Continuous, quantifiable, and simple osmotic preconcentration and sensing within microfluidic devices

Abstract

Insurmountable detection challenges will impede the development of many of the next-generation of lab-on-a-chip devices (e.g., point-of-care and real-time health monitors). Here we present the first membrane-based, microfluidic sample preconcentration method that is continuous, quantifiable, simple, and capable of working with any analyte. Forward osmosis rapidly concentrates analytes by removing water from a stream of sample fluid. 10-100X preconcentration is possible in mere minutes. This requires careful selection of the semi-permeable membrane and draw molecule; therefore, the osmosis performance of several classes of membranes and draw molecules were systematically optimized. Proof-of-concept preconcentration devices were characterized based on their concentration ability and fouling resistance. In-silico theoretical modeling predicts the experimental findings and provides an engineering toolkit for future designs. With this toolkit, inexpensive ready-for-manufacturing prototypes were also developed. These devices provide broad-spectrum detection improvements across many analytes and sensing modalities, enabling next-generation lab-on-a-chip devices.

Opportunities and limitations of membrane-based preconcentration for rapid and continuous diagnostic applications

“…If the osmolarities of both the incoming sample and the draw solution are known, this approach can be rendered more predictable in the amount of preconcentration achieved by allowing the sample stream and the osmotic draw solution to equilibrate in osmolality before reaching the sensor. However, allowing for equilibrium in osmotic strengths limits the input flow rate 29 and can impact the sensor performance (by changing pH or salinity).…”

“…As the results of this study (all of the work in this section) have already been published, the full details of the study have been omitted and can be found in the original publication. 29 However, the main testing procedure and results are summarized here in order to allow for a thoughtful discussion on the method's potential in diagnostics.…”

“…This process can be used in devices which are quite small, or extremely large. For example, microchips with embedded membrane filtration modules have been used to concentrate many biomolecules, such as proteins, viruses, and bacteria; 13,14,21,29 on the other hand, water treatment facilities often use huge sheets of membrane to filter salt water for drinking purposes. 30,31 The methods used to drive fluid through the membrane can vary quite a bit in functionality and complexity.…”

“…30,31 The methods used to drive fluid through the membrane can vary quite a bit in functionality and complexity. For example, some methods include osmotic pressure, 29 electrokinetics, 20,21 and pneumatic pressure. 32…”

“…In our work, methods of fluid removal included osmosis, 29 vacuum, 32 wicking, and pneumatic pressure. 32 Our goal was to find a method which is rapid, reliable, and cost effective to create a device which could easily be integrated into rapid diagnostic tests or continuous diagnostics which require rapid preconcentration to enable ‘real time’ data.…”