Nitrogen-doped carbon nanodots prepared from polyethylenimine for fluorometric determination of salivary uric acid

A novel route for fabrication of yellow emissive carbon dots for selective and sensitive detection of vitamin B12

This study pioneers a sustainable strategy for synthesizing yellow-emissive carbon dots (Y-CDs) using expired rabeprazole sodium tablets, thereby transforming pharmaceutical waste into valuable nanomaterials. The as-prepared Y-CDs displayed a high quantum yield of 48.89%, strong photostability, and pronounced environmental resilience. These attributes establish their potential as reliable fluorometric probes. The fluorescence of Y-CDs was effectively quenched by vitamin B12 through a dual mechanism involving the inner-filter effect (IFE) and static quenching. Under optimized conditions, the fluorescence intensity ratio (F0/F) showed excellent linearity in the range of 0-300 μM and achieved a detection limit of 8.0 nM (S/N = 3). The developed method demonstrated high accuracy (recoveries of 96.8-105.9%) for pharmaceutical formulations. Beyond its analytical merits, this work introduces a green nanotechnology route that addresses pharmaceutical waste management by converting expired drugs into efficient, multifunctional nanomaterials.

Non-enzymatic Detection of Uric Acid in Serum and Urine by Fluorescent and Visual Dual-Mode Sensor Based on 3-aminophenylboric Acid Functionalized Carbon Dots

Herein, we developed a sophisticated dual-mode sensor that utilized 3-aminophenylboric acid functionalized carbon dots (APBA-CDs) to accurately detect uric acid (UA). Our innovative process involved synthesizing APBA-CDs that emitted at 369 nm using a one-step hydrothermal method with 3-aminophenylboric acid and L-glutamine as precursors, ethanol and deionized water as solvents. Once UA was introduced to the APBA-CDs, the fluorescence of the system became visibly quenched. The results of Zeta potential, Fourier transformed infrared (FTIR) spectra, fluorescence lifetime, and other characteristics were analyzed to determine that the reaction mechanism was static quenching. This meant that after UA was mixed with APBA-CDs, it combined with the boric acid function on the surface to form complexes, resulting in a decrease in fluorescence intensity and a blue shift in the absorption peak at about 295 nm in the Ultraviolet-visible (UV-vis) absorption spectra. We were pleased to report that we have successfully used the dual-reading platform to accurately detect UA in serum and human urine. It provided a superior quantitative and visual analysis of UA without the involvement of enzymes. We firmly believe that our innovative dual-mode sensor has immense potential in the fields of biosensing and health monitoring.

Synergistic enhancement of fluorescein-K3[Fe(CN)6] CL by MoO3-x NPs for sensitive and noninvasive detection of uric acid in saliva

MoO3-x NPs was rapidly synthesized at room temperature by an easy stirring method. It was interesting to find that MoO3-x NPs induce OH- to generate active free radicals (ROS), which is a highly promising property in chemiluminescence (CL). Benefiting from the abundant oxygen vacancy, MoO3-x NPs adsorbs H2O2 and turn it into ·OH. The oxidase activity of fluorescein under visible light had already been reported, which catalyzes dissolved oxygen to become O2-· and continue to convert to H2O2. By creating the synergy effect with fluorescein, MoO3-x NPs strengthen the CL intensity of K3[Fe(CN)6]-fluorescein system significantly. Utilizing the quench effect of uric acid for the CL intensity, we developed a rapid, simple, and highly sensitive CL platform for uric acid detection. The linear range was 5-80 µM and the detection limit (LOD) for uric acid was 3.11 µM (S/N = 3). This work expanded the application of MoO3-x NPs in the CL field and developed a simple and highly sensitive CL sensing system to detect UA in human saliva.

Rapid and sensitive determination of Piroxicam by N-doped carbon dots prepared by plant soot

Piroxicam (PX) as a nonsteroidal anti-inflammatory drug (NSAID) can be effectively used for anti-inflammatory and analgesia. However, overdoses may induce side effects such as gastrointestinal ulcers and headaches. Therefore, the assay of piroxicam has considerable significance. In this work, nitrogen-doped carbon dots (N-CDs) was synthesized for PX detection. The fluorescence sensor was fabricated by hydrothermal method with plant soot and ethylenediamine. The strategy exhibited a detection range of 6-200 μg/mL and 250-700 μg/mL with the limited detection of 2 μg/mL. The mechanism of the PX assay base on the fluorescence sensor was the process of electron transfer between the PX and N-CDs. The assay subsequently demonstrated could be successfully used in actual sample. The results indicated that the N-CDs could be a superior candidate nanomaterial for piroxicam monitoring in the healthcare product industry.

