Real-time Electrochemical Detection Research Articles

Sensitive Electrochemical Sensor Based on Amino-Functionalized Graphene Oxide/Polypyrrole Composite for Detection of Pb2+ Ions

In this work, an amino-functionalized graphene oxide/polypyrrole (AMGO/PPy) composite-based novel sensing platform was established to monitor lead ions (Pb2+) at high sensitivity. AMGO was synthesized through a hydrothermal process and later formed a composite with PPy at varying concentrations. A physicochemical investigation of the synthesized materials was carried out using various characterization tools, while the electrochemical properties were examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) methods. The AMGO/PPy composite was deposited on a glassy carbon electrode (GCE), which was used for the real-time electrochemical detection of Pb2+. The AMGO/PPy sensor exhibited lower limits of detection (LOD) of 0.91 nM. In addition, the developed Pb2+ sensor exhibited excellent reproducibility, repeatability, selectivity, sensitivity, and long-term stability for 25 days. The AMGO/PPy composite emerges as a ground-breaking material for the electrochemical detection of Pb2+, holding significant potential for environmental monitoring and the protection of human health.

(Invited) Skin-Interfaced Wearable Sweat Biosensors

The rising research interest in personalized medicine promises to revolutionize traditional medical practices. This presents a tremendous opportunity for developing wearable devices toward predictive analytics and treatment. In this talk, I will introduce our efforts in developing wearable biosensors for non-invasive molecular analysis. Such wearables can autonomously access body fluids (e.g., human sweat) across the activities and continuously measure a broad spectrum of analytes including metabolites, nutrients, hormones, proteins, and drugs. I will highlight our recent works in the design of wearable and wireless devices for the real-time electrochemical detection of picomolar-level proteins (i.e., inflammatory biomarker C-reactive) and hormones (i.e., estradiol) in sweat. Laser engraving, inkjet printing, and direct-ink-writing 3D printing are used to manufacture high-performance nanomaterials-based biosensors at large scale and low cost. The clinical value of our wearable systems is evaluated through various human trials toward precision nutrition, stress/mental health assessment, chronic disease management, and drug personalization. I will also discuss our research progress on energy harvesting from the human body and the environment to realize battery-free wireless wearable sensing. These wearable technologies could open the door to a wide range of personalized monitoring, diagnostic, and therapeutic applications.

Localized accelerated degradation of magnesium: A new insight into the mechanism of its biomedical degradation

Inhomogeneous degradation of Mg results in a potential safety risk for the application of its implants. The particular concern is the occurrence of localized accelerated degradation of Mg under the relatively enclosed condition. The present work investigated such a phenomenon using the Mg-4Zn tube in artificial blood plasma. Its occurrence mechanism was explored through elaborate experiments, including the hydrodynamic platform, real-time electrochemical detection, COMSOL simulation, and morphological observations. It is found the deficiency of Ca2+ and PO43+ in the localized solution induced by the excessively high pH value was responsible for its occurrence.

Graphene supported gold hollow sphere for real-time electrochemical detection of H2O2 released from cells

In this work, graphene undergoes twice oxidization to produce reoxidized-graphene oxide (ROGO), and then ROGO reacts with thiourea to obtain thiol-functionalized reduced ROGO (rROGO-SH), achieving reduction and surface thiolation. Subsequently, Au hollow spheres (Au HS) are decorated on rROGO-SH, and an electrochemical sensor is therefore fabricated by coating rROGO-S-Au HS on a glassy carbon electrode (GCE). rROGO-S-Au HS/GCE exhibits attractive electrochemical performance for H2O2 detection with a wide linear detection range (5 μM to 11.5 mM), low detection limit (5 μM), and good sensitivity (0.19 mA mM−1 cm−2). Due to its good performance for in-vivo detection, rROGO-S-Au HS/GCE can sensitively detect a trace amount of H2O2 released from living tumor cells. Hence, the rROGO-S-Au HS based electrochemical sensing platform shows great potential for online monitoring of H2O2 levels at tumor sites, which is beneficial for the rapid and sensitive diagnosis of cancer, as well as in vivo monitoring of tumor progression.

