Electrochemical Nanoneedle Biosensor Based on Multiwall Carbon Nanotube

Large-Scale Synthesis of Functionalized Nanowires to Construct Nanoelectrodes for Intracellular Sensing

A strategy for one-pot and large-scale synthesis of functionalized core-shell nanowires (NWs) to high-efficiently construct single nanowire electrodes is proposed. Based on the polymerization reaction between 3,4-ethylenedioxythiophene (EDOT) and noble metal cations, manifold noble metal nanoparticles-polyEDOT (PEDOT) nanocomposites can be uniformly modified on the surface of any nonconductive NWs. This provides a facile and versatile approach to produce massive number of core-shell NWs with excellent conductivity, adjustable size, and well-designed properties. Nanoelectrodes manufactured with such core-shell NWs exhibit excellent electrochemical performance and mechanical stability as well as favorable antifouling properties, which are demonstrated by in situ intracellular monitoring of biological molecules (nitric oxide) and unraveling its relevant unclear signaling pathway inside single living cells.

Immobilized nanoneedle-like structures for intracellular delivery, biosensing and cellular surgery

The rapid advancements of nanotechnology over the recent years have reformed the methods used for treating human diseases. Nanostructures including nanoneedles, nanorods, nanowires, nanofibers and nanotubes have exhibited their potential roles in drug delivery, biosensing, cancer therapy, regenerative medicine and intracellular surgery. These high aspect ratio structures enhance targeted drug delivery with spatiotemporal control while also demonstrating their role as an efficient intracellular biosensor with minimal invasiveness. This review discusses the history and emergence of these nanostructures and their fabrication methods. This review also provides an overview of the different applications of nanoneedle systems, further highlighting the importance of greater investigation into these nanostructures for future medicine.

Frontiers in Electrochemical Sensors for Neurotransmitter Detection: Towards Measuring Neurotransmitters as Chemical Diagnostics for Brain Disorders

It is extremely challenging to chemically diagnose disorders of the brain. There is hence great interest in designing and optimizing tools for direct detection of chemical biomarkers implicated in neurological disorders to improve diagnosis and treatment. Tools that are capable of monitoring brain chemicals, neurotransmitters in particular, need to be biocompatible, perform with high spatiotemporal resolution, and ensure high selectivity and sensitivity. Recent advances in electrochemical methods are addressing these criteria; the resulting devices demonstrate great promise for in vivo neurotransmitter detection. None of these devices are currently used for diagnostic purposes, however these cutting-edge technologies are promising more sensitive, selective, faster, and less invasive measurements. Via this review we highlight significant technical advances and in vivo studies, performed in the last 5 years, that we believe will facilitate the development of diagnostic tools for brain disorders.

Highly selective enzymatic-free electrochemical sensor for dopamine detection based on the self-assemblied film of a sandwich mixed (phthalocyaninato) (porphyrinato) europium derivative

An efficient enzymatic-free electrochemical sensor is firstly developed based on the self-assemblied film of a sandwich mixed (phthalocyaninato) (porphyrinato) europium(III) double-decker complex, Eu(Pc)[T(OH)PP], [Pc = phthalocyaninate, T(OH)PP = 5,10,15,tris (4-tert-butylphenyl)-20-(4-hydroxyphenyl)porphyrinate] prepared by using a solution-processing QLS method. The Eu(Pc)[T(OH)PP]semiconducting active layer on an ITO working electrode leads to a good sensing property for the detection of dopamine with an excellent selectivity, due to the high Eu(Pc)[T(OH)PP] molecular ordering/packing in the QLS film and more favorable interaction between the Eu(Pc)[T(OH)PP] and DA molecules. The amperometric responses are linearly proportional to the concentration of dopamine in the range of 8–100 [Formula: see text]M, with a low detection limit of 4.8 [Formula: see text]M and good sensitivity, indicating the great potential of electroactive tetrapyrrole rare earth sandwich type complexes in the field of nonenzymatic electrochemical sensors.

