Microscale memory characteristics of virus-quantum dot hybrids
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(Color online) Device assembly of substrate based system and SAM composition. (a) Schematic of substrate based CPMV-2QD on Au substrate system. Adsorption of mixed disulfide alkane thiol expressing a maleimide group is followed by addition of CPMV-T184C. Water solubilized QDs of red and green emissions are attached to cysteine and lysine residues on the capsid through maleimide and carbodiimide chemistries, respectively. A single QD of each type is represented on one virus particle for simplicity. (b) Composition of mixed disulfide 11-mercaptoundecyl penta(ethylene glycol) terminated maleimide (MED) and hydroxyl terminated disulfide alkanethiol (EG3-EG3) used for SAM assembly. MED contains a disulfide alkane maleimide cross-linker containing a disulfide for chemisorption to the Au substrate, a flexible undecyl alkane linker, an ethylene glycol (PEG) antiadhesion layer, and a reactive maleimide group on opposing end.
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(Color online) Substrate microscopy of virus and hybrid system. (a) SEM of CPMV-T184C deposited on Au substrate with intermediate maleimide SAM. Electron micrograph shows similar grains of Au, with deposition of spherical and well distributed CPMV-T184C particles of . Dark central spotting appearing on each virion is due to surface charging of closest position from the detector. Scale bar of with and magnification was used to visualize CPMVs. Average separation between virions appears to be around , producing substrate. [(b)–(d)] Fluorescence micrograph ( resolution) of green, red, and merged fluorescent images of multi-QD deposited CPMV on Au hybrid system. (b) Green bandpass fluorescence filtered image through objective with a scale bar shows broad range of distributed QDs on final product substrate. (c) Red bandpass fluorescence filtered image with a with scale bar similar of QD coverage in same field of view. Larger clusters are due to defocused image and enlargement by image gain enhancement. (d) A merged image of (b). and (c). images showing an effective dual bandpass filtered fluorescence micrograph in green and red regions. Spatial overlap between most QDs appear as yellow regions. (e) TEM of structurally intact CPMV-2QD hybrids recovered after thermal lift-off, revealing QD decorated CPMV-T184C particles measured as (green arrow) and (red arrow), respectively. Scale bars of for main micrograph and for inset.
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(Color online) Electrical characterization of CPMV-2QD hybrids with device schematic and pulsed wave measurements. (a) Current-voltage behavior of CPMV-2QD nanoelectronic device, demonstrating a multistate switching behavior. Current-voltage controls on ZnS capped CdSe QDs or CPMV-T184C only, showing no switching behavior. Switching behavior in curve on right side appear with two steps, indicated as arrows (referred to as V1 and V2 in text), most likely due to electron transfer to each QD. Schematic of device assembly in lower right corner contains CPMV-2QD hybrids sandwiched within a PVA matrix between two Al electrodes for measurement of conductivity. (b) Pulsed voltage cycles used to demonstrate a functional memory element.
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