Name: fabrication of zero mode waveguides for high concentration single molecule microscopy
Uploaded: 2020-05-12T13:00:00
Description: Watch this Scientific Journal Video about Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy at JoVE.com

This work was supported by NIH grants R01GM080376, R35GM118139, and NSF Center for Engineering MechanoBiology CMMI: 15-48571 to Y.E.G., and by an NIAID pre-doctoral NRSA fellowship F30AI114187 to R.M.J.

NOTE: All steps can be completed in general lab space.
1. Glass coverslip cleaning
<ol>
	<li>To provide a clean surface for evaporative deposition of colloidal particles, place 24 x 30 mm optical borosilicate glass coverslips (0.16&#8722;0.19 mm thickness) within the grooved inserts of a coplin glass staining jar for cleaning. 
	NOTE: Make sure the coverslips stand upright and are well-separated so that all surfaces are clearly exposed during the cleaning process.</li>
	<li>Pour enough ...

For the colloidal self-assembly (protocol section 2), the use of ethanol rather than water as the suspension solvent speeds the evaporation process so that templates are ready in 2&#8722;3 min after deposition rather than 1&#8722;2 h as in previous methods48,49. The evaporative sedimentation protocol presented here is also simpler than previous sedimentation protocols that require controlling surface tilt, temperature, and air volume above the suspension<sup clas...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61154">Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy</a>. A figure was updated.
Figure 3 was updated from:
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61154/61154fig3.jpg" /> 
Figure 3: Representative results from evaporative deposition of colloids. (A) Example of optimal colloid deposition. (B) Example of an acceptable colloid deposition in which conditions were more humid (80% RH) than ideal. Holes in the crystal monolayer are apparent. (C) Example of an acceptable colloid deposition in which conditions were drier (65% RH) than optimal. The monolayer regions are slightly translucent while multilayered areas are white and opaque (perimeter and streaks inward). (D) A colloidal crystal illuminated with white light to highlight the rainbow diffraction from the crystals. (E) AFM image (tapping probe AFM in air) of a monolayer of hexagonally packed polystyrene beads from a successful colloid deposition (scale bar = 10 &#181;m). (F) Expanded AFM image of packed beads (scale bar = 2 &#181;m). <a href="https://www.jove.com/files/ftp_upload/61154/61154fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
to:
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61154/61154fig3v2.jpg" /> 
Figure 3: Representative results from evaporative deposition of colloids. (A) Example of optimal colloid deposition. (B) Example of an acceptable colloid deposition in which conditions were more humid (80% RH) than ideal. Holes in the crystal monolayer are apparent. (C) Example of an acceptable colloid deposition in which conditions were drier (65% RH) than optimal. The monolayer regions are slightly translucent while multilayered areas are white and opaque (perimeter and streaks inward). (D) A colloidal crystal illuminated with white light to highlight the rainbow diffraction from the crystals. (E) AFM image (tapping probe AFM in air) of a monolayer of hexagonally packed polystyrene beads from a successful colloid deposition (scale bar = 10 &#181;m). (F) Expanded AFM image of packed beads (scale bar = 2 &#181;m). <a href="https://www.jove.com/files/ftp_upload/61154/61154fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

An erratum was issued for:&#160;<a href="https://www.jove.com/t/61154">Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy</a>. A figure was updated.

