An analysis system comprising: a sampling cartridge comprising a housing having an inlet for receiving a fluid sample, a sensor, and a guide extending between the inlet and the sensor for guiding sample into contact with the sensor; and an optical detection reader for optically inspecting the sensor; wherein the cartridge housing comprises an inspection window; and the reader comprises a socket to receive at least part of the cartridge, and an optical system for inspecting the sensor through the window, and wherein the cartridge guide (26, 1010, 1020, 1030, 1040, 1050, 1060) comprises at least one microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) for flow of sample from the inlet into contact with the sensor, wherein the sensor comprises a sensor pad, wherein the at least one microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) extends beyond the sensor and comprises: a reagent pad (43, 608) upstream of the sensor pad, a free space diffusion zone between the reagent pad (43, 608) and the sensor pad, the free space diffusion zone being sufficient for comprehensive dissolution of reagent into the sample fluid before reaching the sensor pad, an absorbent pad downstream of the sensor pad, and an opening at the end of the microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) downstream of the absorbent pad to act as a vent to assist sample fluid flow; and wherein each microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) has a cross-sectional area in the range of 0.3 mm 2 to 5 mm 2. a sampling cartridge comprising a housing having an inlet for receiving a fluid sample, a sensor, and a guide extending between the inlet and the sensor for guiding sample into contact with the sensor; and an optical detection reader for optically inspecting the sensor; wherein the cartridge housing comprises an inspection window; and the reader comprises a socket to receive at least part of the cartridge, and an optical system for inspecting the sensor through the window, and wherein the cartridge guide (26, 1010, 1020, 1030, 1040, 1050, 1060) comprises at least one microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) for flow of sample from the inlet into contact with the sensor, wherein the sensor comprises a sensor pad, wherein the at least one microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) extends beyond the sensor and comprises: a reagent pad (43, 608) upstream of the sensor pad, a free space diffusion zone between the reagent pad (43, 608) and the sensor pad, the free space diffusion zone being sufficient for comprehensive dissolution of reagent into the sample fluid before reaching the sensor pad, an absorbent pad downstream of the sensor pad, and an opening at the end of the microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) downstream of the absorbent pad to act as a vent to assist sample fluid flow; and wherein each microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) has a cross-sectional area in the range of 0.3 mm 2 to 5 mm 2. a reagent pad (43, 608) upstream of the sensor pad, a free space diffusion zone between the reagent pad (43, 608) and the sensor pad, the free space diffusion zone being sufficient for comprehensive dissolution of reagent into the sample fluid before reaching the sensor pad, an absorbent pad downstream of the sensor pad, and an opening at the end of the microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) downstream of the absorbent pad to act as a vent to assist sample fluid flow; and wherein each microfluidic channel (42, 1011, 1021, 1031, 1041, 1051, 1061) has a cross-sectional area in the range of 0.3 mm 2 to 5 mm 2.