FeCuS multilayer nanoflowers loaded with N-CDs dual-mode method for the detection of uric acid and gout risk prediction with the aid of chemometrics

Transition metal sulfides have attracted much attention due to their low cost, high stability, adjustable performance, diverse morphology and good catalytic activity. In this work, nitrogen-doped carbon dots (N-CDs) were loaded onto bimetallic sulfides (FeCuS) and FeCuS/N-CDs could act as catalyst and fluorescent probe, which applied to the detection of uric acid (UA) in human blood and urine using dual-model assay (colorimetry and ratiometric fluorescence). The nanozyme has excellent peroxidase-like activity and steady-state kinetic results showed that the material prepared under optimized conditions had better affinity (Km = 0.42 mM) for the substrate and faster reaction rate (Vmax = 14.1 × 10-8 M s-1). •OH and O2•- were involved in the catalytic process of o-phenylenediamine (OPD) by FeCuS/N-CDs nanozymes. A profound discussion and quantitative analysis about the sensing mechanism of UA and fluorescence quenching mechanism between FeCuS/N-CDs and diaminophenazine (DAP) was performed. According to Parker equation, the inhibition efficiency of DAP in FeCuS/N-CDs was as high as 83 % of the total inhibition efficiency, confirming that the inhibition efficiency mainly came from internal filtering effect (IFE). The detection limits of ratiometric fluorescence method and colorimetric method were as low as 0.13 μM and 0.27 μM, respectively. Finally, principal component analysis was used to successfully distinguish three groups of people (healthy people, potential people and gout patients) and the model has potential value in clinical applications.

In situ fabricated gold nanostars on hydrogel beads as photo-oxidase mimics for rapid and sustainable POCT of uric acid

Synthetic enzyme mimics surpass their natural counterparts in terms of stability, efficiency, and cost-effectiveness, making them highly valuable for catalytic applications. Gold nanomaterials, particularly gold nanostars, have emerged as promising enzyme mimetic nanocatalysts due to their enhanced light interaction and superior catalytic efficiency. In this study, gold nanostars grown in situ on the surface of core-shell hydrogel beads exhibited specific oxidase-like activity when exposed to light. Photoexcitation of gold nanostars generates singlet oxygen through the interaction of positive holes and superoxide radicals, resulting in photo-oxidase-like activity. Attaching the gold nanostars to the hydrogel bead surface prevented catalytic activity loss caused by agglomeration, resulting in a marked improvement in catalytic stability. This stability is evident from the sustained catalytic activity of the hydrogel bead-embedded gold nanostars, even after 60 days of prolonged incubation in an aqueous medium, and their strong catalytic performance across multiple reaction cycles. Leveraging this photo-oxidase-like activity, a point-of-care testing (POCT) setup is developed for highly sensitive uric acid detection. The system achieved a remarkable detection limit of 0.9 μM and demonstrated excellent accuracy in blood serum and urine sample analyses. Furthermore, the integration of smartphone technology facilitated rapid and convenient on-site testing, bridging the gap between laboratory settings and real-world applications. This approach offers a practical and sustainable solution for efficient and accurate uric acid monitoring in diverse settings.

Progress in optical sensors-based uric acid detection

The escalating number of patients affected by various diseases, such as gout, attributed to abnormal uric acid (UA) concentrations in body fluids, has underscored the need for rapid, efficient, highly sensitive, and stable UA detection methods and sensors. Optical sensors have garnered significant attention due to their simplicity, cost-effectiveness, and resistance to electromagnetic interference. Notably, research efforts have been directed towards UA on-site detection, enabling daily monitoring at home and facilitating rapid disease screening in the community. This review aims to systematically categorize and provide detailed descriptions of the notable achievements and emerging technologies in UA optical sensors over the past five years. The review highlights the advantages of each sensor while also identifying their limitations in on-site applications. Furthermore, recent progress in instrumentation and the application of UA on-site detection in body fluids is discussed, along with the existing challenges and prospects for future development. The review serves as an informative resource, offering technical insights and promising directions for future research in the design and application of on-site optical sensors for UA detection.

