Glass fibers, chemically etched at their extremities and covered with a thin metal coating, are often present in near-field optical microscopy. Such elongated systems can be used to either probe the evanescent components of the electromagnetic field at the surface of a sample, or locally couple this sample with optical evanescent waves. In this article, we analyze theoretically an alternative tip design made with a silicon core. This kind of probe could be very useful when infrared properties of a surface are to be investigated. The advantages of using such a material for near-field optical detection will be stressed and compared with the performances of a bulk glass fiber.