Amplified Detection of DNA through the Enzyme-Free Autonomous Assembly of Hemin/G-Quadruplex DNAzyme Nanowires

An enzyme-free amplified detection platform is described using the horseradish peroxidase (HRP)-mimicking DNAzyme as an amplifying label. Two hairpin structures that include three-fourths and one-fourth of the HRP-mimicking DNAzyme in caged, inactive configurations are used as functional elements for the amplified detection of the target DNA. In the presence of the analyte DNA, one of the hairpins is opened, and this triggers the autonomous cross-opening of the two hairpins using the strand displacement principle. This leads to the formation of nanowires consisting of the HRP-mimicking DNAzyme. The resulting DNA nanowires act as catalytic labels for the colorimetric or chemiluminescent readout of the sensing processes (the term “enzyme-free” refers to a protein-free catalyst). The analytical platform allows the sensing of the analyte DNA with a detection limit corresponding to 1 × 10^–13 M. The optimized system acts as a versatile sensing platform, and by coaddition of a “helper” hairpin structure any DNA sequence may be analyzed by the system. This is exemplified with the detection of the BRCA1 oncogene with a detection limit of 1 × 10^–13 M

Applying a COVID-19 Sample-pooling Technique to Forensics Identification of Illicit Drugs

This paper presents a method for materially speeding up the identification process of suspect illicit drugs by pooling samples that require GC-MS analysis. This method can be applied to samples seized from a single suspect that are similar in appearance and therefore meet the Israeli Dangerous Drug Ordinance requirements for sampling. A complementary test (GC, TLC, or FTIR) conducted separately on each of the sampled units can prove conclusively that all units contain the same drug. This study shows that even with large differences in relative weight of mixes in a pool, each drug is easily identifiable by GC-MS and dominant peaks do not overshadow minority substances. By using this method, a narcotics lab can improve its throughput of expert opinions in narcotics cases, and at the same time save resources, extend instrument life, and be more environment-friendly

Applying a COVID-19 Sample-pooling Technique to Forensics Identification of Illicit Drugs

This paper presents a method for materially speeding up the identification process of suspect illicit drugs by pooling samples that require GC-MS analysis. This method can be applied to samples seized from a single suspect that are similar in appearance and therefore meet the Israeli Dangerous Drug Ordinance requirements for sampling. A complementary test (GC, TLC, or FTIR) conducted separately on each of the sampled units can prove conclusively that all units contain the same drug. This study shows that even with large differences in relative weight of mixes in a pool, each drug is easily identifiable by GC-MS and dominant peaks do not overshadow minority substances. By using this method, a narcotics lab can improve its throughput of expert opinions in narcotics cases, and at the same time save resources, extend instrument life, and be more environment-friendly

Metal Nanoparticle-Functionalized DNA Tweezers: From Mechanically Programmed Nanostructures to Switchable Fluorescence Properties

DNA tweezers are modified with two 10-nm sized Au NPs and one 5-nm sized Au NP. Upon treatment of the tweezers with fuel and antifuel nucleic acid strands, the switchable closure and opening of the tweezers proceed, leading to the control of programmed nanostructures of the tethered NPs. The tweezers are further modified with a single 10-nm sized nanoparticle, and a fluorophore unit (Cy3), positioned at different distinct sites of the tweezers. The reversible and cyclic fluorescence quenching or fluorescence enhancement phenomena, upon the dynamic opening/closure of the different tweezers, are demonstrated

Autonomous Control of Interfacial Electron Transfer and the Activation of DNA Machines by an Oscillatory pH System

An oscillatory pH system is implemented to drive oscillatory pH-switchable DNA machines and to control pH-stimulated electron transfer at electrode surfaces. The oscillatory pH system drives the autonomous opening and closure of DNA tweezers and activates a DNA pendulum by the pH-stimulated formation and dissociation of i-motif structures. Also, a sequence-programmed nucleic acid monolayer-functionalized electrode undergoes autonomous oscillatory pH transitions between random coil and i-motif configurations, leading to the control of electron transfer at electrode surfaces

Real-Time Monitoring of Transferrin-Induced Endocytic Vesicle Formation by Mid-Infrared Surface Plasmon Resonance

We report on the application of surface plasmon resonance (SPR), based on Fourier transform infrared spectroscopy in the mid-infrared wavelength range, for real-time and label-free sensing of transferrin-induced endocytic processes in human melanoma cells. The evanescent field of the mid-infrared surface plasmon penetrates deep into the cell, allowing highly sensitive SPR measurements of dynamic processes occurring at significant cellular depths. We monitored in real-time, infrared reflectivity spectra in the SPR regime from living cells exposed to human transferrin (Tfn). We show that although fluorescence microscopy measures primarily Tfn accumulation in recycling endosomes located deep in the cell's cytoplasm, the SPR technique measures mainly Tfn-mediated formation of early endocytic organelles located in close proximity to the plasma membrane. Our SPR and fluorescence data are very well described by a kinetic model of Tfn endocytosis, suggested previously in similar cell systems. Hence, our SPR data provide further support to the rather controversial ability of Tfn to stimulate its own endocytosis. Our analysis also yields what we believe is novel information on the role of membrane cholesterol in modulating the kinetics of endocytic vesicle biogenesis and consumption