Electrochemical Microdevice Research Articles

Studies of Polythymine Conformational Changes with Electrochemical Microdevices

Introduction Electrochemical biosensors can offer rapid, scalable, and inexpensive biological and chemical detection compared to more traditional measurement techniques. These devices can sense the presence of drugs for therapeutic drug monitoring or detect biomarkers for early disease diagnostics. DNA, which is frequently used as a recognition element for a biomarker, can exist in single-stranded or double-stranded form, or as an aptamer: a series of oligonucleotides selected to bind to a specific biomolecular species or chemical. Aptamers can be selected for different targets, allowing aptamer-functionalized sensors to detect biomarkers such as varied nucleic acids or proteins1. However, to ensure reliability for aptamer-functionalized sensors, more needs to be understood about the general nature of DNA’s behavior under a variety of chemical and physical conditions. This study employs a microscale electrochemical platform (Fig. 1a) to explore the conformational behavior of immobilized polythymine (polyT) strands of differing lengths and their responses to various physical and chemical stressors (Fig. 1b), as the influence of these factors can have an effect on target binding. Methods The commercially-purchased polyT strands consisting of 10, 20 and 50 thymines (10-mer, 20-mer and 50-mer, respectively), with a thiol on one end and tagged with a methylene blue (MB) moiety at the other (distal) end, were incubated in a TCEP solution to reduce the thiol, and then pipetted onto the electrochemical microdevice to immobilize the DNA on the Au working electrode. Next, a self-assembled monolayer solution of 6-mercaptohexanol was pipetted onto the working electrode and left to incubate for one hour in the dark (as a means of preventing nonspecific binding). After completion of this step, the devices were ready for electrochemical sensing. DNA-functionalized surfaces of the 20-mer were also characterized with x-ray photoemission spectroscopy (XPS) to determine packing density.The reported studies involved custom temperature-controlled electrochemical microdevices with built-in platinum resistive thermometers (PRT) which are used in conjunction with a commercial Peltier unit2. All sensing was done in phosphate buffer saline (PBS) working buffer, which includes varying concentrations of NaCl at a biologically-relevant pH of 7.4. During electrochemical sensing, a PDMS well was placed atop the electrodes, and ~10 µL of the working buffer solution was pipetted into the well and covered to prevent evaporation. The PRT was monitored to provide the approximate temperature of the electrochemical interface (10 ⁰C to 50 ⁰C), which was cooled and heated under voltage control of the Peltier module. Results Conformational changes occurring for the immobilized polyT strands under the influence of varied chemical and thermal environments were signaled by current changes measured using square-wave voltammetry (SWV). Generally, the currents are inversely proportional to the distance between the MB and working electrode. Figure 2 shows thermal profiles (current vs temperature) reflective of varying polyT conformations that were measured for 20-mer polyT at seven different working buffer salt concentrations. Similar plots were acquired for the shorter 10-mer polyT as well as the longer 50-mer polyT, and all of those data were utilized to produce the results in Figure 3, representing how the temperature of maximum current in the range of 10 ⁰C to 50 ⁰C depends on strand length and salt concentration. Conclusion Observations made in these electrochemical studies of the polythymine strands indicated that the conformational behavior of the model system was actually rather complex, with dependencies on the polyT length as well as on the thermal and chemical stressors. The conformational responses can be explained primarily by salt-induced conversion of rigidity to flexibility and thermally driven motion. However, other factors such as strand stretching and overcharging effects also appear to be necessary to understand the acquired profiles. These findings suggest that care must be taken for certain cases of DNA- and aptamer-based electrochemical biosensing, as the functioning of receptors can be quite sensitive to even small changes in the operating conditions.

Unveiling the role of surface P–O group in P-doped Co3O4 for electrocatalytic oxygen evolution by On-chip micro-device

