Long-term Discoloration
Anant and I have been doing long-term discoloration experiments for the past few weeks. We set up samples in “ideal” conditions – pnc-Si in transwells with pnc-Si side down, autoclaved samples and in the incubator (lower OH-). The only non-ideal component is the use of DMEM+10%FBS with high NaHCO3 (3.7 mg/mL). Chips were RTP’ed at 800C for 5 minutes (or not) and then silanized with APTES (or not) according to the liquid silanization protocol on the blog here. Anant previously posted data from this experiment – I’m simply repeating it with a different wafer (w704). Some 2D samples were included as controls, and the experiment was run with duplicates.
This shows the contact angles and approximate values (via ImageJ) of the various samples.
Untreated 45.902
RTP 52.125
APTES 47.961
RTP+APTES 47.961
APTES treatment did not change the contact angle from the untreated sample, but remember that silanization is performed on UV-Ozone treated samples (with presumably extremely low contact angles).
Here are the discoloration pictures:
As expected, the untreated samples in 2D discolored first (2 days) and then the untreated 3D samples discolored next (<7 days). This matches well with Anant’s data. After 2 weeks, the APTES-treated samples have completely discolored, which Anant also showed. This shows that APTES alone offers no benefit over RTP. At week 2, the RTP and RTP+APTES samples have begun to discolor. After 3 weeks, the RTP samples are completely discolored, and the RTP+APTES samples are close behind. This is in contrast with Anant’s experiment, in which the RTP and RTP+APTES samples were not discolored after 3 weeks (or after 7 weeks – stay tuned for that data). It’s possible that my wafer, w704, discolors faster than Anant’s, w638. Alternatively, our handling of the silanization protocol could have led to different silanization efficiencies. However, the trend of discoloration is the same between these experiments: APTES alone is no better at delaying discoloration than RTP alone. Also, we’ve pushed pnc-Si stability out to reasonable cell culture experimental timeframes!