Guangwen Li

Peroxidase-Like Activity of Cupric Oxide Nanoparticle

Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. Besides their fundamental importance, natural enzymes also have significant practical applications in medicine, chemical industry, food processing, and agriculture due to their excellent properties, such as high substrate specificities and high efficiency under mild conditions. However, natural enzymes also bear some serious disadvantages to limit their practical applications. In general, natural enzymes, which are globular proteins, can be digested by proteases. Like all proteins, the secondary, tertiary, and quaternary levels of enzyme structure are maintained by weak, noncovalent forces and can be easily disrupted by environmental changes, such as heating or chemical denaturants, which leading to the loss of their catalytic activity. Furthermore, preparation, purification, and storage of natural enzymes are usually time-consuming and expensive. For years, the design and construction of efficient artificial mimetics of natural enzymes has been a challenging topic for scientists from a variety of disciplines. Mimetics of many natural enzymes (such as cytochrome P450 mimetics, serine proteases mimetics, dioxygenase mimetics, phosphodiesterase mimetics, ligase mimetics, nuclease mimetics, and methanogenesis mimetics) have been developed. 2] Among these, a significant amount of research has been focused on the mimicry of peroxidase, which is a popular detection tool in enzymatic analysis and is also important in the treatment of waste water for oxidizing organic substances. Hemin, hemeatin, hemoglobin, cyclodextrin, and porphyrin have been reported as peroxidase mimetics and applied in the detection of hydrogen peroxide and ascorbic acid. As nanomaterials are of fundamental and technological interest and importance, especially functional nanomaterials have received considerable attention and have been extensively studied in recent years. Unique catalytic activities, homogeneous or heterogeneous, have been reported for transition metal nanomaterials. 6] These size-dependent properties, which are often absent in the bulk materials, are the basis for the design of novel catalysts with multiple applications in energy storage, chemical synthesis, and biomedical applications. Recently, Yan and coworkers have found that iron oxide magnetic nanoparticles (IOMNs) possess an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, though IOMNs are usually thought to be biological and chemical inert. Since this report, increasing attention has been paid to the nanoscaled peroxidase mimetics and their potential applications. The discovery of the enzyme nanomimics is of great significance, because inorganic nanomaterials have several advantages over traditional natural enzymes. Compared to naturally occurring peroxidase enzymes, IOMNs were demonstrated to be a highly effective catalyst to peroxidase substrates, and their binding affinity for the substrate 3,3,5,5-tetramethylbenzidine (TMB) is much higher. Furthermore, nanoparticles are considerably more stable and possess an almost unchanged catalytic activity over a wide range of pH and temperatures, in comparison with enzymes which are susceptible to the reaction conditions. Peroxidase enzymes, prone to proteolytic degradation, are difficult to produce in large quantities. In contrast, iron oxide or other nanoparticles can be readily synthesized in mass yield by chemical means and at relatively low cost. In light of such advantages, inorganic nano-mimetics could potentially replace peroxidase and apply in environmental chemistry and biomedicine fields. The ability to catalyze the oxidation of organic substrates to reduce their toxicity or to produce a color change is frequently used in wastewater treatment or as a detection tool. For instance, glucose can be monitored indirectly by hydrogen peroxide released in its oxidation by glucose oxidase. g] Immunoenzyme assays are also primarily based on chromogenic reactions catalyzed by peroxidase in the presence of hydrogen peroxide. It is well known that peroxidase can catalyze the oxidation of a peroxidase substrate by hydrogen peroxide to produce a color change. Upon the addition of cupric oxide nanoparticles (CuO NPs) to the peroxidase substrate TMB in the presence of H2O2, a blue color product can be formed with a maximum absorbance at l= 652 nm (Figure 1 A), indicating that cupric oxide nanoparticles have peroxidase-like catalytic activity. To further characterize the peroxidase-like activity of the CuO nanoparticles, we repeated the experiments using other typical peroxidase substrates in place of TMB, including 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and 3,3’-diaminobenzidine (DAB). As shown in Figure 1B

