Electrochemical Signal Detection Research Articles

Dually-amplified electrochemical aptasensor based on the self-linking AuPt nanoflowers for ultrasensitive determination of hemagglutinin

BackgroundInfluenza virus can spread from person to person and cause epidemics. Therefore, rapid and sensitive diagnosis of virus is essential in controlling influenza outbreaks. Conventional virus diagnostic techniques are time-consuming, labor-intensive and requires large instruments. In this work, a sandwich electrochemical assay by a pair of aptamers was developed for ultrasensitive determination of hemagglutinin (HA) protein, which is one of the two surface glycoproteins of influenza A (H1N1) virus, using dual signal amplification techniques. ResultsHA was captured and magnetically separated by Fe3O4@SiO2–NH2@Au attached to aptamer 1 (Apt1), creating a sandwich structure with AuPt nanoflowers (AuPtNFs) connected to aptamer 2 (Apt2). Herein, AuPtNFs could catalyze H2O2/hydroquinone (HQ) to generate 1,4-benzoquinone (BQ), and achieved amplification of electrochemical signal detection through differential pulse voltammetry (DPV). The constructed aptasensor expressed a wide linear range (10 pg/mL-100 ng/mL) with limit of detection (LOD) of 2.4 pg/mL. Moreover, a novel strategy for dual signal amplification was developed to further enhance sensitivity. The innovative electrochemical aptasensor could achieve secondary amplification of the detection signal with LOD of 0.3 pg/mL and linear concentration range from 0.5 pg/mL to 100 ng/mL. The secondary amplification could be achieved only through the self-linking process, which allowed for the retention of numerous AuPtNFs by simple complementary base pairing to connect more AuPtNFs onto the above-mentioned sandwich structure. SignificanceOverall, the constructed aptasensor exhibited favorable sensitivity and accuracy, indicating the potential expanded application for the clinical detection of numerous viruses.

Drug Evaluation of Parkinson's Disease Patient-Derived Midbrain Organoids Using Mesoporous Au Nanodot-Patterned 3D Concave Electrode.

Brain organoids are being recognized as valuable tools for drug evaluation in neurodegenerative diseases due to their similarity to the human brain's structure and function. However, a critical challenge is the lack of selective and sensitive electrochemical sensing platforms to detect the response of brain organoids, particularly changes in the neurotransmitter concentration upon drug treatment. This study introduces a 3D concave electrode patterned with a mesoporous Au nanodot for the detection of electrochemical signals of dopamine in response to drugs in brain organoids for the first time. The mesoporous Au nanodot-patterned film was fabricated using laser interference lithography and electrochemical deposition. Then, the film was attached to a polymer-based 3D concave mold to obtain a 3D concave electrode. Midbrain organoids generated from Parkinson's disease (PD) patient-derived iPSCs with gene mutations (named as PD midbrain organoid) or normal midbrain organoids were positioned on the developed 3D concave electrode. The 3D concave electrode showed a 1.4 times higher electrochemical signal of dopamine compared to the bare gold electrode. And the dopamine secreted from normal midbrain organoids or PD midbrain organoids on the 3D concave electrode could be detected electrochemically. After the treatment of PD midbrain organoids with levodopa, the drug for PD, the increase in dopamine level was detected due to the activation of dopaminergic neurons by the drug. The results suggest the potential of the proposed 3D concave electrode combined with brain organoids as a useful tool for assessing drug efficacy. This sensing system can be applied to a variety of organoids for a comprehensive drug evaluation.

A biocatalytic cascade in enzyme/metal continuous-microflow microgel with stable intermediate channel for point-of-care biosensing

A fast and accurate method for ultrasensitive monitoring of substrate is significant for cascade molecular detection. Here, we synthesize a glucose oxidase (GOx) microgel with iron coordination (Fe/GOx microgel). The microgel is cross-linked by chitosan and iron ion coordination which construct a tubular structure. Powder X-ray diffraction and Brunauer-Emmett-Teller results confirm the tubular crystal structure with a high specific surface area is formed in the microgel. The tubular structure offers a stable channel for intermediate transport which ensures the stabilization for the intermediate transport, and high specific surface area enhances the interaction between substrates and catalysts. As a result, the sensitivity of the Fe/GOx microgel is 175.5 μA mM−1 cm−2 and the lowest detection limit is 4.42 μM. In addition, the nanoscale Fe/GOx microgel also has the characteristics of reusability and maintains its activity after five times of catalysis. The generation of free radicals during the catalytic process can be detected by light detection and electrochemical signal detection within different detection limits. Therefore, Fe/GOx microgel provides a new platform and catalyst for the precise detection of cascade catalysis.

