Method For Detection Of Ascorbic Acid Research Articles

Microfluidic chemistry assisted synthesis of cobalt quantum dot embedded nitrogen doped carbon with oxidase-like properties toward ascorbic acid detection

Ascorbic acid (AA) is a powerful antioxidant in food safety and disease treatment. It is of great significance to develop a low-cost, high-stability, and easy-to-operate colorimetric method for quantitative detection of AA in food or human body. Although various nanozymes have been developed for the colorimetric detection of AA, the size regulation of the catalytic center of nanozymes remains a challenge. In this work, we propose a combined strategy of flow chemistry synthesis and pyrolysis to realize the controllable adjustment of the catalytic center size of nanozymes. Zinc-cobalt zeolitic imidazole frameworks (ZnCo-ZIFs) with different sizes are synthesized by flow chemistry. Nitrogen-doped carbon materials with different Co catalytic centers (80 nm–10 nm) are then obtained by pyrolysis of ZnCo-ZIFs precursors. Among them, cobalt quantum dot embedded nitrogen-doped carbon (Co QDs/N-C) exhibits excellent oxidase activity, with Vmax and Km of 4.19 × 10−7 M s−1 and 0.12 mM. Therefore, a simple, low-cost, and stable colorimetric method for the detection of AA is established with a good linear relationship (3–500 μM) and low detection limit (0.40 μM). This work has certain guiding significance for the size regulation of catalytic center of nanozyme, and the detection method has broad application prospects in biochemical sensing field.

Highly sensitive colorimetric sensing for ascorbic acid utilizing Co3O4@MnO2 hollow nanocubes as oxidase mimic

The development of oxidase mimic with favorable catalytic activity is of great significance for the rapid and convenient detection of ascorbic acid (AA). Herein, in this work, a synergistic regulation strategy of heterogeneous interface and hollow structure is proposed to effectively solve the problem of limited active sites obtained with Co3O4. The charge rearrangement at heterointerface could improve the catalytic activity of oxidase mimic. Moreover, the hollow nanocubes structure could increase specific surface area and provide rich active sites. As a result, the target material possesses enhanced oxidase-like catalytic activity and desirable stability compared to bare Co3O4 and MnO2, which also catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to form a blue product (ox-TMB) even without hydrogen peroxide. Ox-TMB is reduced to TMB owing to the strong reducibility of AA, which represents a decrease in absorbance at 652 nm and a colorless solution. Moreover, an efficient biosensing method for the detection of AA is developed. The relative absorbance (∆A) of the sensing platform is linearly related to the concentration of AA in the range of 0–200 μM, and the detection limit is 0.11 μM. This work provides a novel method for the rapid, cost-effective and sensitive detection of AA, and possesses a wide range of potential application value.

CeO2-Co3O4 nanocomposite with oxidase-like activity for colorimetric detection of ascorbic acid.

A CeO2-Co3O4 nanocomposite (NC) was prepared and characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The obtained CeO2-Co3O4 NC displayed biomimicking oxidase-like activity, which can catalytically oxidize the 3, 3', 5, 5'-tetramethylbenzidine (TMB) substrate from colorless to the blue oxidized TMB (ox-TMB) product with a characteristic absorption peak at 652 nm. When ascorbic acid (AA) was present, ox-TMB would be reduced, resulting in a lighter blue and lower absorbance. On the basis of these facts, a simple colorimetric method for detection of AA was established with a linear relationship ranging from 1.0 to 500 μM and a detection limit of 0.25 μM. When this method was used to detect AA in human serum and commercially available vitamin C tablet samples, a good recovery of 92.0% to 109.0% was obtained. Besides, the catalytic oxidation mechanism was investigated, and the possible catalytic mechanism of CeO2-Co3O4 NC can be described as follows. TMB is adsorbed on the CeO2-Co3O4 NC surface and provides lone-pair electrons to the CeO2-Co3O4 NC, leading to an increase in electron density of the CeO2-Co3O4 NC. An increased electron density can improve the electron transfer rate between TMB and the oxygen absorbed on its surface to generate O2˙- and ˙O2, which further oxidize TMB.

Nickel ferrite nanoparticles on a carbonaceous matrix and their colorimetric assay for ascorbic acid detection

In this study, nickel ferrite nanoparticles highly dispersed in a carbonaceous matrix (C/NiFe2O4) demonstrated a high catalytic activity oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) without the use of hydrogen peroxide. The blue color of oxidized TMB decreases by the introduction of ascorbic acid (AA) in the reaction system, which allowed the development of a colorimetric analytical method for AA detection. To achieve the best analytical performance, the parameters such as pH, temperature, reaction time, TMB concentration, and amount of C/NiFe2O4, were optimized. Under optimal conditions, the variation in absorbance measured at 653 nm was found to be proportional in the concentration range of 1.0 to 25 μmol L−1 with a detection limit of 0.26 μmol L−1. C/NiFe2O4 was synthesized following a simple combustion method using egg white as a fuel and carbon source, and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometry.