Polymer Composite with Carbon Nanofibers Aligned during Thermal Drawing as a Microelectrode for Chronic Neural Interfaces

Microelectrodes provide a direct pathway to investigate brain activities electrically from the external world, which has advanced our fundamental understanding of brain functions and has been utilized for rehabilitative applications as brain-machine interfaces. However, minimizing the tissue response and prolonging the functional durations of these devices remain challenging. Therefore, the development of next-generation microelectrodes as neural interfaces is actively progressing from traditional inorganic materials toward biocompatible and functional organic materials with a miniature footprint, good flexibility, and reasonable robustness. In this study, we developed a miniaturized all polymer-based neural probe with carbon nanofiber (CNF) composites as recording electrodes via the scalable thermal drawing process. We demonstrated that in situ CNF unidirectional alignment can be achieved during the thermal drawing, which contributes to a drastic improvement of electrical conductivity by 2 orders of magnitude compared to a conventional polymer electrode, while still maintaining the mechanical compliance with brain tissues. The resulting neural probe has a miniature footprint, including a recording site with a reduced size comparable to a single neuron and maintained impedance that was able to capture neural activities. Its stable functionality as a chronic implant has been demonstrated with the long-term reliable electrophysiological recording with single-spike resolution and the minimal tissue response over the extended period of implantation in wild-type mice. Technology developed here can be applied to basic chronic electrophysiological studies as well as clinical implementation for neuro-rehabilitative applications.

Electrochemical detection of serotonin based on a poly(bromocresol green) film and Fe3O4 nanoparticles in a chitosan matrix

A composite film containing poly(bromocresol green), magnetic nanoparticles and multiwalled carbon nanotubes was fabricated for the sensitive determination of serotonin.

Nanostructured Tip-Shaped Biosensors: Application of Six Sigma Approach for Enhanced Manufacturing

Nanostructured tip-shaped biosensors have drawn attention for biomolecule detection as they are promising for highly sensitive and specific detection of a target analyte. Using a nanostructured tip, the sensitivity is increased to identify individual molecules because of the high aspect ratio structure. Various detection methods, such as electrochemistry, fluorescence microcopy, and Raman spectroscopy, have been attempted to enhance the sensitivity and the specificity. Due to the confined path of electrons, electrochemical measurement using a nanotip enables the detection of single molecules. When an electric field is combined with capillary action and fluid flow, target molecules can be effectively concentrated onto a nanotip surface for detection. To enhance the concentration efficacy, a dendritic nanotip rather than a single tip could be used to detect target analytes, such as nanoparticles, cells, and DNA. However, reproducible fabrication with relation to specific detection remains a challenge due to the instability of a manufacturing method, resulting in inconsistent shape. In this paper, nanostructured biosensors are reviewed with our experimental results using dendritic nanotips for sequence specific detection of DNA. By the aid of the Six Sigma approach, the fabrication yield of dendritic nanotips increases from 20.0% to 86.6%. Using the nanotips, DNA is concentrated and detected in a sequence specific way with the detection limit equivalent to 1000 CFU/mL. The pros and cons of a nanotip biosensor are evaluated in conjunction with future prospects.

An iridium oxide nanoparticle and polythionine thin film based platform for sensitive Leishmania DNA detection

A novel impedimetric label-free genosensor for highly sensitive DNA detection using a sensing platform based on thionine and iridium oxide nanoparticles.

Multi-walled carbon nanotube inhibits CA1 glutamatergic synaptic transmission in rat's hippocampal slices

The purpose of the study was to investigate the neurotoxic effect of multi-walled carbon nanotubes (MWCNTs) on the properties of glutamatergic synaptic transmission in rat's hippocampal slices using whole-cell patch clamp technique. The amplitude and frequency of excitatory postsynaptic current (EPSC) were accessed on the hippocampal pyramidal neurons. The alterations of glutamatergic synaptic transmission in CA3-CA1 were examined by measuring both the amplitude of evoked excitatory postsynaptic current (eEPSC) and paired-pulse ratio (PPR). The data showed that the amplitude of either spontaneous excitatory postsynaptic current (sEPSC) or miniature excitatory postsynaptic current (mEPSC) was significantly inhibited by 1 μg/mL MWCNTs. However, it was found that there was a trend of different change on the frequency index. When 1 μg/mL MWCNTs was applied, there were a decreased frequency of mEPSC and an increased frequency of sEPSC, which might be due to the effect of action potential. Furthermore, the amplitudes of eEPSC at CA3-CA1 synapses were remarkably decreased. And the mean amplitude of AMPAR-mediated eEPSC was significantly reduced as well. Meanwhile, a majority of PPRs data were greater than one. There were no significant differences of PPRs between control and MWCNTs states, but an increased trend of paired-pulse facilitation was found. These results suggested that MWCNT markedly inhibited hippocampal CA1 glutamatergic synaptic transmission in vitro, which provided new insights into the MWCNT toxicology on CNS at cellular level.