Hybrid Supported Lipid Bilayers for Bioinspired Bioelectronics with Enhanced Stability

A promising new class of biosensors leverages the sensing mechanisms of living cells by incorporating native transmembrane proteins into biomimetic membranes. Conducting polymers (CPs) can further improve the detection of electrochemical signals from these biological recognition elements through their low electrical impedance. Supported lipid bilayers (SLBs) on CPs mimic the structure and biology of the cell membrane to enable such sensing, but their extrapolation to new target analytes and healthcare applications has been difficult due to their poor stability and limited membrane properties. Blending native phospholipids with synthetic block copolymers to create a hybrid SLB (HSLB) may address these challenges by allowing for the tuning of chemical and physical properties during membrane design. We establish the first example of HSLBs on a CP device and show that polymer incorporation enhances bilayer resilience and thus offers important benefits toward bio-hybrid bioelectronics for sensing applications. Importantly, HSLBs outperform traditional phospholipid bilayers in stability by exhibiting strong electrical sealing after exposure to physiologically relevant enzymes that cause phospholipid hydrolysis and membrane degradation. We investigate the impact of HSLB composition on membranes and device performance and demonstrate the ability to finely adjust the lateral diffusivity of HSLBs with modest changes in block copolymer content through a large compositional range. The inclusion of the block copolymer into the bilayer does not disrupt electrical sealing on CP electrodes, an essential metric for electrochemical sensors, or the insertion of a representative transmembrane protein. This work interfacing tunable and stable HSLBs with CPs paves the way for future bioinspired sensors that combine the exciting developments from both bioelectronics and synthetic biology.

Direct Electrochemical Signaling in Organic Electrochemical Transistors Comprising High-Conductivity Double-Network Hydrogels.

In composite hydrogels, the high electrical performance of poly(3,4-ethylenedioxythiophene) complexed with poly(styrenesulfonate) (PEDOT:PSS) is integrated with complementary structural and electrochemical functions via a rationally designed poly(acrylamide) second network incorporating phenylboronic acid (PBA). Free-standing double-network hydrogels prepared by a simple one-pot radical polymerization exhibit state-of-the-art electrical conductivity (∼20 S cm-1 in phosphate buffered saline) while retaining a degree of hydration similar to that of biological soft tissues. Low resistance contacts to Au electrodes are formed via facile thermo-mechanical annealing and demonstrate stability over a month of continuous immersion, thus enabling hydrogels to serve as channels of organic electrochemical transistors (OECTs). Despite thicknesses of ∼100 μm, gating of hydrogel OECTs is efficient with transconductances gm ∼ 40 mS and on/off ratios of 103 in saturation mode operation, whereas sufficiently high conductivity enables linear mode operation (gm ∼ 1 mS at -10 mV drain bias). This drives a shift of sensing strategy toward detection of electrochemical signals originating within the bulky channel. A kinetic basis for glucose detection via diol esterification on PBA is identified as the coupling of PBA equilibrium to electrocatalyzed O2 reduction occurring on PEDOT in cathodic potentials. Hydrogel OECTs inherently amplify this direct electrochemical signal, demonstrating the viability of a new class of soft, structural biosensors.

BRAIN COMPUTER INTERFACE APPLICATION IN STROKE DISEASE DIAGNOSIS

Every discovery is geared towards problem solving. This is manifested by the advent of brain computer interface (BCI). Brain computer interface (BCI) is a field of study concern with the detection and utilization of brain signals in establishing the communication path between the brain and the computer system. The knowledge of this science has helped in no small measure in providing solutions to several challenges befalling man and his environment. In this paper, we explored those areas where BCI has proved useful and pointed out as well its possible application in diagnosis of stroke disease. The discourse was centered on detection of electrochemical signals from the brain called electroencephalogram (EEG). The research work also highlighted the technique of recording brain activity via electroencephalogram and using it in making deduction on the status of stroke attack on individual. This can either be normal or abnormal. The presence of delta or theta wave in an awaked adult suggests an abnormal situation. While the observance of alpha, beta and gamma waves are interpreted as normal.