Erratum: Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy

Single-molecule techniques such as single molecule fluorescence resonance energy transfer (smFRET) or single molecule fluorescence correlation spectroscopy (FCS) are powerful tools for molecular biophysics, allowing the study of dynamic movements, conformations, and interactions of individual biomolecules in processes such as transcription1,2,3, translation4,5,6, and many others7. For smFRET, total internal reflection fluorescence (TIRF) microscopy is a common method because many tethered molecules may be followed over time, and the evanescent wave generated by TIR is limited to a 100&#8722;200 nm region adjacent to the coverslip8. However, even with this restriction on excitation volume, fluorophores of interest still need to be diluted to pM or nM ranges in order to detect single molecule signals above background fluorecence9. Since the Michaelis-Menten constants of cellular enzymes are typically in the &#956;M to mM range10, biochemical reactions in single molecule studies are usually much slower than those in the cell. For example, protein synthesis occurs at 15&#8722;20 &#160;amino acids per second in E. coli11,12, while most prokaryotic ribosomes in smFRET experiments translate at 0.1&#8722;1 amino acid per second13. In protein synthesis, crystal structures and smFRET on stalled ribosomes showed that transfer RNAs (tRNAs) fluctuate between &#8216;hybrid&#8217; and &#8216;classical&#8217; states before the tRNA-mRNA translocation step14,15. However, when physiological concentrations of the translocation GTPase factor, EF-G, was present, a different conformation, intermediate between the hybrid and classical states, was observed in smFRET6. Studying dynamic molecular processes at rates and concentrations similar to those in the cell is important, but remains a technical challenge.
A strategy to increase the fluorescent substrate concentration is the use of metal-based, sub-visible wavelength apertures, called zero mode waveguides (ZMWs), to generate confined excitation fields that selectively excite biomolecules localized within the apertures16 (Figure 1). The apertures are typically 100&#8722;200 nm in diameter and 100&#8722;150 nm in depth17. Above a cutoff wavelength related to the size and shape of the wells (&#955;c &#8776; 2.3 times the diameter for circular waveguides with water as the dielectric medium18), no propagating modes are allowed in the waveguide, hence the term zero mode waveguides. However, an oscillating electromagnetic field, termed an evanescent wave, exponentially decaying in intensity still tunnels a short distance into the waveguide18,19. Although similar to TIR evanescent waves, ZMW evanescent waves have a shorter decay constant, resulting in 10&#8722;30 nm effective excitation region within the waveguide. At micromolar concentrations of fluorescently labeled ligands, only one or a few molecules are simultaneously present within the excitation region. This restriction of the excitation volume and consequent reduction of background fluorescence enables fluorescence imaging of single molecules at biologically relevant concentrations. This has been applied to many systems20, including FCS measurements of single protein diffusion21, single molecule FRET measurements of low-affinity ligand-protein22 and protein-protein interactions23, and spectro-electrochemical measurements of single molecular turnover events24.
ZMWs have been produced by directly patterning a metal layer using ion beam milling25,26 or electron beam lithography (EBL) followed by plasma-etching16,27. These maskless lithography methods create waveguides in series and typically require access to specialized nanofabrication facilities, preventing widespread adoption of ZMW technology. Another method, ultraviolet nanoimprint lithography lift-off28, uses a quartz slide mold to press an inverse ZMW template onto a resist film like a stamp. While this method is more streamlined, it still requires EBL for fabrication of the quartz mold. This article presents the protocol for a simple and inexpensive templated fabrication method that does not require EBL or ion-beam milling and is based on close-packing of nanospheres to form a lithographic mask.
Nanosphere or &#8220;natural&#8221; lithography, which was first proposed in 1982 by Deckman and Dunsmuir29,30, uses the self-assembly of monodisperse colloidal particles, ranging from tens of nanometers to tens of micrometers31, to create templates for surface patterning via etching and/or deposition of materials. The two-dimensional (2D) or three-dimensional (3D) extended periodic arrays of colloidal particles, referred to as colloidal crystals, are characterized by a bright iridescence from scattering and diffraction32. Although less widely used than electron-beam or photolithography, this masking methodology is simple, low cost, and easily scaled down to create feature sizes below 100 nm.
Directing the self-assembly of colloidal particles determines the success of using colloidal crystals as masks for surface patterning. If the size and shape of particles are homogeneous, colloidal particles can be readily self-assembled with hexagonal packing, driven by entropic depletion33. Water evaporation after drop-coating is an effective route to sediment the colloidal particles, although other methods include dip-coating34, spin coating35, electrophoretic deposition36, and consolidation at an air-water interface37. The protocol presented below is based on the evaporation sedimentation method, which was the simplest to implement. The triangular interstices between close-packed polystyrene beads form openings in which to plate a sacrificial metal, forming posts (Figure 2 and Supplemental Figure 1). Brief annealing of the beads before this step adjusts the shape and diameter of these posts. The beads are removed, a final metal layer is deposited around the posts, and then the posts are removed. After the two metal deposition steps onto the colloidal nanomask, removal of the intermediate posts, and surface chemistry modification for passivation and tethering, ZMW arrays are ready to use for single molecule imaging. More extensive characterization of the ZMW optical properties after fabrication can found in an accompanying article38. Besides a thermal evaporator for vapor deposition of the metals, no specialized tools are required.

