This study applies MEMS techniques to fabricate a portable system for measuring concentration of nitrite in sea water as shown in Fig.1.Conventional nitrite analysis methods using bulky instruments installed in laboratories have been adopted,despite limitations of portability and convenience [1].On the other hand,the in-situ instruments were portable and delicate,but the accuracy was worse [2].The portable system consists of PDMS microfluidic microsensor,light emitting diode (LED),photodiode (PD),circuits,and LCD display.The size of the nitrite sensor is 70 mm × 27 mm,and only 100 μL of sample and reagent is needed for each measurement.A low refractive material,Teflon AF 1601S,was coated on the wall of microchannel to form a liquid core waveguide (LCW) to increase detection sensitivity.After a micropump injected the sample and reagent into the spiral micromixer simultaneously,both were mixed quickly and adequately.The nitrite sensor also integrated with a passive micromixer and bubble traps,has excellent signal enhancement ability.Both of LED and PD were aligned at the inlet and outlet of the LCW to construct the optic detection system.Light intensity measured by the PD was transformed to voltage which was stored and calculated by a Field Programmable Gate Array (FPGA).Finally,the nitrite concentration of sample can be automatically shown on a LCD display.This study successfully measured concentrations of nitrite standard solutions and constructed a calibration curves as shown in Fig.2.This observation shows the absorbance response as a linear function of a nitrite concentration ranging from 0 nM to 1000 nM.The linearity was excellent with a linear R2 value of 0.998.These analytical results were compared with those measured by a commercial spectrometer (JASCO V-530) to confirm the accuracy and practicability of the portable system.Both results were in good agreement.Finally,the portable system was applied to detect concentration of nitrite in seawater collected at 121.7945°E,25.1476°N.The concentrations calculated from the standardization curve were 513 and 523 nM,respectively.The difference was only 1.91%,demonstrating that simple,accurate,and cheap inspection is possible using the proposed portable system.Therefore,the destination of this study is to provide a potentially low-cost and high efficient approach to stuff up the inspection technology gap between in-situ and laboratory nutrient analyses.