Fabricated micro-nano devices for in vivo and in vitro biomedical applications

In recent years, the innovative use of microelectromechanical systems (MEMSs) and nanoelectromechanical systems (NEMSs) in biomedical applications has opened wide opportunities for precise and accurate human diagnostics and therapeutics. The introduction of nanotechnology in biomedical applications has facilitated the exact control and regulation of biological environments. This ability is derived from the small size of the devices and their multifunctional capabilities to operate at specific sites for selected durations of time. Researchers have developed wide varieties of unique and multifunctional MEMS/NEMS devices with micro and nano features for biomedical applications (BioMEMS/NEMS) using the state of the art microfabrication techniques and biocompatible materials. However, the integration of devices with the biological milieu is still a fundamental issue to be addressed. Devices often fail to operate due to loss of functionality, or generate adverse toxic effects inside the body. The in vitro and in vivo performance of implantable BioMEMS such as biosensors, smart stents, drug delivery systems, and actuation systems are researched extensively to understand the interaction of the BioMEMS devices with physiological environments. BioMEMS developed for drug delivery applications include microneedles, microreservoirs, and micropumps to achieve targeted drug delivery. The biocompatibility of BioMEMS is further enhanced through the application of tissue and smart surface engineering. This involves the application of nanotechnology, which includes the modification of surfaces with polymers or the self-assembly of monolayers of molecules. Thereby, the adverse effects of biofouling can be reduced and the performance of devices can be improved in in vivo and in vitro conditions.

Electrolyte-free Amperometric Immunosensor using a Dendritic Nanotip

Electric detection using a nanocomponent may lead to platforms for rapid and simple biosensing. Sensors composed of nanotips or nanodots have been described for highly sensitive amperometry enabled by confined geometry. However, both fabrication and use of nanostructured sensors remain challenging. This paper describes a dendritic nanotip used as an amperometric biosensor for highly sensitive detection of target bacteria. A dendritic nanotip is structured by Si nanowires coated with single-walled carbon nanotubes (SWCNTs) for generation of a high electric field. For reliable measurement using the dendritic structure, Si nanowires were uniformly fabricated by ultraviolet (UV) lithography and etching. The dendritic structure effectively increased the electric current density near the terminal end of the nanotip according to numerical computation. The electrical characteristics of a dendritic nanotip with additional protein layers was studied by cyclic voltammetry and I-V measurement in deionized (DI) water. When the target bacteria dielectrophoretically captured onto a nanotip were bound with fluorescence antibodies, the electric current through DI water decreased. Measurement results were consistent with fluorescence- and electron microscopy. The sensitivity of the amperometry was 10 cfu/sample volume (103 cfu/mL), which was equivalent to the more laborious fluorescence measurement method. The simple configuration of a dendritic nanotip can potentially offer an electrolyte-free detection platform for sensitive and rapid biosensors.

Flexible direct-growth CNT biosensors

A biosensor was fabricated by growing carbon nanotubes (CNTs) directly on a polyimide flexible substrate at low temperatures (≤400 °C). A biocompatible polymer (poly(para-xylylene), parylene) was subsequently coated on the surface without CNTs as an insulator for future applications of flexible biosensors in in vivo sensing. The feasibility of the CNT flexible biosensor was demonstrated by quantitatively detecting human serum albumin (HSA). The CNT surface was modified with functional groups using UV-ozone, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), and treated with N-hydroxysuccinimide (NHS) to improve the biocompatibility for the conjugation of protein. In addition, anti-HSA (AHSA) was used to capture HSA specifically, and bovine serum albumin (BSA) was applied to block the non-specific sites. The electrical properties of the biosensors applied with various HSA concentrations were measured and quantified using an electrochemical impedance spectroscopy system under AC conditions. The detection limit of the biosensor for HSA detection was approximately 3×10(-11) mg/ml. The proposed sensor has considerable potential for future application in wearable biosensors and implant detection.