<table border="0" cellpadding="0" cellspacing="0" style="width:667px;" width="668">
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			<td height="21" style="height:21px;width:215px;">1. Glass Coverslip Cleaning</td>
			<td style="width:103px;"></td>
			<td style="width:119px;"></td>
			<td style="width:231px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Acetone</td>
			<td style="width:103px;">Sigma</td>
			<td style="width:119px;">32201</td>
			<td>1 L</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Coplin glass staining jar</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">08-817</td>
			<td>Staining jar with 8 grooves and molded glass cover</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Coverslips</td>
			<td style="width:103px;">VWR</td>
			<td style="width:119px;">48404-467</td>
			<td>24 mm x 30 mm (No.1&#189;, Rectangular)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Ethanol</td>
			<td style="width:103px;">Sigma</td>
			<td style="width:119px;">E7023</td>
			<td>1 L</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">KOH</td>
			<td style="width:103px;">Sigma</td>
			<td style="width:119px;">30603</td>
			<td>Potassium hydroxide</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Petri dishes</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">R80115TS</td>
			<td>100 mm diameter, 15 mm deep</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Sonicator</td>
			<td style="width:103px;">Branson</td>
			<td style="width:119px;">Z245143</td>
			<td>Tabletop ultrasonic cleaner, 5510</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">2. Evaporative Deposition of Polystyrene Beads</td>
			<td style="width:103px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Clear storage container</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">50-110-8222</td>
			<td>26 x 18 x 15 in.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Desk fan</td>
			<td style="width:103px;">O2Cool</td>
			<td style="width:119px;">FD05001A</td>
			<td>Any small desk (~5 in.) fan will work</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Glass beaker</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">02-555-25B</td>
			<td>250 mL</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Humidity meter</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">11-661-19</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Microcentrifuge tubes</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">21-402-903</td>
			<td>1.5 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Polystyrene microspheres</td>
			<td style="width:103px;">Polysciences</td>
			<td style="width:119px;">18602-15</td>
			<td>1.00 &#181;m diameter, non-functionalized</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Triton X-100 deturgent</td>
			<td style="width:103px;">Sigma</td>
			<td style="width:119px;">X100</td>
			<td>100 mL</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:215px;">3. Bead Annealing for Reducing Pore Size in the Colloidal Crystal Template</td>
			<td style="width:103px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Aluminum plate</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">AA11062RY</td>
			<td>Customized in-house to 14 cm x 14 cm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Ceramic hotplate</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">HP88857100</td>
			<td>13 x 8.2 x 3.8 in.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Temperature controller</td>
			<td style="width:103px;">McMaster-Carr</td>
			<td style="width:119px;">38615K71</td>
			<td>Read temperature with thermocouple probe</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Thermocouple probe</td>
			<td style="width:103px;">McMaster-Carr</td>
			<td style="width:119px;">9251T93</td>
			<td>Type K, surface probe</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:215px;">4/5. Nanofabrication of Zero Mode Waveguides Using the Colloidal Crystal Template</td>
			<td style="width:103px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Aluminum etchant</td>
			<td style="width:103px;">Transene</td>
			<td style="width:119px;">Type A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Aluminum pellets</td>
			<td style="width:103px;">Kurt J. Lesker</td>
			<td style="width:119px;">EVMAL40QXHB</td>
			<td>For electron beam evaporation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Chloroform</td>
			<td style="width:103px;">Sigma</td>
			<td style="width:119px;">288306</td>
			<td>1 L</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Copper etchant</td>
			<td style="width:103px;">Transene</td>
			<td style="width:119px;">49-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Copper pellets</td>
			<td style="width:103px;">Kurt J. Lesker</td>
			<td style="width:119px;">EVMCU40QXQA</td>
			<td>For electron beam evaporation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Gold pellets</td>
			<td style="width:103px;">Kurt J. Lesker</td>
			<td style="width:119px;">EVMAUXX40G</td>
			<td>For electron beam evaporation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Lens paper</td>
			<td style="width:103px;">Thorlabs</td>
			<td style="width:119px;">MC-5</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Plasma cleaner</td>
			<td style="width:103px;">Harrick Plasma</td>
			<td style="width:119px;">PDC-32G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Scotch tape</td>
			<td style="width:103px;">Staples</td>
			<td style="width:119px;">MMM119</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Thin film deposition system</td>
			<td style="width:103px;">Kurt J. Lesker</td>
			<td style="width:119px;">PVD-75</td>
			<td>Tabletop thermal evaporation system will also work</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Titanium pellets</td>
			<td style="width:103px;">Kurt J. Lesker</td>
			<td style="width:119px;">EVMTI45QXQA</td>
			<td>For electron beam evaporation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Toluene</td>
			<td style="width:103px;">Sigma</td>
			<td style="width:119px;">244511</td>
			<td>1 L</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Representative Results</td>
			<td style="width:103px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">COMSOL Multiphysics Modeling Software</td>
			<td>COMSOL, Inc.</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Dual View spectral splitter</td>
			<td style="width:103px;">Photometrics, Inc.</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

fabrication of zero mode waveguides for high concentration single molecule microscopy