Transition metal phosphides or partially phosphatized oxides usually suffer from surface reconstruction during oxygen evolution reaction (OER), but still possess enhanced catalytic activity than directly synthesized oxides, which has aroused great interest in exploring the causes of such high catalytic activity. To monitor electronic property of catalyst during the OER can provide crucial insights into catalytic ability. Here we design a planar electrochemical microdevice based on individual thin-film catalyst, and for the first time explore the continuous electric conductance evolution of lattice P-doped oxides during the electrochemical activation process. Moreover, combining on-chip electrochemical impedance spectra measurements, in situ I-V measurements, and theoretical simulations of reconstructed lattice P-doped oxides, the effect of P–O groups on new-formed oxides is clarified. The induced electronic coupling between new-formed oxides and P-O groups has been studied and demonstrated. The coupled P–O groups effectively promote the metal–oxygen covalency of new-formed oxides, which accelerates electron transfer between active metallic center and oxygen adsorbates, thus leading to the enhanced electrocatalytic activity. Our study highlights the role of surface P–O groups in Co 3 O 4 during the OER, and such unique on-chip electrochemical microdevice platform can also be applied in other related fields to understand the dynamic behavior of energy materials at nanoscale. By fabricating an individual thin-film-based planar OER microdevice, we unveiled the electronic coupling effect between P-O groups and Co 3 O 4 species in the reconstructed lattice P-doped Co 3 O 4 (P′ 1 -Co 3 O 4 ) at nanoscale. The coupled P-O groups effectively promote the Co–O covalency of Co 3 O 4 species, which accelerates electron transfer between active metallic center and oxygen adsorbates, thus leading to the enhanced electrocatalytic activity. ● The electronic/electrochemical signals of P-Co 3 O 4 thin-film are collected in time using the OER microdevice. ● The electronic coupling effect between the P–O groups and Co 3 O 4 species is clarified at nanoscale. ● In situ I-V measurement and theoretical simulation reveal the promoting effect of P–O groups on reaction kinetics.

Effects of Physical and Chemical Stressors on DNA Conformation Investigated By Temperature-Controlled Electrochemical Microdevices.

Effects of Physical and Chemical Stressors on DNA Conformation Investigated By Temperature-Controlled Electrochemical Microdevices.

Integrated Solid-State Nanopore Electrochemistry Array for Sensitive, Specific, and Label-Free Biodetection.

Nanopore ionic current measurement is currently a prevailing readout and offers considerable opportunities for bioassays. Extending conventional electrochemistry to nanoscale space, albeit noteworthy, remains challenging. Here, we report a versatile electrochemistry array established on a nanofluidic platform by controllably depositing gold layers on the two outer sides of anodic aluminum oxide (AAO) nanopores, leading to form an electrochemical microdevice capable of performing amperometry in a label-free manner. Electroactive species ferricyanide ions passing through gold-decorated nanopores act as electrochemical indicator to generate electrolytic current signal. The electroactive species flux that dominates current signal response is closely related to the nanopore permeability. Such well-characteristic electrolytic current-species flux correlation lays a premise for quantitative electrochemical analysis. As a proof-of-concept demonstration, we preliminarily verify the analytical utility by detection of nucleic acid and protein at picomolar concentration levels. Universal surface modification and molecule assembly, specific target recognition and reliable signal output in nanopore enable direct electrochemical detection of biomolecules without the need of cumbersome probe labeling and signal amplification.

Microdevice with integrated multi-enzyme sensors for the measurement of pork freshness

An electrochemical microdevice for measuring pork freshness was developed based on the value of measurement indicators—K, Ki, and H. Four sensors were integrated to measure the sum of the concentrations appearing in the equations that define the K, Ki, and H values. With standard solutions, the correlation coefficients for sensors 1–4 were 0.888, 0.979, 0.816, and 0.828, respectively. Each sensor could complete one measurement in 2min. A good correlation was obtained between the K values measured by the proposed microdevice and by ultra-performance liquid chromatography. Based on the sensor responses obtained with real pork extract samples, the R2 value between the K and Ki values was 0.843, while that between the K and H values was only 0.807 during a 15-day storage period.

Electrochemical microdevice for on-site determination of ricefreshness

An electrochemical microdevice was fabricated for on-site rapid freshness determination of rice. The activity of peroxidase was used as an indicator for freshness. With hydrogen peroxide and hydroquinone as substrates, the enzymatic reaction of peroxidase produced benzoquinone, which was subsequently reduced on a gold working electrode electrochemically. The progress of the enzymatic reaction could clearly be observed in the change of cyclic voltammograms. Distinct differences were observed in the current change between fresh rice and aged rice, reflecting the remaining activity of peroxide. The current also depended on the time at which rice grains were milled. The result agreed well with those obtained by the conventional fluorometric and guaiacol methods. Comparison of results obtained with different numbers of grains showed that even the measurement with a single grain provided fairly consistent data. Furthermore, the existence of grains of different freshness could be identified using a device with multiple sensingsites.