Hierarchically driven IrO2 nanowire electrocatalysts for direct sensing of biomolecules

Applying nanoscale device fabrications toward biomolecules, ultra sensitive, selective, robust, and reliable chemical or biological microsensors have been one of the most fascinating research directions in our life science. Here we introduce hierarchically driven iridium dioxide (IrO(2)) nanowires directly on a platinum (Pt) microwire, which allows a simple fabrication of the amperometric sensor and shows a favorable electronic property desired for sensing of hydrogen peroxide (H(2)O(2)) and dihydronicotinamide adenine dinucleotide (NADH) without the aid of enzymes. This rational engineering of a nanoscale architecture based on the direct formation of the hierarchical 1-dimensional (1-D) nanostructures on an electrode can offer a useful platform for high-performance electrochemical biosensors, enabling the efficient, ultrasensitive detection of biologically important molecules.

Fabrication of functional micro- and nanoneedle electrodes using a carbon nanotube template and electrodeposition

Carbon nanotube (CNT) is an attractive material for needle-like conducting electrodes because it has high electrical conductivity and mechanical strength. However, CNTs cannot provide the desired properties in certain applications. To obtain micro- and nanoneedles having the desired properties, it is necessary to fabricate functional needles using various other materials. In this study, functional micro- and nanoneedle electrodes were fabricated using a tungsten tip and an atomic force microscope probe with a CNT needle template and electrodeposition. To prepare the conductive needle templates, a single-wall nanotube nanoneedle was attached onto the conductive tip using dielectrophoresis and surface tension. Through electrodeposition, Au, Ni, and polypyrrole were each coated successfully onto CNT nanoneedle electrodes to obtain the desired properties.

Electrochemical behavior of dye-linked L-proline dehydrogenase on glassy carbon electrodes modified by multi-walled carbon nanotubes

A glassy carbon electrode (GC) was modified by multi-walled carbon nanotubes (MWCNTs). The modified electrode showed a pair of redox peaks that resulted from the oxygen-containing functional groups on the nanotube surface. A recombinant thermostable dye-linked L-proline dehydrogenase (L-proDH) from hyperthermophilic archaeon (Thermococcus profundus) was further immobilized by physical adsorption. The modified electrode (GC/MWCNTs/L-proDH) exhibited an electrocatalytic signal for L-proline compared to bare GC, GC/L-proDH and GC/MWCNTs electrodes, which suggested that the presence of MWCNTs efficiently enhances electron transfer between the active site of enzyme and electrode surface. The immobilized L-proDH showed a typical Michaelis-Menten catalytic response with lower apparent constant.

Nanowire Modification to Enhance the Performance of Neurotransmitter Sensors

In this work, we have developed a method to modify the platinum (Pt) working electrode with nanowires using vapor-solid-liquid (VLS) mechanism in order to increase the sensitivity of our microelectrochemical neurotransmitter sensors. Our sensor probes were manufactured from a 300 μm thick silicon (Si) wafer with several electrode designs for implantation in various locations of the human central nervous system. The surfaces of electrodes were observed and characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The complete devices were made and used to demonstrate the enhancement in performance contributed by nanowires in the enzyme-based electrochemical sensing of L-glutamate, which is the most abundant excitatory neurotransmitter. Comparison between electrodes with and without nanowire modification was conducted, showing that the modification method is a good option to improve the performance of electrochemical sensors.

Platinum nanoparticle ensemble-on-graphene hybrid nanosheet: one-pot, rapid synthesis, and used as new electrode material for electrochemical sensing

The development of nanoscience and nanotechnology has inspired scientists to continuously explore new electrode materials for constructing an enhanced electrochemical platform for sensing. In this article, we proposed a new Pt nanoparticle (NP) ensemble-on-graphene hybrid nanosheet (PNEGHNs), a new electrode material, which was rapidly prepared through a one-step microwave-assisted heating procedure. The advantages of PNEGHNs modified glassy carbon electrode (GCE) (PNEGHNs/GCE) are illustrated from comparison with the graphenes (GNs) modified GCE for electrocatalytic and sensing applications. The electrocatalytic activities toward several organic and inorganic electroactive compounds at the PNEGHNs/GCE were investigated, all of which show a remarkable increase in electrochemical performance relative to GNs/GCE. Hydrogen peroxide (H2O2) and trinitrotoluene (TNT) were used as two representative analytes to demonstrate the sensing performance of PNEGHNs. It is found that PNEGHNs modified GCE shows a wide linear range and low detection limit for H2O2 and TNT detection. Therefore, PNEGHNs may be an attractive robust and advanced hybrid electrode material with great promise for electrochemical sensors and biosensors design.

