The methods and apparatus for detecting an analyte in blood are useful for detecting an analyte in tissue of a subject. The apparatus comprises a sensor, which comprises an elongated conductive material having a protrudent end, the protrudent end comprising an electrode that detects the presence of an analyte; a substrate affixed to the conductive material; and a support having an external surface, a proximal end, and a distal end. The conductive material is positioned on the support and the protrudent end of the conductive material protrudes beyond the distal end of the support. Optionally, the sensor is suspended within the lumen of a venous flow device. Typically, only a portion of the sensor is suspended within the lumen of the venous flow device, said portion comprising the protrudent end of the conductive material. Alternatively, the conductive material is positioned on the external surface of the intravenous infusion catheter.