Chemiluminescent cholesterol sensor based on peroxidase-like activity of cupric oxide nanoparticles

A chemiluminescent cholesterol sensor with good selectivity and enhanced sensitivity was constructed based upon the peroxidase-like activity of cupric oxide nanoparticles. Cupric oxide nanoparticles can catalyze the oxidation of luminol by H2O2, which was produced by the reaction of cholesterol and oxygen that was catalyzed by cholesterol oxidase. Therefore, the oxidation of cholesterol could be transduced into the chemiluminescence of luminol by combining these two reactions. Under the optimum conditions, the CL intensity was proportional to the concentration of cholesterol over the range of 0.625-12.5μM and a detection limit was 0.17μM. The applicability of proposed method has been validated by determination of cholesterol in milk powder and human serum samples with satisfactory results.

Methionine-directed fabrication of gold nanoclusters with yellow fluorescent emission for Cu2+ sensing

In the past few years, fluorescent gold nanoclusters (AuNCs) have gained much attention in many areas of physics, chemistry, materials science, and biosciences due to their unique physical, electrical, and optical properties. Herein, we reported for the first time the synthesis of water soluble, monodispersed AuNCs by using methionine both as a reductant and a stabilizer. The synthetic process is green and simple, and the resulting AuNCs capped by methionine (Met-AuNCs) would be biocompatible with bioorganisms. UV-visible absorption, photoluminescence, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) were carried out to demonstrate the chemical composition and optical properties of the as-prepared Met-AuNCs. The Met-AuNCs possess many attractive features including intense yellow fluorescence (emission maximum at 530nm), a long fluorescence lifetime (181ns and 1651ns), high colloidal stability (pH-, temperature-, salt- and time-stability), and a large Stokes shift (110nm), holding great promise as late-model analytical tools for life science and environmental studies. Moreover, the as-synthesized Met-AuNCs can serve as an efficient fluorescent probe for selective detection of Cu(2+) by fluorescence quenching. The limit of detection for Cu(2+) was determined to be 7.9nM and linear response over the Cu(2+) concentrations range from 50nM to 8μM. Furthermore, the new-constructed probe allows simple and rapid detection of the concentrations of Cu(2+) in soil, with results demonstrating its great feasibility for the determination of copper in real samples.

An electrochemical biosensor for detection of PML/RARA fusion gene using capture probe covalently immobilized onto poly-calcon carboxylic acid modified glassy carbon electrode.

In this article, the poly-calcon carboxylic acid (poly-CCA) film modified electrode was prepared by cyclic voltammetry (CV). Then, an electrochemical DNA biosensor was developed for detection of PML/RARA fusion gene in acute promyelocytic leukemia (APL) by using 18-mer single-stranded deoxyribonucleic acid as the capture probe. The capture probe was covalently attached through free amines on the DNA bases using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosulfosuccinimide (NHS) cross-linking reaction on a carboxylate-terminated poly-CCA monolayer modified glassy carbon electrode (GCE). The covalent immobilized capture probe could selectively hybridize with its target DNA to form double-stranded DNA (dsDNA) on GCE surface. The aim of this work is to provide a well-defined recognition interface for the detection of DNA. Differential pulse voltammetry (DPV) was used to monitor the hybridization reaction on the capture probe electrode. The decrease of the peak current of methylene blue (MB), an electroactive indicator, was observed upon hybridization of the probe with the target DNA. The results indicated that in pH 7.0 phosphate buffer solution (PBS), the oxidation peak current was linear with the concentration of complementary strand in the range of 1.0 x 10(-12) to 1.0 x 10(-11)M with a detection limit of 6.7 x 10(-13)M. This new method demonstrates its excellent specificity for single-base mismatch and complementary sequence (dsDNA) after hybridization, and it would be proposed to use in real sample.

Colorimetric sensor based on dual-functional gold nanoparticles: analyte-recognition and peroxidase-like activity.

