Gold Working Electrode Research Articles

LAMP-CRISPR/Cas12a-based impedimetric biosensor powered by Fe3O4@Au-(S-polyA-S)-Au for detection of SARS-CoV-2.

Alow-cost, lab-made polytetrafluoroethylene micro-cell, equipped with three electrodes, wasd evelopedfor the impedimetric detection of SARS-CoV-2. The gold working electrode was modified with a double-ended thiolated poly-adenine probe, which was conjugated with magnetic Fe₃O₄@Au nanoparticles (Fe3O4@Au-(S-polyA-S)-Au). After the loop-mediated isothermal amplification (LAMP) of viral RNA, the single-guide RNA (sgRNA), specifically bound to the SARS-CoV-2 target sequence, activates Cas12a. Cas12a then cleaved the immobilized probe. As a result, the magnetic Fe3O4@Au nanoparticles were released and adsorbed onto the gold electrode surface, using an external magnet. This process increased the physical surface area of the gold electrode, facilitating redox ion ([FeIII/II(CN)6]3-/4-) electron transfer. The decrease in the charge transfer resistance was utilized for SARS-CoV-2 detection. Our LAMP-CRISPR/Cas12a-based impedimetric biosensor, powered by Fe3O4@Au-(S-polyA-S)-Au, demonstrated impressive capabilities, including a remarkable detection limit of 0.8 aM (0.48 copies/µL) and a linear range of 0.01 to 36.06 fM.

Electrochemical biosensing of cerium with a tyrosine‐functionalized EF‐hand loop peptide

AbstractThe significance of easily detecting rare earth elements (REEs) has increased due to the growing demand for REEs. Addressing this need, we present an innovative electrochemical biosensor, focusing on cerium as a model REE. This biosensor utilizes a modified EF‐hand loop peptide sequence, incorporating cysteine for covalent attachment to a gold working electrode and tyrosine as an electrochemically active amino acid. The sensor was designed such that binding to cerium induces a conformational change in the peptide, affecting tyrosine's proximity to the electrode surface, modulating the current. A calibration curve was generated from cyclic voltammetry current peaks at ~0.55–0.65 V versus a silver pseudo‐reference electrode, with cerium concentrations ranging from 0 to 67 μM in artificial urine. The sensor exhibited a biologically relevant limit of detection of 35 μM and a sensitivity of −0.0024 ± 0.002 (μA μM)−1. These findings offer insights into designing peptide sequences for electrochemical biosensing.

Development of ultrasensitive genosensor targeting pathogenic Leptospira DNA detection in artificial urine

In the last decades, to access the stages of leptospirosis pathogenicity, site of infection, progression, monitor disease, and after-treatment were required especially non-invasive techniques. This becomes one of the significant goals for researchers. In this study, we developed a highly sensitive DNA-based electrochemical sensor to detect pathogenic leptospires in urine samples using a gold screen-printed electrode. The gold working electrode was electrodeposited with diazonium salt (CMA) with external carboxylic acid from the surface, and the specific Loa22 single-stranded DNA (ssDNA) probe to Leptospira interrogans was immobilized through a carbodiimide chemical reaction. The modified working electrode was characterized by contact angle measurement, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). After that, targeted DNA testing showed the EIS change in the range of 5 ag mL-1 - 16 fg mL-1 with a correlation R2 of 0.9638. The high sensitivity electrochemical sensor indicated a lower limit of detection to the attomolar level specifically 5 ag mL-1. Additionally, the developed genosensor exhibited high specificity without crossing other bacteria present in urine such as Escherichia coli, Staphylococcus aureus, and S. typhi as well as non-pathogenic leptospires L. biflexa serovar Patoc. Leptospires DNA was analyzed in both buffer solution and diluted artificial urine and detection in diluted artificial urine 1:1,000 was possible despite salt interferences. This study provides a highly sensitive lower detection platform for leptospirosis, offering potential for further development as a portable and point-of-care testing tool.

Rapid assembly of mixed thiols for toll-like receptor-based electrochemical pathogen sensing.