Highly selective and sensitive electrochemical biosensor for ATP based on the dual strategy integrating the cofactor-dependent enzymatic ligation reaction with self-cleaving DNAzyme-amplified electrochemical detection

A dual strategy that combines the adenosine triphosphate (ATP)-dependent enzymatic ligation reaction with self-cleaving DNAzyme-amplified electrochemical detection is employed to construct the biosensor. In this design, the methylene blue-labeled hairpin-structured DNA was self-assembled onto a gold electrode surface to prepare the modified electrode through the interaction of Au–S bond. In the procedure of ATP-dependent ligation reaction, when the specific cofactor ATP was added, the two split oligonucleotide fragments of 8-17 DNAzyme were linked by T4 DNA ligase and then released to hybridize with the labeled hairpin-structured DNA substrate. The linked 8-17 DNAzyme catalyzes the cleavage of the hairpin-structured substrate by the addition of Zn2+, causing the methylene blue which contains high electrochemical activity to leave the surface of the gold electrode, therefore generating a dramatic decrease of electrochemical signal. The decrease of peak current was readily measured by square wave voltammetry and a relatively low detection limit (0.05nM) was obtained with a linear response range from 0.1 to 1000nM. By taking advantage of the highly specific cofactor dependence of the DNA ligation reaction, the proposed ligation-induced DNAzyme cascades demonstrate ultrahigh selectivity toward the target cofactor ATP. A catalytic and molecular beacons strategy is further adopted to amplify the electrochemical signal detection achieved by cycling and regenerating the 8-17 DNAzyme to realize enzymatic multiple turnover, thus one DNAzyme can catalyze the cleavage of several hairpin-structured substrates, which improves the sensitivity of the newly designed electrochemical sensing system.

High Rate Detection of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining an Electrode-Coated Membrane with Hydrodynamic Flow in a Wall-Tube Configuration

We present an experimental system that combines differential electrochemical mass spectrometry with hydrodynamic flow consisting of an impinging jet in a wall-tube configuration. This assembly allows simultaneous detection of electrochemical signals along with monitoring of dissolved gas species using differential electrochemical mass spectrometry under well-defined hydrodynamic conditions and over a wide range of mass transfer rates. The working electrode is deposited directly onto a thin, hydrophobic membrane, which also serves as the inlet to the mass spectrometer. This inlet provides extremely rapid mass detection as well as a high flux of products from the electrode surface into the mass spectrometer. The impinging jet is designed in a wall-tube configuration, in which the jet diameter is large compared to the electrode diameter, thus providing uniform and rapid mass transfer conditions over the entirety of the electrode surface. This combination of rapid detection and controllable flow conditions allows a wide range of hydrodynamic conditions to be accessed with simultaneous electrochemical and mass spectrometric detection of dissolved gas species, which is important in the analysis of a range of electrochemical reactions. The capabilities of this configuration are illustrated using a platinum-coated electrode and several electrochemical reactions, including ferrocyanide oxidation, proton reduction, and oxalic acid oxidation.

Electrochemical measurements of biofilm development using polypyrrole enhanced flexible sensors

Bacterial biofilms can be beneficial or detrimental, and are capable of forming on virtually any surface. There is a great need for an in situ sensor able to detect and characterize the developmental stages of bacterial biofilms. We have developed an electrochemical approach to detect and characterize bacterial biofilms using polypyrrole (PPy) enhanced flexible biofilm sensors based on organic substrates of Polyethylene terephthalate (PET). PPy films act as a functionalization material on gold electrodes to reduce their electrical impedance thereby enhancing the detection of electrochemical signals. Flexible PET substrates enable sensors to be placed in systems with complex geometries and to be produced using low cost roll-to-roll manufacturing. Measurements of electrochemical impedance spectroscopy (EIS) using the PET flexible biofilm sensors were correlated with fluorescence microscopy using bacteria that express green fluorescent protein (GFP). The biofilm sensors successfully detected the changes of charge transfer resistance and capacitance corresponding to the maturing stages of biofilm development. The charge transfer resistance increases during the early stages of biofilm maturation and decreases in the later stages of development.

