Direct Electrochemistry of Cytochrome c at Modified Si(100) Electrodes

This paper demonstrates the direct electron transfer between the heme moiety of horse hearth cytochrome c and a pyridinyl group on self‐assembled‐monolayer‐modified Si(100) electrodes. Self‐assembled monolayers (SAMs) containing the putative receptor ligand were prepared by a step‐wise procedure using “click” reactions of acetylene‐terminated alkyl monolayers and isonicotinic acid azide derivatives. Unoxidized Si(100) electrodes, possessing either isonicotinate or isonicotinamide receptor ligands, were characterized using X‐ray photoelectron spectroscopy, contact‐angle goniometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The ability of isonicotinic acid terminated layers to coordinatively bind the redox center of cytochrome c was found to be restricted to pyridinyl assemblies with a para‐ester linkage present. The protocol detailed here offers an experimentally simple modular approach to producing chemically well‐defined SAMs on silicon surfaces for direct electrochemistry of a well‐studied model redox protein.     

Determination of sulfite in beer samples using an amperometric fill and flow channel biosensor employing sulfite oxidase

A simple method is described to determine sulfite in beer samples using a fill and flow channel biosensor. A droplet of sample is placed into the inlet of a rectangular flow cell and begins to flow through the channel by capillarity. The flow is maintained and controlled by a porous outlet plug of defined porosity. In a rectangular flow cell, the sample solution flows through three consecutive zones: over a predictor electrode, an enzyme layer and a detector electrode. Together these three zones enable the differentiation between current due to sulfite and current due to other electroactive species in the sample. The predictor electrode is located upstream, and on the opposite channel wall to the enzyme layer and detector electrode, and is poised at the same potential (+0.65 V versus Ag/AgCl) as the detector electrode. On this electrode, the current contribution from all species in the sample solution that are oxidized at that potential is determined. The enzyme layer contains sulfite oxidase, which, in the process of oxidizing sulfite, produces hydrogen peroxide, which itself is reduced by excess sulfite. The current at the downstream detector electrode is therefore different from that at the predictor electrode as a result of the enzyme reaction and the difference of the currents, corrected for the dimensions of the electrodes, is proportional to the concentration of sulfite. The method enables a straightforward correction of the interfering current at the detector electrode and a determination of the analyte concentration. The effect of interferences from ascorbic acid, ethanol, sorbic acid and tartaric acid in the detection of sulfite is efficiently removed. The concentration of sulfite in a sample of beer measured by the biosensor is equivalent to that measured using a reference method based on the AOAC-recommended Monier-Williams method.     

Protein electrochemistry using aligned carbon nanotube arrays

The remarkable electrocatalytic properties and small size of carbon nanotubes make them ideal for achieving direct electron transfer to proteins, important in understanding their redox properties and in the development of biosensors. Here, we report shortened SWNTs can be aligned normal to an electrode by self-assembly and act as molecular wires to allow electrical communication between the underlying electrode and redox proteins covalently attached to the ends of the SWNTs, in this case, microperoxidase MP-11. The efficiency of the electron transfer through the SWNTs is demonstrated by electrodes modified with tubes cut to different lengths having the same electron-transfer rate constant.     

The ion gating effect: using a change in flexibility to allow label free electrochemical detection of DNA hybridisation

A label free electrochemical method of detecting DNA hybridisation is presented based on the change in flexibility between a single strand of DNA and a duplex causing an ion-gating effect where hybridisation opens up the electrode to access of ions.     

