Sub-ppt detection limits for copper ions with Gly-Gly-His modified electrodes

An electrochemical metal ion sensor has been developed with a detection limit of less than 0.2 ppt by the covalent attachment of the tripeptide Gly-Gly-His as a recognition element to a 3-mercaptopropionic acid modified gold electrode.     

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Monitoring the heterogeneity in single cell responses to drugs using electrochemical impedance and electrochemical noise

Impedance spectroscopy is a widely used technique for monitoring cell–surface interactions and morphological changes, typically based on averaged signals from thousands of cells. However, acquiring impedance data at the single cell level, can potentially reveal cell-to-cell heterogeneity for example in response to chemotherapeutic agents such as doxorubicin. Here, we present a generic platform where light is used to define and localize the electroactive area, thus enabling the impedance measurements for selected single cells. We firstly tested the platform to assess phenotypic changes in breast cancer cells, at the single cell level, using the change in the cell impedance. We next show that changes in electrochemical noise reflects instantaneous responses of the cells to drugs, prior to any phenotypical changes. We used doxorubicin and monensin as model drugs and found that both drug influx and efflux events affect the impedance noise signals. Finally, we show how the electrochemical noise signal can be combined with fluorescence microscopy, to show that the noise provides information on cell susceptibility and resistance to drugs at the single cell level. Together the combination of electrochemical impedance and electrochemical noise with fluorescence microscopy provides a unique approach to understanding the heterogeneity in the response of single cells to stimuli where there is not phenotypic change.

A light addressable single-cell impedance technique for cell adhesion monitoring and measurement of a cell''s drug response based on electrochemical noise is introduced.     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.     

A Comparative Study of Electrochemical Reduction of 4‐Nitrophenyl Covalently Grafted on Gold and Carbon

4‐Nitrophenyl layers were grafted on gold and glassy carbon surfaces by electrochemical reductive adsorption of the corresponding diazonium salt. Electrochemical conversion efficiencies of 4‐nitrophenyl moieties to 4‐aminophenyl moieties on gold versus on glassy carbon in a protic medium were investigated using X‐ray photoelectron spectroscopy (XPS). In total contrast to all previous comparative studies showing greater electrochemical reactivity of aryl diazonium salt‐derived layers on gold than on glassy carbon, a much lower rate of conversion to 4‐aminophenyl was observed on gold than on glassy carbon by both cyclic voltammetry (CV) and chronoamperometry (CA) methods. The lower electron transfer rate during conversion observed on gold versus glassy carbon was proposed to be due to a mechanism related to the molecular structure rearrangement of 4‐nitrophenyl during the process on glassy carbon. However, whilst complete conversion of 4‐nitrophenyl to 4‐aminophenyl on gold by chronoamperometry was achieved, on glassy carbon complete reduction could not be achieved under the same conditions.     

'Dispersible electrodes': a solution to slow response times of sensitive sensors

Herein, we introduce the concept of utilizing conductive gold-coated magnetic nanoparticles as 'dispersible electrodes', which serve as the active element in the selective capture and direct electro-analytical quantification of analytes. This concept reduces response times and decreases detection limits by bringing the sensor to the analyte rather than the conventional paradigm of the analyte finding the sensor.