Herein, we describe a rapid and facile fabrication of electrochemical sensors utilizing two different toll-like receptor (TLR) proteins as biorecognition elements to detect bacterial pathogen associated molecular patterns (PAMPs). Using potential-assisted self-assembly, binary mixtures of 11-mercaptoundecanoic acid (MUA) and 6-mercapto-1-hexanol (MCH), or MUA and an in-house synthesized zwitterionic sulfobetaine thiol (DPS) were assembled on a gold working electrode within 5 minutes, which is >200 times shorter than other TLR sensors' preparation time. Electrochemical methods and X-ray photoelectron microscopy were used to characterize the SAM layers. SAMs composed of the betaine terminated thiol exhibited superior resistance to nonspecific interactions, and were used to develop the TLR sensors. Biosensors containing two individually immobilized TLRs (TLR4 and TLR9) were fabricated on separate MUA-DPS SAM modified Au electrodes (MUA-DPS/Au) and tested for their response towards their respective PAMPs. The changes to electron transfer resistance in EIS of the TLR4/MUA-DPS/Au sensor showed a detection limit of 4 ng mL-1 for E. coli 0157:H7 endotoxin (lipopolysaccharide, LPS) and a dynamic range of up to 1000 ng mL-1. The TLR4-based sensor showed negligible response when tested with LPS spiked human plasma samples, showing no interference from the plasma matrix. The TLR9/MUA-DPS/Au sensor responded linearly up to 350 μg mL-1 bacterial DNA, with a detection limit of 7 μg mL-1. The rapid assembly of the TLR sensors, excellent antifouling properties of the mixed SAM assembly, small size and ease of operation of EIS hold great promise for the development of a portable and automated broad-spectrum pathogen detection and classification tool.

Is the Interfacial Electrochemical Behavior of Quercetin the Same as That of Catechol Plus Resorcinol?

Background: Electrodeposition of functional films from polyphenol-containing solutions has emerged as a new field of surface functionalization from bio-sourced molecules. There is, however, almost no knowledge about the chemical structure of such complex films. It is the aim of this research to use the known electrodeposition of films made from catechol and resorcinol, two isomers of dihydroxybenzene, to understand the electrodeposition of a more complex polyphenol, quercetin, which is constituted from a fused catechol and resorcinol moiety. The aim of this article is hence to introduce some methodology in the interpretation of the electrochemical behavior of complex polyphenols starting from their building blocks. Methods: Cyclic voltammetry (CV) is used to deposit films from quercetin and from equimolar blends of catechol and resorcinol on amorphous carbon and gold working electrodes. The main experimental parameter was the potential sweep rate used during the CVs. Results: The CV of quercetin is not the exact sum of the CV of the catechol + resorcinol blends, but the major features are conserved, namely the presence of two main oxidation peaks affiliated to those of catechol and resorcinol but shifted to less anodic potentials. In addition, the anodic electron transfer coefficients of the two oxidation waves of quercetin are higher than those measured in the catechol resorcinol blend. However, film deposition ability is reduced with quercetin compared to catechol + resorcinol blend in probable relationship to steric hindrance occurring during the non-electrochemical crosslinking of the deposit. The quercetin-based films deposited at 10 mV·s−1 on gold electrodes are conformal and display some antioxidant activity.

Advancing Alzheimer’s biomarker Detection: A hairpin Aptamer-Based competitive electrochemical biosensor for trace Amyloid beta 40 analysis

Accurate detection of Alzheimer’s disease (AD) core biomarkers in body fluid is critical for identifying latent asymptomatic AD patients and prediction AD progress. Amyloid beta 1–40 (Aβ-40) as one of the core biomarkers, is expected to be an early diagnostic indicator for AD. Here, we establish a competitive method based on hairpin-structured aptamer for rapid and highly sensitive detection of Aβ-40 using square wave voltammetry (SWV). A hairpin aptamer with redox-active moiety methylene blue (MB) are immobilized on a gold working electrode as a recognition element. In the detection, a short complementary oligonucleotide strand is first introduced to switch on the hairpin, whereafter the targets Aβ-40 join in and selectively react with the aptamer in a competitive manner with the complementary strand, leading to the changes in the proximity of MB to the electrode and thereby in the electrochemical signal. Various parameters such as aptamer concentration, complementary chain length, incubation time, and temperature were optimized to achieve maximum sensing performance. By introducing a complementary chain, the sensor significantly reduces the detection limit to 7.14 pg/mL, with a dynamic range of 20 pg/mL to 200 ng/mL. Additionally, high selectivity of the sensor for Aβ-40 monomer (Aβ-40 m) over other forms of Aβ peptides has been validated. The hairpin-mediated detection method enables rapid, facile and highly sensitive detection of Aβ-40 using low-cost screen-printed electrode (SPE) platform, providing a wide range of possibilities for the early diagnosis of AD in point-of-care technologies (POCT).

