We report a label-free and simple approach for the detection of glycoprotein-120 (gp-120) using an aptamer-based liquid crystals (LCs) biosensing platform. The LCs are supported on the surface of a modified glass slide with a suitable amount of B40t77 aptamer, allowing the LCs to be homeotropically aligned. A pronounced topological change was observed on the surface due to a specific interaction between B40t77 and gp-120, which led to the disruption of the homeotropic alignment of LCs. This results in a dark-to-bright transition observed under a polarized optical microscope. With the developed biosensing platform, it was possible to not only identify gp-120, but obtained results were analyzed quantitatively through image analysis. The detection limit of the proposed biosensing platform was investigated to be 0.2 µg/mL of gp-120. Regarding selectivity of the developed platform, no response could be detected when gp-120 was replaced by other proteins, such as bovine serum albumin (BSA), hepatitis A virus capsid protein 1 (Hep A VP1) and immunoglobulin G protein (IgG). Due to attributes such as label-free, high specificity and no need for instrumental read-out, the presented biosensing platform provides the potential to develop a working device for the quick detection of HIV-1 gp-120.
Surface protein gp-120 of HIV-1 virus plays an important role in the infection of HIV-1, but detection of gp-120 during the early stage of infection is very difficult. Herein, we report a binding bioassay based on an RNA aptamer B40t77, which binds specifically to gp-120. The bioassay is built upon a hydrophobic glass slide with surface immobilized gp-120. When the glass surface is incubated in a solution containing B40t77, the aptamer is able to bind to gp-120 specifically and remove it from the surface after a short incubation time of 30 min. The result of the binding event can be amplified by using liquid crystal (LC) into optical signals in the final step. By using this bioassay, we are able to detect as low as 1 μg/ml of gp-120 with high specificity within 30 min. No response is obtained when gp-120 is replaced by other protein such as bovine serum albumin (BSA). This is the first qualitative bioassay which provides a simple way for the detection of gp-120 with the naked eye. The assay is robust, low-cost and does not require additional labeling. Thus, the bioassay is potentially useful for the early detection of HIV-1 in resources-limited regions.
A new sensing methodology has been developed for the detection of Cu(II) ions in water by using biotinylated oligopeptide as a probe whereas liquid crystal (LC) and fluorophore were used as signal reporters. The multidentate oligopeptide ligand was used to investigate Cu(II) as a model metal ion. The alkyl terminal group of the coated dimethyl octadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP) was first activated to aldehydic functional group by UV irridiation for 50 seconds. The activated aldehydic functional group was covalent linked with biotinylated oligopeptide via thiolation reaction. As fabricated oligopeptide probe spotted with metal ions was incubated for 30 minutes and followed by tagging with streptavidin-cyanine-3 as a fluorophore. Polarized optical microscopy (POM) and fluorescence microarray scanner (FMS) were used as characterization techniques. The developed sensing methodology results were reproducible for different concentrations of model Cu (II) ions as confirmed from the characterization techniques. Our methodology highlighted the detection of Cu(II) ions in water as low as 100 nM, and is the lowest concentration so far reported.
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