1. A method for determining biosensor resonance peak shifts, comprising the steps of: (i) obtaining a reference spectrum for the biosensor and a sample spectrum from the biosensor; (ii) determining an initial offset estimate from the reference spectrum and the sample spectrum, the initial offset estimate being an estimate of the amount of resonance peak shift in the sample spectrum; (iii) determining an incremental offset (shift) value; and (iv) updating the initial offset estimate in response to the incremental offset (shift) value, the updated initial offset estimate representing an updated estimate of the amount of resonance peak shift.