In this paper a rhombic shape core based photonic crystal fiber (RC-PCF) has been proposed for aqueous analytes sensing purposes. Proposed RC-PCF structure has been modeled with pure silica and numerically simulated in finite element method (FEM) environment based commercial software package COMSOL Multiphysics version 4.2 by employing anisotropic perfectly matched layered (A-PML). Based on the proposed structure, investigated numerical results illustrate that it attains high sensitivity response with low confinement loss. The influences of geometrical parameters of the RC-PCF have been also studies to realize the effect of other optical parameters. Beside this, some crucial parameters like effective area, nonlinearity, numerical aperture (NA) and V parameter are also examined rigorously. The new proposed RC-PCF based sensor structure is very tiny in physical magnitude and easy to fabricate based on ongoing nanotechnology.