The methods, systems 400 and apparatus disclosed herein concern metal 150 impregnated porous substrates 110, 210. Certain embodiments of the invention concern methods for producing metal-coated porous silicon substrates 110, 210 that exhibit greatly improved uniformity and depth of penetration of metal 150 deposition. The increased uniformity and depth allow improved and more reproducible Raman detection of analytes. In exemplary embodiments of the invention, the methods may comprise oxidation of porous silicon 110, immersion in a metal salt solution 130, drying and thermal decomposition of the metal salt 140 to form a metal deposit 150. In other exemplary embodiments of the invention, the methods may comprise microfluidic impregnation of porous silicon substrates 210 with one or more metal salt solutions 130. Other embodiments of the invention concern apparatus and/or systems 400 for Raman detection of analytes, comprising metal-coated porous silicon substrates 110, 210 prepared by the disclosed methods.