In single molecule fluorescence enzymology, background fluorescence from labeled substrates in solution often limits fluorophore concentration to pico- to nanomolar ranges, several orders of magnitude less than many physiological ligand concentrations. Optical nanostructures called zero mode waveguides (ZMWs), which are 100&#8722;200 nm in diameter apertures fabricated in a thin conducting metal such as aluminum or gold, allow imaging of individual molecules at micromolar concentrations of fluorophores by confining visible light excitation to zeptoliter effective volumes. However, the need for expensive and specialized nanofabrication equipment has precluded the widespread use of ZMWs. Typically, nanostructures such as ZMWs are obtained by direct writing using electron beam lithography, which is sequential and slow. Here, colloidal, or nanosphere, lithography is used as an alternative strategy to create nanometer-scale masks for waveguide fabrication. This report describes the approach in detail, with practical considerations for each phase. The method allows thousands of aluminum or gold ZMWs to be made in parallel, with final waveguide diameters and depths of 100&#8722;200 nm. Only common lab equipment and a thermal evaporator for metal deposition are required. By making ZMWs more accessible to the biochemical community, this method can facilitate the study of molecular processes at cellular concentrations and rates.

The self-assembly of the polystyrene colloidal particles via evaporative sedimentation (steps 2.1&#8722;2.13) can produce a range of results since it requires control of the solvent evaporation rate. However, because the depositions are fast (10&#8722;15 min per round), the procedure can be quickly optimized for different ambient lab conditions. Figure 3A shows a well-formed colloidal template after deposition and evaporation. Macroscopically, the region of beads is circular, with borders de...

Watch this Scientific Journal Video about Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy at JoVE.com

Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy

Described here is a nanosphere lithography method for parallel fabrication of zero mode waveguides, which are arrays of nanoapertures in a metal-clad glass microscopy coverslip for single molecule imaging at nano- to micromolar concentrations of fluorophores. The method takes advantage of colloidal crystal self-assembly to create a waveguide template.

In single molecule fluorescence enzymology, background fluorescence from labeled substrates in solution often limits fluorophore concentration to pico- to ...