P-696 Continuous monitoring of female hormones as a tool to improve IVF treatment’s efficacy

Abstract Study question Is it possible to employ an unobtrusive and injectable biosensor for real-time remote monitoring of patient’s hormone levels (LH, P4, E2) during an ART cycle? Summary answer In-situ implantable biosensors can effectively monitor clinically relevant hormone levels in real-time to improve ART cycle. What is known already Worldwide 48.5 million couples suffer from infertility. Hormonal imbalances can impede pregnancy by compromising the intricate processes of the reproductive system, affecting ovulation, egg quality, fallopian tube function, and endometrial receptivity. In the UK, assisted reproductive treatments (ART) have surged ten-fold in the last 20 years. ART success tremendously depends on the accurate measurement of hormone levels, namely Luteinizing Hormone (LH), oestradiol (E2), and progesterone (P4). These hormone levels change and pulsate during each patient cycle, requiring women to undergo a blood draw and endocrinology analysis every 2-3 days, making ART treatment a highly invasive and time consuming method. Study design, size, duration In order to determine the feasibility of the study question, Impli designed a minimally invasive implantable biosensor to continuously monitor essential hormones for women’s fertility such as LH, P4 and E2 in order to enhance the quality of treatment and improve the ART experience. An implantable electrochemical aptamer-based biosensors has been developed using cutting-edge electronics and electrochemical technologies. This minimally invasive biosensor allows patients to monitor their hormone levels in real-time during ART without venipuncture. Participants/materials, setting, methods The implantable biosensor contains the biorecognition interface, designed using the DNA-based aptamers coupled to the detection gold working electrodes. When the biosensor is in touch with the sample, hormones bind to the respective aptamers, which leads to changes in the electrical properties of the gold electrode. The changes are then monitored and calibrated through sensitive electrochemical techniques such as differential pulse voltammetry (DPV), using CHI potentiostat. Main results and the role of chance The biosensor was tested in vitro in artificial interstitial fluid (ISF) containing the range of 1 pg/ml to 1 µg/ml of hormones yielding a limit of detection (LOD) of 0.46 pg/ml, 1.15 pg/ml, and 0.58 pg/ml for E2, P4 and LH, respectively. Our data was validated using ELISA assays. A notably high linear correlation coefficient (R2) of approximately 0.9 was observed between the signals obtained from the ELISA and the biosensors, confirming the reliability of the aptamer biosensors for hormone analysis. The stability of the biosensor was also investigated over one week. The DPV technique was employed to assess the cross-reactivity of potential interferences with each biosensor. The results revealed that each biosensor exhibited notable selectivity towards its respective analyte over other interferences, at significantly higher concentrations. The biosensor was also characterised by microscopy techniques such as SEM and Raman analysis. Limitations, reasons for caution This novel implantable biosensor technology requires further upcoming validation in animal models to assess its ability for widespread use. Once validated, the appropriate human clinical trials will be undertaken. Wider implications of the findings The development and implementation of an unobtrusive implantable remote and continuous monitoring system, capturing hormone concentrations that are vital for success in an ART procedure, could transform the industry and positively influence patient’s access to care and the patient journey. Trial registration number No clinical trial

Real-time monitoring of daunorubicin pharmacokinetics with nanoporous electrochemical aptamer-based sensors in vivo

The metabolic differences between patients with the anticancer drug daunorubicin (DRN) pose difficulties in providing clinical delivery strategies for different patients. Therefore, it is urgent to develop a pharmacokinetic platform that can real-time monitor drug levels in vivo to achieve precise drug delivery and reduce drug side effects. To this end, an electrochemical aptamer-based (E-AB) sensor was designed to realize real-time and continuous monitoring of DRN levels in vivo and obtain DRN pharmacokinetics of different individuals for the first. Specifically, the binding free energy of the aptamer to the target was calculated by molecular docking simulations. Using nanoporous gold working electrodes with immobilized aptamers as E-AB sensors, which monitored DRN in the blood of different rat models continuously for many hours with nanomolar precision and second resolution, and hundreds of DRN concentration values were obtained, based on which important pharmacokinetic parameters were simulated and computed, including half-life of drug DRN distribution and elimination, and peak concentration in blood. These parameters help to determine the metabolism of drug DRN in different patients and adjust the administered dose in time to achieve precise treatment. Therefore, this E-AB platform may provide a valuable new tool for clinicians to monitor pharmacokinetics in different patients.

