Drop casting TEM grid preparation

Caution

VERY ROUGH DRAFT, NOT AUTHORITATIVE. This is a personal journey written by @bobleesj (Sangjoon Bob Lee) during his first time drop casting. Photos and notes are his own; the actual experiments were done by Guoliang Hu and Caitlyn Obrero. Terminology, step ordering, and parameter values may be wrong or incomplete. The resulting grids have not yet been imaged to confirm the preparation worked. Treat this page as a starting point to refer back to, not as an SOP. A trained user must verify everything before relying on it.

This page documents how a TEM grid was prepared by drop casting a nanoparticle solution. The grid is first plasma cleaned to make the carbon film hydrophilic, then a small volume of solution is pipetted onto the grid and allowed to dry in air.

Acronyms:

• easiGlow : PELCO easiGlow glow discharge / plasma cleaner
• TEM : transmission electron microscope

Materials:

• TEM grids (e.g., carbon-coated copper, lacey carbon, holey carbon)
• Nanoparticle solution(s) in labeled vials
• Micropipette (0.5 to 10 µL range) with matching tips
• Anti-capillary tweezers
• Glass petri dish lined with lens paper or weighing paper
• Aluminum grid-holder plate for the easiGlow
• Filter paper or lens paper to wick excess solvent

Location

Drop casting is done in the PELCO easiGlow bay in Nucleus Labs W024 (Cryogenic Electron Microscopy) inside the Stanford ChEM-H Building.

The easiGlow workstation sits next to the rotary pump and shares the bench with pipettes, tip boxes, and a gold-sample coupon. Solutions, tweezers, and grid boxes stay on the same bench.

Overview

TODO: Record approximate time for each phase once the workflow has been repeated a few times.

Part 1: Plasma clean the grids

Plasma cleaning removes organic contamination and makes the carbon support film hydrophilic, so the aqueous droplet spreads evenly instead of beading up. Skip this step and the solution will roll off the grid or concentrate at the edges.

1.1 Retrieve clean grids

1. Open the grid box

   A user must keep grids in a labeled grid box between uses to avoid contamination. Open the box gently: the grids are thin enough that a gust of air can flip them.

   

2. Lift a grid with a fine-tip tool

   Use a wooden toothpick tip, carbon-tipped vacuum pen, or anti-capillary tweezers to remove a grid. Hold the grid by the edge: pressing on the center will punch a hole through the carbon film.

   

1.2 Load grids onto the easiGlow plate

1. Place grids shiny (carbon) side up on the aluminum plate

   The plate has rows of shallow circular wells sized for standard 3 mm grids. Shiny side up ensures the carbon film faces the plasma and becomes the hydrophilic surface.

   

   If you cannot tell which side is shiny, tilt the grid under the bench light. The side with the carbon film reflects more uniformly.

2. Transfer the plate onto the easiGlow stage

   Slide the plate onto the stainless steel stage inside the easiGlow chamber. Center it under the upper electrode.

   

1.3 Run the glow discharge

1. Close the chamber

   Lower the bell jar onto the O-ring. Press down gently and evenly until you feel the seal engage.

   

2. Select the negative-glow program on the touchscreen

   On the easiGlow control panel, set the following parameters:

   Parameter	Value
   Mode	NEGATIVE
   Gas	GAS 1
   Pressure	TODO: confirm target pressure
   Current	TODO: confirm current (mA)
   Glow time	60 s
   Hold time	TODO: confirm hold time

   

   TODO: Record the exact pressure, current, and hold-time values from the staff-defined recipe the next time the instrument is used.

3. Start the cycle

   Press Auto. The pump pulls the chamber down to the set pressure, then the plasma ignites (a faint purple glow appears inside the bell jar). The cycle auto-vents at the end.

4. Use the grids promptly

   Plasma-cleaned grids lose hydrophilicity over time as the surface re-adsorbs ambient hydrocarbons. Prepare your solution and pipette tips before starting the glow discharge so you can drop cast immediately.

   TODO: Confirm how long after glow discharge the grids remain usable.

Part 2: Drop cast the solution

2.1 Prepare the solution

1. Check that your sample vials are labeled and in a rack

   Each vial should have a unique label (e.g., S1-3, S2-1) matching your lab notebook. Vortex or gently invert any solution that has sat for more than a few minutes to resuspend settled particles.

   

2. Mount a fresh tip on the micropipette

   Use a tip that matches your pipette (e.g., SL-10 XLS, 0.5 to 10 µL). A fresh tip prevents cross-contamination between samples.

   

2.2 Pipette onto the grid

1. Draw solution from the vial

   Press the plunger to the first stop, dip the tip into the solution, and release slowly to draw the volume. Avoid drawing air: a bubble at the tip will spray the droplet off the grid.

   TODO: Record the volume actually used (microliters) and the pipette model/range.

   

2. Deposit the droplet on the grid

   Hold the pipette vertically above the grid. Touch the droplet to the grid surface so it wets across the film. Do not press the tip into the carbon film.

   

   If the droplet beads up and rolls off, the grid was not plasma cleaned recently enough. Repeat Part 1 with a fresh grid.

2.3 Wick and dry

1. Transfer the grid onto a piece of lens paper

   Place the grid sample-side up on clean lens paper or filter paper. The paper wicks excess solvent from the edges without disturbing the deposited particles.

   

2. Let the grid air dry

   Wait until the droplet is fully evaporated. Drying time depends on the solvent and droplet volume.

   Do not blow on the grid to speed drying. Breath moisture deposits contamination, and forced airflow can redistribute particles asymmetrically.

   TODO: Record actual drying time for the solvent(s) used.

Part 3: Store prepared grids

1. Pick up the dried grid with anti-capillary tweezers

   Grip the grid by the edge only. The dark dot visible in the center is the dried sample: touching it will scrape particles off.

   

2. Return the grid to a labeled grid box

   Note the well number and sample ID in your lab notebook.

   

Troubleshooting

TODO: This table is generic drop casting guidance, not validated against the actual SNSF workflow. Verify with Guoliang Hu or Caitlyn Obrero before relying on it.

Changelog

• Apr 22, 2026 - Initial draft captured during first drop casting session. Photos and notes by @bobleesj. Experiments by Guoliang Hu and Caitlyn Obrero. Output not yet verified by TEM imaging.