Highly permselective uric acid detection using kidney cell membrane-functionalized enzymatic biosensors

Iron-carbon dots embedded in molybdenum single-atom nanoflowers as multifunctional nanozyme for dual-mode detection of hydrogen peroxide and uric acid

Single-atom catalysts (SACs) have attracted extensive attention in the field of catalysis due to their excellent catalytic ability and enhanced atomic utilization, but the multi-mode single-atom nanozymes for biosensors remain a challenging issue. In this work, iron-doped carbon dots (Fe CDs) were loaded onto the edges and pores of Mo SACs with nanoflower morphology; accordingly, a composite material Fe CDs/Mo SACs was prepared successfully, which improves the catalytic performance and develops a fluorescence mode without changing the original morphology. The steady-state kinetic data indicates that the material prepared have better affinity for substrates and faster reaction rates under optimized conditions. The specific kinetic parameters Km and Vmax were calculated as 0.39 mM and 7.502×10-7 M·s-1 respectively. The excellent peroxidase-like activity of Fe CDs/Mo SACs allows H2O2 to decompose into •OH, which in turn oxidizes colorless o-phenylenediamine (OPD) to yellow 2,3-diaminophenazine (DAP). At the same time, the fluorescence signal of Fe CDs/Mo SACs quenches obviously by DAP at 460 nm through internal filtration effect (IFE), while the characteristic fluorescence response of DAP gradually increases at 590 nm. Based on this sensing mechanism, a sensitive and accurate dual-mode (colorimetric and ratiometric fluorescent) sensor was constructed to detect H2O2 and uric acid, and the rate of recovery and linearity were acceptable for the detection of UA in human serum and urine samples. This method provides a new strategy for rapid and sensitive detection of UA, and also broadens the development of SACs in the field of biosensors.

Development of a paper-based transcription aptasensor for convenient urinary uric acid self-testing

The abnormal uric acid (UA) level in urine can serve as warning signals of many diseases, such as gout and metabolic cardiovascular diseases. The current methods for detecting UA face limitations of instrument dependence and the requirement for non-invasiveness, making it challenging to fulfill the need for home-based application. In this study, we designed an aptasensor that combined UA-specific transcriptional regulation and a fluorescent RNA aptamer for convenient urinary UA testing. The concentration of UA can be translated into the intensity of fluorescent signals. The aptasensor showed higher sensitivity and more robust anti-interference performance. UA levels in the urine of different volunteers could be accurately tested using this method. In addition, a paper-based aptasensor for UA self-testing was manufactured, in which the urinary UA levels could be determined using a smartphone-based colorimetric approach. This work not only demonstrates a new approach for the design of disease-associated aptasensor, but also offers promising ideas for home-based detection of UA.

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.

Target-triggered 'colorimetric-fluorescence' dual-signal sensing system based on the versatility of MnO2 nanosheets for rapid detection of uric acid

A simple dual-signal assay that combined colorimetric and fluorometric strategy for uric acid (UA) rapid detection was designed based on the versatility of facile synthesized MnO2 nanosheet. The oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) and the fluorescence quenching of quantum dots (QDs) occurred simultaneously in the presence of MnO2 nanosheet. UA could decompose MnO2 nanosheet into Mn2+, resulting in the fluorescence recovery of QDs, along with the fading of the blue color of ox TMB. Based on the principles above, the detection of UA could be realized by the change of the dual signals (colorimetric and fluorometric). The linear range of the colorimetric mode was 5-60 μmol L-1, and the limit of detection (LOD) was 2.65 μmol L-1; the linear range of the fluorescence mode was wide at 5-120 μmol L-1, and the LOD could be as low as 1.33 μmol L-1. The method was successfully used for analyzing UA levels in human serum samples, indicating that this new dual-signal method could be applied in clinical diagnosis.