Rapid and ultrasensitive electrochemical detection of circulating tumor DNA by hybridization on the network of gold-coated magnetic nanoparticles

An accurate and robust method for quantifying the levels of circulating tumor DNA (ctDNA) is vital if this potential biomarker is to be used for the early diagnosis of cancer. The analysis of ctDNA presents unique challenges because of its short half-life and ultralow abundance in early stage cancers. Here we develop an ultrasensitive electrochemical biosensor for rapid detection of ctDNA in whole blood. The sensing of ctDNA is based on hybridization on a network of probe DNA modified gold-coated magnetic nanoparticles (DNA-Au@MNPs). This DNA-Au@MNPs biosensor can selectively detect short- and long-strand DNA targets. It has a broad dynamic range (2 aM to 20 nM) for 22 nucleotide DNA target with an ultralow detection limit of 3.3 aM. For 101 nucleotide ctDNA target, a dynamic range from 200 aM to 20 nM was achieved with a detection limit of 5 fM. This DNA-Au@MNPs based sensor provides a promising method to achieve 20 min response time and minimally invasive cancer early diagnosis.

This study introduces a new electrochemical sensing strategy for the rapid detection of circulating tumor DNA (ctDNA) from whole blood in combination with a network of DNA-Au@MNPs with high sensitivity and excellent selectivity.     

The palladium(II)-catalyzed Nazarov reaction

The PdCl(2)-catalyzed cyclization of alpha-alkoxy dienones leads to 2-hydroxycyclopentenones, whereas the Pd(OAc)(2)-catalyzed reaction leads to cross-conjugated cyclopentenones through an oxidative process. [reaction: see text]     

Paper‐Based Ratiometric Fluorescence Analytical Devices towards Point‐of‐Care Testing of Human Serum Albumin

Monitoring of human serum albumin (HSA) in a point‐of‐care fashion is urgently needed in particular for elderly or chronically ill patients. Herein, a dual‐state emissive chalcone probe having the feature of aggregation‐induced emission was designed and synthesized. The concentration of HSA can be evaluated by the ratios of emission from probes in aggregated and monomeric state, which gives a visually discernible red‐to‐green color change. A simple, portable paper‐based analytical device have been fabricated by integration of the recognition probe in the detection pad and employed for HSA test using the whole blood samples. This paper‐based assay shows the analytical capability comparable to the standard testing methods but is in a point‐of‐care fashion, providing a promising tool for at‐home HSA detection and HSA‐related disease diagnosis.     

Robotic solid phase extraction and high performance liquid chromatographic analysis of ranitidine in serum or plasma.

A fully automated assay for the analysis of ranitidine in serum and plasma, with and without an internal standard, was validated. It utilizes robotic solid phase extraction with on-line high performance liquid chromatographic (HPLC) analysis. The ruggedness of the assay was demonstrated over a three-year period. A Zymark Py Technology II robotic system was used for serial processing from initial aspiration of samples from original collection containers, to final direct injection onto the on-line HPLC system. Automated serial processing with on-line analysis provided uniform sample history and increased productivity by freeing the chemist to analyse data and perform other tasks. The solid phase extraction efficiency was 94% throughout the assay range of 10-250 ng/mL. The coefficients of variation for within- and between-day quality control samples ranged from 1 to 6% and 1 to 5%, respectively. Mean accuracy for between-day standards and quality control results ranged from 97 to 102% of the respective theoretical concentrations.     

A Comparison of Differently Synthesized Gold‐coated Magnetic Nanoparticles as ‘Dispersible Electrodes’

Gold‐coated magnetic nanoparticles (Au@MNPs) have attracted significant interest in electrochemistry in recent years. This is especially the case with their application as dispersible electrodes where modified Au@MNPs are dispersed into a solution, selectively bind to the analyte of interest and are then brought to an electrode via application of a magnetic field for measurement. This paper characterizes four types of Au@MNPs with different sizes, shapes, and method of synthesis as dispersible electrodes. The Au@MNPs were characterized by transmission electron microscopy and X‐ray photoelectron spectroscopy and scanning electron microscopy. In addition, the electrochemical behaviour of Au@MNPs was investigated using cyclic voltammetry. The four sorts of Au@MNPs were evaluated with regards to the three main features required in the dispersible electrodes approach, well‐defined morphology, well‐defined electrochemistry and fast response to a magnetic field. The Cubic‐Au@MNPs, which presents the simplest synthetic route, showed the best electrochemical stability and performance, responding quickly to a magnet and had a well defined shape.