Enhancing catalytic performance of Fe and Mo co-doped dual single-atom catalysts with dual-enzyme activities for sensitive detection of hydrogen peroxide and uric acid

Single-atom catalysts (SACs) have attracted much attention due to their excellent catalytic activity, but the improvement of atomic loading which means that weight fraction (wt%) of metal atom was still facing great challenges. In this work, iron and molybdenum co-doped dual single-atom catalysts (Fe/Mo DSACs) was prepared for the first time by using the soft template sacrifice strategy, which improved significantly the atomic load and exhibited both the oxidase-like (OXD) activity and the dominant peroxidase-like (POD) activity. Further experiments reveal that Fe/Mo DSACs can not only catalyze O₂ to generate O₂^•- and ¹O₂, but also catalyze H₂O₂ to generate a large number of •OH, which caused 3, 3', 5, 5'-tetramethylbenzidine (TMB) to be oxidized to oxTMB, accompanied by the color changing from colorless to blue. The steady-state kinetic test showed that Michaelis-Menten constant (K_m) values and the maximum initial velocity values (V_max) of the POD activity of Fe/Mo DSACs were 0.0018 mM and 12.6 × 10^-8 M s^-1, respectively. The corresponding catalytic efficiency was tens of times higher than Fe SACs and Mo SACs, which proves that the synergistic effect between Fe and Mo has significantly improved the catalytic ability. Based on the excellent POD activity of Fe/Mo DSACs, a colorimetric sensing platform combined with TMB was proposed to realize the sensitive detection of H₂O₂ and uric acid (UA) in a wide range, with limits of detection as low as 0.13 and 0.18 μM, respectively. Finally, accurate and reliable results were obtained in the detection of H₂O₂ in cells, and of UA in human serum and urine.

Design of Smartphone-Assisted Point-of-Care Platform for Colorimetric Sensing of Uric Acid via Visible Light-Induced Oxidase-Like Activity of Covalent Organic Framework

Monitoring of uric acid (UA) levels in biological samples is of great significance for human health, while the development of a simple and effective method for the precise determination of UA content is still challenging. In the present study, a two-dimensional (2D) imine-linked crystalline pyridine-based covalent organic framework (TpBpy COF) was synthesized using 2,4,6-triformylphloroglucinol (Tp) and [2,2'-bipyridine]-5,5'-diamine (Bpy) as precursors via Schiff-base condensation reactions and was characterized with scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) assays. The as-synthesized TpBpy COF exhibited excellent visible light-induced oxidase-like activity, ascribed to the generation of superoxide radicals (O₂^•-) by photo-generated electron transfer. TpBpy COF could efficiently oxidase the colorless substrate 3,3',5,5'-tetramethylbenzydine (TMB) into blue oxidized TMB (oxTMB) under visible light irradiation. Based on the color fade of the TpBpy COF + TMB system by UA, a colorimetric procedure was developed for UA determination with a detection limit of 1.7 μmol L^-1. Moreover, a smartphone-based sensing platform was also constructed for instrument-free and on-site detection of UA with a sensitive detection limit of 3.1 μmol L^-1. The developed sensing system was adopted for UA determination in human urine and serum samples with satisfactory recoveries (96.6-107.8%), suggesting the potential practical application of the TpBpy COF-based sensor for UA detection in biological samples.

Development of a Nonenzymatic Colorimetric Sensor for the Detection of Uric Acid Based on Ionic Liquid-Mediated Nickel Nanostructures

Uric acid (UA) is a metabolic byproduct of purine nucleotides and is excreted as a urine component. Abnormalities in UA metabolism cause localized inflammation due to crystal deposition and can lead to various diseases. In the current study, we successfully fabricated a biosensor based on 1-H-3-methylimidazolium acetate (ionic liquid, IL)-capped nickel nanoparticles (NiNPs) for the detection of uric acid in test samples. The structures of IL-capped NiNPs and their precursors were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The IL-capped NiNPs possessed intrinsic peroxidase-like properties and displayed selective UA quenching after interacting with 3,3',5,5'-tetramethylbenzidine (TMB) solution. Different parameters such as pH, time, IL, TMB, and UA concentration were optimized to obtain the best results for the proposed sensor. The UA biosensor shows good responses in the linear range from 1 × 10^-8 to 2.40 × 10^-6 M, with a lower limit of detection of 1.30 × 10^-7 M, a limit of quantification of 4.3 × 10^-7 M, and an R ² value of 0.9994. For the colorimetric detection of UA, the proposed sensor gave a short time response of 4 min at room temperature and pH 7.5. The proposed sensing probe detects UA in real serum samples and could be used as a selective sensor for UA in the real sample detection.

