The most common means to analyze redox gradients in sediments is by push/pulling electrochemical probes through sediment’ strata while repeating measurements. Yet, as electrodes move up and down they disrupt the texture of the sediment layers thus biasing subsequent measurements. This makes it difficult to obtain reproducible measurements or to study the evolution of electrochemical gradients. One solution for solving this problem is to eliminate actuators and electrode movements altogether, while instead deploying probes with numerous electrodes positioned at various depths in the sediment. This mode of operation requires electrode switching. We discuss an electrode-switching solution for multi-electrode probes, based on Complementary Metal-Oxide-Semiconductor (CMOS) multiplexors. In this solution, electrodes can be individually activated in any order, sequence or time frame through digital software commands. We discuss constraints of CMOS-based multilayer electrochemical probes during cyclic voltammetry.

Marine sediments with rapid oxic/anoxic transitions are difficult to monitor in real time. Organic overload that may lead to anoxia and buildup of hydrogen sulfide can be caused by a variety of factors such as sewage spills, harbor water stagnation, algal blooms and the vicinity of aquaculture operations. We have tested a novel multiprobe technology (named SPEAR) on marine sediments to evaluate its performance in monitoring sediments and overlaying water. Our results show the ability of the SPEAR probes to distinguish electrochemical changes at 2-3 mm scale and at hourly cycles. SPEAR probes have the ability to identify redox interfaces and redox transition zones in sediments, but do not use micromanipulators (which are cumbersome in field and underwater applications). We propose that the best target habitats for SPEAR-type monitoring are rapidly evolving muddy deposits and sediments near aquaculture operations where pollution with organics stresses the ecosystem.