This letter presents a label-free biomolecular imaging technique based on white-light interferometry and spectral detection. The method measures thickness changes caused by specific binding between biomolecules to detect the presence of certain analyte. A spectrum-shifting algorithm is developed to resolve the thickness information from the spectrum. The axial resolution of the experimental instrument can reach ～1 nm, thereby enabling detection of trace amounts (~1 ng/mm2) of proteins or DNA. This letter also presents two experiments to prove the feasibility of the method for detecting proteins and DNA without fluorescent labeling.