Regexp - find specific string in comma separated string

String to find

b

Tested strings

1. b,ffb,x
2. b
3. <empty-string>
4. x,b
5. df,b,x

Poor attempt

[\s|,|^]+(b)[\s|,|$]+

1. [\s|,|^]+ - find white space, comma or beginning of string
2. (b) - find the desired string
3. [\s|,|$]+ - find white space, comma or end of string

Notes

if b defined twice I want to have a match as well