Abstract 7289: PancreaAlert: Intelligent nanoengineered biosensor for pancreatic cancer

Abstract Introduction: Pancreatic cancer accounts for 3% of cancer cases and 7% of cancer deaths in the United States. It is currently in the third position with respect to cancer-related deaths, and it is expected to move to second place as of 2040. This is mainly due to its diagnosis in the later stage. If detected in the first or second stage surgery can be performed thus increasing the patient’s survival rate. The current methods of diagnosis cannot do early stage or asymptomatic detection. So, detecting cancer-specific biomarkers can aid in the prognosis. Serum protein-based biomarkers carbohydrate antigen CA242, CA19-9, and carcinoembryonic antigen CEA are specific to pancreatic cancer. Thus, in this preliminary study, we aim to develop a nanoengineered electrochemical biosensor combined with machine learning to detect pancreatic cancer-specific biomarkers CA242, CA19-9, and CEA. Methodology: Nanoengineering the biosensor: The gold working electrode of the gold- biosensor (DRP-250AT) was coated with graphene oxide nano colloidal solution and kept in UV overnight for the graphene oxide nanosheet to crosslink with the working electrode. Detection of biomarkers using an electrochemical biosensor: First, a Crosslinker (DSP) was added to ethanol cleaned biosensor to bind the analytes. Following that antibody specific to each biomarker were added to the biosensors. The addition of TBS superblock prevented non-specific binding. Then different concentrations of biomarkers were added, and the corresponding sensor was subjected to various electrochemical analyses such as electrochemical impedance spectroscopy and voltammetry. SEM-EDAX analysis: The antigen-antibody binding on the biosensor's surface was confirmed. Automation and machine learning: Python code was developed to automate the analysis process and machine learning models (support vector machine and neural network) were used to classify the concentrations into various risk levels. The sensitivity of the developed tool was high when compared with conventional methods like ELISA and confocal microscopy. Results: From the electrochemical studies we found that with increasing concentration of biomarkers, there was a trend in output parameters: capacitance, resistance, impedance and area under the curve. By analyzing this trend, the concentrations of biomarkers can be detected. Using this data as input the machine learning model (accuracy greater than 80%) classified the concentrations into risk levels (normal, low risk, and high risk). Significance: Nanoengineering with graphene oxide nanosheets enhances the sensitivity of electrochemical biosensors. Automation and machine learning models help in the analysis of large datasets produced by this sensor. Overall, this device aids in the prognosis of pancreatic cancer. Our preliminary results are encouraging but more thorough research is required to make this diagnostic tool a working application. Citation Format: Meenal Karunanidhi, Hemalatha Kanniyappan, Edith Zhan, Ruth Mathew, Yani Sun, Junyi Wu, Yan Yan, Gnanasekar Munirathinum, Mathew T. Mathew. PancreaAlert: Intelligent nanoengineered biosensor for pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7289.

Thermodynamic solvation parameters, cyclic voltammetry for CdBr2 in sodium chloride supporting electrolyte alone and in interaction with succinic acid solutions with Tafel slopes application

In this study, investigated potentials were studied for CdBr2in sodium chloride medium to investigate the voltammetry behavior. Cyclic voltammetry was used to follow the different redox peaks for both salts used alone individually or in the presence of weak organic acid succinic acid in 0.1 M NaCl-supporting electrolyte media. A gold-working electrode was achieved for this study since, on using this electrode, different selective peaks appeared. The different scan rates were studied for the salts under consideration alone and in the presence of succinic acid were also discussed. Catalytic oxidation of succinic acid was studied on using a gold 18-Karat working electrode affected by Au metal.The purpose of this work is to use Tafel plots as an essential tool in cyclic voltammetry for providing valuable information about the kinetic parameters and mechanisms of electrochemical reactions.The innovation of this work is to use Tafelplots whichcan be applied here for analyzing the slopes and intercepts to assess the efficiency of different used materials.Tafel plots were applied for cadmium bromide salts alone and in the presence of succinic acid from cyclic voltammetry data and the mechanism for redox reactions were suggested.The importance of this work understands the redox behavior by help of the thermodynamic solvation parameters.The cyclic voltammetry allows the investigation of multiple electrode processes occurring simultaneously by the thermodynamic functions. Also thermodynamic parameters help for the quantification of species concentration found in measured solutions.The kinetics of the redox reaction can be studied applying the thermodynamic parameters.

