Perspective-Advances in Voltammetric Methods for the Measurement of Biomolecules

Electrochemical detection of creatinine at picomolar scale with an extended linear dynamic range in human body fluids for diagnosis of kidney dysfunction

BACKGROUND

Creatinine levels in different body fluids can serve as an important biomarker for kidney functioning relevant to prostate cancer and chronic kidney disease (CKD). Creatinine levels vary in concentration in different body fluids, such as blood, urine, and saliva. Unlike previously reported sensors, the developed creatinine sensor can be employed for all levels of creatinine in samples of real patients.

RESULTS

In this study, an efficient voltammetric sensor for creatinine is developed by modifying a glassy carbon electrode (GCE) with poly (ethyleneimine) (PEI) capped silver nanoparticles at titanium dioxide (PEI-AgNPs)/TiO2, i.e., titanium dioxide (TiO2)/graphene oxide (GO) nanocomposites (Ag@GO/TiO2-GCE). The Ag@GO/TiO2 nanocomposite was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential, Fourier transform infrared (FT-IR) spectroscopy, and UV-Vis spectrophotometry. Various voltammetric techniques namely cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and differential pulse voltammetry (DPV) were employed. The Ag@GO/TiO2-GCE demonstrated good selectivity, stability, and a quick response time of 1.0 s for creatinine. An extended linear dynamic range (LDR) of creatinine from 0.01 pM (DPV) to 1.0 M (CV) based on different voltammetric techniques is imperative for detecting diverse creatinine levels in various body fluids. The LOD and LOQ of the developed creatinine detection method were found to be 1.15 pM and 3.5 pM, respectively. The electrochemical sensor exhibited an exceptionally high sensitivity of 15.74 μApM-1cm-2.The body fluids from healthy volunteers were spiked with a known amount of creatinine to evaluate sensor efficiency in the context of recovery. Finally, blood serum, saliva, and urine samples of kidney patients were analyzed for creatinine levels.

SIGNIFICANCE

An important merit of the developed creatinine sensor is its ability for non-invasive point-of-care diagnosis in saliva with more than 90 % recovery. The comparison of the developed method with the standard Jaffes' colorimetric method endorsed its reliability and extended ability for the samples where Jaffes' method fails. The low LOD, high sensitivity, extended LDR, and low-cost render the possibility of adopting this method for point-of-care diagnosis.

Evolution and recent development of cellulose-modified, nucleic acid-based and green nanosensors for trace heavy metal ion analyses in complex media: A review

With increased manufacturing activities and energy sector development, monitoring of heavy metal ion (HMI) pollution is becoming increasingly pressing. The discharge of metals from industrial effluents into the waterways could cause major economic and environmental disruption. In situ and on-site detection methods of trace HMIs can be effective countermeasures before the toxicity spreads out to larger areas, affecting the ecosystem. Conventional methods are often lacking in portability and costly. In contrast, electrochemical sensing, especially with nanoplatforms, is promising for trace detection of HMIs in complex media because of the ease of fabrication and adaptability of incorporating green technology. Appropriate electrode selection with suitable modifiers is crucial in complex medium analyses to overcome electrode fouling. In this review, the evolution from metal-based and carbon-based electrodes to advancements in electrode modification involving agro/biocomposite nanomaterials (NMs) such as cellulose, chitosan, and hydroxyapatite is discussed. The fabrication of nucleic acid-based aptasensors for analyzing HMIs and the adoption of smart systems based on microfluidics with high selectivity, operational stability, and sensitivity are highlighted. The challenges and future prospects for trace HMI determination based on electrochemical sensors in real complex media, including blood and industrial effluent or wastewater, are critically examined.

A portable and ecological paper-based device for glucose monitoring in peripheral blood mononuclear cell lysates

The increasing need for point-of-care (POC) testing has prompted a rise in the popularity of affordable biosensors that are eco-friendly, especially paper-based electrochemical sensors. This research introduces a biodegradable paper-based enzymatic biosensor for detecting glucose levels in intricate biological samples, such as cell lysates. This biosensor uses Prussian Blue (PB) as a mediator and glucose oxidase to detect glucose with excellent accuracy using direct electrochemical signals. Screen printing using Whatman filter paper produced a better biosensor than other substrates. The PB concentration of 12.5 mmol L-1 was found to be optimal and resulted in an operating potential of -0.1 V, which helped decrease interference from other active substances and improved its selectivity. Calibration was found to be linear up to a concentration of 2 mmol L-1 with a detection limit of 40 μmol L-1 and a limit of quantification of 120 μmol L-1. Moreover, experiments performed on cell lysates obtained from peripheral blood mononuclear cells (PBMCs) suggest the possible application of biosensors to measure glucose levels in vitro in both stimulated and unstimulated cells. This feature underscores its promise for use in monitoring metabolism and conducting diagnostic applications. The paper-based biosensor is an alternative to the current platform for the development of an eco-friendly, portable glucose-sensitive biosensor for point-of-care monitoring of glucose. Its flexibility and efficiency make it a strong candidate for use in the field of POC diagnostics, especially in areas of limited resources and in conditions where there is a problem with glucose dysregulation including diabetes and other related metabolic disorders.

