The design of Porous Silicon (PSi) integrated micro-resonators is studied for both surface sensing and homogeneous sensing at 1550 nm to optimize the sensors' sensitivity and Limit of Detection (LOD) as a function of the porosity, dimensions and propagation losses of PSi ridge waveguides. A model for estimating the different contributions to the losses of PSi waveguide as a function of the dimensions and the porosity is then developed to allow calculation of the performance of the sensor. Low refractive index difference and high porosities mean that higher sensor performance can be obtained due to the reduction of surface scattering losses as the waveguide dimensions become larger. The sensitivity and limit of detection calculated in this paper for optimized dimensions and porosities of PSi ridge waveguides are respectively 0.04 nm/(pg.mm-2) and 0.5 pg.mm-2 for Bovin Serum Albumin (BSA) molecules surface sensing which are higher than the state of the art. For homogeneous detection, a promising sensitivity of 800 nm/RIU, higher than the sensitivities that can be currently obtained with one micro-resonator, has been estimated. A limit of detection of 1.2.10-4 RIU, which is within the range of state of the art of micro-resonator (MR) based biological sensors, has also been calculated for homogeneous detection. These promising results obtained by the optimization of the porosity and the ridge waveguide dimensions with respect to optical losses reinforce the attraction of PSi for integrated optical sensing application. Highlights:-The performances of micro-ring resonator biological sensor based on porous silicon waveguides are calculated in terms of sensitivity and limit of detection as a function of porosity and waveguide dimensions.-A micro-resonator is designed for both surface and homogeneous sensing by taking into account the optical losses.-A comparison of the performances of micro-resonator sensors for both surface and homogenous detection highlights the interest of porous silicon waveguides having optimized porosities and dimensions, in obtaining the best limit of detection and sensitivity that are currently possible to reach with only one micro-resonator.