Monitoring oxygen consumption of single mouse embryos using an integrated electrochemical microdevice

Oxygen consumption (respiration activity) has been found to be the most remarkable criterion for determining the viability of an embryo produced in vitro. In this study, we propose an accurate, simple, and user-friendly device for measurement of the oxygen consumption of single mammalian embryos. An integrated electrode array was fabricated to determine the oxygen consumption of a single embryo, including the blastocyst stage, which has an inhomogeneous oxygen consumption rate, using a single measurement procedure. A single mouse embryo was positioned in a microwell at the center of an integrated electrode array, using a mouthpiece pipette, and immobilized by a cylindrical micropit with good reproducibility. The oxygen consumption of two-cell, morula, and blastocyst stages was measured amperometrically using the device. The recorded current profile was corrected to take into consideration transient background current during the measurement. A calculation method for oxygen consumption based on spherical diffusion centered on the defined point of the device was developed. This procedure is quite simple because it is not necessary to estimate the radius of the embryo being measured. The calculated values of oxygen consumption for two-cell, morula, and blastocyst stages were 1.36 ± 0.33 × 10 −15 mol s −1, 1.38 ± 0.58 × 10 −15 mol s −1, and 3.44 ± 2.07 × 10 −15 mol s −1, respectively. The increasing pattern of oxygen consumption from morula to blastocyst agreed well with measurements obtained using conventional scanning electrochemical microscopy (SECM).

Monitoring respiration activity of mouse embryo on an integrated electrochemical microdevice

Monitoring respiration activity of mouse embryo on an integrated electrochemical microdevice

Electrochemical Monitoring of Cellular Signal Transduction with a Secreted Alkaline Phosphatase Reporter System

Electrochemical monitoring of cellular signal transduction under three-dimensional (3-D) cell culture conditions has been demonstrated by combining cell-based microarrays with a secreted alkaline phosphatase (SEAP) reporter system. The cells were genetically engineered to produce SEAP under the control of nuclear factor kappaB (NFkappaB) enhancer elements, and they were embedded with a small volume of a collagen gel matrix on a pyramidal-shaped silicon microstructure. Cellular SEAP expression triggered by NFkappaB activation was assessed by two types of electrochemical systems. First, SEAP expression of a 3-D cell array on a chip was continuously monitored in situ for 2 days by scanning electrochemical microscopy (SECM). Since the SECM-based assay enables the evaluation of cellular respiratory activity, simultaneous measurements of cellular viability and signal transduction were possible. Further, we have developed an electrode-integrated cell culture device for parallel evaluation of cellular SEAP expression. The detector electrode was integrated around the silicon microhole. Two kinds of cells were immobilized on the array of microholes on the same chip for comparative characterization of their SEAP activity. This electrochemical microdevice can be applied to evaluate the SEAP expression activity in multiple cellular microarrays by a high-throughput method.

Fabrication of a new generator–collector electrochemical micro-device: Characterization and applications

The fabrication of a new electrochemical cell where a thin layer of solution (6 nL) is confined between two closely-spaced parallel gold electrodes is described. By polarizing both electrodes at suitable potentials, the forced redox cycling ensures that steady-state conditions are attained almost instantaneously. Voltammetry with ferricyanide solutions demonstrated that the twin-electrode thin-layer cell (TETLC) may operate as a generator–collector device with collection efficiency values of 100%. Experimental results for voltammetry and chronoamperometry experiments agreed with predictions based on digital simulation. The increased sensitivity based on the forced redox cycling envisages future applications of the device, as the use of the TETLC as a pre-reactor at quiescent solutions for the determination of paracetamol in solutions containing ascorbic acid.

Electrochemical microdevice with separable electrode and antibody chips for simultaneous detection of pepsinogens 1 and 2

An electrochemical microdevice with separable electrode and antibody chips has been developed and applied to detect atrophic gastritis-related proteins, pepsinogen 1 (PG1) and pepsinogen 2 (PG2), based on sandwich-type enzyme-linked immunosorbent assays (ELISAs) with horseradish peroxidase (HRP)-labeled antibody. To fabricate the electrochemical device for simultaneous analysis of several proteins, the electrode chip with eight electrode elements was assembled along with an antibody chip with eight cavities containing immobilized anti-PG1 or anti-PG2. The immunoreactions occurring in the cavities of the device were detected simultaneously by amperometry. The labeled HRP in the cavity in the presence of hydrogen peroxide catalyzed the oxidation of ferrocenemethanol (FMA) to FMA+, which was detected electrochemically by the electrode chip. The amperometric responses of respective cavities in the device increased with increasing concentration of PG1 or PG2 of 0-50 ng/ml, ensuring the simultaneous detection of PG1 and PG2. The detection limits for both PG1 and PG2 were 0.6 ng/ml (S/N=2). The electrode chip was recovered easily by disassembling the electrochemical device; thereby, it was used repeatedly, whereas the antibody chip was discarded. No marked decrease in electrochemical responses was detected after repeated use. Reuse of the electrode chip is beneficial to reduce costs of protein analysis.