An optical sensor comprising: a sensor head that includes a first optical window, a second optical window, at least one light source, and at least one detector, wherein the at least one light source is configured to emit light through the first optical window into a flow of fluid and the at least one detector is configured to detect fluorescent emissions through the second optical window from the flow of fluid; a flow chamber that includes a housing defining a cavity into which the sensor head is inserted, an inlet port configured to communicate the flow of fluid from outside of the cavity to an interior of the cavity, and an outlet port configured to communicate the flow of fluid from the interior of the cavity to back outside of the cavity, wherein the inlet port defines a first fluid nozzle configured to direct a portion of the flow of fluid against the first optical window and a second fluid nozzle configured to direct a portion of the flow of fluid against the second optical window, wherein the sensor head includes a sensor housing extending from a proximal end to a distal end, the sensor housing including an angular cutout defined by a first planar surface that intersects a second planar surface, wherein the first optical window is positioned on the first planar surface and the second optical window is positioned on the second planar surface, wherein the first fluid nozzle and the second fluid nozzle project away from a wall of the flow chamber into the angular cutout and provide a cleaning function for the first and second optical windows (312, 314), wherein the first optical window is configured to project light from the at least one light source into a first region of the angular cutout, the second optical window is configured to receive optical energy from a second region of the angular cutout and direct the optical energy on the at least one photodetector, wherein the first region overlaps with the second region and the first fluid nozzle and the second fluid nozzle project into a third region of the angular cutout between the first region and the second region without projecting into the first and second regions (402, 404). a sensor head that includes a first optical window, a second optical window, at least one light source, and at least one detector, wherein the at least one light source is configured to emit light through the first optical window into a flow of fluid and the at least one detector is configured to detect fluorescent emissions through the second optical window from the flow of fluid; a flow chamber that includes a housing defining a cavity into which the sensor head is inserted, an inlet port configured to communicate the flow of fluid from outside of the cavity to an interior of the cavity, and an outlet port configured to communicate the flow of fluid from the interior of the cavity to back outside of the cavity, wherein the inlet port defines a first fluid nozzle configured to direct a portion of the flow of fluid against the first optical window and a second fluid nozzle configured to direct a portion of the flow of fluid against the second optical window, wherein the sensor head includes a sensor housing extending from a proximal end to a distal end, the sensor housing including an angular cutout defined by a first planar surface that intersects a second planar surface, wherein the first optical window is positioned on the first planar surface and the second optical window is positioned on the second planar surface, wherein the first fluid nozzle and the second fluid nozzle project away from a wall of the flow chamber into the angular cutout and provide a cleaning function for the first and second optical windows (312, 314), wherein the first optical window is configured to project light from the at least one light source into a first region of the angular cutout, the second optical window is configured to receive optical energy from a second region of the angular cutout and direct the optical energy on the at least one photodetector, wherein the first region overlaps with the second region and the first fluid nozzle and the second fluid nozzle project into a third region of the angular cutout between the first region and the second region without projecting into the first and second regions (402, 404).