochromatographic strips based on colorants of aptamer-functionalized nanogold particles were developed for the detection of micropollutants aflatoxin B1 (AFB1) and chloramphenicol (CAP). The lateral flow immunochromatographic strip was based on a competitive reaction of thiolated-aptamer between micropollutants and bio-DNA probe-streptavidin as capture material immobilized at the test line. General crucial parameters that might influence the sensitivity have been systematically investigated. To test the effectiveness and applicability of the optimized conditions, two structurally unrelated micropollutants, that is, AFB1 and CAP, were chosen for detection. In the present study, lateral flow immunochromatographic strips for AFB1 and CAP analysis by combining the high selectivity and affinity of aptamers with the unique optical properties of nanogold in municipal water samples were reported for the first time. With the optimized conditions, the immunochromatographic strip showed a visual LOD of 10 ppb and a quantitative LOD of 1.05 ppb using an immunochromatographic reader for AFB1 detection and a quantitative LOD of 63.4 ppb using an immunochromatographic reader for CAP detection. Furthermore, the sensitive strip provided a good linear detection range of approximately 0–50 ppm for AFB1 detection and a wider liner detection range of approximately 0–160 ppm for CAP detection. Moreover, the immunochromatographic strip provided recovery rates for water samples of 90–110% in the AFB1 analysis and 84–108% in the CAP analysis. The results demonstrated that the immunochromatographic strip has excellent potential for wide applicability and verified that the strip methods for the optimized conditions are applicable to a variety of micropollutants. The lateral flow immunochromatographic strip could be used as a simple, rapid, and efficient screening tool for rapid on-site detection of a variety of micropollutants.

Nanogravimetric and Optical Characterizations of Thrombin Interaction with a Self-Assembled Thiolated Aptamer

Efficient biorecognition of thrombin (TB), a serine protease with crucial role in physiological and pathological blood coagulation, is a hot topic in medical diagnostics. In this work, we investigate the ability of synthetic thrombin aptamer (TBA), immobilized on a gold substrate, to bind thrombin by two different label-free techniques: the quartz crystal microbalance (QCM) and the spectroscopic ellipsometry (SE). By QCM characterization in the range from 20 to 110 nM, we demonstrate high specificity of TBA-TB interaction and determine affinity constant (Kd) of17.7±0.3 nM, system sensitivity of0.42±0.03 Hz nM−1, and limit of detection (LOD) of240±20 pM. The interaction between TBA and TB is also investigated by SE, an all-optical method, by quantifying the thickness increase of the TBA film assembled on gold substrate. AFM characterization of TBA and TB molecules deposited on flat silicon surface is also supplied.

Study on Specific Binding Interaction Between Protein and DNA Aptamer via Dynamic Force Spectroscopy

Recently the need to design nanoscale, sensitive and flexible bio-sensors or biotic-abiotic interface keeps increasing. One of the essential challenges on this objective is to grasp a thorough understanding of the mechanism governing binding interaction between bio-molecules. In this study we aim to demonstrate the binding specificity and reveal force interaction between the anti-coagulation protein thrombin and the single-stranded DNA thrombin aptamer by application of Atomic Force Microscopy (AFM). The thiolated aptamer was deposited onto gold substrate, and then repeatedly brought into contact with a thrombin-coated AFM tip, and force drop-offs during the pull-off were measured to determine the unbinding force between the thrombin-aptamer pair. The results from experiment show that the thrombin-aptamer pair has specific binding and the force between the pair exhibits loading rate dependence. It was shown that the binding forces of the thrombin-aptamer interaction increases with growth of loading rates. The average binding force for a single thrombin/aptamer pair increased from 20 pN to 40 pN, with loading rate changes from 500pN/s to 13500pN/s. Distribution of the unbinding forces measured for each loading rate can be explained on the basis of single energy barrier model for molecular bond breakage.