A spectrophotometric sensor is provided that includes a mating surface upon which electrical and optical components may be secured and a Faraday shield assembly secured to the mating surface enclosing a photodetector. The Faraday shield assembly includes alignment features that may be employed to provide mechanical registration and/or electrical coupling of the Faraday shield assembly. The spectrophotometric sensor may be placed on a patient's finger, toe, ear, and so forth to obtain hemoglobin oxygen saturation using pulse oximetry, or for other physiological measurements.