Bioconjugation of nanozyme and natural enzyme to enable a one-step cascade reaction for the detection of metabolites

Nanozyme, with enzyme-mimicking activity and excellent stability, has attracted extensive attention. However, some inherent disadvantages, including poor dispersion, low selectivity, and insufficient peroxidase-like activity, still limit its further development. Therefore, an innovative bioconjugation of a nanozyme and natural enzyme was conducted. In the presence of graphene oxide (GO), histidine magnetic nanoparticles (H-Fe₃O₄) were first synthesized by a solvothermal method. The GO-supported H-Fe₃O₄ (GO@H-Fe₃O₄) exhibited superior dispersity and biocompatibility because GO was the carrier and possessed outstanding peroxidase-like activity because of the introduction of histidine. Furthermore, the mechanism of the peroxidase-like activity of GO@H-Fe₃O₄ was the generation of •OH. Uric acid oxidase (UAO) was selected as the model natural enzyme and covalently linked to GO@H-Fe₃O₄ with hydrophilic poly(ethylene glycol) as a linker. UAO could specifically catalyze the oxidation of uric acid (UA) to generate H₂O₂, and subsequently, the newly produced H₂O₂ oxidized the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB under the catalysis of GO@H-Fe₃O₄. Based on the above cascade reaction, the GO@H-Fe₃O₄-linked UAO (GHFU) and GO@H-Fe₃O₄-linked ChOx (GHFC) were used for the detection of UA in serum samples and cholesterol (CS) in milk, respectively. The method based on GHFU exhibited a wide detection range (5-800 μM) and a low detection limit (1.5 μM) for UA, and the method based on GHFC exhibited a wide detection range (4-400 μM) and a low detection limit (1.13 μM) for CS. These results demonstrated that the proposed strategy had great potential in the field of clinical detection and food safety.

Enzyme-free and wide-range portable colorimetric sensing system for uric acid and hydrogen peroxide based on copper nanoparticles

Uric acid (UA) is the final product of purine metabolism. A high concentration of UA in body fluid may lead to kidney stones, gout, and some cardiovascular diseases. Therefore, the non-invasive daily monitoring of UA is of great significance for both hyperuricemia patients and fit people. However, most of the current detection methods for UA are enzyme-dependent which limits the application scenarios and lacks portable instruments for on-site detection, including optics and electrochemistry. In this work, an enzyme-free and wide-range colorimetric sensor for UA and H₂O₂ detection was developed based on a mercaptosuccinic acid (MSA)-modified Cu nanoparticles (CuNPs). Under the action of UA or H₂O₂, with the cleavage of MSAs on the CuNPs surface, small Cu particles are further aggregated into larger particles with a lightning violet color. With the employment of the multi-channel handheld automatic photometer (MHAP), the concentration of UA and H₂O₂ can be determined on-site according to the absorbance measurement by the photodiodes. The linear range of UA was 5 μM-4.5 mM with the limit of detection (LOD) of 3.7 μM, while the linear range of H₂O₂ was 5 mM-500 mM and 5 μM-5 mM with the LOD of 4.3 μM. This approach has been applied to the detection of UA in human urine, providing more possibilities for non-invasive home health monitoring, community medical diagnosis, and broader prospects of on-site disease detection.

Bioconjugation of nanozyme and natural enzyme for ultrasensitive detection of cholesterol

When nanozymes are used in biological analysis, higher activity can improve the detection sensitivity, and better selectivity can eliminate other interference. To improve the specificity and sensitivity, we fabricated an innovative bioconjugated nanozyme with natural enzyme (BNNZ), in which natural ChOx was immobilized onto histidine-modified Fe₃O₄ (His-Fe₃O₄) with hydrophilic poly(ethylene glycol) (PEG) as a linker. ChOx could specifically catalyze the oxidation of cholesterol to generate H₂O₂ molecule, and then the newly formed H₂O₂ oxidized the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue ox-TMB by peroxidase-like His-Fe₃O₄. According to the above cascade reaction, the BNNZ-based colorimetric strategy was proposed for the detection of cholesterol. Wherein, natural enzymes specifically catalyzed substrates, which endowed BNNZ with excellent specificity for target molecules; meanwhile, the introduction of histidine on His-Fe₃O₄ effectively increased the peroxidase-like activity of BNNZ, which provided a guarantee for sensitivity. Furthermore, BNNZ after reaction could be rapidly separated by an external magnetic field without interfering with colorimetric quantitative detection. The proposed strategy exhibited excellent sensitivity with limit of detection of 0.446 μM and was successfully used for the detection of cholesterol in spiked human serum sample with recovery and relative standard deviation in the range of 97.9-103.5% and 2.5-4.0%, respectively. This work indicates that the bioconjugation of nanozyme and natural enzyme may be a universal strategy for synthesis of high-performance enzyme-nanozyme systems, and the new-type BNNZ will be widely used in biological detection and disease treatment.