Highly Sensitive Wearable Sensor Based on (001)-Orientated TiO2 for Real-Time Electrochemical Detection of Dopamine, Tyrosine, and Paracetamol.

The concentration of dopamine (DA) and tyrosine (Tyr) reflects the condition of patients with Parkinson's disease, whereas moderate paracetamol (PA) can help relieve their pain. Therefore, real-time measurements of these bioanalytes have important clinical implications for patients with Parkinson's disease. However, previous sensors suffer from either limited sensitivity or complex fabrication and integration processes. This work introduces a simple and cost-effective method to prepare high-quality, flexible titanium dioxide (TiO2) thin films with highly reactive (001)-facets. The as-fabricated TiO2 film supported by a carbon cloth electrode (i.e., TiO2-CC) allows excellent electrochemical specificity and sensitivity to DA (1.390µAµM-1cm-2), Tyr (0.126µAµM-1cm-2), and PA (0.0841µAµM-1cm-2). More importantly, accurate DA concentration in varied pH conditions can be obtained by decoupling them within a single differential pulse voltammetry measurement without additional sensing units. The TiO2-CC electrochemical sensor can be integrated into a smart diaper to detect the trace amount of DA or an integrated skin-interfaced patch with microfluidic sampling and wireless transmission units for real-time detection of the sweat Try and PA concentration. The wearable sensor based on TiO2-CC prepared by facile manufacturing methods holds great potential in the daily health monitoring and care of patients with neurological disorders.

A wireless patch for the monitoring of C-reactive protein in sweat.

The quantification of protein biomarkers in blood at picomolar-level sensitivity requires labour-intensive incubation and washing steps. Sensing proteins in sweat, which would allow for point-of-care monitoring, is hindered by the typically large interpersonal and intrapersonal variations in its composition. Here we report the design and performance of a wearable and wireless patch for the real-time electrochemical detection of the inflammatory biomarker C-reactive (CRP) protein in sweat. The device integrates iontophoretic sweat extraction, microfluidic channels for sweat sampling and for reagent routing and replacement, and a graphene-based sensor array for quantifying CRP (via an electrode functionalized with anti-CRP capture antibodies-conjugated gold nanoparticles), ionic strength, pH and temperature for the real-time calibration of the CRP sensor. In patients with chronic obstructive pulmonary disease, with active or past infections or who had heart failure, the elevated concentrations of CRP measured via the patch correlated well with the protein's levels in serum. Wearable biosensors for the real-time sensitive analysis of inflammatory proteins in sweat may facilitate the management of chronic diseases.

L-Cysteine functionalized coral-like Ag doped MnO2 nanostructures for the real-time electrochemical detection of lead and cadmium ions

In this report, L-Cysteine functionalized Ag@MnO2 nanocomposite was prepared for selective, rapid, and instantaneous electrochemical sensing of heavy metal ions (HMIs). Hydrothermal method was employed to synthesize L-Cysteine functionalized Ag@MnO2 nanocomposites. The composition and morphology of L-Cys/Ag@MnO2 were characterized by advanced techniques such as XRD, FTIR, UV-Vis and FESEM analysis. XRD spectra confirmed the synthesis of tetragonal L-Cys/Ag@MnO2, while FESEM confirmed the formation of coral like nanostructures. Coral like L-Cys/Ag@MnO2 with sufficient open pores provided high surface area and large number of active sites for sensing of HMIs. The electrochemical parameters were optimized i.e., pH effect, deposition potential, deposition time, and impact of interfering species to enhance HMIs detection. Under optimized conditions, the designed sensor exhibited high sensitivity towards the solution of both Cd+2 and Pb+2 ions over a wide range from 0.1 μM to 0.005 μM of Cd+2 and Pb+2, respectively with LOD = 0.052 nM for Pb+2 and 0.065 nM for Cd+2. The developed sensor's practical applicability was also tested in tap water. Due to the high conductivity, synergistic effect, and high electron transfer kinetics of the prepared material, as designed sensor can be utilized for sensing other toxic metal ions in real samples.