Label-free electrochemical biosensor for direct detection of Oncostatin M (OSM) inflammatory bowel diseases (IBD) biomarker in human serum

Oncostatin M (OSM) is an interleukin-6 (IL-6) member family cytokine implicated in the pathogenesis of chronic diseases including inflammatory bowel disease (IBD). OSM is a novel diagnostic biomarker over-expressed in the serum of IBD patients. This paper reports on the first electrochemical OSM immunosensor, developed using a multistep fabrication process aimed at covalently immobilizing OSM antibodies on a mixed self-assembled monolayer coated gold working electrode. Cyclic voltammetry, atomic force microscopy (AFM), IR spectroscopy and optical characterizations were used to validate the sensor functionalization protocol. Electrochemical impedance spectroscopy (EIS) measurements were performed to assess the reliability of the immunosensor preparation and to verify the antibody-antigen complexes formation. The label-free immunosensor showed high sensitivity identifying OSM at clinically relevant concentrations (37–1000 pg mL−1) with low detection limit of 2.86 pg mL−1. Both sensitivity and selectivity of the proposed immunosensor were also demonstrated in human serum in the presence of interfering biomarkers, making it an innovative potential platform for the OSM biomarker detection in IBD patients’ serum.

A reagentless molecularly imprinted polymer-based electrochemical biosensor for single-step detection of troponin I in biofluids.

Reagentless molecular-imprinted polymer (MIP) electrochemical biosensors can offer the next generation of biosensing platforms for the detection of biomarkers owing to their simplicity, cost-efficacy, tunability, robustness, and accuracy. In this work, a novel combination of Prussian blue (PB), coated as an embedded redox probe on a gold working electrode (GWE), and a signal-off MIP assay has been proposed in an electrochemical format for the detection of troponin I (TnI) in biofluids. TnI is a variant exclusive to heart muscles, and its elevated level in the bloodstream is indicative of acute myocardial infarction (AMI). The proposed lab-manufactured PB/MIP electrochemical biosensor, consisting of a simple signal-off MIP assay and a PB redox probe embedded on the GWE surface, is the first of its kind that allows for reagentless, label-free, and single-step electrochemical biosensing of proteins. The preparation steps of the biosensor were fully characterized by cyclic voltammetry (CV), atomic force microscopy (AFM), and Raman spectroscopy. Finally, the performance of the optimized biosensor was investigated through the determination of various concentrations of TnI, ranging from 10 to 100 pg mL-1 within 5 min, in serum and plasma with limits of detection less than 3.6 pg mL-1, and evaluation of selectivity towards TnI using some relevant proteins that exist in biofluids with higher concentrations.

Graphene oxide-cerium oxide nanocomposite modified gold electrode for ultrasensitive detection of chlorpyrifos pesticide.

This research presents a novel approach for the detection of the pesticide chlorpyrifos (CLP) using a gold working electrode immobilized with a graphene oxide-cerium oxide (GO-CeO2) nanocomposite in a phosphate buffer (PBS) solution with a pH of 7.0. Graphene oxide (GO) was synthesized via a modified Hummer's method, while cerium oxide (CeO2) nanoparticles were prepared using a coprecipitation technique. The GO-CeO2 nanocomposite was synthesized via sonochemical methods. Structural and morphological characterization of the prepared material was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDX). Fourier transform infrared (FTIR) spectroscopy has been conducted for the confirmation of functional group presence in the prepared materials. Cyclic voltammetry (CV) was employed to investigate the interaction between the prepared material and the analyte. Further investigations using varying scan rates (5 mV s-1 to 300 mV s-1) revealed a diffusion-controlled process at the electrode-electrolyte interface. Linear sweep voltammetry (LSV) experiments were conducted across a pH range of 5 to 9, with pH 7.0 showing enhanced response for the target pesticides in the presence of the buffer solution. Subsequent electrochemical measurements were performed at pH 7.0. Chronocoulometry was utilized to measure the effective electrode area for electrochemical interactions. Ultrasensitive square wave voltammetry (SWV) was employed for investigating the sensitivity over a concentration range of 1 fM to 100 μM and yielded the limit of detection (LOD) and limit of quantification (LOQ) as 47.7 fM and 159 fM respectively. Interference studies confirmed the selectivity of the prepared sensor, while stability and reproducibility were assessed through controlled experiments. Electrochemical impedance spectroscopy (EIS) was performed to investigate the interactions at the interface. This study provides insights into the development of selective electrochemical sensors for pesticide detection, with potential applications in environmental monitoring.

