Dispersion of a Nanoliter Bolus in Microfluidic Co-Flow

Area of Science:

• Microfluidics
• Fluid Dynamics
• Analytical Chemistry

Background:

• Microfluidic systems offer precise control over nanoliter-scale reactions and assays.
• Nonuniformities in sample delivery are a significant challenge at the nanoliter scale.
• Understanding mass transport is crucial for determining minimum sample volumes in microfluidic devices.

Purpose of the Study:

• To analyze the transient state of co-flowing laminar streams in microfluidic devices.
• To develop and validate a microfluidic injector for discrete nanoliter bolus injections.
• To establish a metric for evaluating transient-state injection performance against steady-state conditions.

Main Methods:

• Fabrication of a pneumatically controlled microfluidic injector.
• Injection of a 50nL bolus into a two-stream co-flow reactor.
• Dye-based image analysis to quantify mass transport at various flow rates (0.5-10μL/min).
• Comparison of experimental results with theoretical models and simulations.

Main Results:

• The study successfully fabricated and tested a microfluidic injector for precise nanoliter bolus delivery.
• Image analysis quantified mass distribution, enabling comparison between transient and steady-state co-flow.
• A metric was established to assess the approximation of steady-state conditions by transient injections.
• Transient-state injections were shown to approximate steady-state conditions within defined error margins.

Conclusions:

• Transient-state operation in microfluidic co-flow reactors can significantly reduce sample and time consumption.
• The developed microfluidic injector and analysis metric allow for efficient, low-volume measurements.
• This work provides a foundation for optimizing microfluidic assays by leveraging transient flow dynamics.