  Design of microfluidic biochips has led to newer challenges to the EDA
community due to the availability of various flow-based architectures and the
need for catering to diverse applications such as sample preparation,
personalized medicine, point-of-care diagnostics, and drug design. The ongoing
Covid-19 pandemic has increased the demand for low-cost diagnostic lab-on-chips
manifold. Sample preparation (dilution or mixing of biochemical fluids) is an
indispensable step of any biochemical experiment including sensitive detection
and successful assay execution downstream. Although for valve-based
microfluidic biochips various design automation tools are currently available,
they are expensive, and prone to various manufacturing and operational defects.
Additionally, many problems are left open in the domain of free-flowing
biochips, where only a single layer of flow-channels is used for fluid-flow
devoid of any kind of control layer/valves. In this work, we present a
methodology for designing a free-flowing biochip that is capable of performing
fluid dilution according to users requirement. The proposed algorithm for
sample preparation utilizes the Farey-sequence arithmetic of fractions that are
used to represent the concentration factor of the target fluid. We also present
the detailed layout design of a free-flowing microfluidic architecture that
emulates the dilution algorithm. The network is simulated using COMSOL
multi-physics software accounting for relevant hydrodynamic parameters.
Experiments on various test-cases support the efficacy of the proposed design
in terms of accuracy, convergence time, reactant cost, and simplicity of the
fluidic network compared to prior art.
