Power-free, digital and programmable dispensing of picoliter droplets using a Digit Chip

Area of Science:

• Biomedical Engineering
• Microfluidics
• Point-of-Care Diagnostics

Background:

• Resource-limited settings require power-free diagnostic tools for liquid manipulation.
• Existing self-powered devices handle larger volumes but struggle with sub-nanoliter precision.
• Nanoliter and picoliter volumes are essential for droplet assays, capillary sampling, and expensive reagents.

Purpose of the Study:

• To develop a power-free device for programmable, digital manipulation of sub-nanoliter liquid volumes.
• To enable precise dispensing of ultra-small volumes for advanced diagnostic applications.
• To demonstrate the utility of the device in resource-limited environments.

Main Methods:

• Introduction of the Digit Chip with a button interface and capillary valves for digitization.
• Optimization of device geometry using design models and experimental validation.
• Proof-of-principle experiments including concentration gradient construction and antibiotic titration of E. coli.

Main Results:

• The Digit Chip precisely dispenses volumes as low as 21 pL with 97% accuracy.
• Dispensed volumes can be tuned across one order of magnitude in 10 discrete steps with 98% accuracy.
• Successful construction of a 10-concentration gradient and demonstration of E. coli titration using a smartphone-based platform.

Conclusions:

• The Digit Chip offers programmable, power-free digital manipulation of sub-nanoliter volumes.
• The device is suitable for precise reagent actuation and combination on-chip.
• This technology holds significant promise for diagnostic applications in resource-limited settings.