An analysing apparatus comprising: a fluid container defining a sample chamber; a sensor comprising a transparent body with a reverse face and an obverse face, the obverse face having a nanostructured surface, the nanostructured surface comprising a plurality of nanostructures;; an excitation and detection apparatus comprising an excitation source for generating a beam (Li) of polarised radiation and a corresponding radiation detector, wherein, the sensor is coupled to the fluid container such that the nanostructured surface is exposed to the sample chamber, and wherein the excitation and detection apparatus is configured to direct the beam (Li) of incident polarised electromagnetic radiation onto the reverse face of the body at an angle that causes no or substantially no reflection of the polarised radiation from the reverse face, and wherein said excitation and detection apparatus is configured to direct to said detector a beam (Lr) of reflected radiation, said beam of reflected radiation comprising said incident radiation emerging in use from the reverse face after reflection from said nanostructured surface, wherein said nanostructures are elongate, having a respective longitudinal axis that is disposed substantially perpendicularly to the obverse face, so that the incident radiation is polarised with an electrical component along the longitudinal axis of the nanostructures, wherein the excitation and detection apparatus is configured to direct said beam of incident polarised electromagnetic radiation onto the reverse face of the body such that, upon travelling though said body, said incident beam impinges upon said nanostructured surface at an angle less than that required for attenuated total reflection, wherein the nanostructures are formed from an electrically conductive material, wherein the nanostructures are formed on an electrically conductive layer provided at the obverse face of the body, wherein the nanostructures are spaced apart from one another with a spacing of less than 50nm. a fluid container defining a sample chamber; a sensor comprising a transparent body with a reverse face and an obverse face, the obverse face having a nanostructured surface, the nanostructured surface comprising a plurality of nanostructures;; an excitation and detection apparatus comprising an excitation source for generating a beam (Li) of polarised radiation and a corresponding radiation detector, wherein, the sensor is coupled to the fluid container such that the nanostructured surface is exposed to the sample chamber, and wherein the excitation and detection apparatus is configured to direct the beam (Li) of incident polarised electromagnetic radiation onto the reverse face of the body at an angle that causes no or substantially no reflection of the polarised radiation from the reverse face, and wherein said excitation and detection apparatus is configured to direct to said detector a beam (Lr) of reflected radiation, said beam of reflected radiation comprising said incident radiation emerging in use from the reverse face after reflection from said nanostructured surface, wherein said nanostructures are elongate, having a respective longitudinal axis that is disposed substantially perpendicularly to the obverse face, so that the incident radiation is polarised with an electrical component along the longitudinal axis of the nanostructures, wherein the excitation and detection apparatus is configured to direct said beam of incident polarised electromagnetic radiation onto the reverse face of the body such that, upon travelling though said body, said incident beam impinges upon said nanostructured surface at an angle less than that required for attenuated total reflection, wherein the nanostructures are formed from an electrically conductive material, wherein the nanostructures are formed on an electrically conductive layer provided at the obverse face of the body, wherein the nanostructures are spaced apart from one another with a spacing of less than 50nm.