(582f) Harnessing Toy-Inspired Physics for Electricity-Free Thermal Cycling

The conventional thermal cyclers, pivotal for Polymerase Chain Reaction (PCR) testing, are characterized by their substantial size, high energy consumption, and significant cost. These attributes constitute a primary bottleneck in enhancing PCR accessibility and its integration into point-of-care settings. Addressing this challenge, we introduce a new class of thermal cyclers that operate without electricity, inspired by the self-sustaining motion of the drinking bird toy. Our device leverages a similar physical principle, utilizing a capillary-driven tube system. This system cyclically transports fluid from a larger reservoir to a smaller reservoir due to capillary action, which upon reaching a critical fluid volume, empties, causing a shift in the center of mass that dips the tube back into the larger reservoir, perpetuating the oscillatory cycle.

This innovative mechanism enables continuous oscillatory motion of the tube’s head without any external power source. We delve into the physics underlying these oscillations by modeling the system’s kinematics and dynamics, particularly focusing on the integration of the net torque over time to describe the motion the tube within the phase space of the tube angle (θ) and its angular velocity (ω). Through this analytical framework, we identify the critical parameters governing the oscillatory behavior and optimize the system for replicating PCR thermal cycling. An experimental setup was devised to translate these theoretical insights into practice, successfully demonstrating the ability to move a small water tube (analogous to a PCR tube) between hot and cold reservoirs. This process emulates the essential temperature cycling required for PCR, thus achieving thermal cycling devoid of electrical power. Our findings pave the way for a new generation of thermal cyclers that could revolutionize point-of-care PCR testing by eliminating the dependence on electricity, thereby facilitating broader accessibility and application.