In my opinion there are some options that you should take into account:
There are two options.
1. Running all the code with in MATLAB environment, dependent on MATLAB
2. Running all the code with GUI as a standalone application independent of MATLAB
.
If you like to use your application with GUI on PC dependent on Matlab (somebody needs MATLAB installed on his/her PC to run your code), then it is preferable to make this GUI with Matlab tools.
If you like to use this GUI on PC only and on these OS's :Windows Mac OS X Linux you can compile whole code with GUI in MATLAB environment as standalone application.
But if you like this GUI and whole other functions to run on PC or on any embedded device (like raspberry pi, udoo, etc.) and on any OS (Linux, Windows, Mac OS X, Android) as a standalone application you should write the whole code with a tool that has the cross compilation ability for multi platform environment.
In that case I advice you to use QT. For that you should compile all the functions except the GUI as a library in MATLAB and later you should write your code in QT environment with QT's GUI functions and the libraries you compiled in MATLAB.
I can prepare this project for you between 7 or 30 days in which method (QT or MATLAB) you prefer and depending on the GUI pages and their complexity of relation with your functions
What is the subject of your code? How many GUI pages does it have? Can you explain?