Nanoneedle: a multifunctional tool for biological studies in living cells

Studying biology in living cells is methodologically challenging but highly beneficial. Recent advances in nanobiotechnology offer exciting new opportunities to address this challenge. The nanoneedle technology, as an emerging technology that uses a cell membrane-penetrating nanoneedle to probe and manipulate biological processes in living cells, is expected to play an important role in this endeavor. Here we review the recent development and future direction of the nanoneedle technology for biological studies in living cells. The nanoneedle technology is shown to be powerful and versatile, and can offer numerous new ways to explore biological processes and biophysical properties of living cells with high spatial and temporal precision potentially reaching molecular resolution.

Patternable nanowire sensors for electrochemical recording of dopamine

Spatially resolved electrochemical recording of neurochemicals is difficult due to the challenges associated with producing nanometer-scale patternable and integrated sensors. We describe the lithographic fabrication and characterization of patternable gold (Au) nanowire (NW) based sensors for the electrochemical recording of dopamine (DA). We demonstrate a straightforward NW-size-independent approach to align contact pads to NWs. Sensors, with NW widths as small as 30 nm, exhibited considerable insensitivity to scan rates during cyclic voltammetry, a nonlinear increase in oxidation current with increasing NW width, and the selectivity to measure submaximal synaptic concentrations of DA in the presence of interfering ascorbic acid. The electrochemical sensitivity of Au NW electrode sensors was much larger than that of Au thin-film electrodes. In chronoamperometric measurements, the NW sensors were found to be sensitive for submicromolar concentration of DA. Hence, the patternable NW sensors represent an attractive platform for electrochemical sensing and recording.

Review of recent advances in analytical techniques for the determination of neurotransmitters

Methods and advances for monitoring neurotransmitters in vivo or for tissue analysis of neurotransmitters over the last five years are reviewed. The review is organized primarily by neurotransmitter type. Transmitter and related compounds may be monitored by either in vivo sampling coupled to analytical methods or implanted sensors. Sampling is primarily performed using microdialysis, but low-flow push-pull perfusion may offer advantages of spatial resolution while minimizing the tissue disruption associated with higher flow rates. Analytical techniques coupled to these sampling methods include liquid chromatography, capillary electrophoresis, enzyme assays, sensors, and mass spectrometry. Methods for the detection of amino acid, monoamine, neuropeptide, acetylcholine, nucleoside, and soluble gas neurotransmitters have been developed and improved upon. Advances in the speed and sensitivity of these methods have enabled improvements in temporal resolution and increased the number of compounds detectable. Similar advances have enabled improved detection at tissue samples, with a substantial emphasis on single cell and other small samples. Sensors provide excellent temporal and spatial resolution for in vivo monitoring. Advances in application to catecholamines, indoleamines, and amino acids have been prominent. Improvements in stability, sensitivity, and selectivity of the sensors have been of paramount interest.

Electrochemical biosensors at the nanoscale

The general mechanism of chemical sensing is based on molecular recognition linked to different transduction strategies based on electrochemical, optical, gravimetric or thermal effects that can convert the signal to digital information. Electrochemical sensors support accurate, fast, and inexpensive analytical methods with the advantages of being easily embedded and integrated into electronics, and having the greatest potential impact in the areas of healthcare, environmental monitoring (e.g. electronic noses), food packaging and many other applications (E. Bakker and Y. Qin, Anal. Chem., 2006, 78, 3965). Nanoscale electrochemical biosensors offer a new scope and opportunity in analytical chemistry. The reduction in the size of electrochemical biosensors to nanoscale dimensions expands their analytical capability, allowing the exploration of nanoscopic domains, measurements of local concentration profiles, detection in microfluidic systems and in vivo monitoring of neurochemical events by detection of stimulated dopamine release (R. Kennedy, L. Huang, M. Atkinson and P. Dush, Anal. Chem., 1993, 65, 1882). This article reviews both state of art developments in electrochemical nanosensing, and the industrial outlook.

