An electrochemical aptasensor for Δ-tetrahydrocannabinol detection in saliva on a microfluidic platform.

We present a novel "on-off", cost-effective, rapid electrochemical aptasensor combined with a microfluidics cartridge system for the detection of Δ-THC (Δ-tetrahydrocannabinol) in human saliva via differential pulse voltammetry. The assay relied on the competitive binding between the Δ-THC and a soluble redox indicator methylene blue, using an aptamer selected via FRELEX. We found that the aptasensor can detected 1 nM of Δ-THC in PBS in a three-electrode cell system, while the sensitivity and both the dissociation constant (K) and association constant (K) were dependent on the aptamer density.

Electrochemical nutrient removal from natural wastewater sources and its impact on water quality.

In this study, a suite of natural wastewater sources is tested to understand the effects of wastewater composition and source on electrochemically driven nitrogen and phosphorus nutrient removal. Kinetics, electrode behavior, and removal efficiency were evaluated during electrochemical precipitation, whereby a sacrificial magnesium (Mg) anode was used to drive precipitation of ammonium and phosphate. The electrochemical reactor demonstrated fast kinetics in the natural wastewater matrices, removing up to 54% of the phosphate present in natural wastewater within 1 min, with an energy input of only 0.

Electroless Production of Fertilizer (Struvite) and Hydrogen from Synthetic Agricultural Wastewaters.

The drive toward sustainable phosphorus (P) recovery from agricultural and municipal wastewater streams has intensified. However, combining P recovery with energy conservation is perhaps one of the greatest challenges of this century. In this study, we report for the first time the simultaneous electroless production of struvite and dihydrogen from aqueous ammonium dihydrogen phosphate (NHHPO) solutions in contact with either a pure magnesium (Mg) or a Mg alloy as the anode and 316 stainless steel (SS) as the cathode placed in a bench-scale electrochemical reactor.

Directional Preference of DNA-Mediated Electron Transfer in Gold-Tethered DNA Duplexes: Is DNA a Molecular Rectifier?

Electrical properties of self-assembling DNA nanostructures underlie the paradigm of nanoscale bioelectronics, and as such require clear understanding. DNA-mediated electron transfer (ET) from a gold electrode to DNA-bound Methylene Blue (MB) shows directional preference, and it is sequence-specific. During the electrocatalytic reduction of [Fe(CN) ] catalyzed by DNA-bound MB, the ET rate constant for DNA-mediated reduction of MB reaches (1.

Sequence-Specific Electron Transfer Mediated by DNA Duplexes Attached to Gold through the Alkanethiol Linker.

Ability of the DNA double helix to transport electrons is its critical feature, underlying a number of important biological and biotechnological processes. Here, we show that electron transfer (ET) from the gold electrode to the DNA-bound methylene blue (MB) mediated by the DNA base-pair π-stack is less efficient in (dGdC)-rich duplexes compared to pure (dAdT) DNA. The ET rate constant k extrapolated to the DNA surface coverage Γ → 0 is 121 ± 8 s for (dAdT), being almost twofold higher than 67 ± 3 s shown for (dGdC), consistent with the electric-field-disturbed submolecular structure of the (dGdC) duplex earlier shown at electrified interfaces.

Picomolar sensitive and SNP-selective "Off-On" hairpin genosensor based on structure-tunable redox indicator signals.

A robust and sensitive electrochemical assay for chrononocoulometric detection of nucleic acids at a single nucleotide polymorphism (SNP) level has been developed. The assay exploits hybridization-induced conformational switching of gold-tethered TP53-specific 33-mer and truncated 20-mer hairpin DNA probes and methylene blue (MB) as an intercalating redox indicator. We show that by fine tuning of MB-DNA intercations the enhanced binding of MB to hybrids formed with a cancer-biomarker sequence can be achieved, and that results in robust "off-on" sensing of hybridization, while the stem-loop probe design allows minimized, independent of the DNA length background signals.

Electron Transfer in Spacer-Free DNA Duplexes Tethered to Gold via dA Tags.

