Biosensors based on one- or two-dimensional photonic-crystal reflectance filters operating at near-ultraviolet wavelengths. The biosensors feature a tightly confined resonant electric field at the surface of this biosensor and provide a high surface-sensitivity to bulk-sensitivity ratio, enabling enhanced detection resolution for biomolecules adsorbed on the biosensor surface. These new biosensors can be fabricated in mass by replica molding and are especially well suited for applications requiring the detection of small molecules or ultra-low analyte concentrations.