Micromachined Particles for Detecting Metal-Ion Concentration in Fluids

A remote microfluidic metal-ion sensor is developed using an electrochemical system integrated with a compact photovoltaic cell power supply. The sensor is designed to detect the sum of metal ions in a remote environment. The sensor uses electrodeposition to remove ions from the fluid around the sensor and deposit them on an electrode at the tip of a cantilever. The electrodeposited mass changes the resonant frequency of the cantilever, which can be determined upon read-out. The sensor is designed to be dropped in liquids or flow through microfluidic systems and can be used in parallel with many other similar sensors. The photovoltaic cells are directly integrated on the device and are capable of producing tens of microwatts of power at about 15% efficiency with laser excitation. However, the sensor operates at power levels of 50 nW with small voltages and currents using only scavenged daylight or room light. The complete device is integrated into a total volume below 0.046 mm
³
, which is more than two orders of magnitude smaller than other remote electrically-powered sensors reported to date. Although it is expected that multiple devices will be used in parallel to gain statistical data, individual particles detect metal-ion concentration within 24% of the actual concentration, making them suitable for safety testing and endpoint monitoring among other applications