Eutectic solvent-mediated synthesis of manganese molybdate nanosheets: Rapid and real-time electrochemical detection of p-methylaminophenol sulfate(metol)

The present study explores the design of MnMoO4 modified sensing platform for the electrochemical detection of metol. The green synthesis of MnMoO4 nanosheets was accomplished by a low-temperature deep eutectic solvents (DES) assisted hydrothermal protocol. According to structural and electrochemical studies, the large surface area and pore volume of the MnMoO4-based working electrode assembly provided a conduit for the anchoring of the target analytes. Under optimized electrochemical conditions, the modified sensor demonstrated an exceptionally low detection limit (LOD = 0.98 nM) with a sensitivity of 88.8 μA μM−1 cm−2 within a substantial linear working range from 0.01 to 375.6 μM by differential pulse voltammetric (DPV) technique. Benefiting from the significantly improved stability, sensitivity, and reproducibility, the proposed MnMoO4 electrocatalyst showed amplified current responses of metol. The possibility of metol detection without any foreign interference and % recovery between ±99.20–99.90 % opens up new prospects for the efficacious on-site detection of metol.

Construction of ANbO3 (A= Na, K)/f-carbon nanofiber composite: Rapid and real-time electrochemical detection of hydroxychloroquine in environmental samples

Hydroxychloroquine (HCQ) is a significant viral resistant drug widely acknowledged for its immunomodulatory and anti-inflammatory activities. To minimize the impact of HCQ residues on environmental pathways, exploring control measures is vital. In this regard, electrochemical sensing of HCQ using well-structured functional materials is advantageous. This work aims to provide an economical and sustainable route for the synthesis of ANbO3 (A = Na,K) perovskites via a thymol-menthol-based natural deep eutectic solvent. The as-synthesized NaNbO3 and KNbO3 are pinned to functionalized carbon nanofibers (f-CNF) via an ultrasonication approach. Benefitting from the synergistic effect of rapid electron transfer and improved surface area, enhanced electrochemical activity for NaNbO3@f-CNF/GCE is achieved. The fabricated NaNbO3@f-CNF displays a LOD (DPV = 0.01 μM, i-t = 0.007 μM), wide dynamic range (DPV = 0.09–22.5 μM, i-t = 0.006–35 μM), outstanding selectivity, and reproducibility, proving feasible in real-time analysis with good recovery rates (±97.67–99.81%). The NADES-mediated preparation of perovskites evades the incorporation of traditional toxic solvents and yields atom-efficient ANbO3 (A = Na,K) associated with green solvent templates. This validates the sustainable fabrication of electrode materials with reduced energy stipulations for detecting hazardous drug pollutants in the ecosystem.

Electrochemical Impedance-Based Biosensors for the Label-Free Detection of the Nucleocapsid Protein from SARS-CoV-2.

Diagnosis of coronavirus disease (COVID-19) is important because of the emergence and global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Real-time polymerase chain reaction (PCR) is widely used to diagnose COVID-19, but it is time-consuming and requires sending samples to test centers. Thus, the need to detect antigens for rapid on-site diagnosis rather than PCR is increasing. We quantified the nucleocapsid (N) protein in SARS-CoV-2 using an electro-immunosorbent assay (El-ISA) and a multichannel impedance analyzer with a 96-interdigitated microelectrode sensor (ToAD). The El-ISA measures impedance signals from residual detection antibodies after sandwich assays and thus offers highly specific, label-free detection of the N protein with low cross-reactivity. The ToAD sensor enables the real-time electrochemical detection of multiple samples in conventional 96-well plates. The limit of detection for the N protein was 0.1 ng/mL with a detection range up to 10 ng/mL. This system did not detect signals for the S protein. While this study focused on detecting the N protein in SARS-CoV-2, our system can also be widely applicable to detecting various biomolecules involved in antigen–antibody interactions.

