datagridview1 and richtextbox for bold substring in C# 2010

I search about this subject but I don not khow what can I do for my question.

I have these in my form:

1-searchTextBox

2-datagridview

I do these:

1-searchTextBox_TextChanged

2-showing result fromsearchTextBox_TextChanged in datagridview

Please consider that I enter "ab" insearchTextBox. All results that they contains "ab" are listed in datagridview.

I just want to be bold "ab" in all results.

datagridview is read only and user can not enter anythings in it. 

I have seen "RichTextBox Cell in a DataGridView" in CodeProject, but I do not know how I use it for my problem.

Thank you.