Purine Metabolism Dysfunctions: Experimental Methods of Detection and Diagnostic Potential

Purines, such as adenine and guanine, perform several important functions in the cell. They are found in nucleic acids; are structural components of some coenzymes, including NADH and coenzyme A; and have a crucial role in the modulation of energy metabolism and signal transduction. Moreover, purines have been shown to play an important role in the physiology of platelets, muscles, and neurotransmission. All cells require a balanced number of purines for growth, proliferation, and survival. Under physiological conditions, enzymes involved in purines metabolism maintain a balanced ratio between their synthesis and degradation in the cell. In humans, the final product of purine catabolism is uric acid, while most other mammals possess the enzyme uricase that converts uric acid to allantoin, which can be easily eliminated with urine. During the last decades, hyperuricemia has been associated with a number of human extra-articular diseases (in particular, the cardiovascular ones) and their clinical severity. In this review, we go through the methods of investigation of purine metabolism dysfunctions, looking at the functionality of xanthine oxidoreductase and the formation of catabolites in urine and saliva. Finally, we discuss how these molecules can be used as markers of oxidative stress.

A cloth-based single-working-electrode electrochemiluminescence sensor for simultaneous detection of diabetes complication markers

As one of the most common noninfectious diseases, diabetes and diabetic complications (DDC) have attracted great attention in the field of life and health. However, simultaneous detection of DDC markers usually requires labor- and time-consuming steps. Here, a novel cloth-based single-working-electrode electrochemiluminescence (SWE-ECL) sensor was designed for the simultaneous detection of multiple DDC markers. For this sensor, three independent ECL cells are distributed on the SWE, which is a simplification of the configuration of traditional sensors for simultaneous detection. In this way, the modification processes and ECL reactions occur at the back of the SWE, eliminating the adverse effects caused by human intervention on the electrode. Under optimized conditions, glucose, uric acid and lactate were determined, with corresponding linear dynamic ranges of 80-4000 μM, 45-1200 μM and 60-2000 μM, and detection limits of 54.79 μM, 23.95 μM and 25.82 μM, respectively. In addition, the cloth-based SWE-ECL sensor exhibited good specificity and satisfactory reproducibility, and its actual application potential was verified by measuring complex human serum samples. Overall, this work developed a simple, sensitive, low-cost and rapid method for the simultaneous quantitative determination of multiple markers related to DDC and demonstrated a new route for multiple-marker detection.

Tuning the photoluminescence by engineering surface states/size of S, N co-doped carbon dots for cellular imaging applications

In this research, we have synthesized carbon dots (CDs) co-doped with nitrogen and sulfur by facile hydrothermal method, using citric acid and cysteine as carbon source. The effect of solid-state thermic treatment (STT) at 303-453 K on the size, surface, fluorescence and cellular cytotoxicity of the CDs were systematically investigated. Through a simple STT, it was possible to tune surface states and the average size of the CDs, causing a permanent red shift. Initially, CDs showed a decrease in cell viability with increasing concentration. However, after STT, its viability remained constant with an increase in concentration. Here, we show the possibility to label the cells cytoplasm according to the CDs fluorescence emission before (blue emission) and after STT (red emission). The CDs studied in this paper show selective luminescence properties, which are fundamental for any cell imaging application.

Fabrication of nitrogen-enriched carbon dots with green fluorescence for enzyme-free detection of uric acid

Based on the fact that UA directly quenched the green fluorescence of NCDs prepared at RT, a non-invasive sensor was developed.

Enzyme-free fluorescence determination of uric acid and trace Hg(II) in serum using Si/N doped carbon dots

A new fluorescence probe method for the detection of Hg(II) in serum was established, which has the detection limit of 3.57 nM and quantification limit of 5 nM, based on the electrostatic induced agglomeration quenching and complexation between Hg(II) and silicon-nitrogen-doped carbon nanodots (Si/N-CDs). Furthermore, the fluorescence probe also showed the satisfactory results in the determination of Hg(II) in human serum. Subsequently, take advantage of the uric acid (UA) to recover the fluorescence of the Si/N-CDs-Hg(II) complex probe, another enzyme-free ways to determine UA was developed. The complex probe can selectively detect the UA content in the 0.5-30 μM range, and its detection limit can reach 0.14 μM, which has successfully detected the UA in total serum, and the results were no significant difference comparing with the controls.

Developing Activated Carbon Veil Electrode for Sensing Salivary Uric Acid

The paper describes the development of a carbon veil-based electrode (CVE) for determining uric acid (UA) in saliva. The electrode was manufactured by lamination technology, electrochemically activated and used as a highly sensitive voltammetric sensor (CVEact). Potentiostatic polarization of the electrode at 2.0 V in H2SO4 solution resulted in a higher number of oxygen and nitrogen-containing groups on the electrode surface; lower charge transfer resistance; a 1.5 times increase in the effective surface area and a decrease in the UA oxidation potential by over 0.4 V, compared with the non-activated CVE, which was confirmed by energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, chronoamperometry and linear sweep voltammetry. The developed sensor is characterized by a low detection limit of 0.05 µM and a wide linear range (0.09-700 µM). The results suggest that the sensor has perspective applications for quick determination of UA in artificial and human saliva. RSD does not exceed 3.9%, and recovery is 96-105%. UA makes a significant contribution to the antioxidant activity (AOA) of saliva (≈60%). In addition to its high analytical characteristics, the important advantages of the proposed CVEact are the simple, scalable, and cost-effective manufacturing technology and the absence of additional complex and time-consuming modification operations.