Application of Zeolite-Based Materials for Chemical Sensing of VOCs

Considerable levels of pollution produced by urbanization and industrial development have established a need for monitoring the presence of harmful compounds and the assessment of environmental risks to provide a basis for timely reaction and the prevention of disastrous consequences. Chemical sensors offer a reasonable solution; however, the desired properties, such as high sensitivity, selectivity, stability and reliability, ease of fabrication, and cost-effectiveness, are not always easily met. To this end, the incorporation of zeolites in sensor materials has attracted considerable attention. Such hybrid sensor materials exhibit excellent performances due to the unique properties of zeolites, which have been successfully utilized in gas-sensing applications. In this review, we discuss recent findings in the area of the application of zeolites as sensor materials, focusing on the detection of volatile organic compounds and highlighting the role of zeolite frameworks and the proposed mechanisms in the sensing process. Finally, we consider possible future directions for the development of zeolite-based sensor technology, including the application of hierarchical materials, nanosized zeolites, and 2D material-zeolite heterostructures that would fulfill industrial and environmental demands.

Preparation of Electrochemical Sensors Based on Graphene/Ionic Liquids and the Quantitative Detection and Toxicity Evaluation of Tetracycline

Tetracycline antibiotics, which are recognized as emerging environmental pollutants, are overused and retained in large quantities in terminal water bodies, seriously endangering the ecological environment and human health. Therefore, establishing a straightforward, rapid, and sensitive method for quantitatively detecting and evaluating the toxicity of tetracyclines is highly important. Compared with traditional detection methods, emerging electrochemical methods have many advantages, such as simplicity and rapidity. In this work, an electrochemical sensor-a graphene ionic liquid composite glass carbon electrode (Gr/IL/GCE) with excellent catalytic properties for both tetracycline and cellular purine bases-was prepared by modifying a glassy carbon electrode with graphene and an ionic liquid for the quantitative detection of tetracycline and evaluation of its toxicity to cells. Graphene and the ionic liquid were uniformly distributed on the surface of the electrode and increased the electrically active surface area. The linear range of detection of tetracycline by a Gr/IL/GCE was 10-500 μM, with a detection limit of up to 2.06 μM. The Gr/IL/GCE demonstrated remarkable electrocatalytic efficacy against purine bases within human hepatocellular carcinomas (HepG2) cells. To evaluate the cytotoxicity of tetracycline, the median inhibition concentration (IC50) was determined, which was 243.82 μM.

Fast screening of Milk for Deoxynivalenol

A 2D platform was designed and validated for fast screening of milk for deoxynivalenol. The qualitative and quantitative assay of deoxynivalenol in the milk samples was done using a 2D stochastic sensor based on single walled carbon nanotubes modified with [N-(pyridine-4-yl-methyl)]octadec-9-enamide. The working concentration range was between 10-15 and 10-6 g mL-1, with a sensitivity of 5.48 × 105 s-1g-1mL, and a limit of determination of 1 fg mL-1. Recovery values higher than 99.00 % with RSD values lower than 1.00 % were recorded for the determination of deoxynivalenol in cow's and in the vegetarian (coconut milk, soy milk, almond milk) milk.

The measurement of phenols with graphitic carbon fiber microelectrodes and fast-scan cyclic voltammetry

A phenol contains a six-membered, conjugated, aromatic ring bound to a hydroxyl group. These molecules are important in biomedical studies, aromatic food preparation, and petroleum engineering. Traditionally, phenols have been measured with several analytical techniques such as UV-VIS spectroscopy, fluorescence, liquid chromatography, and mass spectrometry. These assays provide for relatively high sensitivity and selectivity measurements, but they suffer from relatively low spatiotemporal resolution, low biocompatibility, long analysis time, high cost, and complex sample treatment. Recently, electrochemistry has served as a viable alternative to the measurement of phenols. In this study, we utilized carbon fiber microelectrodes (CFMEs) with fast-scan cyclic voltammetry for the sensitive and selective measurement of phenols. We tested four common phenolic compounds: phenol, 2-methylaminophenol (2-MAP), 4-methylaminophenol (4-MAP), and 3-hydroxybenzoic acid (3-HBA). We found that phenol, 2-MAP, 4-MAP, and 3-HBA were all partially adsorption and diffusion controlled to the surface of the CFMEs and that all four molecules could be detected with repeated injections. Structural differences led to varied sensitivities amongst the four phenols, and we were able to co-detect and differentiate the phenols in complex solutions with dopamine and serotonin. Lastly, we measured the phenols in simulated urine with a high percent recovery. These assays demonstrate enhanced electrochemical measurement of phenols, which will create more effective diagnostics for these complex molecules to help elucidate their mechanistic properties and ultimate significance in a biological context.

Decoupling Variable Capacitance and Diffusive Components of Active Solid-Liquid Interfaces with Flex Points

Understanding the current transport characteristics of electrode interfaces is essential for optimizing device performance across a wide range of applications including bio-/chemical sensing and energy storage sectors. Cyclic voltammetry (CV) is a popular method for studying interfacial properties, particularly those involving redox systems. However, it remains challenging to differentiate between electron movements that contribute to capacitive and diffusive behaviors. In this study, we introduce a technique called flex point analysis, which uses a single differentiation step to separate capacitive and diffusive electron movements at the electrode interface during a redox reaction. Our results show that the variable capacitance at the electrode surface exhibited both positive and negative values on the order of 10-6 (micro) Farad. This approach provides a clearer understanding of interfacial electron dynamics, enhancing the interpretation of CV data and potentially improving the design and optimization of related materials and devices.