C# Regular Expression Help required.

I need help identifying a regular expression pattern to find the number of occurrences of a specific pattern within a given string.
 
For example, the pattern to be sought is "1" followed by 2 or more zeros and then followed by "1".
 
As such, "00010000011110001111000000100", would have 3 matches. I manage to do this successfully, with the help of pattern ""[1]0+0+[1]".
 
The more complicated one which I am not been able to handle is:
 
"000100001000001001000000101000000000" should be returning 4 matches. This is because a single 1 at position 9 will be used for pattern matching on either side.
 
In RegEx technical terms, I think,, this is called "Backreference constructs", which I am not been able to implement correctly.

I also need an exactly opposite pattern too, which is "0" followed by 2 or more ones and then followed by "0". However, I believe it can easily be done by just flipping numbers around from one correct answer.