Hydrogen Sulfide Sensing Using Lab-on-a-Chip Device for Biomedical and Environmental Use

Hydrogen sulfide (H₂S) detection is an important capability for applications that range from environmental to biomedical use. In medical application, hydrogen sulfide may be an effective marker for various cardiovascular diseases. This work reports progress on H₂S detection using a unique lab-on-a-chip device designed specifically for both environmental and biomedical applications. The chip consisted of three distinct layers of PEO/PDMS structures which have been bonded using various techniques including Reactive Ion Etching (RIE). First layer consisted of capillary channels to organize the flow of the sample. Also, liberation of the sulfide took place at this layer. The second layer was a H₂S selective membrane. The third layer consisted of trapping chamber where trapped H₂S samples were withdrawn for the quantification of H₂S concentration. Fabrication of the first layer was accomplished using photolithography technique. Specifically, the chip incorporated unique design features and operation with advanced liberating chemistry that effectively released H₂S from aqueous solutions introduced to the device. Mixture of poly-dimethylsiloxane-ethylene oxide polymeric (PDMS-b-PEO) and polydimethylsiloxane (PDMS) was cast on Su8 mold which produced super hydrophilic channels that allowed liquid flow via capillary action. The chip has been both fabricated and characterized as reported in this work. For each sample, 150 μL of the reaction volume was loaded in an HPLC vial and analyzed by a Shimadzu Prominence HPLC equipped with fluorescence detection and an eclipse XDB-C18 column. Sulfide transfer increased steadily at a rate of approximately 2% per minute until peaking at approximately 60% at 30 minutes. Percent transfer data show that sulfide diffused into the trapping chamber in a reproducible manner and that it was stable once it reached its peak at 30 minutes. Characterization and testing of the fully assembled device indicates significant promise and utility. Additional improvements may be made by optimizing parameters such as the decreasing ratio of the chamber volumes to the membrane area and the membrane thickness. The performance of this microfludic device was attributed to hydrophilic surface of PEO/PDMS, strong bonding of the chip using 3M transfer tape and well suited PDMS membrane that allow selective diffusion of hydrogen sulfide.