In Situ Single-Cell Stimulation and Real-Time Electrochemical Detection of Lactate Response Using a Microfluidic Probe.

Metabolism of a single cell, even within the same organization, differs from other cells by orders of magnitude. Single-cell analysis provides key information for early diagnosis of cancer as well as drug screening. Any slight change in the microenvironment may affect the state of a single cell. Timely and effective cell monitoring is conducive to better understand the behavior of single cells. The immediate response of a single cell described in this study is a liquid transfer-based approach for real-time electrochemical detection. The cell was in situ stimulated by continuous flow with glucose, and lactate secreted from the cell would diffuse into the microflow. The microflow was aspirated into the detection channel where lactate was then decomposed by coupled enzyme reactions and detected by an electrode. This work provides a novel approach for detecting lactate response from a single cell by noninvasive measurements, and the position resolution of the microfluidic probe reaches the level of a single cell and permits individual heterogeneity in cells to be explored in the diagnosis and treatment of cancer as well as in many other situations.

A metal-organic framework with multienzyme activity as a biosensing platform for real-time electrochemical detection of nitric oxide and hydrogen peroxide.

A Metal-Organic Framework (MOFs) with large surface area, exposed active site, excellent catalytic performance and high chemical stability has been used as an artificial enzyme and designed for nonenzymatic electrochemical sensors. Here, a strategy of using an enhanced electrochemical sensing platform for the detection of nitic oxide (NO) and hydrogen peroxide (H2O2) was designed via a nano-metalloporphyrinic metal-organic framework (NporMOF(Fe)) as an electrode material. By taking advantage of the small size, high surface area and exposed Fe active site, the obtained NporMOF(Fe) displays excellent electrocatalytic activity toward NO and H2O2. The NporMOF(Fe) modified electrode shows high sensing ability toward the in situ generated NO in NO2- containing phosphate buffer (PB) solution with a wide linear detection range of 5 μM to 200 μM and a very low detection limit of 1.3 μM. Moreover, NporMOF(Fe) exhibits high electrocatalytic activity toward the reduction of H2O2 and the practical detection of H2O2 released from HeLa cells. Furthermore, the NporMOF(Fe) modified electrode shows excellent selectivity toward the detection of NO and H2O2 in the presence of other physiologically important analytes. This method shows excellent biosensing performance, implying the universal applicability of MOFs-based artificial nanozymes for biosensors and the potential application for third generation biosensors.

Ultra-sensitive and label-free neutrophil gelatinase-associated lipocalin electrochemical sensor using gold nanoparticles decorated 3D Graphene foam towards acute kidney injury detection

In this work, an ultra-sensitive and highly-specific electrochemical immunosensor was developed based on three-dimensional graphene/nickel foam (GF) decorated with gold nanoparticles (AuNPs) for the detection of Neutrophil Gelatinase-Associated Lipocalin (NGAL), a biomarker of Acute Kidney Injury (AKI). A low NGAL limit of detection (LOD) of 42 pg/ml and a linear range (LR) of 0.05–210 ng/ml were achieved. Though several electrode platforms have been proposed, either LOD or LR are limited for each method. Our platform can achieve low LOD while keeping broad LR of sensing. Self-Assembled-Monolayer (SAM) and 11-mercaptoundecanoic acid (11-MUA) were used to assist antibody binding on AuNPs. Electrochemical determination of NGAL were conducted using cyclic voltammetry and chronoamperometry on ferri/ferrocyanide redox measurement. Specificity was tested for NGAL detection against uric acid and creatinine interference. The attained performances might be ascribed to large specific surface area of GF and AuNPs, improved electron transfer from analyte via graphene‑nickel‑gold electric dipole enhancement. The results demonstrated the proposed platform was potential for ultra-sensitive, highly specific, non-invasive and real-time electrochemical detection of NGAL.

