The Interaction Between Carbon Dots And Enzyme And Their Applications

Enzyme is a biological activity of biological macromolecules. Because of its highly efficient and specific catalytic properties and is widely used in the field of catalysis. But it also has some disadvantages, such as poor stability and catalytic activity can not be regulated. If the above problem is resolved, the economic benefit will be increased. Therefore, to develop a low-cost, high efficiency, high selectivity of enzyme-based composite catalyst is necessary. With large amounts of carbon on earth, so is the cheapest carbon-based materials. And the carbon dots possess a low toxicity, good biocompatibility, strong catalytic activity and fluorescence and excellent optoelectronic properties, etc. So they become the material of choice for preparing the enzyme base hydrits. In this paper, different kinds of enzyme base hybrids were prepared through mild methods and the catalytic activity in the catalysis system was also explored. This paper introduced the preparation, catalytic properties and application of porcine pancreatic lipase/ carbon quantum dots(PPL/CQDs) hybrid catalyst, Laccase/ phosphate functionalized carbon dots(Laccase/PCDs) hybrid catalyst, carbon dots/tyrosinase(CDs/TYR) fluorescence probe, N-doped carbon dots/ Laccase(NCD–LAC) fluorescence probe and C3N4/tyrosinase(C3N4/TYR) fluorescence probe, and further explore the catalytical mechanism of the catalysts. The detailed works included the following parts:1. Enzyme engineering for improved catalysis has wide implications. Here, we report the modulation of enzyme(porcine pancreatic lipase, PPL) catalytic activity in the presence of carbon quantum dots(CQDs) by visible light. Upon visible light irradiation, the activity of PPL/CQDs increased to 10% higher than that of free PPL, whereas without a light source, the activity of PPL/CQDs decreased to 30% lower than that of free PPL. Based on Michaelis–Menten kinetics, CQDs were confirmed to play an important role as a non-competitive inhibitor. Our results present a potential new method for developing hypercatalytic hybrid enzymes for bio-catalytic applications.2. The phosphate functionalized carbon dots(PCDs) with high biocompatibility and low toxicity can be used as efficient additives for the construction of Laccase/PCDs hybrids catalyst. A series of experiments indicated that the activity of Laccase/PCDs was higher than that of free laccase(increased by 47.7%). When Laccase/PCDs hybrids catalyst was irradiated with visible light(Laccase/PCDs-Light), its activity was higher than that of free Laccase(increased by 92.1%). In the present system, the T1 Cu in laccase was combined with the phosphate group on the surface of PCDs, which can increase binding capacity of Laccase/PCDs hybrids and substrate. Further, the visible light irradiation increased the donating and accepting electronic capability of the Laccase/PCDs hybrids, improving their catalytic activity.3. A carbon dots/tyrosinase(CDs/TYR) hybrid as a low-cost fluorescent probe for the detection of dopamine exhibits high sensitivity, stability, and precision. The detection limit of dopamine is as low as 6.000×10-8 mol·L-1, and the wide detection range is from 1.318×10-4 mol·L-1 to 2.060×10-7 mol·L-1. This kind of fluorescent probe did not need enzyme immobilization and modification, and the experiment results could be revealed as soon as the probe–sample incubation was completed. More importantly, these test results are comparable to that of the present clinical fluorescence detection and high-performance liquid chromatography(HPLC), and the results show that the three methods agreed well with each other.4. High-intensity fluorescent carbon dots(CDs) coupled with tyrosinase(TYR) yielded hybrids, as a fluorescent probe, which were efficient, fast, stable and sensitive in the detection of levodopa(L-DOPA). The detection limit of L-DOPA was as low as 9.0×10-8 mol·L-1 with a wide linear range from 3.17×10-4 mol·L-1 to 3.11×10-7 mol·L-1. The efficient selective detection of L-DOPA can be attributed to the CDs that are excellent electron acceptors/donors and exhibit high adsorption capacity of H+. It is worth mentioning that TYR does not require modification and immobilization, and the test results could be read as soon as the probe–sample incubation was completed. Moreover, the test results are comparable to those of the present clinical fluorescence and high performance liquid chromatography(HPLC) methods. Our experimental results indicated that CDs possess great potential in the development of various enzymebased biosensors.5. N-doped carbon dots(NCDs) obtained by one-step reflux treatment of C3N4 with ethane diamine possess good water dispersibility, strong visible fluorescence, low toxicity, proton adsorption capacity, and photo-induced electron-accepting/donating abilities. Based on these unique properties, we demonstrate that the obtained NCDs can be used as a good fluorescent probe for cellar imaging without any further functionalization. Further, the NCDs are combined with laccase(LAC) to form NCDs-laccase(NCD-LAC) hybrids, which are sensitive, stable, and of low cost for the precise detection of catechol and catechol derivatives.6. The C3N4-tyrosinase(TYR) hybrid is a highly accurate, sensitive and simple fluorescent probe for the detection of dopamine(DOPA). Under optimized conditions, the relative fluorescence intensity of C3N4-TYR is proportional to the DOPA concentration in the range from 1×10-3 to 3×10-8 mol·L-1 with a correlation coefficient of 0.995. In the present system, the detection limit achieved is as low as 3×10-8 mol·L-1. Notably, these quantitative detection results for clinical samples are comparable to those of high performance liquid chromatography. Moreover, the enzyme-encapsulated C3N4 sensing arrays on both glass slide and test paper were evaluated, which revealed sensitive detection and excellent stability. The results reported here provide a new approach for the design of a multifunctional nanosensor for the detection of bio-molecules.