Facile synthesis of enzyme functional metal-organic framework for colorimetric detecting H2O2 and ascorbic acid

In this work, a metal-organic frameworks material MIL-88 was prepared easily using solvent-thermal method, and was first found to have catalytic activities similar to those of biological enzymes such as catalase and peroxidase. The material was characterized by XRD, SEM, TEM, EDX, FT-IR techniques and an N2 adsorption method. It exhibited peroxidase-like activity through catalytic oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue-colored solution. Under optimal conditions, the absorbance at 652nm is linearly correlated with the concentration of H2O2 from 2.0×10−6mol/L to 2.03×10−5mol/L (R2=0.981) with a detection limit of 5.62×10−7mol/L (S/N=3). More importantly, a sensitive and selective method for ascorbic acid detection was developed using this material as a catalyst. The analytical method for ascorbic acid detection was observed to have a linear range from 2.57×10−6mol/L to 1.01×10−5mol/L (R2=0.989) with a detection limit of 1.03×10−6mol/L (S/N=3). This work suggests MOFs have advantages of preparing biomimetic catalysts and extends applications of the functional MOFs in the field of biosensor.

A novel ratiometric electrochemical biosensor for sensitive detection of ascorbic acid

In this work, a novel ascorbic acid (AA) ratiometric biosensor was prepared by using the PCN-333 (Al) metal-organic frameworks (MOFs) (PCN stands for porous coordination network) to encapsulate Ketjen black (KB) as catalyst for catalyzing oxidation of AA and thionine (Thi) as an internal reference signal simultaneously. The encapsulation of KB and Thi in the pores of PCN-333 (Al) MOFs not only improved efficiency of KB and Thi greatly because PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface but also enhanced the stability of biosensors because they were immobilized in the pore firmly. Furthermore, PCN-333 (Al) MOFs could also selectively accumulate target analytes into their pores to enhance the selectivity of biosensors. The oxidation peak current of AA catalyzed by KB at −0.05V increased with the increasing concentration of AA, while the oxidation peak current of Thi at −0.24V kept constant, which resulted in a novel ratiometric biosensor for AA detection. The ratiometric biosensor exhibited a wider linear range from 14.1±0.2 to (5.5±0.1) х103μM (R2=0.998) and a lower detection limit of 4.6±0.1μM with high accuracy, selectivity, reproducibility and sensitivity. The ratiometric electrochemical approach is not only a new method for AA detection but also opens a new way for sensitive detection of other analytes.

A rapid, sensitive and selective colorimetric method for detection of ascorbic acid

In this work, we report a colorimetric method for detection of ascorbic acid based on growth of silver nanoparticles by a simple and green photo-catalytic route. This route contains two steps, photo-synthesis of silver nanoclusters (NCs) with papain under UV irradiation, and catalytic growth of silver nanoparticles (NPs) in the presence of ascorbic acid. The produced silver NCs at the first step is excellent catalyzer that could quickly catalyze the growth of silver NPs by Ag+ and ascorbic acid in 1min at room temperature. And thus, in the second step, the color of the mixture changed from colorless to yellow and a strong absorption band near 420nm could be found in their absorption spectra owing to localized surface plasmon resonance (LSPR) of produced silver NPs. We found that the absorbance changes at 420nm have a good relationship with ascorbic acid concentration, and established a spectrophotometric method for the sensing of ascorbic acid in the range from 0.25 to 50.0μM, with a limit of detection (LOD) as low as 79.2nM. We also established a colorimetric assay of ascorbic acid by analyzing the yellow value (Y%) of the silver NPs photographs using cyan, magenta and yellow (CMY) color mode. The lowest detection concentration of ascorbic acid for colorimetric assay by the photographs could be estimated to ∼1μM. Moreover, the method for ascorbic acid detection also has high selectivity. Potential interferes, such as glucose, dopamine, uric acid and cysteine will not affect the detection of ascorbic acid.

Nihon Ketjen targeting 10,000 tonnes of ultra-deep HDS catalysts

In this work, a novel ascorbic acid (AA) ratiometric biosensor was prepared by using the PCN-333 (Al) metal-organic frameworks (MOFs) (PCN stands for porous coordination network) to encapsulate Ketjen black (KB) as catalyst for catalyzing oxidation of AA and thionine (Thi) as an internal reference signal simultaneously. The encapsulation of KB and Thi in the pores of PCN-333 (Al) MOFs not only improved efficiency of KB and Thi greatly because PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface but also enhanced the stability of biosensors because they were immobilized in the pore firmly. Furthermore, PCN-333 (Al) MOFs could also selectively accumulate target analytes into their pores to enhance the selectivity of biosensors. The oxidation peak current of AA catalyzed by KB at −0.05 V increased with the increasing concentration of AA, while the oxidation peak current of Thi at −0.24 V kept constant, which resulted in a novel ratiometric biosensor for AA detection. The ratiometric biosensor exhibited a wider linear range from 14.1 ± 0.2 to (5.5 ± 0.1) х103 μM (R2 = 0.998) and a lower detection limit of 4.6 ± 0.1 μM with high accuracy, selectivity, reproducibility and sensitivity. The ratiometric electrochemical approach is not only a new method for AA detection but also opens a new way for sensitive detection of other analytes.