Electrochemical Impedance Spectroscopy Sensor Research Articles

Anomalous Enhancement of Electrochemical Charge Transfer by a Ru Complex Ion Intercalator.

We have found that the DNA intercalator [Ru(bpy)2DPPZ]2+ (bpy = 2,2'-bipyridine; DPPZ = dipyrido[3,2-a:2',3'-c]phenazine) causes an anomalous increase in charge transfer in electrochemical impedance spectroscopy (EIS). With a carbonaceous electrode and a 1 mM hexacyanoferrate (1 mM [Fe(CN)6]3- and 1 mM [Fe(CN)6]4-) mediator, we found that adding only 1 μM [Ru(bpy)2DPPZ]2+ greatly enhanced the charge transfer between the electrode and hexacyanoferrate mediator, independently of other electrolytes or buffer components. The effect started with a one millionth amount of hexacyanoferrate. Since [Ru(bpy)2DPPZ]2+ can intercalate with dsDNA, the effect is highly applicable for dsDNA detection or PCR monitoring. With further developments of this method, EIS sensors not requiring specific electrode modifications should be possible.

Electrochemical Impedance Spectroscopic Detection of E.coli with Machine Learning

Electrochemical impedance spectroscopy (EIS) is a common method in biosensing detection of pathogens for public health and safety. In its most general form, increases of charge transfer resistance or decrease of double layer capacitance at the interface are used for reporting EIS system changes due to pathogens. However, this strategy is not universally adaptable to various EIS sensors and could lead to inaccurate detection. Herein, we demonstrated a machine learning-based EIS biosensor for E.coli detection with improved accuracy. EIS data was obtained from gold electrodes immobilized with E.coli through antibody binding and fitted with the Randles model to extrapolate multiple impedimetric parameters. A machine learning model, using principle component analysis and support vector regression, was trained to automatically establish a quantitative relationship between multiple impedimetric parameters and bacterial concentrations. Results showed an improved accuracy in determining bacterial concentration. The improvement is due to the integration of both capacitance and resistance information. These results thus pave the way for automatic and accurate EIS biosensors in various applications.

An ultrasensitive electrochemical impedance-based biosensor using insect odorant receptors to detect odorants

Herein, we present that insect odorant receptors reconstituted into the lipid bilayers of liposomes can be successfully immobilized onto a gold surface and selectively and sensitively detect odorant molecules. The odorant receptors (OrXs) Or10a, Or22a, and Or71a from the common fruit fly, Drosophila melanogaster, were recombinantly expressed, purified and integrated into nano-liposomes (100–200 nm). These liposomes were covalently attached to the self-assembled monolayers (SAMs) of a 6-mercaptohexanoic acid (MHA)-modified gold surface. X-ray Photo Electron Spectroscopy (XPS) and Quartz Crystal Microbalance with Dissipation (QCM-D) measurements confirmed the successful modification of the gold surface and immobilization of liposomes. Atomic Force Microscopy (AFM) revealed that the liposomes were covalently attached to the surface without any disruption of vesicles. The liposomes tethered to the gold sensor surface were then treated with a range of known ligands of various concentrations. We demonstrated by Electrochemical Impedance Spectroscopy (EIS) that an OrX/liposome EIS sensor can sensitively and selectively detect its known ligand to femtomolar concentrations by detecting a change in electrical signal upon binding. Our study is the first step towards using purified insect odorant receptors alone in biosensors to enable the development of novel ultrasensitive volatile sensors for medical diagnostic, air quality, food safety and border security applications.

Abstract 18004: The Next Generation of Stretchable Sensors for Intravascular Electrochemical Impedance Spectroscopy of Varying Levels of Lipid Burden and Atherosclerosis

Introduction: Atherosclerosis, a chronic inflammatory arterial disease, persists as the leading cause of acute coronary events or stroke in developed countries. Developing a reliable, reproducible, safe and simple strategy to detect lipid-rich, metabolically active, and mechanically unstable plaques remains an unmet bioengineering challenge. It is recognized that oxidized low-density lipoprotein (oxLDL) and macrophages produce changes in the electrochemical properties of vessel walls that can be measured by electrochemical impedance spectroscopy (EIS). Hypothesis: We tested the hypothesis that a new, 2-point intravascular micro-electrode configuration enables flexible frequency-dependent EIS characterization of lipid-rich lesions. Methods: A simplified yet robust sensor design with higher differentiating capability, featuring individually addressable, flexible round electrodes (Æ = 240 μm), was developed and microfabricated for intravascular EIS investigation. We documented in vivo deployment of stretchable EIS sensors for endoluminal interrogation and impedimetric investigation at multiple levels of the aortic tree characterized by differing stages of atherosclerotic disease in a New Zealand White rabbit model, compared EIS values in vivo and ex vivo, confirmed endoluminal atherosclerotic lesions by intravascular ultrasound, histology and immunohistochemistry, and obtained EIS profiles in epicardial fat tissue. Results: The frequency sweep revealed overlapping tissue resistivity from 1-10 kHz, but distinct capacitive property from 10-300 kHz, thereby providing complementary differentiation in both impedance (Ω) and phase (f) between healthy arteries and varying levels of atherosclerotic lesions. The EIS measurements revealed a significant increase in impedance in the presence of oxLDL-rich lesions from 5219 Ω in control to 5949 Ω in mild, 6988 Ω in moderate and 8351 Ω in severe plaque at 300 kHz (P < 0.05, n = 5 controls, n = 3 atherosclerotic). The correlation between in vivo and ex vivo analyses using Spearman was r = 0.97 (P < 0.0001, n = 8 aortic segments). Conclusion: We demonstrate a new, paired-electrode based EIS sensor for intravascular interrogation of lipid-laden lesions to complement diagnostic angiography.

A novel breast cancer screening platform: An epitope-based biomarker coupled to electrochemical sensor.

9 Background: The subtractive proteomic selection technology called Phage Display (PD) has been extensively used by our group in the discovery of high affinity ligands to target tissues and molecules. We have selected specific ligands against IgG purified from BC tissues, which was successfully coupled to an electrochemical sensor to detect the tumor-specific immune response. Methods: After PD selections, all immunoreactive peptide ligands were further characterized by DNA sequencing, in vitro translated and submitted to bioinformatic analyses. Further validations were performed by ELISA. We then used one synthetic peptide (SF4) for the construction of an immunosensor, which was applied to patients and control samples for final validation. Electrochemical impedance spectroscopy (EIS) was performed. Results: We have selected the F4 peptide for final validation and sensor construction due to its capability of detecting IgG in the peripheral blood and the excellent ELISA ratio BC:BBD, discriminating more than 70% of BC patients. The synthetic peptide reached a good precision in BC diagnosis (68%), but surprisingly, the selected F4 clone presented the highest sensitivity and specificity, (77.8% and 85.7%, respectively), suggesting that it can be used as a diagnostic reagent for early BC screening prior to imaging and pathological analyses. The electrochemical sensor that was built with the epitope-based peptide discriminated all IgG from BC and healthy individuals. Results with the EIS sensor demonstrated that the presence of (SF4) peptide IgG generated higher resistivity (-Z ') compared to the system containing only the peptide or the control sera. This is justified by the fact that with the immobilized biological peptide layer was correctly conjugated with the IgG forming an antigen: antibody complex that led to an increased resistance to the charge transfer system, producing a decrease in electron transfer between the iron-coupled / ferricyanide redox and the electrode surface. Conclusions: An electrochemical sensor using an epitope-based biomarker was developed, which allows for the first time BC screening using a very simple platform that could be an important auxiliary tool to mammography imaging.