Dilution with Digital Microfluidic Biochips: How Unbalanced Splits Corrupt Target-Concentration

TL;DR

This paper analyzes how unbalanced split-errors in digital microfluidic biochips affect the accuracy of target concentrations during sample preparation, emphasizing the importance of understanding error dynamics for improving error-tolerant techniques.

Contribution

It provides a detailed analysis of the impact of volumetric split-errors on target concentration factors and explores worst-case scenarios to enhance error-tolerance without sensing.

Findings

Unbalanced splits cause significant drift in target concentration.

Analysis of worst-case error scenarios for concentration accuracy.

Insights for developing error-tolerant sample preparation methods.

Abstract

Sample preparation is an indispensable component of almost all biochemical protocols, and it involves, among others, making dilutions and mixtures of fluids in certain ratios. Recent microfluidic technologies offer suitable platforms for automating dilutions on-chip, and typically on a digital microfluidic biochip (DMFB), a sequence of (1:1) mix-split operations is performed on fluid droplets to achieve the target concentration factor (CF) of a sample. An (1:1) mixing model ideally comprises mixing of two unit-volume droplets followed by a (balanced) splitting into two unit-volume daughter-droplets. However, a major source of error in fluidic operations is due to unbalanced splitting, where two unequal-volume droplets are produced following a split. Such volumetric split-errors occurring in different mix-split steps of the reaction path often cause a significant drift in the target-CF of the sample, the precision of which cannot be compromised in life-critical assays. In order to circumvent this problem, several error-recovery or error-tolerant techniques have been proposed recently for DMFBs. Unfortunately, the impact of such fluidic errors on a target-CF and the dynamics of their behavior have not yet been rigorously analyzed. In this work, we investigate the effect of multiple volumetric split-errors on various target-CFs during sample preparation. We also perform a detailed analysis of the worst-case scenario, i.e., the condition when the error in a target-CF is maximized. This analysis may lead to the development of new techniques for error-tolerant sample preparation with DMFBs without using any sensing operation.