SEMs of monoliths modified with in situ prepared GNPs. Conditions: Stream 1 - 50 mmol/L HAuCl4, stream 2 - 80 mmol/L (A) or 200 mmol/L trisodium citrate (C-D), flow rate of the streams 1 μL/min (A, C, D) and 0.5 μL/min (B), reaction time 20 min (A, C, D) and 25 min (B).