Electrochemical Bubble Valves Center for Bio-Mems,State University of NewYork at Buffalo

Layout & Dimensions An anode/cathode electrode pair(Pt electrodes-300nm thick& 25  m wide) is placed perpendicular to the channel(25  m square cross section*5.2mm long). The system consists of inlet and outlet reservoir(not shown on figure). Near one pair of electrodes,a neck was created(15  m) to create backpressure and prevent bubble from blowing. Portion of layout of the electrochemical bubble valve chip is shown on right. <Hua,Susan,Sachs,Federick et.al. “ Microfluidic Actuation Using Electrochemically Generated Bubbles”. Analytical Chemistry, 2002, 74, pg: >

Fabrication System was micro-machined on Si wafer. Following photolithography,microchannel was etched using DRIE(deep reactive ion etching). Then the Pt electrodes were deposited by e-beam deposition using a liftoff technique. PDMS film along with silicone tubing(0.3mm diameter) was used to cover and seal channels. The silicone tubing was aligned on the top of inlet/outlet reservoirs.

Valve Mechanism (Valve-Closing) The inlet pressure varies and outlet pressure was kept at atmosphere. A syringe pump connected to a pressure reservoir perfuse the channel with electrolyte(NaCl in distilled water(pH= 6.4)). When voltage(3.3 to 8.0V) is applied, electrochemical reactions occur (H 2 – cathode, Cl 2 - anode) and a bubble is nucleated. As the bubble grows to block the channel, the fluid flow stops. Valve closing rate increases with higher voltage. <Hua,Susan,Sachs,Federick et.al. “ Microfluidic Actuation Using Electrochemically Generated Bubbles”. Analytical Chemistry, 2002, 74, pg: >

Valve Mechanism (Valve-Opening) Full collapse of bubble is not required to open the valve. The valve opens when the hydraulic resistance of the region containing bubble becomes comparable to that of channel. Rate of collapse depends on gas dissolution in to the liquid, surface-to- volume ratio of bubble and interfacial surface tension. For spherical bubbles, rate of collapse at fixed hydrostatic pressure is given by Rcollapse = 3RT  /4r Where  is the permeability of the gas-liquid interface, R is the gas constant,T is the temperature and r is the radius of bubble. When the valve fully opens, the liquid flow washes away the dissolved gas, and the bubble will further collapse. Opening and closing of valve was completed by ~ 30ms.

8-Way Prototype Multiplexer The idea of electrochemical bubble valve were further extended to create a 8-way prototype multiplexer. Channel dimensions were same. This 8 way system consists of one inlet channel and 2^n(n=3) outlet channel. By closing any of three valves, fluid can be distributed to any of the 8-channels. Figure shows flow being switched between two alternate channels.(B- output 6-by closing V1,V6,V11, C- output 5 by closing V1,V6,V12). <Hua,Susan,Sachs,Federick et.al. “ Microfluidic Actuation Using Electrochemically Generated Bubbles”. Analytical Chemistry, 2002, 74, pg: >

Reference Hua,Susan,Sachs,Federick et.al. “ Microfluidic Actuation Using Electrochemically Generated Bubbles”. Analytical Chemistry, 2002, 74, pg: