Highly Stable Potentiometric (Bio)Sensor for Urea and Urease Activity Determination

A novel urease-assisted ratiometric fluorescence sensing platform based on pH-modulated copper-quenched near-infrared carbon dots and methyl red-quenched red carbon dots for selective urea monitoring

A novel and sensitive fluorescence ratiometric method is developed for urea detection based  on the pH-sensitive response of two fluorescent carbon dot (CD) systems: R-CDs/methyl red (MR) and NIR-CDs/Cu2+. The sensing mechanism involves breaking down urea using the enzyme urease, releasing ammonia and increasing pH. At higher pH, the fluorescence of NIR-CDs is quenched due to the enhanced interaction with Cu2+, while the fluorescence of R-CDs is restored as the acidic MR converts to its basic form, removing the inner filter effect. The ratiometric signal (F608/F750) of the R-CDs/MR and NIR-CDs/Cu2+ intensities changed in response to the pH induced by urea hydrolysis, enabling selective and sensitive urea detection. Detailed spectroscopic and morphological investigations confirmed the fluorescence probe design and elucidated the sensing mechanism. The method exhibited excellent sensitivity (0.00028 mM LOD) and linearity range (0.001 - 8.0 mM) for urea detection, with successful application in milk samples for monitoring adulteration, demonstrating negligible interference and high recovery levels (96.5% to 101.0%). This ratiometric fluorescence approach offers a robust strategy for selective urea sensing in complicated matrices.

Oyster Pearl-Shaped Ternary Iron Chalcogenide, FeSe0.5Te0.5, Films on FTO through Electrochemical Growth from the Exchange of Chalcogens Boosted the Enzyme-Free Urea-Sensing Ability toward Real Analytes

Here, iron chalcogenide thin films were developed for the first time by using the less hazardous electrodeposition technique at optimized conditions on an FTO glass substrate. The chalcogenides have different surface, morphological, structural, and optical properties, as well as an enzyme-free sensing behavior toward urea. Numerous small crystallites of about ∼20 to 25 nm for FeSe, ∼18 to 25 nm for FeTe, and ∼18 to 22 nm in diameter for FeSeTe are observed with partial agglomeration under an electron microscope, having a mixed phase of tetragonal and orthorhombic structures of FeSe, FeTe, and, FeSeTe, respectively. Profilometry, XRD, FE-SEM, HR-TEM, XPS, EDX, UV-vis spectroscopy, and FT-IR spectroscopy were used for the analysis of binary and ternary composite semiconductors, FeSe, FeTe, and FeSeTe, respectively. Electrochemical experiments were conducted with the chalcogenide thin films and urea as the analyte in phosphate-buffered media at a pH of ∼ 7.4 in the concentration range of 3-413 μM. Cyclic voltammetry was performed to determine the sensitivity of the prepared electrode at an optimized scan rate of 50 mV s-1. The electrodeposited chalcogenide films appeared with a low detection limit and satisfactory sensitivity, of which the ternary chalcogenide film has the lowest LOD of 1.16 μM and the maximum sensitivity of 74.22 μA μM-1 cm-2. The transition metal electrode has a very wide range of detection limit of 1.25-2400 μM with a short response time of 4 s. This fabricated biosensor is capable of exhibiting almost 75% of its starting activity after 2 weeks of storage in the freezer at 4 °C. Simple methods of preparation, a cost-effective process, and adequate electrochemical sensing of urea confirm that the prepared sensor is suitable as an enzyme-free urea sensor and can be utilized for future studies.

Advances in the Use of Conducting Polymers for Healthcare Monitoring

Conducting polymers (CPs) are an innovative class of materials recognized for their high flexibility and biocompatibility, making them an ideal choice for health monitoring applications that require flexibility. They are active in their design. Advances in fabrication technology allow the incorporation of CPs at various levels, by combining diverse CPs monomers with metal particles, 2D materials, carbon nanomaterials, and copolymers through the process of polymerization and mixing. This method produces materials with unique physicochemical properties and is highly customizable. In particular, the development of CPs with expanded surface area and high conductivity has significantly improved the performance of the sensors, providing high sensitivity and flexibility and expanding the range of available options. However, due to the morphological diversity of new materials and thus the variety of characteristics that can be synthesized by combining CPs and other types of functionalities, choosing the right combination for a sensor application is difficult but becomes important. This review focuses on classifying the role of CP and highlights recent advances in sensor design, especially in the field of healthcare monitoring. It also synthesizes the sensing mechanisms and evaluates the performance of CPs on electrochemical surfaces and in the sensor design. Furthermore, the applications that can be revolutionized by CPs will be discussed in detail.

Wearable potentiometric biosensor for analysis of urea in sweat

Herein, we introduce wearable potentiometric biosensors on screen-printed carbon electrodes (SPCEs) for on-body and on-site monitoring of urea in sweat. The biosensor architecture was judiciously designed to detect urea at different pHs and incorporate a pH sensor, thus containing polyaniline ink, urease bioink and a polyvinylchloride membrane. Urea detection could be performed in the wide range from 5 to 200 mM at pH 7.0, encompassing urea levels in human sweat. The biosensor response was fast (incubation time 5 min), with no interference from other substances in sweat. Reliable urea detection could be done in undiluted human sweat with a skin-worn flexible device using the pH correction strategy afforded by the pH sensor. The performance of the epidermal biosensor was not affected by severe bending strains. The feasibility of mass production was demonstrated by fabricating epidermal flexible biosensors using slot-die coating with a roll-to-roll technique.