Hemolysis-Inspired, Highly Sensitive, Label-Free IgM Detection Using Erythrocyte Membrane-Functionalized Nanomechanical Resonators

Immunoglobulin detection is important for immunoassays, such as diagnosing infectious diseases, evaluating immune status, and determining neutralizing antibody concentrations. However, since most immunoassays rely on labeling methods, there are limitations on determining the limit of detection (LOD) of biosensors. In addition, although the antigen must be immobilized via complex chemical treatment, it is difficult to precisely control the immobilization concentration. This reduces the reproducibility of the biosensor. In this study, we propose a label-free method for antibody detection using microcantilever-based nanomechanical resonators functionalized with erythrocyte membrane (EM). This label-free method focuses on the phenomenon of antibody binding to oligosaccharides (blood type antigen) on the surface of the erythrocyte. We established a method for extracting the EM from erythrocytes and fabricated an EM-functionalized microcantilever (MC), termed EMMC, by surface-coating EM layers on the MC. When the EMMC was treated with immunoglobulin M (IgM), the bioassay was successfully performed in the linear range from 2.2 pM to 22 nM, and the LOD was 2.0 pM. The EMMC also exhibited excellent selectivity compared to other biomolecules such as serum albumin, γ-globulin, and IgM with different paratopes. These results demonstrate that EMMC-based nanotechnology may be utilized in criminal investigations to identify blood types with minimal amounts of blood or to evaluate individual immunity through virus-neutralizing antibody detection.

A Micro Electrochemical Sensor for Multi-Analyte Detection Based on Oxygenated Graphene Modified Screen-Printed Electrode

Electrode interfaces with both antibiofouling properties and electrocatalytic activity can promote the practical application of nonenzymatic electrochemical sensors in biological fluids. Compared with graphene, graphene oxide (GO) possesses unique properties such as superior solubility (hydrophilicity) in water, negative charge, and abundant oxygenated groups (oxo functionalities) in the plane and edge sites, which play an essential role in electrocatalysis and functionalization. In this work, a micro electrochemical sensor consisting of GO-modified screen-printed electrode and PDMS micro-cell was designed to achieve multi-analyte detection with excellent selectivity and anti-biofouling properties by electrochemically tuning the oxygen-containing functional species, hydrophilicity/hydrophobicity, and electrical conductivity. In particular, the presented electrodes demonstrated the potential in the analysis of biological samples in which electrodes often suffer from serious biofouling. The interaction of proteins with electrodes as well as uric acid was investigated and discussed.

Highly Sensitive Uric Acid Detection Based on a Graphene Chemoresistor and Magnetic Beads

In this study, we developed a low-cost, reusable, and highly sensitive analytical platform for the detection of the human metabolite uric acid (UA). This novel analysis platform combines the graphene chemoresistor detection technique with a magnetic bead (MB) system. The heterojunction (single-layer graphene and HfO₂ thin-film material) of our graphene-based biosensor worked as a transducer to detect the pH change caused by the specific catalytic reaction between UA and uricase, and hence acquires a UA concentration. Immobilization of uricase on MBs can decouple the functionalization steps from the sensor surface, which allows the sensor to be reusable. Our microsensor platform exhibits a relatively lower detection limit (1 μM), high sensitivity (5.6 mV/decade), a linear range (from 1 μM to 1000 μM), and excellent linearity (R² = 0.9945). In addition, interference assay and repeatability tests were conducted, and the result suggests that our method is highly stable and not affected by common interfering substances (glucose and urea). The integration of this high-performance and compact biosensor device can create a point-of-care diagnosis system with reduced cost, test time, and reagent volume.