Medical apparatus for diagnosing of a diseased condition of the skin of a subject. The apparatus comprises an electrically conducting probe including a plurality of electrodes, each electrode comprising a plurality of micro-needles, wherein each electrode comprises a base substrate, said micro-needles being integrally formed with said substrate and arranged in a laterally spaced relationship apart from each other and having a length being sufficient to penetrate the stratum corneum, said micro-needles being arranged with an at least partially oblique shape. Furthermore, the present invention relates to an electrode for use in the device, arrays of micro-needle and method for the diagnostics of biological conditions using impedance measurements. The diagnostics is in particular related to cancer, and preferably skin cancer, wherein skin cancer is a basal cell carcinoma, a malignant melanoma, a squamous cell carcinoma, or precursors of such lesions.