A highly sensitive and selective biosensor based on nitrogen-doped graphene for non-enzymatic detection of uric acid and dopamine at biological pH value

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 (1.390 µA µM-1 cm-2), Tyr (0.126 µA µM-1 cm-2), and PA (0.0841 µA µM-1 cm-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.

Sonoelectrochemical exfoliation of defective black phosphorus nanosheet with black phosphorus quantum dots as a uric acid sensor

To maintain human health, the development of rapid uric acid (UA) sensing is crucial. In this study, defective black phosphorus nanosheets with black phosphorus quantum dots (dBPN/BPQDs) were successfully and rapidly prepared by sonoelectrochemical exfoliation. In this process, the intercalation of phosphate ions into the black phosphorus working electrode was improved by coupling ultrasonic radiation with a high intercalating potential (8 V vs. Ag/AgCl/3M). The dBPN/BPQDs with various vacancies (5-9 defects, 5-7-7-5 defects, and 5-8-5 defect vacancies) exhibited a remarkable mass activity (jm, 1.22 × 10-3 mA μg-1) for uric acid oxidation, which was 5.92 times greater than that of reduced graphene oxide (rGO) (2.06 × 10-4 mA μg-1). In addition, the sensitivity of the dBPN/BPQD UA sensor was 474.2 μA mM-1 cm-2 in the linear analysis range of 0.1-1.3 mM. The sensitivity of the sensor was apparently higher than 67.7 μA mM-1cm-2 for rGO. The data from real sample experiments using serum showed that the dBPN/BPQD catalyst had high recoveries (97.3 %-100.2 %) and low related standard deviation (0.44 %-1.52 %). The dBPN/BPQDs exhibited the potential as an amperometric sensor to detect UA without needing enzymes.

A Review of Electroactive Nanomaterials in the Detection of Nitrogen-Containing Organic Compounds and Future Applications

Electrochemical and impedimetric detection of nitrogen-containing organic compounds (NOCs) in blood, urine, sweat, and saliva is widely used in clinical diagnosis. NOC detection is used to identify illnesses such as chronic kidney disease (CKD), end-stage renal disease (ESRD), cardiovascular complications, diabetes, cancer, and others. In recent years, nanomaterials have shown significant potential in the detection of NOCs using electrochemical and impedimetric sensors. This potential is due to the higher surface area, porous nature, and functional groups of nanomaterials, which can aid in improving the sensing performance with inexpensive, direct, and quick-time processing methods. In this review, we discuss nanomaterials, such as metal oxides, graphene nanostructures, and their nanocomposites, for the detection of NOCs. Notably, researchers have considered nanocomposite-based devices, such as a field effect transistor (FET) and printed electrodes, for the detection of NOCs. In this review, we emphasize the significant importance of electrochemical and impedimetric methods in the detection of NOCs, which typically show higher sensitivity and selectivity. So, these methods will open a new way to make embeddable electrodes for point-of-detection (POD) devices. These devices could be used in the next generation of non-invasive analysis for biomedical and clinical applications. This review also summarizes recent state-of-the-art technology for the development of sensors for on-site monitoring and disease diagnosis at an earlier stage.

Sonoelectrochemical nitrided graphene nanosheets with vacancies and their applications for catalysis and sensing of uric acid oxidation

A sonoelectrochemical method for preparing N-doped defective graphene nanosheets (N/O-dGNs) with point defects and 5-9 or 5-8-5 vacancies and oxygen-containing groups was successfully demonstrated. In this one-pot approach, the N-bonding configuration and N content of N/O-dGNs were finely tuned by the ultrasonic power (192, 320, and 640 W). The N content in atomic percentage (at%) for N/O-dGN (N/O-dGN320W) with point defects and 5-8-5 vacancy prepared at 320 W power was 5.6 at%, greater than 3.0 at% and 2.6 at% for N/O-dGN with point defects and 5-9 vacancies at 192 W and 640 W power (N/O-dGN192W and N/O-dGN640W), respectively. N-bonding sites on N/O-dGN320W were dominantly amine N (2.1 at%) and pyrrolic N (2.4 at%). Additionally, the electrocatalytic activity of N/O-dGN192W, N/O-dGN320W, and N/O-dGN640W was successfully demonstrated for the sequential uric acid (UA) oxidation reaction (UOR), in which N/O-dGN320W displayed a significant mass activity (2.51 A/g). As in the transient catalysis of UOR, N/O-dGN320W with amine N showed 400.8 μA mM-1 cm-2 in sensitivity within a wide linear analysis range (1.5 × 10-2-6 mM) for amperometrically sensing UA. The results of real sample experiments using serum samples further demonstrated the potential of N/O-dGN320W as a non-enzymatic UA sensor.

