Osmolarity measurement of a sample fluid, such as tear film, is achieved by depositing an aliquot-sized sample on a sample receiving substrate. The sample fluid is placed on a sample region of the substrate. Energy is imparted to the sample fluid and energy properties of the fluid can be detected to produce a sample fluid reading that indicates osmolarity of the sample fluid. An aliquot-sized volume can comprise, for example, a volume of no more than 20 microliters (L). The aliquot-sized sample volume can be quickly and easily obtained, even from dry eye sufferers. The imparted energy can comprise electrical, optical or thermal energy. In the case of electrical energy, the energy property of the sample fluid can comprise electrical conductivity. In the case of optical energy, the energy property can comprise fluorescence. In the case of thermal energy, the measured property can be the freezing point of the sample fluid. The substrate can be packaged into a chip, such as by using semiconductor fabrication techniques. An ex vivo osmolarity sensor system that uses the chip can detect energy from the sample region and can provide an accurate osmolarity measurement without user intervention.