A photoelectric immunosensor using purple membranes (PM) as the transducer, which contains photoactive bacteriorhodopsin, is here first demonstrated for direct and label-free microbial detection. Biotinylated polyclonal antibodies against Escherichia coli were immobilized on a PM-coated electrode through further surface biotinylation and bridging avidin or NeutrAvidin. The photocurrent generated by the antibody-coated sensor was reduced after incubation with E. coli K-12 cultures, with the reduction level increased with the culture populations. The immunosensor prepared via NeutrAvidin exhibited much better selectivity than the one prepared via avidin, recognizing almost none of the tested Gram-positive bacteria. Cultures with populations ranging from 1 to 107CFU/10mL were detected in a single step without any preprocessing. Both AFM and Raman analysis confirmed the layer-by-layer fabrication of the antibody-coated substrates as well as the binding of microorganisms. By investigating the effect of illumination orientation and simulating the photocurrent responses with an equivalent circuit model containing a chemical capacitance, we suggest that the photocurrent reduction was primarily caused by the light-shielding effect of the captured bacteria. Using the current fabrication technique, versatile bacteriorhodopsin-based photoelectric immunosensors can be readily prepared to detect a wide variety of biological cells.
Antibodies, Immobilized/chemistry , Bacteria/isolation & purification , Bacteriorhodopsins/chemistry , Biosensing Techniques/methods , Halobacterium salinarum/chemistry , Purple Membrane/chemistry , Bacterial Infections/microbiology , Biosensing Techniques/instrumentation , Electrodes , Equipment Design , Escherichia coli/isolation & purification , Escherichia coli Infections/microbiology , Humans
A new donor-acceptor-acceptor (D-A-A) type of conjugated molecule, N-(4-(N',N'-diphenyl)phenylamine)-4-(4'-(2,2-dicyanovinyl)phenyl) naphthalene-1,8-dicarboxylic monoimide (TPA-NI-DCN), consisting of triphenylamine (TPA) donors and naphthalimide (NI)/dicyanovinylene (DCN) acceptors was synthesized and characterized. In conjunction with previously reported D-A based materials, the additional DCN moiety attached as end group in the D-A-A configuration can result in a stable charge transfer (CT) and charge-separated state to maintain the ON state current. The vacuum-deposited TPA-NI-DCN device fabricated as an active memory layer was demonstrated to exhibit write-once-read-many (WORM) switching characteristics of organic nonvolatile memory due to the strong polarity of the TPA-NI-DCN moiety.
The electrical memory characteristics of the n-channel organic field-effect transistors (OFETs) employing diverse polyimide (PI) electrets are reported. The synthesized PIs comprise identical electron donor and three different building blocks with gradually increasing electron-accepting ability. The distinct charge-transfer capabilities of these PIs result in varied type of memory behaviors from the write-one-read-many (WORM) to flash type. Finally, a prominent flexible WORM-type transistor memory is demonstrated and shows not only promising write-many-read-many (WMRM) multilevel data storage but also excellent mechanical and retention stability.
Resins, Synthetic/chemistry , Transistors, Electronic , Electrochemical Techniques , Quantum Theory , Resins, Synthetic/chemical synthesis , Silicon Dioxide/chemistry
Resistance switching memory devices with the configuration of poly(ethylene naphthalate)(PEN)/Al/polyimide (PI) blend/Al are reported. The active layers of the PI blend films were prepared from different compositions of poly[4,4'-diamino-4â³-methyltriphenylamine-hexafluoroisopropylidenediphthalimide] (PI(AMTPA)) and polycyclic aromatic compounds (coronene or N,N-bis[4-(2-octyldodecyloxy)phenyl]-3,4,9,10-perylenetetracarboxylic diimide (PDI-DO)). The additives of large π-conjugated polycyclic compounds can stabilize the charge transfer complex induced by the applied electric field. Thus, the memory device characteristic changes from the volatile to nonvolatile behavior of flash and write-once-read-many times (WORM) as the additive contents increase in both blend systems. The main differences between these two blend systems are the threshold voltage values and the additive content to change the memory behavior. Due to the stronger accepting ability and higher electron affinity of PDI-DO than those of coronene, the PI(AMTPA):PDI-DO blend based memory devices show a smaller threshold voltage and change the memory behavior in a smaller additive content. Besides, the memory devices fabricated on a flexible PEN substrate exhibit an excellent durability upon the bending conditions. These tunable memory performances of the developed PI/polycyclic aromatic compound blends are advantageous for future advanced memory device applications.
A conjugated poly(fluorene-thiophene) donor and a tethered phenanthro[9,10-d]imidazole acceptor (PFT-PI) was used as the active layer in flexible nonvolatile resistor memory devices with low threshold voltages (±2 V), low switching powers (â¼100 µW cm(-2)), large ON/OFF memory windows (10(4)), good retention (>10(4) s) and excellent endurance against electric and mechanical stimulus.
Fluorenes/chemistry , Imidazoles/chemistry , Phenanthrenes/chemistry , Polymers/chemistry , Thiophenes/chemistry , Computer Storage Devices
Bistable resistive switching characteristics obtained using a supramolecular hybrid route to hydrogen-bonded block copolymers (BCP) and graphene oxide (GO) as charge storage materials are reported for write-once-read-many-times (WORM) memory devices.
