Custom Code To Output Cell Range As String

I have come across this wonderful piece of code that kind of accomplishes what I am after, to a point. Though I would like the output string to be displayed with a few extra characters.

Code:
Function Concat(rng As Range, Optional sep As String = " , ") As String
Dim rngCell As Range
Dim strResult As String
For Each rngCell In rng
If rngCell.Value "" Then
strResult = strResult & sep & rngCell.Value
End If

[code].....

I want the output to be:

["cell1" , "cell2" , "cell3" , "cell4" , "cell5"]