Novel LC-MS-TOF method to detect and quantify ascorbic and uric acid simultaneously in different biological matrices

Ascorbic acid (AA) and uric acid (UA) are known as two of the major antioxidants in biological fluids. We report a novel liquid chromatography-mass spectrometry with time-of-flight (LC-MS-TOF) method for the simultaneous quantification of ascorbic and uric acids using MPA, antioxidant solution and acetonitrile as a protein precipitating agent. Both compounds were separated from interferences using a reverse phase C18 column with water and acetonitrile gradient elution (both with formic acid) and identified and quantified by MS in the negative ESI mode. Isotope labeled internal standards were also added to ensure the accuracy of the measures. The method was validated for exhaled breath condensate (EBC), nasal lavage (NL) and plasma samples by assessing selectivity, linearity, accuracy and precision, recovery and matrix effect and stability. Sample volumes below 250 µL were used and linear ranges were determined between 1 - 25 and 1 - 40 µg/mL for ascorbic and uric acid, respectively, for plasma samples, and between 0.05 - 5 (AA) and 0.05 - 7.5 (UA) µg/mL for EBC and NL samples. The new method was successfully applied to real samples from subjects that provided each of the studied matrices. Results showed higher amounts determined in plasma samples, with similar profiles for AA and UA in EBC and NL but at much lower concentrations.

Label-free detection of creatinine using nitrogen-passivated fluorescent carbon dots

In the field of biochemistry and biosensing, the passivation of carbon dots using nitrogen dopants has attracted great attention, as this can control their photoluminescence (PL) properties and quantum yield. To date, in the fabrication of a sensing probe, the impact of the chemical composition of the passivating molecule remained unexplored. In this work, we chose a series of different nitrogen-rich precursors (such as urea, thiourea, cysteine, and glycine) and ascorbic acid to synthesize nitrogen-doped carbon dots (NCDs). A significant change in their surface states was obtained due to the evolution of variable contents of amino, pyridinic and pyrrolic nitrogen species, which is evident from X-ray photoelectron spectroscopy, and this leads to an increment in their PL quantum yields (PLQY ∼ 58%) and average lifetime values. Spectroscopic analysis revealed that a rise in the ratio of pyrrolic : amino groups on the surface of carbon dots cause a bathochromic shift and generate excitation-dependent properties of NCDs. Besides, these NCDs were used as fluorescence off–on sensing probes, where a PA-infested NCD solution was used to detect creatinine. Chiefly, fluorescence restoration was achieved due to the formation of Jaffe chromogen between creatinine and PA. However, all nitrogen-passivated carbon dot surfaces do not respond similarly towards creatinine and only non-amino-rich NCDs exhibit the maximum (50%) PL turn-on response. The PL turn-off–on methodology showed a satisfactory good linearity range between 0 and 150 μM with a detection limit of 0.021 nM for creatinine. Three input molecular logic gates were also designed based on the turn-off–on response of the NCDs@PA towards creatinine. Additionally, for analytical method validation, real-sample analysis was performed for creatinine, which showed good recoveries (93–102%) and verified that nitrogen passivation tailored the physicochemical properties and enhanced the sensing ability.

The role of passivation in CDs using different nitrogen precursors to evaluate its sensing proficiency towards creatinine quantification.

"Turn-on" fluorometric probe for α-glucosidase activity using red fluorescent carbon dots and 3,3',5,5'-tetramethylbenzidine

A turn-on method for determining α-glucosidase activity is described using a chemical redox strategy in which the fluorescence of red fluorescent carbon dots (CDs) is modulated. The red fluorescent CDs were prepared using a solvothermal method with p-phenylenediamine and sodium citrate. The excitation and emission maxima of the CDs were 490 and 618 nm, respectively. Ce⁴⁺ ions catalyze the oxidation of the colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) to give a blue oxidized TMB product (oxTMB). Absorption by oxTMB overlaps with the red light emitted by the CDs because of the fluorescence inner filter effect; therefore the presence of oxTMB decreases the intensity of fluorescence emission by the CDs. However, hydrolysis of L-ascorbic acid-2-O-α-D-glucopyranosyl by the enzyme α-glucosidase causes formation of ascorbic acid . Ascorbic acid reduces oxTMB to TMB, so that the inner filter effect disappeared and the fluorescence recovered. The strategy allows α-glucosidase activity to be successfully determined down to 0.02 U mL^-1 and gives a dynamic linear range of 0-5.5 U mL^-1. The strategy is very selective for α-glucosidase activity in the presence of potentially interfering substances. The method has been successfully applied to the determination of α-glucosidase activity in spiked human serum samples and gave satisfactory results. Graphical Abstract Schematic of the method used to prepare the carbon dots and the mechanisms involved in determining α-glucosidase activity.