Replacement of conventional reference electrode with platinum electrode for electronic tongue based analysis of dairy products

This work demonstrates the utility of platinum metal electrode as replacement for conventional Ag/AgCl reference electrode for voltammetric electronic tongue based analysis of edible dairy products. It overcomes the limitations of conventional silver-based reference electrode that presents a potential health hazard when employed for analysis of edible dairy products. Various dairy products like toned milk, Lassi and skimmed milk powder were tested using a cluster of platinum, gold and rhodium working electrodes. Responses of electrode cluster were captured using cyclic voltammetry. Comparative investigations were carried out between responses with platinum reference electrode and Ag/AgCl reference electrode. Repeatability and reproducibility of results have been examined. Our results suggest that platinum metal reference electrode can be reliably used for voltammetric electronic tongue based analysis of dairy products. Further this shall pave way for commercial development of electronic tongue technology in food sector adhering to hygienic and food safety regulations.

A Preliminary Study of A Lactic Acid Biosensor for the Early Detection of Dental Caries

Statement of Problem: Many mechanisms in the formation of dental caries, but the common point of these mechanisms is the proliferation of microorganisms in the mouth and mostly on the tooth surface. Objective: Although there are approximately 200 to 300 different microorganisms in human dental plaque, Neisseria spp. and S. mutans. The common point of these microorganisms is that they produce lactic acid. In this study, it is aimed to use a biosensor, which is a bioelectrochemical measurement system that combines the measurementcapability of physical analysis systems and the specificity of biochemical systems.Material-Method: In this study, lactate oxidase enzyme was immobilised on the gold working electrode surface by means of bovine serum albumin and gelatine. The enzyme was arrested on the electrode surface with the aid of the cross-linking agent glutaraldehyde. Cyclic voltammetry current scanning was performed in lactic acid biosensor preliminary studies. Optimisation studies were conducted in the current range obtained fromthe peak in the cyclic voltammogram. Within the scope of the optimisation studies, optimum operating temperature and optimum operating pH of the biosensor were tested.Results: An anodic peak at +0.2 V potential was obtained in the cyclic voltammogram drawn according to the reaction on the working electrode surface. In the optimisation studies conducted, it was found that the optimum operating conditions of the biosensor were at 35 °C and pH 6.5.Conclusion: According to the data obtained from the pre-study of the bioelectrochemical method, the concentration of lactic acid in the solution can be determined. With the completion of further studies, a portable lactic acid biosensor can be made. As a result, as a result of the preliminary study, the lactic acidbiosensors designed to determine in vitro lactic acid for the early diagnosis of dental caries in the future is promising.

Microfluidic Electrochemical Glucose Biosensor with In Situ Enzyme Immobilization

The development and characterization of a microfluidic electrochemical glucose biosensor are presented herein. The transducer part is based on thin-film metal electrodes on a glass substrate. The biological recognition element of the biosensor is the pyrroloquinoline quinone-glucose dehydrogenase (PQQ-GdhB) enzyme, selectively in situ immobilized via microcontact printing of a mixed self-assembling monolayer (SAM) on a gold working electrode, while the microfluidic part of the device comprises microchannel and microfluidic connections formed in a polydimethylsiloxane (PDMS) elastomer. The electrode properties throughout all steps of biosensor construction and the biosensor response to glucose concentration and analyte flow rate were characterized by cyclic voltammetry and chronoamperometry. A measurement range of up to 10 mM in glucose concentration with a linear range up to 200 μM was determined. A detection limit of 30 µM in glucose concentration was obtained. Respective biosensor sensitivities of 0.79 nA/µM/mm2 and 0.61 nA/µM/mm2 were estimated with and without a flow at 20 µL/min. The developed approach of in situ enzyme immobilization can find a wide number of applications in the development of microfluidic biosensors, offering a path towards continuous and time-independent detection.

Solution-Phase Electrochemical Aptamer-Based Sensors.

