Integrated Optical Frequency-Resolved Mach-Zehnder Interferometry (IO FR-MZI) is introduced as an alternative, cost-efficient operation principle for integrated optical label-free affinity sensors that can combine high sensitivity with high versatility in terms of potential applications and experimental configurations. A detailed theoretical analysis of the method is presented followed by a semi-analytical approximation and numerical calculations in order to quantify the sensitivity and limits of detection of the FR-MZI over Single Wavelength MZI. The obtained results substantiate that IO FR-MZI- based sensors constitute a generic technological platform of high sensitivity that can be implemented into a plethora of detection schemes. For an optimized optical design well below 1mm in length the limit of detection can be as low as 0.025A in terms of adlayer effective thickness allowing for truly miniaturized integrated optical sensors fabricated with high yield with standard microfabrication techniques.