Measuring Practical Reversibility of Surface-Bound DNA for Mechanistic Insight into Folding-Based Sensors

In this paper, we characterize the mass-transport-limited response of surface-tethered redox moieties via flexible DNA linkers using measured voltammetric peak current and peak potential splitting. We demonstrate that peak splitting can be used to differentiate between reversible, quasi-reversible, and irreversible electrochemical regimes of the tethered redox molecule. Interestingly, the transition from one regime to another is dependent on the length and structure of the DNA probe. For example, as the probe length increases the transition from reversible to quasi-reversible occurs at lower scan rates. Additionally, we directly compare the dependence of the peak splitting and peak current as a function of scan rate for ssDNA, dsDNA, and other structured nucleic acids such as stem-loop and pseudoknot probes. Lastly, we find that by interrogating our surfaces with cyclic voltammetry we can observe quantitative differences in the peak splitting once the aptamer is in a bound state and correlate this to the extent of conformational change the sequence undergoes. The observations reported herein are consistent with the postulation that signaling in this class of sensor architectures is dictated by changes in nucleic acid structure and flexibility, which controls the mass transfer rate of the redox probe to the surface of the electrode.

Fabrication of Nanoarchitectonic AgOx/BiPO4 Electrochemical Sensor for Detection of Resveratrol

In the present study, a novel AgOx/BiPO4 sensor was successfully prepared and used for detecting trans-resveratrol. Prepared samples were characterized using methods including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy. The results demonstrate that the AgOx/BiPO4 is composed of AgO, Ag2O, and BiPO4. In addition, a cyclic voltammetry method was used to measure resveratrol concentration using the electrochemical sensor based on AgOx/BiPO4. AgOx/BiPO4 presents a well-defined voltammetric peak at approximately +460 mV versus Ag/AgCl in phosphate-buffered saline solution. In addition, the sensor exhibits a detection limit of 1.0×10−7 M, and the wide dynamic concentration ranges from 2.0×10−7 to 12.5×10−6 M. Stability and interference tests were performed for 20 days. A possible mechanism for AgOx/BiPO4 detection of trans-resveratrol detection is proposed.

Electropolymerization of N,N'-Diphenylguanidine in Non-Aqueous Aprotic Solvents and Alcohols

Electrooxidation of N,N’-diphenylguanidine (1,3-diphenylguanidine) was investigated in aprotic (acetonitrile, acetone, dimethyl sulfoxide, dimethyl formamide, propyleneoxide, nitromethane) and alcoholic (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, benzyl alcohol) non-aqueous solvents at platinum electrode with cyclic voltammetry. Its concentration was 5 mM in most cases. In acetonitrile and acetone a sharp voltammetric peak appeared around 1 V vs. reference and currents measured in the subsequent scans showed that the electrode fouled quickly. In dimethyl formamide, the anodic peak heights decreased slowly in the subsequent scans but in dimethyl sulfoxide weak deactivation could be observed both in smaller and in higher concentration. In alcohols, continuous deactivation could be also observed during electrooxidation of N,N’-diphenylguanidine. The permeability studies showed that the structure of the formed polymer films varied significantly according to the solvent used for electrodeposition.

On the Contrasting Effect Exerted by a Thin Layer of CdS against the Passivation of Silver Electrodes Coated with Thiols

The passivation of metal electrodes covered by self-assembled monolayers of long-chain thiols is well known. The disappearance of the voltammetric peak of redox species in solution is a classical test for the formation of full layers of thiols. Similar studies on semiconductors are still very limited. We used silver surfaces covered by an ultrathin layer of CdS as substrate for self-assembling of n-hexadecanethiol (C16SH), and we compared the experimental results with those obtained by using the bare silver surface as substrate. The strong insulating effect of C16SH deposited on Ag(III) is shown by the inhibition of the voltammetric peak of Ru(NH3)63+/2+. On the contrary, the voltammogram obtained on CdS-covered Ag(III) is very similar to that obtained on the bare Ag(III) electrode, thus suggesting that the presence of CdS exerts a contrasting effect on the passivation of the silver electrode. A crucial point of our work is to demonstrate the effective formation of C16SH monolayers on Ag(III) covered by CdS. The formation of full layers of C16SH was strongly suggested by the inhibition of the stripping peak of Cd from the CdS deposit covered by C16SH. The presence of C16SH was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements as well as by Auger electron spectroscopy (AES) analysis.

Utility of Activated Glassy Carbon and Pencil Graphite Electrodes for Voltammetric Determination of Nalbuphine Hydrochloride in Pharmaceutical and Biological Fluids

This work compares voltammetric response of nalbuphine hydrochloride (NP·HCl) at both activated glassy carbon and pencil graphite electrodes. The electrochemical oxidation of the drug was studied using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV) techniques. For analytical purpose a well-resolved irreversible diffusion controlled voltammetric peak was established in Britton-Robinson (B-R) buffer solution of pH 6.00 using pencil graphite electrode (PGE). Using activated glassy carbon electrode (GCE) a well-resolved irreversible diffusion controlled voltammetric peak was obtained at pH 7.00 using the same buffer solution. According to the linear relationship between the peak current and NP·HCl concentration, DPV and SWV methods were developed for their quantitative determination in pharmaceutical and human biological fluids. The linear response was obtained in the range from1.6×10-5to1.5×10-4 mol L−1using PGE and from12.5×10-6to13.75×10-5 mol L−1using a GC electrode, respectively. Precision and accuracy of the developed method were checked by recovery studies.