In situ measurement of seawater salinity with an optical refractometer based on total internal reflection method

A 3D-cascade-microlens optofluidic chip for refractometry with adjustable sensitivity

“…Refractive index (RI) sensing as a label-free and non-invasive method has been widely adopted in industrial metrology, 1,2 biochemical analysis 3 and environmental evaluation. 4,5 Since RI is a fundamental optical property of substances and closely related to density, it can be used as a universal parameter for quantitative analyses. Compared with conductivity based approaches, RI sensing has little dependence on the ionic properties of samples, making it suitable for estimating the absolute salinity of seawater and the concentration of nonionic samples.…”

“…Compared with conductivity based approaches, RI sensing has little dependence on the ionic properties of samples, making it suitable for estimating the absolute salinity of seawater and the concentration of nonionic samples. 5 In recent years, optofluidic RI sensors have attracted growing interest due to the combined advantages of microoptics and microfluidics including miniaturization of the sensing system, integration of optical components, flexible modifications of optical properties via fluid manipulation, and real-time measurements of continuousflow samples. [6][7][8][9][10][11] Generally, the RI of a liquid sample can be measured by using interferometric or refractometric methods.…”

Critical-Angle Differential Refractometry of Lossy Media: A Theoretical Study and Practical Design Issues

“…An indicative yet far from exhaustive list of sensing mechanisms relies on plasmonic [8][9][10][11], photonic crystal [12][13][14][15], micro-cavity [16][17][18][19], optical fiber [20][21][22][23] and wave-guide [24][25][26][27] configurations. Associated with Fresnel reflectance properties at planar interfaces, differential refractometry offers an alternative path to sensing refractive index changes, by exploitation of interference [28], deflection [29] or (more relevant to the present work) critical-angle [30][31][32][33][34][35] effects. Today, differential refractometry is not only a standard analytical tool that operates routinely in many laboratories, but also infiltrates emerging optofluidic and lab-on-chip technologies [36][37][38].…”

Water Temperature and Salinity Measurement Using Frequency Comb

“…Based on the principle of light refraction, the refractometer can measure the refractive index of water by recording the beam deviations angle [23,24]. Nevertheless, the beam deviation can be easily affected by the plankton and suspended sediment [25]. In order to solve this problem, the abbe refractometer based on the Snell law has been used.…”

“…In order to solve this problem, the abbe refractometer based on the Snell law has been used. The critical angle of total reflection and the refractive index can be converted to salinity by an empirical formula [25]. However, the refractive index of the auxiliary prism is necessary and the accurate measurement of the angle value is required, which makes the measurement system complicated, and the measurement uncertainty is only at the order of 10 −4 .…”