AIEgens-based fluorescent covalent organic framework in construction of chemiluminescence resonance energy transfer system for serum uric acid detection

A covalent organic framework (COF) with aggregation-induced emission (AIE) property was successfully synthesized through in situ marriage of a commonly used AIE molecule tetraphenylethylene (TPE) with Schiff base network (SNW-1) through a simple one-pot method. The TPE@SNW-1 was characterized with different techniques of Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and nitrogen adsorption/desorption experiments. The fluorescence of the TPE@SNW-1 strongly depends on the composition of tetrahydrofuran-water binary system. The AIE property of TPE@SNW-1 was directly supported with particle size distribution by dynamic light scattering technique. With the TPE@SNW-1 as an energy acceptor, a chemiluminescence resonance energy transfer (CRET) system was constructed with bis(2,4,6-trichlorophenyl) oxalate (TCPO)-hydrogen peroxide (H₂O₂) reaction as an energy donor. The chemiluminescence (CL) signal displays a good linear relationship with concentration of H₂O₂ in the 5.0-1000.0 μmol·L^-1 range, and a detection limit of 2.34 μmol L^-1. The system was further exploited to determine uric acid based on the fact that equal stoichiometric amount of H₂O₂ can be concurrently generated under the catalysis of uricase. The procedure exhibits a linear response to uric acid concentration in the range 10.0-150.0 μmol·L^-1 and a detection limit of 4.94 μmol·L^-1. The practicability of the method was demonstrated  in the determination of uric acid in human serum samples.

Advanced Colorimetric Paper Sensors Using Color Focusing Effect Based on Asymmetric Flow of Fluid

Although paper-based colorimetric sensors utilizing enzymatic reactions are well suited for real-field diagnosis, their widespread use is hindered by signal blurring at the detection spot due to the action of capillary forces on the liquid and the corresponding membrane. In this study, we eliminated signal losses commonly observed during enzyme-mediated colorimetric sensing and achieved pattern-free quantitative analysis of glucose and uric acid by mixing enzymes and color-forming reagents with chitosan oligosaccharide lactate (COL), which resulted in perfectly focused colorimetric signals at the detection spot, using asymmetric flow induced by changing the flow rate of the COL-treated paper. The targets were calibrated with 0-500 mg/dL of glucose and 0-200 mg/dL of uric acid, and the limit of detection was calculated to be 0.6 and 0.03 mg/dL, respectively. In human urine, the correlation has a high response between the measured and spiked concentrations, and the stability of the enzyme mixture including COL increased by 41% for glucose oxidase mixture and 29% for uricase mixture, compared to the corresponding mixtures without COL. Thus, the color focusing and pattern-free sensor, which have the advantages of easy fabrication, easy handling, and high stability, should be applied to real-field diagnosis.

Recent advances in functionalized MnO2 nanosheets for biosensing and biomedicine applications

As one kind of redox active layered transition-metal dioxide nanomaterials, single-layer manganese dioxide (MnO₂) nanosheets have gained significant research attention in the fields of biosensing and biomedicine because of their large surface area, intense and broad optical absorption, strong oxidation ability, catalytic activity, and robust mechanical properties. This review provides a brief overview of the recent advances in the development of MnO₂ nanosheet-based biosensors, bioimaging as well as drug delivery for cancer therapy. The methodologies for the preparation of MnO₂ nanosheets are summarized, followed by an introduction of the nanostructure and properties of MnO₂ nanosheets. Special attention is paid to their applications in biosensing, bioimaging and cancer therapy. Future perspectives and the challenges of high-performance MnO₂ nanosheets are also discussed.

