The high surface area of porous silicon (PSi) makes it attractive for use in chemical and biological sensors. Selectivity, however, will require tailoring its interfacial characteristics with organic molecules. This paper describes in situ functionalizing of PSi during its electrochemical formation with 1-heptyne and 6-heptynoic acid. Fourier transform infrared spectroscopy (FTIR) confirmed the attachment of the organic molecules, which were able to take part in subsequent chemical reactions. However, some disadvantages of in situ functionalization were noted, such as a reduction in the thickness and porosity of the PSi layer, along with incomplete coverage of the PSi; Si-H stretches were still observed on the FTIR spectra. Nevertheless, when the in situ functionalized PSi was treated in boiling 1-decene, all the Si-H groups were converted to S-C bonds, without the 1-decene replacing the molecules attached in the in situ process. Hence, combining in situ and ex situ functionalization, or adding a mixture of organic molecules into the etching solution, may enable different organic molecules with varying chemical functional groups to be incorporated on a single PSi specimen. Finally, the possibility of using PSi functionalized with carbonyl groups as an alcohol sensor was demonstrated by using FTIR to observe reversible shifts in the frequency of the carbonyl stretch on exposure and removal of methanol vapor. (c) 2006 The Electrochemical Society.