Thickness dependence of nanocrystalline tin oxide thin films in capacitive biosensor characterization

Nanocrystalline SnO2 thin films of varying thicknesses (250–50 nm) have been prepared on p-type Si by Langmuir Blodgett technique. Nanocrystalline SnO2/polyaniline (Si/SnO2/PANI) thin film heterostructure has been studied for label free, real time electrochemical detection for model immunoglobulin interactions. Sensor responses were studied using impedance methods, wherein transient capacitance gave fast response for antigen-antibody interaction in picomolar concentration range. From the study of sensor structures with varying film thicknesses, it was observed that SnO2 film with less than 200 nm thickness were effected with insulating (dielectric) properties whereas for thickness higher than 200 nm, it was n-type semiconducting characteristics. This is due to effects of charge on the surface adsorbed species as revealed by capacitance voltage characteristics, suggesting these characteristics as indicators of ionic transport effects in nanostructured metal oxide films in electrochemical cell configuration. The current study clearly states the possibility of fabricating cost effective and stable capacitive sensors with SnO2 films with thickness less than 100 nm. The study helps in optimizing the sensing method for capacitive/conductive biosensors based on nanostructured semiconductor thin films.

Semi-Interpenetrated Hydrogels-Microfibers Electroactive Assemblies for Release and Real-Time Monitoring of Drugs.

Simultaneous drug release and monitoring using a single polymeric platform represents a significant advance in the utilization of biomaterials for therapeutic use. Tracking drug release by real-time electrochemical detection using the same platform is a simple way to guide the dosage of the drug, improve the desired therapeutic effect, and reduce the adverse side effects. The platform developed in this work takes advantage of the flexibility and loading capacity of hydrogels, the mechanical strength of microfibers, and the capacity of conducting polymers to detect the redox properties of drugs. The engineered platform is prepared by assembling two spin-coated layers of poly-γ-glutamic acid hydrogel, loaded with poly(3,4-ethylenedioxythiophene) (PEDOT) microparticles, and separated by a electrospun layer of poly-ε-caprolactone microfibers. Loaded PEDOT microparticles are used as reaction nuclei for the polymerization of poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PHMeDOT), that semi-interpenetrate the whole three layered system while forming a dense network of electrical conduction paths. After demonstrating its properties, the platform is loaded with levofloxacin and its release monitored externally by UV-vis spectroscopy and in situ by using the PHMeDOT network. In situ real-time electrochemical monitoring of the drug release from the engineered platform holds great promise for the development of multi-functional devices for advanced biomedical applications.

Real-Time Electrochemical Detection of Uric Acid, Dopamine and Ascorbic Acid by Heme Directly Modified Carbon Electrode.

Several simple electrochemical sensors were designed for three analytes, uric acid (UA), dopamine (DA) and ascorbic acid (AA) detection via electrolytic deposition of three functional materials heme, Fc(Cys)₂ and Fc-ECG onto glassy carbon electrodes (GCEs) without other medium. Characterization of the modified GCEs was conducted using SEM, TEM and DPV methods. Results showed that the heme/GCE demonstrated notable electro-catalytic capabilities, towards DA, AA, and UA oxidation in a solution of phosphate buffer. The current signals of DPV technique for three analytes shown up three defined oxidated peaks, the peak potential differences was 192 mV for AA and DA, and 142 mV for DA and UA. Under optimal conditions, it can be obtained linear responses for AA, DA and UA in the following concentration ranges: 10 to 50, 5 to 20, and 2.5 to 20 μmol·L-1, and the limits of detection was calculated as 0.76, 0.50 and 0.63 μmol·L-1, respectively. The results demonstrated that the heme directly modified GCE was a well-suited electrochemical sensor for determining UA, DA and AA in actual samples.

Modular, Lightweight, Wireless Potentiostat-on-a-Disc for Electrochemical Detection in Centrifugal Microfluidics.

