How to Prepare SAM

1. Soak a gold-coated glass plate in Piranha solutiona) for 10-15 minutes. Wash the plate with purified water.^a)
2. Dissolve aminoalkanethiol compound in ethanol to prepare several mM to several ten mM solutions.
3. Soak the plate in the aminoalkanethiol solution for a certain time period.^b)
4. Wash the SAM-coated plate with ethanol and then water.
5. Dry the plate under nitrogen atmosphere, if necessary.

a)Piranha solution: sulfuric acid and 30% hydrogen peroxide, 3:1. Piranha solution is a strong oxidizing agent. Extreme care is necessary when using it.
Do not apply Piranha solution to resin-coated plates; it may erode the resin.
b)To prepare a SAM-coated plate with the best performance, aminoalkanethiol concentration and soaking time should be individually determined.

Application of SAM-Preparation of DNA Array (Fig. 1)

1. Use SF10 glass slides (Schott Glass Technologies) coated with 5 nm chromium and 45 nm gold thin film.
2. Soak the glass slide in a 1 mM 1-octadecanethiol (ODT)/ethanol solution overnight to prepare ODT SAM-coated slide.
3. Draw 500 μm x 500 μm patterns on the ODT SAM-coated slide by UV irradiation with an Hg-Xe arc lamp.^a)
4. Soak the slide in a 1 mM 11-amino-1-undecanethiol (AUT)/ethanol solution for 2 hours to form AUT SAM on the 500 μm x 500 μm photopatterned area.
5. Drop 2 mM SPDP solution^b) onto the slide and leave the slide at room temperature.
6. Wash the slide and dry under nitrogen atmosphere.
7. Apply 1 mM thiol-DNA solution^c) to each 500 μm x 500 μm pattern and incubate at room temperature overnight.
8. Incubate the slide with a sample solution for 10 minutes and wash with phosphate buffer, followed by SPR imaging.

a)Irradiation time: 1-1.5 hours
b)SPDP: N-succinimidyl 3-(2-pyridyldithio)propionate. Dissolve SPDP in DMSO to prepare 50 mM solution. Dilute it 25 times with 100 mM triethanolamine buffer, pH 7.0.
c)Dissolve thiol-DNA with 100 mM triethanolamine buffer, pH 8.0.

Fig. 1 DNA Array Preparation Scheme