A novel colorimetric sensor based on the interaction ability with specific analytes and peroxidase-like activity of gold nanoparticles was established in this work. Combining the high-affinity binding between bare gold nanoparticles and melamine with signal amplification procedure based on the catalytic activity of gold nanoparticles for oxidation of TMB, melamine with the concentration as low as 0.02 mg/L can be easily distinguished by naked-eye observation. Such system can be adapted through carefully-controlled surface modifications of gold nanoparticles for determination of other targets.

Synthesis and Peroxidase‐Like Activity of Salt‐Resistant Platinum Nanoparticles by Using Bovine Serum Albumin as the Scaffold

A green approach is proposed for the synthesis of Pt nanoparticles (PtNPs) in the bovine serum albumin (BSA) scaffold through biomineralization. The resulting BSA–PtNPs have been proved to function as peroxidase mimics that can catalyze the reaction of various peroxidase substrates in the presence of H2O2. Kinetic studies indicate that BSA–PtNPs have a much higher affinity for H2O2 than the NPs of other Pt‐based peroxidase mimics. Furthermore, the BSA shell plays an important role in promoting the robust stability of PtNPs. Even in high ionic strength environment (2 M NaCl), the catalytic activity can be well preserved. These excellent properties make the BSA–PtNPs an ideal candidate for a wide range of potential applications as peroxidase mimics.

An IMPLICATION logic gate based on citrate-capped gold nanoparticles with thiocyanate and iodide as inputs

Herein we developed an IMPLICATION logic gate based on citrate-capped AuNPs by employing thiocyanate (SCN(-)) and iodide (I(-)) as inputs, and devised a colorimetric sensor for the determination of I(-) with good selectivity and sensitivity. To the best of our knowledge, this is the first example in which two species of anions serve as inputs to obtain visually observed Boolean outputs. Under the optimum conditions, 0.8 μM I(-) could induce a significant color change and be recognized by the naked eye. The detection limit is 50 nM by using UV-vis spectroscopy.

Determination of tannic acid based on luminol chemiluminescence catalyzed by cupric oxide nanoparticles

In this study, it was found that tannic acid could inhibit the chemiluminescence (CL) intensity of luminol–H2O2–cupric oxide nanoparticles significantly. Based on this inhibition effect, a novel and highly sensitive flow injection method with inhibited chemiluminescence was developed for the determination of tannic acid. Under optimum conditions, the net CL intensity was proportional to the concentration of tannic acid over the range of 10–100 nM and the detection limit was 2.6 nM. The relative standard deviation (RSD) for six repeated determinations of 80 nM tannic acid was 2.8%. Note that this method has been successfully used for the analysis of tannic acid in real Chinese gall samples.

A signal-on fluorescent aptasensor based on single-stranded DNA-sensitized luminescence of terbium (III) for label-free detection of breast cancer cells.

Breast cancer is the most common type of malignant tumor in women. Recently, it has been shown that detection of breast cancer tumor cells outside the primitive tumor is an effective early diagnosis with great prognostic and clinical utility. For this purpose, we developed a signal-on fluorescence aptasensor for label-free, facile and sensitive detection of MCF-7 breast cancer cells. Due to target-aptamer specific recognition and single-stranded DNA-sensitized luminescence of terbium (III), the proposed aptasensor exhibits excellent sensitivity with detection limit as low as 70 cells mL(-1). Compared with common organic dyes and the emerging nano-technological probes, the combination of terbium (III) and single-stranded DNA signal probe (Tb(3+)-SP) serves as a more powerful bio-probe because of its stable optical property, good biocompatibility and free from complex synthesis. The feasibility investigations have illustrated the potential applicability of this aptasensor for selective and sensitive detection of MCF-7 breast cancer cells. Moreover, this proposed aptasensor can be also extended for the determination of other tumor cancers or bio-molecules by altering corresponding aptamers. Taken together, this easy-to-perform aptasensor may represent a promising way for early screening and detection of tumor cancers or other bio-molecules in clinical diagnosis.