Problem with epoxy silane (Random results in glass silanization). What are crucial points to look at?

1. I`m trying to immobilize an antibody onto the glass surface by means of GPTOMS (glycidoxypropyl trimetoxy silane). Using the same protocol (silanization in toluene or acidified ethanol (see below)) I get different results any time, what are key points to check?

2. Looking through literature on immobilization, I see a lot of articles where authors use APTES (aminopropyl triethoxy silane) and only a few using GPTOMS, why? Epoxy group seems so atractive…

For toluene:

1. Rince slides with water
2. Ultrasonicate them in isopropyl alcohol for 3 min, dry them
3. Put for 3 minutes into piranha solution
4. Rinse with distilled water
5. Treat with oxygen plasma for 3 min
6. Slowly put slides into 2 or 4 % silane solution in toluene, incubate for 3 min
7. Rince with toluene and isopropyl alcohol.
8. Put them on dry heater (max temp. of ours is 97 C, most protocols say 110 C), incubate an hour

For ethanol:

1. Rince slides with water
2. Ultrasonicate them in isopropyl alcohol for 3 min, dry them
3. Put for 3 minutes into piranha solution
4. Rinse with distilled water
5. Treat with oxygen plasma for 3 min
6. Put slides slowly into 2% silane in ethanol solution (silane + alcohol + acetic acid (pH 4,5-5,5)), incubate 3 minutes
7. Rince slides with ethanol
8. Put them on dry heater (max temp. of ours is 97 C, most protocols say 110 C), incubate an hour