A Nonoxidative Electrochemical Sensor Based on a Self-Doped Polyaniline/Carbon Nanotube Composite for Sensitive and Selective Detection of the Neurotransmitter Dopamine: A Review

Most of the current techniques for in vivo detection of dopamine exploit the ease of oxidation of this compound. The major problem during the detection is the presence of a high concentration of ascorbic acid that is oxidized at nearly the same potential as dopamine on bare electrodes. Furthermore, the oxidation product of dopamine reacts with ascorbic acid present in samples and regenerates dopamine again, which severely limits the accuracy of the detection. Meanwhile, the product could also form a melanin-like insulating film on the electrode surface, which decreases the sensitivity of the electrode. Various surface modifications on the electrode, new materials for making the electrodes, and new electrochemical techniques have been exploited to solve these problems. Recently we developed a new electrochemical detection method that did not rely on direct oxidation of dopamine on electrodes, which may naturally solve these problems. This approach takes advantage of the high performance of our newly developed poly(anilineboronic acid)/carbon nanotube composite and the excellent permselectivity of the ion-exchange polymer Nafion. The high affinity binding of dopamine to the boronic acid groups of the polymer affects the electrochemical properties of the polyaniline backbone, which act as the basis for the transduction mechanism of this non-oxidative dopamine sensor. The unique reduction capability and high conductivity of single-stranded DNA functionalized single-walled carbon nanotubes greatly improved the electrochemical activity of the polymer in a physiologically-relevant buffer, and the large surface area of the carbon nanotubes increased the density of the boronic acid receptors. The high sensitivity and selectivity of the sensor show excellent promise toward molecular diagnosis of Parkinson's disease. In this review, we will focus on the discussion of this novel detection approach, the new interferences in this detection approach, and how to eliminate these interferences toward in vivo and in vitro detection of the neurotransmitter dopamine.

Electric field and tip geometry effects on dielectrophoretic growth of carbon nanotube nanofibrils on scanning probes

Single-wall carbon nanotube (SWNT) nanofibrils were assembled onto a variety of conductive scanning probes including atomic force microscope (AFM) tips and scanning tunnelling microscope (STM) needles using positive dielectrophoresis (DEP). The magnitude of the applied electric field was varied in the range of 1-20 V to investigate its effect on the dimensions of the assembled SWNT nanofibrils. Both length and diameter grew asymptotically as voltage increased from 5 to 18 V. Below 4 V, stable attachment of SWNT nanofibrils could not be achieved due to the relatively weak DEP force versus Brownian motion. At voltages of 20 V and higher, low quality nanofibrils resulted from incorporating large amounts of impurities. For intermediate voltages, optimal nanofibrils were achieved, though pivotal to this assembly is the wetting behaviour upon tip immersion in the SWNT suspension drop. This process was monitored in situ to correlate wetting angle and probe geometry (cone angles and tip height), revealing that probes with narrow cone angles and long shanks are optimal. It is proposed that this results from less wetting of the probe apex, and therefore reduces capillary forces and especially force transients during the nanofibril drawing process. Relatively rigid probes (force constant ≥2 N m(-1)) exhibited no perceivable cantilever bending upon wetting and de-wetting, resulting in the most stable process control.

Determination of Dopamine in the Presence of Ascorbic Acid by Nafion and Single-Walled Carbon Nanotube Film Modified on Carbon Fiber Microelectrode

Carbon fiber microelectrode (CFME) modified by Nafion and single-walled carbon nanotubes (SWNTs) was studied by voltammetric methods in phosphate buffer saline (PBS) solution at pH 7.4. The Nafion-SWNTs/CFME modified microelectrode exhibited strongly enhanced voltammetric sensitivity and selectivity towards dopamine (DA) determination in the presence of ascorbic acid (AA). Nafion-SWNTs film accelerated the electron transfer reaction of DA, but Nafion film as a negatively charged polymer restrained the electrochemical response of AA. Voltammetric techniques separated the anodic peaks of DA and AA, and the interference from AA was effectively excluded from DA determination. Linear calibration plots were obtained in the DA concentration range of 10 nM - 10 μM and the detection limit of the anodic current was determined to be 5 nM at a signal-to-noise ratio of 3. The study results demonstrate that DA can be determined without any interference from AA at the modified microelectrode, thereby increasing the sensitivity, selectivity, and reproducibility and stability.