Is there a preferred method for estimating the required sample size for testing the accuracy of a gold test against a new under trial test.

My denominator includes only the positives from the gold test. So the question is how many of the gold tests should be done to determine the accuracy of the the trial test. I am aiming for at least 85-90% or higher accuracy (sensitivity).

Basically if sensitivity is my only concern then what should be my approach to sample size estimation?