The nanosphere lithography protocol presented here for fabricating zero mode waveguides is an accessible, low cost method that does not require any specialized fabrication tools or facilities. This method will be useful for single molecule biophysics and allow more researchers to perform single molecule experiments at biologically relevant concentrations of fluorescent reagents. To create a clean surface for evaporative deposition of colloidal particles, place optical borosilicate glass coverslips in the grooved inserts of a Coplin glass staining jar.Fill the staining jar with enough acetone to cover the coverslips and cover the jar. Sonicate the jar for 10 minutes at 40 degrees Celsius. Pour out the acetone and rinse the coverslips three times with distilled water.After repeating the sonication and acetone, fill the jar with enough potassium hydroxide to cover the coverslips. Sonicate the jar again, covered, for 20 minutes at 40 degrees Celsius. Rinse the coverslips with distilled water six times, then sonicate them in ethanol for 10 minutes at 40 degrees Celsius.After washing the coverslips three times with distilled water, gently pick up each coverslip at the edge using forceps. Dry each coverslip with nitrogen gas and place each clean, dry coverslip and its own Petri dish. Centrifuge 50 microliters of one micron non-functionalized polystyrene beads.Discard the supernatant, leaving as little water remaining as possible. Resuspend the beads in 50 microliters of solvent, then mix thoroughly by pipetting. To set up a humidity chamber for deposition, arrange six Petri dishes in a row.Place one coverslip in each Petri dish and leave the lids slightly ajar with the coverslips positioned to be exposed to the environment. Center a hygrometer and a small electric fan behind the Petri dishes, then record the relative humidity in the lab. Fill a 200 milliliter beaker with 150 to 200 milliliters of water at approximately 75 degrees Celsius and place the beaker behind the fan.Turn on the fan and then cover the Petri dishes, fan, beaker, and hygrometer with an overturned, transparent plastic storage container. When the relative humidity reaches 70 to 75%lift the plastic storage container slightly and quickly close the lids of the Petri dishes to prevent overwetting of the coverslips. When the relative humidity in the chamber reaches 85%pipette five microliters of the bead suspension onto the center of each coverslip.Cover each Petri dish immediately after deposition and keep everything covered the storage container between depositions. Bead depositions should be completed as quickly as possible to minimize the loss of humidity. If depositions are too dry or wet, chamber humidity is the most important variable to optimize.When all six depositions are complete, record the relative humidity in the chamber and let the bead droplets spread and dry for five minutes. To provide a uniform temperature surface for annealing of the polystyrene beads, place a flat, milled aluminum plate on top of a standard ceramic hot plate and set the temperature of the hot plate to 107 degrees Celsius, the glass transition temperature of polystyrene. Place a coverslip containing the bead template on the hot aluminum plate.After annealing it for 20 seconds, remove the coverslip from the aluminum plate and promptly place it on a room temperature aluminum surface to cool. Using thermal evaporative deposition, deposit 300 nanometers of copper at two angstroms per second over coverslips containing the bead templates. This will generate posts in the interstices between the beads.To remove the excess copper from the beads, gently press a piece of tape onto the surface and then slowly peel off the tape. Dissolve the polystyrene beads by placing the coverslips in toleune and leaving them overnight. Handling the cover slips carefully, rinse them once with chloroform and twice with ethanol.Dry the templates with nitrogen. Place them in an oxygen plasma cleaner for 30 minutes to remove residual polymer and contaminants. Using thermal evaporative deposition, deposit three nanometers of a titanium adhesion layer at one angstrom per second, then deposit 100 to 150 nanometers of aluminum at four angstroms per second around and on top of the copper posts.Ensure that the samples are not rotating during deposition as is automatically done in some deposition units. To dissolve the copper posts, soak the coverslips in copper etchant for two hours. After rinsing the coverslips in distilled water, dry them with nitrogen, then gently buff the surface with lens paper to expose any posts that are still covered in cladding.Soak the coverslips in copper etchant for another two hours, then rinse them again with distilled water and dry them with nitrogen. After surface passivation, zero mode waveguide coverslips can be paired with quartz slides using double-sided sticky tape to make microfluidic flow chambers for single molecule imaging. success of the colloidal template self-assembly depends critically on the relative humidity.In a well-formed template, the region of beads is circular with borders defined by an opaque multilayered ring. In well-formed templates, most of the templates should contain hexagonally close-packed beads. There will be some defects between grains due to jamming during the evaporative sedimentation.After copper deposition and dissolution of the polystyrene beads, copper posts should be below 150 nanometers in diameter. For a 300 nanometer copper deposition depth, posts are around 250 nanometers tall. After deposition of aluminum cladding and subsequent dissolution of the copper posts, waveguides should be visible by atomic force microscopy and be spaced about 550 nanometers apart.Annealing the polystyrene templates for 20 seconds produced aluminum waveguides with a diameter of 118 nanometers, sufficiently small to cut off propagation of visible light. A typical field of ZMWs for imaging contains 3, 000 waveguides in a 40 by 80 micron field of view. Single molecule FRET was performed to test for ZMW functionality.Single molecule FRET traces were detectable at all concentrations of ambient Cy5 fluorphore tested. In comparison, single molecules would only be detectable in TERF illumination with picomolar to low nanomolar concentrations. After zero mode waveguide fabrication, the devices can be passivated with polymers to reduce non-specific interactions during single molecule imaging.The glass bottoms of the zero mode waveguides can also be etched slightly to enhance single molecule emission. Overall, this new zero mode waveguide fabrication method will allow researchers to more easily investigate dynamic biochemical processes, such as transcription or translation at concentrations and rates closer to those in the cell.

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Multiplexed Single-molecule Force Proteolysis Measurements Using Magnetic Tweezers

The  generation and detection of mechanical forces is a ubiquitous aspect of cell physiology,  with direct relevance to cancer metastasis1, atherogenesis2 ...

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them ...

Microfluidic Picoliter Bioreactor for Microbial Single-cell Analysis: Fabrication, System Setup, and Operation

In this protocol the fabrication, experimental setup and basic operation of the recently introduced microfluidic picoliter bioreactor (PLBR) is described ...

Investigating Receptor-ligand Systems of the Cellulosome with AFM-based Single-molecule Force Spectroscopy

Cellulosomes are discrete multienzyme complexes used by a subset of anaerobic bacteria and fungi to digest lignocellulosic substrates. Assembly of the ...

Manufacture of Concentrated, Lipid-based Oxygen Microbubble Emulsions by High Shear Homogenization and Serial Concentration

Gas-filled microbubbles have been developed as ultrasound contrast and drug delivery agents. Microbubbles can be produced by processing surfactants using ...

High-resolution Spatiotemporal Analysis of Receptor Dynamics by Single-molecule Fluorescence Microscopy

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., ...

Single Molecule Fluorescence Microscopy on Planar Supported Bilayers

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background ...

Label-free Single Molecule Detection Using Microtoroid Optical Resonators

Detecting small concentrations of molecules down to the single molecule limit has impact on areas such as early detection of disease, and fundamental ...

A Microfluidic Platform for High-throughput Single-cell Isolation and Culture

Studying the heterogeneity of single cells is crucial for many biological questions, but is technically difficult. Thus, there is a need for a simple, yet ...