Silicon-based electrochemical microdevices for silicate detection in seawater

Abstract

International audienceThis paper describes the electrochemical characterisation of gold and platinum microdevices mass fabricated using silicon technology. Specific attention was paid to allow in situ electrochemical detection of silicate in seawater. Thus, using a silicon nitride (Si 3 N 4) inorganic passivation layer patterned using Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD), coupled with a non-aggressive lift-off based process, different electrodes were isolated electrically: one gold or platinum working electrode named " macroelectrode " (2 mm of diameter), four gold or platinum working ultramicroelectrodes (UME) (15 ␮m of diameter), one platinum counter electrode and one silver electrode which can be used as a reference electrode after its chlorination. Their small size and mass fabrication make them very promising for oceanographic applications. As some components of microdevices release silicate and contaminate the solution, after being immersed in seawater, these microdevices were inserted in a specific cell that only puts the electrodes in contact with the seawater solution. Gold has been tested as a possible material for working electrodes but its lack of adherence to the passivation layer in seawater solutions led to non-accurate measurements. On the contrary, passivation layer on platinum electrodes resists to the seawater corrosive medium. The analytical performances of the platinum microdevices has been tested through different silicate calibrations and shows an outstanding accuracy and reproducibility when measurements are performed, especially with the macroelectrodes which showed only 2.8% signal variation after four months of use and a limit of quantification of 0.50 ␮mol L −1 suitable for oceanographic applications

Improvement of On-Site Sensor for Simultaneous Determination of Phosphate, Silicic Acid, Nitrate plus Nitrite in Seawater

“…Electrochemical techniques for nutrient measurements facilitate sensor miniaturization, require low power, and in some cases eliminate the need for reagents. Two electrochemical sensors have been reported for H 4 SiO 4 [16][17][18] and PO 4 3− [19,20]. In these sensors, molybdate (MoO 4 2− ) ions are introduced into a working solution (NaCl solution (34.5 g L −1 )) by electrochemical oxidation of a solid Mo wire.…”

First Deployment and Validation of in Situ Silicate Electrochemical Sensor in Seawater

“…We propose to use an electrochemical sensor to detect silicate without any liquid reagent addition using an in situ oxidation of a molybdenum electrode to form the silicomolybdic complex detectable on gold working electrode, thanks to a special design of the electrochemical cell using Nafion R membrane. The limit of quantification achieved using a 2 mm diameter working electrode and commercial potentiostat was 0.5 µmol L −1 (Lacombe et al, 2008;Aguilar et al, 2015).…”

Nutrient Detection Sensors in Seawater Based on ISI Web of Science Database

“…Because of the unavoidable limitation of in situ seawater environment, the development of sensor technology has to be long duration of use, less wastewater output, low energy consumption, less reagent consumption, small volume, and strong ion selectivity. Some products with mature technology in market include Micro-Lab, EcoLAB2, and CYCL Phosphate sensors (Wetlabs, USA), SUNAV2 (Satlantic, Canada), and WIZ sensors (SYSTEA, Italy) [24,25]. However, the main bottlenecks that restrict the development of nutrient sensors are short duration, low precision, narrow range of detection concentration, and poor reproducibility [26,27].…”