A new and sensitive catalytic resonance scattering spectral assay for the detection of laccase using guaiacol as substrate

Fluorescence detection of laccases activity by the photoinduced electron transfer (PET) process

Laccases play a vital role in some physiological processes, for example in morphogenesis, carbon cycle, and defense against parasitism. So, designing a high-sensitivity accurate method is essential for researchers. In this study, a simple fluorescence method based on the function of carbon nitride (g-C₃N₄) by dopamine is synthesized. For the design of this sensor, carbon nitride (g-C₃N₄) is initially synthesis by using a simple method, which is carried out by heating melamine at 550 °C for 3 h and modifying it with dopamine by a linker such as glutaraldehyde. However, the g-C₃N₄-Dopa produced by this method, with an excitation wavelength of 330 nm, has a fluorescence emission at 466 nm. When laccase and g-C₃N₄-Dopa were mixed, dopamine with redox property was oxidized to dopaquinone; this causes the phenomenon of photoinduced electron transfer (PET) process between g-C₃N₄ and the dopaquinone. Hence, fluorescence quenching occurs due to this phenomenon. As a result of these discussions, a sensor for the laccase activity was designed based on the fluorescence quenching degree, supporting a linear range of 0.0-400.0 U L^-1 with the detection limit of 2.0 U L^-1. Using this sensor, the activity of the laccase enzyme in the human serum samples is measured. Dopamine-functionalized carbon nitride was prepared and utilized for the highly sensitive detection of laccases activity.

A Natural Component-Based Oxygen Indicator with In-Pack Activation for Intelligent Food Packaging

Intelligent food packaging can provide consumers with reliable and correct information on the quality and safety of packaged foods. One of the key constituents in intelligent packaging is a colorimetric oxygen indicator, which is widely used to detect oxygen gas involved in food spoilage by means of a color change. Traditional oxygen indicators consisting of redox dyes and strong reducing agents have two major problems: they must be manufactured and stored under anaerobic conditions because air depletes the reductant, and their components are synthetic and toxic. To address both of these serious problems, we have developed a natural component-based oxygen indicator characterized by in-pack activation. The conventional oxygen indicator composed of synthetic and artificial components was redesigned using naturally occurring compounds (laccase, guaiacol, and cysteine). These natural components were physically separated into two compartments by a fragile barrier. Only when the barrier was broken were all of the components mixed and the function as an oxygen indicator was begun (i.e., in-pack activation). Depending on the component concentrations, the natural component-based oxygen indicator exhibited different response times and color differences. The rate of the color change was proportional to the oxygen concentration. This novel colorimetric oxygen indicator will contribute greatly to intelligent packaging for healthier and safer foods.

A novel fluorimetric method for laccase activities measurement using Amplex Red as substrate

In this paper, a novel fluorescence-based method for laccase assay was presented. The method was based on the transformation of Amplex Red into a highly fluorescent and colored resorufin catalyzed by laccase in the presence of O₂. The catalysis and transformation mechanism were investigated in detail. The kinetic parameters of the Amplex Red catalysis by laccase were determined using the Lineweaver-Burk equation. V_max and K_m were estimated to be 15.63μmolmin^-1 and 76.88μmolL^-1, respectively. Under optimal conditions, a good linear correlation was found between fluorescence intensity and laccase activities within 5.62-702UL^-1 (r=0.9992), with a detection limit of 1.76UL^-1 (S/N=3). A series of repeatability measurements (351UL^-1 laccase) gave reproducible results with a relative standard deviation (RSD) of 1.9% (n=11). The recoveries ranged from 93.7% to 100.0% after standard additions. Common existing species such as Mg²⁺, Zn²⁺, Ni²⁺, Al³⁺, Co²⁺, Cd²⁺, K⁺, Ca²⁺, Na⁺, Fe³⁺, Li⁺, Cu²⁺, Mn²⁺, Fe²⁺, l-lysine, glycine, glucose, phenol, humic acid, lignin peroxidase, manganese peroxidase alkaline phosphatase, cellulose, glucose oxidase, urease, catalase, invertase, and horseradish peroxidase did not significantly exhibit interference. The test solution (i.e., Amplex Red stock solution) could stabilize at least three months via storage in dark at 4±0.1°C. These results confirmed that the laccase-Amplex Red system was stable and reproducible with strong anti-interference ability and good selectivity, suggesting that this method can has great potential in practical applications for the assay of laccase activity. The proposed method was further successfully used to detect laccase activities in 38 soil samples. We noticed that the laccase activity significantly correlated with total nitrogen content (r=0.559; p<0.01) of soil, indicating laccase activity assay holds great promise as an index of soil analysis. These findings indicate that this presented method has great perspective in ecological investigation and fundamental research of soil environment.

USPIO assisting degradation of MXC by host/guest-type immobilized laccase in AOT reverse micelle system

The laccase and ultrasmall superparamagnetic iron oxide nanoparticles (USPIO) have been assembled inside the tubular mesoporous silica via co-adsorption technology to prepare host/guest-type immobilized laccase, which is applied to degrade methoxychlor (MXC) in aqueous and reverse micelle environments. The effects of various parameters on degradation of MXC were studied. Under the optimum conditions, the degradation rate could reach maximum value of 45.6 % and remain at 20.8 % after seven cycles. Moreover, the addition of small molecular compound 2, 2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) to the system could greatly improve the degradation efficiency. The MXC degradation process is a first-order reaction, and the activation energy of MXC degradation catalyzed by immobilized laccase (41.46 kJ mol(-1)) is relatively lower than that catalyzed by free laccase (44.91 kJ mol(-1)). Based on the degradation products measured by gas chromatograph-mass spectrometer (GC-MS) and nuclear magnetic resonance (NMR), the degradation mechanism of MXC has also been proposed.

Resonance light scattering determination of trace bisphenol A with signal amplification by aptamer-nanogold catalysis

HAuCl4 was reduced by sodium citrate to prepare 10 nm gold nanoparticles (AuNPs) that were modified by the bisphenol A aptamer (Apt) to obtain an aptamer-nanogold probe (Apt-AuNP) for bisphenol A (BPA). The probes were aggregated nonspecifically to form large clusters, which showed a strong resonance light scattering (RLS) peak at 520 nm, under preparation conditions (pH 7.6 Na2HPO4-NaH2PO4 buffer and ultrasonication). Upon addition of BPA, the probe reacted specifically to form dispersed BPA-Apt-AuNP conjugates that exhibited strong catalysis of the two particle reactions of glucose-Cu(II) and hydrazine hydrochloride-Cu(II) with a strong RLS peak at 360 nm and 510 nm respectively. When the BPA concentration increased, the RLS intensity at 360 nm and 510 nm increased respectively. Accordingly, two new and highly-sensitive RLS methods were established for the detection of BPA, using the Apt-AuNP catalytic amplification.