Electrical properties of DNA critically depend on the way DNA molecules are integrated within the electronics, particularly on DNA-electrode immobilization strategies. Here, we show that the rate of electron transport in DNA duplexes spacer-free tethered to gold via the adenosine terminal region (a dA tag) is enhanced compared to the hitherto reported DNA-metal electrode tethering chemistries. The rate of DNA-mediated electron transfer (ET) between the electrode and methylene blue intercalated into the dA-tagged DNA duplex approached 361 s at a ca.

Submolecular Structure and Orientation of Oligonucleotide Duplexes Tethered to Gold Electrodes Probed by Infrared Reflection Absorption Spectroscopy: Effect of the Electrode Potentials.

Unique electronic and ligand recognition properties of the DNA double helix provide basis for DNA applications in biomolecular electronic and biosensor devices. However, the relation between the structure of DNA at electrified interfaces and its electronic properties is still not well understood. Here, potential-driven changes in the submolecular structure of DNA double helices composed of either adenine-thymine (dAdT) or cytosine-guanine (dGdC) base pairs tethered to the gold electrodes are for the first time analyzed by in situ polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) performed under the electrochemical control.

Chronopotentiometric sensing of specific interactions between lysozyme and the DNA aptamer.

Specific DNA-protein interactions are vital for cellular life maintenance processes, such as transcriptional regulation, chromosome maintenance, replication and DNA repair, and their monitoring gives valuable information on molecular-level organization of those processes. Here, we propose a new method of label-free electrochemical sensing of sequence specific binding between the lysozyme protein and a single stranded DNA aptamer specific for lysozyme (DNA) that exploits the constant current chronopotentiometric stripping (CPS) analysis at modified mercury electrodes. Specific lysozyme-DNA binding was distinguished from nonspecific lysozyme-DNA interactions at thioglycolic acid-modified mercury electrodes, but not at the dithiothreitol-modified or bare mercury electrodes.

Effect of a Dual Charge on the DNA-Conjugated Redox Probe on DNA Sensing by Short Hairpin Beacons Tethered to Gold Electrodes.

Charges of redox species can critically affect both the interfacial state of DNA and electrochemistry of DNA-conjugated redox labels and, as a result, the electroanalytical performance of those systems. Here, we show that the kinetics of electron transfer (ET) between the gold electrode and methylene blue (MB) label conjugated to a double-stranded (ds) DNA tethered to gold strongly depend on the charge of the MB molecule, and that affects the performance of genosensors exploiting MB-labeled hairpin DNA beacons. Positively charged MB binds to dsDNA via electrostatic and intercalative/groove binding, and this binding allows the DNA-mediated electrochemistry of MB intercalated into the duplex and, as a result, a complex mode of the electrochemical signal change upon hairpin hybridization to the target DNA, dominated by the "on-off" signal change mode at nanomolar levels of the analyzed DNA.

Electroanalysis of pM-levels of urokinase plasminogen activator in serum by phosphorothioated RNA aptamer.

Protein biomarkers of cancer allow a dramatic improvement in cancer diagnostics as compared to the traditional histological characterisation of tumours by enabling a non-invasive analysis of cancer development and treatment. Here, an electrochemical label-free assay for urokinase plasminogen activator (uPA), a universal biomarker of several cancers, has been developed based on the recently selected uPA-specific fluorinated RNA aptamer, tethered to a gold electrode via a phosphorothioated dA tag, and soluble redox indicators. The binding properties of the uPA-aptamer couple and interference from the non-specific adsorption of bovine serum albumin (BSA) were modulated by the electrode surface charge.

Determination of zinc in vegetal tissue microsamples by platinum-wire loop in flame atomization atomic absorption spectrometry.

The zinc content of 3 microL of vegetal samples (tree leaves, lichens and grape sap) atomized from a Pt-wire in the methane-air flame has been determined by atomic absorption spectrometry. The effect of gas flow rates and the atomization height in the flame on the absorption of zinc was evaluated at 213.9 nm.