What is a nanoenzyme

Shuang Zhao, Dissertation, Department of Physics, University of Hamburg, 2020:

"Nanomaterial-based photoelectrochemical sensor for multiple detection and additional investigation to improve the photocurrent"


"Nanomaterial Based Photoelectrochemical Sensor for Multiplex Detections and the Further Study of Photocurrent Enhancement"


The full text was published as a book / online document (ISBN) in the ACS Applied Materials Interfaces.

Summary

short version

In the research of sensors, the multiplex transmission system has attracted more and more attention because it can acquire more information of the object to be inspected at one time, thereby greatly improving the inspection efficiency. In this work, a homebuilt photoelectrochemical (PEC) -based sensor electrode under the light addressing operation was used to simultaneously check two enzyme substrates. With the help of an insulating self-organized layer (trans-4,4'-stilbenedithiol), CdSe / ZnS core / shell -Quantum dots (QDs) self-organized on the gold electrode surface to build a sensor electrode (QD electrode). Photocurrent is only generated when light is applied to the electrode; when there is no light, no photocurrent signal is detected. Glucose oxidase (glucose oxidase) or sarsosine osidase (sarsosine osidase) is self-organized on the QD electrode, which enables glucose or sarcosine to be checked. On this basis, glucose oxidase and sarcosine oxidase are self-organized at the same time on the same electrode and form different independent sensor arrays of small size, whereby the simultaneous checking of two analytes with one electrode is achieved. The verification process of the parallel verification of the two analytes is controlled by the laser spot (diameter 0.3 mm) moving on the electrode surface and the detection takes place in three solutions (mixed solution of glucose, sarcosine, glucose and sarcosine), the enzyme reaction can only be detected there where the light spot shines. In the end, if two kinds of test objects exist at the same time, they can overcome the mutual interference and be detected by one sensor chip at the same time. In addition, we used photocurrent imaging technology to characterize the size of a single enzyme array in the x and y axis directions and the size is 1.9 mm * 1.3 mm. In addition, by continuously monitoring the photocurrent, the distribution of enzyme activity on a single enzyme array was successfully characterized. On the other hand, this work try photoelectrochemistry (nanoenzyme) by researching nanoenzymes (nanoenzyme), whether the nanoenzymes in the system (PEC) can replace natural enzymes and quantum dots (QD) to remedy the shortcomings of natural enzymes like easy deactivation and high price and avoid the photocurrent instability caused by these defects. CeO2 nanozyme not only have catalytic properties for H2O2, but also photoelectric properties as semiconductor materials. Therefore, CeO2 nanoparticles can replace some hydrogen peroxide reductase (H2O2 reduction enzyme) and can assemble on the electrode to generate a photocurrent. On this basis, in this article we introduced the research into heterogeneous (hybrid) Au / CeO2 shell / core nanomaterials to further investigate photocurrent amplification technology. Compared to the photocurrent of ordinary CeO2 nanomaterials, the photocurrent of heterogeneous Au / CeO2 nanomaterials is increased in PBS and H2O2, which shows that the heterogeneous nanomaterials have better catalytic and photoelectric properties. The photocurrent results under different wavelengths of monochromatic light (wavelength dependency) prove that the Au core plays an important role in improving the photocurrent of heterogeneous nanomaterials. By introducing a mixture of gold nanoparticles (AuNP) and CeO2 NP and comparing their photocurrent with the photocurrent amplification effect of heterogeneous nanomaterials (Au / CeO2), the gold semi-contact interface (semiconductor-metal) plays a role in the photocurrent.The improvement effect was also verified. Finally, layer-by-layer technology (LBL) is used to further improve the catalytic and photoelectric properties of CeO2 nanomaterials and Au / CeO2 nanomaterials. This is because LBL can improve the coverage of the nanomaterial on the electrode surface, so that ultimately a good H2O2 detection limit (3 µM) is achieved and the linear detection range is 2-1000 µM.

title

short version

Summary

In the effort to improve sensors, the development of multiplex sensing systems is an important trend because this type of system significantly improves the sensors ’efficiency by obtaining more information at one time. In this cumulative dissertation, light-directed multiplex detections of different substrates were realized based on a homebuilt photoelectrochemical (PEC) electrode. To fabricate the electrode, CdSe / ZnS core / shell quantum dots (QDs) were immobilized on a gold (Au) electrode using an insulating self-assembly monolayer (SAM) of trans-4,4′-stilbenedithiol, resulting in a light -triggered photocurrent when light is applied and no photocurrent when the light is turned off. Afterwards, enzymes of glucose oxidase (GOx) or sarcosine oxidase (SOx) were immobilized on the surface of the QD electrode to detect glucose and sarcosine, respectively. Based on those results, the GOx and SOx enzymes were immobilized on a single chip together as discrete and small-sized sensing arrays to selectively detect glucose and sarcosine at the same time. The parallel detections were triggered and controlled by moving a localized laser pointer (0.3 mm) over the sensing arrays in different analytes (glucose, sarcosine, the mixture of glucose and sarcosine). Eventually, two substrates can be detected with single chip simultaneously, overcoming the interference from each other. Moreover, a photocurrent imaging technique was used to characterize the spatial size of a single enzyme array in both the x- and y-direction as 1.9 mm × 1.3 mm. It was also possible to visualize the enzymatic activity distribution of the single enzyme array using continuous photocurrent measurement. Furthermore, to overcome the disadvantages of a natural enzyme, such as easy inactivation and high cost, also to improve the photocurrent stability brought by the disadvantages, another study was conducted for this dissertation, attempting to study if a nanozyme can replace the natural enzyme and QDs. CeO2 nanozyme nanoparticles (NPs) have both mimicking catalytic activity towards H2O2 reduction and photoelectrical properties as semiconductor, so CeO2 can replace the H2O2 reduction enzymes and single-layer CeO2 NPs can be immobilized to generate the basic photocurrent on the PEC electrode. Based on that, technique of photocurrent enhancement was studied by introducing hybrid Au / CeO2 core / shell NPs in this dissertation. The photocurrent of Au / CeO2 was significantly enhanced in both phosphate buffer solution (PBS) and H2O2, indicating that the hybrid NPs have better catalytic and photoelectrical properties than the pure CeO2 NPs. Wavelength dependent measurements were used to verify that the Au core plays an important role in the photocurrent enhancement of hybrid NPs. By introducing a mixture of CeO2 NPs and Au NPs and comparing with hybrid Au / CeO2 NPs, the effect of semiconductor-metal interface on the photocurrent enhancement was also verified. Furthermore, a layer-by-layer (LbL) technique was applied to both the CeO2 NPs and the hybrid Au / CeO2 NPs to further enhance the catalytic and photoelectrical properties by creating more NP coverage, resulting in good H2O2 detection limit of 3μM with a linear detection range of 2–1000 μM.