Abstract
Efficient mass transport through porous networks is essential for achieving rapid response times in sensing applications utilizing porous materials. In this work, we show that open-ended porous membranes can overcome diffusion challenges experienced by closed-ended porous materials in a microfluidic environment. A theoretical model including both transport and reaction kinetics is employed to study the influence of flow velocity, bulk analyte concentration, analyte diffusivity, and adsorption rate on the performance of open-ended and closed-ended porous sensors integrated with flow cells. The analysis shows that open-ended pores enable analyte flow through the pores and greatly reduce the response time and analyte consumption for detecting large molecules with slow diffusivities compared with closed-ended pores for which analytes largely flow over the pores. Experimental confirmation of the results was carried out with open- and closed-ended porous silicon (PSi) microcavities fabricated in flow-through and flow-over sensor configurations, respectively. The adsorption behavior of small analytes onto the inner surfaces of closed-ended and open-ended PSi membrane microcavities was similar. However, for large analytes, PSi membranes in a flow-through scheme showed significant improvement in response times due to more efficient convective transport of analytes. The experimental results and theoretical analysis provide quantitative estimates of the benefits offered by open-ended porous membranes for different analyte systems.
Highlights
In recent years, porous materials have attracted a great deal of interest in research fields such as energy conversion [1, 2], drug delivery [3, 4], and medical diagnostics [5, 6] due to their large internal surface area and tunable pore size distributions
Open-ended pores present in porous membranes are widely used in micro-fuel cells as gas diffusion layers and proton exchange membranes [7, 8], and many studies have been carried out to investigate the mass transport properties of porous membranes in fuel cell applications [9, 10]
In order to realize a label-free flow-through sensing approach with porous silicon (PSi), we developed an open-ended, multilayered, optical microcavity structure fabricated by standard silicon processing that is compatible with integration in on-chip sensor arrays [43]
Summary
Porous materials have attracted a great deal of interest in research fields such as energy conversion [1, 2], drug delivery [3, 4], and medical diagnostics [5, 6] due to their large internal surface area and tunable pore size distributions. Open-ended pores present in porous membranes are widely used in micro-fuel cells as gas diffusion layers and proton exchange membranes [7, 8], and many studies have been carried out to investigate the mass transport properties of porous membranes in fuel cell applications [9, 10]. In biosensing applications, the use of open-ended porous membranes is not common and has not been widely studied. Open-ended porous membranes [18,19,20] and nanohole arrays [21,22,23] offer the possibility to overcome inefficient mass transport and achieve fast sensor response by allowing analytes to flow through the pores and interact more favorably with their inner surfaces. An enhancement in the rate of mass transport through such membranes has been reported
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