A "signal off-on" fluorescence bioassay based on 2D-MoS2-tetrahedral DNA bioconjugate for rapid virus detection.

In this work we present the preparation of a 2D molybdenum disulphide nanosheets (2D-MoS2) and tetrahedral DNA nanostructures (TDNs) bioconjugate, and its application to the development of a bioassay for rapid and easy virus detection. The bioconjugate has been prepared by using TDNs carrying the capture probe labelled with 6-carboxyfluoresceine (6-FAM). As case of study to assess the utility of the assay developed, we have chosen the SARS-CoV-2 virus. Hence, as probe we have used a DNA sequence complementary to a region of the SARS-CoV-2 ORF1ab gene (TDN-ORF-FAM). This 6-FAM labelled capture probe is located on the top vertex of the tetrahedral DNA nanostructure, the three left vertices of TDNs have a thiol group. These TDNs are bounded to 2D-MoS2 surface through the three thiol groups, allowing the capture probe to be oriented to favour the biorecognition reaction with the analyte. This biorecognition resulting platform has finally been challenged to the detection of the SARS-CoV-2 ORF1ab gene sequence as the target model by measuring fluorescence before and after the hybridization event with a detection limit of 19.7fM. Furthermore, due to high sensitivity of the proposed methodology, it has been applied to directly detect the virus in nasopharyngeal samples of infected patients without the need of any amplification step. The developed bioassay has a wide range of applicability since it can be applied to the detection of any pathogen by changing the probe corresponding to the target sequence. Thus, a novel, hands-on strategy for rapid pathogen detection has proposed and has a high potential application value in the early diagnosis of infections causes by virus or bacteria.

Breast cancer biomarker detection through the photoluminescence of epitaxial monolayer MoS2 flakes.

In this work we report on the characterization and biological functionalization of 2D MoS2 flakes, epitaxially grown on sapphire, to develop an optical biosensor for the breast cancer biomarker miRNA21. The MoS2 flakes were modified with a thiolated DNA probe complementary to the target biomarker. Based on the photoluminescence of MoS2, the hybridization events were analyzed for the target (miRNA21c) and the control non-complementary sequence (miRNA21nc). A specific redshift was observed for the hybridization with miRNA21c, but not for the control, demonstrating the biomarker recognition via PL. The homogeneity of these MoS2 platforms was verified with microscopic maps. The detailed spectroscopic analysis of the spectra reveals changes in the trion to excitation ratio, being the redshift after the hybridization ascribed to both peaks. The results demonstrate the benefits of optical biosensors based on MoS2 monolayer for future commercial devices.