Variations in the Assembly Protocol for Carboxy- and Amine-Terminated Alkanethiols

Most thiols can be assembled successfully using the protocol described in "How to Prepare Self-Assembled Monolayers". However, some thiols have been found to form better SAMs(Self
Assembled Monolayers) by using a modified protocol. Variations for the assembly of carboxy- (COOH) and amineterminated alkanethiols are listed below. Asemblon does not guarantee that the protocols listed below will work for all COOH and amine- terminated alkanethiols, but provides them as a starting point for the creating of high-quality monolayer surfaces. The interested reader is referred to the references provided herein.

Carboxy- (COOH) terminated Alkanethiols

Monolayers of carboxy-terminated alkanethiols form more highly ordered layers when assembled from and/or rinsed with acidic ethanol solutions.1, 2Assembly from an acidic solution assures that the carboxy terminus remains protonated and reduces multilayer formation. It has also been suggested that using a polar aprotic solvent can reduce multilayer formation and increase ordering in COOH SAMs(Self Assembled Monolayers).3

Variations from the standard protocol

Step 2c: Alkanethiol solution for self-assembly

After the addition of the alkanethiol to the ethanol, slowly add drops of acid (typically conc.hydrochloric acid (HCl), trichloroacetic acid or trifluoroacetic acid) until the solution is highly acidic, pH~2.

Step 4a and b: Rinsing solvent modification

• When ready to rinse the samples, use ethanol that has been acidified to pH~2 by adding a few drops of acid.
• Rinse the samples for 10 to 15 seconds under a steady stream of the acidic ethanol.
• Place the samples into individual containers with a few milliliters of acidic ethanol, cap the container, and sonicate the samples for 1 to 3 minutes.
• Rinse the samples with fresh neutral ethanol.
• Dry samples with a stream of N2 gas.

Amine-terminated Alkanethiols

Monolayers of amine terminated thiols form more complete and well ordered monolayers when assembled from and/or rinsed with basic ethanol solutions.2 Assembly from basic solution assures that the amine terminus remains deprotonated and reduces multilayer formation. Variations from the standard protocol:

Variations from the standard protocol

Step 2c: Alkanethiol solution for self-assembly

After addition of the alkanethiol to the ethanol, slowly add drops of base (typically ammonium hydroxide or triethylamine) until the solution is highly basic, pH~12.

Step 4a and b: Rinsing solvent modification

• When ready to rinse the samples, use ethanol that has been adjusted to pH~12 by adding a few drops of base (basic ethanol).
• Rinse the samples for 10 to 15 seconds under a steady stream of the basic ethanol.
• Place the samples into individual containers with a few milliliters of basic ethanol, cap the
container, and sonicate the samples for 1 to 3 minutes.
• Rinse the samples with fresh neutral ethanol.
• Dry samples with a stream of N2 gas.

Chemical Waste Disposal:

Follow standard protocols established in your lab for handling and disposing of acidic and basic solutions.

References:
1. Arnold, R.; Azzam, W.; Terfort, A.; Woll, C., Langmuir 2002, 18, 3980-3992.
2. Wang, H.; Chen, S. F.; Li, L. Y.; Jiang, S. Y., Langmuir 2005, 21, 2633-2636.
3. Noh, J.; Konno, K.; Ito, E.; Hara, M., Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes
Rev. Pap. 2005, 44, 1052-1054.