High resolution microarray assay for rapid taxonomic assessment of Pseudo-nitzschia spp. (Bacillariophyceae) in the field

Deployable methods facilitating rapid microbial identification provide opportunities to respond quickly when pathogenic or toxin-producing organisms threaten water quality. We developed a microarray assay to streamline identification of microorganisms in the field, focusing on the harmful algal bloom diatom Pseudo-nitzschia. The assay employed electrochemical signal detection and a simplified protocol, allowing identification of specific taxa onboard research vessels within 7h of water collection. Microarrays targeted the internal transcribed spacer (ITS1) region between the 18S and 28S ribosomal RNA genes using 307 oligonucleotide probes. The probes, ranging from broadly specific to unique, represented 118 Pseudo-nitzschia ribotypes from 15 species available at the time of assay development. Hybridization signals from multiple probes for each target strain were integrated using a novel algorithm for data analysis. Designated the ‘integrated sumscore data analysis’ (ISDA), the algorithm used probe specificity metrics for signal integration, with uniqueness corresponding to higher probe weight values. The integrated signals provided a ‘sumscore’ for each ribotype represented on the array, indicating its presence or absence in the sample. The algorithm was ‘trained’ by comparison with data from scanning electron microscopy, and cloning and sequence analysis of Pseudo-nitzschia ITS1 ribotypes from 7 laboratory cultures and a complex environmental sample. The ISDA provided correct identification and target sequences for all tested strains. Through design of custom probes (up to 12,000 on a microarray chip), this approach may be used to identify additional microbial taxa of interest and provides rapid, reliable shipboard assays for basic research or water quality monitoring.

Development and Application of 16-Channel Two-Mode Recording System for Neurochemical and Neuroelectrical Signals

Abstract A 16-channel two-mode recording system used for detection of neurochemical and neuroeletrical signals was developed. The instrument system consists of hardware and software components whose current and voltage resolutions are 10 pA and 0.6 μV, respectively. The software adopted multithreading, multicache, and other techniques to achieve real-time detection, spike separation, IIR filter, chronoamperometry, cyclic voltammetry, etc. The performance of the system was demonstrated in electrophysiological experiment and dopamine concentration measurement. The signal-to-noise ratio ( S/N ) recorded from VTA of SD rat was 9.7. The current response increased linearly with the concentration of dopamine in the range of 0.1–378 μM with a correlation coefficient of 0.9958. The results indicated that the recording system had high resolution and was suitable for electrophysiological and the electrochemical signal detection.

Effects of nanopatterned RGD peptide layer on electrochemical detection of neural cell chip

The cell-based chip is becoming a popular tool for monitoring living cell viability under various conditions. In this study, several biomaterials, such as synthetic Cys-(Arg-Gly-Asp) 4 (C(RGD) 4), Arg-Gly-Asp-Multi Armed-Cys (RGD-MAP-C) peptide, and poly- l-lysine (PLL) nano-dots were fabricated on the gold surface of a neural cell chip. The material-dependent effects both on electrochemical signal detection in neural cells and on cellular adhesion were analyzed. The nano-dot structures were fabricated through a nanoporous alumina mask, and the structural formations were confirmed by scanning electron microscopy (SEM). PC12 cells were allowed to attach on several peptide nanopatterned surfaces, and electrochemical tools were applied to neural cells attached on the chip surface. The RGD-MAP-C peptide nanopatterned surface provided the strongest voltammetric signals when the cell was exposed to cyclic voltammetry (CV) and differential pulse voltammetry (DPV) after 48 h of incubation, which may largely be due to an enhanced affinity between cells and the Au surface. Chemical toxicity assessments were conducted in the fabricated cell chip, and they showed negative correlations between neural cell viability and the concentration of chemicals. In conclusion, a nanopatterned RGD-MAP-C layer improved cell-binding affinity to Au substrates and showed sufficient sensitivity for electrochemical detection of cell viability.

