Minecraft 1.10.2 Problem: Expected token 'm' [duplicate]

I am making an adventure map that includes a sort of redstone clock. I want to set a command block connected to the clock and have it spawn items. Unfortunately, I am not very skilled in command blocks and could use a little help.

This is my command:

/setblock 138 93 254 minecraft:command_block 0 replace {Command:"/summon Item 140 115 245 {Item:{id:"minecraft:gold_nugget",Count:1}}"}

When I execute the command, it returns with this output:

Data tag parsing failed: Unexpected token 'm' at: minecraft:gold_nugget",Count:1}}"

Can anyone please help me? Thank you.