Highly efficient redox reaction between potassium permanganate and 3,3',5,5'-tetramethylbenzidine for application in hydrogen peroxide based colorimetric assays

Potassium permanganate (KMnO4) is one of the most important oxidants, which plays important roles in many fields. Here, we found that KMnO4 could directly induce the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate an oxidized product with a color change. This redox reaction is highly efficient, and 1 μM KMnO4 is enough to cause detectable changes in the absorbance signal. Meanwhile, this reaction is very fast and the generated blue product can stabilize for a relatively long period, which has great advantages in practical applications. Since hydrogen peroxide (H2O2) is able to react with KMnO4 under acidic conditions, the KMnO4-TMB system can be used for the detection of H2O2; the absorbance signal induced by 5 μM H2O2 can be easily detected in this method. Meanwhile, the KMnO4-TMB system can also be used for the detection of glucose by monitoring the generation of H2O2, which is the main product of glucose oxidation; this method permits detection of concentrations as low as 10 μM glucose, and the sensitivity is comparable to or higher than most peroxidase mimetic based methods, but avoiding the preparation and storage of the nanomaterials. Furthermore, the KMnO4-TMB system can even be used for analyzing glucose in serum samples, which can also be expected to be used in immunoassays.

The catalytic evaluation of bimetallic Pd-based nanocatalysts supported on ion exchange resin in nitro and alkyne reduction reactions

A simple protocol to produce bimetallic Pd-based nanocatalysts supported on Amberlite resin is presented. Superior catalytic activity and selectivity in nitro and alkyne reduction reactions was achieved, opening up new possibilities in the development of cheaper and selective catalysts for these important industrial reactions.

Determination of uric acid in biological samples by high performance liquid chromatography-electrospray ionization-tandem mass spectrometry and study on pathogenesis of pulmonary arterial hypertension in pulmonary artery endothelium cells

Pulmonary arterial hypertension (PAH) is a severe cardiovascular disease that can lead to vascular remodelling and hypertension. Clinical diagnosis of PAH is very difficult. Uric acid (UA) can act as a biological marker for screening of PAH in patients. Multiple studies have indicated that reactive oxygen species (ROS) play an important role in the development of PAH. Thus, it is important to study the relationship between UA and ROS based on the pathogenesis of PAH. For monitoring PAH, a high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) method was developed to measure the concentration of UA from rat models and pulmonary arterial endothelial cells (PAECs) models, which were induced by monocrotaline (MCT) and hypoxia, respectively. In addition, the treatment groups were treated by N-acetyl-l-cysteine (NAC), a ROS scavenger. With the confirmation from hematoxylin-eosin (H&E) staining, the HPLC-ESI-MS/MS method was adopted to successfully analyze the concentration of UA. In this study, for the first time, thymine was used as an internal standard (I.S.) of uric acid. The results showed that the UA concentration in the PAH groups was higher than that in the normal groups, while the UA concentration in the treatment groups decreased compared to that in the PAH group (p < 0.05). It was experimentally proven that the HPLC-ESI-MS/MS method is a rapid, efficient and reliable quantitative method to detect PAH. Furthermore, our results indicated that UA and ROS have a double-regulator role.

A conventional chemical reaction for use in an unconventional assay: A colorimetric immunoassay for aflatoxin B1 by using enzyme-responsive just-in-time generation of a MnO2 based nanocatalyst