Evaluation of chrono-amperometric signal detection for the analysis of genotoxicity by a whole cell biosensor

Electrochemical signal detection can be readily integrated in biosensors and is thus an attractive alternative to optical detection methods. In the field of environmental chemistry and ecotoxicology there is a growing demand for lab-independent devices based on whole cell biosensors for the detection of genotoxic compounds. Because of the broad occurrence of pre-genotoxic compounds that need to be bio-activated, the integration of a system for metabolic activation into such a biosensor is important. The present study evaluates a chrono-amperometric detection method in which para-aminophenyl β- d-galactopyranoside is used as substrate for a reporter gene assay based on the bacterial SOS-response in comparison to a test system for the determination of genotoxicity in water that is standardized according to the International Organization for Standardization (ISO). The evaluation was done in order to analyze the potential of the electrochemical signal detection to be used as a complementary method for the standard test system and thus to evaluate the usability of electrochemical biosensors for the assessment of genotoxicity of environmental samples. In the present study it is shown that the chrono-amperometric detection of para-aminophenol is specific even in the presence of electro-active species generated by the enzymatic system used for the external bio-activation of contaminants. Under optimized conditions electrochemistry is sufficiently sensitive with a limit of detection that is comparable to the respective ISO-standard.

GRAVI: Robotized Microfluidics for Fast and Automated Immunoassays in Low Volume

GRAVI, presented here in its automated version, is a new bench-top sized immunoassay platform combining the advantages of microfluidics with those of simplified robotics. Characterized by dramatically reduced time to result (< 10 min) and significantly decreased sample/reagent consumption, the cost-efficient biosensor instrumentation allows performing multimenu analysis with minimal laboratory infrastructure. Coupled to a robotic liquid handler, the system dispenses samples and reagents from conventional plates or tubes into microchannels of a microchip (GRAVI- Chip), in which assays are processed and results readout. As in conventional 96-well microtiter plates, the microchannels have a standard spacing of 9 mm to facilitate automation. With solely gravity and capillary force-driven fluidics within the microchannels, liquids are free to flow while magnetic beads, functionalized with the antibody of choice, are trapped nearby incorporated electrodes by virtue of a magnet array. Following assay performance and electrochemical signal detection in the parallel microchannels, chips are regenerated by magnet release and rinsing of beads out from the microchannels. Applicability of the presented immunoassay platform, delivering 100 results per hour, is exemplified here with results from the validation of an immunoglobulin assay for antibody quantification in mammalian cell cultures. Adapted to run on the GRAVI platform, this competitive assay covers a dynamic range of two orders of magnitude.

Spatial and temporal patterns of serotonin release in the rat’s lumbar spinal cord following electrical stimulation of the nucleus raphe magnus

The monoamine neurotransmitter serotonin is released from spinal terminals of nucleus raphe magnus (NRM) neurons and important in sensory and motor control, but its pattern of release has remained unclear. Serotonin was measured by the high-resolution method of fast cyclic voltammetry (2 Hz) with carbon-fiber microelectrodes in lumbar segments (L3–L6) of halothane-anesthetized rats during electrical stimulation of the NRM. Because sites of serotonin release are often histologically remote from membrane transporters and receptors, rapid emergence into aggregate extracellular space was expected. Increased monoamine oxidation currents were found in 94% of trials of 50-Hz, 20-s NRM stimulation across all laminae. The estimated peak serotonin concentration averaged 37.8 nM (maximum 287 nM), and was greater in dorsal and ventral laminae (I–III and VIII–IX) than in intermediate laminae (IV–VI). When measured near NRM-evoked changes, basal monoamine levels (relative to dorsal white matter) were highest in intermediate laminae, while changes in norepinephrine level produced by locus ceruleus (LC) stimulation were lowest in laminae II/III and VII. The NRM-evoked monoamine peak was linearly proportional to stimulus frequency (10–100 Hz). The peak often occurred before the stimulus ended (mean 15.6 s at 50 Hz, range 4–35 s) regardless of frequency, suggesting that release per impulse was constant during the rise but fell later. The latency from stimulus onset to electrochemical signal detection (mean 4.2 s, range 1–23 s) was inversely correlated with peak amplitude and directly correlated with time-to-peak. Quantitative modeling suggested that shorter latencies mostly reflected the time below detection threshold (5–10 nM), so that extrasynaptic serotonin was significantly elevated well within 1 s. Longer latencies (>5 s), which were confined to intermediate laminae, appeared mainly to be due to diffusion from distant sources. In conclusion, except possibly in intermediate laminae, serotonergic volume transmission is a significant mode of spinal control by the NRM.