Luminol–hydrogen peroxide chemiluminescence produced by sweet potato peroxidase

Enhancement effect of 2, 3-dimethyl maleic acid on luminol chemiluminescence reactions and its application in detection of sequence-specific DNA related to hepatitis B virus

2, 3-dimethyl maleic acid (DMMA) was found to enhance luminol-H₂O₂ chemiluminescent (CL) reactions, among which the strongest enhancement effect was observed by using polyethyleneimine-templated gold nanoclusters (PEI-Au NCs) as the catalyst. With the addition of DMMA, the CL signal of the PEI-Au NCs-catalyzed luminol-H₂O₂ reaction enhanced about 630-fold, and a flash-type CL profile was obtained. Mechanism studies showed that the luminophore was still 3-aminophthalate anions in the excited state (3-APA*), and superoxide radical (O₂^·-) played an important role during the CL process. Under the optimized experimental conditions, the lowest concentration of PEI-Au NCs can be detected was 0.168 nM which was 82-fold lower than that without an enhancer. Furthermore, the catalytic activity of biotinylated PEI-Au NCs in the DMMA-enhanced luminol system was similar to PEI-Au NCs, providing a good opportunity for the development of CL bioanalysis platforms using PEI-Au NCs as the label. Thus, the DMMA-enhanced luminol-H₂O₂ system was applied to the CL detection of sequence-specific DNA related to the hepatitis B virus (HBV) using PEI-Au NCs as the label. The CL platform exhibited linearly enhanced CL response with the increasing amount of target DNA ranging from 0.0025 to 0.5 pmol. As low as 0.002 pmol of HBV DNA could be sensitively detected, which was superior to the previously reported methods.

Luminol-hydrogen peroxide-horseradish peroxidase chemiluminescence intensification by kosmotrope ammonium sulfate

The kosmotropic effect induced by ammonium sulfate (AS) at concentrations greater than approximately 2.8 M allows the marked intensification of chemiluminescence (CL) arising from a conventional luminol-hydrogen peroxide (H2O2)-horseradish peroxidase (HRP) reaction. Because of the kosmotropic effect, CL is intensified by at least three orders of magnitude than that from the conventional HRP-catalyzed luminol reaction with no AS; the linear relationship between the CL intensity and the HRP concentration is established over the range of 0.3 pM to several tens of pM. The novel CL intensification effect on the HRP-catalyzed luminol CL can be stably and reproducibly induced.

Natural catalyst for Luminol chemiluminesence - Application to validate peroxide levels in commercial hair dyes

Herein, we report hydrothermally treated green leaves (Moringa Oleifera) extract exploited as an efficient and highly-sensitive catalyst to catalyse the Chemiluminescence (CL) reaction of luminol. In the absence of enhancer, this green and hydrothermally treated catalyst (GHT) was found to significantly enhance the CL intensity about 3.5 fold as compared to the traditionally used K₃ Fe(CN)₆ catalyst. The structure and surface morphology of the catalyst was elucidated by XPS, SEM, XRD and Raman spectroscopy. The synergistic effect of the catalyst in the CL reaction was systematically investigated in the presence of hydrogen peroxide using UV Visible and chemiluminesence spectroscopy. Studies show that the sensitivity of the catalyst could be amplified by adjusting several parameters such as pH of the medium, concentrations of the base and luminol. The sensitivity of the novel-type catalyst was examined through the validation of hydrogen peroxide levels in the commercial hair dye samples. Remarkably, the catalyst displayed ultra-sensitivity to hydrogen peroxide as the limit of detection (LOD) of H₂ O₂ using this catalyst is determined to be 0.02 μM under optimized conditions. In general, the proposed inexpensive, eco-friendly, and non-toxic catalyst could enable the determination of the hydrogen peroxide for diverse analytical applications.

In-vivo electrochemical monitoring of H2O2 production induced by root-inoculated endophytic bacteria in Agave tequilana leaves

A dual-function platinum disc microelectrode sensor was used for in-situ monitoring of H₂O₂ produced in A. tequilana leaves after inoculation of their endophytic bacteria (Enterobacter cloacae). Voltammetric experiments were carried out from 0.0 to -1.0V, a potential range where H₂O₂ is electrochemically reduced. A needle was used to create a small cavity in the upper epidermis of A. tequilana leaves, where the fabricated electrochemical sensor was inserted by using a manual three-dimensional micropositioner. Control experiments were performed with untreated plants and the obtained electrochemical results clearly proved the formation of H₂O₂ in the leaves of plants 3h after the E. cloacae inoculation, according to a mechanism involving endogenous signaling pathways. In order to compare the sensitivity of the microelectrode sensor, the presence of H₂O₂ was detected in the root hairs by 3,3-diaminobenzidine (DAB) stain 72h after bacterial inoculation. In-situ pH measurements were also carried out with a gold disc microelectrode modified with a film of iridium oxide and lower pH values were found in A. tequilana leaves treated with bacteria, which may indicate the plant produces acidic substances by biosynthesis of secondary metabolites. This microsensor could be an advantageous tool for further studies on the understanding of the mechanism of H₂O₂ production during the plant-endophyte interaction.

Advantages of soybean peroxidase over horseradish peroxidase as the enzyme label in chemiluminescent enzyme-linked immunosorbent assay of sulfamethoxypyridazine

An indirect competitive chemiluminescent enzyme-linked immunosorbent assay (CL-ELISA) of sulfamethoxypyridazine (SMP) was developed. The conjugates of streptavidin with cationic horseradish peroxidase (HRP) and anionic soybean peroxidase (SbP) were used in CL-ELISA for the detection of biotinylated anti-SMP antibodies. For streptavidin-HRP conjugate-catalyzed chemiluminescence measured 20 s after the initiation of the enhanced chemiluminescence reaction (ECR), the limit of detection (IC(10)), the IC(50) value, and the working range in CL-ELISA of SMP are 0.3, 12.4, and 1.2-85.0 ng/mL, respectively. An increase in the time interval between the ECR initiation and the luminescence measurement results in the loss in the quality of analytical measurements because of the time-dependent quenching of chemiluminescence typical of the HRP-catalyzed ECR. In the case of SbP-based CL-ELISA of SMP, the limit of detection, the IC(50) value, and the working range (0.025, 0.17, and 0.045-0.63 ng/mL, respectively) are better than those for HRP-based CL-ELISA. Furthermore, the analytical parameters of SbP-based CL-ELISA remain unchanged during a long period of time (for at least 30 min). The recovery values from four spiked milk samples with different concentrations of SMP in SbP-based CL-ELISA vary from 70 to 130%.

3-(10'-Phenothiazinyl)propane-1-sulfonate is a potent enhancer of soybean peroxidase-induced chemiluminescence

3-(10'-Phenothiazinyl)propane-1-sulfonate (SPTZ) was shown to be a potent enhancer of soybean peroxidase (SbP)-induced chemiluminescence. To the best of our knowledge, SPTZ is the first enhancer of SbP to be discovered. Optimal conditions for SbP-catalyzed oxidation of luminol in the presence of SPTZ were determined. The SbP-SPTZ system showed better sensitivity and a lower detection limit (LDL) with respect to the horseradish peroxidase-4-iodophenol system traditionally used in chemiluminescent enzyme-linked immunosorbent assay (ELISA). The addition of 4-morpholinopyridine (MORP) to the SbP-SPTZ system improved its analytical parameters by decreasing the LDL of SbP to 0.03pM. These results open up very promising perspectives for using the SbP-SPTZ-MORP system in ultrasensitive immunoassay.