Electrochemical aptamer-based sensors (EABs) using self-assembled monolayers on gold working-electrodes have now been in-vivo demonstrated for multiple-analytes, demonstrating their sensitivity and specificity even in a continuous sensing format. However, longevity has been demonstrated for only 24 hours and sensitivity has been challenging for highly dilute analytes (nM regime). A novel approach is reported here using electrochemical aptamer-based sensing that is not covalently-bound to a gold-working electrode but where aptamers are freely mobile in solution. This alternative approach has the potential to improve longevity by reducing electrode surface degradation and improving sensitivity using aptamer binding constructs that are not available for aptamers when covalently bound to the electrode. Specifically, a molecular-beacon (fluorescent) cortisol aptamer was adapted into an amperometry solution-phase cortisol EAB sensor, demonstrating ∼5% signal gain starting at only 10 nM and a saturated signal gain of ∼70% at several μM. A robust signal was achieved due to use of methylene-blue redox-tagged aptamer that was measured through amperometry with interdigitated electrodes. While this result demonstrates the basic feasibility of solution-phase EAB sensors, the result also required a self-assembled monolayer alkylthiolate blocking-layer on the gold working electrode which restricts potential device longevity. These results cumulatively suggest that initial significance of solution-phase EAB sensors may be strongest for point-of-care type testing applications and further development would be required for long-lasting continuous sensing applications.

Ultrasensitive electrochemical phosphate detection by pyridine–zinc(II) complex

Phosphorous is an important environmental health parameter as the availability of phosphorus within water systems plays an essential role in the prevalence of harmful algal blooms (cyanobacteria blooms). Currently, phosphates are detected using sensitive chromatographic and colorimetric techniques; however, major disadvantages stem from the lack of anion selectivity in samples with complex matrices, as well as the high cost of analysis. Electrochemical techniques utilizing self-assembled monolayers can provide a cheaper yet sensitive method of detection. This work explores the modification of a gold working electrode using pyridine–zinc(II) complexes. The implementation of self-assembled monolayers allows for an ultrasensitive and selective method of indirect detection of the H2PO4 − species, ranging in concentrations between 0.0 and 1.2 fmol/L phosphate. Electrochemical techniques such as cyclic voltammetry and square-wave voltammetry were explored for their phosphate-detection abilities, with detection limits of 4.0 × 10−16 and 9.0 × 10−17 mol/L H2PO4 −, respectively. X-ray photoelectron spectroscopy measurements were also taken to confirm the modification of the electrode. The selectivity of this sensor towards phosphate anions was successfully explored for this sensor in the presence of potential interfering agents (sulfate, chlorine, carbonate, fluoride, nitrite, and hypochlorite ions), and applicability of sensor was also explored through the detection of phosphate in a tap and lake water sample.

Aqueous Complexation for the Interaction of SeO2 ‎with both Succinic acid and Dithizone in KCl ‎Solution ‎‎(Cyclic Voltammetry) Using Gold Working ‎Electrode (GWE)‎

Aqueous Complexation for the Interaction of SeO2 ‎with both Succinic acid and Dithizone in KCl ‎Solution ‎‎(Cyclic Voltammetry) Using Gold Working ‎Electrode (GWE)‎

Citrate and glutathione capped gold nanoparticles for electrochemical immunosensing of atrazine: Effect of conjugation chemistry

Recently, the exposure of pesticides/herbicides to the living organisms is increased especially due to agricultural malpractices and industrial processes. In particular, the exposure of pesticides/herbicides (e.g., atrazine) can impart several harsh effects on the human health. The development of efficient detection systems can be crucial in monitoring the atrazine in water and food/plant products, which can be decisive in controlling the deadly exposures of atrazine. Herein, we have developed electrochemical immunosensors for atrazine by employing monoclonal anti-atrazine antibody conjugated gold nanoparticles. Two types of gold nanoparticles (i.e., citrate and glutathione (GSH)-capped AuNPs) were used to modify gold working electrode and utilized for the development of atrazine immunosensors. The conjugation of immunoprobe on working electrode was especially designed to obtain stable and efficient sensing signals. The nanosensing immunoprobes fabricated using citrate-AuNPs and GSH-AuNPs exhibited comparable responses for a wide linear working range of 50 ng/L- 30 μg/L with limit of detection (LOD) values of 0.08 and 0.06 ng/L for atrazine, respectively.