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Using optical tweezers, the authors measure the displacement fluctuations of a trapped colloidal probe embedded in a chemically active bath driven by the Cu-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The non-equilibrium chemical bath drives an anomalous >20% surge in Gaussian positional variance with a flat power spectrum up to 7 kHz, while leaving the trap's corner frequency unchanged. This reveals that the mechanical fluctuations decouple from the macroscopic reaction rate and cannot be modeled as a sum of independent molecular force dipoles, establishing a breakdown of standard additive non-equilibrium Langevin models.
Chemical reactions drive mechanical fluctuations orders of magnitude beyond what individual molecular dipoles allow, proving that active chemical baths exert fundamentally collective, non-additive mechanical forces.
Using optical tweezers, we demonstrate that the CuAAC click reaction increases the positional fluctuations of a trapped 2 micrometer colloid by at least 20% without altering the trap's corner frequency. This excess variance relaxes to the thermal baseline as reagents are depleted. The additional noise is Gaussian, with a flat power spectrum extending past the corner frequency up to 7 kHz. Notably, the noise amplitude decouples from the macroscale reaction rate, and independent molecular force dipoles are orders of magnitude too small to generate the observed variance. Although the chemical free energy released locally exceeds the energy absorbed by the bead by five orders of magnitude, this energy couples inefficiently. The mechanical action of the reacting bath cannot be represented as a sum of independent molecular events.
