The present invention is drawn toward a chemical or biological sensor that can comprise a semi-conducting nanowire and a chemical or biological sensing molecule tethered to the semi-conducting nanowire through a spacer group including a hydrophilic reactive group. In one embodiment, the semi-conducting nanowire can be part of an array of like or similar semi-conducting nanowires. Electrical leads can provide an electrical current to the array, and a signal measurement apparatus can be electrically coupled to the array, and can be configured for detecting changes in the electrical current of the array.