Nanoscale biomemory composed of recombinant azurin on a nanogap electrode

Sub-5 nm nanogap electrodes towards single-molecular biosensing

Nanogap electrodes (NGEs) with sub-5 nm gap has been widely used in single-molecule sensing and sequencing, with the characteristics of label-free, high sensitivity, rapid detection and low-cost. However, the fabrication of sub-5 nm gap electrodes with high controllability and reproducibility still remains a great challenge that impedes the experimental research and the commercialization of the nanogap device. Here, we review the common currently used fabrication methods of nanogap electrodes, such as gap narrowing deposition, mechanical controllable break junctions and the fabrication methods combined with nanopore or nanochannel. We then highlight the typical applications of nanogap electrodes in biological/chemical sensing fields, including single molecule recognition, single molecule sequencing and chemical kinetics analysis. Finally, the challenges of nanogap electrodes in single molecule sensing/sequencing are outlined and the future directions for sensing perspectives are suggested.

Heterologous expression of azurin from Pseudomonas aeruginosa in the yeast Pichia pastoris

Azurin, which is a bacterial secondary metabolite has been attracted as a potential anticancer agent in recent years because induced death of cancer cells and inhibited their growth. In this study, the production of azurin under the control of the alcohol oxidase promoter which is frequently used in the Pichia pastoris expression system was performed. The azurin gene amplified from Pseudomonas aeruginosa genomic DNA and inserted into the pPICZαA was cloned in Escherichia coli cells. Then, a linearized recombinant vector was transferred to the P. pastoris X-33 cells. Antibiotic resistance test and colony PCR were performed for the selection of multicopy transformants. Protein expression capacities of selected transformants were compared at the end of 48 h incubation. Both extracellular and intracellular protein expressions were observed in all of them by Western blot analysis. The relative expression levels of both intracellular and extracellular protein that belongs to the first clone were higher than the others. On the other hand, it was seen that the 4th clone had the highest protein secretion ability. The molecular mass of the extracellular azurin protein which is produced by recombinant clones was found to be about 20 kDa. This is the first report on azurin expression in P. pastoris.

Investigation of Hemoglobin/Gold Nanoparticle Heterolayer on Micro-Gap for Electrochemical Biosensor Application

In the present study, we fabricated a hemoglobin/gold nanoparticle (Hb/GNP) heterolayer immobilized on the Au micro-gap to confirm H₂O₂ detection with a signal-enhancement effect. The hemoglobin which contained the heme group catalyzed the reduction of H₂O₂. To facilitate the electron transfer between hemoglobin and Au micro-gap electrode, a gold nanoparticle was introduced. The Au micro-gap electrode that has gap size of 5 µm was fabricated by conventional photolithographic technique to locate working and counter electrodes oppositely in a single chip for the signal sensitivity and reliability. The hemoglobin was self-assembled onto the Au surface via chemical linker 6-mercaptohexanoic acid (6-MHA). Then, the gold nanoparticles were adsorbed onto hemoglobin/6-MHA heterolayers by the layer-by-layer (LbL) method. The fabrication of the Hb/GNP heterolayer was confirmed by atomic force microscopy (AFM) and surface-enhanced Raman spectroscopy (SERS). The redox property and H₂O₂ detection of Hb/GNP on the micro-gap electrode was investigated by a cyclic voltammetry (CV) experiment. Taken together, the present results show that the electrochemical signal-enhancement effect of a hemoglobin/nanoparticle heterolayer was well confirmed on the micro-scale electrode for biosensor applications.

A biomemory chip composed of a myoglobin/CNT heterolayer fabricated by the protein-adsorption-precipitation-crosslinking (PAPC) technique

In this study, a biomemory chip consisting of a myoglobin/carbon nanotube (CNT) heterolayer is fabricated via the protein-adsorption-precipitation-crosslinking (PAPC) technique for electrochemical signal enhancement, long-term stability, and improved memory function. The PAPC technique is used to fabricate a myoglobin/CNT heterolayer with a CNT core and a high-density myoglobin-shell structure to achieve efficient heterolayer formation and improved performance of the heterolayer. The fabricated myoglobin/CNT heterolayer is immobilized onto a Au substrate through a chemical linker. The surface morphology of the deposited heterolayer is investigated via transmission electron microscopy and atomic force microscopy. The redox properties of the myoglobin/CNT heterolayer are investigated by cyclic voltammetry, and the memory function of the heterolayer, including the "write step" and "erase step," is measured by chronoamperometry. Compared with the myoglobin monolayer without CNT, the myoglobin/CNT heterolayer fabricated by the PAPC technique exhibits greater electrochemical signal enhancement, long-term stability at room temperature, and improved memory function. The results suggest that the proposed myoglobin/CNT heterolayer produced via the PAPC technique can be applied as a platform for bioelectronic devices to achieve improved signal intensity and durability.