Interfacing electrochemical sensors in a lab-on-a-disc (LoD) system with a potentiostat is often tedious and challenging. We here present the first multichannel, modular, lightweight, and wirelessly powered, custom-built potentiostat-on-a-disc (PoD) for centrifugal microfluidic applications. The developed potentiostat is in the form factor of a typical digital video disc (DVD) and weighs only 127 g. The design of the potentiostat facilitates easy and robust interfacing with the electrodes in the LoD system, while enabling real-time electrochemical detection during rotation. The device can perform different electroanalytical techniques such as cyclic voltammetry, square wave voltammetry, and amperometry while being controlled by custom-made software. Measurements were conducted with and without rotation using both in-house fabricated and commercial electrodes. The performance of the PoD was in good agreement with the results obtained using a commercial potentiostat with a measured current resolution of 200 pA. As a proof of concept, we performed a real-time release study of an electrochemically active compound from microdevices used for drug delivery.

A fully integrated passive microfluidic Lab-on-a-Chip for real-time electrochemical detection of ammonium: Sewage applications

The present work reports on the development of a new generation of Lab-on-a-chip (LOC) to perform in-situ and real-time potentiometric measurements in flowing water. The device consisted of two differentiated parts: a poly (dimethylsiloxane) (PDMS) microfluidic structure obtained by soft lithography and a fully integrated chemical sensing platform including four working microelectrodes, two reference microelectrodes and one counter microelectrode for detecting ammonium in a continuous mode. The performance of the device was evaluated following its potentiometric response when analyzing ammonium containing samples. As a key parameter, its time of response was compared to that of a commercially available electrical conductivity sensor used as reference sensor during tests in laboratory using flowing tap water and technical scale using flowing wastewater. As a result, the LOC showed a slope of 55 mV/decade, a limit of detection of 4·10−5 M and a time of full response between 10 and 12 s. It was demonstrated that the device can provide fast and reliable data at real time when immersed in a laminar flow of water. Moreover, the test of robustness showed that it was still functional after immersion in sewage for at least 15 min. Besides, the LOC reported here can be helpful for a wide variety of flowing-water applications such as aqua culture outlets control, in-situ and continuous analysis of rivers effluents and sea waters monitoring among others.

A novel voltammetric approach for real-time electrochemical detection of targeted nucleic acid sequences using LAMP

We have developed a novel voltammetric DNA chip for real-time electrochemical detection of targeted nucleic acid sequences using loop-mediated isothermal amplification (LAMP) and ruthenium hexaamine (RuHex) as the intercalative redox compound. A GspSSD DNA polymerase was used for LAMP owing to its tolerance of the intercalative redox compound. The electrochemical reaction of 1 mM RuHex in the LAMP solution was measured continuously by linear sweep voltammetry at 65 °C using an electrochemical DNA chip. According to the LAMP reaction of the positive sample, the cathodic peak current of RuHex increased and the cathodic peak potential of RuHex shifted to negative voltage. The initial number of copies of the targeted nucleic acid was correlated with both the time when the cathodic current began to increase and the time when the cathodic potential began to shift rapidly. 103 to 106 copies/50 μL of the targeted nucleic acid were detected quantitatively and the detection limit was 101 copies within an hour. We expect these results to lead to the realization of simple and stable electrochemical real-time monitoring of targeted nucleic acids while also facilitating the implementation of electrochemical DNA chips in molecular testing.

Biochip for Real-Time Monitoring of Hepatitis B Virus (HBV) by Combined Loop-Mediated Isothermal Amplification and Solution-Phase Electrochemical Detection

Accurate in situ diagnostic tests play a key role in patient management and control of most infectious diseases. To achieve this, use of handheld biochips that implement sample handling, sample analysis, and result readout together is an ideal approach. We present herein a fluid-handling biochip for real-time electrochemical monitoring of nucleic acid amplification based on loop-mediated isothermal amplification and real-time electrochemical detection on a microfluidic platform. Intercalation between amplifying DNA and free redox probe in solution phase was used to monitor the number of DNA copies. The whole diagnostic process is completed within 70 min. Our platform offers a fast and easy tool for quantification of viral pathogens in shorter time and with limited risk of all potential forms of cross-contamination. Such diagnostic tools have potential to make a huge difference to the lives of millions of people worldwide.