The authors describe a colorimetric immunoassay for the model nalyte aflatoxin B₁ (AFB₁). It is based on the just-in-time generation of an MnO₂ nanocatalyst. Unlike previously developed immunoassay, the chromogenic reaction relies on the just-in-time formation of an oxidase mimic without the aid of the substrate. Potassium permanganate (KMnO₄) is converted into manganese dioxide (MnO₂) which acts as an oxidase mimic that catalyzes the oxidation 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen to give a blue colored product. In the presence of ascorbic acid (AA), KMnO₄ is reduced to Mn(II) ions. This results in a decrease in the amount of MnO₂ nanocatalyst. Hence, the oxidation of TMB does not take place. By adding ascorbate oxidase, AA is converted into dehydroascorbic acid which cannot reduce KMnO₄. Based on these observations, a colorimetric competitive enzyme immunoassay was developed where ascorbate oxidase and gold nanoparticle-labeled antibody against AFB₁ and magnetic beads carrying bovine serum albumin conjugated to AFB₁ are used for the determination of AFB₁. In presence of AFB₁, it will compete with the BSA-conjugated AFB₁ (on the magnetic beads) for the labeled antibody against AFB₁ on the gold nanoparticles. This makes the amount of ascorbate oxidase/anti-AFB₁ antibody-labeled gold nanoparticles, which conjugated on magnetic beads, reduce, and resulted in an increase of ascorbic acid. Under optimal conditions, the absorbance (measured at 652 nm) decreases with increasing AFB₁ concentrations in the range from 0.1 to 100 ng mL^-1, with a 0.1 ng mL^-1 detection limit (at the 3S_blank level). The accuracy of the assay was validated by analyzing spiked peanut samples. The results matched well with those obtained with a commercial ELISA kit. Conceivably, the method is not limited to aflatoxins but has a wide scope in that it may be applied to many other analytes for which respective antibodies are available. Graphical abstract Schematic illustration of ascorbate oxidase (AOx)-mediated potassium permanganate (KMnO₄)-responsive ascorbic acid (AA) for visual colorimetric immunoassay of aflatoxin B₁ (AFB₁) by coupling with hydrolytic reaction of AOx toward AA and the KMnO₄-Mn(II)-TMB system [note: 3,3',5,5'-tetramethylbenzidine: TMB].

A bimetallic nanoparticle/graphene oxide/thionine composite-modified glassy carbon electrode used as a facile ratiometric electrochemical sensor for sensitive uric acid determination

A novel and facile ratiometric electrochemical sensor was developed for sensitive determination of uric acid.

Unique dual responsive activity of a platinum nanozyme stabilized by a green solvent: deep eutectic solvents

A single pot cascade reaction revealed the natural uricase and peroxidase enzyme mimicking behaviours of Pt nanocubes.

Nanomolar Level Detection of Uric Acid in Blood Serum and Pest-Infested Grain Samples by an Amphiphilic Probe

A pyrene based amphiphilic receptor has been utilized in the nanomolar detection of uric acid at physiological pH in water. The compound shows a unique concentration-dependent modulation in optical response toward uric acid. In intramolecular/static excimer form (low concentration range), it displays a ratiometric response, while a "turn-off" sensing is observed specifically in the presence of intermolecular/dynamic excimer (high concentration range). The present protocol is then employed for the estimation of uric acid in blood serum samples of healthy individuals. Bland-Altman analysis in comparison to clinically approved uricase assay indicated the high accuracy of the present method. Additionally, the extent of insect infestation in stored grain samples was determined by measuring the uric acid content of their aqueous extracts. Low-cost color strips were developed for on-site detection of uric acid without involving any sophisticated instrument or trained personnel.

A redox-modulated fluorescent strategy for the highly sensitive detection of metabolites by using graphene quantum dots

In this paper, a redox-modulated fluorescent strategy based on the transformation of Fe²⁺/Fe³⁺ couple and enzymatic reaction for rapid monitoring glucose and uric acid using graphene quantum dots (GQDs) as fluorescent probe was developed. Hydrogen peroxide (H₂O₂) can be produced by the enzymatic reaction of a series of metabolites, such as glucose and uric acid. In the presence of hydrogen peroxide, Fe²⁺ can be oxidized and converted to Fe³⁺, which have a significant quenching difference in the fluorescence of graphene quantum dots (GQDs). Thus, a sensitive and label-free biosensor for the detection of uric acid and glucose was developed. Under the optimized experimental conditions, the fluorescence intensity was linearly correlated with the concentration of uric acid and glucose in the range of 0.1-45 μmolL^-1 and 0.1-30 μmolL^-1 with a detection limit of 0.026 μmolL^-1and 0.021 μmolL^-1, respectively. The proposed method was applied to the determination of uric acid and glucose in human serum samples with satisfactory results, which had potential application to detect metabolites associated with H₂O₂ release.