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

Rational design of mini protein mimicking uricase: Encapsulation in ZIF-8 for uric acid detection

Five mini proteins mimicking uricase comprising 20, 40, 60, 80, and 100 amino acids were designed based on the conserved active site residues within the same dimer, using the crystal structure of tetrameric uricase from Arthrobacter globiformis (PDB ID: 2yzb) as a template. Based on molecular docking analysis, the smallest mini protein, mp20, shared similar residues to that of native uricase that formed hydrogen bonds with uric acid and was chosen for further studies. Although purified recombinant mp20 did not exhibit uricase activity, it showed specific binding towards uric acid and evinced excellent thermotolerance and structural stability at temperatures ranging from 10°C to 100°C, emulating its natural origin. To explore the potential of mp20 as a bioreceptor in uric acid sensing, mp20 was encapsulated within zeolitic imidazolate framework-8 (mp20@ZIF-8) followed by the modification on rGO-screen printed electrode (rGO/SPCE) to maintain the structural stability. An irreversible anodic peak and increased semicircular arcs of the Nyquist plot with an increase of the analyte concentrations were observed by utilizing cyclic voltammetry and electrochemical impedance spectroscopy (EIS), suggesting the detection of uric acid occurred, which is based on substrate-mp20 interaction.

Optimization of the Urea Removal in a Wearable Dialysis Device Using Nitrogen-Doped and Phosphorus-Doped Graphene

Dialysis has been recognized as an essential treatment for end-stage renal disease (ESRD). This therapy, however, suffers from several limitations leading to numerous complications in the patients. As dialysis cannot completely substitute healthy kidney functions, the health condition of an ESRD patient is ultimately affected. Wearable artificial kidney (WAK) can resolve the restrictions of blood purification by the dialysis method. However, absorbing large amounts of urea produced in the body is one of the main challenges of these WAK and overcoming this is necessary to improve both functionality and footprint of the device. This study investigates the adsorption capabilities of N- and P-doped graphene nanosorbents for the first time by using molecular dynamic simulation. Urea removal on carbon nanosheets was simulated with different percentages of phosphorus and nitrogen dopants along with the pristine graphene. Specifically, the effects of interaction energy, adsorption percentage, gyration radius, hydrogen bonding, and other molecular dynamic analyses on urea removal were also investigated. The results from this study match well with the existing research, demonstrating the accuracy of the model. The results further suggest that graphene nanosheets doped by 10% nitrogen are likely the most effective in removing urea given that it is associated with the maximum radial distribution function (RDF), the maximum reduction in gyration radius, a high number of hydrogen bonds, and the most negative adsorption energy. This molecular study offers attractive suggestions for the novel adsorbents of artificial kidney devices and paves the way for the development of novel and enhanced urea adsorbents.

Fluorescent Carbon Dots Prepared from Hazelnut Kohl as an Affordable Probe for Determination of Dopamine

In this investigation, a simple, green and facile fluorescence mrtod using carbon dots (CDs) of hazelnut kohl is described for selective detection of dopamine (DA). The sensing system is based on hazelnut kohl (the black soot of kohl) which is used as a carbon source. Generally, kohl is a traditional eye cosmetic that used in different parts of the world and synthesized by the combustion process like burning natural materials. Here, it has been proven that black soot (kohl) obtained from hazelnut has a carbon dot structure and can be used for sensory applications. Some characterization methods are carried out to reveal the kohl structure. Also, the photoluminescence properties of the prepared CDs of kohl are investigated. It is found that the size of CDs is 2-4 nm. Besides, under the optimal conditions, the fluorescence of CDs is used for DA determination. CDs fluorescence intensity is decreased linearly with the increase of DA concentration. By using the fluorescence dependency toward the DA concentration, DA can be determined in the range 0.5-30 μM with the limit of detection of 0.30 μM. Finally, this method is successfully applied to discriminate the DA in the real samples (healthy human serum and cerebrospinal fluid (CSF)) which shows acceptable efficiently for diagnostic purposes. The fluorescence of carbon dots, prepared from Hazelnut Kohl, is quenched in the presence of dopamine.

α-MoO3 nanostructure on carbon cloth substrate for dopamine detection

Orthorhombic molybdenum oxide (α-MoO₃) nanostructures were deposited on the surface of carbon cloth (CC) as a flexible and high conductive scaffold by reactive RF magnetron sputtering technique. Structure and morphology of the as prepared molybdenum coated carbon cloth (MoO₃CC) were thoroughly characterized with field emission scanning electron microscopy, x-ray diffraction, energy dispersive x-ray and Raman spectroscopy. Benefiting from high surface area and superior conductivity of CC as well as electrocatalytic activity of α-MoO₃ nanostructures, an electrochemical sensor was fabricated. The electrochemical behavior of this new sensor toward determination of dopamine was studied in detail by cyclic voltammetry, amperometry (AM) and square wave voltammetry (SWV). Results reported here reveal that using SWV not only enhances the sensitivity of sensors to dopamine by more than 14 times compared to AM, but also offers higher linear dynamic range (1-700 μM compared to 5-550 μM). Limit of detection, for signal to noise ratio 3, was calculated to be 0.48 μM. Applicability of the proposed sensor for measurement of dopamine in real samples, like urine and pharmaceutical formulation, was also evaluated that concluded to satisfactory results.