The study of microscopic structure of a liquid/liquid interface is of fundamental importance due to its close relation to the thermodynamics and kinetics of interfacial charge transfer reactions.In this article,the microscopic structure of a non-polarizable water/nitrobenzene(W/NB)interface was evaluated by scanning ion conductance microscope(SICM).Using SICM with a nanometer-sized quartz pipette filled with an electrolyte solution as the probe,the thickness of this type of W/NB interface could be measured at sub-nanometer scale,based on the continuous change of ionic current from one phase to another one.The effects for thicknesses of the non-polarizable W/NB interfaces with different electrolyte concentrations,the Galvani potentials at the interface and the applied potentials on the probe were measured and systematically analyzed.Both experimental setups,that is an organic phase up and an aqueous down,and a reverse version,were employed to acquire the approach curves.These data were compared with those of an ideal polarizable interface under the similar experimental conditions,and several characteristics of non-polarizable interfaces were found.The thickness of a non-polarizable interface increases with the decrease of electrolyte concentration and the increase of applied potential,which is similar to the situation of a polarizable liquid/liquid interface.We also find that the Galvani potential across a non-polarizable interface can also influence the interfacial thickness,this phenomenon is difficult to observe when using polarizable interface.Most importantly,by the comparison of two kinds of liquid/liquid interfaces,we experimentally proved that much more excess ions are gathered in the space charge layer of non-polarizable interfaces than in that of polarizable interfaces.These results are consistent with the predictions of molecular dynamic simulations and X-ray reflectivity measurements.
We applied the combination of in situ electrochemical liquid-phase microextraction and square-wave voltammetric stripping analysis for the first time as a highly sensitive and selective approach for the detection of dopamine. A mixed gel of graphene sheets and an ionic liquid of 1-octyl-3-methylimidazolium hexaflurophosphate(OMim PF6) was used as a micro liquid-phase to pre-concentrate dopamine by controlled potential electrolysis from an aqueous solution(as a donor phase), followed by square-wave voltammetric stripping detection. Under optimized conditions, a linear calibration curve was obtained in the range of 0.05 to 1.0 ?mol/L in the presence of excess ascorbic acid and uric acid. The detection limit has been found to be 8.0 nmol/L(S/N=3).
We report an ultrasensitive protocol for electrochemical sensing using the hydroxyl-rich C-dots assisted synthesis of gold nanoparticles(C-dots@AuNP) as labels with copper depositon reaction. The C-dots catalyzing copper deposition reaction was implemented for the first time. We constructed a sandwich-type immunosensor on the chitosan modified glassy carbon electrode(GCE) by glutaraldehyde(GA) crosslinking, with C-dots@AuNP as biolabels. Copper was deposited on the catalytic surfaces of second antibody-conjugated C-dots@AuNP nanoparticles through CuSO_4-ascorbic acid reduction, because both C-dots and AuNPs could strongly catalyze the CuSO_4 and ascorbic acid to form Cu particles, which amplified the detection signal. Then the corresponding antigen was quantified based on simultaneous chemical-dissolution/cathodic-preconcentration of copper for insitu analysis using anodic stripping square wave voltammetry(ASSWV) directly on the modified electrode. Under optimized conditions, these electrodes were employed for sandwich-type immunoanaly sis, pushing the lower limits of detection(LODs)down to the fg mL^(-1) level for human immunoglobulin G(IgG) and cardiac troponin I(cTnI), a cardiac biomarker. These novel sensors have good stability and acceptable accuracy and reproducibility, suggesting potential applications in clinical diagnostics.
Silica mesochannels(SMCs) vertically and regularly oriented to the surface of indium tin oxide(ITO) electrodes were prepared and utilized for preconcentration and detection of methylene blue(MB) in aqueous solution. The positively charged MB can be adsorbed to the SMCs by following the pseudo-first-order kinetic model. The negative value of ?G=?34.73 k J/mol derived from the Langmuir adsorption isotherm indicated the thermodynamic feasibility of the adsorption and the spontaneous nature of the process. Moreover, the adsorbed MB can undergo an electrochemical reaction on the ITO electrode at a suitable potential and the resulting electrical current can be utilized to quantify the MB in aqueous solution. A good analytical performance for MB with a linear range from 10 nmol/L to 1.0 ?mol/L and a detection limit at the nmol/L level was obtained. We believe that such a platform consisting of SMCs perpendicularly tethered to the underlying electrode surface simultaneously allows enrichment and electrochemical detection and can be extended for the detection of various charged dyes, as well as many other charged species.
Fingerprints have been used as an indispensable tool for personal identification in forensic investigations since the late 19 th century. At present, fingerprinting technology has moved away from its forensic roots and is incorporating a broader scientific range, e.g., material science, spectroscopy and spectral analysis, and even in vitro diagnosis. After a brief introduction to latent fingerprints, this mini-review presents the pioneering progresses of fingerprinting technologies including(i) material and electrochemical techniques, and(ii) spectral and spectroscopy imaging techniques and immunological techniques capable of both the visualization of a fingerprint and the detection of chemicals present in it. Finally, perspectives on this rapidly developing field are discussed.
